Why General Relativity (and Newton's Laws) tell us The Sky is Falling Up
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- Опубликовано: 17 май 2024
- Understanding the Equivalence Principle is pretty straightforward -- so long as you're willing to throw out some basic intuitions about your everyday motion. Indeed, there is an astonishing truth about why objects actually "fall" at the surface of the earth that most people are completely oblivious to. Join us as we take to rocket ships, rooftops, cow pens, and other exotic settings in an attempt to expose it. Plus: plenty of monkey business along the way!
Support us on Patreon: / dialect_philosophy
Contents:
00:00 - Introduction
01:02 - Intuition, a Fickle Mistress
02:20 - The Operative Definition
03:58 - Motion in a Rocket Ship
07:27 - Motion at the Surface of the Earth
09:48 - The Equivalence Principle
12:37 - The "Switch"
15:11 - Motion Falling off of a Building
17:54 - Tidal Forces
20:48 - The Sky is Falling Up! 
Наука
"Gravity Don't Make Things Fall"
"Gravity Things Doesn't Fall Make"
Yet again a fantastic video!
Coming from you, that is high praise! You're one of the best content providers for this subject matter (no pun intended).
Your support has made a world of difference for us. There isn't thanks enough we can give.
@@dialectphilosophy Your content is always superb. I've learned a lot from both you and ScienceClic.
Was just thinking that Dialect's video style narration animation etc resembles Science Clic...😁
If you're on board then I can trust everything in this video wholeheartedly. I love each and every single one of your videos. They truly are the benchmark for which all others must strive to become. You are at the top for helping others to become more enlightened about physics and spacetime. I think about your videos often and rewatch them just to stay current with my knowledge. I can never thank you enough. 😊
P.S. I love the background music so very much as it actually helps me to stay focused on your subject matter. Please don't change it. 🙏
Great video! But: How does tidal forces towards the end of the video explain the problem with "earth falling up in all directions"? You asked the right question there but I am not sure if I understand how your explanation answers how the Earth can "fall up" in all directions? Also, you mentioned it's as if the objects are sucking the space-time around them. So this also goes against the Earth/sky falling up in all directions. Do they suck in or do they fall up?
Yes, those 2 things cancel each other out (after millions of years after the formation of the Earth) perfectly, so the Earth continues to have the same shape.
The Earth is moving outwards in spacetime due to the Earth's own internal geological pressure, and spacetime itself, is falling inwards due to the Earth's energy density "sucking in" local spacetime.
You could imagine that the Earth is flat and accelerating upwards but in a curved spacetime! All of a sudden, time at different altitudes runs either faster or slower and the entire shape of the flat Earth takes the shape of the local spacetime... Basically, a sphere.
That doesn't mean that the superimposed spacetime, isn't equally Deus ex machina as it is with Newton's force of Gravity. It's just a more sophisticated Deus ex machina that takes more stuff into account, and gives an accurate result that respects the speed of light limit.
But the explanation isn't any more or less "magical" than that of Newton.
I believe that it is the time-curvature in 'spacetime' curvature. Notice the gravitational subtractions were all done in space. The residual is the space curvature. Nearly all the effects of gravity near a body such as the earth or sun are due to the curvature of time. (I'm not 100% sure about this, because I would explain the concept differently, but I'm pretty sure that is what is explained).
The earth accelerating 'up' is caused by the time curvature. If you are sitting on the earth in empty space, then relative to the earth you are stationary and thus not traveling through space, so you should not be influenced by space curvature, but you are still traveling in time, so you do experience time curvature.
Falling off a building, you do then experience both space and time curvature since you are moving relative to the earth. But he space curvature is a tiny fraction of the overall gravitational effect.
Here is the thing though with the above explanation at the end. If you consider that the earth is dragging spacetime into itself, then it seems more like objects that are stationary in that spacetime are indeed being pulled toward the earth, rather than the earth accelerating outwards. That is at odds with the video and the inertial frame of reference idea. - EXCEPT the inertial frame of reference is still local. Suppose you took the view of the earth as a whole as int he video with the apples on each side of the earth. You then have 2 people jumping off roofs in the US and Australia. Now has the act of jumping off the roof switched off the gravitational field? No, it has not. IDK, this then gets way deeper than a youtube reply. But locally the earth is accelerating up due to time-curvature - it is accelerating into you in time, not space.
@@edwardjenner1381 The best explanation is, that gravity is a real force which obeys Einsteins equations. Like it would be if gravitons would exist.
The rocks, which make up this thing we call the Earth, are in currently in hydrostatic equilibrium between the outwards electrostatic forces in the atoms of the rocks, and the pressure of spacetime getting squeezed inwards by gravity.
Gravity is making the space that the Earth occupies "physically shrink"... you don't see the Earth actually shrinking though, because the core of the Earth, the mantle, the crust, etc. are stretching out by exactly the same amount that space is shrinking. (Here on the surface, that stretching out is about 9.8m/s of linear acceleration... going "up")
Smaller rocky bodies in our solar system, like asteroids and stuff, are not compressed enough by gravity for their rocks to get squished into a sphere. The electrostatic forces in the rocks are greater than the "force" of gravity, so they are not in hydrostatic equilibrium. (The rocks don't flow like a liquid.)
I should also mention, the ~15PSI (760mm Hg) atmospheric pressure we have here on the surface of the Earth is also due to gravity compressing spacetime. Literally compressing a gas... Water pressure in the oceans is also for the same reason.
We're all floating on top of a big ball of liquid rocks and metals.
Also, below the surface of the Earth, the local acceleration that you feel -- your weight -- decreases until you reach the center of mass of the Earth, where you will feel weightless, as if you were floating in space (because you are). (This is assuming a hypothetical situation if there was a room at the core of the earth which was comfortable for a human being, and not actually a 9800°F blob of iron.)
@@justintime9714 That makes no sense at all. Firstly it most definitely is NOT the best explanation to say that gravity is a real force which obeys Einstein’s equations because the only way to obey said equations is for gravity to not actually be a force at all. And what exactly does it even mean “like it would be if gravitons exist”? What would actually change if gravitons existed and more to the point, how could you possibly have any idea whatsoever about how anything would change by postulating the existence of imaginary particles?
