Can a Photon's Energy Approach Zero?

AI Thread Summary
The discussion centers on whether a photon can reach a theoretical minimum energy value as its wavelength approaches infinity. It explores the implications of the universe's expansion and redshift on photon energy, particularly in relation to cosmic microwave background radiation. One participant argues that there is no lower bound to photon energy, although practical factors like the presence of free electrons in the universe complicate their behavior. The conversation also touches on calculating the energy of a photon with an extremely long wavelength, emphasizing the complexities involved. Ultimately, the topic raises questions about the nature of photons in an expanding universe.
jonmtkisco
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Is there any theoretical minimum energy value for a photon of near-infinite wavelength?

As the expansion of the universe continues redshifting the photons of free radiation (e.g., the remnants of the CMB), is it theoretically possible that the energy of individual photons could decrease to infinitely close to zero, or is there some sort of minimum cutoff value?

Jon
 
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No, there is no lower bound.
 
Except, of course, that the real universe we live in has lots of free electrons (along with protons), albeit rather far apart (on average).

This means photons will have an interesting existence (shall we say) if their frequency is below the plasma frequency of the IGM ...
 
Thanks.

Jon
 
Calculate the energy of a photon with a wavelength of about 13.7 billion light years.
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
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