# Is spacetime really bending?

by mdl
Tags: bending, gravity, spacetime
P: 4,251
 Quote by PatrickPowers Hmmm. I agree that ALL physics theories are just mental concepts. But everyone seems to find they have a useful relation with the real world. If you want to use General Relativity then you use its concepts and definitions. If you don't want to, fine. But I will mention that if you bend the paper then it affects the motion of grains of sand on the paper, right?
 Quote by mdl IMHO that model is misleading, because you need another external space (where grains could exist, where the observer is, and where you actually can bend a paper).
Yes, grains of sand rolling on a bend paper have nothing to do with General Relativity. This is a better analogy:
http://www.physics.ucla.edu/demoweb/...spacetime.html
http://www.relativitet.se/spacetime1.html
P: 65
Obviously there's some conflict between everyday usages of these words and their mathematical definitions. I agree with the OP about people living on a sheet of paper not being able to tell if it had been rolled or not.

This caught me eye though:
 Quote by mdl That's what I don't understand. Why will it take shorter time? Light (or equivalent pulse) would allways pass the same number of molecules (the same amount of paper) regardless of how the paper is bent.
Please correct me if I'm wrong, but isn't this exactly the kind of thing the curvature of space-time effects? If you have a massive object, space-time curves around it. Think about if you were surveying distances by how long it took you to walk from place to place, moving at a steady pace. Of course since gravity sucks you in, you would get to that massive object much faster than you had expected, based upon how long it took you to get to that same spot when it was empty. Therefore (absent a proper understanding of higher physics) you would have to conclude that somehow the distance between the two spots had shrunk.

So it seems like the curvature would produce results suggesting the distance between the points really had shrunk, even though maybe at first glance no "space" had evaporated?

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