🚀 go-pugleaf

Matt Carey wrote:
> 
> Uncle Al wrote:
> 
> >
> > More interesting is the purported mass of the heaviest neutrino:
> > 0.05 eV.  An electron comes in at 511 KeV, and it is charged.
> > What does 0.05 eV mean!  Every neutrino would be relativistic
> > (kinetic energy exceeds rest mass) near room temp, and almost all
> > of them ultra-relativistic in the extreme.  If you can't catch up
> > to and pass by a free particle with spin you cannot invert its
> > handedness - neutrinos stay absolutely left-handed.
> 
> I guess I have a hard time understanding the logic here.
> 
> 1) the low mass is sort of the point, isn't it?  If it has
> a larger mass there wouldn't be a question, would there?

A few eV would still elicit cries of wonder, but 0.05 eV is
ridiculous.  What's in there?
 
> 2) What is the "Room Temperature" of the universe?  The bright
> boys at Bell Labs measured the background radiation of the universe
> at about 3K (2.77K?) as I recall.  About 0.01 what we consider
> room temperature.  kbT is about 1/40 eV at RT, so the background
> "temperature" of the universe would be about 1/4000 eV.  Hardly
> enough to make a neutrino relativistic.

Neutrinos are born nuclear hot and they have no collision
cross-section to speak of (50% attenuation through a lightyear of
lead).  They've got the pedal to the metal.
 
> 3) the whole arguement in 2) is useless anyway.  A rule of
> thumb is that a particle needs about 10 collisions to become thermalized
> (assuming the mass differences aren't huge, as they are here). But,
> what is it a neutrino would bounce off of to become thermalized?

The interior of an erupting supernova will bounce them pretty
good - which won't cool them in the slightest.

-- 
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
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