[pfdietz]

The CMBR requires the existence of a dense, optically thick, hot state early in the universe. That's pretty much the Big Bang. There's nothing speculative about that, it follows from rather simple physics.

But anyway, give an alternative model that explains it. I'll wait.

[misja111]

It's pretty much the Big Bang but not quite. The Big Bang theory claims more than that: it claims that our universe started from nothing or from a single point. It needs some fancy new physics to explain our current universe from that: e.g. hyper inflation.

There are some alternatives to the Big Bang theory, e.g. the Big Bounce. This also claims the existence of a thick hot early state, but a bit more than a single point. This theory also explains cosmic background radiation.

[pfdietz]

No, the Big Bang doesn't assume the universe started from "a single point". Nor does it assume inflation. The Big Bang theory doesn't even go back to t=0. It leaves unspecified what happens at very early times. The BB is compatible with inflation, but theories of inflation were proposed well after the BB theory itself.

[misja111]

I didn't say the BB assumes inflation, I said it needed fancy physics such as inflation to explain the current state of the universe.

> The BB is compatible with inflation, but theories of inflation were proposed well after the BB theory itself.

Exactly, and the reason these theories were proposed was to 'fix' the BB itself. So of course they are compatible with the BB. There is no observation that asks us to consider something like hyper inflation, except if you assume that there has been a BB.