i loved your historical discussion of the evolution of the notion of energy and momentum. please have a series of videos about this historic evolution.
I have no formal education in physics, just a lifelong fascination with the limits of what we can know about the universe, Dr Lincoln has been one of the most easily digestible educators out there, many thanks ❤️
Such a rabbit hole of a fascinating field. I love cryptography because it's the intersection of math and computer science (my primary field), but with quantum computing we have had to think of interesting ways to get around Shor's algorithm which will break our modern asymmetric key exchange protocols (DH-RSA, DH-ECC, etc.). So one of the solutions we have come up with is a brilliant quantum key exchange protocol called BB-84; its security actually relies on physics instead of math. Shor's breaks our current algorithms because they rely on the discreet logarithms and the hard np-complete problem of factoring huge prime numbers, which is not a problem for quantum computers due to superpositional calculation. BB-84 relies on photon orientation and is theoretical information secure and naturally authenticated because once any of the photons are observed and tested for their orientation by an attacker, they are changed. This is remarkably awesome!
@@aethrya Few years ago I watched a documentary about China advancements in cryptography, they had a prototype information system that used entanglement as the security protocol to make sure info isn’t hacked, basically destroys the message when someone attempts a hack which breaks the entanglement really insane stuff, at least to me, I’ve never tried to be good at math, but nature uses it beautifully
Science with out the gobbkdy gook for no shit.or no cherry picking and showing you how physics get there results..guess..I mean hidden variables and blag models that are guessed .hav alook u wont be disappointed..physics truth not for funding...❤
Thank you for a great video. However, I think it missed an idea more fundamental and therefore enlightening than any of those expressed. Energy is the ability to cause change. (I don't think that word was used even once!) A system without any energy is unable to change, under any circumstances, without the introduction of an external ability to create change. Potential energy recognises the existence of a blockage that prevents change from happening. On releasing the blockage, change happens and physicists say that potential energy was converted to kinetic energy. An example of a blockage is a table that stops a spoon from falling. Without the table, it falls, demonstrating that the ability to change (the energy) existed when the spoon was on the table. Another is the structure within an atom that keeps the ability to change within the atom. Disturb that structure and that ability to make change can be released. That release can cause the release of the energy blocked inside neighbouring atoms which can then escalate - called a chain reaction, and we have an atomic bomb. It is instructive to think about what a system that cannot change (has no energy) would be like. My imagination says that the value of every field within that system would be the same at every point.
@@cloudpoint0 perhaps it would be better to say that Garry's description describes the intrinsic nature of entropy, which is an immutable feature of energy. the quality of energy that he's describing is relational in essence, which is to say that it's a great way of looking at energy as a series of disturbances in a series of boundless fields. perhaps your definition holds to the quantizable aspects of energy, and thus would see entropy as an external quality rather than necessarily implicit; i would like to know what you think, and how it relates to my assumption on your behalf.
@@owfan4134 Energy doesn’t really exist, at least not independently. It’s purely an abstract numerical measurement like velocity, distance or temperature, none of which you can say is something on its own beyond some mathematical existence. Energy is just a property that we measure between two objects - one object alone can’t really have energy just like one object alone can’t really have a distance - the measurement has to be compared to some reference object. This means energy is relative - and different observers see the same measurement as a different number. The train rider sees the train as having no (kinetic) energy while the person waiting on the platform sees the arriving train as loaded with energy. I don’t know what an overall statistical measurement of a large group of many things, like entropy, has to do with the description of a single measurement between two things in that group. And I can’t connect Garry’s description to entropy. Since energy is conserved, entropy doesn’t change energy, entropy is just an expression of energy’s disorder. Maybe going back to basics will help here… *What the HECK is Energy?* ruclips.net/video/snj1wBtn6I8/видео.html
@@owfan4134 @cloudpoint Thanks for your replies. I am not confident that I have understood all the implications /meanings of your responses but I have picked up 3 issues - intrinsicness, relativity and entropy. 1. Intrinsic. I don't know how to define this in this context, and I suspect that the distinction provides little information that helps someone understand energy. The fact is that if we observe two otherwise identical systems, one involving a collision of a fast moving object and the other a slow moving object the fast moving one will cause more change and will have more energy. I don't believe that these two observations can be distinguished. It will always be true, irrespective of the design of the system. That conforms with what I would call intrinsic. I think that @cloudpoint has agreed with me on this in his latter reply. 2 Relativity, I agree that depending on the frames of reference, two observers will disagree on the speed of the objects in a collision. However, they will not disagree on the amount of change the collision has caused nor on the amount of work done and therefore the amount of energy used. So, I contend that velocity is relativistic, but energy is not. 3. Entropy. There is clearly a relationship between energy and entropy, but I don't think that makes them the same thing. My comment is about energy, not entropy. If I understand correctly, I think @cloudpoint has answered this issue much better than I have.
I like the definition. As an "ability" it is clear that energy is connected to physical entities, rather than something that can be seen in a pure form. I've often thought of "Energy = the ability to change the state of motion of objects" but I see reading the comments that I might have to add "or the arrangement" of objects, thinking about entropy. Just a novice take
While the definition of energy can be very vague, the best I came across was that energy was a number that we associate with the configuration of a system or the motion of a particle. It can also be defined as a quantity that interacts with matter and can bring changes to its shape, state, temperature, configuration or motion.
"Energy is the ability of a system to perform work on another system.". What's vague about that? Please explain in great length and detail. Please explain in addition why you weren't paying any attention in high school science class. ;-)
So far, it appears that the universe started as something tiny and started to expand to what we can observe and detect today. It also appears that anything we can observe or detect is made from extremely tiny particles which interact and combine with each other based on some fundamental predetermined rules. We have identified quit a few of these extremely tiny particles and have identified quit a few of the rules these particles follow to interact and combine. Perhaps most of the particles and most of the rules but there probably are more. We also discovered that anything that we can observe or detect is made from the same basic stuff and we call this stuff energy. We know this because we have figured out how to calculate a value or quantity of energy for anything that we can observe or detect. I think we can say the fabric of the universe is space time but we can also say that the fabric of the universe is energy time because we now know that space is not empty and is also some type of energy and we can calculate or at least estimate how much energy is in a given volume of space. It also appears that after the universe started to expand, no more energy was added or removed as it continued to expand. We do not know what the rules were that determined the amount of energy in the universe nor what caused the energy in the universe to start expanding. The rules for how energy expands, transforms, interacts and combines cause energy to cycle from concentrated to diluted states. Although the cycles can be repeated almost an infinite number of times, there will be a time when they stop because as the cycles keep repeating, the total amount of energy in the universe keeps becoming more and more diluted. We call this rule entropy. At some point in time, all the energy will become so diluted that it will not be able to cycle back into more concentrated states and we think this is when the universe ends. We still do not know the rules before the universe started to expand and we still do not know the rules after the universe ends and there are probably still many rules that we do not know about that causes the energy in the universe to cycle back and forth from concentrated to diluted states as it continues to expand.
Well, with this definition energy will not be the fundamental entity of the nature but a consequence: the onsequence of the motion of fields and their interactions. But then we are faced again with the question of what causes the motion of the fields and their interactions. Looks like we are back to a cicular argument, since motions and interactions can only be understood due to the presence of energy in the first place. Similarly, the existence of fields begs the explanantion about their very existence due to something else which we would like to call energy again. I think energy must be defined and understood independently of its consequences but it is almost impossible how we can do that.
The lecture was awesome. However, while you were talking in length about kinetic & potential energies, I was also waiting to hear about heat energy, which somehow you skipped, or, maybe you mentioned, but I missed.
When I was first introduced to E=MC^2 my first question was.. yes but 'what is energy'? I mean we can understand what mass, and the speed of light are.. But when fission begins converting mass into 'energy' exactly what does that mean. And I was told, well, mainly heat and light. But then I was left wondering how heat and light could erase a pacific atol. 'What is energy' is a great title, and I'm sorry to say, though I love your video, you didn't really give me the epiphany my 11 year old self required.
I know what you mean. I was stuck on that Star Trek episode where Mr. Spock says, "fascinating captain, pure energy." I looked for what energy was for years until I realized it was a property something else has just like length and weight. There is no "pure energy" any more than there are "pure inches" or "pure ounces". Perhaps everybody takes this for granted and so never emphasize the fact in their explanations, only allude to it briefly before moving on.
Hello Dr. Lincoln @Fermilab - was this video inspired by a recent conversation you had in Orlando about Kugelblitzes, hmm? :-) Thank you for producing this. What I think is interesting is that a moving, unaccelerated object has "kinetic" energy, but within its own reference frame it is stationary. The thing having what we call "potential" energy is actually not stationary, but following a straight line through curved spacetime - in the same way that a basketball is actually travelling along a straight line through a curvature in (mostly) time. I think I need to consider kinetic and potential energy the way we consider electricity and magnetism to help my brain make sense of the difference. Thanks again, and after I watch this a couple more times I look forward to your next videos.
Not sure how helpful the concept is but Voltage is always 'relative' right? Could this also mean that a region of space can have its own 'ambient' level of charge, zero to its own reference? And it's similar for mass-related energy? Dont mind me I'm just an electronics geek tryna make sense of this stuff :)
I was taught along with all you have mentioned that energy just is. It can’t be made or destroyed only transformed. Because of quantum mechanics energy never stops even at absolute zero because at the very small mass is vibrating. If string theory is true the filament is vibrating. Hence energy. Photons have no mass yet their motion is energy. So it’s not just mass it’s motion. Potential energy is in motion because everything vibrates on a subatomic level.
You got the absolute zero thing backwards, nothing can reach absolute zero _because_ everything has some non-zero vacuum state of energy, not that energy happens at absolute zero as well.
I enjoyed it, but feel you did not provide the answer asked in the title "what is energy". You described things that have energy, but I'm as confused as ever as to "what is energy"
Thanks Don, great video. BUT ... what about heat? an everyday example is car brakes turning the kinetic energy of the car into heat to halt the car. Or the engine converting chemical energy into heat in the combustion chamber which is then converted to kinetic energy (of the car) by various moving parts.
You are a great teacher, sir, but this time I feel I'm left at the same point where I started. 'Potential energy is force fields and their interaction with objects, kinetic energy is the motion of those fields'. So what are forcefields? I mean, what is force in the first place? What is this thing forming a 'field'? What is it made of? Well, I know that science doesn't have all the answers, of course, as it is the search for the answers.
I recently saw a video where the presenter was dismissive of an analogy of the Universe expanding being the same from an outside perspective as if it's contents are shrinking, saying he didn'tgive credence to pseudo science, and I would love to know why we do look at the universe in the particular way that we do? It struck me that over galactic scales gravitational effects observed around the edges have taken thousands of years to propagate and if the mass content was steadily shrinking (while remaining fairly consistent in structure and form), the effects felt on the outer parts would have been caused by a larger gravitational force than is currently present at the centre and is acting on matter that has also diminished in mass but not structure, so would appear stronger still. Similarly, with photons losing energy over distance, why do they and into what? With energy in the quantum foam seeming to appear out of nothing, could a steady radiating of energy from matter be a contributor to that? Blackholes in the very early universe could have been formed in the way we observe stellar mass blackholes but would not lose their scale and mass/energy content at the same rate as the surrounding matter, by the nature of what they are, isolated pockets of space, therefore becoming the dominant gravitational force in early galaxies (without requiring spontaneous collapse, primordial blackholes or many many many collisions with other blackholes to get to billions of stellar masses). We observe entropy and waveforms dissipating their energy in every other aspect of our world, but i've not seen a reason given why it's not postulated for the foundational packets of waveforms and energy we call particles. Sorry if that was a lot in one go, and I am very aware my knowledge of physics is limited, so with those observations there are probably many simple or complex interactions that i've missed that answer why the above is not the current consensus. Thank you for the video, it's always a pleasure seeing your content
❤❤❤❤ If you do not know what energy is, there is no need to feel bad about it. As a physicist once said "Before I entered this prestigious university to do my PHD in physics, I know exactly what energy is but after I was awarded my PHD, I have absolutely no idea what energy is ! 😂😂😂😂 Dr HW Looi
mass energy equivalence I think can be understood under this thought experiment: take a box with perfect mirror walls on inside that has no mass then trap some photons inside. The box will now have mass and weigh something. or if the box has already some mass, it will increase depending on the energy of the photons. I think this is how particles could actually get mass like interactions with the Higgs field could be a phenomenon that is equivalent to this
Its interesting to think that an object has gravitational potential energy with a concentration of energy. But how should we look at a double AA battery. Is the difference between a full battery and a dead battery all electrical chemical + gravitational, or is all the gravitational potential = electro chemical.
