I didn't even know they were Catholic...

June 1, 2010 8:27 PM

Apparently Neutrinos have mass.
posted by Confess, Fletch (83 comments total)

You just blew my mind.
posted by stoneweaver at 8:30 PM on June 1, 2010

Cool. A really, really, REALLY, difficult experiment that produced a confounding result. Yay, science.
posted by unSane at 8:31 PM on June 1, 2010 [1 favorite]

No they don't.
posted by furiousxgeorge at 8:32 PM on June 1, 2010 [1 favorite]

Nobody noticed all this time because they always wore vertical stripes.
posted by oneswellfoop at 8:34 PM on June 1, 2010 [19 favorites]

Kickass.
posted by Durn Bronzefist at 8:36 PM on June 1, 2010

I only go at Christmas.
posted by doublehappy at 8:38 PM on June 1, 2010

My first thought was "Holy shit."
posted by Joe Beese at 8:43 PM on June 1, 2010

Wow, the particle beam from CERN has been spewing neutrinos for 4 years now and they've only gotten one hit on their detector? Talk about a needle in a haystack - good thing they got something before their grants come up for renewal.

So if neutrinos have mass, could this somehow be related to dark matter?

By the way, we've heard about the lab at Gran Sasso before: this is the place that used lead ingots from an ancient Roman shipwreck for their radiation shielding.
posted by Quietgal at 8:51 PM on June 1, 2010 [2 favorites]

Awsome news. But I could have conducted a level three subspace sensor sweep and told you the same thing.
posted by Avenger at 8:53 PM on June 1, 2010

Goddamn, I did not see the title.

Anyway, for those who, like me, don't really know what a neutrino is, here are neutrinos:

- on WikipediA
- in 60 seconds
- with their friends
- at Georgia State University
- in Feynmann diagrams

and

- making people laugh.
posted by doublehappy at 8:53 PM on June 1, 2010 [4 favorites]

Can anybody provide a translation for non-particle physicists?
posted by Pope Guilty at 8:54 PM on June 1, 2010 [2 favorites]

A footnote to the standard model, nothing more. Wake me up when they discover they have a non zero charge.
posted by kush at 8:58 PM on June 1, 2010

Like tall
And painless guillotines, they fall
Down through our heads into the grass.
posted by kid ichorous at 8:58 PM on June 1, 2010 [4 favorites]

Pope Guilty,

Try this.
posted by lukemeister at 8:58 PM on June 1, 2010 [6 favorites]

Holy crap, we may be at the dawn of a new physics. Amazing.
posted by Ron Thanagar at 8:58 PM on June 1, 2010

The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davis beginning in the 1960s.

Taus will be muons and muons will be taus...
posted by Anything at 8:59 PM on June 1, 2010 [4 favorites]

Taus and muons are obviously just different moments in wave-form processes. To pretend other is asinine and wastes everybody's time.
posted by clockzero at 9:03 PM on June 1, 2010 [1 favorite]

My brother Fred was at Los Alamos when they found evidence for neutrino mass fourteen years ago. So yeah, I was thinking neutrinos had mass way before it became cool.
posted by Jpfed at 9:05 PM on June 1, 2010 [4 favorites]

I thought the universe was pretty hot way before it became cool.
posted by Dumsnill at 9:08 PM on June 1, 2010 [6 favorites]

Hah, suck it Trekkies! In a few years' time, grade school kids will see an episode of TNG and say, "Did people really believe that neutrinos have no mass? Duh!"
posted by 1adam12 at 9:11 PM on June 1, 2010

Well, shit.

(Said in the awed tones of a person who has just witnessed an alien abduction or something)
posted by KathrynT at 9:12 PM on June 1, 2010 [1 favorite]

Is this a huge surprise? I somehow already thought we were pretty sure they had mass before today.
posted by floam at 9:12 PM on June 1, 2010

When they say that this was "the final missing piece of the puzzle", they really mean "late to the party". There's been strong evidence of neutrino oscillations (as observed here) for at least ten years. It seems like this was just the first result from an accelerator? Everything else has been from observations of "naturally" generated neutrinos (solar or atmospheric).

I somehow already thought we were pretty sure they had mass before today.

Yeah. We were.
posted by mr_roboto at 9:17 PM on June 1, 2010 [1 favorite]

From Wikipeida: In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos do indeed flavor oscillate, and therefore have mass.

