I Can there be some kind of photon emission caused by space expansion?

AI Thread Summary
Photon emission is not caused by the expansion of spacetime, as spacetime expansion is merely a geometric change without affecting the objects within it. In their own frames of reference, objects are not moving apart in a way that would lead to photon emission. The concept of expansion is a coordinate effect rather than a physical motion. While there is a positive expansion scalar related to comoving observers, this does not lead to any emission processes. Overall, spacetime is not expanding; it simply exists as a framework for understanding distances and motion.
Suekdccia
Messages
352
Reaction score
30
TL;DR Summary
Can there be some kind of photon emission caused by cosmological expansion?
Are there any kind of observed and experimentally verified processes or mechanisms where photon emission occurs and which are directly cause by spacetime expansion in some way?
 
Space news on Phys.org
No. Why would there be? Spacetime expansion is just geometry changing. Nothing is happening to the things that are moving apart. In their own frames of reference they are not even moving (other than whatever motion they have aside from expansion).

Put another way, expansion is coordinate motion, not proper motion.
 
Suekdccia said:
spacetime expansion
Spacetime is not expanding. Spacetime just is.

"Space" is expanding if we choose standard FRW coordinates for our universe, but as @phinds says, this is really a coordinate effect and can't cause anything.

There is a physical invariant that can also be described as "expansion" in our universe, namely the positive expansion scalar of the congruence of comoving observers, but these observers are in free fall and free fall can't cause any emission process either.
 
PeterDonis said:
scalar of the congruence
Just a sanity check please: Is this what an ordinary person would call "distance apart"? I really need to learn this stuff...
 
hutchphd said:
Just a sanity check please: Is this what an ordinary person would call "distance apart"? I need to learn this stuff...
The expansion scalar is the coordinate-free generalisation of the naive "how fast the volume this stuff occupies is increasing".
 
  • Like
Likes PeterDonis and hutchphd
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...
Back
Top