This video explained lasers in such an incredibly immensely simplified way that no one can really be satisfied with it, or, let alone understanding the concept.
So true. Explaining lasers isn't simple. But this isn't even the beginning of an explanation. This is the kind of false explanation that you will find interesting if you already know how it works.
I've found this explanation here, currently watching fully to see if it appropriately answers the question, but it should be a good starting point for other questions you may have. ruclips.net/video/DA7a_v96Jsw/видео.html
You know, these physicists delight in complicating matters so don't blame your cat. Just pass a Ray of light through a man made quartz crystal which does have the power to disperse that light so it comes out pint point accurate according to what beam intensity you put in.
If he could explain why these things happen in a RUclips video people wouldn't need to spend years at universities. These videos are for entertainment and to inspire people to seek their own answers, so thank you MinutePhysics for making up these metaphors, it's things like your videos that are the reason that I'm studying Physics today.
This video explains the one thing I had not been able to find, and that is... "how can the photons be in phase if they are not generated at the same time." Also the coin flip analogy really helps understand the process. There are so many great articles out there that explain how lasers are built and the basics of what they do, but without the points from this video you can't really get an intuitive understanding... Thank you for the great overview!!
i cannot believe i am 23 and saying this, but the background music sounds like when steve is drawing a clue on blue's clues. on another note, i love this channel. i learn so much...(after watching the same video like 3 times in a row)
I have actually seriously thought about this sometimes, sometimes, except with light instead of lasers, with light I am pretty sure it would be un-observable because even the smallest crack would allow light to escape, and because light moves at the speed of light and the light source is no longer there we will never know if the light dims in the room of mirrors. Is this correct?
this is really awesome. this explains why if you look at the reflected dot from a laser on certain surfaces, you see the much smaller individual dots making it up moving all over the place within the dot
Explaining what photons do is not the same as explaining why they do what they do. For example, in showing that there is a greater probability of finding photons in the same "state," (at 00:50) you still don't yet have any rationale for giving a "Therefore...." This probability has nothing to do with why photons from the output of a good laser are in phase. Laser designers don't say, "The light will probably be in phase." Certainly you'd agree that their design specifications have something to do with it. If the specifications are more relevant than probabilities, why not include them in a "How lasers work" video if the intention is to show how lasers work? It may be worth your while, also, in studying why the theoretical physicists some years ago said laser light wasn't possible, and how they treated the people who said it was. Some of the speculations in modern physics have to be let go, it seems to me, considering the fact that laser light is obviously possible.
Caleb I totally agree, but the channel name is minutephysics. I think he did alright with the brevity but he could have alluded more to some follow up for more interested viewers.
"Photon's want to be together", I feel like we are regressing a bit here. A little more detail please, maybe refer us to a sixty symbols video at least.
It's a little more special because you can do it with integer-spin particles (like light, sound, gravitational waves, and the charge-pairs in a superconductor) but not half-integer spin particles (like electrons, protons, neutrons, neutrinos). Light is indistinguishable in a way that it can "condense" into the same state while electrons are indistinguishible in a way that only one can occupy a state. Once you have that sort of indistinguishability, though, the probability does work that way.
LASER (Light Amplification by Stimulated Emission of Radiation) is an acronym so it isn't a Laser it's LASER beam (of light), as said in the video but I don't think people understand that subtle point.
+David Hughes Well, it's more commonly referred to as simple 'a laser' or general laser light, regardless of any formalities or technicalities. So as long as everyone understand what it is, eh?
Atoms have diameters measured in picometers, so you would never see one no matter how excited it was. It could be undergoing fission and you still wouldn't be able to notice. I'm not sure if your question was meant to be serious. The "static" you see is caused by imperfections in the laser emitter's optics. Some of the light is scattered instead of perfectly focused. Cheaper lasers will exhibit this effect more strongly than more expensive, quality units.
why everyone is hating , he's trying to simplify the idea so that everyone understands and i think you did a great job .. I take physics this year and the video explained a lot of what i didnt understand .Thank you
Funny... I looked all over the web for a simple explanation... I actually noticed this and went on (0n my search). After a while, I got tired and watched this! It solved all my problems :3
This is a pretty poor description. How can you meaningfully discuss the operation of a laser without the concepts of phase coherence and population inversion?
He isn't 'meaningfully discussing' the operation of a laser; he is vulgarising the process in order to make it comprehensible and appealing to a larger audience whilst keeping the explanation concise.
Chaossdruid He isn't "vulgarizing" it, he's utterly raping it with a chainsaw. This explanation was almost completely wrong. It always baffles me how people think that an explanation being "accessible to a larger audience" makes it any less wrong. Uh, hello? If it's wrong, it should *not* be taught to a larger audience! Leave the wrong, appealing bullshit to scifi writers. Science this ain't.
gogerychwyrndrobwll There's a common analogy teachers use when teaching basic arithmetic. Imagine a man walking forward on a train that's also moving forward. What is the man's speed relative to the ground? According to the teacher, it's the man's speed on the train plus the train's speed on the ground. But that's false. Relativity tells us his speed is actually a little slower than that. By your logic, teachers shouldn't use this analogy because it's factually incorrect. Their students would go into the world with the wrong idea about how the world works. It wouldn't matter that the students' understanding and the reality is off by mere trillionths of a m/s: wrong is wrong, period. Maybe you're actually right. This video isn't accurate, and it's off from the reality by a lot more than the train situation is from reality. But unlike basic arithmetic, which has many possible analogies that a teacher could use, the physics of lasers is awfully complicated. This video shows what very well may be the simplest analogy possible that gets the basic idea of lasers across. It might be technically wrong, but a basic idea is better than no idea at all, right? If you can think of a more accurate but equally simple analogy, I would honestly love to know it. I want to know more about lasers, too. You could even try making a video about it. If it's as entertaining and even more educational than these videos are, people will love to watch it.