So that neutrinos have mass was already known. I believe this experiment actually showed the oscillation as it happened.
posted by CheeseDigestsAll at 9:18 PM on June 1, 2010

So...a question from someone with no physics knowledge beyond GTR. Does this mean that distinct, mass-bearing particles can occupy the same point in spacetime? I ask because it seems odd that neutrinos could pass through matter unhindered, yet themselves have mass.
posted by voltairemodern at 9:19 PM on June 1, 2010

lukemeister: "Pope Guilty,

Try this."

Good article.

If I understood it correctly, this may be an important advance in understanding dark matter. Which would have implications concerning The Ultimate Fate of the Universe?
posted by Joe Beese at 9:21 PM on June 1, 2010

It's been years since I have gone near this, so I am sure I have a lot of it wrong:

Okay, so, neutrinos were once a theoretical byproduct of making certain equations balance. Basically, they were placeholders to preserve things like conservation of angular momentum and linear momentum and energy. However, nobody would see the bloody things. Just zoom off and let's pretend these exist, even they we cannot see them and they do not want to interact with anything.

This went on for a few years until we figured out how to detect them, but they really do not want to interact with normal matter, so you have to do things like fill abandoned mines with super-pure water doped with some particular element (just the right chlorine isotope, or gallium) and then line the whole thing with photo detectors waiting to see one photon of just the right frequency show up once a month because that just might mean a neutrino interacted with whatever you have your mine filled up with. They interact "weakly," which is to say they ignore the electromagnetic force and the strong nuclear force. It's just gravity and weak nuclear forces for these guys.

Now, the Standard Model is this sort of physics construction which says, "Given most of our observations, this is a good predictive model for particle physics." Most physicists agree that it cannot be the end-all, but it works. One of the bits in it is that the lightweight particles, leptons, come in three families. (There's some fun astrophysical bits showing that, say, five families would result in a very different proportion of helium to hydrogen and we'd have noticed that by now). So the electron, being a lepton, has some buddies ... the bigger, heavier cousins, known as the muon and the tauon (aka "tau particle").

However, one feature of the Standard Model is that it predicts neutrinos with zero rest mass. That means they'd travel at c, just like another popular bit of fluff with zero rest mass, the photon. The Standard Model has other problems, but this is one of the parts we can test ... maybe.

So some astrophysicists wait around for things like supernovas, and then try to see if the photons arrive before the neutrinos do — if so, then the neutrinos are not traveling at c and, if other things are ruled out, one explanation might be that they have a non-zero rest mass.

A brief jump into QM — particles decay because they can. If you're a very heavy particle, and you could turn into a bunch of smaller particles and preserve various conservation properties, you fall apart. So the electron's sisters fall apart whenever possible, which sucks for dreams like muon-catalyzed fusion, but that's beside the point. Oh, and let's throw in the antimatter evil twin Skippy particles, the positron and its dark relations.

The neutrino, also being a lepton (it's as leppy as a lepton could ever lep, that's how lightweight it is) should also come in families just like the electron. So we call these the electron neutrino, the muon neutrino, and the tauon neutrino. Of course, a neutrino can't quite fall apart into anything else, because, damn, they're small already, but they could shift back and forth (oscillate) between being an electron neutrino or a muon neutrino or whatever. Oscillation requires mass. And we sort of suspected this because we have this whole glut of neutrinos we really expect to see from the Sun, but we only get maybe a half, maybe a third of the expected number. Hrm! A third? Three families, sharing the neutrino estate from the Sun?

So the experiment starts off with a beam of muon neutrinos, which sometimes disappear, but now, for the first time, we see tau neutrinos appearing in our once-pure beam of muon neutrinos. One type has become another type.

tl;dr: We have detected neutrino oscillation. Not had evidence for, but actually caught. That means neutrinos have mass. That's a big whack against the Standard Model, which was suspected, but not exactly ironclad We Know That.

Also, neutrino oscillation totally ruins a Stephen Baxter hard-sf novel. Sorry, photino birds.
posted by adipocere at 9:26 PM on June 1, 2010 [180 favorites]

Does this mean we can spaceships?

I am waiting for proper spaceships.
posted by The Whelk at 9:29 PM on June 1, 2010 [7 favorites]

I was totally gonna say what adipocere said.
posted by codswallop at 9:31 PM on June 1, 2010 [13 favorites]

For those who are new to the amazingness of neutrinos, I recommend the recent May 2010 issue of Scientific American, starting on p. 38. It's a fine overview of the different types of neutrinos and why they morph from one type to another over distance, in addition to talking about the Ice Cube detector at the S. pole.
posted by hanoixan at 9:31 PM on June 1, 2010 [1 favorite]

So that explains that tickle on the back of my neck.
posted by bwg at 9:32 PM on June 1, 2010

Does this mean we can spaceships?

