Chameleon-Like Behavior of Neutrino Confirmed

Anonymous Apcoheur writes "Scientists from CERN and INFN of the OPERA Collaboration have announced the first direct observation of a muon neutrino turning into a tau neutrino. 'The OPERA result follows seven years of preparation and over three years of beam provided by CERN. During that time, billions of billions of muon-neutrinos have been sent from CERN to Gran Sasso, taking just 2.4 milliseconds to make the trip. The rarity of neutrino oscillation, coupled with the fact that neutrinos interact very weakly with matter, makes this kind of experiment extremely subtle to conduct. ... While closing a chapter on understanding the nature of neutrinos, the observation of neutrino oscillations is strong evidence for new physics. The Standard Model of fundamental particles posits no mass for the neutrino. For them to be able to oscillate, however, they must have mass.'"

Comments

Who would have guessed

[Anonymous Coward]

Something missing from the Standard Model?
Shocking!

Re:Who would have guessed

[NotQuiteReal]

Nobody every buys the Standard Model. If you have the money you get the Luxury Model. Otherwise, most folks just aim for the middle and get the Sports model.

Re:Who would have guessed

[Fieryphoenix]

Don't forget the Executive model.

Re:Who would have guessed

[b4upoo]

This particularly applies to women. If you are offered a model ask for a real one instead. Real women are far more user friendly.

Re:Who would have guessed

[thijsh]

I also prefer real women, not one that has turned from a muon into a tau...

Re:Who would have guessed

[Gilmoure]

Where's the Eddy Bauer version fit in; between Sports and Luxury?

Re:Who would have guessed

[metacell]

Sorority chicks??!

What if...

[Anonymous Coward]

they don't have mass but still oscillate?

Re:What if...

[Steve Max]

You'd need a pretty complex theory to get non-mass oscillations to match all the data we got over the past 12 years, which is very compatible with a three-state, mass-driven oscillation scenario. Besides, you'd have to explain more than what the current "new standard model" (the SM with added neutrino masses) does if you want your theory to be accepted. If two theories explain the same data equally well, the simplest is more likely.

Re: What if...

[Black Parrot]

If two theories explain the same data equally well, the simplest is more likely./quote?
Make that "more preferred". In general we don't know anything about likelihood.

The thing about Occam's Razor is that it filters out "special pleading" type arguments. If you want your pet in the show, you've got to provide motivation for including it.

Re:What if...

[dimeglio]

This is not a theory. It was demonstrated experimentally.

Re:What if...

[BitterOak]

That would be pretty amazing as it would violate the Special Theory of Relativity, one of the most tested theories of all time. The problem is, according to Special Relativity, massless particles move at the speed of light, and time does not advance for them. (If you could build a massless clock, its hands would never move.) Oscillations require a time scale. There is a time period of oscillation, or rather the probabilities of being found in a specific state (mu vs. tau, for instance) oscillate with time. Since time stands still for massless particles, this can't happen.

Re:What if...

[Anonymous Coward]

What is "this" and "it" in your sentence? Neutrino oscillations were demonstrated experimentally. Neutrino mass was not. The dispute is over the statement "neutrino oscillation implies mass", which is a theory.

Re:What if...

[Anonymous Coward]

God did it.

Re: What if...

[Steve Max]

Thanks, good catch.

Re:What if...

[Zaphod The 42nd]

You misunderstand the word theory.

Re:What if...

[Dragoniz3r]

So that's why fat people live shorter lives! Time really just moves faster for them, because they have more mass!

Re:What if...

[KagatoLNX]

Why couldn't the particle stay the same, but the whole universe oscillates around it?

I actually don't mean to be ironic here. Perhaps they're mathematically the same. IANAPP (I am not a particle physicist). Still, just because something appears to change doesn't mean that it wasn't the observer that changed, right?

Re:What if...

[khayman80]

That's the way I've always understood the mass/oscillation connection too. But then I thought... wait... don't photons oscillate too? They're just coherent oscillations of the EM field; oscillating back and forth between electric and transverse magnetic in free space. If there's something different about neutrino oscillation which makes it necessary for the neutrino to travel at sublight, what is it specifically?

Re:What if...

[euxneks]

If two theories explain the same data equally well, the simplest is more likely.

Is that really the case? That seems like it's a very hominid-centric assumption. I can't think of any counter examples but it seems very naïve to assume that the nature of the Universe would be simple...? Though, perhaps my understanding is limited.

Re:What if...

[wrf3]

Why couldn't the particle stay the same, but the whole universe oscillates around it?

Did Spock come from the future to tell you that you discovered this?

Re:What if...

[oldhack]

All you wise guys think this is funny, but what if it turns out to be true? Huh?!

Re:What if...

[Steve Max]

The point is that, if two different theories have the exact same predictions, they are for all intents and purposes the same theory, and describe the same universe. If that is the case, why would you spend more time teaching and learning the more complex one, when a simple explanation is enough and (by definition, since they have the same predictions) you can't tell which one is correct?