Why do you believe there is any need for yet another imaginary and completely unnecessary particle? What would change if gravitons were discovered? It’s as if you’re insinuating that gravity has some requirement to be quantised, which is clearly incorrect. How do you know it’s not quantum mechanics which needs to be gravitised?
I appreciate that you acknowledge the left over questions most viewers are left with. Just that makes me comfortable accepting the model for now. Great presentation and work.
One of the few channels where I don't need subtitles, perfect diction! The switch-off gravity idea switched something on in my head. Thank you!
I have watched many videos on gravity over the years and I think this was one of the best . Thanks
The ability to effectively explain complex concepts isn’t just extraordinary, it's a service to the world!
Wonderful and insightful video. Love it. I’m looking forward to going through all of this channel’s videos.
Interesting how well presented logical fallacies smoothly take us down the road of inaccuracy 😮😮😮
bro the “sky is falling up” is a great name for some horror movie
Galileo didn't actually drop balls from the Tower of Pisa, he rolled them down inclined planes.
Actually it was Simon Stevin who did the proof years earlier. But he wasn't Italian.
Breakthrough concepts for the layman patiently and convincingly explained. Kudos
Thanks for your support!
One of the best videos I've seen explaining how the equivalence principles of freefall to zero-G and gravity to acceleration can still work despite facts like gravity gets weaker over distance and causes things to fall radially.
"The river model of general relativity, where mass eats space" - aha, that's exactly how I've been making sense of it! I need to see more about this interpretation!
They mostly only refer the river model to black holes but it should be used for all matter, black holes only do it on a more intense scale.
Does it " eat" space or is it a diffrent form of space ? Space in a different state
@@gtitboij2586 don't know, probably just returns to its previous state or dimension. Space and matter are most likely anti-pair states of something. Were use to hearing about anti particles and they destroy each other releasing energy, but gravity is space being erased or converted, but the matter stays.
Most likely converted to the time dimension.
@@dexter8705 we all know that matter and energy in the universe are conserved so I am of the opinion that it is a diffrent form of space , the wave model suggest that space is excited via electromagnetic waves therefore there must be a quantized point where space becomes matter thus allowing for the formation of non- degenerate bosonic particles ...
@@gtitboij2586 I like that idea but wouldn't that cause other objects to be push away and not pulled in? I'm trying to visually imagine and physic'ally because sound can do something similar but thats due to the compression of the atmosphere, I wonder if the excited state of matter and space from the electromagnetic wave are doing something similar but with enough force to pull it in...
Thanks for the clarification, most of my questions has been responded yet, but yeah more videos about this are very good idea to put all more clear.
Amazing video -- really crystallizes the concepts in a way that feels incredibly easy to grasp. And without any compromise on correctness as well. Technically I knew all the stuff about GR presented here but this made me really *feel* it.
I need a better/more thorough explanation of how all points on the surface of a sphere can be accelerating “outward” simultaneously, while the sphere itself remains intact.
Agreed. Where exactly is the acceleration happening if the surface is actually not moving relative to the sphere it is compromised of? Here's another one...if you are really at rest when you are falling in open space, why is the sensation of falling so internal and striking? That one has some explanations I think but it's interesting.
When you have a cloud of gas in empty space, it expands, due to the gases' internal pressure, which occurs in every direction. This explains how the earth is accelerating in every direction, because the materials inside the earth exert pressure outward. Now to explain why the earth does not fall apart, we can't use the "force of gravity", because it is fictitious. So instead, we are forced to conclude that the volume of the spatial region encompassed by the earth is shrinking over time due to spacetime curvature(more precisely Ricci curvature). If you are wondering where this spacetime curvature comes from, it is shown in the Einstein Field Equations that mass and energy density cause spacetime curvature.
This is something he does a horrible job at explaining, and you have the a knee-jerk reaction anyone should have from hearing his ideas. There isn't any acceleration of the surface of our planet, in the kinematic sense of the word "acceleration" that you ordinarily experience. But there IS acceleration, in the sense that there is a net non-gravitational force, which is equivalent from the observer's point of view of being in deep space and actually accelerating.
What's really going on, is that spacetime is collapsing in on itself, in the region of a gravitational field. Constraint forces "accelerate" objects on the surface of this planet outward, against the space collapsing. We are therefore "running to stay still" as a consequence of constraint forces preventing us from following the collapsing spacetime.
Two points on opposite sides of the earth have been accelerating away from each other at what appears to be a fairly constant rate for quite a while now. Even in just one year, their relative velocities were approaching c. Isn't that what's called "exploding"?
@@dontmeansquat He has a new video out that explains this, called "The River Model of General Relativity", and it's very similar to what I described in my previous comment.
Your channel and ScienceClic are by far the best channels on this subject. Keep up the good work. Look forward to seeing new videos from your channel!
I was so excited to see this recommended for me after watching your other videos. One of your best yet!
From what I understand, standing on Earth is LIKE traveling in a ship with an acceleration of 9.81 m/s/s. It does not make the ship the same mass as the Earth or the Earth the same mass as the ship. Having a large mass can curve the spacetime around it, but the ship has accelerated motion which is a curve through spacetime. To me it seems more plausible that all objects with mass are "falling" though time and objects with large mass can slow time increasingly with proximity, causing other nearby objects with mass "fall" through time towards the massive object until they hit and then continue "falling" through time parallel with the massive object. If you stop accelerating through spacetime then you stop the curvature and "gravity". Jumping off a building does not stop the curvature of spacetime that the mass of Earth has affected, it only removes the object that was keeping you from "falling" through time to the Earth. It seems unlikely, to me, that the surface of the Earth is racing outward thousands of feet in all directions to meet every object within thousands of feet. That's an incredibly large bat hitting a lot of small balls, not to mention the surface of the Earth rushing outwards to meet every air molecule in the atmosphere. However, I'm no genius, so please direct me to where can I read the peer reviewed proofs of this theory of the surfaces of massive objects racing outward in all directions?
This was a very good video. The caption @ 21:31 describes my first impression of the channel. I'm happy to be proven wrong, and as a new subscriber, I'm excited to finish the learning journey with you!
