
Neutrino Asymmetry Passes Critical Threshold - bainsfather
https://www.quantamagazine.org/neutrino-evidence-could-explain-matter-antimatter-asymmetry-20200415/
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andrewflnr
So... would this mean neutrinos are for sure not Majorana fermions? Because
you'd think that a particle couldn't be its own anti-particle if it's anti-
particle has different properties, but quantum mechanics has surprised me
before.

[https://en.wikipedia.org/wiki/Majorana_fermion](https://en.wikipedia.org/wiki/Majorana_fermion)

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aspenmayer
Well it’s tricky, see. Normal science might try to solve a paradox logically,
but maybe this is the universe solving a paradox by multiplying both sides of
the equation by a reciprocal paradox? The different properties of the anti-
particle result in a remainder which is where all of the something rather than
nothing comes from.

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aspenmayer
I guess my metaphor was a little too fast and loose and lost some key detail.
I don’t want to misrepresent the science so here’s a link that explains the
math better than I can.

[https://en.wikipedia.org/wiki/Spinor](https://en.wikipedia.org/wiki/Spinor)

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badrabbit
> ...further explaining why anything at all exists today, since matter and
> antimatter in equal portions would have mutually annihilated.

Shouldn't this read 'how' instead of why? I am far from an academic so please
enlighten me. I presume 'why' to question reason and 'how' to explain means.

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aspenmayer
I agree. “Why” implies or presupposes such reason or reasons exists. “How” is
more about context, explicability, understanding, justification, verification,
and proofs. That’s just my reasoning anyway.

It’s a matter of the “why’s” of ontology versus the “how’s” of deontology.

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liquidify
That 12 story tank looks amazing.

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aspenmayer
Am I the only one who finds megastructures like this surreal? It’s not
agoraphobia per se, but sometimes when I behold things like this tank or
especially when I gaze upwards at a skyscraper, I get this sense that of not-
rightness that it exists and that I’m so close to it to be looking at it from
this angle. Vertigo maybe? It happens even in pictures so I’m sure it’s
something about my mind thinking something is amiss somehow but I don’t know
why. I actually am quite fascinated with megastructures like these but have a
hard time appreciating them sometimes while grappling with the extrasensory
overload that viewing them can induce.

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ben_w
I had something like that in NCY a few years ago. The upper parts of the new
world trade centre building were always so far away they lacked parallax, so
it was like looking at a skybox in a sprite-based FPS.

I don’t get the effect with pictures of big things, but in addition to not
finding the lack of parallax confusing in that situation, I also know that is
part of my mind getting the scale wrong.

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halfdan
Would this also imply that even today new mass could be created? Similar to
how Hawking Radiation assumes virtual matter/antimatter pairs getting created
all the time would it be plausible for neutrinos and their antimatter
counterparts to pop into existence without fully annihilating each other?

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zvrba
A question to particle physicists: I've always thought that matter and anti-
matter qualifications applied only to charged particles. Neutrinos have no
charge, so how can it have an antiparticle? Does there exist an "anti-neutron"
as well?

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bonzini
Not a physicist but I can answer this.

Antineutrinos have opposite lepton number compared to neutrinos. Lepton number
is preserved by all particle reactions[1] so for example beta decay must
produce an antineutrino (L=-1) in addition to an electron (L=1).

Antineutrons also exist. Neutrons are composed of three quarks, uud (u has
charge 1/3 and d had charge -2/3), while antineutrons are composed of two up
antiquarks (charge -1/3) and one down antiquark (charge 2/3). And as in the
case of neutrinos, neutrons have baryonic number 1 like protons and
antineutrons have baryonic number -1 like antiproton a. Hence, for example, a
beta decay will always turn a neutron into a proton and an antineutron into an
antiproton (though the latter is theoretical).

[1] More precisely there is a lepton number for each generation
(electron/muon/tau) and all three are separately preserved.

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canjobear
How does this square with the idea that antiparticles are particles traveling
backwards in time?

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maxnoe
That's not an idea, it's what some of the math in the standard model looks
like.

The fact that we are here tells us there are fundamental differences between
matter and anti matter, otherwise the big bang would have created exactly
equal amounts that would have annihilated.

CP asymmetry is an observational fact, measured also bei LHC.

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michaelcampbell
Is there anything in the science about locality? That is, is there anything
that says there might be somewhere that has an abundance of anti-matter
exactly offsetting our abundance of matter?

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maxnoe
[https://arxiv.org/abs/1204.4186](https://arxiv.org/abs/1204.4186)