Of course, if the new theory offers a good explanation to current data, but has a different prediction than the standard model in other, still-non-tested scenarios, the theory is more interesting. You can test it at the new scenario, and you'll be able to tell them apart. This is why* we study, for example, supersymmetry and extra dimensions theories: they behave just like the standard model where we have tested it, but can be different in other cases such as the LHC.

* = of course there are other motivations to develop the theories, but they are taken seriously because they are compatible with the SM and are testable. A theory whose predictions were exactly the same as the SM for every case wouldn't be worth studying, simply because you'd never be able to see if it is right.

Re:What if...

[Hurricane78]

No it is not more likely. That’s a common misconception. It is only the one you should pursuit first. Actual facts make things more likely. Not simplicity. Simplification is a artifact injected by humans, because they prefer it for efficiency. (What is commonly calley “laziness”)

Re:What if...

[BitterOak]

That's the way I've always understood the mass/oscillation connection too. But then I thought... wait... don't photons oscillate too? They're just coherent oscillations of the EM field; oscillating back and forth between electric and transverse magnetic in free space. If there's something different about neutrino oscillation which makes it necessary for the neutrino to travel at sublight, what is it specifically?

The situation you describe with the EM field is an example of wave-particle duality. Light can behave like both a wave and a particle, but it doesn't make sense to analyze it both ways at the same time. As a wave, it does manifest itself as oscillating electric and magnetic fields and as a particle, it manifests itself as a photon, which doesn't change into a different type of particle. (There's no such thing as an "electric photon" and a "magnetic photon".)

Neutrinos, too, are described quantum mechanically by wavefunctions, and these wavefunctions have frequencies associated with them, related to the energy of the particle. But these have nothing to do with the oscillation frequencies described here, in which a neutrino of one flavor (eg. mu) can change into a different flavor (eg. tau). Quantum mechanically speaking, we say the mass eigenstates of the neutrino (states of definite mass) don't coincide with the weak eigenstates (states of definite flavor: i.e. e, mu, or tau). Without mass, there would be no distinct mass eigenstates at all, and so mixing of the weak eigenstates would not occur as the neutrino propagates through free space.

Re:What if...

[Anonymous Coward]

Kolmogorov complexity is defined logically, it is not an "artifact injected by humans", unless you're stating that all mathematics are an "artifact injected by humans".
The poster means that, on the tree of all theories, the ones with the smallest Kolmogorov complexity, are also the one with the highest number of branches, and therefore the ones that are most likely, by the definition of the word "likely".

This doesn't seem to have anything to do with "laziness".

Re:What if...

[Steve Max]

No, they're not the same. Mass-induced oscillation is a known fact in particle physics (search for "neutron kaon oscillation" for background), and neutrinos behave in exactly the predicted way; only with big mixing angles, unlike the almost-zero angles in the quark sector's CKM matrix.

Re:What if...

[khayman80]

Thanks. I just found some equations that appear to reinforce what you said.

Since the oscillation frequency is proportional to the difference of the squared masses of the mass eigenstates, perhaps it's more accurate to say that neutrino flavor oscillation implies the existence of several mass eigenstates which aren't identical to flavor eigenstates. Since two mass eigenstates would need different eigenvalues in order to be distinguishable, this means at least one mass eigenvalue has to be nonzero. There's probably some sort of "superselection rule" which prevents particles from oscillating between massless and massive eigenstates, so both mass eigenstates have to be non-zero. Cool.

Re:What if...

[Burz]

The problem is, according to Special Relativity, massless particles move at the speed of light, and time does not advance for them.

But can't photons be generated and absorbed? Wouldn't that be a change in state over time? How about Doppler shifting.. doesn't that indicate the frequency and energy level of a photon can change over time?

Maybe massless particles can change over time if they are being changed by some (unknown) property of spacetime.

Re:What if...

[Entropius]

It's that all the bits of the nature of the Universe that we /do/ understand are simple, so we figure that the bits we're still trying to understand are probably also simple.

Re:What if...

[Entropius]

I don't know of any superselection-rule -- it's possible, in theory, for the electron neutrino to have zero mass but the muon neutrino to have nonzero mass.

But then you'd have to explain why one flavor was massive while the other was massless, which has never happened before. Since there's lots of precedent for three flavors with different nonzero masses, people just figure that the neutrinos are the same way.

Re:What if...

[khayman80]

I don't know of any superselection-rule -- it's possible, in theory, for the electron neutrino to have zero mass but the muon neutrino to have nonzero mass.

That's fascinating. Do you have a good reference in mind that discusses this topic? I find the idea of a superposition which sometimes travels at lightspeed and sometimes travels slower than light to be... very bizarre.

Re:What if...

