# Tag Info

## Hot answers tagged cmb

6

The anisotropies in the CMB are caused by four effects; three at the surface of last scattering (SoLS), and one after: Temperature differences Denser regions will be more compressed and thus hotter, on average. Hence, an overdensity will result in a hotter spot, with a fractional fluctuation $\Delta T/T_0$. Gravitational redshift Photons climbing up (or ...

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By request: Beyond the fact that the cosmic microwave background (CMB) is a direct prediction of the big bang model, there is the question of how you would produce it in any other way. It is remarkably close to being isotropic and remarkably close to being a blackbody spectrum - i.e. it is almost a perfect blackbody radiation field. A blackbody radiation ...

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That is what is done. This is shown in an old xkcd comic https://xkcd.com/54/ The curve shows the distribution of frequencies in the CMB, and by using the marked value of the maximum you can determine the value of T, the apparent (red-shifted) temperature of the CMB

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The (late time) ISW is caused by the evolution of cosmic structures as photons of the cosmic microwave background traverse them on their way to our detectors. It may cause a redshift or blueshift with respect to the redshift predicted for a homogeneous expanding universe. A bit more detail: If a photon "falls" into a potential well, its frequency and energy ...

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If time started in our Universe at the Big Bang, then in what time dimension (outside of ours) do collisions between Universes occur? In inflationary cosmologies, time did not start at the Big Bang. There are many models, but in at least some of them, there is an "inflating" universe which extends infinitely in past (and possibly future) time, constantly ...

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Whichever direction we look in the universe, we are looking back in time. If we observe a galaxy that is $10$ million light years away then we are observing photons that were emitted $10$ million years ago. If we observe a galaxy that is $1$ billion light years away then we are observing photons that were emitted $1$ billion years ago. And the further away ...

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