If it works exactly like a ball that is placed on top of a cloth, doesn’t the celestial bodies that is rotating around the ball will eventually get sucked into the center?
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That analogy is OK for getting a very general idea of how gravity can be viewed geometrically, but it’s a very oversimplified picture. The biggest flaw is that it makes it seem as if the “warping” is all in space, but that’s simply not the case. See, in general relativity, (Einstein’s model of gravity, which is the best model of gravity we currently have), space and time aren’t independent entities, but rather different components of one thing, which we uncreatively call “spacetime”. So, in the simple fabric analogy, the fabric represents not *space* but *spacetime*. And, here’s the key point, except in very extreme cases like with black hopes, almost all the “warping” of spacetime from massive objects happens not to the space components of spacetime, but to the time component. So, objects even as massive as planets have very little affect on the *space* surrounding them — instead, the gravitational affect they have on nearby objects is mostly an effect on those objects’ *time* trajectories.
This video does a really good job of breaking this all down and giving an intuitive and *visual* understanding. It’s one of the best ELI5-type explanations I’ve seen on any topic precisely because of how visual it makes things. In actually specifically starts with the simple ball on fabric picture, explains the problems with it, and then, piece-by-piece, fixes the problems and ultimately ends up with something much more accurate and yet still as intuitive as possible. I came across it a couple years ago and it really stuck with me. https://youtu.be/wrwgIjBUYVc
That analogy is OK for getting a very general idea of how gravity can be viewed geometrically, but it’s a very oversimplified picture. The biggest flaw is that it makes it seem as if the “warping” is all in space, but that’s simply not the case. See, in general relativity, (Einstein’s model of gravity, which is the best model of gravity we currently have), space and time aren’t independent entities, but rather different components of one thing, which we uncreatively call “spacetime”. So, in the simple fabric analogy, the fabric represents not *space* but *spacetime*. And, here’s the key point, except in very extreme cases like with black hopes, almost all the “warping” of spacetime from massive objects happens not to the space components of spacetime, but to the time component. So, objects even as massive as planets have very little affect on the *space* surrounding them — instead, the gravitational affect they have on nearby objects is mostly an effect on those objects’ *time* trajectories.
This video does a really good job of breaking this all down and giving an intuitive and *visual* understanding. It’s one of the best ELI5-type explanations I’ve seen on any topic precisely because of how visual it makes things. In actually specifically starts with the simple ball on fabric picture, explains the problems with it, and then, piece-by-piece, fixes the problems and ultimately ends up with something much more accurate and yet still as intuitive as possible. I came across it a couple years ago and it really stuck with me. https://youtu.be/wrwgIjBUYVc
No. I’m sorry for so many conflicting answers on here. In your analogy, you’re referring to “the shape of spacetime”.
So the “shape” of spacetime is like a cloth wrapped around a ball. It is also just the surface of a ball. But the surface of the ball contains our entire 3d universe There isn’t any middle for anything to fall into. There is nothing above or below the surface of the ball. Moreover, that nothing above and below the surface of the ball isn’t “nothing” like space is a vacuum, it’s just not.
To explain a different way, the shape of spacetime is “the surface of a sphere” and it isn’t “a sphere”.
It’s really strange to think of the universe this way because it doesn’t make sense to or 3d minds. If you think it is strange or weird or didn’t make any sense, then you’re on the right track.
No. I’m sorry for so many conflicting answers on here. In your analogy, you’re referring to “the shape of spacetime”.
So the “shape” of spacetime is like a cloth wrapped around a ball. It is also just the surface of a ball. But the surface of the ball contains our entire 3d universe There isn’t any middle for anything to fall into. There is nothing above or below the surface of the ball. Moreover, that nothing above and below the surface of the ball isn’t “nothing” like space is a vacuum, it’s just not.
To explain a different way, the shape of spacetime is “the surface of a sphere” and it isn’t “a sphere”.
It’s really strange to think of the universe this way because it doesn’t make sense to or 3d minds. If you think it is strange or weird or didn’t make any sense, then you’re on the right track.
No. I’m sorry for so many conflicting answers on here. In your analogy, you’re referring to “the shape of spacetime”.
So the “shape” of spacetime is like a cloth wrapped around a ball. It is also just the surface of a ball. But the surface of the ball contains our entire 3d universe There isn’t any middle for anything to fall into. There is nothing above or below the surface of the ball. Moreover, that nothing above and below the surface of the ball isn’t “nothing” like space is a vacuum, it’s just not.
To explain a different way, the shape of spacetime is “the surface of a sphere” and it isn’t “a sphere”.
It’s really strange to think of the universe this way because it doesn’t make sense to or 3d minds. If you think it is strange or weird or didn’t make any sense, then you’re on the right track.
