What is the fabric of space-time made up of?

  • #1
Shourya Tripathi
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TL;DR Summary
Since it seems so non intuitive that due to its curvature, the space tends to push us towards that mass. I thought that there could be something that is responsible for that, since how can nothing push something?
Also why can't we apply laws of gravity to the quantum world? Can gravitational forces affect the subatomic particles such as protons and neutrons.
 
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  • #2
"Fabric" is a metaphor at best. Spacetime isn't made of anything as far as we're aware. The curvature is purely geometric.

We can apply gravity to quantum objects. What we don't understand is how to describe gravitational fields generated by objects for which quantum effects are significant.
 
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  • #3
Shourya Tripathi said:
Can gravitational forces affect the subatomic particles such as protons and neutrons.
We know experimentally that the Newtionian gravitational potential acts just like any other potential in the Hamiltonian. So in that sense, yes, we know that gravity affects quantum particles.
 
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  • #4
Regarding the title, "What is the fabric of space-time made up of?" -- Suppose we ignore all but one dimension of space. What is the answer to the question: "What is an inch made of?"
It is simply a geometry with units of measure. It is not made of anything physical.
Shourya Tripathi said:
Also why can't we apply laws of gravity to the quantum world? Can gravitational forces affect the subatomic particles such as protons and neutrons.
Are you asking about gravitational forces between subatomic particles? If so, it is worth remembering how weak the gravitational force is. It is about ##10^{38}## times weaker than the strong force. Even if there was a theory, I wonder if it could be detected by any experiment.
 
  • #5
Shourya Tripathi said:
TL;DR Summary: Since it seems so non intuitive that due to its curvature, the space tends to push us towards that mass. I thought that there could be something that is responsible for that, since how can nothing push something?
Search this forum for the video made by our own member @A.T. - the one that gives the curved spacetime explanation of a falling apple.
 
  • #6
Shourya Tripathi said:
TL;DR Summary: Since it seems so non intuitive that due to its curvature, the space tends to push us towards that mass. I thought that there could be something that is responsible for that, since how can nothing push something?

Also why can't we apply laws of gravity to the quantum world? Can gravitational forces affect the subatomic particles such as protons and neutrons.
There's no "pushing" involved, objects just follow geodesic paths (the curved space analog of straight lines in flat space).

Also, it has been experimentally established that subatomic particles are indeed affected by gravity, in quite a few experiments. Even antimatter is now known to be affected in the same way as matter. All of this is completely in accord with the predictions of general relativity.
 
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  • #7
ersmith said:
Even antimatter is now known to be affected in the same way as matter.
Oh, I didn’t know that experiment had finally been done. Do you have a reference or a scientist name?
 
  • #8
Shourya Tripathi said:
TL;DR Summary: Since it seems so non intuitive that due to its curvature, the space tends to push us towards that mass. I thought that there could be something that is responsible for that, since how can nothing push something?
May I suggest the following paragraph from the Gravitation by Misner, Thorne, and Wheeler:

1712745257320.png
 
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  • #9
Dale said:
Oh, I didn’t know that experiment had finally been done. Do you have a reference or a scientist name?
https://www.theguardian.com/science/2023/sep/27/scientists-find-antimatter-is-subject-to-gravity

The study, by scientists at Cern, showed conclusively that gravity pulls antihydrogen downwards and that, at least for antimatter, antigravity does not exist.
The gravitational acceleration was found to be within 25% of normal gravity, meaning that it could be identical to the gravitational force experienced by ordinary matter – or at least, similar.

“It has taken us 30 years to learn how to make this anti-atom, to hold on to it, and to control it well enough that we could actually drop it in a way that it would be sensitive to the force of gravity,” said Hangst. “The next step is to measure the acceleration as precisely as we can.”
 
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  • #10
The OP hasn't been back, so I am not sure there's a sense of immediacy here. AFAIK, the fabric of space-time is made of the same stuff yoha pants are made of. When the universe was young, everything was smooth and continuous, but now that the universe is older, things are wrinklier and lumpier.
 
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