Re: Mossbauer effect and retarded interactions

Igor Khavkine wrote:
> Eugene Stefanovich wrote:
>
>>In the Mossbauer effect a radioactive nucleus in the crystal
>>lattice emits a gamma quantum and the recoil is felt instantaneously
>>by the entire crystal. Do you smell any controversy between this
>>fact and the retarded propagation of interactions required by
>>the special theory of relativity?
>
>
> No, no controversy. Your assertion is incorrect. Disturbances in a
> solid propagate with the speed of sound. For metals, the speed of sound
> is on the order of km/s.

Most often this is true, but not always. The Mossbauer effect is an
exception, that's what makes it so delicious.

In the Mossbauer effect, a radioactive nucleus in the crystal lattice
emits a photon. Normally, such an emmission should be
accompanied by recoil: the nucleus jerks back causing creation of the
phonon (sound) wave propagating outside in all directions.

That's not what happens in rare cases when the Mossbauer effect
works. In these cases, the emitted photon gets coupled to the
so-called "zero-phonon" vibrational mode of the crystal. This is
simply the mode in which all atoms in the crystal move together
in one direction. No lattice vibrations (phonons) are created.
In these cases the recoil momentum is spread evenly (and
instantaneously) between all atoms in the crystal lattice.
Moreover, there is no reduction of the photon's energy due to the
recoil effect. The photon can be absorbed (in resonance) by
similar nucleus in another crystal. The possibility of the resonance
absorption is what makes the Mossbauer effect so valuable in
experimental studies.

I suggest to look at another property of the Mossbauer effect.
Excitation of the zero-phonon mode means that the crystal
behaves as an absolutely rigid body: the recoil momentum
is transferred instantaneously to all parts of the crystal.
This is expressly forbidden by the special relativity.
This is exactly what RQD would predict.

Eugene.

.