[BitterOak]

I don't know of any superselection-rule -- it's possible, in theory, for the electron neutrino to have zero mass but the muon neutrino to have nonzero mass.

You can't have oscillations between massless and massive states. Remember, SR says that time stands still for massless particles. If you look at the equations for neutrino oscillations, for example here, you'll see there are expressions involving both the mass squared (for the time evolution of the wavefunction), and mass difference squared, for the mixing amplitudes. So, for quantum mechanical mixing between states, you need both non-zero masses and non-zero mass differences. There may be other, weird mixing theories which don't require mass differences, but they would be quite exotic. On the other hand, mixing of particles with zero masses would violate SR, which would be highly surprising!

Re:What if...

[ceoyoyo]

In our experience nature also prefers simplicity. Note that simplicity has a special meaning in this case. It is more likely, based on all our experiience, that a theory that manages to explain more with fewer rules is correct.

Re:What if...

[Jarjarthejedi]

The basic idea isn't that the 'simpler' theory wins (relativity >> newton in complexity) but rather the simplest model that explains all the data. A model that adequately explains everything we've observed without resorting to special cases (i.e. "the universe does X unless these extremely specific conditions are met, in which case it does Y') is far more likely to be true than a model that resorts to special cases, since the universe doesn't exactly check to see if the planets happen to be aligned when determining the gravitational attraction of an object.

Occam's razor is less about simplicity and more about elegant simplicity, if your theory has X rules and mine has 2X but mine explains all the data without special cases and yours requires a dozen special cases mine is more likely to be true. By the same merit the odds that massless particles obey the standard model unless they happen to be neutrinos in which case they oscillate is less likely than either the assumption that neutrinos are massless or the assumption that massless particles in general can't oscillate is incorrect.

Re:What if...

[BiggerIsBetter]

Firstly, neutrinos have non-zero mass. Go ahead at read some of the links on Wikipedia.

Secondly, that only holds if you assume a 3D + time-arrow universe. At these scales I'm not sure you can make that assumption.

Re:What if...

[Hurricane78]

You should first learn to make logically sound arguments.

Experience is not likeliness. It is only a hint that this could be more likely.
Example: Go to Africa. Your experience of nearly all people around you being white will suddenly not have anything to do with the likeliness anymore. And it does not need to be Africa. Some parts of the US suffice. Or South America for example.

As you see, there are more factors to likeliness than just “pure experience”. Because experience is a function with a nearly endless amount of parameters. And you never know whether you didn’t miss a crucial, maybe even previously completely unknown, factor.

Those factors are the actual circumstances. Which I called “facts” in GP comment.

Also, nature does not prefer simplicity. It does prefer efficiency. And I hate, how apparently most software designers fell for oversimplification and not only oversimplified the software, but also the goal, by thinking they could losslessly replace “efficient” with “simple”. Even though it actually has become less efficient. (Just look at Clippy for a prime example.)
But even then, a preference does not mean, that things did in fact happen that way. Or do you drive air line all the time?
Of course not. There is stuff in the way.
And that stuff, again, is those factors/parameters from above, that you might have missed.

You also fell for your own dog food of oversimplification. Some things just can’t be simplified any more. Some things are even mathematically proven to not be simplifiable (is that a word?) even more.

Re:What if...

[Steve Max]

No. All flavour eigenstates MUST be massive: they are superpositions of the three mass eigenstates, one of which can have zero mass. Calling the three mass eigenstates n1, n2 and n3; and the three flavour eigenstates ne, nm and nt, we'd have:

ne=Ue1*n1+Ue2*n2+Ue3*n3

nm=Um1*n1+Um2*n2+Um3*n3

nt=Ut1*n1+Ut2*n2+Ut3*n3

So, if any of n1, n2 or n3 has a non-zero mass (and at least two of them MUST have non-zero masses, since we know two different and non-zero mass differences), all three flavour eigenstates have non-zero masses.

Also, remember that the limit for the neutrino mass is at about 1eV, while it's hard to have neutrinos travelling with energies under 10^6 eV. In other words, the gamma factor is huge, and they're always ultrarelativistic, travelling practically at "c".

Another point is that the mass differences are really, really small; of the order of 0.01 eV. This is ridiculously small; so small that the uncertainty principle makes it possible for one state to "tunnel" to the other.

I really can't go any deeper than that without resorting to quantuim field theory. I can only say that standard QM is not compatible with relativity: Schrödinger's equation comes from the classical Hamiltonian, for example. To take special relativity into account, you need a different set of equations (Dirac's), which use the relativistic Hamiltonian. In this particular case, the result is the same using Dirac, Schrödinger or the full QFT, but the three-line Schrödinger solution becomes a full-page Dirac calculation, or ten pages of QFT. In this particular case, unfortunately, the best I can do is say "trust me, it works; you'll see it when you get more background".

Re:What if...