Thank you 😂. The journey will continue!
One time when I was drunk, I could actually see spacetime flowing through me into the Earth.
How do I get some of what you were drinking?
We have all been there.
Your videos are a great find! I feel the aha! moment and not some headache. I deeply admire your effort. Looking forward for the next ones!
I was wondering when something new was coming from this channel- awesome as always.
Thank you for an amazing video with insightful delicate points highlighted. It would be nice if you add a segment or another video showing explicitly how we can glean this from the metric tensor mixing parameters under the effect of mass, so we see the flow of space expressed in the rather simple algebra. There is an audience here that is not afraid of seeing math.
being able to come up with effective analogies is a hella underrated skill, and you have it in spades, terrific video 10/10
1. What experiment shows that my local gravity disappears *instantly* when I step off the building, thus proving the ground is accelerating up?
2. I can't imagine convincing anyone that the apple isn't falling. Which part of this disproved gravity is a force pulling things down?
Combining slapstick with general relativity. Brilliant as always.
Just found this channel and love its content. However, I'd appreciate a better explanation by the idea that the ground accelerates up toward objects we would normally consider as falling down. I understood everything this video said from the standpoint of vectors and so forth, and even learned a few new ways to think about GR. But when we got to the question about how Earth, a solid sphere, can accelerate upward in all directions, I felt the answer was glossed over. I'm not saying the answer isn't there, it was just rushed past. Having thoroughly enjoyed all four videos about how easy it is to pick apart solutions for the Twin Paradox by asking simple questions pointing out contradictory or incomplete answers, it is my feeling that saying that Earth, or at least the local ground, accelerates up makes way for contradictory or incomplete answers. After all, this video even points out how strange it would be for two apples to be released on opposite ends of the planet, implying Earth is accelerating in two opposing directions at the same time. Again, I'm not saying the explanation isn't there or doesn't make sense, I'm just saying it would be nice to revisit this idea I'm greater depth. Is saying the ground accelerates up merely a colloquial tool to make sense of the various vectors which add in some directions and eliminate themselves in others? Or are we to literally expect huge columns of dirt and rock to shoot up from beneath our feet every time an apple lets loose from a branch? Or is there a third way of phrasing it which a future video can explore? Thank you for considering my query as I would be very interested to learn this topic in greater depth, which I'm sure there is much yet to cover.
Glad you're enjoying the content! And you're right that a lot of information is glossed over -- we didn't want a 40-minute video on our hands, so we're breaking the topic into multiple videos (like we did with the twin paradox series). The next video in the series will tackle the question of how the earth can accelerate in many directions at once... stay tuned!
@@dialectphilosophy Thanks for the response. Can't wait to see what's next.
@@dialectphilosophy It defies common sense that channel with such quality is in fact proposing rather radical idea as earth accelerating up. It is so contraintuitive and propostereus that it should be backed with some serious evidences. So far you have not provide any. That said, everything else is among best of the best on youtube regarding relativity and physics...
The idea that we are accelerating at the surface of the earth is not a new idea invented by the creators of this channel. This has been the understanding of proponents of general relativity for decades
I thought they figured out a long time ago that gravity isn't a force...
What every mechanic and some engineers know is that just because it makes sense on paper or works in a computer simulation doesn't mean it actually applies to reality.
That's only true in the framework of _general_ relativity and classical mechanics.
Great watch an unbiased video that asks the difficult but simple questions
12:27 Reducing the acceleration of the reference frame obviously means that it will no longer accelerate at e.g. 9.81m/s^2. That's not primarily an "experiment" within the reference frame, but altering the crucial parameter of the reference frame itself.
Wow, I knew the equivalence principle was locally true for a homogeneous field, but I never thought about it using the tidal forces and the subtraction of vector component. Well done !!!!!
for a homogenous field isn't it globally true?
@@hiZarki Indeed
The production level with so many animations is superb.
Way to go!
This channel is criminally under valued.
Superb and outstanding video. Excellent narration and your explanation is very engaging.
Well done, great video. You’ve come a long way
Do you still disagree with his earlier vids, him saying other youtube vids about gravity are wrong?
@@Cee_H My comment is in response to his style of video. His earlier videos came across as unprofessional due to the attacking nature of bringing down other creators' works. He should continue to make videos like this one
@@jordanjohn01 Well said! I also prefer his tone in this video, but I'm equally impressed with his ability to bring attention and dialog to the Equivalence Principle and other abstract concepts.
Excellent video with comprehensible explanations and great animations! Astonishing job at making hard concepts of our physical world easily accessible! Thank you!
very very thorough, i love how precise you are in the way you speak
brilliantly lucid illustrations - thank you for make all this be so apparent
Outstanding video production and exceptionally well narrated. You presented information in a compelling, interesting and engaging way. I get your point, …absolutely, but my intuition still struggles with the reality of the matter.
It's presented well but is it TRUE
@@blurta2011 The concept is not intuitive, thus, hard to get my full understanding. But, so was Relativity when Einstein presented it in 1905 - he was ridiculed, insulted, etc. Today, w/out the necessary adjustments mandated by Relativity, geopositioning would not work (GPS), and many other tech advances.
another great vid keep em coming, i can guarantee that this channel will blow up once people start seeing the quality in these vids.
Enjoy all your videos very much but you have outdone yourself with this one...have learned alot,many thanks 😎
on my way to ace my next mechanics test, my professor won't even see it coming.
What you are doing here and ScienceClic English on his channel (by the way ScienceClic, your last clip called "The Electromagnetic field, how Electric and Magnetic forces arise" is extraordinary) is THE REAL DEAL. I'm really surprised that you only have so few subscribers. Much closer to the value of the content promoted here would be at least 3 - 4 million subscribers, but if you keep it up, you will get there in the shortest time, which is what I wish for you from the bottom of my heart. I only ask you to maintain this rigor in the future and we want as many and more frequent videos like this from you (and from ScienceClic as well!). I can't wait to watch the videos in which you treat the topics you opened up with the questions at the end of this video. All the best in the future in your journey through ... space time (SIC!).
