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

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.
In this video, we will explore why the curvature of time, and not the space, produces the illusion of gravity. We will also understand how the same time curvature allows the ground to accelerate up without the earth having to expand.
This episode was sponsored by Brilliant.org.

[@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.

[@vinit.khandelwal]

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 ?

[@vinit.khandelwal]

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

[@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.

[@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.

[@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

[@user-el4sy8iy8g]

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

[@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]

😂😂

[@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.

[@DxvidEisboerg]

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

[@Luke-pk9fe]

How do you see the dislikes?

[@enriquea.fonolla4495]

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

[@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.

[@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

[@paultaylor3213]

Loved the nod to Pitch Meeting. 👍

[@pvanukoff]

References to other youtube channels is TIGHT!

[@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

[@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!

[@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

[@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.

[@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 :).

[@elmolewis9123]

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

[@IPWCsInTheory]

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

[@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.

[@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

[@chekote]

2:23 I got that reference

[@user-ep1ki9qr7t]

17:21 so basically time creates gravity? So theres no such thing as gravity? Dude you have my mind blown right now!

[@rickcarroll]

Really well done. Best description I have seen. Keep up the great work. Ricko

[@theoreticalexercise]

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

[@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!

[@MichaelRicksAherne]

My brain hurts in a good way.

[@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!

[@andreyassa7638]

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

[@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! 🎉🎉🎉

[@savaged]

Thank you for making this complex topic so very simple to understand

[@aidenparamore9398]

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!

[@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.

[@mongz11]

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

[@thomastang2587]

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

[@caput_in_astris]

Love all your videos but this particular one is EXTRAORDINARY !!! I have been teached GR only by its formulas and without getting any intuition of it, and this is the first explanation I have seen explaining free fall by the time dilatation. Great job!!!!!!

[@3moirai]

Another excellent video! You make Relativity so approachable.

[@user-ky5dy5hl4d]

At some points wrong.

[@ADITYA-dv4uq]

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

[@user-ky5dy5hl4d]

Some things are wrong there.

[@frozencanuck3521]

My brain has completely melted

[@waffling0]

Wow, this is the best demonstration of this subject that I have ever seen - I have never quite grasped spacetime diagrams in this way until now. Great video!!

[@DrZedDrZedDrZed]

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

[@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.

[@andik70]

I think this is a very important question. What is a bit of a problem with your explanation is, that (in the sense of differential geometry) your examples are not curved. A cylinder is not curved. If you can make it out of a flat paper without distortion: it is not curved.

[@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.

[@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.

[@icreatesomethin3835]

This guy explains astrophysics better in less than 30 minutes than any of the physics professors in my school has done in a whole year Such a LEGEND 🗿🗿

[@45003]

Really say this is best explanation of space time curves I have seen yet good job man👍👍

[@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

[@drawlikeme9]

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

[@zebrabw01]

deng bud you doing well ?

[@michaeldeloatch7461]

Excellent! You have clarified this beyond my wildest dreams for the first time in 60 years of my life! You are a superb teacher. I have just subscribed.

[@alvaroballon7133]

As an expert on the topic, thank you. Most people and science/physics influencers get this so wrong. This video is a gem.

[@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.

[@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_MIshra]

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.

[@KingShinyRotom]

I've never seen someone so excited talking about time-space curvature! Great video!

[@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

[@Dr.RiccoMastermind]

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.

[@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!

[@kxqe]

Another way to look at gravitational red shift is via loss of momentum. If you throw a massive object up away from a gravity well, it will lose momentum (energy) because the ground is accelerating up and "catching up" to the object. But since light has no mass and must travel at a fixed speed it loses momentum (energy) by lowering its frequency.

[@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.

[@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.

[@bMonsterPro]

Your enthusiasm is contagious!! Superb science communication; thank you for uploading!

[@Aki-lw7vw]

Thank you , it's amazing how much you can teach so much and capture every bit of our attention in like 20 minutes.

[@talkinghand1977]

I knew that interstellar reference was coming lol

[@Mahesh_Shenoy]

How could I not? :D

[@mrgriff6122]

Nice shirt 😊

[@devankurkashyap1031]

I actually shouted out at 17:03. Beautiful explanation sir.

[@shankhadipbhattacharjee528]

The video is the best explanation of Red shift and the concept that gravity is actually acceleration. Hats off to you.

[@binbots]

We observe the universe in the present moment (wave function collapse) surrounded by the observable therefore, predictable past (general relativity) moving towards the unobserved therefore, probabilistic future (quantum mechanics).

[@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?

[@juliancamacho1304]

Your excitement and personality make it such a great time to watch and understand this!

[@godzillagodzilla4405]

Amazing. Never realized how time and gravity were linked until that visual demonstration. Thank you 🙂

[@jasimmathsandphysics]

8:10 Epstein?😨

[@thedeemon]

Lewis Carroll Epstein is the author of "Relativity Visualized" book he's using here.

[@jasimmathsandphysics]

@@thedeemon thank u

[@tc_military964]

Fantastic explanation. I wish it had been taught this way in high school!

