"Bastian" wrote in message
m...
My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field.

Actually it will radiate. When there is a relative acceleration of charge
and detector/observer, radation will be detected.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less.

That's the radiation reaction that you're refering to (aka self force).
However for a constant acceleration there is no radiation reaction.

For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.

The detection of the radiation is observer dependant.


So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this

This has been studied in detail in the physics literature. You can see a
summary from these various papers here

http://www.geocities.com/physics_wor...ing_charge.htm

Referances are included.

Pmb