How does time curvature (not space) create an illusion of gravity?

[@Mahesh_Shenoy]

To try everything Brilliant has to offer-free-for a full 30 days, visit brilliant.org/FloatHeadPhysics . You’ll also get 20% off an annual premium subscription.

[@ngneerin]

I'm going to take this using your link

[@classicalmechanic8914]

Time curvature does not exist according to Einstein. Einstein's theories describe only spacetime curvature.

[@KingLutherQ]

I subscribed today. Your videos are amazing.

[@thetormentor07]

This video is 5 hours ago , but your comment is 13 hours ago. Is this Time dilation on KZbin ?

[@ngneerin]

@@thetormentor07 oooh. What an observation. It's either a KZbin bug or their comment server is near a black hole

[@RussellSubedi]

That Ryan George reference was TIGHT !!

[@summitxjz9029]

Wow...wow...wow...wow

[@jasonbeardsley7059]

You need to get all the way off of his back about that!

[@chrismagoon6088]

Okay then

[@RussellSubedi]

@@jasonbeardsley7059oh okay let me get off of that thing.

[@dogcarman]

Nah, it was easy for him, barely an inconvenience.

[@ZenMogwai]

I watch a lot of this type of stuff, and I have to say that for a smaller channel (comparatively) this is one of the best explanations I've ever heard!

[@steele.in.motion]

@Mahesh_Shenoy I don't have any higher education in physics or mathematics, but I do work in the 3D CGI field, so spatial reference frames and acceleration are comfortable subjects. Because of this, I've been devouring physics for about fifteen years. I must say in all that time, I have never come across a lecturer who can so easily and accurately translate these complex ideas in such an effective way! Please keep this up!

[@timoex]

Brilliant. You've been helping so much more than many others who have tried to explain these things.

[@vyvianalcott1681]

So really no matter what we do, we are always falling through time. The ground slows down how fast we fall like a parachute, the bigger your parachute (planet) the slower you fall through time. This helps make the dimensional aspect of time more intuitive, the way space and time interact makes a lot more sense to me now. You are incredible, thank you.

[@michaelzoran]

Your description of a parachute explains "Time Dilation," but it still does not clarify "Gravity." Perhaps I will need to watch this video again. The way I understand this video, it is as if the Earth wants to explode outward - sort of like what would happen to a person in outer space if there were no air pressure. But that is still not a cause for "Gravity."

[@vyvianalcott1681]

@@michaelzoranI'm not paraphrasing the video this is my own thought derived from the video. If you didn't understand my comment you need to watch the video again.

[@jasonbrown7330]

You have it wrong it’s the opposite of what you say when you go fast in an airplane, the clock slows down or in a spacecraft the clock slows down time slows down. I really appreciate your humbleness when you say Einstein Siri is more powerful instead of trying to say it’s the correct one because it may not be the correct one yet we have to find out still and you recognize that and that is beautiful excellent video. Keep doing these my man people need to be educated and not miss lead and that I think you do and you do it pretty well better than I could. I’m sure have a great day.

[@mr.roblocraftsk9897]

2:28 how do you know that landing area is tilted? what if they are the same length and shape, I mean what if end of it (on image) is rotated same as start...

[@Mahesh_Shenoy]

That's a great question. Light, as a wave, should always have it's wavefronts perpendicular the direction of motion!

[@jonKowalski3210]

This has got be like the sixth time you've opened a third eye I didn't even know I have. These videos are so good for developing an intuition for physics concepts beyond the typical analogies given to a lay public.

[@flyhighcreative]

I really appreciate your energy and excitement, man. Always great vibes.

[@akirasthecat]

Brilliant teacher. Nothing left to say.

[@alb1reo]

Can you explain the difference between time and space curvature and what effects what?

[@jmanj3917]

11:01 ...I shouldn't have crumpled it... 🤣🤣🤣

[@michaelcole506]

In order for curvature of time to do this, does this also confirm that EVERYTHING at its most fundamental level is constantly moving? I mean, in order for a car to become non inertial within a turn, the car must be moving; following a path; changing velocity; a curve. Are particles within matter affected this way inside a curved spacetime? Either way I feel like something has to be moving, literally.

[@Chiragdhoble]

Bro never fails to blow my mind...

[@charlesvanneste2834]

A pendulum clock here on earth ticks at a particular rate. If placed on the moon it would tick significantly slower. Has timed changed between the two places, or is it the measurement device you are using to keep time is altered to give you a perception that the time is different? I think the measurement method is ultimately flawed, this goes for atomic clocks as well.

[@todradmaker4297]

Bingo! You're on to the dirty little secret that physicists don't want to talk about. If you put an atomic clock in a freezer it would slow down. Would that mean that temperature could affect time?

[@todradmaker4297]

.... or if time is based on the speed of light, does time slow down under water?

[@Leif-yv5ql]

Time and space are arbitrary coordinates in curved spacetime.

[@kxqe]

I think if our ordinary experience was to move around at relativistic speeds, we would not see time and space as separate entities and would would just experience spacetime as one thing.

[@brettvanwey9419]

Ahhh so the reason I’m balding, yet my toes just keep getting hairier, is because my head is older than my feet.

[@RitikKumar-ud3gc]

😂😂

[@cucumber-juice]

Look on the bright side: these things might be a sign of high testosterone

[@vikrantsinghsolanki4506]

actually, you are correct.. lol

[@NinjaGhost.bgmi9800]

😂😂😂😂

[@keemo63301]

Best description ever. Feynman would be very proud of you taking on his legacy of translating comlicated theories to us simple minded folks. Keep it up.

[@ripjawsquad]

complicated*

[@se7964]

Time doesn’t curve - spacetime does. This is a terrible video and the explanation it gives has already long been debunked by Sabine Hossenfelder

[@antoniojpan]

@@se7964Can you put the link to that video of Sabine? Thanks

[@jddang3738]

@@se7964 it’s actually correct and you’re wrong. Spacetime curves, yes. But they are two components, space and time curve at the same rate. In 1 second, you have barely traveled much through space. But you have traveled 300,000 km through time. The curvature of time actually approximates Newtons gravity. That’s why Newton’s formulas work for almost everything except really strong gravity fields and/or high speeds. It’s called the Newtonian approximation of low velocity weak fields. The curvature of space has almost no effect on anything we encounter in our lives. But the effects of the curvature of time is immense. Every object has a 4-velocity, 3 of space, 1 of time, and it must always have a magnitude of c. When an object encounters a time gradient (like that caused by gravity), the part of the object that encounters slower time darts towards the slower time. Why? It has to maintain that 4-velocity. Since time is slower on one side, the objects velocity must speed up to compensate. And that’s how things “fall.”

[@sameerkpatil123]

@jddang3738 thanks. Your comment gave me even better insight.

[@DxvidEisboerg]

I think that the 7 dislikes are Newton with 7 alt accounts

[@Luke-pk9fe]

How do you see the dislikes?

[@Existidor.Serial137]

yeah wtf?? Maybe he is in a different universe@@Luke-pk9fe

[@chetacheese2789]

@@Luke-pk9feon a computer, you can download an extension to see dislikes

[@Lowraith]

That math ain't mathin'

[@paromita_ghosh]

🤡 Newton would be in awe not dislike

[@el3ktrik296]

Class ❌ KZbin✅

[@aliensarerealttsa6198]

This is disinformation or the uploader has around 50 IQ.

[@CatFish107]

Heck, at this point, I'm as old / older than most of the teachers. I can learn and keep fresh without asking to take high school physics again!

