Rolando

I do not quite understand what you are trying to tell. It is true that the question of why the photons are not affected by the geometry on their way makes sense only within alternative (1). The other alternative is not involved here.

If the difference is due to the atoms emitting the photons at a different frequency, there must be a reason for this. In GR, this reason lies in the geometry. Then it does make sense to ask why the photons are not affected by this geometry on their way. As for the alternative, I understand myself that it fails to account for time dilation, (which was absent in Einstein's model of 1911). I agree that one cannot choose both.

In alternative (1), this is described in terms of the atoms emitting the radiation. My particular question concerns this alternative alone. You talk as if it was me who had made these claims. I only retell what Atkins and many others claim.

This is indeed fairly straightforward, but it involves much more than required here, and it does not answer my question.

The equation is identical, and my question really concerns only one of the descriptions, namely that given in the book by Atkins, which I referred to as alternative (1). In this alternative, the phenomenon is explained through the behaviour of atoms that emit radiation of lower frequency the deeper they are located in a potential well, while the frequency of the radiation does not change on its way to a different height. Time is dilated in gravitational wells, and this is an effect of the curvature of space-time. My question was: why is the light itself not affected by this curvature?

I have no problem with the math at the level that this requires. I would have if it would require handling tensors.

I do not speculate. Nor do I challenge accepted theories. I just ask a question that involves no more than the simplest equation for gravitaional time dilation and redshift.

I do have a sufficient understanding of what these two descriptions are about, and the math is not the problem at this level. I do not argue about the maths, and you are right in that I have just to accept what the experts say when it becomes more advanced. I argue about the descriptions. To me, they cannot be simply different views of the same model. One of them, I can see as representative of the model Einstein used in 1911. If it is claimed to be a description of GR, this is severely misleading. The other one is adequate to GR, but it rises my question.

Couldn’t you step down from your high horses, so that we can talk on equal footing? I have no experience in calculations within the frame of GR, of which I have only a superficial knowledge. I cannot see myself whether any advanced equation presented in this thread is commonplace or innovative. I do have many years of experience in teaching the scientific method, which involves the use of models, hypothesis testing, evaluation of theories, etc. to advanced students, whom I encourage to adopt a critical attitude, perhaps only with moderate success. It is more comfortable to just follow with the stream. However, in my experience, most of the reviewers of empirical scientific papers expose a similarly critical attitude as I do. I came to this forum because I noticed deficiencies in both of the ways in which GR is commonly presented to non-specialists, even to physicists whose focus lies somewhere else. Since I am not sufficiently knowledgeable within this field myself, I asked a question that might bring light into this affair. Sure, this identifies me as one of those cranks with a scientific agenda, whom xyzt hates so much. On the other hand, you do not need to tell me what a model is and similar things, because in this area, I feel more competent myself.

By alternative (1), I mean the alternative that I have called so, and which is that presented by Atkins. If you wish to propose a different alternative, please describe it in words as well. Calling it alternative (1) and accusing me for making false claims is just confusing. This is, of course, impossible. It is clear only in the models (alternatives). If you have just two sources, you can't tell for sure which has changed. In the cases you mention, there are lots of additional sources that allow a calibration and also physical reasons that help.

In general, one has to take care that no relevant factor disappears, which can happen if it is not known for sure which the relevant factors are. However, In the present case, the two alternatives (models) under discussion are at least more elaborate than the theory alone. The latter does not tell at all where the effects it predicts arise.

You are right in that models are nearly always used in order to allow a mathematical treatment of a problem. The difference between theoretical physics and most other branches of science lies in that the former is much more theory-centered, so that "model" is almost synonymous with "theory", while in most other sciences "model" is more often closer to "nature". The models are more phenomenological. Think of medical or psychological research, for instance. I do not quite understand your question. The experiments that have been done have been mentioned, and the two alternatives under discussion differ in where the frequency change is assumed to occur. In alternative (1), the frequency is given at the source and remains unchanged on its way to the receiver. In alternative (2), the frequency changes on the way between source and receiver. Alternative (1) agrees with all observations, but gives rise to my question. Alternative (2) is incompatible with time dilation (in the long run). By the way, these "alternatives" can be considered as different "models".

I can assure you that in this respect, theoretical physicists are in minority among scientists.