Great video - thank you. So, per the statement at 7:50, photons reaching the earth from the farthest discernible galaxies have lost energy compared to when they were emitted (i.e., red shift)... if these photons are traveling at the speed of light, doesn't that mean that, for them, no time has passed in that journey... so, from their perspective, "when" did the the energy loss occur? Or, are they in two different energy states simultaneously?
Photons don't have a perspective as they don't qualify as an observer. Nothing happens to the photon, energy isn't "lost" the photon is just be emitted and received in different reference frames.
Energy is a gift of universe. Laws of physics tells us in univers everything is in motion. Kinetic energy expression is with motion. But what sets all objects in motion?
when i thought about big bang i was wondering that if there is neither time nor the space existed before it how can it happen and can we describe it as an event.if i skip thinking about it,another confusion rises, why and how infinitly dense ball of pure energy suddenly inflate faster than speed of light,why it wasn't stay as it was.and if every thing made of same energy why fundermantal particles act very different from each other, where were the elementary charges came from? and why there is no negetive mass and negetive energy to cancel out positive ones?and if even everything can emerege from nothing why somthing can't be smaller than plank length,and how 'faster than light inflation' of the early universe efect the flow of time?
That quip about energy not being conserved in expanding spacetime... I think there is something there that can connect gravity to other forms of energy. If we treat the energy of the electromagnetic field as conserved and dipping into some sort of field that give space and time their geometric properties, what are the results? Anything worthwhile, or just math gibberish?
I enjoyed that explanation. OK so in an expanding universe where does the 'additional' energy come from and likewise where does the additional 'space-time' come from ?
It's not exactly the right question. "Where X comes from?" and "additional X" imply there are points A and B between which an amount of X is transferred with its absolute totality being constant. It's an accurate assumption, but only _in_ spacetime, not _of_ it, just like when you say "expansion", you correctly assume that something must expand into somewhere. However, spacetime itself is not governed by the same laws as objects in space. There's no additional spacetime, it's just the total amount of identical units of space increases with time; in other words, the Universe is not stretching a given amount of spacetime, it's constantly _creating_ it. With energy being an inherent property of space, that means in an expanding Universe, energy is also created, not transferred, so basically, it appears from nothing, spontaneously, with no cause other than there being more space than before.
@@Hisu0 You have a totally wrong understanding - the physics is solely that of the matter content of the universe moving apart at large enough length scales. There is no such thing as space being created or expanding anywhere in physics, and certainly no such thing as energy being a property of space.
If mass has energy by virtue of it's particles moving around and if you had knowledge of the momentum of each particle that make up an object, could you rewrite Einstein's energy equation purely in terms of momentum and the speed of light?
One quibble, and it’s probably because you are a physicist. The script goes something like “dirt becomes grass….” Dirt does not become grass! Air becomes grass, or more specifically carbon dioxide becomes grass. Dirt only plays an essential but minor role.
I have something called the Motion-Energy Hypothesis, it's here on RUclips. Basically my thoughts are that things that are not considered as being things, are actually things.
The only thing that surprised me was the mention of Émile du Châtelet. I have been reading the history of science for sixty years but somehow have never heard of her. I am satisfied to think of energy as the capacity to do work.
Thank you for your feedback! I'm glad you found the video informative. The Segway Portable PowerStation Cube Series is a great choice for outdoor enthusiasts like us. It offers a massive capacity, fast recharging, and versatile use. Check it out if you're looking for a reliable power backup solution for your outdoor adventures or home needs. Keep up the learning and enjoy your camping trips!
I like Dons way. He describes the fundamental topics of science in an easy to understand way, but he never talks down to you,. You are an excellent teacher, Don
"If mass is just energy swirling in a single location, with the swirling energy not moving - basically a stationary tornando - then we're back to the definition of kinetic and potential energy". That's mind blowing! 🤯
I understand the quarks have some very small basic mass given by Higgs field (no idea how it happens) and then the most of the mass is kinetic energy. If we just could slower down the quarks and use that energy... Electrons and neutrinos have mass of different origin.
This channel has helped educate me on many things that previously had been beyond my level of understanding. I still get a little confused on some things but its becoming much more clearer on how things in physics work. Thank you, 🙂👍
@Fermilab, and @Dr. Don Lincoln, thank you for trying to educate us science enthusiasts. 😊 Dr. Lincoln is a great teacher and luckily mankind will always have these lectures.
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The one thing I've never liked about the term "energy" is that sometimes it's used in reference to a property of something (e.g. the energy of a photon) while other times it refers to energy as "stuff" in its own right (e.g. when someone says that photon ARE energy flying through space). I definitely prefer the former use over the latter. Saying that energy is "stuff" is a bit like saying "height is stuff". It's not actually a thing that exists on its own without context though, it's a property of things that exist in fields. It's kind of like how velocity isn't an object, it's a property of an object you can measure. Same with energy, it's not an object itself but a property of objects (some which have mass and some which don't) that you can measure.
exactly, I had big problems of grasping the idea of energy because it was being used interchangeably ("has" - "is") all the time which is just stupid and makes a big mess of such a simple thing, that's actually ridiculous
The thing is that there is nothing that is not energy. You could say everything is energy and everything is light just in a conserved state. But that would not be useful when we talk about energy we usually mean useful accessable energy or at least energy we are interested in observing - we don't care that a sandwich has enough energy to outshine the sun for a few milliseconds we are interested in the few poor calories that we can access by eating it. On the same time energy is the only thing that isn't convertible you can make matter out of photons and you can make photons out of matter but you can't turn matter/photons into nothing or nothing into matter/photons.
@@fischX You actually can “turn nothing into something” when it comes to energy in quantum mechanics due to uncertainty. Quantum vacuum fluctuations allow for apparent nothing to split into pairs of somethings which have properties which destructively interfere and cancel when combined again. Also your reply exemplifies my issue, namely that “energy” is used for both a measurement of a property that things in the universe have and also the name we give the stuff that has that property we’re measuring. People say “photons are pure energy” but really they mean “photons are massless things which have a property we call energy that can be measured. But energy isn’t the only property photons have, they also have spin for example which is distinct property from their energy. But we don’t say “photons are pure spin”, even though they all have it as do all the quantum particles.
@@gabevee3 I agree, but that's irrelevant to my issue. I'm saying the terminology which uses "energy" for two somewhat different meanings would have more clarity if it referred specifically to a quantity being measured and not to it as an object. For example, as I mentioned in the reply above, you can measure a photon's spin and you can measure its energy, but we don't say a photon "is spin". And yet people say a photon "is energy".
Sounds like energy is just an invariant value that is a consequence of symmetry of physical laws. It’s too bad that this video didn’t point out that energy is relative, in the sense that two different observers will agree that it is conserved but might not agree on the actual calculated value of the energy.
I'm suddenly imagining gravitational wells around or within every single person object and thing. These wells when they intersect, like water droplets, can get larger in radius in direct proportion to the amalgamated mass focused into a single space. I think that if enough of these gravity wells accumulate, they create the planetary scale gravitational effects we see. Just as merging black holes result in a larger event horizon. The warping of spacetime is only strong and noticeable on larger scales but on smaller scales I imagine it is there. Everywhere there is mass, there is a warping of spacetime, a "gravity well" at all scales. Weak at small scales, strong at accumulative large scales. There might not actually be any "gravitons" and instead gravity may simply be an emergent property of mass at sufficiently large scales and/or mathematical extremes. Since mass and energy are considered equivalent, it can then be thought that gravity is therefore just another property of energy as it affects spacetime dependent on how much of it is concentrated in one place. It could also also be said that the more massive a thing is, the more "energetic" it is; the higher it's energy content is. I'm just an autistic lamen though. All of this fascinates me
The mathematical challenge in what your mind’s eye is showing you is at the heart of the mysteries of quantum gravity. One issue where everything gets stuck is in that in quantum mechanics, the wave function mathematically “smears” the position of subatomic particles, so the question becomes at what location the spacetime distorting effects of mass at a given location actually happen. If you can visualize how that works and put the math behind it, there’ll be a massive Nobel Prize with your name on it! 🙂
Yes, you got the concepts. Juuust those doesn't fit yet. Gravity should be quantised, but can't do it yet. All we have in quantum experiments is electromagnetism, but gravity at small scale doesn't have enough strength. And anyway it acts regardless of electric charge, it "attracts" matter with or without mass, doesn't matter which quantum numbers it has, Gravity works. One more idea for you. We have this stuff in a 4D vector Space. That's something we can't really imagine. But we have the projection of 3d objects, shadows on a wall. A cilinder there may appear to be a rectangle, a circle, and everything in between as you rotate the cilinder its shadow,, down one dimension from 3 to 2 appears to morph. But in 3D we perceive what's going on. 👍🤓
@@misterlau5246 maybe it isn't quantized and only emerges as a property of mass on larger than quantum scales due to mysterious processes. Of course idk either way but...I am always trying to think about these concepts and trying to work them out in my head in my own autistic way even though I am well aware I couldn't math my way to the solution, not with my severe lack of mathing ability and my lack of resolve to dedicate my whole life to it when I have other goals for my life. But ponder and question I shall because at the very least, it amuses me when I am bored and helps distract me from the darkness of humanity. The fabric of spacetime itself, the "thing" that is warped by the presence of mass; is a mystery to me. It's never been defined or at least I have yet to find explanation as to what exactly this "fabric of spacetime" actually is. This thing labled space-time that warps in the presence of mass, what is it composed of and what about it causes it to warp in the presence of mass? And what would existence barron of spacetime be considered? Would it be a void of the nothingness that is actually a mysterious something or would it be a true emptiness of all things if not a blackness of probability and buzzing virtual particles? I am in serious lack of the mathematical ability to work out the details and try figuring it out myself. I hope people smarter than me can find out the answers and I can find out through them. Best I can do is ask lots of questions, think, ponder, make art, and make music. I have nothing but great respect for those with more mathematically capable brains than my own who strive to define reality as it presents itself as precisely as possible for the betterment of all. Part of me hopes that maybe one of the questions I ask will one day be one nobody else has asked or thought of before, a question leading to efforts by those with all the resources needed to find answers and possibly lead to something good and revolutionary. But I suppose there's nothing wrong with being part of the audience to great scientific breakthroughs instead of being among those who manage to actually achieve them
@@misterlau5246 your explanation implies gravity is a separate thing from mass. If it is, and with it being defined as warps in the fabric of spacetime, maybe then gravity is the result of spacetime itself not being static on quantum scales, tiny random fluctuations in spacetime could be constantly occuring to draw in material to then react to the presence of accumulated material by warping more and more til it overcomes whatever energy would be causing the random spacetime fluctuations and becomes a stable non fluctuating warp that then acts like fluid drops in that if one warp merges with another, the combination results in a bigger warp... Whatever spacetime actually is, it's a probable candidate for the origin of gravity as far as I can tell.
@@Sigmaairav "maybe it isn't quantized and only emerges as a property of mass on larger than quantum scales due to mysterious processes." That is our current understanding of gravity as general relativity describes it. It would be weird however if gravity simply stopped working precisely at the scale we start to encounter relevant quantum effects. Additionally, if you consider that all our very successful quantum field theories obey special relativity, you'd need to find some mechanism that preserves some relativistic spacetime effects but not others (I'm not well educated enough to explain fully, but I hope you understand the issue). "The fabric of spacetime itself, the "thing" that is warped by the presence of mass; is a mystery to me. It's never been defined or at least I have yet to find explanation as to what exactly this "fabric of spacetime" actually is." The "fabric" of spacetime is just an analogy. It's not made of anything. It's a mathematical space that has certain properties (for more information, the technical term for the kind of 3+1 dimensional spacetime we see is Minkowski space). "what about it causes it to warp in the presence of mass?" The presence of mass is what causes it to warp. The warping of spacetime in the Einstein field equations is defined as a function of the presence of mass (or more precisely, energy flux density). Asking what causes spacetime to warp in the presence of mass is like asking what causes momentum to increase if the velocity of a constant mass object increases. Spacetime curvature and energy contained within spacetime are both properties of the spacetime that directly depend on each other, just like momentum and velocity are properties of an object that directly depend on each other. "And what would existence barron of spacetime be considered? Would it be a void of the nothingness that is actually a mysterious something or would it be a true emptiness of all things if not a blackness of probability and buzzing virtual particles?" This is a very interesting question in my opinion, because 1) many people like to ask and think about this very thing because it is somewhat philosophical in nature and 2) it has a very clear answer in mathematical terms. A space in mathematical terms is much more general that the 3D or 3+1D space/spacetime we normally talk about. It is essentially a list of possible states. If we talk about physical 3D space, it's just a list of places we can point to in order to define a location. In 3+1D spacetime, it's a list of places, but also of points in time, so we can say where something happens and when it happens. Any variable has its own space, a moving object occupies some position in velocity space for example. Without a space to occupy, there is no variable. Without physical spacetime, there is nowhere to be, not even time to spend looking at nothing. The state space of quantum particles (Hilbert space) has a dimension for every property of the particle, so if we consider there may still be particles without spacetime (which we can, at least if we disregard quantum field theory), there would be "something" there, like mass, charge and spin of any given particle, but it wouldn't matter since without being able to change over time nothing could happen.
