Quote:
Originally Posted by Archy
I asked how can the "redshift" of a single photon be measured
Renormalised replied "...Very easily, with a photomultiplier tube and in exactly the same way as you measure a redshifted spectrum. You look at (or determine via theory) what the original wavelength/frequency of the photon was when it left the source and compare that with what you measured at the photomultiplier."
Bojan replied inter alia
Bojan's reply that the redshift cannot be measured contradicts Renormalised. I agree with Bojan the redshift of a single photon can't be determined. Others in the thread were unwilling or unable to answer the question. When I pressed for an answer gave wrong, irrelevant or evasive replies and cast aspersions on my motives. Gentlemen, whether you answer questions or not is your prerogative: but what you have indulged in just wastes space.
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No, you chose one reply which was not based on anything to do with your initial and subsequent inquiries. Bojan stated that because he had no clue as to what the source of the original photon was, he couldn't measure anything other than its energy as registered on his equipment.
So, all you are trying to do here is pit one person's answer against another and try to make something of it.
My initial reply to your question was correct and is as correct as Bojan's.
If you know the source of your photon, it's a simple matter of working backwards with the observation and using the appropriate redshift equations to give a redshift for that photon. And all you need is the photomulitplier tube (which will do the job, if you know how to convert the measured intensity to wavelength) to find the wavelength of the photon at detection.
Exactly the same way they read a redshifted spectrum.
If you can't understand that, then you shouldn't have asked the question in the first place.
Or, are you just out to cause arguments.