WMAP Data Redshift and Background Radiation

  • Thread starter cowmoo32
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  • #1
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Let's assume that the universe has been expanding & accelerating since the big bang, we all know this redshifts any radiation directed toward our planet. We also know it's safe to say that the universe is ~13.7 billion years old given the fact that that's as far back as we can see in the background radiation from the WMAP satellite and the radio "noise" Hubble first encountered. Here's my question: If expansion & acceleration are constant, how do we know that any radiation beyond the 13.7 billion year mark hasn't been shifted to a wavelength below radio waves? Is it possible that there is/was radiation present before that time but we have no way of "seeing" it?
 

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  • #2
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We are quite sure according to the inflationary model of the universe there was LOTS of stuff we will never observe. especially radiation.

You are asking in effect "How big did the universe get before radiation resulting from the big bang and the inflationary era got through the charged "atmosphere."

We might be looking at the equivalent of a grain of sand and know nothing of all the beaches in the world....It could be infinite; nobody knows how big the universe is beyond what we can observe/detect.
 
  • #3
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What I'm really getting at is how do we know the age of the universe if we can only see 13.7 billion light years into the past?
 
  • #4
JesseM
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What I'm really getting at is how do we know the age of the universe if we can only see 13.7 billion light years into the past?
I think it's basically by assuming the universe is described by a FLRW metric from general relativity, and using observational data to get estimates of the value of parameters in the metric like density and the cosmological constant, which determine how far you have to go back to reach the Big Bang singularity in the metric. General relativity doesn't support the possibility of a stable universe that remains at a fixed nonzero density forever, the universe pretty much has to be expanding from a past singularity or contracting to a future singularity according to the theory (a theory of quantum gravity might get rid of the singularity but it would be expected to agree with general relativity once the energy density gets lower than the Planck scale which would be extremely hot and dense), and there's a lot of evidence for the idea that the singularity (or Planck density) occurred shortly before the time of recombination when the light from the cosmic microwave background radiation is thought to have been emitted (before that it would have been too hot and dense for atoms to form, the universe would have been filled with a plasma of particles that would absorb photons quickly after they were emitted, so we wouldn't see any light from this era though it may eventually be possible to "see" earlier times with neutrinos or gravitational waves).
 
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