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If photons are emitted at intervals a, from the top of a tower of height $h$, down to earth, is this formula correct for the intervals b in which they are received at earth? $b=a(1-gh/c^2)$ If so, how does it not lead to a paradox, if say we wait a long time N, then at the top of the tower, N/a photons have been emitted. But a photon is received at earth every b seconds, so N/b>N/a, so eventually more photons have been received then emitted?

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You assume a universal time elapse rate along the tower. That is not true. – Siyuan Ren Jul 1 '12 at 16:08
up vote 2 down vote accepted

Who waits a long time $N$? The observer at the top of the tower or at the bottom of the tower?

After a time $N$ has elapsed at the top of the tower, a shorter time has elapsed at the bottom of the tower, so no paradox.

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