[@elestudiodebuenavista628]

This wasn't taught in my school. Even one time I told my teacher that gravity is not a force, but at that time I couldn't explain myself. Now I can explain why gravity is not a force but that teacher isn't here 😢

[@lyrimetacurl0]

As long as it confirms to the following then it's okay: kzbin.info/www/bejne/hpu3aWh3rbmgf5Isi=Bwhqcu0YPisAQyz4

[@zohntyzexsongaming1016]

Yes

[@scienceisdope]

I dunno how you do it, Mahesh, but with every video, relativity becomes clearer for me. I can also see why Einstein called it the special theory. And this, the general theory.

[@Mahesh_Shenoy]

Glad to hear that, Pranav :)

[@TheEshanDas]

​@@Mahesh_Shenoy glad pranav also watches this channel 😊

[@Rudyard_Stripling]

Time dilation explained before Einstein was even born, revelation from God. Pearl of Great Price Abraham 3 Pearl of Great Price First Edition (1851) This account was drafted in 1838 and first published in 1842 in the Times and Seasons, the Church’s newspaper in Nauvoo, Illinois. It was part of a longer history dictated by Joseph. In 1851 Franklin D. Richards of the Quorum of the Twelve Apostles compiled this account with other writings, translations, and revelations into a pamphlet titled the Pearl of Great Price. The volume was later canonized by unanimous vote at the October 1880 general conference. 4 And the Lord said unto me, by the Urim and Thummim, that Kolob was after the manner of the Lord, according to its times and seasons in the revolutions thereof; that one revolution was a day unto the Lord, after his manner of reckoning, it being one thousand years according to the time appointed unto that whereon thou standest. This is the reckoning of the Lord’s time, according to the reckoning of Kolob. 5 And the Lord said unto me: The planet which is the lesser light, lesser than that which is to rule the day, even the night, is above or greater than that upon which thou standest in point of reckoning, for it moveth in order more slow; this is in order because it standeth above the earth upon which thou standest, therefore the reckoning of its time is not so many as to its number of days, and of months, and of years. 6 And the Lord said unto me: Now, Abraham, these two facts exist, behold thine eyes see it; it is given unto thee to know the times of reckoning, and the set time, yea, the set time of the earth upon which thou standest, and the set time of the greater light which is set to rule the day, and the set time of the lesser light which is set to rule the night. 7 Now the set time of the lesser light is a longer time as to its reckoning than the reckoning of the time of the earth upon which thou standest. 8 And where these two facts exist, there shall be another fact above them, that is, there shall be another planet whose reckoning of time shall be longer still; 9 And thus there shall be the reckoning of the time of one planet above another, until thou come nigh unto Kolob, which Kolob is after the reckoning of the Lord’s time; which Kolob is set nigh unto the throne of God, to govern all those planets which belong to the same order as that upon which thou standest. 10 And it is given unto thee to know the set time of all the stars that are set to give light, until thou come near unto the throne of God. 11 Thus I, Abraham, talked with the Lord, face to face, as one man talketh with another; and he told me of the works which his hands had made; 12 And he said unto me: My son, my son (and his hand was stretched out), behold I will show you all these. And he put his hand upon mine eyes, and I saw those things which his hands had made, which were many; and they multiplied before mine eyes, and I could not see the end thereof. 13 And he said unto me: This is Shinehah, which is the sun. And he said unto me: Kokob, which is star. And he said unto me: Olea, which is the moon. And he said unto me: Kokaubeam, which signifies stars, or all the great lights, which were in the firmament of heaven. 14 And it was in the night time when the Lord spake these words unto me: I will multiply thee, and thy seed after thee, like unto these; and if thou canst count the number of sands, so shall be the number of thy seeds. 15 And the Lord said unto me: Abraham, I show these things unto thee before ye go into Egypt, that ye may declare all these words. 16 If two things exist, and there be one above the other, there shall be greater things above them; therefore Kolob is the greatest of all the Kokaubeam that thou hast seen, because it is nearest unto me. 17 Now, if there be two things, one above the other, and the moon be above the earth, then it may be that a planet or a star may exist above it; and there is nothing that the Lord thy God shall take in his heart to do but what he will do it. @@Mahesh_Shenoy

[@shinzonohara3114]

Hey Mahesh I'm your long time follower but please don't reply to such hate mongers comments . This @scienceisdope man is disgusting and always spreads anti Hindu hate on his channel ​@@Mahesh_Shenoy

[@shinzonohara3114]

​@@Mahesh_Shenoyyou got a long journey ahead in KZbin so it's my suggestion to not reply to such people's comment

[@Christian-y8o1i]

I don’t usually leave comments, but I have been loving your channel for science videos. No joke, I gasped and paused the video at 17:30 and had to take it all in. I know it’s science and physics and all that, but things like this truly feel magical.

[@TheAlison1456]

because they are magical just because we understand something, and despite what is usual for people to say, it doesn't mean it's no longer magical.

[@syiridium703]

​@@TheAlison1456I agree. The more I understand the physics, the more everyday things feel like real magic.

[@bredmond812]

I also felt something at that time. I saw your comment at the beginning of the video and I felt the whole video that I am not seeing the point, but now I see how the ground is accelerating up. I'm going to need a while to process that.

[@dananorth895]

Energy appears in many forms and always moves. All interactions come down to processes or conversion of forms/manifestations of energy. I think the primary dificulty in concieving of whats going on here is misappropriation of terms. Something is occuring on the forensic/ fundamental level involving transformation of energy from one form to another which as an equivalency appears as ground accelerating upwards or an object accelerating downwards but both miss the actual process occuring.

[@billant2]

Even magicians use physics to fool you at their shows you're paying for. lol

[@nukulator]

This channel deserves so much more recognition than it gets. Your videos are amazing!

[@danielz000]

It was the only channel that described the twin paradox without contradicting itself, and I watched a lot of other 'explanations'

[@autodoctordr]

This is also why I prefer a different illustration of general relativity, showing space and time curvature as a distorted 3 dimensional grid, where not only are the grid lines distorted around the massive object, but the grid lines move inwards over time

[@xcoder1122]

I know the illustration you are referring to but I don't like it because what should "the grid line move inwards over time" mean? What is moving there? There is nothing moving inwards. This illustration gives the false impression, that massive objects "suck in space" and thus constantly need to expand to stay the same size and not get sucked into itself. Yet none of that is happening. Bending space time is not a repeating process. The earth is not bending space time over and over again throughout time, it just bends it once and this bend is then stationary. There is nothing moving once space time has been bent. The movement that makes all the effects happen is a movement through time, a movement through a 4th dimension but the illustration you are referring to cannot show that as you cannot illustrate 4 dimension using a 2D graphics. Already illustrating 3 dimensions on a 2D screen has limitations.

[@VonJay]

But Einstein never wrote it as “extrinsic” curvature. He wrote it as intrinsic. So all of those 3D grids you see on KZbin are wrong.

[@das_it_mane]

What does intrinsic mean in this context?

[@VonJay]

@@das_it_mane i can list like fifteen or so things. I’ll give two The simplest answer out of all of them is that Einstein used “a” differential geometry which naturally incorporates intrinsic curvature. This in turn directly leads to testable predictions in spacetime. Extrinsic depictions often imply an observer’s vantage point from outside the spacetime being described, akin to looking at a deformed grid or fabric. In reality, we exist within spacetime, and there is no external viewpoint from which to observe its curvature as an object within a higher-dimensional space.

