The steady state theory VS the big bang

[Az]

I hope you treat my question respectfully, KH.

How is uniform background radiation proof of a big bang?

[KrazyHorse]

Looks like they came up with some dumb nucleosynthesis explanation. Looks cobbled-together. Why take a simple answer when you can create some enormously complicated one.



For the quasar stuff to be right we'd need all the quasars to be ejected in a direction away from us. Otherwise we'd see half blue-shifted (slightly less than half, but that's another matter).

Basically, you can create a steady-state theory that works. It just involves "the undue multiplication of entities"...

[KrazyHorse]

Originally posted by Az
I hope you treat my question respectfully, KH.

How is uniform background radiation proof of a big bang?

The uniform background radiation stems from the point in the history of the expansion of the Universe known as "recombination" where the temperature dropped low enough that electrons bonded with protons. Virtually overnight the Universe went from being optically dense to being optically diffuse. Mean free path for light went from a few thousand parsecs to billions of parsecs. Therefore, this also represents the last time that the light was in thermal equilibrium with the rest of the Universe, providing us with what is fundamentally a "snapshot" of the Universe at that exact moment. The existence of the CMB was a direct consequence of the Big Bang theory, and was actually used as proof against it (what sort of ridiculousness is this? there's some sort of uniform relic radiation in the Universe). It was seen 10 years or more after it was first proposed (by mistake! by Penzias and Wilson), at which point the steady-staters basically gave up and died. Since then, kooks have constantly tried to resurrect the steady-state view through hokey low-level mechanisms to explain away all the inconsistencies, but if it walks like a duck and talks like a duck...

[KrazyHorse]

Steady-state theory nowadays is just so much a priori rot. You've made up your mind what you want the answer to be, so you bend all the evidence into the semblance of a reasonable theory.

[Az]

yes, but why is it coming at us from all directions?

[KrazyHorse]

Why wouldn't it? The Universe has been uniform and isotropic at all points in time.

By the way, in case you hadn't realised it, if the Universe is either flat or open it's also infinite in extent...

[KrazyHorse]

Assuming the Universe is flat (which it is to a good approximation), you must imagine it as an infinite plane on which galaxies etc are distributed uniformly (sort of...but that's large-scale structure stuff which I won't go into). The only reason we talk about the "size" of the Universe is that it represents the visible horizon; what we can see is limited due to finite age and the finite speed of light.

This infinite plane is being stretched like a piece of rubber by the universe's expansion. Recombination happened at virtually the same moment (coordinate time) at all places on this rubber sheet, so the light we see from the last scattering surface is coming to us in basically a straight line from all points around us (on the sheet it's a ring; in the 3-d real universe it's a spherical shell). As time goes on, this background radiation is coming to us from a ring that's larger and larger (it expands faster than the universe does, so it's progressing backwards even in comoving coordinates), but that doesn't matter because it should look the same no matter where we draw that ring (this is the isotropic and uniform part).

[KrazyHorse]

What we're seeing with the CMB is a snapshot of what the sky looked like at all points on a spherical shell located at redshift 1300(?) or so.

It all looks the same, modulo some acoustic oscillations (which are what create that power spectrum I showed you)...