21:44 I don't think putting this as a footnote is pedagogically wise. The intuition that the ground is accelerating upwards, for everyone on earth's surface, is clearly impossible unless space is doing something funny (which it absolutely is doing funny in general relativity). Thus, the river model of spacetime curvature is vital to understanding this viewpoint. If you're going to cover it in a future video (which I am excited for), then that's great, but in terms of good educational practices, "just trust us" is practically blasphemy.
@@narfwhals7843 yeah but that is the entire reason why this viewpoint can even sensibly work. I would've started with that, and then analyzed the implications of the equivalence principle in light of that understanding of spacetime.
Plus, I've been wanting a video on the river/flow model from this channel for a while. Really different but valid viewpoint of the way general relativity describes spacetime curvature.
You need to understand that both Newton and Einstein basically say that magic makes the apple fall towards the Earth.
The only difference, is that for Newton the explanation doesn't include a speed limit, where for Einstein it does.
And thus, we can say, "look, the Earth is exploding outwars but at the same time spacetime is imploding inwards, so the whole thing balances each other out, and any free from any other forces body will hit the Earth because it's basically caught between 2 opposing events that counter each other.
But that is still an explanation that at some level, still requires the use of "magic". The true difference from Newtons magical force of gravity, is that Einstein's magic is more sophisticated than Newton's magic, because Einstein takes into consideration the limitations of the speed of light and the hyperbolic geometry of spacetime.
And that is true for all science. Quantum Mechanics uses similar kings of magic itself too. Fields, particles etc... All made us mathematical abstract objects and models to probe deeper into the unknown truth of the Universe, that still remains unrevealed.
@@soopergoof232 I think you're missing something, which is that the flow model is a MODEL. It's a way to view the equations. There is also the B-theory of time (also known as the block universe model). These are analogies, ways we make more sense of the mathematics. And the idea that spacetime is a superfluid is not anywhere near a proven statement. It's an interesting conjecture that some physicists are working with.
@@-_Nuke_- all I will say to that is, neither Newtonian nor Einsteinian gravitation remotely qualify as "magic." Magic is something human beings control with their thinking or actions. The laws of physics, on the other hand, are blind and apathetic to our will.
BELIEVING that the same results mean the same cause is a MISTAKE
22:02 Ok ..
For those still wondering how it can be that the Earth or any celestial body isn't expanding or exploding or anything, which would be perfectly reasonable question because it hasn't been answered yet. Dialect will as I understand, but in the meantime a mathematical description about this "river model". (Waterfall model, Gullstrand-Painleve coordinates, raindrop coordinates, Kruskal Szekeres coordinates etc etc, they all have their advantages).
(GP coordinates for example gets rids of the coordinate singularity at the event horizon for example and Kruskal Szekeres coordinates gets rid od the "swapping of space and time at the event horizon" as often said in popular science. And also gives a clear picture about singularities using a Kruskal diagram.)
But mathematically you've got this equation in GR:
\frac{d^{2}r}{d \tau^{2}}=a^{r}-\Gamma {_{tt}}^{r}(u^{t})^{2}
(Im sorry I can't write math properly in a RUclips comment, but write it in a Latex editor.)
This sais that the second derivative of your position with respect to time is equal to your acceleration, or of a falling apple or whatever (going radially outwards/upwards) which is just a=F/m. In flat spacetime that would be all, as simple as that, if you're accelerating in flat spacetime your spatial coordinates would have to change. But in a gravitational field spacetime is not flat. And the term with the Christoffel symbol, just accept it please, because it would become far too much to explain. Really hope Dialect well delve into it a bit further in future videos 👍. But it's related to the curvature of spacetime and the last term is your "velocity" through time squared.
So since you're position is not changing, you're spatial coordinates don't change even though you accelerating radially outwards or "up". The first term is zero, which means the acceleration must be exactly equal to the Christoffel symbol term times the "velocity" through time squared.
So you get:
a^{r}=\Gamma {_{tt}}^{r}(u^{t})^{2}.
Thus in curved spacetime you need to accelerate just to "stand still" (for the observers "standing still" with you on Earth, but thus actually all accelerate .. it doesn't involve an inertial frame of reference, what the main problem was with the gravitational time dilation causing gravity nonsense).
That's the easiest way to explain it, but this only holds for in the weak field limit, for in the Newtonian limit really. With strong fields and extreme angular momentum lots more Christoffel symbols are involved. The equations are not this simple anymore.
.. I watched the video again and really hope Dialect will explain it all in more depth, and yeah 22:02 for now I'll trust you'll explain in a future video how the sky, the ground, the oceans .. everything really, is acceleting radially outwards without changing position. You simply need to use the equations, even though it's RUclips and it's hard for your audience. (But .. Otherwise it isn't explained at all. Well a little bit in the river model video, but not truly imo. Because saying space falls in equally is, well let's be honest, poetic speak and coordinate system dependant.)
Really curious how you'll do that, and to be completely honest I still have problems with that bit in strong fields.
So yeah. If you even explain it for strong fields and extreme angular momentum (Kerr) that would be awesome! 👍
I have been trying to make sense of GR for many years now, yet each of your videos is an eye opener to me. It must be nice to be clever, i'll never know. Thank you very much for sharing this understanding and for the great animations.
Do you have any knowledge/opinion about Laurent Nottale's Scale Relativity ? From the little i understand of it, it is very elegant. At its core it's an extension of GR to scales (=>there's no such thing as zooming/unzooming), it leads to many experimentally verified results both in micro and astro scales, and yet for some reason it has been completely ignored by the scientific community since it came out in the early 90s.
I'm not intelligent enough to decide or claim that it is right or wrong, but it is so impressive that it should at least deserve some interest, even if only for debunking.
the very same for me - i spent years trying to understand tensor calculus - that is a very intuitive way to attempt to grasp GR. This makes it so much more LUCID 🙂
BTW I had a look at your YAG videos - VERY Good - Kudos
However I was reminded by the insanity of heterogeneous dice systems of resolution -- this and other long standing issues of most RPGs simply rub me wrong -- I am creating my own RPG system that utilizes a much simpler method of ordinary playing cards (which can be digitized as in YAG) - Face Cards allow for 'now for something different' - several face cards in a row result in something TOTALLY different.