Another exquisite video, thank you Dr. Lincoln. That said, I'm sticking with Dr. Richard Feynman who said, "It is important to realize that in physics today, we have no knowledge of what energy is." "Energy is the interaction and motion of fields..." - a much more eloquent description than "the ability to do work" but still unsatisfying in defining what energy actually IS. Just a layman but my two cents.
Time complexity. Our lives are lived at scales that do not match questions we can form. See underdetermination to gain a sense that we may not form useful questions. This may be related to the fact that brains evolve solely to compare and store sensory input useful to an organism and its biological/trophic niche. So you may be in need of broader education as to things at even your scale, like evolutionary pressure. Physics alone does not answer -- see the astonishing errors in some physicists' speculations on cellular biology, like Penrose's. Seek knowledge of what occurs at differing scales, as well as the mathematics of dynamical complexity to start.
You may ask, "what is time?" But you are not equipped to understand the concept, even with considerable food calculus. Measurement breaks down at extreme scales. Ask, "what is tension?" From which you may make analogies of physical properties as "energy" , "fields", and other phenomena, which break down when dimensional variables occur or are used to define factors in variation. Again, one can ask what occurs in space
(For some reason an autocorrection of "food" calculus occurred. But even that error, if absorbed, will lead a questioner to seek what occurs to a brain self-signaling some lacks, which distort perception.
It's worth noting that interpretation models also have symmetries. Under implication symmetry, "time symmetry implies energy conservation," TS>EC, forms a doublet with "energy conservation implies time symmetry," EC>TS. Another successful physics search rule is "simpler is deeper." Under simpler-is-deeper, Noether's delightful and beautiful TS>EC argument places Minkowski's infinitely differentiable and functionally complex spacetime to the left of a small set of conserved quantities. EC>TS, in contrast, places the conserved quantities, including energy, to the left of spacetime and hypothesizes that sufficiently complex conservation scenarios approximate Minkowski's spacetime. Besides scoring better under simpler-is-deeper, EC>TS ("Rehteon's theorem") also removes the needless century-long separation of relativity and quantum theory that Minkowski created by inserting a concept of spacetime whose precision exceeds anything possible with Einstein's original 1905 real-matter clocks and rulers. EC>TS, in contrast, unavoidably requires space and time to be variable-resolution quantum properties of matter.
if you travel towards a galaxy on a fast spaceship , its light will be bluer, but it is the same light that you see redder on Earth. So the energy of that light is not changed.your perception did.
why do people define energy by what it does and not what it is? Do scientists really know what the heck energy really is or do they know some of the things that energy can do? You can define something by what it does if there are multiple versions of that thing, but what is it really?
Thank you! Great video, as usual! I have one question that I would love if you could make a video about them: 1. Is there any theoretical maximum limit for frequency of an electromagnetic wave?
The maximum frequency of an EM wave can be more easily described by its wavelength. The minimum for that is the Planck length. Any shorter, and it's a black hole made by energy, a Kugelblitz
for 1) That is exactly what Dr. Don wanted to say with the phrase Energy is not conserved in an expanding universe. for 2) sure see here: en.wikipedia.org/wiki/Planck_units The black hole maybe or maybe not a consequence, but mattio79 seems a bit ahead of modern physics as so far nobody has an accepted model of quantum gravity and without that we simply can't say.
@@Techmagus76 Gravity is an effect of the curved distortion of spacetime by a local massive object. It's like saying there's centrifugal force. It's not a force, it's an effect. When neutron stars or black holes merge, the spacetime distortion propagates outwards like a wave caused by an object thrown into a body of water.
I watch a lot of youtube shows related to physics explanations. PBS Spacetime, ScienceClic, The Science Asylum etc... This is the first time I've ever seen something like the backdrop of a chalk board with things that I am surprised to say I actually recognize the writing on. Whenever I've seen similar backdrops, I've always glossed over it as nothing I'd be able to make sense of but this time I looked and couldn't believe I recognized over half of it. I love all of you educators that break down the concepts in physics to the rest of us. I may still not be able to solve any of those equations, (I only took basic calc) but the fact that I can now just recognize them and what they represent is awesome. It makes me want to learn more math again. Thank You.
I like your description. So many people think that energy is a physical, tangible "thing." As if someone could "get" an energy and carry it around in their pocket. But really, it's just an abstract concept. Like you say: "a capacity." Or an ability. No one says they can carry a capacity around, just like no one says mystical "ability to move things" pours out of crystals and into one's hands. But they say that about energy because it's almost completely misunderstood by the majority of people. Even a high percentage of physics students get it mixed up.
This was beautiful. It's always amazing to get a new insight and a different perspective so that you can modify or re-interpret what you've learned. I remember a grad school prof saying that every time he read "Feynman Lectures on Physics", he learned something new, and this was a person whose colleagues considered him to be brilliant. This video was like that for me.
To me, Energy was always "measure of how much can happen without outside influence": Potential energy is how much can a thing move (towards center of gravity) "on it's own". Kinetic energy is how many glass windows will an object break before it stops. Thermal energy is how much heat can escape object before it reaches absolute zero. Chemical energy is how mush heat you get by setting something on fire. Baby energy is how long will baby survive after it's parent have gone mad...
@@ObjectsInMotion That's wrong because objects with less energy can do more work than objects that have high energy. Air has a lot of energy but can't give us a lot of work. Using work in the definition could be ambiguous. Moreover, in thermodynamics work is defined as the energy is transfer. The definitions become circular if we define energy using work.
Ive been watching this channel for a while now. As a 6th grader, i never really understood my teachers, I thought everything was complicated and very difficult to learn. Thank you, Don. I can guarantee if this channel was the only reason i was able to achieve good marks in my physics exam. Much appreciated, keep it up.
How to I make a request for a topic? I'm curios to know: What is Space? Not space as in outer space, but, what are the structure and components of a volume of area that is empty of all matter and energy? Is there any theory about what space (ultimately spacetime, I guess) actually is in physics terms?
There is the possibility that the big bang is BS. There is no theoretical justification for accelerating expansion. It was not predicted, so the theory was adjusted ad hoc to fit the data. Lack of energy conservation indicates to me that the theory has failed. Physicists might try looking again at tired light, where the redshift is exponential decay of light energy.
I very much enjoyed the information you presented in this video. What I really respect about it is that you talked about two women, Emilie du Chatelet and Emmy Noether with the same reverence as Newton and Leibniz. In my Physics and Philosophy education I never learned about women's contribution to the science and art of Physics (except Marie Curie). I only knew of Emmy Noether because in graduate school I coauthored a paper on Noether's Theorem in Classical Physics. It saddens me that our educational system is so male dominated that we seldom learn about the import contributions made by women. It is kind of sad that the fact you talked about these great minds makes your video exceptional, but it is also great that your video is exceptional.
Is it possible that some of the energy driving expansion is sapped from photons and neutrinos as they travel through empty space and get red-shifted? Or alternatively, is there a frame of reference in which that's how it appears?
A volume of space will expand proportional to the third power of the volume's radius, while the photon's energy loss is dictated by the inverse square law meaning the energy loss is portional to the squared radius in a volume. Meaning photons lose energy slower than space expands so the expansion couldn't be driven by the energy sapped away from photons.
@@ThatCrazyKid0007 This is not true. A photon does not lose energy by an inverse square law. I think you're confusing the energy of a photon with the intensity of a collection of photons radiating from a source. The intensity of a beam of light diminishes by an inverse square law, due to some simple mathematics, but not the individual photons. Furthermore, even if we decide to talk about the intensity of a ray of light, a volume of space being proportional to the third power of a volume's radius doesn't matter. This isn't a complexity analysis at some asymptote. Being proportional to the volume has no bearing on any other factors that might relate the expansion, and it's easy to see where a case can be made such that other factors diminish the growth of the cube versus the square in the range at which we observe it. You're basically extrapolating from a relatively tiny data set and pretending that it has to generalize, which is poor thinking.
Thank you for this. I have for a long time tried to understand « what is energy ? », and my readings haven’t so far allowed me to find a satisfactory answer. It isn’t too hard to understand what energy ‘does’ or what constraints it obeys, but what it ‘is’ remains an open question. The clearest suggestion so far seems to be that it is « an accounting principle ». Be as it may, it seems that in the current state of knowledge in physics the two fundamental constituents of Reality (this unknown thing with capital R) are Energy and Information, both of which are conserved. So the next question, is: how do the two relate? and are there fundamental equations that describe how the two relate in different conditions? Thanks again!
You have it exactly right - it's an accounting principle. If a system is time-translation invariant then we can assign the system by an arbitrary scalar we call "energy" that is a constant of motion. What this means is that the interactions are fixed over time, for example the coupling constants stay constant, then how the system evolves will be constrained by these interactions in a way that is predictable. The conceptual problems emerge when we ask "what is energy" which implicitly assumes that energy is a something in the first place, which we've known is false since the days of Count Rumford's cannon boring experiments.
Perhaps we should say that a thing is what it does, or, more generally, what is true of it, or how it relates to things. Then, when we are describing how much energy there is in each part of some system, and how that changes, we *are* describing what energy is?
@@drdca8263 Energy doesn't physically exist so can't do anything. You can assign any system any value of a energy you want and it doesn't change anything. What is physical is that particle interact and it is the interactions the govern the dynamical evolution. Since the coupling strengths are constant over the evolution of any system is constrained which allows the assignment of a conserved quantity, the hamiltonian, which is we usually associate with the total energy.
@@kylelochlann5053 seeing as the Hamiltonian is the generator of time evolution, and the Hamiltonian operator is an operator which sorta represents energy, it seems reasonable to me to say that the Hamiltonian operator does things. Of course, the Hamiltonian operator isn’t a “physical object”, but, eh
@@drdca8263 Exactly, the Hamiltonian isn't a physical thing that "out there" living a life outside our heads that's bending the world into a particular form. This is actually all very clear in relativity, but runs into the risk of boring the readers.
While I appreciate mentioning du Châtelet, the way it is done here is a bit misleading. Peloni and 's Gravesande both did the ball-dropping experiment before du Châtelet. She was replicating and publicizing 's Gravesande's work, but the video presents it as original research. Additionally, it's disingenuous to say du Châtelet "sorted everything out", as the vis viva debate continued past her work.
I think there's no one video or book explaining the concept of energy this much simple, complete and at the same time persice. It fulfils different physics knowledge levels. Thanks a lot.
I seriously doubt anyone understands the basic concepts because of watching this video. Not all of it is bad but neither is it good. You deserve something better, try Feynman if you look for depth, simplicity and precision. That is old but unequalled. Fineman explains with the precision of a surgeon's knife in competent hands, in comparison, this looks like someone tearing down a wall with a sledge hammer.
“The Final Theory: Rethinking Our Scientific Legacy “, Mark McCutcheon for proper physics including the CAUSE of gravity, electricity, magnetism, light and well.... everything.
@@AntonvanUitertthanks alot for your suggestion. Yeah! Feynman's lectures are exceptional in this point of view. I was looking for a good explanation or maybe the definition of energy for high school students and this video was very good at it. It starts from simple examples to higher level ones and tries to give a reasonable definition for energy.
I don't buy the claim that redshift indicates a change in (loss of) energy. - Redshift can occur because of the motion of the observer (Doppler Effect). There's relative motion, so it appears to be a different frequency and thus a different energy. That observed energy is constant, so there is no loss. The problem would be the acceleration of that relative motion, which ought to require energy input and thus where that energy comes from. - Redshift also occurs from light escaping a gravity well. Since per Einstein's theories gravity is the same as acceleration, light moving 'against' gravity experiences a Doppler Effect, too, and so it appears redder. There is no loss of energy. Energy is conserved. Instead, it's the observation that the frequency is different than what it would be without relative motion or gravity. Observing that cars on the highway move more slowly when we are also in a car on the highway does not mean they 'lost' energy. It only means our reference is different.
