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Does the curvature of spacetime theory assume gravity?
Forgive my naivete as I am not schooled in Physics or Mathematics.
I was watching NOVA's "The Fabric of the Cosmos" last night. The subject was basically spacetime and how our conception of it moved from the Newtonian description to the Einsteinian. i.e. That spacetime is like a fabric stretched across the universe and that large objects like planets and stars create a depression in the spacetime fabric and the orbiting of satellites is really just the satellite getting caught in the "swirl" of the depression.
The narrator used a pool table surface as an example of the fabric of spacetime and then with some CGI he dropped a bowling ball on it which caused a depression and then shot a pool ball near it which caused the pool ball to get caught in the swirl.
I found myself pondering the following though:
I find it really hard to believe that there is a "This Side Up" arrow for spacetime. But if there is, what causes it? You can see a diagram of what I'm trying to describe in this Gravity Probe B article. I understand that spacetime can be twisted so I'm guessing reality is more like the depressions are at all orientations through the universe (sorry, I lack the language to describe this). But I still wonder: Why is the depression one orientation and not the other?
What is the effect of the other side of the depression? i.e. If the swirl on the other side pulls objects in, does the other side of the depression repulse objects?
Warning: any answers that include mathematics will be lost on me.
Any suggestions for further layperson reading on this fascinating subject welcome.
Thanks!
