How the Neutrino’s Tiny Mass Could Help Solve Big Mysteries | Hacker News Reader

How the Neutrino’s Tiny Mass Could Help Solve Big Mysteries

quantamagazine.org

37 pointstheafh35 comments

Not really related but I like how they are trying to detect neutrinos to discover a supernova before it happens [1]. As the neutrinos leave the star hours before they collapse (because the neutrinos can easily escape the star due to it's low mass).

[1] https://en.wikipedia.org/wiki/SuperNova_Early_Warning_System

A small correction- it’s not the small mass of the neutrino that allows it to escape quickly, but the fact that they are electrically neutral, and also do not interact with the strong force and do not get caught by the nucleus of atoms. Photons have no mass, but they arrive after the neutrinos because they are slowed down by being constantly absorbed and remitted by the atoms of the star through the electromagnetic force.

Thank you. When supernova 1987A was first detected, I thought I recalled reading an article that talked about how we detected neutrinos from it ~1hr before its visible light. I thought I was misremembering this, but apparently not.

Thanks for clarifying!

Do you think neutrinos could be used to produce electricity?

Because they are electrically neutral, and do not interact with electromagnetic fields, it would be quite hard.

Well, generally speaking, in the world of elementary particles there may be other kinds of interactions (and decay paths) as well as the good old mechanical energy - all waiting to be converted into the electromotive force.

Are there new types of interactions underway that may make neutrinos interaction feasible?

A hypothetical idea is to direct a neutrino beam at the core of a pulsating star, which modulates its frequency and allows for efficient interstellar communication.

https://www.economist.com/science-and-technology/2011/04/07/...

https://arxiv.org/pdf/0809.0339.pdf is the paper

Thing is, neutrinos hardly interact with anything at all, we need huge sensors just to detect a few signals once in a while so they would be na horribly inefficient way to capture energy.

For the sun it's probably easier to capture the 98% of energy that's radiated as light.

The sun is by far the best source of neutrinos.

For a standard core collapse supernova, the vast majority of the released energy is in the form of neutrinos.

That always astounded me: Neutrinos hardly interact at all, but as I understand supernovas it is the neutrinos that cause all the outer layers of the star to blow off at high speed. Supposedly some of the elements heavier than iron get formed by fusion during that explosion. That's a lot of energy transferred to a lot of mass just from neutrinos. So, that's a LOT of neutrinos.

The actual source of the neutrinos is what, something about making a neutron star out of the iron core of the star? Would that be too many neutrinos for just the iron core?

They are primarily coming from neutron capture (electron + proton -> electron neutrino + neutron). During much of the collapse even these weakly-interacting neutrinos get trapped behind the high-density shock wave. As it expands and the density becomes lower, they escape in what's known as the neutronization burst.

Thanks. Makes sense: The big push, e.g., the shock wave, is not all just directly from just the neutrinos from just the collapsing iron core. Thanks.

I'm no expert, but as far as I'm aware it's a combination of beta decay and thermal neutrino pair production.

Thanks!

> While neutrino oscillation experiments have measured the differences between the mass states, experiments like KATRIN home in on a kind of average of the three. Combining the two types of measurements can reveal the value of each mass state, favoring certain theories of neutrino mass over others.

Since the universe's cruel trick seems to be that the Standard Model -- in all its ugly glory -- refuses to be falisified, what is the least surprising outcome for this experiment? Is there a set of neutrino masses that is minimally-illuminating of physics beyond the standard model?

> Is there a set of neutrino masses that is minimally-illuminating of physics beyond the standard model?

There are no neutrino masses at all in the Standard Model. You can put them in by hand, but then you break half the nice ideas used to construct the Standard Model in the first place. Or you can put them in more properly, but then there are perhaps hundreds of distinct ways to do it, and we don't know which one is realized in nature. In other words, the state we're at with neutrinos is roughly where we were at with everything else in the 1960s. In some sense neutrinos have been "new physics" for decades -- we didn't understand them 30 years ago and we don't now.

As for specific mass measurements, there are theories that predict exceptionally nice values for the neutrino mass, but also plenty that don't have any such order. It's certainly possible that knowing all the neutrino masses to high precision wouldn't help at all. After all, we know the quark masses to high precision, and that precision hasn't helped us find an origin for the pattern in their masses. We just have to take them as free parameters.