You will levitate!
posted by doublehappy at 9:42 PM on June 1, 2010

Can we somehow block an oil pipe with neutrinos now that they have mass?
posted by rainy at 9:51 PM on June 1, 2010 [14 favorites]

I don't think canned spaceship is very tasty, regardless of the mass of neutrinos.
posted by nat at 10:01 PM on June 1, 2010 [2 favorites]

If I understood it correctly, this may be an important advance in understanding dark matter. Which would have implications concerning The Ultimate Fate of the Universe?

Right. To some extent, whether the universe will expand forever or not just depends on how much dark matter (and something else called dark energy) there is. We think we have measured the amounts of dark matter and dark energy. However, to predict the future of the universe (and also to understand the structure of galaxies in the current universe), we need to know what dark matter and dark energy are "made of", which we don't. Here is a blog post by Sean Carroll which goes into some of this.

Despite the new result, neutrinos are unlikely to comprise most of the dark matter. They like to do their own thing (as adipocere discussed), so it's hard to get them to hang around galaxies as dark matter seems to do.
posted by lukemeister at 10:07 PM on June 1, 2010

voltairemodern: AIUI, even though they don't interact much, neutrinos are still fermions, and would still resist being crammed into the same box, if you could figure out a way to do that. (On the other side of the fence, consider the photon, which is definitely a boson and will happily occupy the same position as other photons, but interacts with matter very readily.) It's possible for massive bosons to exist— the W and Z bosons, e.g..

If neutrinos have mass, though, it makes me wonder if you could slow them down. Could you get a bucket of cold neutrinos?
posted by hattifattener at 10:22 PM on June 1, 2010

Does this mean that distinct, mass-bearing particles can occupy the same point in spacetime? I ask because it seems odd that neutrinos could pass through matter unhindered, yet themselves have mass.

The dirty secret that they don't tell you in basic physics is that matter is actually mostly empty. There's a whole lot of space between atoms, and between the nucleons and electrons that make up those atoms. Neutrinos are expected to have masses on the order of 1.5 electron volts — for comparison, the electron has a mass somewhere in the neighborhood of 500 keV, and protons and neutrons weigh in around 1 GeV. Neutrinos are tiny. They also move very fast (somewhere around 0.99c).

So what this comes down to is that the 65 billion or so solar neutrinos that pass through every square centimeter of the Earth's surface every second tend to whiz through the gaps between atoms (or subatomic particles) without interacting with other particles, and that whole rule about two mass-bearing particles occupying the same point is still valid. This is also why observing anything to do with neutrinos takes a long, long time — you have to generate a lot of the damn things before you get lucky enough for one of them to hit something in your detector.
posted by spitefulcrow at 10:27 PM on June 1, 2010

The way I understood it (from something I saw on the Science channel a couple of years ago) the reason neutrinos need mass to oscillate is that because they are moving at c they have no time. Time slows down as you approach the speed of light and (apparently) STOPS at c.

And that's how they know it has some mass, because it oscillates between the 3 states.
posted by Bonzai at 10:47 PM on June 1, 2010 [3 favorites]

Spaceships in cans!
Neutrinos in your underwear!
Underwear in your spaceships!
Cans in your neutrinos!
posted by blue_beetle at 10:54 PM on June 1, 2010 [1 favorite]

kush: Wake me up when they discover they have a non zero charge.

Your mom has a non-zero charge!!

I'msorryI'msorryI'msorryI'msorryI'msorry!! I also apologize to kush
posted by Greg_Ace at 11:10 PM on June 1, 2010

So...a question from someone with no physics knowledge beyond GTR. Does this mean that distinct, mass-bearing particles can occupy the same point in spacetime? I ask because it seems odd that neutrinos could pass through matter unhindered, yet themselves have mass.

IANAP.

Can two particles occupy the same point? Yes. See "Pauli Exclusion". In the electron shell of every atom, it's possible for each electron position to hold two electrons, and chemically speaking the atom won't really be happy unless there are two there. (That's why everything except the noble gases likes being in chemical compounds.)

An atom with a lonely electron in its shell is called a "radical" and they are usually very chemically reactive.

But that has nothing to do with neutrinos passing through matter. Normal "solid" matter is far from being solid. It's actually mostly empty space. Nearly all the mass is concentrated in the nuclei of atoms, which are surrounded by immense (relatively speaking) open spaces that contain nothing except electron wave functions.

Matter which has all that space collapsed down is called neutronium and the density is beyond belief.

But even neutronium may be mostly empty space. Best guess these days is that leptons and quarks are mathematical points with no diameter, so even hadrons may be mostly empty space.