*****"By your logic, teachers shouldn't use this analogy because it's factually incorrect. " That's not my logic at all. That's your supposition of what my logic is. The explanation given by the teacher is the low energy (Newtonian) approximation to the full relativistic dynamics. It is the leading term in an asymptotic expansion in v/c. It's clearly appropriate to the problem at hand. Further, it's *more* appropriate than the full relativistic expression since any and all corrections that are of higher order in v/c get entirely swamped by experimental error and are unobservable, even in principle. Strictly speaking they can't be said to be there at all. So the Newtonian approximation is entirely justified, rigorous, and accurate. In contrast, I know of a certain physics youtuber who dislikes Newtonian approximations... watch?v=IM630Z8lho8 D'oh! The problem with the exposition in this video is not that it's "simplified", or even "outdated". It's *fictional*. It was never true, it never even resembled anything that could be construed as an explanation for a laser. You can easily see that this simple entropic argument cannot work by noting that if it were true you'd see lasing merely by placing on mirror in front of the other. This obviously doesn't happen. You *need* to understand stimulated emission and gain media. You *need* to understand population inversion. Population inversion is quite interesting by itself, since it leads to the subject of negative temperatures which are surprising and fascinating. A competent physics youtuber attempting to explain these concepts would have to find creative ways to make them accessible. Veritasium is typically very good at this. Minutephysics, on the other hand, tends to just make up whatever fictional explanation would sound sexy, even if it has only a passing resemblance to reality. "You could even try making a video about it." I've been meaning to try to start a physics channel, but honestly I don't think I have the competence or charisma to make videos that the average person would find interesting.
gogerychwyrndrobwll "D'oh"? Nah, I used the man-on-the-train situation for that very reason. Glad you caught that! So, you're right. Henry's reasoning doesn't approximate reality in the slightest. (Side note: From my own education, he's usually not wrong in most of his videos. This video seems to be an outlier than an accurate trend in Henry's scientific accuracy.) But that raises a question I've seen other people approach in this video and others: namely, is it possible for his more... interesting ideas to be wrong in principle but right in practice? Henry's videos may be factually incorrect, but they do expose a broad audience to interesting scientific phenomena. So, is it better that people watch these videos even if they're wrong? Or would it be better if people didn't watch these at all? I do think the former is preferable, since intrigued viewers might go on to learn more about the subject on their own, but that's just an opinion. I am curious to read your own, if you care to share. I've been meaning to start my own physics channel, too, but I haven't found the time to write a script or set up a film area. Also, yeah, making videos interesting would be another problem to handle. Still love to try though.
you can, if you use the .9 infinitesimal rule. also, there are systems for counting besides the metric system. if you use the dozenal system it is quite easy to express two thirds, and 1/3 as decimal.
I love how whenever people try to explain the universe simply they're like "Well imagine that time is a line." then later on it's all "Time's not a line, that was just an easy way of explaining it."
If there is any room for another electron in a lower energy state around an atom, an electron in a higher energy state will release a photon to reach that lower energy state (it's a bit more complicated than that, but that's the main idea). So, it's not really possible to "hold" an electron in a higher energy state than it "wants" to be in. Also, As you go to higher an higher energy levels, the differences between the levels becomes exponentially smaller, so there is a limit on the energy.
I love stuff like this because it basically illustrates using maths to break our understanding of the universe. When i first learned about the uncertainty principle, i parsed it as "we can only know position or velocity because of the way we measure" implying that there was a way to measure both, even if only in magical theory land and never in reality. Because we tend to relate everything to what we can experience, i was still subconsciously thinking of electrons and photons as "objects". But i later realized that the duality is litteraly unknowable, even theoretically, because photons and electrons arent like anything were used to. They arent lines or dots, and they dont operate on the kind of logic we do. I once was watching a lecture on how one could sorta try to visualize 4D shapes, and it just became so obvious that stuff like this just operates on a completely different plane. We can try to kinda mush it into something that we can sorta make sense of, but in reality its as incomprehensible to us as imagining a new color. Its just beyond the ability of our brains. We can understand it, use equations, but in the end were basically just interpreting something that we can never really perceive the truth of.
You should also consider that if something seems impossible to figure out; that you dont have a solid enough grasp on what it is youre talking about. Such as photons. Theyve never been measured as a thing. Its just a name given to the phenomena of light/energy being produced. Although the reason photons as a concept exist, is because people seem to believe they must attribute the phenomena of energy conversion/light production to a particle in it of itself. Instead perhaps it is simply a product of fundamental aspects of how things work, that energy is produced. Energy in it of itself, not photons. Instead of photons being a thing that are produced, "light" is "produced" by the processes of universal laws. Light in itself isnt a thing. It isnt a particle. It is a function of equations of electromagnetic fields. It isnt a product or an addition, simply a piece of an equation which is everpresent. I.e. the equation cant exist without the entirety of the equation. You cant have X and T interact without "producing" Z. Producing is used lightly, as it isnt a product, it is simply a piece of a law which exists simultaneously along the other pieces of the law, and none of the pieces can exist without having that interaction being a whole of all of the individual aspects.
