--- On Fri, 7/10/09, Henry Cobb <henry.cobb@...> wrote:
On Fri, Jul 10, 2009 at 12:18 AM, Erik Max Francis<max@alcyone. com> wrote:

>>After all, you hardly need general relativity to explain why being able
>>to pull a body out of a gravitational field doesn't violation
>>conservation of energy; it's because you're supplying the energy by
>>pulling it out, doing work against the force of gravity.

>Take a certain amount of energy and create an electron-positron
>pair in deep space.

>Then move this pair to the surface of the moon and turn them
>back into a pair of gamma rays and measure them locally and
>you will see the same amount of energy as before.

Only if you absorbed the extra energy generated by lowering
the electron and positron into the gravity well. On the
other hand, if you just let them freefall to the surface
of the moon, then their extra kinetic energy will be
added to the resulting gamma rays.

>But if you send these gamma rays out into deep space you
>will find there that you don't have quite enough energy
>to remake the electron-positron pair because of the
>gravitational red shift than manifests as a difference
>in time rates.

The gamma rays generated by the freefalling pair will
have just enough extra energy to compensate for the
red shift.

Isaac Kuo mechdan@...