Did I mention that IANAP?
posted by Chocolate Pickle at 11:29 PM on June 1, 2010

FWIW, Here's a picture of the core of the sun, taken by the 'light' of neutrinos emanating from it...from the Super-Kamiokande neutrino detector. Oh, and the picture was taken through the earth.
posted by sexyrobot at 12:29 AM on June 2, 2010 [9 favorites]

"From Wikipeida: In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos do indeed flavor oscillate, and therefore have mass."

I'm just popping into this thread to mention that The Super-Kamiokande makes awesome desktop wallpaper. That is all.
posted by mullingitover at 12:48 AM on June 2, 2010 [4 favorites]

Can two particles occupy the same point? Yes. See "Pauli Exclusion". In the electron shell of every atom, it's possible for each electron position to hold two electrons, and chemically speaking the atom won't really be happy unless there are two there.

That's not correct at all. First of all, you're completly confused. There are two different types (well, there are lots of types, but two types for this discussion) Bosons and Fermions. Bosons (like a photon) can occupy the same location as other bosons, and Fermions can't (actually the same quantum state, but that includes location).

Of course, Electrons are fermions, so they can't be in the same quantum state. They can be in the same location if they have different spins, though (I think)

But that's all beside the point because you're talking about electron shells which are much larger then the electrons themselves. In fact, in the standard model electrons have zero volume. If two electrons are in the same shell, that doesn't mean they are in the same physical location.
posted by delmoi at 1:05 AM on June 2, 2010

Here's a second tl;dr comment to complement the nice one from adipocere above.

The first thing that I notice is that there doesn't seem to be any draft of a technical paper yet. I see a colloquium announcement from two weeks ago that suggests the experimental team had analyzed part of their data and was getting ready to "open the box" and apply their analysis to their entire dataset. It's plausible that there are lots of other papers written during the development of the experiment that describe how the detector works and what a tau event would look like, and that the eventual paper will say "we got one event as described in ref. 5" and spend the other pages ruminating about dark matter. The OPERA experiment has 170 collaborators, so the absence of a paper doesn't put the result in the same sort of unreviewed no-man's-land as other famous examples of science by press release. Still, it's a little smelly.

So what's the physics here? If you were ever awake in a science class, you probably know that atoms are made of heavy protons and neutrons, that live in the dense center of the atom, and comparatively lightweight electrons that "orbit" the nucleus. The protons and neutrons can be treated as if they are made lighter particles, "quarks," glued together by the "color" force. But so far there is no evidence that you can break electrons or quarks into anything simpler. When people talk about particles, then, they start with electrons and quarks and build more complicated things from there. Because this only approximates reality, it's a "model"; because everyone does it this way, it's "standard": the "standard model." There have been a succession of "standard" models over the past fifty years and we're basically stuck with that dumb name.

In the standard model, it turns out that one electron isn't enough: there are particles that behave like electrons, in that they have electric charge ±e and ignore the color force, with at least three different masses. The heavy electrons, the tau and the mu, are unstable and decay by turning into the lighter electrons. But the "flavor" of these particles (together: "leptons") is conserved in a funny way. When you make a lepton, you always make it with an antilepton that has the same flavor. It's pretty easy to make pairs of electrons and antielectrons, or pairs of muons and antimuons, but you never see a track in a detector where you create an electron and an antimuon. Does not happen: the number of particles with each lepton flavor, minus the number of antiparticles with that lepton flavor, seems to be a conserved quantity. It does happen that a muon traveling through a detector will change into an electron. But when that happens, the muon/electron's momentum and spin change, and change in a way that's consistent with emitting two massless, electrically neutral (and therefore invisible) particles: a neutrino with muon flavor and an antineutrino with electron flavor. This is why people believe in neutrinos.

Here's a flaw in the above description. I said that the difference between an electron and a muon was their mass. But an electron neutrino and a muon neutrino have the same mass in the standard model: zero. What makes them different? Is a particle's flavor determined by its mass? Is its mass determined by its flavor? It turns out the best answer is really neither of these. There are three flavors of neutrino (e, mu, tau) and three masses of neutrino (lightest, middle, heaviest), and a rotation between the two. You can think of this like the three independent directions on the earth (north, east, up) and their easily-measured approximations (magnetic north, the direction of sunrise, perpendicular to the ground). Sure the two bases are related, but depending on where you happen to be that relationship may or may not be simple. The relationship between neutrino flavors and masses is as complicated as is allowed. But the rules for what a particular neutrino does are rather simpler. When a neutrino interacts with an atom, it has a definite flavor: if it's an electron neutrino, it can scatter from the atom by turning into an electron; if it's a muon neutrino, it can turn into a muon; if it's a tau neutrino, it can turn into a tau. (Since this these transitions change the lepton's electric charge, they're called "charged current" interactions. There's also a "neutral current" where a neutrino of any flavor can knock an atom around without making new charged leptons.) When a neutrino is not interacting with an atom, it can have any flavor it wants. But if the neutrino is flying a long way, a small change in its mass has a big effect on its transit time; neutrinos in transit tend to settle into some particular mass state and "forget" what flavor they started out with.