[@danielaudipoy2350]

It's an amazing video, it's really clear. Well done

[@rebeuhsin6410]

This has been debunked, but I'm not educated enough to know.

[@eustab.anas-mann9510]

Dialect has a video on the debunking.

[@skhotzim_bacon]

Yeah I also recommend dialects video and then go learn relativity from a textbook.

[@drcatspaw]

​@@skhotzim_baconDon't know if you will see this, but I tried to find that video where dialect debunks this. I found a video from a year ago, The true cause of gravity, or something like that. There they argue against the idea other's have floated that the time gradient causes things to move. But that's not what is being shown here. They both seem to agree that it's actually the ground accelerating up. Did I get the wrong video?

[@skhotzim_bacon]

@@drcatspaw Yeah the gradient exists due to the curvature of spacetime from mass and energy. Gravity is not an illusion caused by gravitational time dilation. Gravity is a real phenomenon due to the curvature of spacetime from the presence of mass and energy.

[@skhotzim_bacon]

@drcatspaw I'm pretty sure you found the right video if he mentions Science Asylum's video in it. He has follow-up videos as well.

[@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.

[@user-lj9qo7hw2t]

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

[@adonisds]

After the previous video and before watching this one I thought I finally understood why the ground needs to accelerate to stay still using the rubber sheet analogy, so I'm curious to know why you think it's so bad. Here what I thought: When you have marbles on a rubber sheet, they barely distort its curvature and stay almost still relative to each other, but when you place an anvil on the rubber sheet the marbles quickly move towards it. The marbles weren't pushed towards the anvil, the space below them curved and they just kept travelling downhill. If you want to keep the marbles still, you have to impose a force on them to prevent them from going downhill. So for us, since Earth funneled the space-time, that's why the ground has to accelerate to stay still. Mahesh's explanation is more powerful and precise, but I think mine is easier to understand without having to draw and to memorize. I'd love if someone with more knowledge would comment on what is wrong with it and what are the limitations of the rubber sheet analogy

[@todradmaker4297]

The rubber sheet only works if you have an external force of gravity. It is a poor analogy.

[@Mooouuuse]

I was only introduced to your Channel a few days ago but, man, I think you're great. The way you communicate is up there with Neil Tyson and Brian Cox. Keep it up!

[@KilledByAPixel]

Amazing analogy of space time curvature that I've never seen before and much better then that stretched fabric bs, awesome work!

[@user-ct9ic5us3m]

I have been waiting for the next video

[@everybodyyogastudio212]

This is the first time ive run into your channel. Aaaaand youve earned my follow.😊

[@AdamGoodlet]

Really, really good stuff. Thank you for explaining with such passion and enthusiasm! Seems like it’s barely an inconvenience to you. Epic!

[@low_quality_films]

Yet another historically accurate and meaningful conversation between Einstein and Mahesh

[@neelkanthsapre3254]

Amazing video, Mahesh. You make it so much easier to visualize. I have seen very few videos made in India that are as high quality as yours.

[@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!

[@ErikSmuts]

Fantasitic explanation and visualisation. I love your enthusiasm in explaining these concepts. Keep it up!

[@renedekker9806]

Nice. Excellent visualisation. I have seen it this way before.

[@CalmSnow_]

Every of your videos is a gem. Thank you very much for all the information. Finally, I can understand Physics!

[@patriciasamper9412]

Thanks a lot for your videos !! I LOVE them you make all this complex concepts very undestandable

[@alanviolet4102]

Thankyou, finally an explanation that doesn't leave me with questions.

[@calebvantassel1936]

Your excitement is contagious. Great explanations too!

[@CastorQuinn]

This was an incredibly engaging presentation but still so information sense. Incredibly helpful. Thank you so much.

[@marcusa.ragnos1041]

14:53 This video is grown-up Blue’s Clues. I’m just here yelling at the screen “MAKE IT A CONE SHAPE!” like trying to point out a blue paw print.

[@flyhighcreative]

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

[@HairyDalek]

I’ve always had problems trying to get my head around this whole space/time curvature thing. I’m by no way a physicist or a mathematician, and I’ve found that rubber sheet and balls model to be confusing, but I’ve not really been able to explain to myself why. This video has helped me start to visualise it. I like the curving paper. For me, that feels like a better illustration for what’s going on, so thank you. It’s still mind boggling, but having an understandable model helps.

[@logic3686]

Thank you. I've been struggling visualizing this concept.

[@ezigwe]

This has to be one the best demonstrations of gravitational time dilation I've ever seen. Thank you!! Subscribed!!!

[@N1ghtR1der666]

I know people say this a lot on these kind of videos and I don't normally say it myself but this is actually the easiest explanation of space time curvature I have seen, and I have watched dozens at least, well done man! subbed.

[@jetds8466]

You do a very great job demonstrating and explaining these concepts ive recommended you to a friend keep up the good work

[@norukamo]

Amazing. I've always been confused about this from watching Veritasium's video (which I coincidentally watched a few days ago) and this blew my mind. You are amazing. Subscribed.