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> Why CMB is emitted at the edge of our Universe only? I thought CMB was emitted everywhere.

oneshtein 3y ago
CMB is produced by atoms, right? We see darker/lighter regions in CMB, so we should see a transition somewhere. 300M years is very short period of time, unless everything cooled very very uniformly, which is not the case. Sometimes, somewhere there must be a galaxy past CMB.
- bigbillheck 3y ago
  > a transition somewhere A transition from what to what? > which is not the case. Why not? > Sometimes, somewhere there must be a galaxy past CMB. If there is we'd have to wait for the light from it to get to us, by which time the CMB will have receded further and it would then be in front of the CMB.
  - oneshtein 3y ago
    > A transition from what to what? A transition from plasma to the cold mater in the form of galaxies we see. > Why not? As you see, there are big clusters everywhere. It means that some regions were cooler from the start, to form these cluster in so short period of time. It means that regions around them were hotter, thus they should emit light longer. > If there is we'd have to wait for the light from it to get to us, by which time the CMB will have receded further and it would then be in front of the CMB. 300My is a short period of time. Why they cannot sometimes overlap?
- ben_w 3y ago
  > 300M years is very short period of time, unless everything cooled very very uniformly, which is not the case ~300M years is the time between the Big Bang singularity and the CMB, but not really relevant. The entire universe was everywhere as hot as the surface of a star at the time of the CMB, so any evidence of galaxies forming before that is surprising. The surprisingly high uniformity of the temperature of the CMB — isotropic to roughly one part in 100,000 — is one of the reasons the Big Bang model replaced one of the older competing hypotheses (continuous creation IIRC). So it is in fact the case that everything cooled very very uniformly and I'm not sure why you think otherwise? I'm also not clear what you're saying with > so we should see a transition somewhere Given the CMB is itself the transition that we see. > Sometimes, somewhere there must be a galaxy past CMB. I think here you're mixing up space and time. It's reasonable (please permit my use of conventional language rather than 4-vectors) to assume that a galaxy exists on the other side in space of the CMB as we see it now, but that happens at a point in time after the recombination epoch began and space became transparent, and light from that event hasn't reached us yet; when it does, the apparent distance of the CMB will be large enough for the galaxy to appear on this side. Are you familiar with light cones and the convention of one space axis and one time axis? It might help you visualise it if you draw what's going on.
  - oneshtein 3y ago
    https://en.wikipedia.org/wiki/GLASS-z12 https://en.wikipedia.org/wiki/GLASS-z12 GLASS-z12 is 33.2Bly away from us. It should be behind some of the CMB produced by BB, isn't? > Given the CMB is itself the transition that we see. In BB model, CMB emitted by hot plasma. Where it is, that plasma? In steady universe model, CMB is light with z=1000, emitted by distant galaxies, in range of 4Tly. It explains high uniformity of temperature. It's like the temperature of a water stream from underground: it's uniform across a climate area because underground temperature averages seasonal temperature shifting.
    - DiogenesKynikos 3y ago
      GLASS-z12 is way in front of the CMB. You have to be careful with what you mean by "distance" at cosmic scales. Space is expanding with time, and there are several different definitions of "distance" that give very different results at cosmic scales. The best "distance" measure here is simply redshift. GLASS-z12 is at redshift z=12, as the name suggests. The CMB is at redshift z=1100, so it's father away. In fact, for very straightforward physical reasons, no light can reach us from beyond the CMB. The universe was opaque before the time of the CMB, because it was ionized and dense. Before the CMB time, photons could not travel very far at all before they hit an electron and were scattered.
      - oneshtein 3y ago
        Nobody pointed to a source of energy for this "expansion" of "space". Usually, coordinate system doesn't expand with time. An extraordinary claim requires extraordinary evidence. Yes, CMB emitters are much further away, at a distance of about 4Tly, while BB claimed to be just 14By ago. Your claim, that CMB is produced by BB, requires a lot of stretching.
        ben_w 3y ago
        > Nobody pointed to a source of energy for this "expansion" of "space". Several have been made, the suggestions have issues. > Usually, coordinate system doesn't expand with time. Define "usually". Do you have experience of other universes? > An extraordinary claim requires extraordinary evidence. Indeed, but this comment box is too small to do the evidence justice. Edit: that's unhelpful in retrospect, so I suggest the Youtube channel "PBS Space Time". The videos build on each other, so start at the beginning and work through the back catalogue. > Yes, CMB emitters are much further away, at a distance of about 4Tly, I have no idea where you got this belief from.
consilient 3y ago
The CMB is everywhere, but it was emitted by the initial formation of neutral hydrogen (from plasma) in the early universe. When people talk about the CMB being far away they're really talking about the last scattering surface, which is that early plasma as seen 13+ billion years later.