The first evidence for this came about ten years ago when the "solar neutrino problem" was solved. The sun, of course, turns four protons into a helium nucleus with two protons and two neutrons; this means that solar each fission has to emit two antielectrons, which must be accompanied by two electron neutrinos. It's pretty easy to calculate how many solar neutrinos there should be, since we know how bright the sun is and we know the masses of hydrogen and helium. The first forty years of measurements of the solar neutrino flux used detectors that looked for charged-current events, and so only saw electron neutrinos. These experiments showed that there are only a third as many electron neutrinos coming from the sun as we might expect. Finally a solar neutrino experiment (at SNO, I think) used a detector sensitive to both charged current and neutral current interactions. That showed that the total number of neutrinos coming from the sun had been right for fifty years; it was only the electron neutrinos that were missing.

A second important result came from the Kamland experiment in the Kamioka mine in Japan (not the Super Kamioka detector, but a smaller one in the same mine). Japan has a fairly rich ecosystem of nuclear power plants, which emit lots of electron antineutrinos; some of the plants are close to Kamioka, and some are farther away. By coordinating their detector recordkeeping with the operation of these plants, the Kamland folks were able to figure out which plant a particular neutrino probably came from, and measured just how far an electron antineutrino goes before it begins to forget its flavor. That tells you something about how far apart the masses of two of the different neutrinos are.

If OPERA has really seen that muon neutrinos oscillate "up" to tau neutrinos, then the relationships between the different neutrino masses have just become much more constrained.
posted by fantabulous timewaster at 1:07 AM on June 2, 2010 [33 favorites]

i read the line and every comment like three times and i'm just now kind of certain of what this whole neutrino thing is and is doing and implies.
I am 100% that this is totally awesome, though.
posted by The Esteemed Doctor Bunsen Honeydew at 2:34 AM on June 2, 2010 [1 favorite]

Can anybody provide a translation for non-particle physicists?

Very, very, very small things are made of even smaller things than that.

that's as far as my brain goes with it
posted by Devils Rancher at 5:08 AM on June 2, 2010

A Higgs-Boson walks into a church, the priest says "We don't allow Higgs-Bosons in here."
The Higgs-Boson says "But without me how can you have mass?"
posted by exogenous at 5:23 AM on June 2, 2010 [15 favorites]

"Holy crap, we may be at the dawn of a new physics."

Do you know what this could mean for science? It could mean actual advances in the field of science!
posted by markkraft at 6:18 AM on June 2, 2010

Thanks for the explanations!
posted by Pope Guilty at 6:28 AM on June 2, 2010

A neutron walks in to a bar and asks the bartender "How much for a beer?" Bartender says, "For you, no charge."
posted by Blazecock Pileon at 6:34 AM on June 2, 2010 [2 favorites]

But even neutronium may be mostly empty space. Best guess these days is that leptons and quarks are mathematical points with no diameter, so even hadrons may be mostly empty space.

The problem here is that the whole idea of solid object versus empty space is another one of those macroscopic human concepts that just doesn't translate to the scale of subatomic particles / quarks.
posted by aught at 6:38 AM on June 2, 2010 [1 favorite]

i read the line and every comment like three times and i'm just now kind of certain of what this whole neutrino thing is and is doing and implies.

posted by The Esteemed Doctor Bunsen Honeydew

Eponysterical.
posted by nevercalm at 7:21 AM on June 2, 2010 [1 favorite]

I am so liking this. In the early 70's, I was a gofer for a small part of DUMAND. Because there was so little experimental evidence (these critters don't leave tracks, much) the theoreticians kept coming up with explanations that had experimentalists pulling their hair out.

One I remember was when the low solar neutrino counts were discovered somebody explained it by saying that the sun had gone out. Maybe it had and maybe it hadn't. The problem was to come up with an experiment that would produce a little evidence without waiting ten thousand years for daylight to get a little dimmer.

So they come up with an experimental scheme and as they're going into it, an alternate hypothesis blows the experiment up by saying what it the only thing keeping the Sun hot is a little bitty black hole in the middle of it.