[@vyvianalcott1681]

This is the misconception I had before these videos, go back and watch last weeks then watch this one again. These two videos are the best explanation of the relationship between space and time you will find anywhere. Time is a spatial dimension, it just acts differently for reasons he explained last week.

[@tripat_singh828]

I am in class 6 ( 7th soon exams are over ) and i absolutely love your channel and videos. You are the reason I love physics more than anything else. You also motivated me to learn higher level maths in order to understand physics and... it's beautiful BUT NOT MORE THAN YOUR EXPLANATIONS!! Thank you for everything Mahesh sir.

[@mrgyani]

Kid if you are watching this in class 6-7, how far will you go in life when you turn older?

[@neelabhjodutta2759]

Well we have been watching these cuz they are fun and feel magical !because it's fun! {I am in class 6 (soon to be 7)}

[@tripat_singh828]

@mrgyani I don't know I just want to support my family. Getting a job will help probably.

[@tripat_singh828]

@neelabhjodutta2759 Nothing better than getting some extra knowledge while having fun.

[@laughingbeast4481]

​@@mrgyaniWho knows ? There's plenty of kids like that whose life is failure. It can be actually hard for them to succeed.

[@francoisnadal5391]

I'm teaching my 10 years daughter about space time.. And she gets it, naturally, intuitively, she is even one step beyond of my explanations, every litle time. And what you are doing here is absolutely amazing, you're helping people being better in their everyday life because they understand where they live, how things work. Thank you 1000 times 🙏 you're brilliant 😉 (yes we are a subscriber) and you must be as many smart people are, a kid with big dreams.

[@fullyawakened]

except this is wrong, so don't praise it too highly. please reference actual scientific journals not youtube videos for educational purposes.

[@HR-yd5ib]

@fullyawakened Any video that gets it right?

[@adorp]

​@@HR-yd5ib​ None. Gravity is still a mystery. Even if gravity is an emergent property (not "illusion") created by time curvature, and not space; curvature itself is defined as a property of space, and space should be quantized (the solution to Zeno's paradox requires it). But none of it has been proven. We can't measure the geometry of space at Planck length, while the radius of a graviton is its Schwarzschild radius, which means we will never be able to detect it, at least not directly. The only "right way" to learn this is to study the actual maths behind it, and that only reveals how much we do not know.

[@lande7510]

@@fullyawakened and you may as well return to the cave you came from

[@singh2702]

@@adorp Math breaks down at the Planck length though , Quantum theory and General Relativity cannot coexist , just like Zeno's paradox having no definite answer except a concept of infinitely small. The mechanics of gravity is not a mystery , as we can calculate the orbit of Mercury or have an accurate GPS system etc via GR. The other 3 forces are due to opposite charges , however the APPARENT ATTRACTION between masses is not an attraction at all , there are no negative masses and positive masses. Mass and energy are equivalent. This man in this video is attempting to explain gravity by geodesics, and attributing acceleration to this phenomenon. Gravity is a real force, by that I mean a force field acting on all particles just like an electromagnetic force field acts on charged particles. The field is continuous yet the particles are discrete, electromagnetism has been solved by Maxwell's equations but because matter has no opposite matter no one can explain the true physics between the apparent attraction between masses.

[@paultaylor3213]

Loved the nod to Pitch Meeting. 👍

[@pvanukoff]

References to other youtube channels is TIGHT!

[@skhotzim_bacon]

*This Video Contains Various Misconceptions* In response to the video titled "How Time Curvature (Not Space) Creates an Illusion of Gravity," it's crucial to address the misconception perpetuated about the relationship between time dilation and gravity. This misconception stems from misinterpreting a coordinate transformation in general relativity. It's crucial to first distinguish between relativistic time dilation and gravitational time dilation. The former is observer-dependent and occurs due to relative motion or gravitational fields, while the latter is an inherent consequence of spacetime curvature caused by mass and energy. Contrary to the video's claim, gravity is not an illusion caused by time dilation. Instead, it's the curvature of spacetime by mass and energy that truly shapes gravity. This understanding aligns with the principle of causality: gravity arises from the presence of mass and energy, leading to spacetime curvature, which, in turn, manifests as gravitational effects such as gravitational time dilation which is a result of this curvature, not its cause. it's not just the proximity to the Earth's center that causes time dilation but rather the gravitational potential. This means that time runs slower in stronger gravitational fields, regardless of altitude. It's essential to correct this misconception and spread awareness about the genuine mechanisms behind gravity. By debunking myths and understanding the true nature of gravity, we can foster a more accurate understanding of the universe.

[@zusammeneinganzes8751]

Thank you, the video seemed way off, he just proves his point with excitement, not by the explanation actually making Sense. Why should the ground move? But not the apple? What's causing time dilation when it's just an illusion? Thanks for your explanation

[@issaczheng5067]

ChatGPT ahh comment

[@skhotzim_bacon]

@@issaczheng5067 Is there a point you're trying to make? It's not like what I posted wasn't true. Yeah, I used ChatGPT, but I'm the one who noticed the misconception and wrote the prompt. Then, I had to revise it to include another misconception. Looking back on it, the only thing I would remove is the last line because "debunking" was not my original intention. Just trying to clarify a common misconception with a simplified explanation that's clear and concise, that the majority of people can understand. I'm not that good at writing. If I had done it myself, then it would be too technical, incoherent, and full of grammatical errors. That's why I used ChatGPT. Fyi, I used ChatGPT to write this too

[@rgc121044]

You are both right! The curvature of space creates gravity, but the curvature of time creates the illusion of gravity! It is an intriguing mathematical construct!

[@skhotzim_bacon]

@@rgc121044 No, gravity is not an illusion caused by the curvature of time.

[@X4Alpha4X]

im having an issue trying to understand why we would use a straight line in the curved example. since an object at rest has 0 spatial velocity, it would follow the path of time right? so why would the apple not follow the time axis around the inner curve?

[@Zagref7937]

Good point. I like his videos but i think mahesh is wrong this time. I dont know but the idea that time dilation caused gravity never sit right for me. Theres this youtuber named dialect that maybe not as fun/ not as good as mahesh in explaining things, but after watched several his video about this matter, i think he has the correct idea & more intuitive model about this: That the space around earth (or any massive object) is "flowing inward" like a waterfall as "the earth accelerating upward/outward" thingy. Thats why the earth didn't blow up & we feel this -force- illusion we called gravity

[@tintun8918]

@X4Alpha4X the apple will follow the curved path together with the earth if it is sitting on a shelf. Since the shelf, the earth and the apple will be accelerating togetber, it will seem as if they are all stationary. The apple when not on the shelf is not hindered to follow its inertial path, which is a straight line in the curved space time. Thats why it will hit the ground. Why did einstein come up with this model? It is to show that object in free fall exhibit the exact same behavior as objects in inertial motion. This fact is experimentally proven. That can only be true if it is not the object but the ground itself that is accelerating in the curved space time.

[@trisinogy]

Exactly. The video fails miserably at explaining why the apple falls. I am sorry, but it’s a downvote for me.

[@OrichalcumHammer]

The apple doesn't fall, the earth is accelerates upwards to catch it. He explains it through Einsteinian model. Check out other videos. He explains the space curvature and also time curvature whose curvature together create the effect of gravity/weight.

[@robertmontague5650]

This shows that time curvature has nothing to do with gravity and is not dependent of any mass being present. An apple moving through space does not experience gravity. It experiences time curvature.