When an atom's electrons move from an energy level to an lower energy level, it emits an photon (completly making up names and values, but the concept is correct) Electron Level 4= lets say 6 energys Electron Level 3=4 energys when an electron moves from Lvl. 4 to Lvl.3; there are 2 extra energys that the electron needed in Lvl.4 are no longer needed in Lvl.3 thus the energys get emitted as photons The reverse happens when an atom "absorbs" an photon
The fact that the laser beam is directional ( that it is not emitted in all the directions) comes from the way the mirrors are positioned. In this example, parallel mirrors are used. Only the photons that are emitted along the axis that is perpendicular to the mirrors will get to stay in the cavity and induce other emissions and be reflected again, etc. The beam that goes trough the little hole is thus strongly directional.
for those who can't remember highschool science the atoms are excited by the amounts of quantified energy it can absorb in the form of a photon (quantified energies being the amounts of energy belonging to a jump or fall in levels of excitation). In the same way the atom can emit an equal amount of quantified energy in the form of a photon. These energies correspond to certain light wave lengths. So if you take a bunch of the same atoms which absorb and emit the same photons in exchanging the same quantified energy you'll get a bunch of the same colour of light (same wavelengths in the visible light spectrum). And this video explains how the light comes out in a beam.
It builds up until the imperfections in your mirrors absorb as much energy as you're putting in. Or the light that's bouncing around starts hitting the atoms and re-exciting them all the time, and you can't put any more energy in because there's nothing to do. Or both. Anyway, there's a limit to how powerful a beam you can get out of any particular laser by charging it longer. You need more atoms or atoms that get more excited.
Actually, light scatters off of clean air only a negligible amount. If there is dust, humidity, or smoke in the air however, you are right that some scattering occurs and you can see the beam.
I'm not sure if this has already been said but unless there is a way to measure the light from outside the mirror box wouldn't you never be able to prove whether the light is reflected an unlimited number of times. Anything inside the box will absorb the light before it can complete its "infinite" dance around the box. Also I think it goes without saying that this theoretical box would be a perfect vacuum for best results.
First of all you need to understand that E=/=m (Where E is energy and m is mass) E=mc^2 (c is the speed of light) Secondly, you need to understand that photons are particles and they generally have no mass. Hopefully that helps clarify it a bit for you.
It's not like only one photon is excited with energy. They are all excited (all have energy) so the photon passing by, is only causing the other excited photon to go the same direction(or do the same thing). it already has energy, but now its doing the same thing as the other photon. It is an already "excited" photon. 0:58.
@MinutePhysics Wait... why do mirrors reflect a photon rather than absorbing it? We see red because a red surface absorbs all but red, so would that mean ta mirror has no colour?
Light just bounces off a mirror the same way it bounces off a white object. The difference is that mirrors don't scatter the light, they reflect it at the same angle.
But if light is a wave and only a particle when observed(interacted with) then why is it more likly for the light from a laser to hit the same area then from a non-laser light?
You cannot see a photon "whizzing by" since in order to see something it has to emit a photon towards your retina (either transmit or reflect). That photon is then absorbed by your light sensitive cells and converted to electrical pulse going trough your nerve into your brain. so You cannot see a photon going by, you only sense a photon coming into your eye.
Generally, the side of the mirror that light is being projected from is partially silvered, and moved to a miniscule angle, enough to allow the light to shine through, but the hole he described was just figurative, since this is minute physics :P
There are two answers I have heard to this, I have no idea which is right but I'll start with the one I think is. Not entirely. Wood is made of a lot of different things. Unlike water or metal or rock, wood has a bunch of things in it that melt/evaporate at different temperatures. Obviously you would have to do this in a vacuum to prevent combustion, but at one temperature you could have a lot melted, and then a little higher and stuff starts evaporating. Or Can you melt dry ice?
I take issue with the supposition that the light emissions are different from flipping two coins. Just because you can't tell them apart doesn't mean that they don't behave in the same way. And the probability that two coins will land on the "same" side or "different" sides is 50-50. Just because you can't measure the state of individual photons doesn't collapse their heads-tails and tails-heads outcomes into a single possibility. It would still be 2 ways that they end up in different states.
How does passing light stimulate it to emit even more light? Where did that extra energy suddenly come from? Isn't that breaking the 2nd law of thermodynamic because we are extracting energy out it?
So I a box with perfectly reflective sides and walls we would be cooked from the infinite energy bouncing around. Or would we interrupt the system by just existing within it?
The reason you normally can't see lasers is that all of the light is traveling in the same direction - toward the target - and therefore none of the light is traveling into your eye for you to see. This is very different from lightbulbs, which send light in all directions. The reason you can see a bright spot on the target is that once the laser hits, some of the light scatters out in all directions...including into your eye. But unlike a laser, probably not enough to blind you!
you need a gas or such to electrify to make the light....co2, helium, nitrogen, argon are comon gases use to power a laser..as yes the fuel does run out as light is energy loss from a heated mass(though most is wasred as heat) re directing the super heated gas(plasma) itself is a "Phaser", while consentrating micro-wave emmisions make a "Maser" You can also use ultrasonic sound waves as a consentrated beam for welding steel and melting plastic
when an exited electron drops down one energy level it will emit a foton (simply because the energy left it and has to go somewhere and travel away in some form). the reason the electron wants to drop down is because diffrent atoms has a diffrent number of electron shells, and each shell layer contains a diffrent number of electrons when in equlibrium with about equal energy state. i could continue explaining subatomic attracting and replusing forces but thats too much. thats how ive understood.
think of photons as two coins that can be either up or down there are 3 options: 1. up+up 2. down+down 3. up+down now as you see out of three they have a 2/3 of being the same kind and 1/3 to be different
they don't necessarily "cut" things, they just excite the atoms of the target location enough to change states by escaping in the form of vapor, or creating a chemical reaction (oxidation/fire) or melt... so when flesh is cut by a laser, it's because the tissue in the path of the laser has been vaporized (and left a gap which we could call a cut at a macroscopic level).
most lasers use up massive amounts of energy, so the energy being released in the form of photons is indeed being constantly replenished by it's powersource (battery).. so the battery which is providing the energy for excitation will eventually run out of stored energy, causing the laser to shut down. So in short to your question, Yes. And you can see the light from a lightbulb, just stare at it ... it won't be pleasant lol...