Not big enough to swallow it, but enough to generate enough radiation pressure from the stuff falling into it crashing into each other on this side of the event horizon. This was explained as black holes not really being black, but actually a very very deep red.

This conumdrum produced a lot of furrowed brows and deep silences for a while until somebody figured out that it wasn't so and maybe the neutrinos were wobbling.

One of the side efforts from DUMAND was the notorious submarine detector. The idea was that since reactors emitted neutrinos, if you had a sensitive enough neutrino detector, the nuke boats would show up on it as weak, but rapidly moving sources. This caused all sorts of problems because there was some liaison with the Russians on DUMAND. Rumors of espionage and other nonsense - since nothing was secret, the idea of spying on an open collaborative project was silly, but there were just enough people willing to be silly.

So there was this conference and it's got a report and the report has an illustration with a picture of a ship on it. And some joker had named the ship Glomar DUMAND, after the Glomar Explorer (Seymour Hersh had just run his expose.) The Russians hit the ceiling and there was a big flap. By the time I heard about it, everybody had calmed down, but there was still a lot of snickering going on.

Later the Navy funded some work to see if neutrino beams could be used to communicate with. The answer was yes, but the rate was something like 2 - 4 bits / hour, so theoretically yes but practically you've got to be out of your mind.

So these recent results are cool. Like I said, critters this small don't leave much in the way of tracks. It sounds like they actually caught one changing, rather than just having a difference in mass counts so you could infer that they were changing.
posted by warbaby at 7:50 AM on June 2, 2010 [5 favorites]

@adipocere & fantabulous:

If you two were writing the physics articles for WPedia, they'd be good for something besides refreshing physicists.

You both win the June 2 Gamow Award for meritorious service unwinding gobbledygook.
posted by Twang at 7:57 AM on June 2, 2010

...When a neutrino interacts with an atom, it has a definite flavor: if it's an electron neutrino, it can scatter from the atom by turning into an electron; if it's a muon neutrino, it can turn into a muon; if it's a tau neutrino, it can turn into a tau. (Since this these transitions change the lepton's electric charge, they're called "charged current" interactions. There's also a "neutral current" where a neutrino of any flavor can knock an atom around without making new charged leptons.) When a neutrino is not interacting with an atom, it can have any flavor it wants...

Does anyone else secretly suspect that physicists, years ago, discovered that the universe actually runs on magic and are now just gently mocking the rest of us?

adipocere and fantabulous timewaster - Thanks for those awesome posts. Even if you're just furthering the big Physics Comedy Conspiracy, I'm pretty sure I understand a lot more after reading them. And I'm unusually dense when it comes to physics.
posted by metaBugs at 7:59 AM on June 2, 2010 [1 favorite]

To be precise, fermions are quite capable of occupying the same space, but they can't occupy the same quantum state. Quantum states typically have a defined density and momentum that vary with position, and they have an associated spin orientation. If you jam a bunch of electrons (a kind of fermion) into a box, their quantum waveforms will all be distributed all throughout the box (but not uniformly, there will be ripples). None of the electrons would be in the same state, but you might find two that had the same distribution of position and momentum but had their spin in opposite directions ---they're basically right on top of each other.

In our macroscopic world, it makes sense to have an idea like "no two objects can occupy the same space", but in the subatomic world, it's nonsense. In quantum field theory, all particles are modeled as point particles, e.g. they formally have zero volume. So looked at one way all space is empty space. I think it's more reasonable to think about the density of quantum fields. Since they spread out and occupy a volume, in a region that's dense with matter most space is filled ---but particles may still be able to travel through it. If you've ever seen pictures of electron orbitals in atoms, those are attempts to depict these waveforms, and they all overlap somewhat.
posted by Humanzee at 8:04 AM on June 2, 2010

A neutrino can't walk into a bar, because it's traveling at almost the speed of light.
posted by lukemeister at 8:35 AM on June 2, 2010 [3 favorites]

I don't want to get into specifics, but I'd be lying if I said that I wasn't going to use this for evil.
posted by quin at 8:35 AM on June 2, 2010 [3 favorites]

A neutrino can't walk into a bar, because it's traveling at almost the speed of light.

Fine, we'll go to a bar moving at or near the speed of light.

There's one of those in Chelsea, right?
posted by The Whelk at 8:38 AM on June 2, 2010

in addition to talking about the Ice Cube detector at the S. pole

Dude's kinda hard to miss.
posted by adamdschneider at 8:41 AM on June 2, 2010 [4 favorites]

Just to reiterate what others have said, we've known about neutrino masses for a while. We have never observed muon neutrinos oscillating to tau neutrinos before, though. This is exciting because it might help us to better understand the differences between the neutrino types (mass eigenstates).
posted by Premeditated Symmetry Breaking at 9:23 AM on June 2, 2010

Have you been to the neutrino ice cream shop?

