Neutrinos are infuriating, but we still have to study them

The particles hold the keys to new physics. If only we could understand them.

See full article...

 

[osgat]

It should be the difference between the masses squared and not the square of the difference (which must be positive, making absolute value redundant)

 

[mrjk]

Just a note - Ice Cube is actually relatively cheap - It cost way less than a half a billion dollars - less than many other high energy experiments. Running it isn't outrageous either. It is weird how working in Antarctica kind of forces small Teams and thus smaller budgets than one would think.

 

[MMarsh]

I'm surprised to see Super-K and IceCube mentioned, but SNO omitted. The combination of data from Super-K and SNO (a thousand-ton D₂O detector capable of distinguishing between charged current and neutral current interactions, and therefore of reporting the electron neutrino flux separately from the total flux of all three flavours) was critical in identifying that neutrino oscillations were real, and in developing our understanding of all this. The 2015 Nobel Prize was awarded jointly to the directors of the two teams.

I had the good fortune of taking a course and several seminars under Dr. Art McDonald during his tenure as SNO director. While some of the math was a bit daunting at the time, it was undeniably cool to get a view deep into the leading-edge frontier of physics – a region in which "we genuinely don't have a clue yet" was a common answer, and the excitement of new discovery permeated everything.

Also, a (perhaps minor) nitpick. The SN1987a neutrino detection would have been during the time of KamiokaNDE-II. Super-K did not come online until 1996.

 

[MST2.021K]

Like so many other things in particle physics, it's not so much that something exists moreso that enough energy/matter stays roughly in a spot long enough that we call it a thing. My mind continues to break at the thought of the subatomic world and how nebulous it seems, so neutrinos are just another piece of things that are, but really aren't fully there.

Makes me wonder if dimensions work like electron energy levels- things can jump up and down, maybe stay in between or exist across multiple. So much more to learn.

 

[Simk]

I really enjoyed that article! I'm none the wiser for having read it, but that seems fitting for the subject matter.

 

[cbridgeman]

This kind of article is why I love Ars!

 

[NameRedacted]

Back when I first graduated with my engineering degree, I really wanted to go back and get a PHD in physics because I loved QM so much.

Every time I read one of these articles, I’m glad I didn’t. Don’t get me wrong, this stuff is exciting: but I don’t think I could handle how much the universe “wants” to perplex us.

I have little doubt that the physics world will need to completely change everything to figure out all four of the big “mysteries”: Neutrinos, Dark Matter, Dark Energy, and the Hubble Constant. I also have little doubt that the solution will be complex, expensive, and be an advancement on the level of QM (I.e. atomic energy and semiconductors).

I hope I’m alive for when it happens, but god am I ever glad I haven’t spent my career trying to sort it out.

 

[ip_what]

Like so many other things in particle physics, it's not so much that something exists moreso that enough energy/matter stays roughly in a spot long enough that we call it a thing. My mind continues to break at the thought of the subatomic world and how nebulous it seems, so neutrinos are just another piece of things that are, but really aren't fully there.

Makes me wonder if dimensions work like electron energy levels- things can jump up and down, maybe stay in between or exist across multiple. So much more to learn.

Planck constant - Wikipedia

en.wikipedia.org

Pack an ansible in case you need help escaping from this quantum rabbit hole.

 

[karadoc]

Neutrinos being left-handed has always been something that I've found very interesting... But I've forgotten something. Actually I've forgotten a lot, no doubt, but one particular thing is this: since neutrinos have mass, they can't travel at the speed of light. Therefore it is possible to overtake one by moving faster than it is, such that relative to you the neutrino's direction of motion would then be reversed (compared to before you overtook it)... so then I'd expect that to be a right-handed neutrino from the point of view of that speedy observer.

Is that the case? I suppose we can't really know, because can barely detect neutrinos at all let alone detect them with something moving near light-speed relative to... something. Anyway, there's something fishy going on there.

 

[NameRedacted]

such that relative to you the neutrino's direction of motion would then be reversed (compared to before you overtook it)... so then I'd expect that to be a right-handed neutrino from the point of view of that speedy observer.

I may be very wrong here, but I think that the entire point of chirality is that you can’t just reverse it by changing your perspective.

 

[ip_what]

Back when I first graduated with my engineering degree, I really wanted to go back and get a PHD in physics because I loved QM so much.