Common cheap lasers use a rod made of ruby (corundum) as a medium, with an electromagnetic coil wrapped around the rod. There's a lot more to it, but somehow energizing the coil causes the ruby rod to generate a red light in a focused beam. I think they might also use a lens to focus it even better.
at school i am right now going into nuclear physics, i want to ask you about the light that is emmited by the atoms. what i understand right now, if the atom is excited it goes out 1 step of energy level. if it goes down 1 step of energy level, then it releases the excess energy as light? so does laser work by exciting and de-exciting the atoms repeatedly?
+cok Bagus maybe a little more accurate is to say that the shell electrons are excited to a higher energy level shell and then emits light when the electron returns to the original state.
uchiha viranga sorry but I don't understand your question. the energy of the light emitted is a function of the difference in shell energy levels the the electrons dance between
Technically speaking, you have to specify that you are differentiating with respect to x. If you were to differentiate with respect to any variable other than x, this would be 0. Furthermore, you have to say that x is an element of the reals and the expression exists solely within the reals (without specifying, the simple rules of differentiation could not be true). The derivative with respect to x assuming reals is 3x^2 + 10x - 4, a simple power rule is all that was necessary.
try more like this; neon, argon or helium gass in a container, have a strong electrical charge through the gass, now you have light. now you need to work on bouncing them back and forth then slip it through a little whole... but i'm afraid you only built a laser which is visible and won't burn anything... the amount of energy in the photons corrosonds to the "states" the gasses were exited and decent to. which is different in the different types of gasses
Black holes. A gravitational singularity at the hilt would pull light back almost instantaneously with significant shielding to contain the gravitational forces.
MOST IMPORTANT: if you cannot distinguish between 2 photons then there is only one way for them to be in different states, unlike coins. This is hard to grasp, but is absolutely critical.
You wanna know what i love about minute physics and vsauce? All these theories i made up when i was in elementary school were laughed at, then I come on here and these guys prove me right. I drew a schematic (albeit in crayon) for this type of laser in 5th grade
It's for the same reason you can't actually see the light from a bulb, you only see what is illuminated, also why you can't see sound, only the matter it vibrates. Higher intensity lasers can be seen because they heat the air as they pass through it, thus causing a small amount of light to be diffused from the beam.
No, because it is made of crystalline molecules. In other words, it has a distinct melting point (although wood has no liquid state). Only amorphous molecules can melt, because they deform as heat grows greater. I just learned about this in school.
@Deathray75 There's two main ways, collisions and light. Collisions would be like heat and light would be like solar cells. When atoms collide they release heat, so a greater number of hot atoms (like a fire) produces more heat (like fire heating metal). Light excites atoms by making their electrons "jump" to a higher energy level. When the valence (outermost) electrons are excited like this they escape from their orbits and are released as electricity.
This has to do with entropy, correct? Like the deck of cards analogy (it's easier for them to be in ANY order rather than in new deck order), it's easier for the photons to be in the same state, rather than different states?
I tried explaining this to my cat and he's still baffled.
Bob O.
wtf? >.> i done runned over yer cat last munth, hes not baffled no more. shuck-a-muk!
Bob O.
Mindblown.
my cat "gets" it, i don't see the problem, try harder
My cat is behind this whole science show.
@@guymcguyenson3858 It's been 4 years,so it's highly likely your cat's daddy is dead.
Photon peer pressure :(
good one!
Erich Shan All the cool subatomic particles are doing weed?
Lmfao
This video explained lasers in such an incredibly immensely simplified way that no one can really be satisfied with it, or, let alone understanding the concept.
So true. Explaining lasers isn't simple. But this isn't even the beginning of an explanation. This is the kind of false explanation that you will find interesting if you already know how it works.
@@fabiena1787 what’s the proper explanation? I think it was pretty good for a 2 min video.
I've found this explanation here, currently watching fully to see if it appropriately answers the question, but it should be a good starting point for other questions you may have.
ruclips.net/video/DA7a_v96Jsw/видео.html
You know, these physicists delight in complicating matters so don't blame your cat. Just pass a Ray of light through a man made quartz crystal which does have the power to disperse that light so it comes out pint point accurate according to what beam intensity you put in.
I found love the last time I got trapped between two mirrors too
that's sad
Do you mean a mirror maze???
You're loosing concentration.
❤️❤️
1:06 best love story ever. ;(
Kevin AnimalCrossing Still a better love story than Twilight
Dror Bazer which is still a better love story than 50 shades of grey
i dunno its kinda creepy 1:08
in only 2 seconds it turns from aww to pedo
kevinalb007 Better love story than twilight
So are photons in their own field surrounding us at all time but we only see the ones that phase in?
So THIS is the first step to making a lightsaber!
If he could explain why these things happen in a RUclips video people wouldn't need to spend years at universities.
These videos are for entertainment and to inspire people to seek their own answers, so thank you MinutePhysics for making up these metaphors, it's things like your videos that are the reason that I'm studying Physics today.
This video explains the one thing I had not been able to find, and that is... "how can the photons be in phase if they are not generated at the same time." Also the coin flip analogy really helps understand the process. There are so many great articles out there that explain how lasers are built and the basics of what they do, but without the points from this video you can't really get an intuitive understanding... Thank you for the great overview!!
