Big bang and first proton

Alain De Vos

Maybe this question is already asked, but how did the first proton came into existence?
A soup of quarks cooling down?At which temperature? How late was it on the clock? What was the size was the universe? How long did this proton lived? Did this proton had an impuls,energy,entropy?

Mark M

The first nucleons formed during the Hadron epoch, 10^-6 seconds after the big bang. This includes the proton. This occurred after the quark epoch, in which quarks managed outnumber anti-quarks, coupling together with gluons to form an obscenely hot quark-gluon plasma. After the universe cooled to a sufficiently low temperature, this plasma broke up. Because of quark confinement, these quarks quickly merged into hadrons. See here:

http://en.m.wikipedia.org/wiki/Hadron_epoch

Also, note that all protons formed then, and have lasted until today. We have no evidence that a proton can decay. Even if it can, it would take a time far longer than the age of the universe.

collinsmark

It's true that there is no evidence that an isolated proton every decays, but a proton can decay/change if it is within the nucleus of an atom though processes known as β⁺ decay and electron capture. (http://en.wikipedia.org/wiki/Beta_decay.) For these to occur, the decay must be allowed energetically. Essentially, when energetically allowed, a proton can change into a neutron (and there are a couple of other particles involved).

An example (of a β⁺ that is allowed energetically) is Potassium 40 decaying into an argon 40 atom:

⁴⁰K → ⁴⁰Ar + e⁺ + ν_e

(where ν_e is a neutrino, and e⁺ is a positron).


Also, β^- decay, where a neutron essentially turns into a proton (plus an electron and anti-neutrino), is more common still. So it's not correct to say that "all proton's formed then, ..." since protons are still being created today as the result of β^- decay.

Mark M

Oh, thanks for correcting that.

Chalnoth

Well, no direct evidence. But it would be very hard to make sense of the asymmetry of matter and anti-matter if protons don't decay.

Mark M

Why is that? Wasn't the asymmetry established before any protons formed?

EDIT: Oh, I see. Proton decay would imply that the conservation of baryon number could be violated, allowing for processes in which quarks could outnumber anti-quarks.

Chalnoth

Yup! Though usually I think about it in the reverse sense.

BillSaltLake

There is the possibility that there were essentially no protons immediately after the hadron epoch, and that almost all the hadrons were neutrons, of which the majority soon decayed to protons.

Lino

Hi, Accepting that these posts answer the spirit of the OP, do the processes associated with neutron stars / blackholes / colliders (like LHC) / etc. change the nature of the protons such that a proportion of those initial protons are no longer in existence?

Regards,

Noel.

Chalnoth

I'm not sure this question makes much sense. If, for example, a proton converts into a neutron through inverse beta decay, and then back to a proton through beta decay, is that the same proton or a different one?

Lino

Thanks Chalnoth. Your question makes sense ... but I don't know the answer (I don't know the implications for the characteristics of the proton)! Can I ask what your view is?


Regards,


Noel.

Chalnoth

As far as I'm concerned, there is no answer because it's not a good question. The problem is that you can't put a label on a subatomic particle: a proton is a proton is a proton, and there is no way to tell which is which. This fact has critical importance in quantum mechanics, where the ambiguity of which proton is which is essential in computing the correct behavior of proton interactions. Because it is fundamentally impossible to tell one proton from another, it doesn't make sense to ask the question of whether a proton has been around since the beginning of the universe or not, because that proton's timeline has been mixed up with the timelines of all the other protons it's come into contact with.

Lino

Thanks Chalnoth. That makes sense.

Regards,

Noel.

Blahboy

Does anyone have any theories on how the big bang started?

Chalnoth

Well, the short answer is yes. There are lots of people with lots of different theories between them. The main issue at the moment is a lack of experimental evidence to determine which (if any) of them are accurate.