# The Naked Scientists Forum

### Author Topic: The equivalence principle and experiments concerning it?  (Read 897 times)

#### Darawan

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##### The equivalence principle and experiments concerning it?
« on: 06/08/2015 13:45:59 »
Hi!

Imagine that we are in a rocket accelerating with some magnitude a1 = dx2/d2y, also imagine that we have a stationary rocket ship in close proximity to ours, stationary relative to our reference frame, we will notice the stationary ship to measure time (If we have a clock onboard that ship which is visible to ours) at some time t0.

Now the question leads to this, the time measured on our ship will be moving relative to the stationary ship, but the equivalence principle tells us that if we accelerate at some magnitude we can't tell it apart from gravity, but gravity bends spacetime in such a manner that time will be slowed relative to some reference frame, but if we compare the two clocks on these ships, ours and the stationary one, will our measurement account for the bending of spacetime due to the acceleration?

I live in Sweden so my English might not be perfect, excuses are made.

Now debate.
« Last Edit: 06/08/2015 13:47:48 by Darawan »

#### PmbPhy

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##### Re: The equivalence principle and experiments concerning it?
« Reply #1 on: 06/08/2015 21:35:55 »
Quote from: Darawan
Now the question leads to this, the time measured on our ship will be moving relative to the stationary ship, but the equivalence principle tells us that if we accelerate at some magnitude we can't tell it apart from gravity, but gravity bends spacetime...
A common misconception in general relativity is that Einstein demonstrated that gravity is a curvature in spacetime. That's totally wrong. Einstein never said or even implied it. Max Von Laue sent Einstein a copy of the book he wrote on relativity for him to look over. In that book von Laue wrote that gravity is a curvature in spacetime. When Einstein sent back his comments on the book back to him he wrote
Quote from: Einstein
... what characterizes the existence of a gravitational field from the empirical standpoint is the non-vanishing of the components of [the affine connection], not the vanishing of the [components of the Riemann tensor]. If one does not think in such intuitive (anschaulich) ways, one cannot grasp why something like curvature should have anything at all to do with gravitation. In any case, no rational person would have hit upon anything otherwise. The key to the understanding of the equality
The components of the affine connection describe how the particle is accelerating in spacetime. The components of the Riemann tensor describes how two particles accelerate relative to each other which when its non-zero the spacetime is curved. Important note: If the spacetime curvature is flat then you can't change to any set of coordinates in which the spacetime is curved.