Einstein's general relativity says gravity is spacetime curvature, but what does that mean? Let's take a look at how gravitational time dilation results in a...
They call it the “fabric of reality” because that’s a good metaphor to describe how gravity works. (Or at least I assume that’s where it came from, I could very well be wrong.)
When you stretch a fabric thin, and place something heavy in it, it’s going to sink and stretch the fabric down with it. Then, if you place a smaller object next to the larger one, it’s going to roll around the larger one, gradually moving closer as it goes down the slope created by the larger object.
That might be hard to visualize, so here’s a neat video I found.
If cosmic inflation is correct, probably not. Inflation is our best theory of the beginning of the universe.
According to inflation, spacetime expanded exponentially from an infinitesimal point to many billions of light-years across. As far as we can tell, the universe is expanding again but at a much slower rate, due to dark energy.
Spacetime survived the inflationary period, so it looks like it doesn’t have a “tear” mechanism.
Another way to think of it, is to assume once torn, what is it tearing “into”. If you rip a bit of fabric, you look through to the other side, nothing special. If you tear our 4-dimentional spacetime, what are you looking at when you look “through” the ripped portion? This implies that out 4D spacetime is somehow existing in a higher dimensional reality.
What if it is getting ripped/torn but there’s just more space ‘underneath’ that instantly fills the gaps as they are created? I guess at that point it’s indistinguishable from stretching but it’s interesting to think about
Indeed, it’s a neat way to visualize gravity, but that’s it. It lacks any sort of explanation of why masses appear to be pulled towards one another. (I will point to the other person in this thread saying it “explains gravity with gravity”.) This is why I think the metaphor you mentioned detracts from the original video.
One could be picky and say you’re explaining gravity with gravity. But for the sake of simplicity that’s OK.
I’ve once read an article where someone complained about that and tried to explain it with the actual cause, curvature of space time, like using a model car with glue attached to the wheels. But that was not really intuitive and simple to understand.
I found a video once where the guy built a device to demonstrate curving based on mass, to avoid the gravity simulating gravity problem, but I failed to find it again when searching. It was something he’d bend to show larger mass, and you’d see the effect with the bands along it or something. Even that isn’t accurate, but visualizing 4D can be challenging, especially if you then have to put it in 2D media.
Exactly that one. Thanks, I’m glad I said something. It wasn’t anything new, just a new way to present it, and when he did the warped version and the straight line, I was like, okay, makes sense. Then he returned it to our “viewpoint” on the warped space seeing things straight, and even though it was the same lines, it was amazing to see those paths go precisely where we expect. All because of a warped graph. I think it was more incredulous because it wasn’t some animation, but a physical demonstration.
I think of it as a 2d cross section of the experiment (it’s happening in every direction possible tangent to the ball), which necessarily breaks into a third dimension. In our 3-spatial-dimension reality that’s the best we can do.
Yes, but the smaller object is dragged into the valley formed by a heavier object due to gravity (of the earth), not due to following the curvature of the blanket.
They call it the “fabric of reality” because that’s a good metaphor to describe how gravity works. (Or at least I assume that’s where it came from, I could very well be wrong.)
When you stretch a fabric thin, and place something heavy in it, it’s going to sink and stretch the fabric down with it. Then, if you place a smaller object next to the larger one, it’s going to roll around the larger one, gradually moving closer as it goes down the slope created by the larger object.
That might be hard to visualize, so here’s a neat video I found.
Can spacetime be ripped or torn? Or is the fabric metaphor simply a way of understanding and visualizing it?
If cosmic inflation is correct, probably not. Inflation is our best theory of the beginning of the universe.
According to inflation, spacetime expanded exponentially from an infinitesimal point to many billions of light-years across. As far as we can tell, the universe is expanding again but at a much slower rate, due to dark energy.
Spacetime survived the inflationary period, so it looks like it doesn’t have a “tear” mechanism.
Another way to think of it, is to assume once torn, what is it tearing “into”. If you rip a bit of fabric, you look through to the other side, nothing special. If you tear our 4-dimentional spacetime, what are you looking at when you look “through” the ripped portion? This implies that out 4D spacetime is somehow existing in a higher dimensional reality.
What if it is getting ripped/torn but there’s just more space ‘underneath’ that instantly fills the gaps as they are created? I guess at that point it’s indistinguishable from stretching but it’s interesting to think about
I think that explains the “how” more than the “why”.
What I meant was that’s “why” we use the term “fabric of reality”— because of “how” gravity works.
Indeed, it’s a neat way to visualize gravity, but that’s it. It lacks any sort of explanation of why masses appear to be pulled towards one another. (I will point to the other person in this thread saying it “explains gravity with gravity”.) This is why I think the metaphor you mentioned detracts from the original video.
One could be picky and say you’re explaining gravity with gravity. But for the sake of simplicity that’s OK.
I’ve once read an article where someone complained about that and tried to explain it with the actual cause, curvature of space time, like using a model car with glue attached to the wheels. But that was not really intuitive and simple to understand.
I find the metaphor frustrating because of that.
I found a video once where the guy built a device to demonstrate curving based on mass, to avoid the gravity simulating gravity problem, but I failed to find it again when searching. It was something he’d bend to show larger mass, and you’d see the effect with the bands along it or something. Even that isn’t accurate, but visualizing 4D can be challenging, especially if you then have to put it in 2D media.
Here, probably this one. The only good explanation I’ve seen.
Exactly that one. Thanks, I’m glad I said something. It wasn’t anything new, just a new way to present it, and when he did the warped version and the straight line, I was like, okay, makes sense. Then he returned it to our “viewpoint” on the warped space seeing things straight, and even though it was the same lines, it was amazing to see those paths go precisely where we expect. All because of a warped graph. I think it was more incredulous because it wasn’t some animation, but a physical demonstration.
I think of it as a 2d cross section of the experiment (it’s happening in every direction possible tangent to the ball), which necessarily breaks into a third dimension. In our 3-spatial-dimension reality that’s the best we can do.
Yes, but the smaller object is dragged into the valley formed by a heavier object due to gravity (of the earth), not due to following the curvature of the blanket.
Or, if you prefer, here is “Einstein” explaining it.
https://www.youtube.com/watch?v=duW_CPDrUpE
Not gonna lie I really thought it was gonna be Neil DeGrasse Tyson