I do not understand what "trolling" means. I find only "troll" in my English dictionary, but it makes no sense here. However, the remainder of your utterances tells me that this is just another load of the rubbish you need to keep throwing at people ad nauseam. From your previous posting, I got the impression that you might now be ready to contribute to this discourse in a civilized manner. I regret that I was in error. I am aware that this is often so when theoretical physicists talk about a model. But here, it was me who used the word, and I am not a theoretical physicist. For me, a model is a simplified representation of reality that keeps only the aspects that are relevant in the context in question.

Thanks for your effort. Unfortunately, it does not answer my question. I did not ask about how to calculate the effects, and I have told that they have all been observed. Your equations are perfectly in agreement with alternative (1), which gave rise to my question. In order to answer it, it is necessary to talk about the model, not the math. Where do the effects arise in the model or in the real world along the line between source and receiver, including these themselves? By the way, how can it be that you were not aware of the fact that alternative (1) used to be widely tought, (at the level of Atkins' book)? Maybe you can also tell us why alternative (2) has gained popularity in the past 20 years or so? Isn't it clear that it involves a loss of periods, and so is in conflict with time dilation (clock retardation)? How is this conflict resolved?

Well, it is the theory that predicts things, but the two alternatives seem to put restrictions on the theory. Let me skip this. There may be a misunderstanding invlolved here, but I do not think we are in disagreement. There is clear experimental evidence for the existence of a frequency difference and the consequent difference in signal power or photon energy between identical radiation sources at different levels and there is also clear evidence for a difference in the readings of clocks at different levels, which even needs to be taken into consideration in the GPS and in other satelite systems. This means that the problem we discuss is not just an “academic” one. Let me restate my original question with slight modifications. The gravitational redshift is described in the literature mainly in two ways: (1) the phenomenon is explained through the behaviour of atoms that emit radiation of lower frequency (or clocks that run more slowly) the deeper they are located in a potential well, while the frequency of the light (or photons) does not change on its way to a different height. This kind of description is found in basic textbooks, such as “Physics” by Kenneth R. Atkins, of which I possess a version in German. It is illustrated in http://en.wikipedia....tional_redshift [see the colorful illustration there and compare it with Abbildung 25-14 (b), above]. If alternative (2) were true, there would be no time dilation, i.e, clocks closer to an attractive body would not be observed to be slow (in the long run). While alternative (2) is incompatible with GR, alternative (1) seems to me to be incompatible with the idea behind GR as well. According to GR, time is dilated in gravitational wells, and this is an effect of the curvature of space-time. However, if this is so, then why is the light itself not affected by this curvature? If it was affected to the same extent as the atoms, the gravitational frequency shift would be zero, and if it is necessary to assume that light propagates through a different space-time, this is very much in need of a logical explanation. The alternatives (1) and (2) cannot be applied together, since in this case the gravitational frequency shift would turn out to be twice as high as observed and predicted by GR. I think that nothing of essential import has come forward in the discussion. My question remained unanswered. However, a further alternative has been briefly mentioned: (3) The phenomenon might be interpretable as Doppler shift. In this case, there can be no discrepancy between frequency shifts and time dilation. I have not yet read the relevant paper.

The text on the first line is the kind of response that is valuable to me. Thanks for it. The rest is just annoying rubbish.

My rhetorical question was about the contribution of the quoted utterances to the topic under discussion. Not about your definition of a ”crank”. According to my limited knowledge, the internal Schwarzschild solution applies inside the event horizon of black holes. Does it really apply below the surface of the Earth or did you happen to confuse the Earth with a black hole?

Do you really believe that this kind of argumentation is convincing? Especially if it comes from somebody who tells me that I do not understad what I am reading and only afterwards asks me for the text in question? If you wish to tell me where you think that I went wrong in my reasoning, please do so - but without adding rubbish like this.

I do not quite agree. They explicitly worked on the basis of Einstein (1911), which they showed to agree with their result. It reflects wishful thinking to interprete their experiment as test of GR, which merely predicts the same result (if the experiment is performed above ground level, as it was).

