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this post was submitted on 03 Sep 2024
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Today I Learned
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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.
Edit: guys I think you're reading too much into this I wasn't trying to provide a foolproof explanation of how gravity works I was just trying to relate an interesting metaphor to a piece of linguistics.
And I wasn't even right, a quick google search says the term predates our understanding of the universe. Its probably a coincidence.
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 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.
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 find the metaphor frustrating because of that.
https://youtu.be/DYq774z4dws
This video includes a much better representation of what gravity is IMO. The creator had the same issue with people describing gravity with gravity.
Thanks for the deep dive.
It's worth noting that spacetime isn't static. Space "flows" into mass. It's akin to a treadmill, you need to constantly move "upwards" to stay in place.
This is also the reason that uniform gravity, and acceleration are identical. With acceleration, the "ground" is constantly moving upwards into new space, pushing you along. With gravity, space is constantly moving down through the floor, trying to push you into the floor. It's functionally the same thing.
That's a really interesting perspective. I don't think I've ever seen it described that way before, but it's very easy for me to grasp. Do you have any resources I can look into for more information? Does that concept have a name I can look up?
It was the initial description used in my 1st year physics degree course. Not sure if it has an explicit name. We also jumped fairly quickly from there to the maths.
Basically space time can stretch infinitely, and flows towards mass. Anything on that spacetime is drawn along. It's functionally identical to a standard force. Straight lines twist into spacetime spirals (aka orbits etc).
Physics has lots of interesting mental models for different things. Unfortunately, most are flawed, so dont lean on tgem too hard. What actually happens is way beyond what our monkey brains can interpret. The best we can do if follow the maths, and try and fit something to the end result.
Yeah, I'm aware that all or numbers and models are, at best, representative of what is really happening. That's what I love about the limits of our knowledge: there always something more to learn.
I wonder how spacetime around a black hole's ergosphere is represented by the "flow" analogy. Maybe like water swirling around a drain?
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.
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
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.
It would make black holes more interesting if they were tears, anything over x mass just ziiiiippppp
Oh. That's a thought
i'm aboslutely certain it's bunk or science would have been all over that. Feels right tho...
One could argue that's what primrose squares show. In fact I think that's how primrose came up with them
https://m.youtube.com/watch?v=4v9A9hQUcBQ&pp=ygUacHJpbXJvc2Ugc3F1YXJlcyBzcGFjZXRpbWU%3D
That would probably be analogous to false vacuum decay; don't try to make it happen
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