# Physics

By michemix

@michemix (22)

Mexico

December 21, 2006 11:15pm CST

Einstein's principle of equivalence says that you can't tell the difference between being in a stationary elevator in a gravitational field and an accelerating elevator in free space. However, if the stationary elevator is in a field that has the magnitude of that of a black hole, your temperature will increase due to Hawking radiation. If you are accelerating in free space (at a value equal to g of the black hole) your temperature will increase according to the Davies-Unruh effect. However, the Hawking formula predicts a different temperature to the Davies-Unruh formula. So, we can imagine a thought experiment where we can measure this difference, and hence tell if the elevator is accelerating or not. Does this violate Einstein's principle of equivalence? Explain.

1 response

@AJMSmith (112)

•

12 Feb 07

Einstein's principal is saying that you can not tell the difference between an a force resisting an accelleration (stationary elevator in a gravitational field) and an accellerating elevator in free space. The requirement that you are in free space means that you must be at a great distance from any significant mass (strictly intergalactic distances are not enough). This is of course not a realistic situation. The area of space surrounding a black hole is about as far from free space as anywhere else.