To judge from the abstracts, in http://arxiv.org/abs/0808.1081, it is the cosmological redshift, not the gravitational redshift, that is interpreted in terms of a Doppler shift, and http://arxiv.org/abs/0911.3536 disagrees. (I have run across similar discussions previously.) The relativistic modification of the Doppler effect, http://en.m.wikipedi..._Doppler_effect, needs to be considered at high velocities, while the problem under discussion in the present thread arises at very low velocities as well (e.g., the velocity at at which Powel & Rebka needed to move one of their radiation sources to compensate for the gravitational frequency shift). In http://en.m.wikipedia.org/wiki/Redshift, one can read: ”This gravitational redshift result can be derived from the assumptions of special relativity and the equivalence principle; the full theory of general relativity is not required.” While this is correct, it does not hold for cumulative effects, as I said above. The paper by Narlikar http://www.iucaa.ern...1/211A_1994.pdf is most to the point, but it requires some effort to read. Thanks for having drawn my attention to it. This paper by A. Sfarti describes a proposal – not an actually performed experiment, and it is written by an author who shows no awareness of the difference between GR and Newtonian physics. This is clear already in the first clause of the Abstract, which reads ”Einstein predicted a change in the energy of photons in the proximity of a gravitational field, the change being directly proportional to the distance from the gravitational source.” This is true of Einstein (1911), but nowadays everybody associates Einstein in this context with GR (1916), and in GR, it is not true! [in GR, there is a difference in energy but no change.] Actually, Pound and Rebka reasoned similarly. They were not concerned with GR either. They referred only to Einstein (1911). Although Sfarti proposes a mineshaft experiment of the kind I asked for, he does not consider its potential of falsifying one of the theories. [Edited: I am not sure that the predictions differ.] I wanted to be a little funny, but having had a quick look at several papers by Pound & Rebka again, I am left with the impression that they were just disinterested in GR. There is no difference between these, but in Newtonian theory the photon frequency change is not matched by a corresponding difference in elapsed time at the two places. Let me try it: [Edited: I should rather simply say that I cannot.]

It requires counting the periods emitted and received. I do not know whether this is practically feasible. However, there is another, much simpler way to test the alternatives against each other. When I read the paper by Pound & Rebka about their experimental verification of the existence of a gravitational frequency shift, I was somewhat disappointed (I think this was in the past century). These people just went to the close-by tower in their institute without considering that in this stetting Newtonian theory predicts practically the same frequency shift as GR. In Newtonian theory the frequency shift is due to the difference in the gravitational acceleration g between the two levels. In GR, it is instead due to the difference in the gravitational potential φ. Above the surface of the Earth, g is nearly proportional to -φ. This is not so below the surface of the Earth, where φ becomes still more negative as we go down, while g decreases (it has its maximum value close to the surface of the Earth). If these researchers had not been so lazy, they could have done their experiment within a sufficently deep mine instead and so come up with a conclusive test of the theories, i.e., with a falsification of one of them. Has the experiment ever been repeated in such a setting?

I am sorry for havig been too narrow-minded, which may have narrowed your minds as well. The two alternatives are equivalent explanations of frequency shifts (and shifts in power these imply) such as observed by Pound & Rebka. As for cumulative effects, they lead to different predictions. Only alternative (1) predicts a general time dilation. Alternative (2) does not predict clocks further down in a gravitational well to appear to be slow. Instead, it predicts periods of the radiation to be lost on its way up.

While this is true, their theoretical background is different, and only one of them can be appropriate within a given theoretical frame. Given the frame of Newtonian mechanics, photons will lose energy when they move out of a gravtiational field. Their frequency will therefore shift to the red. This is in agreement with alternative (2), and also Einstein treated the question in this way before he presented GR. It is clear that alternative (1) is inappropriate within this frame. In GR, gravitation is basically not a force, but just geometry. If photons on their way out of a gravitational field are not affected by a force, they will not lose any energy. Therefore, alternative (2) is inappropriate within this frame. The observable redshift is, instead, ascribed to gravitational time dilation, which is effective at the source, although it can only be seen by an observer that is higher up in the potential well. This is the background to alternative (1). I am not comfortable with alternative (1) either, since I do not understand how it can be that geometry (space-time curvature) can affect atoms when it fails to affect photons. I noticed a third alternative in a link added by Mordred, 22 January 2015 in the related threed: Gravitational Red Shift Confusion: http://cosmology101.wikidot.com/redshift-and-expansion There, the gravitational redshift is interpreted as a Doppler shift in a curved space-time. I find this reasonable, it might solve my problem, but the account is too short and superficial to be fully intelligible.

It suffices to mention the textbook ”Physics” by Kenneth R. Atkins, which was widely used during the last quarter of the past century. Sorry, I used ”light” as an abbreviation for ”electromagnetic radiation”. If the resonance frequency of the Fe at the first level differs from that at the second level by a factor of [math]\frac{f'}{f}=\sqrt{\frac{1-r_s/r}{1-r_s/r'}}[/math] and the frequency of the radiation also changes by the same factor while it propagates from the first to the second level, there will be no observable change. The radiation will arrive at a frequency that agrees with the resonance frequency of the Fe at the second level.