Interestingly enough, as I was eating breakfast, I asked myself “what exactly is energy?” And later this video appears on my notification. Very nice coincidence. While eating breakfast I said to myself that energy is the battle between existence and non-existence via virtual particles popping in and out of existence itself which is the fundamental basis of all that exists.
For something to pop into existence, there needs to be an underlying energy field. If you hold your breath and stay still, there's no motion or movement and yet it requires energy to maintain that seemingly static state. There's an interesting interplay between the static and dynamic, where one forms the basis for the other.
I think Dr Don just told us that matter is largely the energy binding quarks, so then the topology of space time is a function of the distribution of energy. A discussion of the relationship between energy and entropy would be helpful.
At a fundamental level, all types of energy can be reduced to potential and kinetic, and massless particles like photons create fields of potentials. How can even potential and kinetic energy be unified into a single thing? I have a conception for how, but I've never seen it phrased this way, and I might be way off base (I'm not a physicist and I'm confused as hell). Energy is the quantity of displacement from zero in a field. Probably a quantum field, but I'm visualizing it as a classical field. All fields have values that overlap in the same point in spacetime. These field values can sometimes be converted to a different form (e.g. pair production from photons, weak interactions, etc.) , but the sum of their displacements can never change. The sum of the displacements within a system is equal to that system's absolute internal energy. When the displacements are stationary (or possibly modeled as standing waves), you have potential energy, and when they are moving, you have kinetic. Am I on the right track? The difficult thing about understanding potential energy is that it doesn't seem to actually exist anywhere in conventional explanations. An apple held 1 meter off the ground is said to have gravitational potential energy which transforms into kinetic if it's dropped. But this potential "feels" fictitious without something like this to make it tangible and unify it with kinetic energy.
When I was in high school I contemplated the definition of energy. My thought was "the ability to do work" was a horrible definition, as it doesn't take into account energy that doesn't influence our physical environment, such as mental. The definition I came up with is "unbalanced forces". I still believe this definition is more accurate and inclusive.
Well what is 'mental energy'? There's the phenomenon you feel of course (like feeling exhausted or even 'energised'), but that's just subjective. From a physics standpoint, it's basically a complicated dance of electric currents (and some chemicals) flowing around in your brain. And that takes us right back to how physics conceives of energy, which already covers electrical and chemical energy. The physical environment, after all, also includes the environment inside of ourselves, all of which is influenced by those currents.
What kind of nonsense reasoning is "mental energy"? Of course "mental energy" affects your physical environment. Your body has to burn calories and generate heat in order to do those mental processes.
I have a definition of energy... Suppose you're watching a video of a ball in a slow straight trajectory going into a jar of peanut butter, without more informations. The video stops and you have to decide what happens next. There's in fact, two possibility : 1) You're watching a normal speed video, shot in space : since the ball is going slow, the ball will simply slowly bounce off the jar. 2) You're watching some ultra- slow-motion video : the jar and maybe the ball are going to explode in millions of pieces all over the place. The importance fact here : you can't decide which video you're watching until you know the time speed of the video. So we can deduce : energy is relative to time. Now you want to know, between the two situation, indepently of time, what's different. You realize : it's the speed of sound in the objects. In the first video : sound goes fast, therefor forces has enough time to propagate into the objects and inverse the global motion of the ball. In the second video : the ball goes faster than the sound. The wave of pressure due to the contact doesn't have time to propagate into the objects : so both explodes. So kinetic energy is relative to an absolute property of the objects : the speed of sound inside them. So my conclusion is energy is relative to the scale of sub components of systems, which in turn define a time scale. (for instance the speed of sound in objects in theory allow you to measure the time scale of videos of them)
I'm sure this has been considered, but I've never heard anyone mention this: Does the loss of energy of photons as they travel through expanding space not account for dark energy? If space is expanding and needs energy to do that, and photons travelling through expanding space are losing energy, then is it possible it's their energy that is converted into what we call dark energy? I do realize that this explanation is incomplete since it doesn't describe why the energy conversion happens in the first place. But it's an interesting thought and as I said, I don't recall this being discussed in any physics RUclipsrs' videos.
Yes it was asked and answered in an episode of PBS spacetime, and no they don't balance out the increase in dark energy is much larger than the loss from photons.
There is no reason to expect energy to be conserved in an expanding universe. Noether's Theorem just does not apply in an expanding universe; because space is expanding, there is no time-translation symmetry.
Ordinary matter is only 5% of the universe. And photons are ordinary matter. 27% is dark matter and 68% dark energy. How can 5% ordinary matter account for 68% dark energy?
That point about photons being red-shifted thus losing energy and energy therefore not being conserved is something I don't understand. Isn't it just the doppler effect in action over a longer distance? That's what Varitaisum claims in his video "What Actually Expands In An Expanding Universe?". So measuring the doppler effect of photons on a local level here on Earth should equally imply the non-conservation of energy then? I thought red-shifting photons in the universe are just a consequence of the constant density of dark energy. The ultimate culprit is still dark energy. Please help me understand 7:36
Awesome video as always. @Fermilab, I would suggest embedding links to previous videos within the video when they are referenced, rather than just in the description, similar to @SpaceTime. It makes it more likely the viewer will click through and check out those older videos, and eventually get hooked when they discover how much great content this channel has :)
I think kinetic energy and potential energy are literally the same thing, but we don't yet understand gravity or atoms. I think energy is preserved at a cosmic scale, but we don't yet understand where it is going to or coming from. I think neither time nor space are fundamental because both collapse in black holes and at the big bang. I think they emerge from something we don't understand enough to see yet.
I've never 100% believed that energy is conserved. It's just that "potential energy" is defined in such a way as to make energy appear to be conserved. I could equally claim that, say, the "blueness of the sky" is conserved. If you say no, the sky turns black at night, I can just reply that it has "potential blueness" at night, which will be converted back to actual blueness when the sun rises tomorrow. OK, I know there must be a flaw in this argument, but I can't see what it is.
I've always had the same gripe. Like, raising a microphone higher up doesn't actually give the microphone more energy - it doesn't contain the potential energy. It's almost like potential energy is a purely mathematical construct to make conservation laws make sense, but also that conservation laws are a purely mathematical construct to make energy make sense? I asked about this on a Science Asylum video, and I can't remember exactly what Nick said, but it was something so simple, and kinda mindblowing, something to the effect of "all energy is just numbers," (but probably a bit more sciencey, haha). Even if we think just about kinetic energy, I get confused. A simple object with a simple velocity. But, in what reference frame does this object have velocity? There's no absolute space, absolute time, or absolute speed, so does this mean the object has different energies in different reference frames? The way I look at it now, energy isn't a property of an object, but a property of an interaction (or potential interaction) between multiple objects, and that's why potential energy can make sense. The microphone doesn't physically have that energy, but it will impart that energy upon impact with the ground. If the ground starts to move away just before impact, that impact will be less energetic, but the microphone's energy hasn't changed; it's just the interaction between the two objects have changed. Anyway, that's my little unqualified thought on the matter. I too think there must be a flaw in my argument, so I hope some even smarter people can weigh in.
@@c4ashley Raise the mic 1 cm and drop it. Next, raise the mic 10 feet and drop it. If it hits louder the second time, it had more PE with respect to the floor.
The best explanation for energy is that it is a state function. It is a way of assigning a number to a physical system that is hella useful for predicting what can and cannot happen to the system. It doesn't help that the word energy is used for several related, but not quite identical things. The ability to do work, or the "accessible" energy, is the one people most commonly think of, but then they get tripped up when they think about heat or potential energy of chemical bonds, which can only be made to do work in special circumstances, and can't understand why you can't make a chemical engine running on pure water.
@@mikeyoung9810 It may not be satisfying, but it is the most accurate description of what energy is. It's not some physical substance that's moving in the world, it's just a quantity we ascribe to things. When you lose touch with the mathematical nature of energy and focus too hard on "what" energy physically is, you are liable to either go insane, or start coming up with new mystical beliefs and religions. It's mostly an issue with quantum mechanics, since that one's a much more esoteric piece of math, but I've heard a fair share of outlandish ideas about energy from people who focus on material reality without really accepting that it's just some numbers physicists find useful.
I mean, even this video explains energy by talking about the mathematical expression for kinetic energy, and that the potential for causing motion is also energy. Notice it doesn't really talk about what energy is, it talks about what goes into the math, which depending on your starting point may or may not help you understand it.
The reason why American scientists have never been able to define energy unambiguously accurately is lack of profound knowledge of the English language and physics, although they can pinpoint examples of energy Energy is actually an ambiguous term for forces which can be either natural or artificial So, "energy is force to do work " You guys can see my definition of energy is so simple, but accurately concise without any ambiguity at all Forces are the fundamental foundation of all forms of matter or existence in the entire infinite space of the universe, and they are created whenever transformations of forms of matter take place Another example of ambiguity in scientific definition is " the observable universe" which can be interpreted as that the universe is observable while actually human beings have so far been able to observe only an extremely small part of it. It should be put clearly without any ambiguity like this: " Only an extremely tiny part of the universe is observable to human limited knowledge" Your definition of kinetic energy as to be a thing that can move or vibrate is incorrect because a thing or things which can move is a moving thing or moving things, but not any form of energy That is why American English is ambiguous, which can make very simple concepts complicated or confusing to students, thus hinders public education. Energy is any form of force, and kinetic energy is any form of force which makes things move. such as electromotive force emf which drives electrons around in a circuit, gravitational force which pulls objects toward the centre of the Earth, chemical force released in chemical reactions, nuclear force in nuclear fission reactions, air pressure force due to different mass concentrations at different locations in space, applied force by humans and human-invented machines
i loved your historical discussion of the evolution of the notion of energy and momentum. please have a series of videos about this historic evolution.
I have no formal education in physics, just a lifelong fascination with the limits of what we can know about the universe, Dr Lincoln has been one of the most easily digestible educators out there, many thanks ❤️
🙂👍
Dr Lincoln is a great educator, love his vids on this channel
Such a rabbit hole of a fascinating field. I love cryptography because it's the intersection of math and computer science (my primary field), but with quantum computing we have had to think of interesting ways to get around Shor's algorithm which will break our modern asymmetric key exchange protocols (DH-RSA, DH-ECC, etc.).
So one of the solutions we have come up with is a brilliant quantum key exchange protocol called BB-84; its security actually relies on physics instead of math.
Shor's breaks our current algorithms because they rely on the discreet logarithms and the hard np-complete problem of factoring huge prime numbers, which is not a problem for quantum computers due to superpositional calculation.
BB-84 relies on photon orientation and is theoretical information secure and naturally authenticated because once any of the photons are observed and tested for their orientation by an attacker, they are changed.
This is remarkably awesome!
@@aethrya
Few years ago I watched a documentary about China advancements in cryptography, they had a prototype information system that used entanglement as the security protocol to make sure info isn’t hacked, basically destroys the message when someone attempts a hack which breaks the entanglement really insane stuff, at least to me, I’ve never tried to be good at math, but nature uses it beautifully
Science with out the gobbkdy gook for no shit.or no cherry picking and showing you how physics get there results..guess..I mean hidden variables and blag models that are guessed .hav alook u wont be disappointed..physics truth not for funding...❤
Thank you for a great video. However, I think it missed an idea more fundamental and therefore enlightening than any of those expressed. Energy is the ability to cause change. (I don't think that word was used even once!) A system without any energy is unable to change, under any circumstances, without the introduction of an external ability to create change. Potential energy recognises the existence of a blockage that prevents change from happening. On releasing the blockage, change happens and physicists say that potential energy was converted to kinetic energy. An example of a blockage is a table that stops a spoon from falling. Without the table, it falls, demonstrating that the ability to change (the energy) existed when the spoon was on the table. Another is the structure within an atom that keeps the ability to change within the atom. Disturb that structure and that ability to make change can be released. That release can cause the release of the energy blocked inside neighbouring atoms which can then escalate - called a chain reaction, and we have an atomic bomb.
It is instructive to think about what a system that cannot change (has no energy) would be like. My imagination says that the value of every field within that system would be the same at every point.
“Energy is the ability to cause change.”
This is an outward feature of energy more than its intrinsic nature.
@@cloudpoint0 perhaps it would be better to say that Garry's description describes the intrinsic nature of entropy, which is an immutable feature of energy. the quality of energy that he's describing is relational in essence, which is to say that it's a great way of looking at energy as a series of disturbances in a series of boundless fields. perhaps your definition holds to the quantizable aspects of energy, and thus would see entropy as an external quality rather than necessarily implicit; i would like to know what you think, and how it relates to my assumption on your behalf.