@@bernardputersznit64 Hi, thanks a lot for the kind words about Yag :-) There is unfortunately no card management system in Yag atm because i still haven't got a good idea of how to correctly make this. It's a difficult subject^^
Anyway, i'll stop talking about Yag here as it would be impolite to take the focus out of this video. Feel free to contact me outside of those comments if you want to talk about this. Cheers.
We have a little bit of knowledge of that theory -- mostly cause Sabine Hossenfender bashed rather hard on it lol -- but the desire to understand theories like that also motivated our desire to better understand GR in the first place. So we can't say much about it atm but will probably be looking into it in the future. Cool gameboard design, btw.
What an amazing channel to stumble across, the algorithm has truly blessed my day. I feel like I finally have some kind of understanding of general relativity. Keep it up and this channel will go so far! (Also, I joined the Patreon hope my tiny contribution helps :))
Clearest explanation I have seen. Thank you so much
With a title like "Gravity things doesn't fall make," I was expecting this video to be narrated by Yoda.
This was really good, thank you. I had always been bothered by the fact that most people discussing the equivalence principle almost never mentioned its locality, and it needlessly confused me for years. The "kill engine switch" idea was really cool. It's also very nice to see that the tidal forces are like a less extreme version of the "spaghettification" that occurs when falling into a black hole.
@Science Revolution
Interesting?
The tidal forces are purely geometric in a classical, Newtonian sense, whereas the idea of upward acceleration of the ground doesn't actually exist in (Newtonian) geometry and thus the theory he presents is inconsistent and flawed. Just consider that a falling object experiences acceleration (weightlessness) not just at its lower contact point (feet) but also internally (e.g. butterflies in the tummy). How does the acceleration of ground upwards cause this??? Also look at floating in water, or gravity inside the earth's core ... it is 4.3m/s² IN EVERY DIRECTION ... which implies the earth is "falling inwards" but you won't have any actual or apparent motion at all, and you can't "turn off gravity" by jumping off something (you float without being weightless).
@@tomszabo7350 …
Re: “butterflies in the tummy”…
Ever drive your car at speed, over a hump (such as a railroad crossing)?
You are driving along at a constant speed, and in a “uniform” direction (therefore, experiencing little or no acceleration)…. Until you encounter the hump. At that point, you experience an upward acceleration, followed by a very brief moment of “weightlessness”, then a “downward” movement, followed by an abrupt “halt” of “downward motion”.
The point at which you feel the “butterflies”…. Is during that brief moment of “weightlessness”, which (from one perspective) can be described as being the moment in which “your acceleration is switched off”.
If interpreted in this way…. It can be argued that “butterflies” are not caused by acceleration, but instead by the “switching off” of acceleration.
I’m not claiming to have a better understanding of all of this than you do…. Nor am I saying that I fully agree with the claims of this video…
Just pointing out how “interpretation” can influence one’s “conclusions”.
Personally…. I need a much more thorough explanation of how all points along the surface of a sphere can be accelerating “outward” simultaneously, while the sphere remains “intact”.
@Bob in the West A roller coaster or even an elevator can give you the same feeling ... never mind a fighter jet! It is a nervous system reaction in the abdominal wall to a change in acceleration. My point was that the ground "falling upward" can't explain it. Gravity is not indirect. The creator of the video does have it partially correct though. In the time domain the ground and everything else "falls" up (expands outward). This happens at the speed of light. If there is no mass present, then the time domain expands smoothly and space-time is "flat". The presence of mass creates "kinks" in the time domain which causes space-time to curve. It is tricky to visualize time like this ... perhaps try imagining the universe as a diorama that you can somehow observe from outside. Now zoom in on Earth ... you are still outside the universe diorama but all of a sudden everything is much bigger. Now zoom back out to billion light year scale ... everything now appears relatively smaller. That is essentially time (though it only seems to zoom in). But to everybody inside the universe diorama there is no change (expansion) in scale since in 3 dimensions all observed objects are relative. We only detect the "passage of time". Yet the expansion itself is very real including the generation of actual quanta of space (that we can't detect in 3 dimensions). The mechanics of how this time domain expansion actually happens remains to be solved though string theory and the holographic principle are probably on the right path.
One rebuttal: the accelerator pedal (or any theoretically perfect apparatus) cannot instantaneously make the gravity vanish.
Kinda like how when you release the top of a long hanging spring, the bottom stays stationary until the top of the spring reaches the bottom at the speed of sound. Letting go of the force moving the car will not mean that the ball pendulum stops accelerating faster than the speed of light, in fact it doesn't even happen faster than the speed of sound. (Speed of sound travelling through a car metal frame)
So rather than giving allowing the pendulum to seem like an example, it should be made explicitly clear that only gravity vanishing far away would be a problem. (For example, say the car travelled 1km from a starting point, then stopped accelerating at an ending point. Looking from the ending point, the gravity at the starting point vanish at a response speed that's faster than the speed of light.)
@15:10. This is the most intuitive explanation of Einsteins equivalence principle I've ever seen. Brilliant work as usual
Great video! Look forward to your next one with the "answers"
I am impressed (and grateful) for your highly instructive and easy-to-follow videos offering a novel perspective to help make general relativity more intuitive to everyone. I also appreciate your overall attitude of calling out misinformation and inconsistencies in other youtube videos without making it personal or vindictive. It's refreshing to learn a new formulation while keeping the ego and blood pressure low and calm.
The apparent "absolute" nature of acceleration in Relativity, which dispenses with previously absolute conceptions of motion, distance (space) and time, does seem odd and you're right to draw attention to it. And as you point out, even Einstein himself felt quite uncomfortable with this anomaly.
It's interesting to consider your reformulation - that Earth is accelerating up in all directions to meet the apple falling from the tree rather than the other way around. Your new perspective aligns with the feeling we share in our bodies all the time here on the surface of our planet - equivalent to how we would feel if inside a jet moving with constant acceleration.
One question I have is how does the discovery of gravitational waves impact your perspective on gravity?
As an aside, I am curious to hear if you can share whether any of the other physics RUclipsrs have reached out to you or made any acknowledgement that you are correct and they got it wrong, or whether they doubled down and still think their earlier videos got it right. Would be interesting to know their reaction either way..