Every time I read one of these articles, I’m glad I didn’t. Don’t get me wrong, this stuff is exciting: but I don’t think I could handle how much the universe “wants” to perplex us.

I have little doubt that the physics world will need to completely change everything to figure out all four of the big “mysteries”: Neutrinos, Dark Matter, Dark Energy, and the Hubble Constant. I also have little doubt that the solution will be complex, expensive, and be an advancement on the level of QM (I.e. atomic energy and semiconductors).

I hope I’m alive for when it happens, but god am I ever glad I haven’t spent my career trying to sort it out.

Mad props to the tiny number of people who have the ability and desire both to understand the math of things like eigenstates and talk about them in a way that’s more or less coherent to those of us with an interest in science but not the brain melting math.

At one point in my life I was pretty good at linear algebra, for an undergrad engineering student, which I figure puts me somewhere in the top couple percent of math knowers. The math that these physicists get up to makes me want to crawl into a hole.

Which, I suppose, is a long way of saying great article!

 

[Faanchou]

Neutrinos being left-handed has always been something that I've found very interesting... But I've forgotten something. Actually I've forgotten a lot, no doubt, but one particular thing is this: since neutrinos have mass, they can't travel at the speed of light. Therefore it is possible to overtake one by moving faster than it is, such that relative to you the neutrino's direction of motion would then be reversed (compared to before you overtook it)... so then I'd expect that to be a right-handed neutrino from the point of view of that speedy observer.

Is that the case? I suppose we can't really know, because can barely detect neutrinos at all let alone detect them with something moving near light-speed relative to... something. Anyway, there's something fishy going on there.

That is one of those situations where it's imperative to make a distinction between obserbable helicity and inherent chirality. Just because they might have the same value at the massless limit that doesn't make them the same thing.
"The direction of a particle’s spin relative to its direction of momentum" used in the article better describes helicity, while chiral handedness is more ... spinory, for lack of a better word.

 

[Antron Argaiv]

By "driving scientists crazy", the authors really mean "providing full employment for newly minted Theoretical Physics PhDs"

[waits to see Einstein proved right again]

 

[Troglodytes troglodytes indigenus]

"It started out innocently enough. Nobody asked for or predicted the existence of neutrinos, ..."

Get your facts straight.

The neutrino was predicted in 1930, 26 years before we found them, the simple consequence of the law of conservation of momentum.

 

[baloroth]

Neutrinos being left-handed has always been something that I've found very interesting... But I've forgotten something. Actually I've forgotten a lot, no doubt, but one particular thing is this: since neutrinos have mass, they can't travel at the speed of light. Therefore it is possible to overtake one by moving faster than it is, such that relative to you the neutrino's direction of motion would then be reversed (compared to before you overtook it)... so then I'd expect that to be a right-handed neutrino from the point of view of that speedy observer.

Is that the case? I suppose we can't really know, because can barely detect neutrinos at all let alone detect them with something moving near light-speed relative to... something. Anyway, there's something fishy going on there.

That is the 11 million krona question. If neutrinos are a Majorana particle, then all neutrinos are a combination of a left-handed neutrino and a right-handed anti neutrino, so you'll see a right-handed anti neutrino. You don't even need to travel faster than the neutrino to make that observation: since a massive neutrino is always in a mix of the two states (albeit normally dominated by the left-handed component), so you can sometimes measure a neutrino as an anti neutrino. That's what neutrinoless double beta decay experiments are looking for: neutrinos acting as their own anti particle.

If OTOH neutrinos are Dirac particles (i.e. not their own antiparticle), I'm not sure what you'd see. Probably nothing: there are some theories about right-handed neutrino states that simply don't interact with anything (so called "sterie neutrinos", which are a dark matter candidate), but those are pretty speculative and by definition impossible to directly detect.

 

[dmsilev]

• The sum of all three neutrino masses cannot be more than around 0.1 eV/c2
• The absolute value of the square of the difference between m2 and m1 is 0.000074 eV/c2
• The absolute value of the square of the difference between m2 and m3 is 0.00251 eV/c2

One thing which the article didn't mention is that there's an additional question hiding in these constraints. Usually, mass scales with family; the electron is lighter than the muon is lighter than the tau, and similarly for the quarks. We assume that that's the case for neutrinos as well, that m1 (the major constituent of electron neutrinos) is less than m2 is less than m3. That's called the "normal hierarchy" solution. However, the data doesn't prove that. There's also an "inverted hierarchy" fully consistent with the data which swaps the ordering. And we can't tell which one is correct. The only reason for the somewhat prejudicial names "normal" and "inverted" is the sense of elegance that the laws of physics should be somewhat consistent.

