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jeremyfiennes
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What is the mathematical formula for the time dilation (clock-slowing factor) for a clock in a gravitational field g, equivalent to the Lorentz factor γ for a clock traveling at a relative speed v?
There's no way to answer that question without more information.Not quite with you. I have a clock A in outer space where there is no gravity. And one, B, stationary in a gravitational field g. By what factor does B run slower than A?
It depends on the gravitational potential (usually denoted ##\phi##), not the gravitational acceleration (usually denoted ##g##). So your question has no answer as asked.Not quite with you. I have a clock A in outer space where there is no gravity. And one, B, stationary in a gravitational field g. By what factor does B run slower than A?
Indeed. Start with a light pulse of frequency f at one height and send it upwards, convert it to a mass, drop the mass, and convert it back into energy. The light needs to have lost the same amount of energy on the upwards leg as the mass gained on the downwards leg, or else we have an energy-creating device here. Thus gravitational redshift, which is the same as gravitational time dilation.You actually do not need the general expression to derive the approximations. Just using the equivalence principle will work perfectly fine.
You can also just take the exact Rindler case, and note that by local Lorentz character of any GR manifold, that for a near stationary case in GR, it must be equivalent to first order to the Rindler case in SR.Indeed. Start with a light pulse of frequency f at one height and send it upwards, convert it to a mass, drop the mass, and convert it back into energy. The light needs to have lost the same amount of energy on the upwards leg as the mass gained on the downwards leg, or else we have an energy-creating device here. Thus gravitational redshift, which is the same as gravitational time dilation.
Ok. Thanks. Nice clear reply. I've got it now. Not as simple as I had thought.There's no way to answer that question without more information.
For example, if you compare a clock sitting on the surface of the Earth to a clock sitting on the surface of a world with twice the radius and 4 times the mass, they will run at different rates (with the on on the larger world running slower) even though both clocks are at 1g.