I did not get the coin flip analogy
This is the power of friendship
1:16 oof look how happy those three look together awie 💕
You guys are awesome! Helped me to understand the lasers for my physics research. Thank you!
clicks on one vid of minute physics *five min later* i cant stop watching vid after vid
I love these! I'm sure my physics teacher would be agree
So, how the LASER really works?
Henry, apart from thinking your videos are fantastic, I LOVE your choice of music.
next thing you know .. people are fighting for photon marriage rights ...
Please don't give ideas to Tumblr
Star Trek Voyager did it.
yeah because marriage rights for gays is such a rediculous idea that you have to parody it
*#howtotriggeratumblruser101*
@@Angel_foxxo its not unatural. We see it in the animal kingdom.
After watching to many videos , this video finally made me to understand
The best explanation I have ever seen! Great!
The better grammer i have ever seen
+Reptile estrin LOL.
i cannot believe i am 23 and saying this, but the background music sounds like when steve is drawing a clue on blue's clues. on another note, i love this channel. i learn so much...(after watching the same video like 3 times in a row)
I have actually seriously thought about this sometimes, sometimes, except with light instead of lasers, with light I am pretty sure it would be un-observable because even the smallest crack would allow light to escape, and because light moves at the speed of light and the light source is no longer there we will never know if the light dims in the room of mirrors. Is this correct?
Please introduce yourself, the person who makes these awesome videos...
149 photons were different
this is the happiest way to explain lasers ever!!!
It's pretty amazing to think that the light that comes out of a laser is only 4% of the light created within the laser.
Literally explained it in the most coolest way possible and understood it the first time itself
Wow, now I know what Einstein meant by "everything should be made as simple as possible, but no simpler"...
this is really awesome. this explains why if you look at the reflected dot from a laser on certain surfaces, you see the much smaller individual dots making it up moving all over the place within the dot
Explaining what photons do is not the same as explaining why they do what they do. For example, in showing that there is a greater probability of finding photons in the same "state," (at 00:50) you still don't yet have any rationale for giving a "Therefore...." This probability has nothing to do with why photons from the output of a good laser are in phase. Laser designers don't say, "The light will probably be in phase."
Certainly you'd agree that their design specifications have something to do with it. If the specifications are more relevant than probabilities, why not include them in a "How lasers work" video if the intention is to show how lasers work?
It may be worth your while, also, in studying why the theoretical physicists some years ago said laser light wasn't possible, and how they treated the people who said it was. Some of the speculations in modern physics have to be let go, it seems to me, considering the fact that laser light is obviously possible.
Caleb I totally agree, but the channel name is minutephysics. I think he did alright with the brevity but he could have alluded more to some follow up for more interested viewers.
Back in the days when minutephysics was minute physics
"Photon's want to be together", I feel like we are regressing a bit here. A little more detail please, maybe refer us to a sixty symbols video at least.
It's a little more special because you can do it with integer-spin particles (like light, sound, gravitational waves, and the charge-pairs in a superconductor) but not half-integer spin particles (like electrons, protons, neutrons, neutrinos). Light is indistinguishable in a way that it can "condense" into the same state while electrons are indistinguishible in a way that only one can occupy a state. Once you have that sort of indistinguishability, though, the probability does work that way.
if you just slowed down talking a bit..that would be really helpful.
RUclips have 0.5 and 0.25 video speed
I always love the bass jammin' away in the background in these videos.
LASER (Light Amplification by Stimulated Emission of Radiation) is an acronym so it isn't a Laser it's LASER beam (of light), as said in the video but I don't think people understand that subtle point.
+David Hughes Well, it's more commonly referred to as simple 'a laser' or general laser light, regardless of any formalities or technicalities. So as long as everyone understand what it is, eh?
+David Hughes It's become just a word in the English language just like Kleenex is interchangeable with tissue
Atoms have diameters measured in picometers, so you would never see one no matter how excited it was. It could be undergoing fission and you still wouldn't be able to notice. I'm not sure if your question was meant to be serious. The "static" you see is caused by imperfections in the laser emitter's optics. Some of the light is scattered instead of perfectly focused. Cheaper lasers will exhibit this effect more strongly than more expensive, quality units.
ALL YOU HAVE TO DO. /ALL/ YOU HAVE TO DO.
why everyone is hating , he's trying to simplify the idea so that everyone understands and i think you did a great job .. I take physics this year and the video explained a lot of what i didnt understand .Thank you
"The most romantic love story I have ever heard"
- Sheldon Cooper
Funny... I looked all over the web for a simple explanation... I actually noticed this and went on (0n my search). After a while, I got tired and watched this! It solved all my problems :3
This is a pretty poor description. How can you meaningfully discuss the operation of a laser without the concepts of phase coherence and population inversion?
He isn't 'meaningfully discussing' the operation of a laser; he is vulgarising the process in order to make it comprehensible and appealing to a larger audience whilst keeping the explanation concise.
Chaossdruid He isn't "vulgarizing" it, he's utterly raping it with a chainsaw. This explanation was almost completely wrong.
It always baffles me how people think that an explanation being "accessible to a larger audience" makes it any less wrong. Uh, hello? If it's wrong, it should *not* be taught to a larger audience!
Leave the wrong, appealing bullshit to scifi writers. Science this ain't.
gogerychwyrndrobwll There's a common analogy teachers use when teaching basic arithmetic. Imagine a man walking forward on a train that's also moving forward. What is the man's speed relative to the ground? According to the teacher, it's the man's speed on the train plus the train's speed on the ground. But that's false. Relativity tells us his speed is actually a little slower than that.
By your logic, teachers shouldn't use this analogy because it's factually incorrect. Their students would go into the world with the wrong idea about how the world works. It wouldn't matter that the students' understanding and the reality is off by mere trillionths of a m/s: wrong is wrong, period.