CMB is produced by atoms, right? We see darker/lighter regions in CMB, so we should see a transition somewhere. 300M years is very short period of time, unless everything cooled very very uniformly, which is not the case. Sometimes, somewhere there must be a galaxy past CMB.

bigbillheck 3y ago
> a transition somewhere A transition from what to what? > which is not the case. Why not? > Sometimes, somewhere there must be a galaxy past CMB. If there is we'd have to wait for the light from it to get to us, by which time the CMB will have receded further and it would then be in front of the CMB.
- oneshtein 3y ago
  > A transition from what to what? A transition from plasma to the cold mater in the form of galaxies we see. > Why not? As you see, there are big clusters everywhere. It means that some regions were cooler from the start, to form these cluster in so short period of time. It means that regions around them were hotter, thus they should emit light longer. > If there is we'd have to wait for the light from it to get to us, by which time the CMB will have receded further and it would then be in front of the CMB. 300My is a short period of time. Why they cannot sometimes overlap?
ben_w 3y ago
> 300M years is very short period of time, unless everything cooled very very uniformly, which is not the case ~300M years is the time between the Big Bang singularity and the CMB, but not really relevant. The entire universe was everywhere as hot as the surface of a star at the time of the CMB, so any evidence of galaxies forming before that is surprising. The surprisingly high uniformity of the temperature of the CMB — isotropic to roughly one part in 100,000 — is one of the reasons the Big Bang model replaced one of the older competing hypotheses (continuous creation IIRC). So it is in fact the case that everything cooled very very uniformly and I'm not sure why you think otherwise? I'm also not clear what you're saying with > so we should see a transition somewhere Given the CMB is itself the transition that we see. > Sometimes, somewhere there must be a galaxy past CMB. I think here you're mixing up space and time. It's reasonable (please permit my use of conventional language rather than 4-vectors) to assume that a galaxy exists on the other side in space of the CMB as we see it now, but that happens at a point in time after the recombination epoch began and space became transparent, and light from that event hasn't reached us yet; when it does, the apparent distance of the CMB will be large enough for the galaxy to appear on this side. Are you familiar with light cones and the convention of one space axis and one time axis? It might help you visualise it if you draw what's going on.
- oneshtein 3y ago
  https://en.wikipedia.org/wiki/GLASS-z12 https://en.wikipedia.org/wiki/GLASS-z12 GLASS-z12 is 33.2Bly away from us. It should be behind some of the CMB produced by BB, isn't? > Given the CMB is itself the transition that we see. In BB model, CMB emitted by hot plasma. Where it is, that plasma? In steady universe model, CMB is light with z=1000, emitted by distant galaxies, in range of 4Tly. It explains high uniformity of temperature. It's like the temperature of a water stream from underground: it's uniform across a climate area because underground temperature averages seasonal temperature shifting.
  - DiogenesKynikos 3y ago
    GLASS-z12 is way in front of the CMB. You have to be careful with what you mean by "distance" at cosmic scales. Space is expanding with time, and there are several different definitions of "distance" that give very different results at cosmic scales. The best "distance" measure here is simply redshift. GLASS-z12 is at redshift z=12, as the name suggests. The CMB is at redshift z=1100, so it's father away. In fact, for very straightforward physical reasons, no light can reach us from beyond the CMB. The universe was opaque before the time of the CMB, because it was ionized and dense. Before the CMB time, photons could not travel very far at all before they hit an electron and were scattered.
    - oneshtein 3y ago
      Nobody pointed to a source of energy for this "expansion" of "space". Usually, coordinate system doesn't expand with time. An extraordinary claim requires extraordinary evidence. Yes, CMB emitters are much further away, at a distance of about 4Tly, while BB claimed to be just 14By ago. Your claim, that CMB is produced by BB, requires a lot of stretching.
      - ben_w 3y ago
        > Nobody pointed to a source of energy for this "expansion" of "space". Several have been made, the suggestions have issues. > Usually, coordinate system doesn't expand with time. Define "usually". Do you have experience of other universes? > An extraordinary claim requires extraordinary evidence. Indeed, but this comment box is too small to do the evidence justice. Edit: that's unhelpful in retrospect, so I suggest the Youtube channel "PBS Space Time". The videos build on each other, so start at the beginning and work through the back catalogue. > Yes, CMB emitters are much further away, at a distance of about 4Tly, I have no idea where you got this belief from.

consilient 3y ago

The CMB is everywhere, but it was emitted by the initial formation of neutral hydrogen (from plasma) in the early universe. When people talk about the CMB being far away they're really talking about the last scattering surface, which is that early plasma as seen 13+ billion years later.