[@elmolewis9123]

I'm beginning to think this Einstein was pretty smart. Nice job, Mahesh.

[@lande7510]

'Pretty' is an understatement. The guy was multiple times genius

[@anonymes2884]

I'm not big on blowing smoke up you know where in comments but this is easily one of - if not - _the_ best physics channels on KZbin right now IMO. Simple but so well thought out. So, y'know, basically, thanks :).

[@veervishalmishra4526]

So it simply means that gravity is due to acceleration of massive objects in the 4th dimension , so from where does that acceleration comes from?

[@otaku-chan4888]

well, the earth's accelerating upwards (creating the effect of gravity) because the sun, which the earth's orbiting around (in the sun's frame of reference) is _also_ moving through space, since the solar system's trapped in an orbit inside our galaxy. That movement in space gives earth an acceleration.

[@veervishalmishra4526]

@@otaku-chan4888 but well if it's movement in space than it should have positive acceleration in the direction of it's motion(imagine standing at some place in direction of motion of earth then earth will seem to come toward you) ,so gravity, then it should also have negative acceleration (imagine standing at some place from where the earth seems to move away from you), so does it mean negative gravity? so maybe because of this reason we can remove the option of acceleration in space?

[@Navansha]

Same question.

[@otaku-chan4888]

@@veervishalmishra4526 no, all we can perceive is the movement of the earth 'pulling us down' as the earth accelerates "upwards". We're so tiny that we're like ants on a huge ball that looks almost flat. You think ants can perceive (put understanding aside, just consider sensation) positive or negative acceleration, no matter how much they tried? Nope, they'll feel "gravity" from what the ants were standing on and that's it. We're much closer to ants even in the scope of our solar system. For example, we might see tides and know that the moon exerts "gravity", but we don't feel any of it. When we feel no positive acceleration, there's no negative acceleration either.

[@khuti007]

Sry mate, but your mixing up 2 different theories here. The general theory of relativity and The special theory of relativity You might need to read a little bit more on this. You have almost got it. It is confusing, its not natural from our accelerated point of view.. The misses told me to give you pointer. Ok here are 2 1. There actually is no Gravity, amazing isnt it. There is actually only spacetime curvature. 2. The difference in the percieved time difference from the top of your head to your feet, is only a local effect because your in an accelerated frame of reference. If you step off a cliff, and you are now in an inertial frame (not accelerating) The effect disappears and head and feet experience the same time. Time dialation does not cause Gravity. There is no Gravity

[@MichaelRicksAherne]

My brain hurts in a good way.

[@jmcsquared18]

This is the most important reason why the trampoline analogy is so awful. The overwhelming majority of the perturbation of the metric from flat Minkowski spacetime for weak fields is found in its time component. So, in the weak-field limit of general relativity, that is the only term that contributes to the traditional Newtonian potential. Representing that as a "ball on a trampoline" is as close to blasphemous as a sentence could get in science. So, I love seeing more content creators addressing it.

[@user-zy8ct8yr7n]

Time = motion Reason why time is used to measure motion Same way a ruler is used to measure distance

[@faisalkhatri7284]

I have been around on KZbin for years watching science videos. Coming across your channel feels like a blessing to me. There are so many famous KZbinrs with all those animations but they lack simplicity and a good flow of information. What you are describing is one of the most complex subjects in physics to understand. The way you do it is.. (ran out of vocabulary) This is where I press the bell icon.

[@b.s.7693]

When this model is so widely accepted, why does modern physics postulate a Graviton? How is this coming togehter?!

[@kylelochlann5053]

If Maxwell's equations are so widely accepted, why postulate the photon?

[@Mahesh_Shenoy]

Because general relativity doesn’t work with quantum mechanics!

[@ExistenceUniversity]

​@@Mahesh_ShenoyPenrose would like a word with you Mahesh

[@b.s.7693]

​@@Mahesh_Shenoy Don't get this. Must gravity really explained differently on a quantum level? Especially, bc gravity plays almost no role on these scales, it kind of vanishes.

[@lewis7515]

If you can satisfactorily describe a building well enough to explain what one is, where it is, how you get there and how it's supposed to be used - why would you ever need to describe the bricks its made from, or even need to know what bricks are?.. Your description works perfectly well, up to a point. After that point, your description is fundamentally incomplete - which is a quite unhappy situation that deprives you of all kinds of knowledge, and the potential that knowledge woukd give you access to. Without that knowledge, you can be a tenant of that building, indefinitely - but you can never, ever, be an architect.

[@alanbarnett6993]

Your explanation contains one subtle but very important error. At about 11:00, you state (correctly) that rolling the paper into a cylinder doesn't make the surface curved. You further state that you could crumble the paper and it still would remain flat. This is not quite true; for "ideal" paper, which cannot be deformed, along the creases the surface is not "smooth", so the curvature of the surface is undefined there. Real paper can deform, so the surface is curved at the creases. The true statement is that any shape that can be made from the paper without creasing it is flat. Clearly, a sheet of paper can be made into a cylinder without creasing it. At about 15:00 you roll the paper into a cylinder and claim that this represents gravity. But, as you correctly implied before, the surface of a cylinder is not curved, so,if gravity is curvature of space-time, this cannot describe gravity. What it actually shows is the use of an accelerating reference frame. The actual shape of the paper representing the space-time near the surface of the earth differs ever-so-slightly from a cylinder. The fact that it can be well approximated by a cylinder is an illustration of the principle of equivalence. You do show the need for the surface to be curved at 15:47, where you show the effect of gravity on opposite sides of the Earth using two cylinders with their wide sides pointing in opposite directions. It's clear that those two cylinders cannot be made from a sheet of paper without creasing it; any single surface containing both off those cylinders would have to be curved; this is the gravitational field. One more comment; you say gravity is caused by curvature of time, which doesn't make much sense. The object that is curved is the 2D surface described by one time dimension and one spatial dimension.

[@skhotzim_bacon]

Yeah he needs to add the corrections in the description or something. This is ridiculous. It just furthers misconceptions about physics

[@chekote]

2:23 I got that reference

[@pablofernandezpena1045]

I'm sorry, but I have to say it, what you explain from 14:00 onward is wrong. You certainly explain it rigth that the rubber surface is a pretty bad representation of gravity, but although you really aproximates to a better explanation/representation of what gravity is with your cone-shape of spacetime, is not accurate because that spacetime is still FLAT. Gravity is due to CURVED spacetime, and by CURVED means that the "surface" (2D in your example, although we already know is a simplification of the real 4D one) of spacetime must NOT conform a FLAT "surface", your cone-shaped surface is really FLAT, the "deformation" you show from the original spacetime fabric to the cone-shaped one results from a change in coordinates, always in a FLAT spacetime, in physical terms it means you are observing the FLAT spacetime from an accelerated reference frame (you are observing from an accelerating rocket for example) not a real CURVED spacetime (gravity). Gravity is the result of a "deformation" of the fabric of spacetime in a manner that is not more FLAT but CURVED, by maintaining your analogy, the resulting CURVED surface is like the surface of an orange peel, and that surface is really CURVED, because a FLAT surface cannot conforms it (try to conform a sheet of paper to it), but your cone-shaped one certainly can be conformed by a FLAT one (your representation is a sheet of paper, which is FLAT). Gravity is due to TIME CURVATURE, so the concept you are trying to explain is correct, but that cone-shaped surface is not CURVED, is FLAT, the orange peel analogy is really CURVED, and over that representation you should have discussed the subject, and the horror you mention with the rubber sheet analogy is still (much more disguised) present in your cone-shaped one. Unfortunally this is not the first time I see this misconception, I think is due to the book by Epstein you mention, although I haven't read it, so I don't want to blame it. This is a hard subject, spacetime is not intuitive, and frequently accelerated reference frames are confused with CURVED spacetime (Gravity). By no means I want to be offensive, but this misconception must be warned to the unaware viewer, also, the FLAT and CURVED uppercase is to make emphasis, not for shouting.

