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Hey crazies, for 250 years we treated gravity as if it was a force like any other. That model explained both falling on Earth and orbits in space. It seemed universal, but about a century ago we learned that model is wrong.
Explore how gravity arises from time dilation and curvature of space-time, not as a traditional force, with clear examples and implications.
Ask about this video. Answers come from its transcript only — with the timestamp, so you can check them.
Generated from the transcript and can be wrong — check the timestamp.
Key Takeaways
- Gravity is not a force but a result of time dilation and space-time curvature.
- Time passes at different rates in different gravitational potentials, causing objects to fall.
- Gravitational time dilation is essential for accurate GPS functioning.
- Even point-like particles experience gravity due to infinitesimal differences in time flow.
- The universe’s gravity phenomena can be explained by gradients in the flow of time.
What the video covers
- Gravity was traditionally treated as a force for 250 years, explaining falling objects and orbits.
- Modern physics shows gravity is actually curvature of space-time, with most gravity on Earth due to curvature in time.
- Time dilation means clocks tick at different rates depending on their position in a gravitational field.
- A simple photon experiment shows clocks at higher altitudes tick faster than those at ground level.
- Gravitational time dilation causes objects to fall, even in a universe imagined without gravity as a force.
- The difference in time flow rates creates a gradient that directs objects toward Earth, explaining gravity.
- This time gradient concept also explains orbital motion, such as the Moon orbiting Earth.
- Point particles experience gravity through infinitesimal differences in time rates, explained by calculus.
- Gravity is fundamentally about time passing at different rates near massive objects, not a force exerted by them.
- Understanding gravity as time curvature is crucial for technologies like GPS, which rely on precise time measurements.
Chapters
- 00:00Introduction: Gravity as a Force vs Curvature
- 00:38Understanding Time Curvature and Initial Experiment
- 01:14Photon Timer Experiment and Time Dilation
- 01:47Implications of Time Dilation on Earth and GPS
- 02:51Imagining a Gravity-Free World and Time Dilation Effects
- 03:23Squirrel Clock Experiment and Space-Time Graphs
- 04:21How Time Gradients Cause Falling and Orbits
- 05:55Point Particles and Calculus in Gravity
- 06:55Gravity as Time Flow Gradient and Conclusion
- 07:28Additional Clarifications and Closing Remarks
Full Transcript — Download SRT & Markdown
Speaker A
Gravity is actually curvature of space-time, and most of the gravity we experience on Earth is curvature in time. Yes, time can curve. This episode was made possible by generous supporters on Patreon. To be fair, I can understand if
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you're shocked or confused right now. Or golf, you can probably picture some kind of space curvature. It's not a huge stretch, but time curvature? What does that even mean? It's a fair question, so let's start with a simple experiment. See, we've got a tall
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building, like really tall. It's poking out into space. We're ignoring any engineering difficulties, just just go with it. On the ground floor there's a photon launcher. It sends out a photon every second. On the top floor there's a photon
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timer. It receives the photons and measures the time between them. If we assume an absolute time frame for everyone and everything in the universe, which is certainly what our intuitions tell us to do, we'd expect the photon timer to receive a photon every second.
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But that's not what happens. The photon timer actually receives a photon every 1.00000000001 seconds. Yes, I know that's a hundredth of a nanosecond difference, but it's still a difference.
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That means clocks on the top floor of a building tick just a tiny bit faster than clocks on the ground floor. When two independent clocks tick at different rates, we call that time dilation. I would have called the time variation instead,
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'cause it isn't actually dilating, but so be it. The point is, time passes at different rates in different places. For example, time passes more slowly the closer you are to the Earth. The Earth causes it. That's what time
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curvature looks like around the Earth. That's how it's perceived. I know, right? Time dilation is real and it matters. Our GPS network would fail rather quickly if we didn't account for it. Within a day of turning it on, your location would have a
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seven-mile error. But it gets even crazier than that. The type of time dilation involved in that building experiment is called gravitational time dilation, not because it comes from gravity, but because it causes gravity. I know that sounds weird, but, but hear me
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out just for a minute. Forget everything you know about gravity. Imagine it doesn't exist. In that imaginary world, there's no reason for this world to fall. It just floats there. That's Newton's laws at play. No unbalanced force means no
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acceleration. No acceleration means if it wasn't already moving, it's not gonna start now. Next, let's say there's time dilation caused by the Earth. Remember, time passes at different rates in different places. The heights of the clocks don't have to be that different,
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though any difference will do. So imagine we attach two clocks to a squirrel, one on his head and one on his feet. They should tick at different rates. The difference isn't that much. In fact, it's even smaller than it was for the
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building. It's only an extra four hundredths of a femtosecond at the head for every whole second at the feet. But any difference will do. No matter how small. Unfortunately, watching clocks tick doesn't actually give us the right
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intuition. Let's try something a little different. If we only consider the up-and-down direction, that frees up the sideways direction for something else, like time, for example. This is just a space versus time graph, nothing too crazy. We've been looking at graphs like
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that for hundreds of years to look for patterns in motion. Except the squirrel isn't moving. Remember, we're still in that imaginary world with no force of gravity. That means we expect this squirrel to be at the same height
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at all times. It has no reason to fall to the ground. Or does it? Let's take everything we've learned so far and put it all together. The squirrel is hovering above the Earth and space, but it's moving forward in
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time. I mean, everything is moving through time, but we also know time flows at different rates in different places. You could think of it like a flow gradient around the Earth. And what happens when there's a gradient? Stuff gradients are
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the reason that anything happens ever. Oh, the squirrel's head moves faster through time than his feet. This gradually turns his motion arrow, what we call the four-velocity, over time. It points more and more toward the Earth. The squirrel falls
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to the ground simply because time dilation exists. Surprise! We just predicted gravity. This whole time we've been imagining a universe without a force of gravity, but as long as time passes at different rates in different places, things will
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fall anyway. Gravity exists even if we don't treat it as a force. Why does the squirrel fall? Because there's a flow gradient in time. Why does the moon orbit the Earth? Because there's a flow gradient in time. The weird universe
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we've been imagining is our universe. Whoa, dude. To be clear though, it's not time itself that's flowing. Time doesn't do that, and neither does space. The flow you're seeing in this animation, it's just there to give you intuition. I've
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just replaced the ticking clocks with a bunch of imaginary point particles. So wait, what about point particles? What about it? If they feel gravity, sure. How do they feel that time gradient flow thingy? They don't have any size.
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Well, because calculus. While we consider all these elementary particles to be points with no size, we don't actually know that's true. They're just smaller than we can measure. But even if they are points with no size, the math doesn't
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treat them that way. If we shrink this world down to subatomic scales, the two clocks get closer and closer, but they're never at exactly the same place and they're never ticking at exactly the same rate. There are always two clocks. Sometimes
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they're just infinitesimally close to each other. So where does gravity come from? It comes from time dilation. That's the idea that time passes at different rates in different places. Large masses like the Earth don't exert a force. They
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just make time pass more slowly nearby them. This creates a gradient in the flow of time, which bends space-time paths. Gravity is just time curving into space. Time is more fundamental than gravity. So, got any questions about gravity? Please
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ask in the comments. Thanks for liking and sharing this video. Don't forget to subscribe if you'd like to keep up with us. And until next time, remember it's okay to be a little crazy. Several of you asked about electron orbits in the last
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video. No, electrons do not orbit. An orbital is not an orbit. It's a visual representation of the probabilistic existence of quantum particles. Anyway, thanks for watching.
Topics:gravitytime dilationspace-time curvaturegeneral relativitygravitational time dilationphysicsspace-timeGPSNewtonian gravityquantum particles