[Steve Max]

The time-dependent Schrödinger's equation doesn't apply for massless particles. It was never intended to. It isn't relativistic. Try to apply a simple boost and you'll see it's not Poincaré invariant. The main point is that you get the same probabilities if you use a relativistic theory, but you need A LOT of work to get there.

Oscillations work and happen in QFT, which is Poincaré-invariant and assumes special relativity. I can't find any references in a quick search, but I've done all the (quite painful) calculations a long time ago to make sure it works. It's one of those cases where the added complexity of relativistic quantum field theory doesn't change the results from a simple Schrödinger solution.

Re:What if...

[Anonymous Coward]

A theory whose predictions were exactly the same as the SM for every case wouldn't be worth studying, simply because you'd never be able to see if it is right.

Well, except for the (unlikely) case that this hypothetical theory is actually simpler than the SM. In this case, you'd apply Occams Razor and use the simpler theory, of course...

Re:What if...

[BitterOak]

The time-dependent Schrödinger's equation doesn't apply for massless particles. It was never intended to. It isn't relativistic. Try to apply a simple boost and you'll see it's not Poincaré invariant. The main point is that you get the same probabilities if you use a relativistic theory, but you need A LOT of work to get there.

Who said anything about Schrödinger's equation? The equations on the web page I referred to in my post are all relativistically correct. Unfortunately those equations aren't numbered, but if you look at the third equation in the section labelled "Propagation and Interference" you'll see that it was derived under the assumption of ultrarelativistic particles (whose energy is much greater than its rest mass times c^2).

Re:What if...

[Ungrounded Lightning]

You can't have oscillations between massless and massive states. Remember, SR says that time stands still for massless particles.

Not only that but (rest-)massless particles move at the speed of light and particles with rest mass move at some velocity less than that. Converting from one to the other (without interacting with another particle) would violate the conservation of momentum.

Re:What if...

[Steve Max]

That's the classical deduction using Schrödinger's equation. The only "relativistic" approximation is the dispersion relation, but they use Schrödinger's equation to get the kets. We use spinors, not bras/kets, when you solve the (relativistic) Dirac equation; in that case, you get the same probabilities.

See this for a reasonably simple deduction using Schrödinger's equation, that gives you the exact same formulae as your Wiki link. If you use a fully relativistic approach, you get the same final results but no dependency on the mass (only on mass splitings).

Re:What if...

[Daspaz]

There's still something that doesn't quite work with this argument as far as I can see. (I am a particle experimentalist and not a theorist, but hear me out. I'd be very interested to see if you have an argument for why the following idea doesn't work.) I understand that mass is necessary for flavour oscillations, but my issue is with the argument of SR banning any time dependence for massless particles. Sure there's no "Electric photon" or "Magnetic photon" as you say, but there IS a distinct, measurable, time dependent difference between, say, a horizontally and a vertically polarized photon. Say I have a circularly polarized photon fired at a horizontal filter. The probability of that photon passing the filter is dependent on the photon's time of flight before hitting it. It seems to me like I could experimentally measure a time dependent property of the photon: The same experiment performed at different times on an identically prepared photon yields different results. So how does this "mesh" with the SR argument? Perhaps you're being too general?

Re:What if...

[badkarmadayaccount]

Considering mass energy duality, where does the neutrino get that extra energy to change mass, and, if it has mass, how does it move at light speed?

Re:What if...

[khayman80]

... Also, remember that the limit for the neutrino mass is at about 1eV, while it's hard to have neutrinos travelling with energies under 10^6 eV. ...

Is this because most nuclear (or other?) reactions producing neutrinos give them so much energy, or something to do with QFT propagation?

Anyway, thanks for all your insights. Until I can go back to school and take QFT for real, it's always a pleasant surprise to meet someone willing and able to answer these questions.

Re:What if...

[Anonymous Coward]

The problem is, according to Special Relativity, massless particles move at the speed of light, and time does not advance for them. (If you could build a massless clock, its hands would never move.)

In my opinion, the massless clock would move at speed of light as stated above, even its hands since they are massless and they must move at speed c. The age of the clock on the other hand would always be the same.
But ignore me im just an Anonymous Coward :D

Re:What if...

[ceoyoyo]

I don't think I'm the one with problems making logically sound arguments, although perhaps you should work on "organized" and "coherent" first.

You are right about one thing, experience isn't the same thing as likelihood. Rather, it is the only method we have to estimate likelihood. If you take a stats course they call experience "sampling."

As for your ill-constructed example about Africa, since we're actually talking about the laws of physics we're pretty sure that we didn't suddenly switch universes. We may have, and our experience may be a biased sample, but to make progress we assume it is not unless presented with evidence to the contrary.

I don't understand what you're talking about oversimplification. I said that our experience indicates the simplest explanation (and note the restricted definition of "simplest") that explains the observations is more likely to be correct. No, you can't oversimplify, because an overly simple explanation would not explain all the observations. Hence, "oversimplified."