The ball-and-cloth analogy is a bit misleading since, in that analogy, the ball is making a dent in the cloth because it is pushing down on it due to gravity. But the analogy is supposed to explain how gravity works in the first place, so it ends up being circular (and so the short answer to your question is: it does not work exactly like that).
The point the analogy tries to convey is that gravity, in Einstein’s theory of General Relativity, can be understood as “bending spacetime”. So what does that mean? Well, recall Newton’s first law: objects move in a straight line unless a force acts upon them. In classical mechanics, we understand gravity as exerting such a force, and this explains e.g. why planets orbit stars: the star exerts a force on the planets that causes them to follow a curved trajectory rather than a straight one. In Einstein’s view, gravity is instead better understood as locally changing the definition of “straight”. So, planets orbiting a star don’t experience any force, and they keep moving in a straight line, but that line is warped by gravity so that it goes around in a circle around the star.
(If it helps, think of taking a piece of graphing paper and rolling it up into a cylinder so that the ends of the graphing grid meet. Now imagine an ant walking along the grid lines (it helps if you also think about the ant as being two-dimensional). From the ant’s perspective, the lines seem to be straight. And yet, if it follows one of the lines that wraps around the cylinder, then it ends up back where it stared.)
If that (i.e. a force vs. bending of spacetime) seems like splitting hairs or arguing semantics, that’s because this different way of thinking doesn’t really make a difference for many day-to-day situations or basic physics problems, and so often Newton’s theories work just as well and are easier to understand intuitively. But Newton’s theory of gravity can’t explain why, for instance, light is affected by gravity, seeing as light consists of photons and photons have no mass. In Newton’s theory of gravity, you gotta have mass in order to experience gravitational forces – it says so right in his formulas. In Einstein’s theory, you don’t, because spacetime around you is warped and you are moving in spacetime, and therefore a straight line becomes a curved one whether you have mass or not.
As for your final question: again the analogy breaks down here and for the same reason that I said at the start, as it is trying to explain gravity with an analogy that itself invokes gravity, which messes with your intuition for how things will play out. Just think of the orbiting object as following a straight line that happens to go in a circle around the mass it orbits. In an idealized situation, this means the object will stay in orbit forever. In practice, there are various mechanisms that cause [orbital decay](https://en.wikipedia.org/wiki/Orbital_decay), and so eventually orbiting objects will fall towards the mass they orbit.
The ball-and-cloth analogy is a bit misleading since, in that analogy, the ball is making a dent in the cloth because it is pushing down on it due to gravity. But the analogy is supposed to explain how gravity works in the first place, so it ends up being circular (and so the short answer to your question is: it does not work exactly like that).
The point the analogy tries to convey is that gravity, in Einstein’s theory of General Relativity, can be understood as “bending spacetime”. So what does that mean? Well, recall Newton’s first law: objects move in a straight line unless a force acts upon them. In classical mechanics, we understand gravity as exerting such a force, and this explains e.g. why planets orbit stars: the star exerts a force on the planets that causes them to follow a curved trajectory rather than a straight one. In Einstein’s view, gravity is instead better understood as locally changing the definition of “straight”. So, planets orbiting a star don’t experience any force, and they keep moving in a straight line, but that line is warped by gravity so that it goes around in a circle around the star.
(If it helps, think of taking a piece of graphing paper and rolling it up into a cylinder so that the ends of the graphing grid meet. Now imagine an ant walking along the grid lines (it helps if you also think about the ant as being two-dimensional). From the ant’s perspective, the lines seem to be straight. And yet, if it follows one of the lines that wraps around the cylinder, then it ends up back where it stared.)
If that (i.e. a force vs. bending of spacetime) seems like splitting hairs or arguing semantics, that’s because this different way of thinking doesn’t really make a difference for many day-to-day situations or basic physics problems, and so often Newton’s theories work just as well and are easier to understand intuitively. But Newton’s theory of gravity can’t explain why, for instance, light is affected by gravity, seeing as light consists of photons and photons have no mass. In Newton’s theory of gravity, you gotta have mass in order to experience gravitational forces – it says so right in his formulas. In Einstein’s theory, you don’t, because spacetime around you is warped and you are moving in spacetime, and therefore a straight line becomes a curved one whether you have mass or not.
As for your final question: again the analogy breaks down here and for the same reason that I said at the start, as it is trying to explain gravity with an analogy that itself invokes gravity, which messes with your intuition for how things will play out. Just think of the orbiting object as following a straight line that happens to go in a circle around the mass it orbits. In an idealized situation, this means the object will stay in orbit forever. In practice, there are various mechanisms that cause [orbital decay](https://en.wikipedia.org/wiki/Orbital_decay), and so eventually orbiting objects will fall towards the mass they orbit.
The ball-and-cloth analogy is a bit misleading since, in that analogy, the ball is making a dent in the cloth because it is pushing down on it due to gravity. But the analogy is supposed to explain how gravity works in the first place, so it ends up being circular (and so the short answer to your question is: it does not work exactly like that).