There are a few interesting things that we could get from looking at neutrino masses.

The first has to do more with the nature of the mass than the mass itself. In the standard model, electrons, muons, and taus get their mass from the Higgs field. There's a way for neutrinos to get their mass in other ways, but it requires them to be their own antiparticles. And this gives a satisfactory answer as to why their masses are so tiny, and suggests some new particles (although at electroweak unification scale, so not anything we're going to achieve with a collider any time soon). There are a number of double-beta decay experiments trying to measure the Majorana mass of neutrinos.

The other would be if the neutrino hierarchy is "inverted". The tau is heavier than the muon is heavier than the electron. Right now, with neutrinos, we can only measure the difference in masses. And so it's not clear if the neutrino with the most election portion[1] is the lightest or if the neutrino with the most tau portion is. The latter would be "inverted" from what we expect, and trying to figure out why might be interesting, though I don't know that it immediately implies new physics.

There're also other things related to masses that are interesting. Neutrino oscillations are determined by the differences in mass. Looking at these, we might be able to discover more generations of neutrino (beyond electron, mu, and tau), which would be new physics.

[1] the mass eigenstates of the neutrino (that is, the things with well-defined masses) are not weak force eigenstates, so they contain mixtures of the electron, mu, and tau neutrinos

Q. So, an atom decays and gives off some particles including a neutrino. So, we look at the mass-energy arithmetic before and after the decay and see that it all adds up but does need the tiny mass-energy of a neutrino.

That fact, that small difference, seems curious, maybe toward new physics? That is, somehow maybe the mass-energy amounts are, once again in science, whole number multiples of something small. If so, then we can look for how the other particles are whole number multiples??

I have to expect that 99+% of physics students have already thought of this.

Is there anything curious about that tiny bit of mass, e.g., why it has to be there at all?

It's a bit different than that. The decay of a neutron into a proton and an electron conserved charge, mass-energy (to an expected degree), and momentum. However, spin was not conserved. The neutrino was dreamed up as kind of a placeholder for the spin. However, it turned out that it was a real thing!

The mass-energy arithmetic should not be the thing you look at for a couple of reasons. First, it's quite difficult to measure with exactitude. Second, the binding energy for particles and their constituents plays a part that is easily within error bounds.

Thanks.

> First, it's quite difficult to measure with exactitude.

I wondered about something like that -- the mechanism really is exact to tiny accuracy, no fuzz, but it's super tough actually to measure that accurately, or some such. If my startup works, I'll return to physics!!! I promise!! Thanks.

If there are more generations of neutrinos, would that also imply extra generations of the charged leptons?

It's a reasonable hypothesis. But the new physics might also lie in why we don't see more than 3 generations of charged leptons or quarks.

In the standard model neutrino masses are 0....

Adding masses is a trivial extension, though, by giving them masses in the same way that electrons and other leptons do.

The Neutrino has always fascinated me since I first learned about particles. It's almost not of this realm with the way it interacts with matter compared to everything else.

I'm curious if there's new physics underway that may make neutrino interactions at a large scale feasible. Experiments that I know usually detect one to five neutrinos a year and I'm wondering if we could ever come up with method that can capture orders of magnitude more than that

It's not quite so bad, with many experiments looking at solar or atmospheric neutrinos seeing hundreds to thousands of neutrino events per year. Experiments at particle accelerator-based neutrino beams can see much larger event rates despite the small cross section, and as one example, the upcoming SBND experiment (https://sbn-nd.fnal.gov/) will see 7 million neutrino interactions in about three years.

Would need to make ultra dense materials which would require subatomic engineering.

Would such a thing even be attainable on earth without the tremendous forces that collapse atoms into neutrons? Does matter in a neutron density state convert back to atomic density state in the absence of such forces?

I think it would be unstable in general but perhaps some shielding could be created to help but even so it seems like strong forces would need to be used to hold the ultradense target together.

Dupe: https://news.ycombinator.com/item?id=21268086

Merged thither. Thanks!

Edit: oops, this one was posted earlier and that was the dupe. Fixed now.

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