They only have 1 flavor.
But if you get 2 scoops, you might end up with a different flavor.
posted by vacapinta at 9:55 AM on June 2, 2010 [1 favorite]

A neutron walks in to a bar and asks the bartender "How much for a beer?" Bartender says, "For you, no charge."

A cation walks into a bar, screaming "I'VE LOST AN ELECTRON!" The bartender asks, "Are you sure?" and the cation says

I'm positive.
posted by ROU_Xenophobe at 9:58 AM on June 2, 2010 [1 favorite]

I love the picture of that neutrino detector because it took me a while to load. As the JPG interlaced, line by line, it's possible that the detector could be any size, but when it got down to the tiny people in the left hand corner, it was clear just how big it was, and how much work had gone into it.
posted by codacorolla at 10:52 AM on June 2, 2010 [1 favorite]

Hah, suck it Trekkies! In a few years' time, grade school kids will see an episode of TNG and say, "Did people really believe that neutrinos have no mass? Duh!"

I always found it amusing that Geordi could see them with his visor, being how much smaller it was than an abandoned salt mine and not obviously lined with PMTs.

Does anyone else secretly suspect that physicists, years ago, discovered that the universe actually runs on magic and are now just gently mocking the rest of us?

A fairly large subset of us, while having no proof, have held this hypothesis for quite some time. Sorry if you feel mocked, see also Hanlon's Razor.
posted by 7segment at 11:10 AM on June 2, 2010

Does anyone else secretly suspect that physicists, years ago, discovered that the universe actually runs on magic and are now just gently mocking the rest of us?

That discovery was made by Arthur C. Clarke, but we're not mocking anybody.

hattifattener: here's an interesting suggestion about the consequences of slowed-down ("cold") massive neutrinos.
posted by fantabulous timewaster at 11:12 AM on June 2, 2010 [1 favorite]

Since the different flavors of neutrinos have different masses, when they change from one flavor to another flying along not interacting with anything else, do they speed up and slow down to satisfy conservation of momentum?

I looked at an abstract or two that seemed to be addressing this question, but didn't understand them.
posted by jamjam at 12:25 PM on June 2, 2010

jamjam, I think it doesn't. Like I wrote above, the flavor states and the mass states are similar but not the same. As the neutrino travels it evolves from its initial state with definite flavor towards one of the states with definite mass. Once it has a definite mass, the neutrino is in a mixture of the available flavors and doesn't "choose" one until it scatters from an atom again.

Note that the neutrino's rest mass is probably about one eV, but observable neutrinos have energies of millions or billions of eV. A difference of less than one part per million in the travel time of two species of neutrino is probably not something that will ever be measured directly.
posted by fantabulous timewaster at 12:46 PM on June 2, 2010 [1 favorite]

there doesn't seem to be any draft of a technical paper yet

From Nature's blog: A preprint paper should follow in a few days on Arxiv.org.
posted by lukemeister at 1:04 PM on June 2, 2010

Your mom has a non-zero charge!!

I'm sorry

Don't be. She's very attractive.
posted by rokusan at 1:56 PM on June 2, 2010 [6 favorites]

Question: how do they know the neutrino they detected is from the beam they produced? If there are billions of neutrinos flying through everything all the time, then it seems like the whole idea of a pure one-flavor beam* falls apart. Or is it just a numbers game based on the fact that the vast majority of neutrinos will be coming from the direction of the sun?

*Mmmm... pure one-flavor bean...
posted by dephlogisticated at 2:33 PM on June 2, 2010

What did the tau neutrino say to the muon neutrino?

I don't know. Do I look like a particle physicist? These are extremely complex theories requiring years of erudition and observation. One can't just expound on the nature of the interaction between particles which are nearly mental abstractions their existence is so ephemeral. These things are femtometers in length or something. They couldn't be said to communicate at all much less in words in English such that we could understand it in any meaningful way. Usually transmissions between particles are described in mathematical models in one of the four fundamental interactions of nature, not in words in some sort of human environment setting. The entire premise of the question is as ridiculous as trying to get a disabled man with one arm out of a tree by making him reflexively wave back at you. Obviously if a handicapped individual is stuck in a tree you would require at least another person and perhaps some rope or preferably some aid equipment like a bucket truck so he could be lowered to the ground safely.