[@Mahesh_Shenoy]

Agreed. The whole point is to discover this idea, rather than just state it. If you extend this over an entire planet, you will eventually get a curved space time. Which we will get to eventually in subsequent videos

[@DrDnd4nyer]

Welcome to the Science Pitch Meeting!! Hands down the best explanation and visualization! And your excitement is contagious! Can't wait to see the video on Mercury!

[@PaulBrassington_flutter_expert]

This was very good until the curvature is wildly exploded, your curved picture is actually a rectangle, the difference in time is tiny, so small it does NOT explain as you say, the start was brilliant but fell apart when the time different is massive to explain the principle, but, in the real world, the time difference is so tiny it can be ignored.

[@lawandorder-e3d]

bro its an illustration for helping us

[@firasmaaroufi9809]

This video is a masterpiece. I enjoyed every second of my proper time. I've seen so many videos on spacetime curvature, but yours is by far the most satisfying one, thank you very much.

[@fullyawakened]

and wrong

[@HarshaadShukoor]

Sir, at 14:55 why Did the space time diagram modify as a cone? why not anything else that increases the radius as we move towards the Ground?

[@karthikeyanv661]

Ockham's razor, sometimes the simplest explanation is the best explanation.

[@musicalfringe]

This is the first time I've ever seen someone point out that the rubber-sheet analogy uses gravity to explain gravity. Kudos.

[@davidmalawey]

embarrassed to say i’ve been an engineer for 15 years and now i think i understand e=mc^2

[@Lucas_Stradeus]

It might be a stupid question, but why does mass causes time dilation? I'm assuming gravity is just a consequence of time dilation, if I understood it right. So what's the connection between time and mass? I'm sorry if that's stupid.

[@knutfranke6846]

It's not a stupid question, but I suspect no one really knows an answer to it. As far as general relativity is concerned, "mass/energy curves spacetime" (and thus creates time dilation) is a postulate. It's basically what the Einstein field equation says (in a more precise way), and that was ultimately derived from observation (plus some thought experiments) , not from some deeper insight into the nature of mass (other than it being linked to energy).

[@Lucas_Stradeus]

@@knutfranke6846 Oh, I was really curious about it, thanks for the reply.

[@todradmaker4297]

It's a great question and I'll give you an answer that everyone will tell you is wrong. It is not that gravity changes time but rather the clocks that measures that time. But as long as they get the math right GPS systems will still work.

[@drcatspaw]

Scientists are still working this out. I may be wrong buy I'm pretty sure those big expensive particle accelerators were built to find part of the answer. The high boson. How does that give mass properties? Lots and lots of math.

[@jorgepeterbarton]

​@@drcatspaw that is to explore what gives particles mass not the gravitational effects of mass

[@disobeythegravity]

Forgive my probably dumb question. Isn't the "proper time" axis in the curved diagram also curved? Wouldn't this mean to represent an object moving through time, on the diagram, we would have to draw the blue arrow following the time axis? This would make it also curved and parallel to the ground.

[@mawallet]

Finally, a physicist who can explain things using better models. I was always so confused by the two dimensional time/space description. Your cone makes so much more sense!

[@Eianex]

Okay the explanation is cristal clear and I love it. But why time gets curved by mass in the first place? Why does Earth's mass equal more time at the ground? Edit 1: I've just watched the video of black hole time dilation of this series. I reformulate my question: Why do accelerated frames of reference (like the ones created by masses's accelerations towards each other) create time dilation in the first place? Edit 2: I've watched space curvature around the sun video. New reformulated question. Why do both: time ticks slower down in a gravitational field And space is expanded near massive objects too?

[@ChrisGlenski]

This is your best video yet! Literally the clearest explanation of curved space time I have heard, I can’t wait to share this to someone

[@matthiasreimold7836]

Thank you so much! Your videos are absolutely great! Physics is just a hobby for me, but I do teach at a university and it is obvious that your videos are didactically exemplary! Understanding the equations of general relativity is one of the things, I want to accomplish in my lifetime, and thanks to your videos, reaching this goal seems more realistic than ever ;-) However, I really have a hard time wrapping my head around the fact that on the one hand, the effect of gravity on time dilation is really small (different ageing of head and feet). But on the other hand, this small effect is supposed to lead to a spacetime curvature that leads to effect as dramatic as an acceleration of 9.8 m/s^2. How is this possible? If anyone can explain this to a layman like me, I am sure, it is you...

[@IPWCsInTheory]

This has become my new favorite channel rather quickly. This dude's analogies are perfect.

[@jeffroberts6865]

I enjoyed your video and have three points to make. 1) I bought the Epstein book online a few years back. It was out of print (it still is, I think) and so I had to buy it second hand and it is quite expensive. It’s a good read and helps with getting an intuitive understanding of relativity. 2) I think there is a risk with the Epstein diagrams of mixing-up gravitational time dilation (GTD) with spacetime curvature. GTD arises when you think you are stationary and yet you are actually in an accelerated frame of reference, as indeed we are standing on the surface of the Earth. GTD is observer dependent, meaning it is possible to find observers that do not see it (a free falling observer won’t experience GTD for example). Where there is GTD, there is apparent (or fake) gravity. Once we accept the Earth is accelerating upwards, it is actually unsurprising that apples appear to fall and that all objects regardless of their mass ‘fall’ at the same rate, because the Earth is actually accelerating upwards at the same rate. Most of what we see as gravity on Earth is because of its acceleration upwards. What is holding the Earth in, keeping it the same size? Spacetime curvature. Spacetime curvature is caused by mass and energy. It is observer independent; all observers will agree on the curvature. Spacetime curvature is what gives rise to real gravity, and what attracts objects together in space. It emerges in the form of what we call tidal forces. 3) The Epstein diagram you used is flat space (actually I think you said that) but rolled into a cone to illustrate the time dilation. When it is flattened out the Proper Time axis is curved, while the free falling world line (of an apple) is not. This is a spacetime diagram drawn from the perspective of an accelerating reference frame (us, the observer standing on the Earth). The time dilation is a result of our accelerating reference frame. I think there is a risk with Epstein diagrams of thinking this is spacetime curvature, unless it is spelled out that it is curved because it’s an accelerating frame of reference.

[@physicsmorons6312]

This is Wrong. With all due respect you are doing the exact same thing. Taking the Gravity into account and creating time dilation , and then using that time dilation to prove that look guys - We have discovered gravity. This is circular. The thing you are explaining here is the gravitational attraction. The attraction between two bodies due to the curvature of spacetime. Let me ask you 1 thing- Why did you consider the time is running slow for that clock at 5:17 ? Because it is closer to Earth, which means there is gravity, and gravitational attraction. If Earth is present then there is curvature and THIS CURVATURE IS GRAVITY. You can't say that let's consider Earth and the time dilation. The dilation itself is coming from curvature of space - WHICH is GRAVITY. I have been watching you for a long time and started my youtube channel by getting inspired by you. But I thing this is a misinformation. I have this explanation before in "THE SCIENCE ASYLUM" channel but sadly this is wrong. You can't take Earth and create the time dilation and then propose that time dilation creates gravity. The time dilation exists because of gravity, because of matter, because of energy.