I look forward to future videos from you.
Thank you for watching, and we appreciate your support! Our original inspiration for making videos on RUclips was due to the inaccuracies we kept coming across in other videos, so addressing misinformation will always be a integral part of our channel (though we are often criticized for our lack of "bedside manner", and we have been trying to go about it more professionally lately.) But we've yet to receive any acknowledgment or clarification from other RUclipsrs about such topics. While it is quite human to err, and we have quite a few mistakes of our own in our older videos, it is a little disappointing that none of these larger channels are willing to address these large-scale misconceptions they have presented their viewers with.
Our current understanding is that gravity waves can be viewed as the propagation of changes in local tidal forces. So, while gravitational fields still remain the fictitious consequence of accelerating, the amount you need to accelerate in order to remain stationary with respect to nearby bodies could momentarily change, should a big enough gravity wave roll through your neighborhood.
this video is really really great! but could you put some sources/references in the description ?
He can't because this is classic pseudoscience. He picked one statement and completely misinterpreted it, made it sound sciencey, and claimed he was an expert.
@@souvikchakraborty2019 that is why i asked for them :D
RUclips is overrun by AI-voiced pseudoscience videos these days. What even motivates creating something like this?
Sounds like a good defense for a car accident
"I wasn't accelerating, my frame of reference was"
This channel is underrated af, waiting for the next one,
If the equivalence principle holds for the observers within their frame of reference R, does this mean that in theory they can experience a constant acceleration of e.g. 9.81 m/s^2 indefinitely, because time will slow down within R, while from the outside it looks as if R asymptotically approaches light speed?
May i ask if you have a degree or any sort of certificates on physics?
In watching their other videos I am quite certain the content creators have no formal training in physics and if you asked them to solve a random end-of-chapter question out of Wald or Schutz even, they wouldn't have any idea whatsoever on how to solve it, but that said, this video is quite good and fairly consistent with relativity.
Are you asking the person behind the video or the AI voice narrating it?
5:20 Tiny mistake here. Astronauts orbiting earth are NOT in zero-gravity. The gravity from Earth is actually about the same where the ISS orbits as it is at sea level (0.89x to be precise). They are floating because they are in *free fall,* because they are orbiting. Which, appropriately for your video, is indistinguishable for the observer within that frame.
"Zero-gravity" was actually coined to describe astronauts in orbit, so it's conflation with free-fall has existed since its origin. However, since there is no difference between free-fall and zero-gravity, both terms are appropriate in the situation.
@@dialectphilosophy No, they're not appropriate.
"Zero Gravity - Noun
the state or condition in which there is no apparent force of gravity acting on a body..."
Zero gravity doesn't mean there is no gravity, just that it is not apparent. His usage of the term was correct.
This Chanel is a paradise for physicists and who are interested in physics. You're doing great. I don't know how to thank you.
Your best one yet! Miss ya.
Man this is _really _*_really_* one of those moments in which I wish I had happily and accidentally stumbled upon a mostly completed RUclips series...
I actually didn't even have as many questions as were shown in the end, and I _still_ feel like I've been left on a cliff-hanger.
I'll agree that the explanatory power of this video and it's production quality are *_well_* above its weight class in subs and views, but then again, I doubt many don't...
Thank you for the kind words, glad you found us!
You blew my mind! However, there is always going to be the argument that the objects falling towards the ground do not lose (pull the plug on) the gravitational field, it only appears so because the measuring methods and tools are also accelerating with it and the complete system within the frame of reference seems to do so, at the end all of the objects are relative to each other in the same frame of reference.
Exactly. The analogy does fail with another respect: The objects with the monkey DO feel downward force due to acceleration because that frame is NOT moving at a constant velocity. Implying that it does, is incorrect from both a relativity standpoint and a Newtonian one. The "force" is not actually "turned off". There is a massive difference between constant velocity and constant acceleration - pun intended.
Hahaha. This was so good. Keep at it , D. 1, pretty solid proof by contradiction vs. certain other "explanations" of the twin paradox, I think, on first view anyway; 2, I'd not yet heard of the River model and I'm enjoying what I see, so thanks for that as well.
Thank you for watching! ScienceClic does a great job of tackling the River Model in his videos on visualizing General Relativity, so we can recommend you start there, though we'll be taking a deeper look into it at some point in the future.
@@dialectphilosophy from what I heard the river model is an interpretation for one solution of a black hole, which you seem to extrapolate on all the universe. Is this correct?
@@Robinson8491 The river model was originally conceived in 1921 for static spacetime and was extended to stationary spacetimes (.e.g. Kerr black holes) in 2004 by Hamilton, though I don't think it can be (or at least it hasn't been) extended to time-dependent gravitational fields (FLRW, gravitational waves, etc).
Conclusion: Energy needs to eat space in order to sustain itself
I am not a cosmologist, but I logically can't understand that if the earth's surface is accelerating at 32 feet per second squared, then why isn't the earth expanding. I mean if the earth is coming up to push me and there is someone in China being pushed in the opposite direction, the earth, being a sphere, would have to expand, wouldn't it?
Hey, thanks for watching! We recommend checking out the follow-up video to this one, "The River Model of General Relativity" for answers to your questions!
@@dialectphilosophy So, you don't know the answer? Now I know where not to go to get an answer. Thanks for trying, anyway.
The earth is actually pushing against space simply because it is a solid mass... gravity is greater at the surface of the because it is the surface of the earth that is doing the pushing....further away from the surface gravity weakens....where there is mass there is gravity
"GRAVITIY MAKE FALL - DOESN'T THINGS"
Hi, great video, very informative, I'm much closer to understanding, thank you. If 2 people jump from space at the same time, one in the northern hemisphere and one at the exact opposite, would the earth hit both people at the same time; if so, is this due to the size of the earth with the affect of curved space time, and are the jumpers stationary in space time or in motion?
Two people "falling" at antipodal ends of the earth would both see the earth accelerate towards them at the same rate, meaning they would get hit in the same amount of elapsed time.
