[ExI] Public draft of my book 'Tales of the Turing Church

John Clark johnkclark at gmail.com
Tue Oct 23 00:08:58 UTC 2018

On Sun, Oct 21, 2018 at 11:13 PM Stuart LaForge <avant at sollegro.com> wrote:

> > An expanding gas isn't always cooled, for example if I divide a chamber in
>> two and there is a gas at high pressure in half of it and a vacuum in the
>> other half and I suddenly remove the barrier between the two the gas expands
>> to fill the entire chamber, but the gas isn't cooled because it did no
>> work.  Work is force over distance and that didn't happen.  During the
>> exponential expansion phase Guth's inflation field did the work not the
>> hot gas.
> > *But there was no gas because there were was no matter.*

That was true during the Inflation Era of the universe that lasted  about
10^-35 to 10^-34 seconds, during that time most of the energy in the
universe was in the form of the inflation field. After that the inflation
field decayed away and the Universe entered the Radiation Era where most of
the energy was in the form of photons.

> >
> *You could talk about a gas of photons but every time the universe doubled
> in size during inflation so would have the wavelengths of those photons.*

That is also true, as the universe got larger not only did the density of
photons become less but due to redshifting the energy in the individual
photons became less too. After 48,000 years the photons had been redshifted
by a factor of 3600 and they no longer contained most of the mass/energy in
the universe and the Radiation Era ended and the Matter Era started. By
"matter" I mean a combination of regular matter and dark matter. The Matter
Era lasted from 48,000 to 9.8 billion years after the Big Bang and we've
been in the Dark Energy Era for the last 4 billion years. The Matter Era
ended because Dark Energy seems to be a property of space itself so as the
universe got larger the amount of matter in it remained constant but the
amount of Dark Energy in it did not.

For the sake of honesty I must admit that much of what I said above about
the very early universe is conjecture because the oldest thing anybody has
ever detected is the Cosmic Black Body Radiation, and that doesn't come
from the Big Bang itself but from a time 380,000 years after it when the
universe had cooled to less than 3000K and neutral hydrogen atoms could
form and everything was no longer opaque to electromagnetic waves.

> *So how did it reheat itself afterwards?*

By making the first stars, it's called reionization and there is evidence
it happened about 180 million years after the Big Bang. By the way, I think
it's pretty neat that this evidence came from a small team of astronomers
and a radio telescope no larger than your kitchen table:


John K Clark
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