Two questions regarding neutrinos
Daniel G. Emilio
1. Therefore, shouldn't neutrinos obey the law of entropy and slow down
and stop over countless eons through strikes with other neutrinos or
other particles?
2. But maybe the age of the universe is too short for neutrinos to have
made sufficient strikes to slow down yet because neutrinos simply pass
through everything virtually unaffected. But if there were no
neutrinos in existence before the big bang (no universe at all), then
neutrinos must have propagated as a result of the big bang. But in
that event, shouldn't all neutrinos appear to be coming from the same
region of space?
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"Daniel G. Emilio" <dge...@gmail.com> wrote in message
news:1142180383....@u72g2000cwu.googlegroups.com...
> We know that neutrinos have mass.
>
> 1. Therefore, shouldn't neutrinos obey the law of
> entropy and slow down and stop over countless
> eons through strikes with other neutrinos or
> other particles?
We are detecting them *now*. So they are stopping.
> 2. But maybe the age of the universe is too
> short for neutrinos to have made sufficient
> strikes to slow down yet because neutrinos
> simply pass through everything virtually
> unaffected.
We are detecting them now.
> But if there were no neutrinos in existence
> before the big bang (no universe at all), then
> neutrinos must have propagated as a result
> of the big bang.
That is current theory, yes.
> But in that event, shouldn't all neutrinos
> appear to be coming from the same
> region of space?
The CMBR was in the same "region of space" that the Big Bang was,
and we are completely surrounded by it. So we could be being
bathed in BB-sourced neutrinos, and never know it.
By the way, I believe that neutrinos are not expected to be
produced in the Big Bang itself, but some short time later, when
the various binding forces were expressed.
David A. Smith
Tom Roberts
> We know that neutrinos have mass.
All that is firmly established is that 2 out of 3 neutrino mass
eigenstates have nonzero mass. But for the third to be truly zero
requires careful "tuning", which most physicists consider unlikely.
> 1. Therefore, shouldn't neutrinos obey the law of entropy and slow down
> and stop over countless eons through strikes with other neutrinos or
> other particles?
The time required to reach thermal equilibrium depends on the strength
of interactions. Neutrinos have such a small cross-section for
interactions that they have not yet come anywhere close to equilibrium.
> 2. But maybe the age of the universe is too short for neutrinos to have
> made sufficient strikes to slow down yet because neutrinos simply pass
> through everything virtually unaffected.
Yes.
> But if there were no
> neutrinos in existence before the big bang (no universe at all), then
> neutrinos must have propagated as a result of the big bang. But in
> that event, shouldn't all neutrinos appear to be coming from the same
> region of space?
No. In big bang cosmologies there is no "single region of space" in
which the big bang occurred -- it happened "everywhere". And there are
other sources of neutrinos.
Note there is expected to be a cosmic neutrino background, but AFAIK it
has not been detected.
Tom Roberts tjro...@lucent.com