@@owfan4134
Energy doesn’t really exist, at least not independently. It’s purely an abstract numerical measurement like velocity, distance or temperature, none of which you can say is something on its own beyond some mathematical existence. Energy is just a property that we measure between two objects - one object alone can’t really have energy just like one object alone can’t really have a distance - the measurement has to be compared to some reference object. This means energy is relative - and different observers see the same measurement as a different number. The train rider sees the train as having no (kinetic) energy while the person waiting on the platform sees the arriving train as loaded with energy.
I don’t know what an overall statistical measurement of a large group of many things, like entropy, has to do with the description of a single measurement between two things in that group. And I can’t connect Garry’s description to entropy. Since energy is conserved, entropy doesn’t change energy, entropy is just an expression of energy’s disorder.
Maybe going back to basics will help here…
*What the HECK is Energy?*
ruclips.net/video/snj1wBtn6I8/видео.html
@@owfan4134 @cloudpoint Thanks for your replies. I am not confident that I have understood all the implications /meanings of your responses but I have picked up 3 issues - intrinsicness, relativity and entropy.
1. Intrinsic. I don't know how to define this in this context, and I suspect that the distinction provides little information that helps someone understand energy. The fact is that if we observe two otherwise identical systems, one involving a collision of a fast moving object and the other a slow moving object the fast moving one will cause more change and will have more energy. I don't believe that these two observations can be distinguished. It will always be true, irrespective of the design of the system. That conforms with what I would call intrinsic. I think that @cloudpoint has agreed with me on this in his latter reply.
2 Relativity, I agree that depending on the frames of reference, two observers will disagree on the speed of the objects in a collision. However, they will not disagree on the amount of change the collision has caused nor on the amount of work done and therefore the amount of energy used. So, I contend that velocity is relativistic, but energy is not.
3. Entropy. There is clearly a relationship between energy and entropy, but I don't think that makes them the same thing. My comment is about energy, not entropy. If I understand correctly, I think @cloudpoint has answered this issue much better than I have.
I like the definition. As an "ability" it is clear that energy is connected to physical entities, rather than something that can be seen in a pure form.
I've often thought of "Energy = the ability to change the state of motion of objects" but I see reading the comments that I might have to add "or the arrangement" of objects, thinking about entropy.
Just a novice take
While the definition of energy can be very vague, the best I came across was that energy was a number that we associate with the configuration of a system or the motion of a particle. It can also be defined as a quantity that interacts with matter and can bring changes to its shape, state, temperature, configuration or motion.
"Energy is the ability of a system to perform work on another system.". What's vague about that? Please explain in great length and detail. Please explain in addition why you weren't paying any attention in high school science class. ;-)
Many thanks ! While watching I thought there are 3 forms of energy. The third form is teaching.
Energy is the ability to work, from our high school physics teacher. still remember it all these years. Mrs. Lainez 😌
So far, it appears that the universe started as something tiny and started to expand to what we can observe and detect today. It also appears that anything we can observe or detect is made from extremely tiny particles which interact and combine with each other based on some fundamental predetermined rules. We have identified quit a few of these extremely tiny particles and have identified quit a few of the rules these particles follow to interact and combine. Perhaps most of the particles and most of the rules but there probably are more.
We also discovered that anything that we can observe or detect is made from the same basic stuff and we call this stuff energy. We know this because we have figured out how to calculate a value or quantity of energy for anything that we can observe or detect. I think we can say the fabric of the universe is space time but we can also say that the fabric of the universe is energy time because we now know that space is not empty and is also some type of energy and we can calculate or at least estimate how much energy is in a given volume of space.
It also appears that after the universe started to expand, no more energy was added or removed as it continued to expand. We do not know what the rules were that determined the amount of energy in the universe nor what caused the energy in the universe to start expanding. The rules for how energy expands, transforms, interacts and combines cause energy to cycle from concentrated to diluted states. Although the cycles can be repeated almost an infinite number of times, there will be a time when they stop because as the cycles keep repeating, the total amount of energy in the universe keeps becoming more and more diluted. We call this rule entropy.
At some point in time, all the energy will become so diluted that it will not be able to cycle back into more concentrated states and we think this is when the universe ends. We still do not know the rules before the universe started to expand and we still do not know the rules after the universe ends and there are probably still many rules that we do not know about that causes the energy in the universe to cycle back and forth from concentrated to diluted states as it continues to expand.
Well, with this definition energy will not be the fundamental entity of the nature but a consequence: the onsequence of the motion of fields and their interactions. But then we are faced again with the question of what causes the motion of the fields and their interactions. Looks like we are back to a cicular argument, since motions and interactions can only be understood due to the presence of energy in the first place. Similarly, the existence of fields begs the explanantion about their very existence due to something else which we would like to call energy again. I think energy must be defined and understood independently of its consequences but it is almost impossible how we can do that.
The lecture was awesome. However, while you were talking in length about kinetic & potential energies, I was also waiting to hear about heat energy, which somehow you skipped, or, maybe you mentioned, but I missed.
When I was first introduced to E=MC^2 my first question was.. yes but 'what is energy'?
I mean we can understand what mass, and the speed of light are.. But when fission begins converting mass into 'energy' exactly what does that mean.
And I was told, well, mainly heat and light. But then I was left wondering how heat and light could erase a pacific atol.
'What is energy' is a great title, and I'm sorry to say, though I love your video, you didn't really give me the epiphany my 11 year old self required.
I know what you mean. I was stuck on that Star Trek episode where Mr. Spock says, "fascinating captain, pure energy." I looked for what energy was for years until I realized it was a property something else has just like length and weight. There is no "pure energy" any more than there are "pure inches" or "pure ounces". Perhaps everybody takes this for granted and so never emphasize the fact in their explanations, only allude to it briefly before moving on.
Hello Dr. Lincoln @Fermilab - was this video inspired by a recent conversation you had in Orlando about Kugelblitzes, hmm? :-)
Thank you for producing this. What I think is interesting is that a moving, unaccelerated object has "kinetic" energy, but within its own reference frame it is stationary. The thing having what we call "potential" energy is actually not stationary, but following a straight line through curved spacetime - in the same way that a basketball is actually travelling along a straight line through a curvature in (mostly) time. I think I need to consider kinetic and potential energy the way we consider electricity and magnetism to help my brain make sense of the difference.
Thanks again, and after I watch this a couple more times I look forward to your next videos.
Not sure how helpful the concept is but Voltage is always 'relative' right? Could this also mean that a region of space can have its own 'ambient' level of charge, zero to its own reference? And it's similar for mass-related energy? Dont mind me I'm just an electronics geek tryna make sense of this stuff :)
@@petegaslondon lol. As a software person I barely understand that on airplane hardware you have to float your grounds, so I can empathize. ;-)
The thing is, we have absolutely no idea what energy actually is. We can only describe what energy does.
We have absolutely no idea what a troll is. But we can describe what they do. They keep begging for attention. ;-)
I don't have so much knowledge about PHYISCS now but I've have curiosity to know more and more about it.
Then you take a undergraduate course in Physics and go for Post graduate course
Best science videos I have ever seen and heard.
This guy deserves more subs guys.
I was taught along with all you have mentioned that energy just is. It can’t be made or destroyed only transformed. Because of quantum mechanics energy never stops even at absolute zero because at the very small mass is vibrating. If string theory is true the filament is vibrating. Hence energy. Photons have no mass yet their motion is energy. So it’s not just mass it’s motion. Potential energy is in motion because everything vibrates on a subatomic level.
You got the absolute zero thing backwards, nothing can reach absolute zero _because_ everything has some non-zero vacuum state of energy, not that energy happens at absolute zero as well.
Thank you for your effort to educate the public.
I enjoyed it, but feel you did not provide the answer asked in the title "what is energy". You described things that have energy, but I'm as confused as ever as to "what is energy"
Thanks Don, great video. BUT ... what about heat? an everyday example is car brakes turning the kinetic energy of the car into heat to halt the car. Or the engine converting chemical energy into heat in the combustion chamber which is then converted to kinetic energy (of the car) by various moving parts.
This was a great video Dr. Lincoln!
I've got thru half of this, and I have to go to sleep now. Will check back after I drive my semi another 10 hours tomorrow. 🚛💥💨
You are a great teacher, sir, but this time I feel I'm left at the same point where I started.
'Potential energy is force fields and their interaction with objects, kinetic energy is the motion of those fields'.
So what are forcefields? I mean, what is force in the first place? What is this thing forming a 'field'? What is it made of? Well, I know that science doesn't have all the answers, of course, as it is the search for the answers.
“Flowing through all there is balance.”
I recently saw a video where the presenter was dismissive of an analogy of the Universe expanding being the same from an outside perspective as if it's contents are shrinking, saying he didn'tgive credence to pseudo science, and I would love to know why we do look at the universe in the particular way that we do? It struck me that over galactic scales gravitational effects observed around the edges have taken thousands of years to propagate and if the mass content was steadily shrinking (while remaining fairly consistent in structure and form), the effects felt on the outer parts would have been caused by a larger gravitational force than is currently present at the centre and is acting on matter that has also diminished in mass but not structure, so would appear stronger still. Similarly, with photons losing energy over distance, why do they and into what? With energy in the quantum foam seeming to appear out of nothing, could a steady radiating of energy from matter be a contributor to that? Blackholes in the very early universe could have been formed in the way we observe stellar mass blackholes but would not lose their scale and mass/energy content at the same rate as the surrounding matter, by the nature of what they are, isolated pockets of space, therefore becoming the dominant gravitational force in early galaxies (without requiring spontaneous collapse, primordial blackholes or many many many collisions with other blackholes to get to billions of stellar masses). We observe entropy and waveforms dissipating their energy in every other aspect of our world, but i've not seen a reason given why it's not postulated for the foundational packets of waveforms and energy we call particles.
Sorry if that was a lot in one go, and I am very aware my knowledge of physics is limited, so with those observations there are probably many simple or complex interactions that i've missed that answer why the above is not the current consensus. Thank you for the video, it's always a pleasure seeing your content
❤❤❤❤ If you do not know what energy is, there is no need to feel bad about it. As a physicist once said "Before I entered this prestigious university to do my PHD in physics, I know exactly what energy is but after I was awarded my PHD, I have absolutely no idea what energy is ! 😂😂😂😂 Dr HW Looi
"Energy" is a parenthetic:
Potential ) Kinetic ( Energy ) static
P ) K ( E ) v = low P ) k ( E ) v~relativistic
P ) K ( E ) v= c
mass energy equivalence I think can be understood under this thought experiment: take a box with perfect mirror walls on inside that has no mass then trap some photons inside. The box will now have mass and weigh something. or if the box has already some mass, it will increase depending on the energy of the photons.
I think this is how particles could actually get mass like interactions with the Higgs field could be a phenomenon that is equivalent to this
I'm interest to learn more about energy from thought/intentions.
Its interesting to think that an object has gravitational potential energy with a concentration of energy.
But how should we look at a double AA battery. Is the difference between a full battery and a dead battery all electrical chemical + gravitational, or is all the gravitational potential = electro chemical.
Great video - thank you. So, per the statement at 7:50, photons reaching the earth from the farthest discernible galaxies have lost energy compared to when they were emitted (i.e., red shift)... if these photons are traveling at the speed of light, doesn't that mean that, for them, no time has passed in that journey... so, from their perspective, "when" did the the energy loss occur? Or, are they in two different energy states simultaneously?
Photons don't have a perspective as they don't qualify as an observer. Nothing happens to the photon, energy isn't "lost" the photon is just be emitted and received in different reference frames.
Energy is a gift of universe. Laws of physics tells us in univers everything is in motion. Kinetic energy expression is with motion.
But what sets all objects in motion?
when i thought about big bang i was wondering that if there is neither time nor the space existed before it how can it happen and can we describe it as an event.if i skip thinking about it,another confusion rises, why and how infinitly dense ball of pure energy suddenly inflate faster than speed of light,why it wasn't stay as it was.and if every thing made of same energy why fundermantal particles act very different from each other, where were the elementary charges came from? and why there is no negetive mass and negetive energy to cancel out positive ones?and if even everything can emerege from nothing why somthing can't be smaller than plank length,and how 'faster than light inflation' of the early universe efect the flow of time?
That quip about energy not being conserved in expanding spacetime... I think there is something there that can connect gravity to other forms of energy.
If we treat the energy of the electromagnetic field as conserved and dipping into some sort of field that give space and time their geometric properties, what are the results? Anything worthwhile, or just math gibberish?
Hello! Can you please explain fenomen "Axis of Evil" and can it be prove that Earth is the center of Universe? Thank you.
I enjoyed that explanation. OK so in an expanding universe where does the 'additional' energy come from and likewise where does the additional 'space-time' come from ?