Maybe you're actually right. This video isn't accurate, and it's off from the reality by a lot more than the train situation is from reality. But unlike basic arithmetic, which has many possible analogies that a teacher could use, the physics of lasers is awfully complicated. This video shows what very well may be the simplest analogy possible that gets the basic idea of lasers across. It might be technically wrong, but a basic idea is better than no idea at all, right?
If you can think of a more accurate but equally simple analogy, I would honestly love to know it. I want to know more about lasers, too. You could even try making a video about it. If it's as entertaining and even more educational than these videos are, people will love to watch it.
*****"By your logic, teachers shouldn't use this analogy because it's factually incorrect. "
That's not my logic at all. That's your supposition of what my logic is.
The explanation given by the teacher is the low energy (Newtonian) approximation to the full relativistic dynamics. It is the leading term in an asymptotic expansion in v/c. It's clearly appropriate to the problem at hand. Further, it's *more* appropriate than the full relativistic expression since any and all corrections that are of higher order in v/c get entirely swamped by experimental error and are unobservable, even in principle. Strictly speaking they can't be said to be there at all. So the Newtonian approximation is entirely justified, rigorous, and accurate.
In contrast, I know of a certain physics youtuber who dislikes Newtonian approximations... watch?v=IM630Z8lho8
D'oh!
The problem with the exposition in this video is not that it's "simplified", or even "outdated". It's *fictional*. It was never true, it never even resembled anything that could be construed as an explanation for a laser. You can easily see that this simple entropic argument cannot work by noting that if it were true you'd see lasing merely by placing on mirror in front of the other. This obviously doesn't happen. You *need* to understand stimulated emission and gain media. You *need* to understand population inversion. Population inversion is quite interesting by itself, since it leads to the subject of negative temperatures which are surprising and fascinating.
A competent physics youtuber attempting to explain these concepts would have to find creative ways to make them accessible. Veritasium is typically very good at this. Minutephysics, on the other hand, tends to just make up whatever fictional explanation would sound sexy, even if it has only a passing resemblance to reality.
"You could even try making a video about it."
I've been meaning to try to start a physics channel, but honestly I don't think I have the competence or charisma to make videos that the average person would find interesting.
gogerychwyrndrobwll "D'oh"? Nah, I used the man-on-the-train situation for that very reason. Glad you caught that!
So, you're right. Henry's reasoning doesn't approximate reality in the slightest. (Side note: From my own education, he's usually not wrong in most of his videos. This video seems to be an outlier than an accurate trend in Henry's scientific accuracy.) But that raises a question I've seen other people approach in this video and others: namely, is it possible for his more... interesting ideas to be wrong in principle but right in practice?
Henry's videos may be factually incorrect, but they do expose a broad audience to interesting scientific phenomena. So, is it better that people watch these videos even if they're wrong? Or would it be better if people didn't watch these at all? I do think the former is preferable, since intrigued viewers might go on to learn more about the subject on their own, but that's just an opinion. I am curious to read your own, if you care to share.
I've been meaning to start my own physics channel, too, but I haven't found the time to write a script or set up a film area. Also, yeah, making videos interesting would be another problem to handle. Still love to try though.
This is the only one of your videos that makes sense
you can, if you use the .9 infinitesimal rule. also, there are systems for counting besides the metric system. if you use the dozenal system it is quite easy to express two thirds, and 1/3 as decimal.
Lazers are created when recycled plastics are converted into light photons, creating ultra strong lasers actually. It can create many colors.
I love how whenever people try to explain the universe simply they're like "Well imagine that time is a line." then later on it's all "Time's not a line, that was just an easy way of explaining it."
If there is any room for another electron in a lower energy state around an atom, an electron in a higher energy state will release a photon to reach that lower energy state (it's a bit more complicated than that, but that's the main idea). So, it's not really possible to "hold" an electron in a higher energy state than it "wants" to be in.
Also, As you go to higher an higher energy levels, the differences between the levels becomes exponentially smaller, so there is a limit on the energy.
I love stuff like this because it basically illustrates using maths to break our understanding of the universe. When i first learned about the uncertainty principle, i parsed it as "we can only know position or velocity because of the way we measure" implying that there was a way to measure both, even if only in magical theory land and never in reality. Because we tend to relate everything to what we can experience, i was still subconsciously thinking of electrons and photons as "objects". But i later realized that the duality is litteraly unknowable, even theoretically, because photons and electrons arent like anything were used to. They arent lines or dots, and they dont operate on the kind of logic we do.
I once was watching a lecture on how one could sorta try to visualize 4D shapes, and it just became so obvious that stuff like this just operates on a completely different plane. We can try to kinda mush it into something that we can sorta make sense of, but in reality its as incomprehensible to us as imagining a new color. Its just beyond the ability of our brains. We can understand it, use equations, but in the end were basically just interpreting something that we can never really perceive the truth of.
You should also consider that if something seems impossible to figure out; that you dont have a solid enough grasp on what it is youre talking about. Such as photons. Theyve never been measured as a thing. Its just a name given to the phenomena of light/energy being produced. Although the reason photons as a concept exist, is because people seem to believe they must attribute the phenomena of energy conversion/light production to a particle in it of itself. Instead perhaps it is simply a product of fundamental aspects of how things work, that energy is produced. Energy in it of itself, not photons. Instead of photons being a thing that are produced, "light" is "produced" by the processes of universal laws. Light in itself isnt a thing. It isnt a particle. It is a function of equations of electromagnetic fields. It isnt a product or an addition, simply a piece of an equation which is everpresent. I.e. the equation cant exist without the entirety of the equation. You cant have X and T interact without "producing" Z. Producing is used lightly, as it isnt a product, it is simply a piece of a law which exists simultaneously along the other pieces of the law, and none of the pieces can exist without having that interaction being a whole of all of the individual aspects.