The jumpers are stationary with respect to space. But (and this is jumping ahead somewhat) we can say that space is "moving" relative to the center of the earth, i.e. the source of curvature. As space gets "sucked into" the center of the earth, the two antipodal falling observers, though at rest in their own frames, will move closer together.
@@dialectphilosophy wow, that's mind bending stuff; facts are really stranger than fiction.Thanks again, and look forward to watching your other videos.
@@dialectphilosophy Why are you guys saying that "space" is sucked in, instead of "spacetime" is sucked in?
Isn't General Relativity about both space and time? So spacetime as a whole? Why is only space sucked in and not time?
@@-_Nuke_- it’s because spacetime is conceived as a singular static entity - it doesn’t exist in space or time as it subsumes both. (The “block” reality.) The effect of spacetime curvature on space is to make it seem like space is moving relative to a mass.
@@-_Nuke_- There isn't anything being "sucked" inward. In the river model we construct a foliation of space-like hypersurfaces which propagated inward by a shift vector. This shift vector is the "flow" of the spatial coordinates that is called the "river".
Great info--keep it coming!
If it's the earth that's moving upwards instead of the apple falling down, then how do you explain when something falls to the earth, *its distance to the moon increases*
Because the Earth's surface doesn't have a kinematic acceleration as we normally experience it, that is upward toward the moon. The Earth has an acceleration as General Relativity defines the term, but not as introductory kinematics defines the term. What really is happening, is that spacetime collapses inward on massive objects that are the source of gravitational fields. The normal force is accelerating you upward, so that you are "running to stay still" in this collapsing field of spacetime that we normally consider to be a gravitational field.
@@carultch if spacetime collapses inward, and normal force accelerates outward, you are adding two accelerating forces: so which one is it: the earth moving outwards or the space flowing inwards? You can't have both, and you are mixing them up in your answer! Double acceleration!
@@Robinson8491 The answer is that they add up to zero, when looking at it from our point of view and the Newtonian explanation. Or more specifically, very close to zero, after you account for all the kinematic acceleration associated with the planet's motion.
That's why I say "running to stay still". Spacetime is collapsing inward on itself, when in a gravitational field. Constraint forces accelerate you outward, relative to the collapsing spacetime. The net result is that you aren't falling toward the center, or expanding outward, but that Earth maintains a constant size and keeps you on its surface from the equilibrium of structural forces and the gravitational field. When you stop "accelerating upward" from the normal force, you are forced to follow the collapsing spacetime. It feels as if there are zero forces acting on you, from your point of view, because unless you are sensitive enough to feel tidal forces, you cannot feel gravity.
it appears to me this is all just convention and if you switch signs and say the mass is accelerating "inwards" and spacetime "outwards" everything stays the same just by the arbitrary definition of those words.
Its like those engineere who insist the earth on which they found their building is pushing with a negative sign against their buidling. It just doesnt matter it you dont mix it up.
@@carultch This man gets a gold star. The surface doesn't fall up. Actually we don't really fall down either, but rather we fall in.
I actually checked the date of upload.
And was surprised it wasn't April the first!
amazing video , the switch of falling part was epic
I just found your channel, when I first watched a video from you I thought this was a multi-million sub channel. Your production quality is absurd and your content is top notch! Your videos deserve much more attention.
Thank you for the kind words and for your support!
@@dialectphilosophy If the ground is accelerating upwards, wouldn't that imply that the earth is constantly getting bigger in size and as such we should be able to measure it?
@@zverh Check out the River Model video for those answers!
@@dialectphilosophy Yes, I watched it. Thanks a lot, it really clarified a lot of things.
None of the examples that you give where the gravitational field is "instantly" turned off are correct.
You cannot instantly remove your foot from the car's accelerator and even if you could the car's engine does not instantly turn off. The same applies for the rocket's kill switch. You also cannot instantly step off a building unless you travel at the speed of light. In each case the gravitational field will gradually (not instantly)diminish (if you choose to view it that way) .
I think the point stands. It doesn't have to be "instantly." The point is that it's FTL and if it's FTL then that should throw up red flags and alarm bells.
You can step off the pedal at a velocity of a m/s. At some distant part of space, gravity will turn off for you faster than light.
So the a velocity isn't important here.
@@bradbadley1 it's never FTL, he is flat out wrong.
@@-_Nuke_- no, there is no point in the universe where gravity will deactivate FTL. There is a spacetime contraction/decontraction that flows through the atoms in your body as you accelerate or decelerate. His explanation is bad and Eugene Koryanki had it right the first time.
@@bradbadley1 My point is that it cannot be FTL. How can your foot move of the accelerator FTL?
Good video. I was just thinking about how gravity works recently. This "charge" that gravity exerts would be a mirror of mass equivalence when a force F is applied to an object O for time T. Mass M defined by a volume V would have an energy equivalence that causes its center of gravity to accelerate towards the sky. IMO it's more akin to mass folding space inwards based on this energy equivalence, so we get the same time dilation effects that would occur with velocity. I think this "folding space inwards" would be how matter stays matter through time. Escape velocity would be to essentially escape from one guy folding in space, only be attracted by another guy folding in space. Since the edge of our observable expands at c(and where time stops) it's akin to an event horizon and will be the ultimate attractor for those that leave their home bodies, which would also explain why galaxies stretch further and further apart.
excellent presentation. thank you
Masterful work, thank you!
daily dose of relativity contradictions ☕😮💨.
Sounds so crazy theoretical....you give no good answering to the sky falling up, just that it is a theoretical trick.....still confused
I love your Work. Keep Going on enlighten the world!
This channel is stellar. 10/10!
Great video. I had this idea from various readings. But never found good youtube video like this one on this topic. I am still grappling to visualize how a body can "continuously" suck the space in. Once it sucks something, how is the space at that point get replenished. Since it is not sucking space beyond a region, how can it keeping sucking more space.... Dear @dialectphilosophy can you please explain my confusion here.
Definitely another great video, as usual.
I have a theory of the genesis of flat earthers. When we combine what's stated independently into an independent model rather than depending on a basis for our philosophical view we get the flat earth. Since one educator says the ground is moving up, but others say the planet is not getting larger and the speed of light is constant, not increasing exponentially, along with the permittivity and permeability of free space, particle masses, etc, then the earth's radius must be infinite and thus its surface is flat.