It's not exactly the right question. "Where X comes from?" and "additional X" imply there are points A and B between which an amount of X is transferred with its absolute totality being constant. It's an accurate assumption, but only _in_ spacetime, not _of_ it, just like when you say "expansion", you correctly assume that something must expand into somewhere. However, spacetime itself is not governed by the same laws as objects in space. There's no additional spacetime, it's just the total amount of identical units of space increases with time; in other words, the Universe is not stretching a given amount of spacetime, it's constantly _creating_ it. With energy being an inherent property of space, that means in an expanding Universe, energy is also created, not transferred, so basically, it appears from nothing, spontaneously, with no cause other than there being more space than before.
@@Hisu0 You have a totally wrong understanding - the physics is solely that of the matter content of the universe moving apart at large enough length scales. There is no such thing as space being created or expanding anywhere in physics, and certainly no such thing as energy being a property of space.
@@Hisu0 Many thanks
If mass has energy by virtue of it's particles moving around and if you had knowledge of the momentum of each particle that make up an object, could you rewrite Einstein's energy equation purely in terms of momentum and the speed of light?
2:53
She literally got balls of steel
A Woman with balls?
What about energy density contained in force fields?
Do Quarks emit heat loss? Does entropy affect dark energy?
One quibble, and it’s probably because you are a physicist. The script goes something like “dirt becomes grass….” Dirt does not become grass! Air becomes grass, or more specifically carbon dioxide becomes grass. Dirt only plays an essential but minor role.
Signs of energy is heat dissipation.
Any thoughts on "zero point energy "
Still, what is energy?
Take a physics class and much more math to avoid further stupidity.
Modern science still don't know...
I have something called the Motion-Energy Hypothesis, it's here on RUclips. Basically my thoughts are that things that are not considered as being things, are actually things.
The ability of a body to do work
Why can't we make a photon 2.0 and call it an energon.
The only thing that surprised me was the mention of Émile du Châtelet. I have been reading the history of science for sixty years but somehow have never heard of her. I am satisfied to think of energy as the capacity to do work.
Emile was a noted scientist and mathematician in her day. Produced many children and died at an early age.
Thank you Doctor Lincoln, I appreciate your efforts to educate us and I try to learn. Keep up the good work.
Thank you for your feedback! I'm glad you found the video informative. The Segway Portable PowerStation Cube Series is a great choice for outdoor enthusiasts like us. It offers a massive capacity, fast recharging, and versatile use. Check it out if you're looking for a reliable power backup solution for your outdoor adventures or home needs. Keep up the learning and enjoy your camping trips!
I like Dons way. He describes the fundamental topics of science in an easy to understand way, but he never talks down to you,. You are an excellent teacher, Don
Another incredibly informative video from Fermilab. These are top knotch, please keep spreading the knowledge
"If mass is just energy swirling in a single location, with the swirling energy not moving - basically a stationary tornando - then we're back to the definition of kinetic and potential energy".
That's mind blowing! 🤯
I understand the quarks have some very small basic mass given by Higgs field (no idea how it happens) and then the most of the mass is kinetic energy. If we just could slower down the quarks and use that energy...
Electrons and neutrinos have mass of different origin.
@@hartunstart electrons also get their mass from the higgs, similar to the way quarks do, but yes neutrino masses are most likely a different origin.
Energy is what indiscernible but exist, or can't be found in space but can be found in time.
@@MegavoltHomeschool what is energy?
Swirling is moving.
And just like school I have no idea what he is talking about.
Energy
I am MOVED by this excellent lecture. 🤓
This lecture is full of Potential. 😏
Love this channel. Definitely learned new things about energy conservation.
This channel has helped educate me on many things that previously had been beyond my level of understanding. I still get a little confused on some things but its becoming much more clearer on how things in physics work. Thank you, 🙂👍
@Fermilab, and @Dr. Don Lincoln, thank you for trying to educate us science enthusiasts. 😊 Dr. Lincoln is a great teacher and luckily mankind will always have these lectures.
As long as RUclips let's you have it.
Thank you for sharing your appreciation for the educational content. It's great to see Dr. Don Lincoln educating science enthusiasts. Speaking of energy, have you heard about the Segway Portable PowerStation Cube Series? It's a versatile powerhouse that could be a game-changer for outdoor enthusiasts like us. With its massive capacity, powerful output, and fast recharging, it's the perfect companion for camping and backup power needs. Check it out!
Espresso and gummy bears are a typical breakfast for me.
The one thing I've never liked about the term "energy" is that sometimes it's used in reference to a property of something (e.g. the energy of a photon) while other times it refers to energy as "stuff" in its own right (e.g. when someone says that photon ARE energy flying through space). I definitely prefer the former use over the latter. Saying that energy is "stuff" is a bit like saying "height is stuff". It's not actually a thing that exists on its own without context though, it's a property of things that exist in fields. It's kind of like how velocity isn't an object, it's a property of an object you can measure. Same with energy, it's not an object itself but a property of objects (some which have mass and some which don't) that you can measure.
exactly, I had big problems of grasping the idea of energy because it was being used interchangeably ("has" - "is") all the time which is just stupid and makes a big mess of such a simple thing, that's actually ridiculous
The thing is that there is nothing that is not energy. You could say everything is energy and everything is light just in a conserved state. But that would not be useful when we talk about energy we usually mean useful accessable energy or at least energy we are interested in observing - we don't care that a sandwich has enough energy to outshine the sun for a few milliseconds we are interested in the few poor calories that we can access by eating it. On the same time energy is the only thing that isn't convertible you can make matter out of photons and you can make photons out of matter but you can't turn matter/photons into nothing or nothing into matter/photons.
Science is about what can be measured or demonstrated and explained, not what one "likes". 😉
@@fischX You actually can “turn nothing into something” when it comes to energy in quantum mechanics due to uncertainty. Quantum vacuum fluctuations allow for apparent nothing to split into pairs of somethings which have properties which destructively interfere and cancel when combined again.
Also your reply exemplifies my issue, namely that “energy” is used for both a measurement of a property that things in the universe have and also the name we give the stuff that has that property we’re measuring. People say “photons are pure energy” but really they mean “photons are massless things which have a property we call energy that can be measured. But energy isn’t the only property photons have, they also have spin for example which is distinct property from their energy. But we don’t say “photons are pure spin”, even though they all have it as do all the quantum particles.
@@gabevee3 I agree, but that's irrelevant to my issue. I'm saying the terminology which uses "energy" for two somewhat different meanings would have more clarity if it referred specifically to a quantity being measured and not to it as an object.
For example, as I mentioned in the reply above, you can measure a photon's spin and you can measure its energy, but we don't say a photon "is spin". And yet people say a photon "is energy".
Sounds like energy is just an invariant value that is a consequence of symmetry of physical laws. It’s too bad that this video didn’t point out that energy is relative, in the sense that two different observers will agree that it is conserved but might not agree on the actual calculated value of the energy.
Absolutely love this channel! It’s always interesting and I’ve learned a to! 👍
I'm suddenly imagining gravitational wells around or within every single person object and thing. These wells when they intersect, like water droplets, can get larger in radius in direct proportion to the amalgamated mass focused into a single space.
I think that if enough of these gravity wells accumulate, they create the planetary scale gravitational effects we see. Just as merging black holes result in a larger event horizon.
The warping of spacetime is only strong and noticeable on larger scales but on smaller scales I imagine it is there. Everywhere there is mass, there is a warping of spacetime, a "gravity well" at all scales. Weak at small scales, strong at accumulative large scales. There might not actually be any "gravitons" and instead gravity may simply be an emergent property of mass at sufficiently large scales and/or mathematical extremes.
Since mass and energy are considered equivalent, it can then be thought that gravity is therefore just another property of energy as it affects spacetime dependent on how much of it is concentrated in one place.
It could also also be said that the more massive a thing is, the more "energetic" it is; the higher it's energy content is.
I'm just an autistic lamen though. All of this fascinates me
The mathematical challenge in what your mind’s eye is showing you is at the heart of the mysteries of quantum gravity.
One issue where everything gets stuck is in that in quantum mechanics, the wave function mathematically “smears” the position of subatomic particles, so the question becomes at what location the spacetime distorting effects of mass at a given location actually happen.
If you can visualize how that works and put the math behind it, there’ll be a massive Nobel Prize with your name on it! 🙂
Yes, you got the concepts.
Juuust those doesn't fit yet.
Gravity should be quantised, but can't do it yet.
All we have in quantum experiments is electromagnetism, but gravity at small scale doesn't have enough strength. And anyway it acts regardless of electric charge, it "attracts" matter with or without mass, doesn't matter which quantum numbers it has, Gravity works.
One more idea for you.
We have this stuff in a 4D vector Space.
That's something we can't really imagine.
But we have the projection of 3d objects, shadows on a wall.
A cilinder there may appear to be a rectangle, a circle, and everything in between as you rotate the cilinder its shadow,, down one dimension from 3 to 2 appears to morph. But in 3D we perceive what's going on.
👍🤓
@@misterlau5246 maybe it isn't quantized and only emerges as a property of mass on larger than quantum scales due to mysterious processes. Of course idk either way but...I am always trying to think about these concepts and trying to work them out in my head in my own autistic way even though I am well aware I couldn't math my way to the solution, not with my severe lack of mathing ability and my lack of resolve to dedicate my whole life to it when I have other goals for my life. But ponder and question I shall because at the very least, it amuses me when I am bored and helps distract me from the darkness of humanity.
The fabric of spacetime itself, the "thing" that is warped by the presence of mass; is a mystery to me. It's never been defined or at least I have yet to find explanation as to what exactly this "fabric of spacetime" actually is. This thing labled space-time that warps in the presence of mass, what is it composed of and what about it causes it to warp in the presence of mass? And what would existence barron of spacetime be considered? Would it be a void of the nothingness that is actually a mysterious something or would it be a true emptiness of all things if not a blackness of probability and buzzing virtual particles?
I am in serious lack of the mathematical ability to work out the details and try figuring it out myself. I hope people smarter than me can find out the answers and I can find out through them.
Best I can do is ask lots of questions, think, ponder, make art, and make music.
I have nothing but great respect for those with more mathematically capable brains than my own who strive to define reality as it presents itself as precisely as possible for the betterment of all.
Part of me hopes that maybe one of the questions I ask will one day be one nobody else has asked or thought of before, a question leading to efforts by those with all the resources needed to find answers and possibly lead to something good and revolutionary. But I suppose there's nothing wrong with being part of the audience to great scientific breakthroughs instead of being among those who manage to actually achieve them
@@misterlau5246 your explanation implies gravity is a separate thing from mass. If it is, and with it being defined as warps in the fabric of spacetime, maybe then gravity is the result of spacetime itself not being static on quantum scales, tiny random fluctuations in spacetime could be constantly occuring to draw in material to then react to the presence of accumulated material by warping more and more til it overcomes whatever energy would be causing the random spacetime fluctuations and becomes a stable non fluctuating warp that then acts like fluid drops in that if one warp merges with another, the combination results in a bigger warp...
Whatever spacetime actually is, it's a probable candidate for the origin of gravity as far as I can tell.
@@Sigmaairav "maybe it isn't quantized and only emerges as a property of mass on larger than quantum scales due to mysterious processes."
That is our current understanding of gravity as general relativity describes it. It would be weird however if gravity simply stopped working precisely at the scale we start to encounter relevant quantum effects. Additionally, if you consider that all our very successful quantum field theories obey special relativity, you'd need to find some mechanism that preserves some relativistic spacetime effects but not others (I'm not well educated enough to explain fully, but I hope you understand the issue).
"The fabric of spacetime itself, the "thing" that is warped by the presence of mass; is a mystery to me. It's never been defined or at least I have yet to find explanation as to what exactly this "fabric of spacetime" actually is."
The "fabric" of spacetime is just an analogy. It's not made of anything. It's a mathematical space that has certain properties (for more information, the technical term for the kind of 3+1 dimensional spacetime we see is Minkowski space).
"what about it causes it to warp in the presence of mass?"
The presence of mass is what causes it to warp. The warping of spacetime in the Einstein field equations is defined as a function of the presence of mass (or more precisely, energy flux density). Asking what causes spacetime to warp in the presence of mass is like asking what causes momentum to increase if the velocity of a constant mass object increases. Spacetime curvature and energy contained within spacetime are both properties of the spacetime that directly depend on each other, just like momentum and velocity are properties of an object that directly depend on each other.
"And what would existence barron of spacetime be considered? Would it be a void of the nothingness that is actually a mysterious something or would it be a true emptiness of all things if not a blackness of probability and buzzing virtual particles?"