If you have prior knowledge of this stuff then this video will be a best summary
When an atom's electrons move from an energy level to an lower energy level, it emits an photon
(completly making up names and values, but the concept is correct)
Electron Level 4= lets say 6 energys
Electron Level 3=4 energys
when an electron moves from Lvl. 4 to Lvl.3; there are 2 extra energys that the electron needed in Lvl.4 are no longer needed in Lvl.3 thus the energys get emitted as photons
The reverse happens when an atom "absorbs" an photon
The fact that the laser beam is directional ( that it is not emitted in all the directions) comes from the way the mirrors are positioned. In this example, parallel mirrors are used. Only the photons that are emitted along the axis that is perpendicular to the mirrors will get to stay in the cavity and induce other emissions and be reflected again, etc. The beam that goes trough the little hole is thus strongly directional.
for those who can't remember highschool science the atoms are excited by the amounts of quantified energy it can absorb in the form of a photon (quantified energies being the amounts of energy belonging to a jump or fall in levels of excitation). In the same way the atom can emit an equal amount of quantified energy in the form of a photon. These energies correspond to certain light wave lengths. So if you take a bunch of the same atoms which absorb and emit the same photons in exchanging the same quantified energy you'll get a bunch of the same colour of light (same wavelengths in the visible light spectrum). And this video explains how the light comes out in a beam.
I knew it was concentrated light but this explained it much better than I could have.
It builds up until the imperfections in your mirrors absorb as much energy as you're putting in. Or the light that's bouncing around starts hitting the atoms and re-exciting them all the time, and you can't put any more energy in because there's nothing to do. Or both. Anyway, there's a limit to how powerful a beam you can get out of any particular laser by charging it longer. You need more atoms or atoms that get more excited.
Your videos make me think of science in a very adorable way.
Actually, light scatters off of clean air only a negligible amount. If there is dust, humidity, or smoke in the air however, you are right that some scattering occurs and you can see the beam.
I'm not sure if this has already been said but unless there is a way to measure the light from outside the mirror box wouldn't you never be able to prove whether the light is reflected an unlimited number of times. Anything inside the box will absorb the light before it can complete its "infinite" dance around the box.
Also I think it goes without saying that this theoretical box would be a perfect vacuum for best results.
I love lots of your videos, but this one was extremely simplified i coullndt learn much in this video D:
Yes! I only just discovered them like 3 days ago and have been watching non-stop.
Cool concept, the one with the fotons. Your analogy was good too.
Ah the science section of youtube. Sometimes it even seems like you're on a completely different website because it's amazing. :)
Excellente vidéo explicative ! Superbe réalisation
Nice! And very concise!Thank you!
First of all you need to understand that E=/=m
(Where E is energy and m is mass)
E=mc^2
(c is the speed of light)
Secondly, you need to understand that photons are particles and they generally have no mass.
Hopefully that helps clarify it a bit for you.
what kinds of atoms are best suited for lasers? just any kind? how much energy is needed to excite these atoms?
It's not like only one photon is excited with energy. They are all excited (all have energy) so the photon passing by, is only causing the other excited photon to go the same direction(or do the same thing). it already has energy, but now its doing the same thing as the other photon. It is an already "excited" photon. 0:58.
@MinutePhysics Wait... why do mirrors reflect a photon rather than absorbing it? We see red because a red surface absorbs all but red, so would that mean ta mirror has no colour?
Light just bounces off a mirror the same way it bounces off a white object. The difference is that mirrors don't scatter the light, they reflect it at the same angle.
But if light is a wave and only a particle when observed(interacted with) then why is it more likly for the light from a laser to hit the same area then from a non-laser light?
You cannot see a photon "whizzing by" since in order to see something it has to emit a photon towards your retina (either transmit or reflect). That photon is then absorbed by your light sensitive cells and converted to electrical pulse going trough your nerve into your brain. so You cannot see a photon going by, you only sense a photon coming into your eye.
Generally, the side of the mirror that light is being projected from is partially silvered, and moved to a miniscule angle, enough to allow the light to shine through, but the hole he described was just figurative, since this is minute physics :P
There are two answers I have heard to this, I have no idea which is right but I'll start with the one I think is.
Not entirely. Wood is made of a lot of different things. Unlike water or metal or rock, wood has a bunch of things in it that melt/evaporate at different temperatures. Obviously you would have to do this in a vacuum to prevent combustion, but at one temperature you could have a lot melted, and then a little higher and stuff starts evaporating.
Or
Can you melt dry ice?
even before the second photon exists. this is why science is exiting.
I take issue with the supposition that the light emissions are different from flipping two coins. Just because you can't tell them apart doesn't mean that they don't behave in the same way. And the probability that two coins will land on the "same" side or "different" sides is 50-50. Just because you can't measure the state of individual photons doesn't collapse their heads-tails and tails-heads outcomes into a single possibility. It would still be 2 ways that they end up in different states.
How does passing light stimulate it to emit even more light? Where did that extra energy suddenly come from? Isn't that breaking the 2nd law of thermodynamic because we are extracting energy out it?
So I a box with perfectly reflective sides and walls we would be cooked from the infinite energy bouncing around. Or would we interrupt the system by just existing within it?
The reason you normally can't see lasers is that all of the light is traveling in the same direction - toward the target - and therefore none of the light is traveling into your eye for you to see. This is very different from lightbulbs, which send light in all directions. The reason you can see a bright spot on the target is that once the laser hits, some of the light scatters out in all directions...including into your eye. But unlike a laser, probably not enough to blind you!