 

[Nazgutek]

That was a fun read. I feel like I've climbed a single Dunning-Kruger step and now I feel like I know that I know less about the universe than I did before reading this article!

 

[NinjaNerd56]

Maybe ask the oldtrinos what the neutrinos are up to….

 

[DovePig]

I may be very wrong here, but I think that the entire point of chirality is that you can’t just reverse it by changing your perspective.

IANAP (so apologies if I got it wrong), but doesn't that only apply to massless particles (moving at c) ?

For all others, helicity ≠ chirality.

 

[eldakka]

Why do I have a sudden craving for ice cream?

 

[neil_w]

Well, the properties of neutrinos don’t line up like this. They’re weird. When we see an electron-neutrino in an experiment, we’re not seeing a single particle with a single set of properties. Instead we’re seeing a composite particle—a trio of particles that exist in a quantum superposition with each other that all work together to give the appearance of an electron-neutrino.

For a moment I considered just closing the browser tab after reading this paragraph.

This was a very good article, trying to explain the nearly unexplainable. Hat tip to the physicists who are able to grasp it all.

 

[Peevester]

IANAP (so apologies if I got it wrong), but doesn't that only apply to massless particles (moving at c) ?

For all others, helicity ≠ chirality.

Correct, at least as I understand it. Chirality is Lorenz Invariant, Helicity isn't, for particles with a mass. if a particle doesn't have mass, it travels at the speed of light, and there's no frame of reference where you can see a reversed helicity.

I am not sure I even understand what I wrote there, honestly, but it's all I've managed to puzzle out on the topic of particle handedness.

 

[DovePig]

Correct, at least as I understand it. Chirality is Lorenz Invariant, Helicity isn't, for particles with a mass. if a particle doesn't have mass, it travels at the speed of light, and there's no frame of reference where you can see a reversed helicity.

I am not sure I even understand what I wrote there, honestly, but it's all I've managed to puzzle out on the topic of particle handedness.

I like to think of it in terms of an analogy of observing a baseball pitch from a high speed train – going in one direction, you'd see a fastball, going back, you'd see a curveball. Lorentz invariant massless particle would be you observing the pitch sitting on the sideline.

Of course, as all such analogies, it's quite probably inherently flawed, but it's the only way I can wrap my feeble aging brain around it

 

[All4vols]

Like others, I really enjoyed the article. I'm also almost completely ignorant of the math and science of this (I struggled with quantum mechanics in college). But... the description portrayed here of neutrinos makes me think of the old thought experiment about an entity that exists in 2 dimensions interacting with an object that has 3 dimensions. How would that entity perceive the 3D object? Now image us being the 2D beings and the neutrinos being a horse galloping across our field of perception with us only aware of the hooves when they hit our reality. That's the best my poor brain can come up with to try to accept this article without going into vapor lock.

Good luck to all you math people. I'm not built to deal with our reality at this level. Maybe more articles like this as we learn more will keep me engaged and sane.

 

[baloroth]

I may be very wrong here, but I think that the entire point of chirality is that you can’t just reverse it by changing your perspective.

Yes, but massive particles can't exist in a pure chiral state. So neutrinos (having mass) must be in a mixed state. The question is, what is that mixture. It's mostly the left handed chiral state, but what is the other component?

 

[JEE]

Loved the article!

 

[osgat]

Neutrinos being left-handed has always been something that I've found very interesting... But I've forgotten something. Actually I've forgotten a lot, no doubt, but one particular thing is this: since neutrinos have mass, they can't travel at the speed of light. Therefore it is possible to overtake one by moving faster than it is, such that relative to you the neutrino's direction of motion would then be reversed (compared to before you overtook it)... so then I'd expect that to be a right-handed neutrino from the point of view of that speedy observer.

Is that the case? I suppose we can't really know, because can barely detect neutrinos at all let alone detect them with something moving near light-speed relative to... something. Anyway, there's something fishy going on there.