[@RiteshKumar-kv7if]

Thank God!! At last one guy who understand the basics of Relativity!! Subscribing to your channel

[@physicsmorons6312]

Thanks @@RiteshKumar-kv7if

[@skhotzim_bacon]

Thank you. I also posted a comment about this. I'm tried of seeing KZbinrs being tricked by a coordinate transformation or just regurgitating information they don't fully understand and continuing to spread these misconceptions to their audience.

[@drcatspaw]

Well, in the exact sense, you are right that time curvature isn't the entire story when it comes to gravity. But in non-extream gravity (like earth) and non-extream velocities (anything not close to light speed) the time curvature dominates the equations for observed effects. That's not to say that time dilation causes the effects of gravity. It's that the curvature of timespace causes both the observed effects, time dilation and things falling. Which is how I interpreted his explanation. But I admit, that is just my interpretation. I do agree that any good science explanation like this needs the disclaimer of "this isn't exactly how it works, its just to help visualize it." But that's a generic complaint I have about almost any physics talk.

[@StevePerry-r5w]

Agreed. Dialect refuted this reasoning a while ago. kzbin.info/www/bejne/hpu3aWh3rbmgf5Isi=qXEcHVz4e9RJmSG6

[@anirudhmohan9957]

Hi Mahesh sir. Big fan... Just wanted to clarify something.. due to gravity, the 2D representation of space in the cylindrical model doesn't become a cone right? It's probably like a bell I think. Because the cone shape curves the time axis as well as the ground.. so in this conical model it seems like the ground is not accelerating (it's relatively still parallel to the time axis).. if it's a bell shape, I think the time axis still would remain straight and the ground would curve showing an accelerating ground.. I guess you used the cone as it would be impossible to make a bell shape with a sheet of paper.. But I hope I get an answer to my query.. because I learned all this just from you.. thank you

[@xxronnocxx2]

I knew that interstellar reference was coming lol

[@Mahesh_Shenoy]

How could I not? :D

[@rtbeerzi]

I have some questions. This is the second video I've watched and from the very little I understand about Quantum Physics, there seems to be this insisting thought in my mind, and the first 30 seconds with your elevator made me think of it literally: Is there any scientific basis, given light is only a particle when observed (Please correct this notion if I'm mislead or incorrect), that one could unequivocally say that; When trapped inside of an elevator, you could certainly be sure outside of this elevator is the world in which you left to enter it, and not the middle of space? Or another dimension or perhaps, in a space of floating probability where you're not actually "anywhere" as we understand it? Why do children and animals lack "Object Permanence"? and could that be related to physics? If a tree falls in the forest and nobody is around to hear it, I'd go as far to ask: Is there even a forest? Is there even a tree? What does this mean for light and us? Could there be a day where we can trick the Universe into thinking we are anywhere somehow? Or are all of these questions based in a sort of ignorance? Because somehow despite all of these grand questions, I've never ended up anywhere strange, and the world is exactly as we leave it every day, and the Sun still rises (relatively). I wonder if that has anything to do with the fact there is more than one observer, which does bring me to my final question: If we take the logic that light is only a particle when observed, then how can we be sure that the creation of our universe isn't just a form of "last thursday-ism"? To say that if light is a wave when not observed; at some point in history there were no people, and supposing there is life somewhere else, they had to start at somepoint as well as us. How can a universe exist with no observers, unless we are going to play the "God" game of chess and just assume the universe ITSELF is an observer but I think that's... idk what to think of that actually. Summary: Assume the axiom "light only condenses into a particle when observed or measured" How can we be sure of an objective reality? Without an infinite observer, how is the universe here in the first place? Is there theoretically any way to use these illusions or facts to our advantage? Thank you for reading and responding if you choose to. Much love and stay educated everybody

[@thomastang2587]

Finally someone who speaks like a normal person , explains ideas like a normal person, and treats his audience like average people! 👍

[@joestitz239]

Like james burke said at the end of his 1990's connections series. 'Its einsteins universe now, so you can, drop the apple!'

[@drawlikeme9]

I'm in 11th,i found your channel recently and i love your content, please dont stoppp

[@zebrabw01]

deng bud you doing well ?

[@mmesamesa]

Can you theorize about the actual path through space-time for any item like a rocket overcoming gravity apparently going "straight" upwards away from the ground? Would it be the same path as falling but in reverse?

[@theoreticalexercise]

I can't believe you're able to explain this the way you do. This is amazing. Thank you

[@auriuman78]

So, time (like actual time, not the solar time we made up) seems truly linked to light speed, and we're moving at time and gravity being connected here as well... So are we coming to a consensus that light > time > gravity? I mean that's kinda the path, right, that they're all linked into each other by some underlying law? I typed this at the beginning of the video and now waiting to see if you answer me in the video... And partly yes you did 😉🤯 so I have 2 big questions after this... 1. doesn't this lead into the thought that gravity, if susceptible to red shift also, is governed by photons and therefore also electromagnetic at it's core? 2. This feels like there's another dimension, at least one maybe more, that were just not equipped to sense, or at least sense fully. because obviously it's influencing the dimensions we can sense fully. Does this track with what you're saying, or am I missing it entirely?

[@ProgressiveMastermind]

Interesting model, but why should the apple im the air be different than the ground? I mean the apple must also be affected by the curvature of time, mustn't? Your flat cone diagram basically transforms the time axis right? Thus must affect everything else in the same frame if reference too?

[@Mahesh_Shenoy]

Yes, the curvature causes the apple's velocity to increase in space (without acceleration)

[@hce2455]

I asked the same question myself then I realized apple’s time is also curved as you stated, but not as much as the center of the earth. As you go closer to the earth, your time curvature gets closer to earth I guess. He draw a straight line with ruler but maybe that’s just a simple demonstration. Make it more curvy as you get closer to the earth. I hope someone explains if I am right.

[@musa8693]

I have to be be truthful I didn’t understand shit after halfway through. I don’t think I know enough physics at my current level.

[@mrgriff6122]

Nice shirt 😊

[@gajalakshmi9266]

Hmm... U have done a really good job giving the intuition of the concept but I also expected a bit of the underlying mathematics. So maybe you could make a video on that (like the equation for gravitational time dilation)

[@kashemvai5025]

The thing I like the most about your channel is that you ask and answer the most critical of questions that NO OTHER content creators are doing

[@johnhulbert8185]

What I don't understand, is why time is the thing that gets dilated? Time is a measurement, a thing that's happening but doesn't exist materially. Light is the stuff that you are measuring and it is actually there, existing. So call me crazy, but would it not make more sense if it was light that dilated rather than time? At the start you talk about how using gravity to explain gravity is not a good explanation. Then you went on to describe light bending because of time dilation, when time is measured with light. Time can't dilated because it can't do anything, it just is. Sounds absurd to me. I mean, I got the concept when I found about it but I never really assumed people took it literally. Like the Multiverse or Dark Matter. Not to mention all that other insane spill of shite that came from the confusion over the 'observer'.

[@pujamathssolution9906]

Please tell what is photoelectric effect of Einstein

[@carultch]

The phenomena that population of photons doesn't eject electrons from a charged metal in a vacuum, but rather frequency does, due to frequency directly determining the energy per photon.