I'm not sure what software developers or Clippy have to do with physics. Have you had your coffee this morning?

Re:What if...

[Anonymous Coward]

relativity >> newton in complexity

This is true of the respective theories of universal gravitation, but not true of mechanics that occur in a gravitational potential in the limit of a weak (local) gravitaional field (or in any wholly uniform gravitational potential at all), which are very common in the universe.

Special Relativity is not really that difficult compared to Newtonian Mechanics; it just builds in a Lorentz-FitzGerald transformation that is negligible at low relative velocities. In fact, it reproduces Newtonian Mechanics to the limit of testability in most situations in which mechanics are useful, so one can disregard the c^4 terms and counter-terms much as one uses c^2 rather than the fuller c^4 terms when rest masses (or momenta or relative velocities) are vanishingly small.

There is a bit more bookkeeping involved in SR than in NM - they are not vastly different.

General Relativity, on the other hand, is actually profoundly different than the Newtonian Theory of Gravitation. The latter is purely empirical and proposes no mechanism to explain what gravity is, or how inertia arises (e.g., it does not explain how inertia over here is affected by mass over there, it only allows the influence to be quantified). GR on the other hand is a geometrical theory of gravitation, and explains that gravity is equivalent to inertial motion through curved space-time, and that one can (through rotation or a suitable choice of units) treat the three spatial and one time dimensions equivalently for all equations of state or evolutions of dynamical systems. This is handy because it allows for insights into the theory itself, and means by which one can distinguish it from other theories of gravitation including those arrived at purely empirically (the PPNA is a tool to do this). Moreover, GR's fundamental insight is that spacetime itself is empty (and meaningless) in the absence of objects and oscillators, and that therefore any useful coordinate system must be based on those.

However, GR uses tensors, which are harder for human beings to use than vectors or scalars. Programmable computers don't have any problem with them, though!

GR's biggest practical problem is that one can use arbitrary coordinate systems (such as the Schwartzchild metric, analogous to polar coordinates) and transforming from one to the other requires careful thought. In practice, one aims for a "patch" of space-time which has minimal curvature (e.g. arising *only* from the objects under study) by carefully choosing a coordinate system that allows that; that's not really automatable at this time.

Because space-time curvature arises from mass-energy, objects which themselves are highly energetic are also self-gravitating, so a high-energy fundamental particle with a given intrinsic frequency will find itself curving space-time substantially. Since you can model space-time curvature as a change in the rate at which clocks tick, when curvature is non-negligible at the (spatial)scale of the wavelengths of fundamental particles, you can't use renormalization theory to recover the particles or make predictions about what the particles' (temporal)frequency should be at any given moment.

Re:What if...

[Anonymous Coward]

massless particles move at the speed of light, and time does not advance for them. (If you could build a massless clock, its hands would never move.)

I have a clock with zero rest mass - it's a photon. I keep it in a trap. The photon has a fundamental frequency, which I can measure any time I choose. My timescale advances at the frequency of my photon. [footnote]

With zero rest mass, the resistance to acceleration is zero -- the input of *any* energy accelerates a zero rest mass object to the relativistic speed limit.

Photon wavelength is related to its frequency: frequency = c/wavelength.

However, photons doppler shift (again, easy to measure using doppler radar) so when moving towards a source of photons with a uniform wavelength from the point of view of the source, the photons' wavelength will be foreshortened (blueshifting); when moving away, the photons will lengthen (redshifting).

An observer receding from a source of photons at c will see an infinite redshift and will not interact causally with those photons; however there are lots of photons in the universe so the same observer looking in the direction of travel would see a wall of infinitely high energy photons (since E = h * frequency).

In other words, at c, looking at a clock in the opposite direction of travel would reveal no clock, and looking at a clock in the direction of travel would show it ticking extremely fast.

It would not tick "infinitely fast" because in general relativity energy causes spacetime curvature and the axes of spacetime are equivalent under a suitable choice of units or under a suitable rotation. In other words, while the recession direction would look the same as under special relativity (i.e., the photons vanish) gravitational interactions between the ultrarelativistic observer and photons in the direction of travel would necessarily lead both along longer geodesics; as a clock moving along a longer geodesic ticks slower than that moving along a shorter one, this gravitational time dilation "cools" the wall of photons in the direction of travel from infinitely energetic to merely enormously energetic. Moreover, the metric expansion of space further "cools" the wall of photons in the direction of travel (in fact it "cools" all distant photons).

Consequently, although it is a prediction (and commonly repeated line) of special relativity, it is not really accurate to say that an observer moving at precisely c (i.e., a photon) experiences no time at all, since the space-time it transits is not empty or static, and therefore there are differences in curvature that will be observable as anisotropies in the view of the observer's sky. Moreover, the observer's local clock will tick normally no matter what the observer is doing with respect to acceleration or relative velocity.