That's a very good question. As others pointed out, helicity, the relative direction of a particle's spin and its velocity is the same as its chirality only when it's massless. For massive particles the wiki says

That is, helicity is a constant of motion, but it is not Lorentz invariant. Chirality is Lorentz invariant, but is not a constant of motion: a massive left-handed spinor, when propagating, will evolve into a right handed spinor over time, and vice versa.

so that we actually know that right-handed neutrinos exist. The thing is that according to the electroweak theory, only left-handed neutrinos couple to other particles, and the detectable neutrinos are ultra-relativistic whose chirality oscillations is very weak, it's an open question whether right-handed there are is a significant population of right-handed neutrinos in our frame of reference

 

[Winston11]

"It started out innocently enough. Nobody asked for or predicted the existence of neutrinos, ..."

Get your facts straight.

The neutrino was predicted in 1930, 26 years before we found them, the simple consequence of the law of conservation of momentum.

Actually it was the apparent lack of conservation of energy, momentum and angular momentum during beta decay which caused the confusion at the time. Niels Bohr even proposed (erroneously) that energy conservation was invalid during beta decay.

 

[orwelldesign]

"If I hand you an electron, you have… an electron. It has a specific mass. A specific spin. A specific charge. A specific generation"

No you don't. You have a set of measured properties that science has attached a name to. Don't let that fool you into thinking that you understand whatever it is that is responsible for those properties.

This for me is the central issue with subatomic physics. We are attaching names to quantified observations and then talking about those names as though they are things we understand. We do not. No one knows what an electron is made of, whether it is a real particle, or why it behaves the way it does, and the same goes for every other subatomic particle.

What we have is a model, which is just a convention for being able to think about and talk about things we really don't understand.

We have a very consistent model that seems to accurately reflect something about how the world works -- models that make predictions which are, very, very often borne out by experiments.

If you ask a particle physicist whether or not they understand particle physics, they'll say they don't know much.

But that's different than not understanding. We use our understandings to do things that would seem like magic to someone from a hundred years ago, but we understand electrons well enough to control them and utilize them in ways consistent with theory.

I guess my point is that "why" is not actually a physics question. "Why" is more of a fiction that an electron ever could be.

 

[everynone]

the trouble with neutrinos is that we keep eliminating other options. The higgs particle is where it should be. Dark matter/energy remains elusive. SuSy remains a pipe dream. Where else is the new physics hiding except with the particle that is the hardest to detect?

 

[SGJ]

I spent yesterday visiting Woolsthorpe Manor, the birthplace and family home of Isaac Newton - physics was so so much simpler in the 17th century!

 

[Derecho Imminent]

I marvel at how God, a trinitarian God, has imprinted his nature on his creation. Our understanding of the Trinity is as elusive as our understanding of neutrinos, it seems. Yet, there appear to be stunning parallels.

Assuming you believe in God and know that your God is greater than the universe, and also know that you do not understand the universe, you should realize that you cannot possibly understand the nature of God. His nature being beyond your understanding means that it makes no sense to say that he imprinted his nature on the universe.

 

[TroubleMan]

The Sun is pumping out enough neutrinos that approximately 6 billion of them pass through the area of your thumbnail every single second.

I've always dreamed of a world where we could harvest the energy of neutrinos passing through us. It would be nearly infinite energy. We could harvest the sun's energy from anywhere, even underground. Neutrinos individually don't carry a lot of energy, but there are billions passing through any place on the earth per second.

That would of course require a material that's all weak force to catch them, which is well beyond our capabilities right now.

 

[Smashing Young Man]

I've been a science nerd since childhood, but physics have become so inscrutable for a layperson such as myself that I can no longer find much excitement in their esoteric mysteries. The eye-watering costs associated with exploring these mysteries just leaves me hoping that some practical applications will eventually come from it, like neutrino toothpaste or whatever.

 

[Dave's not here]

Planck constant - Wikipedia

en.wikipedia.org

Pack an ansible in case you need help escaping from this quantum rabbit hole.

So, do I have this right? A photon traveling at the speed of light (of course,) travels one Planck unit of length in one Planck unit of time?

 

[phred14]

Interesting side-note. When the solar neutrino problem was still un-solved, Arthur C Clarke wrote Songs of Distant Earth. His proposed solution was that hydrogen fusion in the core had stopped and was getting set to change to helium fusion - the sun was getting ready to change and render the Earth uninhabitable. We had a thousand-year warning and began a massive multi-stage interstellar exodus. The story proper was about the interaction of people from two of those stages.

The story could only have been written during a limited time window.