Primordial Nucleosynthesis & Fusion Reactions.

Thus spake Chalky
On Jul 23, 8:25 am, Oh No wrote:
This has nothing to do with inflation, as you say BBN is well after
that. Any expansion model in which big bang nucleosynthesis takes place
needs the correct rate of expansion during that phase, in order to
ensure the observed proton-neutron balance.

I would be very interested in finding out precisely why.

Essentially it is to do with the period of time during which free
neutrons were able to decay to protons. Prior to about 1 sec after the
big bang, strong interactions maintained an equal balance of protons and
neutrons. After a few minutes H, He, Li, were formed and the neutrons
became stabilised within atoms. The amount of time between the two
critically affects the observed balance of light elements.

Is there
anything on the internet which explains that? That would be preferable
to a book ref., because of ordering delays. (Rob's recommended ref for
Einstein, for example, just landed on my doorstep this morning.)

Stacks. Google Big Bang Nucleosynthesis. Also, for a detailed account:
arXiv:astro-ph/0408076 v2
arXiv:astro-ph/0511534 v1

If the universe is expanding at the speed of light,

expansion at the speed of light is a phrase which makes no sense.

changes in density
as a function of time are going to be pretty much the same at the
fundamental level (during BBN), no matter how mortals choose to
arrange their spacetime bookkeeping.

The fact that it does work
out correctly with the age of the universe as it is can be regarded as a
success of current models.

I get from this that EFE is a rather delicate flower, which needs a
lot of care and attention, in order for it to work at all.

This is not to do with the EFE, but to do with very well laboratory
established laws of elementary particle physics. Any model would have to
pass this test to be credible, imv. Otherwise you have to start messing
with the way protons and neutrons behave in other times and places and
once you start doing that it becomes impossible to establish anything
scientifically.

Fortunately for the teleconnection model,
which is expanding at half the rate of the standard model, the age of
the universe calculated from SN data comes out almost exactly the same.

In FRW cosmologies the initial rate of expansion is, to good
approximation, dependent only on the age of the universe.

I don't understand this either. Surely you are not saying that the
initial rate of expansion is different for an observer located in our
past, and different again for an observer located in our future?

Of course not. Observers at these different times will measure different
values of Hubble's constant.

Well, since nobody has actually asked them, this is itself a
speculation which depends on your cosmological model (and field
equation) : - )

I was speaking in the context of FRW models.

Clearly the rate of expansion during BBN
will be the same for all of them.

So why should it make any difference to BBN, how they choose to
interpret the evidence for expansion/accelerating expansion, in their
present?

I think perhaps you are right that this is a standard text book
result. However, it looks to me from what you have said thus far, that
this merely represents another example of EFE not being particularly
robust, at the fundamental level.

It is robust in this context because it gives the correct prediction for
the balance of light elements which we observe. As I say, any
cosmological model must pass the same test. If, as you appears to
suggest, the early expansion under chalky's law takes place at a
different rate, that is a bit of a killer.

Regards

--
Charles Francis
moderator sci.physics.foundations.
substitute charles for NotI to email

On Jul 23, 12:43 pm, Oh No wrote:
Thus spake Chalky

On Jul 23, 8:25 am, Oh No wrote:
This has nothing to do with inflation, as you say BBN is well after
that. Any expansion model in which big bang nucleosynthesis takes place
needs the correct rate of expansion during that phase, in order to
ensure the observed proton-neutron balance.

I would be very interested in finding out precisely why.

Essentially it is to do with the period of time during which free
neutrons were able to decay to protons. Prior to about 1 sec after the
big bang, strong interactions maintained an equal balance of protons and
neutrons. After a few minutes H, He, Li, were formed and the neutrons
became stabilised within atoms. The amount of time between the two
critically affects the observed balance of light elements.

Is there
anything on the internet which explains that? That would be preferable
to a book ref., because of ordering delays. (Rob's recommended ref for
Einstein, for example, just landed on my doorstep this morning.)

Stacks. Google Big Bang Nucleosynthesis. Also, for a detailed account:
arXiv:astro-ph/0408076 v2
arXiv:astro-ph/0511534 v1

Thanks. I will come back to you on this, after adequate reading.

If the universe is expanding at the speed of light,

expansion at the speed of light is a phrase which makes no sense.

It does to me. Say, for the sake of argument, that the universe now is
expanding at 2 cm/sec/light year.This means that a universe with a
radius now of 15 billion light years (relative to the observer now),
is expanding at 3 x 10^10 cm/sec. Plug in more accurate figures for
both Ho and the light travel time from the big bang to now, and you
will find that this rather simplistic explanation works pretty well.

[snip]

I think perhaps you are right that this is a standard text book
result. However, it looks to me from what you have said thus far, that
this merely represents another example of EFE not being particularly
robust, at the fundamental level.

It is robust in this context because it gives the correct prediction for
the balance of light elements which we observe. As I say, any
cosmological model must pass the same test. If, as you appears to
suggest, the early expansion under chalky's law takes place at a
different rate, that is a bit of a killer.

I think you are jumping the gun here. I see no reason why nuclear
reactions should proceed at different rates in different cosmological
models. I also see no reason, as yet, why the rate of change of
temperature with time should differ either, for any conceivable
universe which is expanding at the speed of light.


C

On Jul 23, 3:40 pm, Chalky wrote:
On Jul 23, 12:43 pm, Oh No wrote:
Essentially it is to do with the period of time during which free
neutrons were able to decay to protons. Prior to about 1 sec after the
big bang, strong interactions maintained an equal balance of protons and
neutrons. After a few minutes H, He, Li, were formed and the neutrons
became stabilised within atoms. The amount of time between the two
critically affects the observed balance of light elements.

Is there
anything on the internet which explains that? That would be preferable
to a book ref., because of ordering delays. (Rob's recommended ref for
Einstein, for example, just landed on my doorstep this morning.)

Stacks. Google Big Bang Nucleosynthesis.

Thanks. I will come back to you on this, after adequate reading.

OK, what I have read thus far indicates that it is the hugely
subcritical baryon density which determines relative abundances, not
cooling time. I am sticking to my contention that the cooling time is
going to be pretty much the same, over the first few minutes,
irrespective of what the acceleration/deceleration parameter is
postulated to be, in those first few minutes.


C

On Jul 16, 9:05 am, Kent Paul Dolan wrote:
Chalky wrote:

3) After the first course (quark soup), were we
served up with protons, neutrons, and electrons in
equal numbers?

Nope. The whole baryonic universe is just scraps
leftover because the anti-matter versus matter
balance didn't quite cancel out exactly. IIRC, there
is some mirror symmetry breaking that accounts for
that.

I think you will find that this matter/antimatter thing is still a
thorn in the side of published theory. According to wiki, it is still
an unresolved problem.

Some figures here might be handy.

What is the ratio of matter to antimatter now?
What was the ratio initially?
How long did this mutual annihilation period last?
How much spare energy was generated by these matter/antimatter
annihilations?

Thanks for your other points too.

C