So, according to Einstein's theory of general relativity, gravity is not a force instead it is a consequence of objects with mass deforming spacetime, right? And so, according to him, there is no difference between standing on a platform accelerating upwards at 9.81 m/s^2 and standing on Earth, right? But, there is a difference. At least, I think it's a valid difference. If you drop two apples from a high altitude on Earth, not only will they accelerate downwards at 9.81m/s^2 but they will also slightly move towards each other because the Earth is a sphere and gravity acts radially inwards pulling the two apples closer to each other. But if you drop the apples from the same height above the accelerating platform, the apples will only appear to accelerate downwards at 9.81 m/s^2 but will not move towards each other like they would on Earth. Why is this true? Is this even a valid difference? If it isn't, why isn't it?
Answer
The equivalence principle applies only for a very small size lab, where it is not possible to make the parallel vs radial distinction you mentioned. Small size indicates, it is local.
More over, there are other ways to distinguish between the two, if the size of the lab is big enough. One example - gravity changes with height and the acceleration inside an accelerating lab would not. And that would enable the lab to use time dilation for the distinction.
No comments:
Post a Comment