Talk:Pound-Rebka experiment

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I've lost an hours work so this is the brief version. Apart from the discussion, at the end, of importance, all comments are on one small paragraph:-

"The energy associated with gravitational redshift over a distance of 22.5 meters is very small. The fractional change in energy is given by δE/E, is equal to gh/c2=2.5x10-15. Therefore high energy (small wavelength) photons are required to detect such minute differences. (Think of wave length as the distance between marks on a ruler). The 14 keV gamma rays emitted by iron-57 when it transitions to its base state proved to be sufficient for this experiment."

0. The point that it is the change in height (distance from the centre of the Earth) that provides the required change in gravitational potential is not brought out.

1. Variables not explained.

2. Algebraic convention used is not explained (c2 [=c squared?])

2b. best to leave a space before and after the equals sign

3. Units not given for the equation gh/c2 = 2.5x10-15. If these are MKS units, should it not say so?

4. photon and wavelength sentences confused, apparently wrong and a disproportionate level of explanation - given the relative simplicity of linear measurement - compared to the rest of the article.

5. The particular state transition of iron57 would benefit from a little more explanation, although I suppose it can be taken as read and is not pivotal to the main thrust. What was the start state? (Or if the resultant state was not iron57, say so, and what it was).

6. I dare not look back now for fear of losing this text this time, but is the accuracy given? This is a strong point I believe.

7. Cannot teX or something like it be used to make the algebra and number clearer? (e.g. 2.5x10-15). If so, the TeX would instead be something like, if left as inline, $2.5 * 10^{-15}$. (And c2 if meaning squared, would be, if left as inline, $c^2$).

8. Bearing in mind the corrections required still for points 1, 2, 3 and 5 above, I suggest as an interim measure, the following for this paragraph:-

The energy associated with gravitational redshift over a vertical (i.e. Earth radial) distance of 22.5 meters at the surface of the Earth is very small. The fractional change in energy (δE/E), is equal to gh/c2 = 2.5x10-15 [MKS units?]. Where g=?, h=?(height, not e.g. Planck's constant), c=?. The 14 keV gamma rays emitted by iron-57 on a transition to its base state proved to be sufficient for this experiment.

Importance: Agreed, the importance to the Theory of Physics of the experiment may not be as great as the Michelson- Morley experiment for example, provided one is prepared to accept other, indirect evidence of the validity of this outcome of the General Theory of Relativity. But should we be prepared to do that? No I suggest. This was direct, Earth-based, evidence and therefore, even though 'just an experiment'!, it ranks highly in my view, not least because of its ingenuity, which I suspect does not fully come out in the article yet. We should not fall into the trap of denigrating temporal activities relative to THEORY that changes our mind-set just because they have 'merely validated' our understanding rather than changed it forever.

Now for those all-important (I hope) tildes: 1seek2find (talk) 00:42, 10 December 2007 (UTC)