[@LytraVolt1]

I don’t get it, you lost me at the bending of paper. I don’t understand time as a dimension please maks a better analogy, earth isn’t expanding so it can’t be moving, IM JUST SO CONFUSED all you’ve done is confuse me further please help me

[@bodhi-pickahfilecoinlurker5964]

The rolling of the paper is just to make the 2d representation of our spacial dimensions into more of a 3d representation and the circle of the rolled up tube becomes a clock as your rotate the cylinder

[@bodhi-pickahfilecoinlurker5964]

Imagine you're the apple and you just released from the tree. You feel like you're not moving but the earth is coming towards you

[@todradmaker4297]

I think the reason you're confused is because it's a poor analogy. While the math might suggest that this is how "spacetime" operates, I think it is a major mistake to illustrate time as a spacial dimension.

[@jessicasajwani5356]

@@todradmaker4297 i also have a really hard time to think of time as a dimension Why do you think that it should not be interpretated that way?

[@JJ-ui4ph]

@@todradmaker4297 No he wasn’t using any mathematics in his illustration. How would you illustrate time then? Because it’s not a spatial dimension, how exactly would you add it?

[@LeTtRrZ]

I have some reservations about this interpretation. A few years ago there was a wave of hype over the notion of time dilation causing gravitational acceleration. This is not how it works. Gravity causes the geometric spacetime warp, and it’s the warping that causes time dilation. It is not the other way around. I am suspicious of this source that insists the speed of light can appear different at different parts of the beam. Again, it doesn’t work that way. Light always follows geodesics at its speed (assuming a vacuum). Edit to add: You should check out Dialect’s video on the true cause of gravity in General Relativity.

[@mongz11]

Blew my mind. All those wormhole diagrams are making sense now! Thank you so very much sir

[@ЦветанСпасов-ш5ж]

This is so wrong! I mean - literally - this is wrong on so many levels... First of all - time is imaginary. Time is derivative of space and its deformations. For example - if you know - space or universe is expanding. And this expansion is everywhere, in the same moment equally everywhere in the universe. So when you get an balloon membrane and draw a line on it with its sections for every mill. If you stretch this membrane - the line became longer with bigger millimeter sections, but this line still start from 0 mill, and ends on 10 mill, like before stretching. But if you measure this distance from another point of view - you gust get wrong measurements, because you are using wrong tool, in wrong dimension, in wrong way. That's why we are thinking that the time is bended. But it is not! The space is bended but we can not measure this bending because we are part of this bending. When something gets out of our field and enter in another field, with different bending coefficient - then if we can make measurements - we will still get correctly measured unit. But if we coexist in 2 field of bending - then we will recieve wrong measurements. So this is this case! There is something more interesting!

[@AdityaPratapMusic]

This has to be one of the mind blowing videos of yours Great job Mahesh.

[@roy04]

nit: When using the red apple and blue apple analogy, I think it's helpful to specify that each unit vector specifies one unit of time, and the time on the y axis is from the red apple's frame of reference. Great video otherwise!

[@DrZedDrZedDrZed]

This was an absolutely amazing educational model. Kudos. Really, really stellar teaching.

[@franksanns3738]

Good video. Fine point though is your explanation of a larger cylinder closer to the earth than the one farther away. When you combine them at around the 15 minute mark in your video, you show a cone. It would actually not be simple linear cone because gravity changes with the distance squared. The cone would be an R squared function flaring out more and more as it got closer to earth. You most likely left this out for simplicity for the viewers so it is understandable but slightly misleading.

[@heronimousbrapson863]

I won't be getting any sleep tonight thinking about this.

[@Path_k_pradeep]

You are an incredibly gifted teacher. I hope the Indian media would change to the extent that it regularly sends out invites to individuals like you to help advance the physical sciences in India. Many "scientists" exist in India, although most of them are essentially calculators with no real knowledge of the field.We merely oversee the infrastructure and system in India; they have no interest in furthering science, only using it as a source of income, and they misappropriate public funds without any remorse. Institutes of research also play a role in this illness.

[@jensphiliphohmann1876]

08:53 I still have to criticise the swapping of proper time and coordinate time. I admit that it's convenient because you don't have to deal with the MINKOWSKI metric but can apply PYTHAGORAS instead. However, you trade it for a disadvantage: A point in proper time is _not_ the temporal equivalent of a position. If you want to meet with someone, you must agree on ▪︎a common reference clock U (for "Uhr", German for clock), ▪︎a position relative to U and, of course, ▪︎a U coordinate time i.e. the time U shows. If you move quickly enough with respect to U, your clock will have fallen back compared to U.

[@kylelochlann5053]

The value in thinking about world-lines has nothing to do with the flat-space metric, but rather that the world-time doesn't physically exist and so the advantage of thinking in terms of world-lines is that it gives a more intuitive picture of the physics.

[@thedeemon]

@@kylelochlann5053 but taking "proper time" as an axis is so weird and counter-intuitive. Like, pick a point somewhere between two world-lines of two objects, what exactly that point corresponds to? whose proper time is its Y coordinate? this particular chart is super confusing

[@kylelochlann5053]

@@thedeemon The event in-between the two world-lines has no independent meaning, which was Einstein's point. As far as being goes, sure, all your exposure was to a single system of coordinates. You would likely find Minkowski diagrams confusing if all you learned on were Brehme or Loedel diagrams.

[@thedeemon]

@@kylelochlann5053 Minkowski spacetime charts are fine. I'm used to having coordinate time as on of the axis, not proper time. Never heard of Brehme or Loedel tho.

[@kylelochlann5053]

@@thedeemon Keep in mind the the world-time doesn't exist, and that the Minkowski diagram depicts a pair of proper time world-lines, same as the others (Epstein, Loedel, etc). The world-time "t" is the proper time of the Minkowski observer. It takes its form as the global time coordinate by imagining an infinite set of synchronized clocks, a "confluence of time-like curves" that are perpendicular to the foliation of spatial hypersurfaces, e.g. the "x-axis" at t=0. There's a really great elaboration of Epstein's book, relativity.li I think it is (anyways it's called Epstein Explains Einstein). You have to search around the site to get the full book.

[@kirillsleptsov1680]

These explanations are so dumb making absolutely no sense, it probably requires heavy math to make it clear.

[@andreyassa7638]

Simply brilliant! Thanks for another video which makes complex stuff easily comprehensible. It's worth the effort!

[@InvaderMixo]

What about two equal objects floating near each other at rest in space? Neither is traveling a different angle through spacetime, but traditionally there will be a gravitational pull between them.

[@shaihulud4515]

Can this be coincidence? I literally came here AFTER watching another of my famous YT-channels, Pitch Meeting, so that reference at 2:25 was not lost on me. This, combined with a very well done video on one of my favorite subjects - I just had to leave a thumbs up, and subscribe! Well done, sir!

[@AanjE]

Hi Mahesh, great video. I have a question, the difference between the time two metres above the ground and time at the ground is infinitesimally small yet the apple falls quite quickly. Is this because time moves at C and the time dilation difference between the two events = the time it takes light to travel between the two events.

[@aiden.paramore]

I don't often comment on YT but this is one of the best representations of Einstein's theory I've ever seen. Made so much more sense than the curved space example everyone seems to give. Thank you so much for such an excellent video!

[@centarian2559]

Gravity pulls equally on all particles in and around you so your total mass does not matter as all of you is being attracted by the same force, now the total force applied to an object being pulled on by gravity is higher the more mass it has, but the force applied to each individual particle remains the same.