When an apple falls to the Earth, the apple *is* accelerating down, while at the same time, the Earth *is* accelerating up (the sky is falling up at the same time the apple is falling down). The center of “pull” (acceleration) between those two objects is well within the Earth, so from our standpoint above the surface of the Earth, it is hard to see the Earth moving(accelerating) at all because: we can't see the central reference point the Earth and apple are accelerating to, and the Earth is moving much slower than the apple.
Better to visualize two objects of the exact same size, density, etc. “falling” toward each other (one on 'top' the other on 'bottom'). Imagine two large balls of some pliable substance (perhaps blobs of some fluid) in space. They start moving (falling/accelerating) towards each other, toward the center of the common acceleration/gravitational point. As the spheres move toward each other (neglecting tidal forces), when the surface points closest to each other meet, you can now see the center point of the acceleration. The surrounding soft material on each side will still be accelerating toward that center. As the material of each sphere starts to interact (electromagnetic push and pull, strain between the atoms of the two spheres) they experience (feel) the acceleration(deceleration) of the motion they already had. That center point continues to cause acceleration of the rest of the material until the forces balance out and a new single sphere is created.
The point is, both the Earth *and* the apple are accelerating (experiencing free-fall, Up-Earth, Down-Apple) toward the common center of mass. Lines of gravitational force should be diagrammed through the Earth and any satellite (like the moon or even an apple) with an exaggeration to shown the central point of gravity. Diagram a 2 body system like the Earth and Moon to more easily see the central gravitation point the both bodies accelerate to ~(1700 kM / 6371 kM = about a quarter the distance from the surface down to the center of the Earth in an Earth/Moon diagram).
this is a great explanation/ correction of the concept depicted quite inaccurate in the video.
Haven't even seen the vid and I know it's gonna be brilliant. Thanks.
Narrator: but it wasn't brilliant
@Dialect 19:48 I understand the traditional "gravitational time dilation" referred to by many people is actually coordinate dependent (i.e. a free-falling observer/an observer at infinity wouldn't see clocks running slower closer to the massive body while a "stationary" observer in the gravitational field would) but this makes me wonder.... Does curvature/tidal forces produce any time dilation effects that all observers will agree on since it cannot be transformed away? If so, is there a known mathematical formula for such a relationship? (say in the case of the schwarzchild metric for example)
Gravitational red shifting is something that all observers can measure the same from any reference frame. It only depends on spacetime curvature. (This is different from kinematic red shifting, for example, which does depend on the choice of reference frame.)
I think it makes more sense to say "The Earth is Falling Up" ... and based on your other explanation (that uses river-model analogy), it makes sense to say "The Sky is Falling Down".
I love this little monkey.
Please bring him back in future videos.
By Faith, and Faith alone, embrace, Believing where we cannot prove.
There it is, the video I was waiting for; I liked ur switch explanation, nice
His switch explanation is not valid though. He claims instantaneous deactivation of the gravitational field which is impossible. The atoms and observers in the car do not decelerate instantaneously, they each experience a slight time delay depending on their distance from the engine of the car. His claim of debunking Eugene Koryanski is flat out wrong.
@@salvatronprime9882 interesting point; what claim about eugene? u mean the twins paradox explanation?
@@salvatronprime9882 Hey there, thanks for watching. You've made a simple a confusion. The change in acceleration (the "jerk") is of course not instantaneous, but the field mimics this change everywhere instantaneously, which is not possible under special relativity.
Eugene Khurtoryanski's understanding of GR is unfortunately extremely cursory and flawed, and you're bound to end up with many a misconception if you watch him. We'd recommend ScienceClic instead.
@@salvatronprime9882 also, isn't the instantaneity the key point? "the vanishing of the gravitational field thus cannot be attributable to any real counteractive force meaning the observer in the car must conclude the field was fictitous"
If its the ground hurling up then if a person steps off a hovering helicopter and is attached to rope which is attached to the top of a spring within the copter , will the spring compress or not?
I like these videos and the concepts they contain but I have what I think is a simple question. When I jumped out of an aeroplane on a parachute course, my nervous system definitely felt an initial acceleration, which suggests to me that it was me accelerating towards the ground, not the ground accelerating up. How do we explain this? Was it imagined? A similar example that maybe more people have experienced is the abrupt sensation of dropping that you can experience in a aeroplane when it suddenly loses height because of turbulence.
I have been thinking about this and will have a go at answering my own question. I guess the feeling I am describing, which I am sure many people have experienced, could be a result of the sudden removal of the upwards acceleration (in these examples the upwards acceleration is provided by the aeroplane’s lift) that our insides are used to feeling and when that happens our senses naturally interpret the sensation as ‘I am falling’ but we should not interpret it as ‘I am now accelerating downwards’.
Your own solution is probably the correct one, as the "drop in your gut" is certainly tied the sensation of your gut no longer being compressed due to acceleration.
Most likely the removal/reduction in acceleration. If you ever fly out of John Wayne airport in Orange County, because of the $$$ that lives in the flight path, they take off really really steep at full power, then when it leaves the airport and is over the residential area, they lower the power and angle a little, the sudden reduction of thrust gives that same feeling as a free fall. We are still gaining speed but not as fast.
UNBELIEVABLE, THIS IS THE BEST DAMN VIDEO I HAVE SEEN IN A LONG TIME , AWESOME WORK.... GOOD FOR YOU 👏👏👏👏
Hey Dilect, where can one find more information on Gravitational Tidal Forces?
There are some PBS Spacetime educational videos based on Newtonian physics and classical tidal accelerations. I'm not sure of your physics background, but there are also advanced-level relativistic descriptions connecting tidal forces to spacetime curvature.
omg I love this channel so much you are a genius. As a small hint to help spread your message, at 19:51 if you want to show directed forces, maybe you can find a better visualization than a bunch of equilateral triangles! which way are they pointing?! 😀❤ ignoring the exact implementation, the picture is beautiful and I thank you for sharing this.
The less gravity the lower you fall, opposites attract, the more gravity the higher you climb, the more you accomplish in a positive way