This is a very interesting question in my opinion, because 1) many people like to ask and think about this very thing because it is somewhat philosophical in nature and 2) it has a very clear answer in mathematical terms. A space in mathematical terms is much more general that the 3D or 3+1D space/spacetime we normally talk about. It is essentially a list of possible states. If we talk about physical 3D space, it's just a list of places we can point to in order to define a location. In 3+1D spacetime, it's a list of places, but also of points in time, so we can say where something happens and when it happens. Any variable has its own space, a moving object occupies some position in velocity space for example. Without a space to occupy, there is no variable. Without physical spacetime, there is nowhere to be, not even time to spend looking at nothing. The state space of quantum particles (Hilbert space) has a dimension for every property of the particle, so if we consider there may still be particles without spacetime (which we can, at least if we disregard quantum field theory), there would be "something" there, like mass, charge and spin of any given particle, but it wouldn't matter since without being able to change over time nothing could happen.
Another exquisite video, thank you Dr. Lincoln. That said, I'm sticking with Dr. Richard Feynman who said, "It is important to realize that in physics today, we have no knowledge of what energy is." "Energy is the interaction and motion of fields..." - a much more eloquent description than "the ability to do work" but still unsatisfying in defining what energy actually IS. Just a layman but my two cents.
I agree with you, because the question is, what makes those fields move?
Time complexity. Our lives are lived at scales that do not match questions we can form. See underdetermination to gain a sense that we may not form useful questions.
This may be related to the fact that brains evolve solely to compare and store sensory input useful to an organism and its biological/trophic niche.
So you may be in need of broader education as to things at even your scale, like evolutionary pressure.
Physics alone does not answer -- see the astonishing errors in some physicists' speculations on cellular biology, like Penrose's.
Seek knowledge of what occurs at differing scales, as well as the mathematics of dynamical complexity to start.
You may ask, "what is time?" But you are not equipped to understand the concept, even with considerable food calculus. Measurement breaks down at extreme scales.
Ask, "what is tension?" From which you may make analogies of physical properties as "energy" , "fields", and other phenomena, which break down when dimensional variables occur or are used to define factors in variation.
Again, one can ask what occurs in space
(For some reason an autocorrection of "food" calculus occurred. But even that error, if absorbed, will lead a questioner to seek what occurs to a brain self-signaling some lacks, which distort perception.
It's worth noting that interpretation models also have symmetries. Under implication symmetry, "time symmetry implies energy conservation," TS>EC, forms a doublet with "energy conservation implies time symmetry," EC>TS. Another successful physics search rule is "simpler is deeper." Under simpler-is-deeper, Noether's delightful and beautiful TS>EC argument places Minkowski's infinitely differentiable and functionally complex spacetime to the left of a small set of conserved quantities. EC>TS, in contrast, places the conserved quantities, including energy, to the left of spacetime and hypothesizes that sufficiently complex conservation scenarios approximate Minkowski's spacetime. Besides scoring better under simpler-is-deeper, EC>TS ("Rehteon's theorem") also removes the needless century-long separation of relativity and quantum theory that Minkowski created by inserting a concept of spacetime whose precision exceeds anything possible with Einstein's original 1905 real-matter clocks and rulers. EC>TS, in contrast, unavoidably requires space and time to be variable-resolution quantum properties of matter.
if you travel towards a galaxy on a fast spaceship , its light will be bluer, but it is the same light that you see redder on Earth. So the energy of that light is not changed.your perception did.
I feel like this is a video that never tells you what energy is, but more what we observe from energy.
why do people define energy by what it does and not what it is? Do scientists really know what the heck energy really is or do they know some of the things that energy can do?
You can define something by what it does if there are multiple versions of that thing, but what is it really?
Thank you! Great video, as usual!
I have one question that I would love if you could make a video about them:
1. Is there any theoretical maximum limit for frequency of an electromagnetic wave?
The maximum frequency of an EM wave can be more easily described by its wavelength. The minimum for that is the Planck length. Any shorter, and it's a black hole made by energy, a Kugelblitz
for 1) That is exactly what Dr. Don wanted to say with the phrase Energy is not conserved in an expanding universe.
for 2) sure see here: en.wikipedia.org/wiki/Planck_units
The black hole maybe or maybe not a consequence, but mattio79 seems a bit ahead of modern physics as so far nobody has an accepted model of quantum gravity and without that we simply can't say.
With what kind of high tech apparatus, one can make EM-waves with shorter wavelength than Planck Length..?
@@pelimies1818 It's kind of implied. None.
@@Techmagus76 Gravity is an effect of the curved distortion of spacetime by a local massive object. It's like saying there's centrifugal force. It's not a force, it's an effect. When neutron stars or black holes merge, the spacetime distortion propagates outwards like a wave caused by an object thrown into a body of water.
A particle is a mass of distinct, durable waves.
We miss the 'stache Dr. Lincoln!
Thanks for bringing this educational content to anyone who's willing to listen.
I watch a lot of youtube shows related to physics explanations. PBS Spacetime, ScienceClic, The Science Asylum etc... This is the first time I've ever seen something like the backdrop of a chalk board with things that I am surprised to say I actually recognize the writing on. Whenever I've seen similar backdrops, I've always glossed over it as nothing I'd be able to make sense of but this time I looked and couldn't believe I recognized over half of it. I love all of you educators that break down the concepts in physics to the rest of us. I may still not be able to solve any of those equations, (I only took basic calc) but the fact that I can now just recognize them and what they represent is awesome. It makes me want to learn more math again. Thank You.
I think it was Einstein who defined genius as one can take something complicated and simplify it so everyone can understand
I like your description. So many people think that energy is a physical, tangible "thing." As if someone could "get" an energy and carry it around in their pocket. But really, it's just an abstract concept. Like you say: "a capacity." Or an ability. No one says they can carry a capacity around, just like no one says mystical "ability to move things" pours out of crystals and into one's hands. But they say that about energy because it's almost completely misunderstood by the majority of people. Even a high percentage of physics students get it mixed up.
This was beautiful. It's always amazing to get a new insight and a different perspective so that you can modify or re-interpret what you've learned. I remember a grad school prof saying that every time he read "Feynman Lectures on Physics", he learned something new, and this was a person whose colleagues considered him to be brilliant. This video was like that for me.
To me, Energy was always "measure of how much can happen without outside influence":
Potential energy is how much can a thing move (towards center of gravity) "on it's own".
Kinetic energy is how many glass windows will an object break before it stops.
Thermal energy is how much heat can escape object before it reaches absolute zero.
Chemical energy is how mush heat you get by setting something on fire.
Baby energy is how long will baby survive after it's parent have gone mad...
and "the outside influence" is energy too?
That's just the normal definition of energy already in the video, the amount of work that can be done by a system.
@@ObjectsInMotion That's wrong because objects with less energy can do more work than objects that have high energy. Air has a lot of energy but can't give us a lot of work. Using work in the definition could be ambiguous. Moreover, in thermodynamics work is defined as the energy is transfer. The definitions become circular if we define energy using work.
@@harshitrajput6865 Energy is the potential to do work, not work itself. There is no circular definition there.
@@ObjectsInMotion No No I mean how would we define work then? Work is defined as energy in transfer right
Ive been watching this channel for a while now. As a 6th grader, i never really understood my teachers, I thought everything was complicated and very difficult to learn. Thank you, Don. I can guarantee if this channel was the only reason i was able to achieve good marks in my physics exam. Much appreciated, keep it up.
Where are you from brother
@@charlie-yn3mf may i ask why? I dont usually say when im from or any private information on the internet
How to I make a request for a topic? I'm curios to know: What is Space? Not space as in outer space, but, what are the structure and components of a volume of area that is empty of all matter and energy? Is there any theory about what space (ultimately spacetime, I guess) actually is in physics terms?
My mind has been blown 🤯 I always was thought energy was ALWAYS conserved. Thanks Don. I look forward to learning more.
There is the possibility that the big bang is BS. There is no theoretical justification for accelerating expansion. It was not predicted, so the theory was adjusted ad hoc to fit the data. Lack of energy conservation indicates to me that the theory has failed. Physicists might try looking again at tired light, where the redshift is exponential decay of light energy.
Mustaches are, apparently, not always conserved, either.
Well, it's always conserved in a closed system. Problem is that at least the observable universe isn't a closed system.
energy is always conserved. you just can't know how much there is beyond the uncertainty principle.
@@arboldenjenkins3105 uncertainty principle on the cosmic scale?
I very much enjoyed the information you presented in this video. What I really respect about it is that you talked about two women, Emilie du Chatelet and Emmy Noether with the same reverence as Newton and Leibniz. In my Physics and Philosophy education I never learned about women's contribution to the science and art of Physics (except Marie Curie). I only knew of Emmy Noether because in graduate school I coauthored a paper on Noether's Theorem in Classical Physics. It saddens me that our educational system is so male dominated that we seldom learn about the import contributions made by women. It is kind of sad that the fact you talked about these great minds makes your video exceptional, but it is also great that your video is exceptional.
Is it possible that some of the energy driving expansion is sapped from photons and neutrinos as they travel through empty space and get red-shifted? Or alternatively, is there a frame of reference in which that's how it appears?
My question exactly!
A volume of space will expand proportional to the third power of the volume's radius, while the photon's energy loss is dictated by the inverse square law meaning the energy loss is portional to the squared radius in a volume. Meaning photons lose energy slower than space expands so the expansion couldn't be driven by the energy sapped away from photons.
@@ThatCrazyKid0007 This is not true. A photon does not lose energy by an inverse square law. I think you're confusing the energy of a photon with the intensity of a collection of photons radiating from a source. The intensity of a beam of light diminishes by an inverse square law, due to some simple mathematics, but not the individual photons.
Furthermore, even if we decide to talk about the intensity of a ray of light, a volume of space being proportional to the third power of a volume's radius doesn't matter. This isn't a complexity analysis at some asymptote. Being proportional to the volume has no bearing on any other factors that might relate the expansion, and it's easy to see where a case can be made such that other factors diminish the growth of the cube versus the square in the range at which we observe it. You're basically extrapolating from a relatively tiny data set and pretending that it has to generalize, which is poor thinking.
Thank you for this. I have for a long time tried to understand « what is energy ? », and my readings haven’t so far allowed me to find a satisfactory answer. It isn’t too hard to understand what energy ‘does’ or what constraints it obeys, but what it ‘is’ remains an open question. The clearest suggestion so far seems to be that it is « an accounting principle ». Be as it may, it seems that in the current state of knowledge in physics the two fundamental constituents of Reality (this unknown thing with capital R) are Energy and Information, both of which are conserved. So the next question, is: how do the two relate? and are there fundamental equations that describe how the two relate in different conditions? Thanks again!
You have it exactly right - it's an accounting principle. If a system is time-translation invariant then we can assign the system by an arbitrary scalar we call "energy" that is a constant of motion. What this means is that the interactions are fixed over time, for example the coupling constants stay constant, then how the system evolves will be constrained by these interactions in a way that is predictable. The conceptual problems emerge when we ask "what is energy" which implicitly assumes that energy is a something in the first place, which we've known is false since the days of Count Rumford's cannon boring experiments.
Perhaps we should say that a thing is what it does, or, more generally, what is true of it, or how it relates to things.
Then, when we are describing how much energy there is in each part of some system, and how that changes, we *are* describing what energy is?
@@drdca8263 Energy doesn't physically exist so can't do anything. You can assign any system any value of a energy you want and it doesn't change anything. What is physical is that particle interact and it is the interactions the govern the dynamical evolution. Since the coupling strengths are constant over the evolution of any system is constrained which allows the assignment of a conserved quantity, the hamiltonian, which is we usually associate with the total energy.
@@kylelochlann5053 seeing as the Hamiltonian is the generator of time evolution, and the Hamiltonian operator is an operator which sorta represents energy, it seems reasonable to me to say that the Hamiltonian operator does things. Of course, the Hamiltonian operator isn’t a “physical object”, but, eh
@@drdca8263 Exactly, the Hamiltonian isn't a physical thing that "out there" living a life outside our heads that's bending the world into a particular form. This is actually all very clear in relativity, but runs into the risk of boring the readers.
While I appreciate mentioning du Châtelet, the way it is done here is a bit misleading. Peloni and 's Gravesande both did the ball-dropping experiment before du Châtelet. She was replicating and publicizing 's Gravesande's work, but the video presents it as original research. Additionally, it's disingenuous to say du Châtelet "sorted everything out", as the vis viva debate continued past her work.
I love Fermilab.
I think there's no one video or book explaining the concept of energy this much simple, complete and at the same time persice. It fulfils different physics knowledge levels. Thanks a lot.