(Under SR no observer with a nonzero rest mass can reach c; it is unlikely but not actually forbidden in general relativity in part because energy is not conserved in an expanding or contracting universe (because of the energy-momentum conservation (nabla_mu T^(munu) = 0) -- we just have to put more of the expanding universe on the recession side of a massive object seeking to reach c), but the practical rule is that objects with a heavier rest mass offer much greater resistance to acceleration, especially near c, than lighter objects).

Oscillations require a time scale

In GR, space-time requires oscillators in order for its coordinate system to be meaningful; that's the resolution of the Hole Argument.

[footnote] I can only measure the frequency once, however. So I really need a number of trapped photons.

Re:What if...

[Anonymous Coward]

That's fine, because in a non-static universe there is a conservation of energy-momentum (nabla_mu T^(mu nu) = 0 is the GR conservation law). Since there is a metric expansion of space and therefore a large curvature to space-time, there is a lot of extra energy being created in the universe if the vacuum energy is constant (which it would be if the cosmological constant is inertial; quintessence and other mechanisms for the metric expansion of space don't really change that).

So converting momentum into rest mass is perfectly fine and vice-versa, at least in general relativity (which in turn faithfully reproduces SR locally in flat "slices" of spacetime).

Yes, this is different from the conservation of invariant mass normally written down E^2-|\vec(p)|^2c^2 = m^2c^4 with a specially chosen inertial frame of reference such that \vec(p) = 0 as the SR formulation explicitly ignores gravitational energy. The classic mass-energy equivalence obviously does not forbid trading kinetic energy and rest mass; the invariance of the invariant (i.e., rest) mass is however (like classical SR itself) background-dependent.

No.

[gbutler69]

Something PROVED TO BE missing from the Standard Model? Shocking!^H^H^H^H^H^H^H^H INTERESTING

There, fixed that for you

Excited!

[SpeedyDX]

Reading TFS made me very excited about the potential fundamental developments in physics. Except I don't know a thing about physics, so I'm really not sure what I'm excited about. All these words like muon, tau, and neutrino have little place in my everyday life, but they sound so interesting!

This is what the Average American must feel like when they hear stories about Web x.0 laden with the latest buzzwords on CNN. I can finally relate!

Re:Excited!

[Anonymous Coward]

I agree... we need some Slashdotter to come up with a car analogy to help us non-physicists out.

Re:Excited!

[Anonymous Coward]

Indeed, the only thing I could refer to was "Opera", but I don't think they're talking about the Web Browser...

Re:Excited!

[biryokumaru]

Imagine your definition of sports cars (massless particles, thus no time) didn't include convertibles (time-based oscillation). For a car to be convertible, it has to be a luxury car (have mass), not a sports car. Then, you see a sports car drive by a few times, and one of the times the top is down. You have to wonder, is it not really a sports car (the way we think neutrinos work must change), or is your definition of sports cars broken (the way we think mass works must change)?

How's that sound?

Re:Excited!

[Anonymous Coward]

http://www.fisicx.com/quickreference/images/medium_particle_chart.jpg that should help.

Re:Excited!

[$RANDOMLUSER]

...we need some Slashdotter to come up with a car analogy to help us non-physicists out.

Glad to oblige.

Imagine a highway. All the north-bound cars are WHITE Toyota Camrys, and all the south-bound cars are BLACK Toyota Camrys. All the cars are moving very very very fast. At a certain point in the road, workers open gates that cause the two streams of traffic to plow into each other, head on. At the crash site, common sense would tell you that pieces of Toyota Camrys would come flying out, but instead, complete vehicles of other makes and models (Honda Civics and Nissan Sentras, many others, including vehicles larger than two Camrys, like Peterbilt 18-wheelers) appear instead. After a few seconds, some of these vehicles break apart, and become other vehicles, say a Peterbilt breaks apart and becomes a Ford F-150 and two Harley Davidson motorcycles. Particle physicists make a living by crashing different streams of vehicles into each other and observing the new vehicles that come out. They've put together a list of these, like "Peterbuilt --> Ford F-150 + 2(Harley Davidson Motorcycles)". They call this list the Standard Model. This new experiment shows that sometimes, after a while, one of the Harleys suddenly changes models, say from a Fat Boy to an Electra Glide.

Hope this helps.

Re:Excited!

[oldhack]

Depends. Are they German or Japanese?

Re:Excited!

[darkmeridian]

The significance of this discovery is that the Standard Model is wrong. The transformation of neutrinos mean they have mass, whereas the Standard Model predicts that they have no mass. Neutrinos having mass mean they interact with matter, and that they can constitute dark matter. Or something like that. This is about all I know/or think I know about the subject.

I hope I'm alive when the Next Big Nerd figures out the Next Big Thing regarding a Theory of Everything.

Re:Excited!

[Entropius]

How exactly does the standard model demand that neutrinos have mass?