The point the analogy tries to convey is that gravity, in Einstein’s theory of General Relativity, can be understood as “bending spacetime”. So what does that mean? Well, recall Newton’s first law: objects move in a straight line unless a force acts upon them. In classical mechanics, we understand gravity as exerting such a force, and this explains e.g. why planets orbit stars: the star exerts a force on the planets that causes them to follow a curved trajectory rather than a straight one. In Einstein’s view, gravity is instead better understood as locally changing the definition of “straight”. So, planets orbiting a star don’t experience any force, and they keep moving in a straight line, but that line is warped by gravity so that it goes around in a circle around the star.
(If it helps, think of taking a piece of graphing paper and rolling it up into a cylinder so that the ends of the graphing grid meet. Now imagine an ant walking along the grid lines (it helps if you also think about the ant as being two-dimensional). From the ant’s perspective, the lines seem to be straight. And yet, if it follows one of the lines that wraps around the cylinder, then it ends up back where it stared.)
If that (i.e. a force vs. bending of spacetime) seems like splitting hairs or arguing semantics, that’s because this different way of thinking doesn’t really make a difference for many day-to-day situations or basic physics problems, and so often Newton’s theories work just as well and are easier to understand intuitively. But Newton’s theory of gravity can’t explain why, for instance, light is affected by gravity, seeing as light consists of photons and photons have no mass. In Newton’s theory of gravity, you gotta have mass in order to experience gravitational forces – it says so right in his formulas. In Einstein’s theory, you don’t, because spacetime around you is warped and you are moving in spacetime, and therefore a straight line becomes a curved one whether you have mass or not.
As for your final question: again the analogy breaks down here and for the same reason that I said at the start, as it is trying to explain gravity with an analogy that itself invokes gravity, which messes with your intuition for how things will play out. Just think of the orbiting object as following a straight line that happens to go in a circle around the mass it orbits. In an idealized situation, this means the object will stay in orbit forever. In practice, there are various mechanisms that cause [orbital decay](https://en.wikipedia.org/wiki/Orbital_decay), and so eventually orbiting objects will fall towards the mass they orbit.
The fabric of space is often using a different definition of fabric which is more like composition of or nature of. And it draws on metaphors that are apt, like the elastic nature of space, but no matter how many dimensions you live in, you can’t reach out and touch the fabric of space. And the ball on a cloth demonstration I find really lacking where VSauce excels which is what causes the ball to curve. Most people, the first time they see it, don’t question it because they know the ball will curve. But the issue is, Earth’s gravity is the thing causing the ball to curve. Not the larger mass you use for the demonstration. So it uses gravity to explain gravity, typically being a no-no.
What’s really happening is the ball is travelling in a straight line from it’s perspective. If you walk straight north anywhere on Earth, you will feel like you’re walking a straight line, you won’t feel any force pushing you side to side, you won’t experience any acceleration (except down due to gravity). However, if you and your friend start 10 miles apart at the equator, both walking north, your initial paths are parallel. Parallel lines in euclidean, flat space should never meet. Yet you both meet at the north pole. The Earth is not flat, therefore, parallel lines will bend relative to an outside observer, just like the ball on the sheet curves from your perspective as an outside observer. But from your perspective walking on Earth and the ball’s perspective, floating through “space” the path you take is perfectly straight, you feel no acceleration or force. You feel weightless. And objects in motion tend to stay in that same motion unless acted on by an outside force.
The fabric of space is often using a different definition of fabric which is more like composition of or nature of. And it draws on metaphors that are apt, like the elastic nature of space, but no matter how many dimensions you live in, you can’t reach out and touch the fabric of space. And the ball on a cloth demonstration I find really lacking where VSauce excels which is what causes the ball to curve. Most people, the first time they see it, don’t question it because they know the ball will curve. But the issue is, Earth’s gravity is the thing causing the ball to curve. Not the larger mass you use for the demonstration. So it uses gravity to explain gravity, typically being a no-no.
What’s really happening is the ball is travelling in a straight line from it’s perspective. If you walk straight north anywhere on Earth, you will feel like you’re walking a straight line, you won’t feel any force pushing you side to side, you won’t experience any acceleration (except down due to gravity). However, if you and your friend start 10 miles apart at the equator, both walking north, your initial paths are parallel. Parallel lines in euclidean, flat space should never meet. Yet you both meet at the north pole. The Earth is not flat, therefore, parallel lines will bend relative to an outside observer, just like the ball on the sheet curves from your perspective as an outside observer. But from your perspective walking on Earth and the ball’s perspective, floating through “space” the path you take is perfectly straight, you feel no acceleration or force. You feel weightless. And objects in motion tend to stay in that same motion unless acted on by an outside force.
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