I really like this channel....sometime i understand little.sometime i dont..
The narrator going way to fast before understanding anything.
i wish i could give my high school projects like he does his videos
you need a gas or such to electrify to make the light....co2, helium, nitrogen, argon are comon gases use to power a laser..as yes the fuel does run out as light is energy loss from a heated mass(though most is wasred as heat)
re directing the super heated gas(plasma) itself is a "Phaser", while consentrating micro-wave emmisions make a "Maser"
You can also use ultrasonic sound waves as a consentrated beam for welding steel and melting plastic
I LOVE THE BASS LINE!
I'm glad Jesse Eisenberg has decided to expand his hobbies since the Social Network
I think the explanation behind lightsabers is actually more plausible than the explanation I just heard for lasers.
when an exited electron drops down one energy level it will emit a foton (simply because the energy left it and has to go somewhere and travel away in some form). the reason the electron wants to drop down is because diffrent atoms has a diffrent number of electron shells, and each shell layer contains a diffrent number of electrons when in equlibrium with about equal energy state. i could continue explaining subatomic attracting and replusing forces but thats too much. thats how ive understood.
Can I also just add that he explains "Science" far better than any of you could.
think of photons as two coins that can be either up or down
there are 3 options:
1. up+up
2. down+down
3. up+down
now as you see out of three they have a 2/3 of being the same kind and 1/3 to be different
they don't necessarily "cut" things, they just excite the atoms of the target location enough to change states by escaping in the form of vapor, or creating a chemical reaction (oxidation/fire) or melt... so when flesh is cut by a laser, it's because the tissue in the path of the laser has been vaporized (and left a gap which we could call a cut at a macroscopic level).
most lasers use up massive amounts of energy, so the energy being released in the form of photons is indeed being constantly replenished by it's powersource (battery).. so the battery which is providing the energy for excitation will eventually run out of stored energy, causing the laser to shut down. So in short to your question, Yes. And you can see the light from a lightbulb, just stare at it ... it won't be pleasant lol...
Common cheap lasers use a rod made of ruby (corundum) as a medium, with an electromagnetic coil wrapped around the rod. There's a lot more to it, but somehow energizing the coil causes the ruby rod to generate a red light in a focused beam. I think they might also use a lens to focus it even better.
at school i am right now going into nuclear physics, i want to ask you about the light that is emmited by the atoms.
what i understand right now, if the atom is excited it goes out 1 step of energy level. if it goes down 1 step of energy level, then it releases the excess energy as light?
so does laser work by exciting and de-exciting the atoms repeatedly?
+cok Bagus Yes, that's it
+Sandstrand Fjeldstein alright thanks!
+cok Bagus maybe a little more accurate is to say that the shell electrons are excited to a higher energy level shell and then emits light when the electron returns to the original state.
+phishfearme2 but what makes laser so powerfull i thought when a electron returns to its original state they relese hydrogen spectral series
uchiha viranga sorry but I don't understand your question. the energy of the light emitted is a function of the difference in shell energy levels the the electrons dance between
Technically speaking, you have to specify that you are differentiating with respect to x. If you were to differentiate with respect to any variable other than x, this would be 0. Furthermore, you have to say that x is an element of the reals and the expression exists solely within the reals (without specifying, the simple rules of differentiation could not be true). The derivative with respect to x assuming reals is 3x^2 + 10x - 4, a simple power rule is all that was necessary.
Awesome video, as always! But this is only a theory though....? What aren't we definite about in regards to lasers?
try more like this; neon, argon or helium gass in a container, have a strong electrical charge through the gass, now you have light. now you need to work on bouncing them back and forth then slip it through a little whole... but i'm afraid you only built a laser which is visible and won't burn anything... the amount of energy in the photons corrosonds to the "states" the gasses were exited and decent to. which is different in the different types of gasses
Black holes. A gravitational singularity at the hilt would pull light back almost instantaneously with significant shielding to contain the gravitational forces.
MOST IMPORTANT: if you cannot distinguish between 2 photons then there is only one way for them to be in different states, unlike coins. This is hard to grasp, but is absolutely critical.
You wanna know what i love about minute physics and vsauce? All these theories i made up when i was in elementary school were laughed at, then I come on here and these guys prove me right. I drew a schematic (albeit in crayon) for this type of laser in 5th grade
Geez, the same happened to me, i drew magnetic force trains and 2 years later japan made some
It's for the same reason you can't actually see the light from a bulb, you only see what is illuminated, also why you can't see sound, only the matter it vibrates. Higher intensity lasers can be seen because they heat the air as they pass through it, thus causing a small amount of light to be diffused from the beam.
No, because it is made of crystalline molecules. In other words, it has a distinct melting point (although wood has no liquid state). Only amorphous molecules can melt, because they deform as heat grows greater. I just learned about this in school.
It's an electromagnetic wave. It's a complicated idea, but think of it as energy. Photons are essentially light particles (matter) that have no mass
@Deathray75 There's two main ways, collisions and light. Collisions would be like heat and light would be like solar cells. When atoms collide they release heat, so a greater number of hot atoms (like a fire) produces more heat (like fire heating metal). Light excites atoms by making their electrons "jump" to a higher energy level. When the valence (outermost) electrons are excited like this they escape from their orbits and are released as electricity.
Cheers mate, really great when you have a video on a topic for my chem project =P Making everything a lot easier
This has to do with entropy, correct? Like the deck of cards analogy (it's easier for them to be in ANY order rather than in new deck order), it's easier for the photons to be in the same state, rather than different states?