On 23/01/2017 03:50, wrote:
On Monday, January 2, 2017 at 10:03:49 PM UTC-8, jacobnavia wrote:
After the big bang, the gas was too hot to form stars. A time must pass
to cool the universe so that the star formation could begin.=20

The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...=20

It doesn't seem relevant or perhaps even important to me what the
number is. The Big Bang is an idea that the universe explosively
began. But the idea that it originated from a tiny point basically
suggests that our universe originated (if correct) from the interior
of a black hole that breached confinement. Call it a singularity
or whatever, things exploded out of a tiny volume.

The phrase "Big Bang" was a derogatory term coined by Fred Hoyle to
ridicule the expanding universe hypothesis then supported by Hubble's
observations, early radioastronomy and Einstein-Lemaitre's mathematics.

But the Big Bang doesn't posit what existed outside of that
singularity. There could have been an entire universe around a
black hole that breached confinement for all we know.

There doesn't need to be anything outside though. You are imagining a
spacetime with nothing in it apart from a dense proto universe. The
mathematics of GR permits a solution where at the singularity there is
nothing - no space *OR* time and no "before" either. This is in the
realm of metaphysics since there is no way we could test it. Quantum
effects means that this is almost certainly wrong for sizes less than
the Planck length but we have no testable theories for that era.

I am entrigued by the cyclic possibilities of the Steinhardt-Turok
ekpyrotic (sp?) model of the universe which might yet be validated by
observations and would circumvent the need for Guth's inflation.

The point is to do the studies and search for the galaxies in the
oldest parts of the universe. And if we can find a bunch of them
in places they should not be able to be, then we will need to ponder
how to modify the big bang to include the new findings.

I don't think we are likely to see anything that alters present models
that way. We can already see the relics of the Big Bang back to the
surface of last scattering when the universe first became transparent
and just how very nearly uniform it was at that stage.

It's entirely possible that one region of the universe was cooler
than another so that stars and a galaxy could form unusually early.
It's possible a wave of star formation ripped through an entire
cloud of gas, fully forming a massive galaxy within a short period
of time.

No it isn't. That is already ruled out observationally. The cosmic
microwave background is very uniform - embarrassingly so with only tiny
fluctuations of temperature and density visible in WMAP.

Water freezes at 0C. But under high pressure, it requires a lower
temp to freeze. It's possible that star formation in highly
compressed regions could have taken place at higher T than your
estimate.

Compressing a region of gas without raising its temperature and pressure
is the trick though. There is a limit to how quickly a star can form
given an ambient background temperature. The current models might be
imperfect but they are not likely to be hugely wrong.

--
Regards,
Martin Brown