Whatever Happened to Ning Li?

[edd]

I said Pauli predicted the neutrino to account for the missing energy in beta decay, which is typically about the same as the electron mass-energy of 511keV. For a particle with a 2ev rest mass to take away 511keV of energy the gamma factor is about 250,000. So if √(1-v²/c²) = 1/250,000 then 1-v²/c² = 1/250,000² so v is less than c by a factor of 1/62500000000. It isn't much. For SN 1987A which is 164,000 light years away, then with 32 million seconds in a year it's only about 8 seconds. Somebody check my arithmetic.

Well yes and no. There's a reason I specified 10MeV in my post for the neutrino energy, and neutrino energies typically have a range of values, but half a MeV won't make much difference. And you've lost a factor of 2 - see ctamblyn's approximation to leading order which is very accurate for high Lorentz factors. But again never mind about that - you're in the right ballpark.

No, this is why I said neutrinos travel at c. You can't distinguish the difference.

I don't think people (at least I) would have had a problem if in this context you'd said 'indistinguishable from c' more clearly.

I think other people can take care of other comments.

 

[ben m]

I
No, this is why I said neutrinos travel at c. You can't distinguish the difference. And the important point is that you can't make a neutrino not travel at c in any way you can measure.

Sure you can. The whole point of high-precision tritium beta decay experiments is this: to measure the neutrino mass, you detect the electron from the (rare) subset of decays where the neutrino is nonrelativistic. (It happens all the time, the appropriate events are not objectively speaking rare, it's just hard to do the measurement precisely). The cosmic neutrino background is also nonrelativistic.

And if photons had some kind of internal dynamics that made them "concertina" through space such that their speed varied, their mass would vary too. As far as we know they don't, but neutrinos do.

Utter gibberish. You've taken something horribly wrong from that classical spring analogy, and I don't care to diagnose what it is.

 

[edd]

Sure you can. The whole point of high-precision tritium beta decay experiments is this: to measure the neutrino mass, you detect the electron from the (rare) subset of decays where the neutrino is nonrelativistic. (It happens all the time, the appropriate events are not objectively speaking rare, it's just hard to do the measurement precisely). The cosmic neutrino background is also nonrelativistic.

To be fair you don't directly measure the speed of the neutrinos in those cases do you? But those are good points.

And I think I find the rest of what Farsight said as incomprehensible as you did, ben.

 

[ben m]

Again do your own research, search on neutrino and helical. See for example hyperphysics. Or search on photon helical wavefunction.

Hoo boy. Hyperphysics: are you looking at "helicity"? That's a technical term which has nothing to do with actual helix-shapes of any sort. The Google search (after fixing a typo): I see (a) one unpublished ArXiV upload, which describes itself as an "educated guess" by an nonacademic author with no other particle/quantum/theory work of any sort. (He appears to work in scientific IT.), (b) anonymous-user-comments on random science articles, and (c) irrelevant stuff, like the helical magnets used in certain accelerator beamlines. "Photon helical wavefunction": sure, thanks to modern optics, you can construct a photon field with any shape you want. One of my colleagues has been working with knotted configurations. This has nothing to do with neutrinos or fundamental physics.

In other words, this is yet another standard Farsight argument: you strike up the attitude ("do your own research") of dismissing your interlocutor with your superior command of the facts, but in truth you're just posting some guesswork ("I just did this Google search and the hits looked good to me").

 

[ctamblyn]

It couldn't work in the strict beta-decay relationship described above. I was supposing that the system wasn't closed specifically to particles involved in the beta-decay process. If that system was just approximately closed, I was supposing that the charge could be conserved elsewhere, since it would be so small. Based on what I've learned about neutrinos over the past couple of days, I'd say this isn't the case. If neutrinos were to carry an electric charge, there'd have to be another local particle to cancel the charge out, but there doesn't seem to be such a particle.

Yes, that's pretty much it: there'd have to be another particle involved in the decay process to balance the neutrino's hypothetical charge. From the paper I linked to earlier, both particles would have to carry charges of less than 10^-21e in magnitude to be consistent with experiment. Personally I'd have thought, though, that we'd have noticed the "missing" energy from weak decay processes by now.

Still, I'd be curious to see attempts at inducing a charge on a neutrino.
http://arxiv.org/pdf/hep-ph/9305308v2.pdf

If I understand correctly, the neutrinos only interact with the e/m field indirectly, via virtual charged particles (electrons/positrons and W^± bosons), and that's how they polarize the medium in that paper. The neutrinos themselves always remain neutral, though.

The reason that a neutrino has mass, but no electric charge is a problem that a unified field theory of gravity and electromagnetism would have to work out, but it's hardly reason to doubt the existence of gravity-electromagnetism unification in nature. The fact that all atomic-level matter and beyond has mass and electric charge(at least a little in some places) is reason enough to suspect unification in nature.

I'm not sure this has relevance to possible future unified field theories, but I couldn't say. I think Ziggurat's response to your last sentence is worth bearing in mind though.

 

[Reality Check]

Somebody check my arithmetic.

Your arithmetic is correct: v is less than c by a factor of 1/62500000000.

Therefore: neutrinos do not travel at c !

No, this is why I said neutrinos travel at c. You can't distinguish the difference.

Did you understand your arithmetic that actually distinguished the difference between the velocity of neutrinos and c?

We cannot measure the difference because the events that produce neutrinos do not produce photons at the exact same time (and so there is no "start the neutrino timing" signal to measure the difference).

We can measure neutrino oscillation. Neutrino oscillation only happens if neutrinos have mass. A particle with mass cannot travel at c.

 

[WhatRoughBeast]

I don't know exactly.

Ah. Silly me. Sorry for wasting your time with irrelevant questions.