Although I am interested in what this does to handedness (chirality).
posted by Smedleyman at 2:48 PM on June 2, 2010 [2 favorites]

I knew it...
posted by Increase at 2:49 PM on June 2, 2010

dephlogisticated: the neutrinos coming from the sun generally don't have enough kinetic energy to make muons in matter at rest on earth. The beam coming from CERN has much higher energy. So when a shower of particles in the detector starts with a muon whose momentum is pointing away from CERN, appearing alone in the middle of the detector, it's reasonable to say that it came from the beam of nearly-all muon neutrinos coming from CERN. It helps that when folks at CERN turn off the muon neutrino beam, the muons stop appearing the detector.

The press release says there were "billions and billions" of muon events associated with this single newsworthy tau event. They ran for a couple of years, which is sixty billion seconds. So when the accelerator was on they were probably seeing a muon every few seconds.

Probably the biggest background was cosmic-ray muons from the top of the atmosphere making it into the detector. But those also tend to have fairly small kinetic energies, and furthermore they are most likely to travel straight down.
posted by fantabulous timewaster at 3:04 PM on June 2, 2010

Humanzee wrote: "In our macroscopic world, it makes sense to have an idea like "no two objects can occupy the same space", but in the subatomic world, it's nonsense."

All this time, I was operating under the impression that subatomic particles do indeed have an absolute position that cannot be occupied by another particle at the same time, but that we cannot measure said position, thus the use of probabilities to describe where a particle likely is at any given time.

In other words, I thought the electron cloud was a better description of the electrons orbiting an atom simply because the precise state of the electrons cannot be measured without changing that state, so we rely on probability instead.
posted by wierdo at 3:27 PM on June 2, 2010

Noooo!!

When I was in school I learned that because nutrinos have inertia but no mass, they can be described as "nothing, spinning".

Now it seems that's not true.

If you stick around long enough everything you learn about science turns out not to be true.
posted by Herodios at 5:16 PM on June 2, 2010 [2 favorites]

If you stick around long enough everything you learn about science turns out not to be true.

Neat, huh?
posted by Pope Guilty at 5:52 PM on June 2, 2010 [6 favorites]

Does anyone else secretly suspect that physicists, years ago, discovered that the universe actually runs on magic and are now just gently mocking the rest of us?

"Nextwave know that science is a trick on white people and that the shamans of the mountains, the jungle, the desert and the steppe have hated Stephen Hawking for five thousand years."
posted by straight at 2:44 PM on June 3, 2010

They ran for a couple of years, which is sixty billion seconds.

You should move to a POSIX-compliant universe.
posted by ryanrs at 10:40 PM on June 3, 2010 [1 favorite]

motherfucker. you'd think at some point in my life I'd have learned to count.
posted by fantabulous timewaster at 5:08 AM on June 4, 2010

weirdo: sorry, just noticed your comment. In the standard model, particles are quantum fields, which have point-like and wave-like properties but are in fact neither points nor waves. One illustration of this is the double-slit experiment. Since this idea is complicated, it gets simplified in popular discourse to the point that most discussions of it bear almost no resemblance to the real theory. For instance, the Heisenberg uncertainty principle is purely a result of the wave-like nature of particles, yet it's popular to discuss it as though it was some sort of practical effect from disturbing particles with insufficiently gentle measurements.
posted by Humanzee at 7:34 AM on June 4, 2010

There was enough to be worrying about during the last days of the Cold War, what with global thermonuclear destruction and all, and these things caused some distress to a small boy. Then a well-meaning aunt gave me a beginner astronomy book that explained the tortuous path that emitted energy from the Sun's fusion core had to take to get to the surface. That many millennia could pass before it made it, but then it would zip right over to the earth in only 8 minutes or so. The book then mentioned in passing the neutrino and its ability to give us an "immediate" (well, 8 minute-old) window into the Solar core, and waxed lyrical about the fact that there were much less neutrinos being detected coming from the sun as had been expected, and ho ho wouldn't it be funny if thus meant the Sun's core was variable, and had dimmed... but that we didn't need to worry right away because it could take hundreds of thousands of years before a dimmed core energy output began to freeze Earth. The chapter then ended, I recall, with a little quip about that being all well and good, except what if the dimming had happened many millennia ago and we were in fact due for Global Cooling?

I was an impressionable kid and I believe my rather confused parents had to spend significant amounts of time convincing a crying, non-sleeping child that the Sun was not, in fact, going to go out and would, in fact, rise the next morning. It was *years* before I read about the neutrino oscillation theory that finally put my young mind at rest.

I am very glad to find further proof that neutrinos, in fact, do transform. I don't know who wrote that damn book that scared me so much but my money is on Patrick Moore.
posted by meehawl at 9:54 PM on June 4, 2010 [2 favorites]