The SM works just fine with massive neutrinos. After all, most of the fun stuff in the SM concerns the gauge couplings; whether or not a few fermions have mass doesn't affect the overall theory.

Neutrinos could constitute dark matter if they had *more* mass. But we can put an upper limit on the masses of the electron, muon, and tau neutrinos, and that's not enough to account for the amount of dark matter we know is out there. Some sort of exotic thing -- sterile neutrino flavors or some SUSY mumbo-jumbo -- /could/ be a dark matter candidate.

Re:Excited!

[Dachannien]

Particle physicists make a living by crashing different streams of vehicles into each other and observing the new vehicles that come out.

Are you sure you're not talking about the Mythbusters?

Re:Excited!

[$RANDOMLUSER]

Good grief. I started this to see how ridiculously far I could stretch the car analogy. ;D

Re:Excited!

[Anonymous Coward]

So if I crash a Ford Pinto, I might get something better instead? COOL!!! *shifty eyes*

Re:Excited!

[Dynetrekk]

This car analogy was pretty awesome. Just one detail: The CNGS (CERN Neutrinos to Gran Sasso) experiment is based on slamming cars (in fact, protons) into a mountainside (or a metallic target) and seeing what comes out on the backside of the mountain (730 km away). This is where the car analogy breaks down, and the Standard Model takes over.

Re:Excited!

[Anonymous Coward]

So, what you're saying is that if I crash my car, I might get an Harley Davidson out of it? Neato! Got to try this.

Re:Excited!

[Anonymous Coward]

Excellent. Now, as it's World Cup season do you have one for the offside rule?

Re:Excited!

[rumith]

'Tis one of the best comments I've ever come across on Slashdot :)

Re:Excited!

[Anonymous Coward]

Easy.

When you want to crash your car into your garage, you must always ensure that there is at least one other car of yours between the point where you start slamming the pedal and the garagedoor. When you slam the accelerator when there is no other car of yours between you and the garagedoor you are offside and your crash is void.

Re:Excited!

[thijsh]

I'd say longer than the longest stretch limo... :)

Re:Excited!

[Anonymous Coward]

Or is it a hard top or a soft top?

Re:Excited!

[tohoward]

So, if I'm reading this right, the Standard Model assumes that cars and motorcycles are the same class of vehicle, correct? It's obvious that the Standard Model is broken if it fails on so fundamental of a level.

Re:Excited!

[Steve Max]

The problem with massive neutrinos in the SM is in the anomaly cancellation. If you add right-handed neutrinos (in order to have neutrino mass), each fermion family ends up with a net anomaly (at least in 3+1 dimensions), while the "normal" SM is anomaly-free in each family.

Re:Excited!

[Anonymous Coward]

How about Japanese car show models in bikinis hanging over a German car?

Re:Excited!

[David Gerard]

They had a lot of trouble accounting for quad bikes.

Re:Excited!

[Anonymous Coward]

Someday they might even discover these vehicles are actually made of even smaller, indivisible 'atoms'.

Re:Excited!

[EdIII]

The CNGS (CERN Neutrinos to Gran Sasso) experiment is based on slamming cars (in fact, protons) into a mountainside (or a metallic target) and seeing what comes out on the backside of the mountain (730 km away).

Your forgot to mention that the experiment involves a heavily modified Ford E-Series van capable of Mach 1 and specially outfitted with an Oscillation Overthruster.

Re:Excited!

[Anonymous Coward]

...we need some Slashdotter to come up with a car analogy to help us non-physicists out.

Glad to oblige.

Imagine a highway. All the north-bound cars are WHITE Toyota Camrys, and all the south-bound cars are BLACK Toyota Camrys. All the cars are moving very very very fast. At a certain point in the road, workers open gates that cause the two streams of traffic to plow into each other, head on. At the crash site, common sense would tell you that pieces of Toyota Camrys would come flying out, but instead, complete vehicles of other makes and models (Honda Civics and Nissan Sentras, many others, including vehicles larger than two Camrys, like Peterbilt 18-wheelers) appear instead. After a few seconds, some of these vehicles break apart, and become other vehicles, say a Peterbilt breaks apart and becomes a Ford F-150 and two Harley Davidson motorcycles. Particle physicists make a living by crashing different streams of vehicles into each other and observing the new vehicles that come out. They've put together a list of these, like "Peterbuilt --> Ford F-150 + 2(Harley Davidson Motorcycles)". They call this list the Standard Model. This new experiment shows that sometimes, after a while, one of the Harleys suddenly changes models, say from a Fat Boy to an Electra Glide.

Hope this helps.

YOU ARE AWESOME

Chameleon-Like Behavior?

[Randle_Revar]

I don't see how changing from one thing into another is "chameleon-like behavior". I have never heard of a chameleon turning into a skink, or anything else for that matter

Re:Chameleon-Like Behavior?