I seriously doubt anyone understands the basic concepts because of watching this video. Not all of it is bad but neither is it good. You deserve something better, try Feynman if you look for depth, simplicity and precision. That is old but unequalled. Fineman explains with the precision of a surgeon's knife in competent hands, in comparison, this looks like someone tearing down a wall with a sledge hammer.
“The Final Theory: Rethinking Our Scientific Legacy “, Mark McCutcheon for proper physics including the CAUSE of gravity, electricity, magnetism, light and well.... everything.
@@AntonvanUitertthanks alot for your suggestion. Yeah! Feynman's lectures are exceptional in this point of view. I was looking for a good explanation or maybe the definition of energy for high school students and this video was very good at it. It starts from simple examples to higher level ones and tries to give a reasonable definition for energy.
@@davidrandell2224 thanks a lot, I will definitely check this book out.
He’s not explaining what energy is, he’s explaining how energy manifests itself
Nunca me pierdo un video de Don Lincoln
I don't buy the claim that redshift indicates a change in (loss of) energy.
- Redshift can occur because of the motion of the observer (Doppler Effect). There's relative motion, so it appears to be a different frequency and thus a different energy. That observed energy is constant, so there is no loss. The problem would be the acceleration of that relative motion, which ought to require energy input and thus where that energy comes from.
- Redshift also occurs from light escaping a gravity well. Since per Einstein's theories gravity is the same as acceleration, light moving 'against' gravity experiences a Doppler Effect, too, and so it appears redder.
There is no loss of energy. Energy is conserved. Instead, it's the observation that the frequency is different than what it would be without relative motion or gravity. Observing that cars on the highway move more slowly when we are also in a car on the highway does not mean they 'lost' energy. It only means our reference is different.
Interestingly enough, as I was eating breakfast, I asked myself “what exactly is energy?” And later this video appears on my notification. Very nice coincidence.
While eating breakfast I said to myself that energy is the battle between existence and non-existence via virtual particles popping in and out of existence itself which is the fundamental basis of all that exists.
For something to pop into existence, there needs to be an underlying energy field. If you hold your breath and stay still, there's no motion or movement and yet it requires energy to maintain that seemingly static state. There's an interesting interplay between the static and dynamic, where one forms the basis for the other.
At least you didn’t stat with: “Interestingly enough, as I was sitting on the porcelain throne, I asked myself….”
Energy is the property that is invariant in the closed system. Ie, PE + KE = constant.
All things are ‘energy’.. Energy is what exists..
spaceandmotion
coincidentally my breakfast popped out of existence this morning too
This video is a refreshing cold shower for my brain. thanks!
Thank you, Dr Lincoln, for finally giving credit to women in science!
Dreams are beyond time and space. Therefore, physics is not everything.
I think Dr Don just told us that matter is largely the energy binding quarks, so then the topology of space time is a function of the distribution of energy.
A discussion of the relationship between energy and entropy would be helpful.
not the topology but the geometry
Quarks are potential energy too, since if it collides with an anti-quark they release all their mass into kinetic energy.
At a fundamental level, all types of energy can be reduced to potential and kinetic, and massless particles like photons create fields of potentials. How can even potential and kinetic energy be unified into a single thing? I have a conception for how, but I've never seen it phrased this way, and I might be way off base (I'm not a physicist and I'm confused as hell). Energy is the quantity of displacement from zero in a field. Probably a quantum field, but I'm visualizing it as a classical field. All fields have values that overlap in the same point in spacetime. These field values can sometimes be converted to a different form (e.g. pair production from photons, weak interactions, etc.) , but the sum of their displacements can never change. The sum of the displacements within a system is equal to that system's absolute internal energy. When the displacements are stationary (or possibly modeled as standing waves), you have potential energy, and when they are moving, you have kinetic.
Am I on the right track? The difficult thing about understanding potential energy is that it doesn't seem to actually exist anywhere in conventional explanations. An apple held 1 meter off the ground is said to have gravitational potential energy which transforms into kinetic if it's dropped. But this potential "feels" fictitious without something like this to make it tangible and unify it with kinetic energy.
When I was in high school I contemplated the definition of energy.
My thought was "the ability to do work" was a horrible definition, as it doesn't take into account energy that doesn't influence our physical environment, such as mental.
The definition I came up with is "unbalanced forces".
I still believe this definition is more accurate and inclusive.
I like that.
Like squeezing a crystal out of equillibrium (piso-electricity)... :-)
Well what is 'mental energy'? There's the phenomenon you feel of course (like feeling exhausted or even 'energised'), but that's just subjective. From a physics standpoint, it's basically a complicated dance of electric currents (and some chemicals) flowing around in your brain. And that takes us right back to how physics conceives of energy, which already covers electrical and chemical energy. The physical environment, after all, also includes the environment inside of ourselves, all of which is influenced by those currents.
Unbalanced forces *is* work.
What kind of nonsense reasoning is "mental energy"? Of course "mental energy" affects your physical environment. Your body has to burn calories and generate heat in order to do those mental processes.
I have a definition of energy... Suppose you're watching a video of a ball in a slow straight trajectory going into a jar of peanut butter, without more informations. The video stops and you have to decide what happens next. There's in fact, two possibility :
1) You're watching a normal speed video, shot in space : since the ball is going slow, the ball will simply slowly bounce off the jar.
2) You're watching some ultra- slow-motion video : the jar and maybe the ball are going to explode in millions of pieces all over the place.
The importance fact here : you can't decide which video you're watching until you know the time speed of the video. So we can deduce : energy is relative to time.
Now you want to know, between the two situation, indepently of time, what's different. You realize : it's the speed of sound in the objects. In the first video : sound goes fast, therefor forces has enough time to propagate into the objects and inverse the global motion of the ball. In the second video : the ball goes faster than the sound. The wave of pressure due to the contact doesn't have time to propagate into the objects : so both explodes. So kinetic energy is relative to an absolute property of the objects : the speed of sound inside them. So my conclusion is energy is relative to the scale of sub components of systems, which in turn define a time scale. (for instance the speed of sound in objects in theory allow you to measure the time scale of videos of them)
I'm sure this has been considered, but I've never heard anyone mention this: Does the loss of energy of photons as they travel through expanding space not account for dark energy? If space is expanding and needs energy to do that, and photons travelling through expanding space are losing energy, then is it possible it's their energy that is converted into what we call dark energy? I do realize that this explanation is incomplete since it doesn't describe why the energy conversion happens in the first place. But it's an interesting thought and as I said, I don't recall this being discussed in any physics RUclipsrs' videos.
Yes it was asked and answered in an episode of PBS spacetime, and no they don't balance out the increase in dark energy is much larger than the loss from photons.
There is no reason to expect energy to be conserved in an expanding universe. Noether's Theorem just does not apply in an expanding universe; because space is expanding, there is no time-translation symmetry.
Ordinary matter is only 5% of the universe. And photons are ordinary matter. 27% is dark matter and 68% dark energy.
How can 5% ordinary matter account for 68% dark energy?
Photons are losing energy as heat? Or radiation? (Correct me if I'm wrong) 🙃
What does heat have to do with dark matter/energy?
For me is the same thing to say that the dark energy is created by your coffee getting colder and losing energy
That point about photons being red-shifted thus losing energy and energy therefore not being conserved is something I don't understand. Isn't it just the doppler effect in action over a longer distance? That's what Varitaisum claims in his video "What Actually Expands In An Expanding Universe?".
So measuring the doppler effect of photons on a local level here on Earth should equally imply the non-conservation of energy then? I thought red-shifting photons in the universe are just a consequence of the constant density of dark energy. The ultimate culprit is still dark energy.
Please help me understand 7:36
Commenting before watching. Probably great work Don Lincoln.
I’m pretty sure espresso would make a 4yo explode, the gummy bears are enough.
Awesome video as always.
@Fermilab, I would suggest embedding links to previous videos within the video when they are referenced, rather than just in the description, similar to @SpaceTime. It makes it more likely the viewer will click through and check out those older videos, and eventually get hooked when they discover how much great content this channel has :)
I think kinetic energy and potential energy are literally the same thing, but we don't yet understand gravity or atoms.
I think energy is preserved at a cosmic scale, but we don't yet understand where it is going to or coming from.
I think neither time nor space are fundamental because both collapse in black holes and at the big bang. I think they emerge from something we don't understand enough to see yet.
I've never 100% believed that energy is conserved. It's just that "potential energy" is defined in such a way as to make energy appear to be conserved. I could equally claim that, say, the "blueness of the sky" is conserved. If you say no, the sky turns black at night, I can just reply that it has "potential blueness" at night, which will be converted back to actual blueness when the sun rises tomorrow.
OK, I know there must be a flaw in this argument, but I can't see what it is.
I've always had the same gripe. Like, raising a microphone higher up doesn't actually give the microphone more energy - it doesn't contain the potential energy. It's almost like potential energy is a purely mathematical construct to make conservation laws make sense, but also that conservation laws are a purely mathematical construct to make energy make sense? I asked about this on a Science Asylum video, and I can't remember exactly what Nick said, but it was something so simple, and kinda mindblowing, something to the effect of "all energy is just numbers," (but probably a bit more sciencey, haha).
Even if we think just about kinetic energy, I get confused. A simple object with a simple velocity. But, in what reference frame does this object have velocity? There's no absolute space, absolute time, or absolute speed, so does this mean the object has different energies in different reference frames?
The way I look at it now, energy isn't a property of an object, but a property of an interaction (or potential interaction) between multiple objects, and that's why potential energy can make sense. The microphone doesn't physically have that energy, but it will impart that energy upon impact with the ground. If the ground starts to move away just before impact, that impact will be less energetic, but the microphone's energy hasn't changed; it's just the interaction between the two objects have changed.
Anyway, that's my little unqualified thought on the matter. I too think there must be a flaw in my argument, so I hope some even smarter people can weigh in.
@@c4ashley Raise the mic 1 cm and drop it. Next, raise the mic 10 feet and drop it. If it hits louder the second time, it had more PE with respect to the floor.
mmmm... energy is density of mass times square of velocity. it is movement. so matter is just potential energy (work). so what does that make light?
The best explanation for energy is that it is a state function. It is a way of assigning a number to a physical system that is hella useful for predicting what can and cannot happen to the system. It doesn't help that the word energy is used for several related, but not quite identical things. The ability to do work, or the "accessible" energy, is the one people most commonly think of, but then they get tripped up when they think about heat or potential energy of chemical bonds, which can only be made to do work in special circumstances, and can't understand why you can't make a chemical engine running on pure water.
I don't see how a label is the best explanation for energy How is assigning numbers to systems a good explanation?
@@mikeyoung9810 It may not be satisfying, but it is the most accurate description of what energy is. It's not some physical substance that's moving in the world, it's just a quantity we ascribe to things. When you lose touch with the mathematical nature of energy and focus too hard on "what" energy physically is, you are liable to either go insane, or start coming up with new mystical beliefs and religions. It's mostly an issue with quantum mechanics, since that one's a much more esoteric piece of math, but I've heard a fair share of outlandish ideas about energy from people who focus on material reality without really accepting that it's just some numbers physicists find useful.
I mean, even this video explains energy by talking about the mathematical expression for kinetic energy, and that the potential for causing motion is also energy. Notice it doesn't really talk about what energy is, it talks about what goes into the math, which depending on your starting point may or may not help you understand it.
The reason why American scientists have never been able to define energy unambiguously accurately is lack of profound knowledge of the English language and physics, although they can pinpoint examples of energy
Energy is actually an ambiguous term for forces which can be either natural or artificial
So, "energy is force to do work "
You guys can see my definition of energy is so simple, but accurately concise without any ambiguity at all
Forces are the fundamental foundation of all forms of matter or existence in the entire infinite space of the universe, and they are created whenever transformations of forms of matter take place
Another example of ambiguity in scientific definition is " the observable universe" which can be interpreted as that the universe is observable while actually human beings have so far been able to observe only an extremely small part of it. It should be put clearly without any ambiguity like this: " Only an extremely tiny part of the universe is observable to human limited knowledge"
Your definition of kinetic energy as to be a thing that can move or vibrate is incorrect because a thing or things which can move is a moving thing or moving things, but not any form of energy
That is why American English is ambiguous, which can make very simple concepts complicated or confusing to students, thus hinders public education.
Energy is any form of force, and kinetic energy is any form of force which makes things move. such as electromotive force emf which drives electrons around in a circuit, gravitational force which pulls objects toward the centre of the Earth, chemical force released in chemical reactions, nuclear force in nuclear fission reactions, air pressure force due to different mass concentrations at different locations in space, applied force by humans and human-invented machines