[@marveljustice]

This channel is simply too underrated. Deserves millions of subscribers. You've got one of the best and most intuitive content on your channel Mahesh. I mean I have been into relativities and such stuff for like 3 years. Am currently studying in 10th standard. I've watched the arvin ash, veritasium, gsf, the science asylum, minute physics and all such during these years. But honestly saying, your content is much more unique and elegant. For eg. none of these have got any videos on what you actually mean by electron spin and there's so much more! You are doing a really great job sir! 🎉🎉🎉

[@phoenixpierlsberg3229]

Wow, I could FINALLY actually understand and see what time curvature means. This illustration was so clear and easy to understand

[@giin97]

Huh. Guess it's time to start googling, I've never heard of "time curvature" before.

[@BondJFK]

@@giin97 Space time curvature mans both space component and time component are curved

[@debrainwasher]

Gravitational redshift does not exist. Only redshift caused by spacetime-curvature, since light follows geodesic lines [sic]. And the nice thing is, frequency decreases upon concave (attractive) curvature (e.g. produced by masses, that displace spacetime somewhat as the «container» of quantum fields), while a (repulsive) convexe curvatures (to use the rubber-sheet model) create a blueshift - for the very same geometrical reason as redshift occurs. Proof: Quantum-fields can never leave their field spaces and interact with each other - only intermediatied by gauge bosons. And yes, concave and convexe spacetime-curvatures can be created without masses from a flat Minkovsky-spacetime. Unfortunately, nobody wants to know how this works and those who know don't want share this knowledge with people, wo don't know. And the female physicist, who had figured out, how exactly this works and wich technology is required, passed away on July 27, 2021 (R.I.P).

[@narfwhals7843]

"redshift caused by spacetime-curvature" That is what gravitational redshift means.

[@debrainwasher]

@@narfwhals7843 Then we happily agree.I simply feel somehow unrelaxed about the term «gravitational redshift», since it implies gravitation would be the cause, while it is clearly not.

[@narfwhals7843]

@debrainwasher we have dubbed basically everything related to spacetime curvature as "gravitational" because it stems from a theory of gravity. Gravitational redshift, -lensing, -time dilation, -waves, etc.

[@benl9694]

Hi Mahesh, On the last apple in your video you drew a straight line on the apple as it advanced through time and that caused the apple to hit the ground as the ground was accelerating due to the curve in time. Drawing the line this way, directly on flat space-time, from the apple, instead of on a cone, made me think of this question. Do things at rest, regardless of their vicinity to a massive body, not experience the slow down in time? What I mean is, if I am at rest (or in Newtonian thinking free-fall) do I not experience a time rate discrepancy between my head and my feet, the way I do when standing on the earth's surface? If that's not correct, why didn't you draw the apple at rest on the conic paper? And if you had, would the planet of it had still collided (it would seem intuitively to me they would not). Thank you for the videos. I very much look forward to watching them as soon as they are out!

[@stevenlarson3316]

I hope he answers your question because I didn't understand that either. This is as close as I could come to an answer. Even though an object in freefall is in an inertial frame and not experiencing any gravitational forces locally, it still undergoes time dilation due to the curvature of spacetime caused by the presence of the massive body. Therefore, clocks on the object in freefall would show a difference in elapsed time compared to clocks at a distance from the massive body, demonstrating the impact of gravitational time dilation on objects moving in gravitational fields. Proper time refers to the time measured by an observer in their own rest frame, while time dilation near a massive object is a consequence of the curvature of spacetime caused by the presence of mass. So, it seems like even though the apple is in an inertial frame, it still experiences time dilation. The video seems to be saying that time dilation is the cause of gravity rather than an effect of curved spacetime. And if it isn't saying that, then this would just be a confusing way to describe curved spacetime in which the effects of both time dilation and gravity are present. I don't know if that was helpful. But maybe it's something to think about.

[@benl9694]

@stevenlarson3316 I think time dilation is creating the effect of gravity, but that there's no gravitational force. So mass, rather than create gravity, reduce the rate at which we a body travels through time, but since the speed in space time for all things is the speed of light the only thing that must change is the "distance" in space-time. But if a body is experiencing the same amount of time dilation, say 100 m above earth's surface regardless of free fall or at the top of a building then I don't see why the apples line, the free fall body, wouldn't be drawn on the cone. But I find myself often confused. Matt on PBS space time and the guy from science asylum made the same argument (although Mahesh's version is much more comprehensive and does a better job of explaining the theory and Dialect did several videos disputing this interpretation. )

[@stevenlarson3316]

@@benl9694 Trouble is, as far as I can tell general relativity doesn't go beyond saying gravity is caused by curved spacetime.

[@davidyoung2990]

Maybe everything actually is just expanding? I mean, we can observe that on a macroscopic scale looking at the observable universe… so why can’t it be happening right here? And, in fact, everywhere?? How would we be able to tell, even in theory, that isn’t the case? 😂

[@benl9694]

@davidyoung2990 this is a theory Scott Adam's advanced (from dilbert) many years ago. The problem I can see with it is that it's unfalsifiable. But I suppose it's plausable.

[@msnt]

Why can't we travel with speed which is more than speed of light? In this video he has given a clear example of a torch, in which, When we turn on the torch in high gravitational fields, the upper layer of the light has to travel with greater speed when compared with lower layer of light. But, according to Einstein, this is not possible. But, why is this not possible? It is because, increase in speed of an object, always results in increase of it's relativistic mass. So, when an object approaches speed of light or it tries to cross the speed of light, it's relativistic mass reaches infinity. But, an object having infinite mass is not possible. So, this is why an object cannot travel with speed more than speed of light, even light itself. But, have you ever wondered why does the object's mass increases with increase in it's speed? Well, if anybody of you is wondering why the mass of the object increases with increase in it's speed, here's the answer: It is because of the equation E = mc^2 equation. This equation represents the equivalence of mass and energy. Energy is directly proportional to mass. But, what does this has to do with increase in mass of the object? So, what happens is that when speed of an object increases, it's kinetic energy also increases. K.E = 1/2 mv^2 And as we know, increase in energy, results in increase in mass. I was wondering about this topic after watching the video. I wrote this so that if anybody else is also wondering like me, their doubt would get solved. By the way, Nice Explanation!

[@TankEsq]

1:21 I've always said this it's a circular reasoning analogy!! It only works because of gravity anyway

[@thedeemon]

Not necessarily. If we take a 2D plane and stretch it into 3rd dimension like that famous funnel, such that distances grow near the big mass, and calculate how geodesic lines work in such curved 2D space, we'll find they also curve towards the center, as if there is some gravity present. So it's a valid description of how a 2D section of space curves and makes straight motion look like there is gravity in absence of any external gravity.

[@TankEsq]

@@thedeemon if the example is mathematically identical as an analogy then I stand corrected, otherwise doesn't seem helpful, especially conceptually because the only reason the balls fall in is gravity from earth below. That doesn't provide a visual representation as to why a warped spacetime would cause mass to be attracted to each other because the balls are just going down. The time gradient makes more sense as it provides a dimension of explanation outside of gravity to explain gravity

[@LuisAldamiz]

So... what happens inside Earth is that the cone is reversed in shape (thinner diameter down) and as you slide downwards towards the center (in your typical imaginary, incompressible and otherwise impervious to everything, tube from Madrid to Auckland) your clock goes slower and slower until... what? Zero gravity at the exact center of Earth (or a black hole or whatever) does not mean that time has become infinitely fast, right?, certainly not for light (EM radiation, causality), right? But does it mean that stuff at zero gravity go necessarily at c speed and only because faster is impossible?