[Anonymous Coward]

The changes might be likened to a red photon suddenly turning into a blue photon. Apparently energy is being exchanged in a yet to be discovered manner. Or, perhaps the observed changes indicate that the Neutrinos simply came out of the closet.

Re:Chameleon-Like Behavior?

[dumuzi]

I agree. In QCD quarks and gluons can undergo colour changes, this would be "chameleon-like behavior". Neutrinos on the other hand change flavour, this would be "Willy Wonka like behavior".

Re:Chameleon-Like Behavior?

[Steve Max]

No, it may not. The neutrino's energy (which is the exact analog to a photon's "colour") is conserved. The rest energy changes, but this means the original neutrino and the resulting one are on different rest referentials (and the change in mass is very small, inside the uncertainty principle). There is nothing "yet to be discovered", except possibly what is the mass generation mechanism (Dirac, like all other particles, or Marjorana).
"Chameleon-like behaviour" is just the "scientific" journalist's way of saying he understands nothing about what he is paid to write; but we all know journalists rarely know much of what they write anyway.

Re:Chameleon-Like Behavior?

[Jorl17]

I'm sure you'd prefer the non-falacious "chamaleon-skin-color-like behaviour". Though that might not fit it either.

Re:Chameleon-Like Behavior?

[buchner.johannes]

I don't see how changing from one thing into another is "chameleon-like behavior". I have never heard of a chameleon turning into a skink, or anything else for that matter

Try combining a chameleon with a hammer or a microwave. Then you will understand the experiments analogy.

Re:Chameleon-Like Behavior?

[Anonymous Coward]

I don't see how changing from one thing into another is "chameleon-like behavior". I have never heard of a chameleon turning into a skink, or anything else for that matter

Try combining a chameleon with a hammer or a microwave. Then you will understand the experiments analogy.

Splattered lizard guts?

Re:Chameleon-Like Behavior?

[biryokumaru]

You could say they're acting wonky.

Re:Chameleon-Like Behavior?

[jnnnnn]

One of the properties of subatomic particles is referred to as colour. The particles are not coloured (they are far smaller than the wavelengths of light that give colour), but it is a simple system of classifying particles, similar to resistor colour codes or the "terrorist" alert system.

The study of the colour properties is called "chromodynamics", and I guess "chameleon" must be a similar extension of the metaphor.

Re:Chameleon-Like Behavior?

[Anonymous Coward]

My entire house is made out of chameleons you insensitive clod!

Re:Chameleon-Like Behavior?

[mog007]

Neutrinos do not see the strong force, which is where the color charge comes from. Neutrinos interact with the weak force, and gravity. They have no color charge, and no electric charge, so they are basically dumb to the idea of the strong and electromagnetic forces.

Re:Chameleon-Like Behavior?

[Anonymous Coward]

No but they can turn into dinner :D

Neutrinos acting like Microwaves

[snowgirl]

Just find the people from the Movie 2012 to help you figure out how to make the Neutrinos act like Microwaves, then you could totally make this experiment easy! ... seriously... did anyone else need a friend to "dumb up" the science dialog for them?

Re:Neutrinos acting like Microwaves

[Anonymous Coward]

Easy there, snowgirl. It's just a movie, designed for entertainment purposes only. It's not a scientific documentary nor was it meant to be. Sit back and just enjoy the show :)

Re:Neutrinos acting like Microwaves

[Anonymous Coward]

I needed quite a few pauses on that movie to laugh at its science dialog. I can't imagine it being any more wrong. Solar neutrinos (very low energy) heating up the Earth's core? "The first time neutrinos have a physical reaction"? Really? Was their science advisor a magic 8-ball?

Re:Neutrinos acting like Microwaves

[snowgirl]

Was their science advisor a magic 8-ball?

My sources say no.

Re:Neutrinos acting like Microwaves

[biryokumaru]

Signs point to yes.

Re:Neutrinos acting like Microwaves

[Mr. Underbridge]

Just find the people from the Movie 2012 to help you figure out how to make the Neutrinos act like Microwaves, then you could totally make this experiment easy! ... seriously... did anyone else need a friend to "dumb up" the science dialog for them?

I had the pleasure of (involuntarily) watching that piece of shit this weekend. Sadly, the liberties taken with science were the least of that movie's problems. I'd start with the terrible script, lack of editing (solid hour too long), screwed up pacing, repetitive scenes, 70s-grade CGI, and heavy handed moralizing. Compared to that, they could have said that neutrinos turn into faerie dust and I'd have been fine.

Re:Neutrinos acting like Microwaves

[snowgirl]

Compared to that, they could have said that neutrinos turn into faerie dust and I'd have been fine.

This I at least could have understood.

None of their scientific babbling made any sense to me until my friend's boyfriend explained what the heck they were trying to say.

oscillation

[Spazmania]

The Standard Model of fundamental particles posits no mass for the neutrino. For them to be able to oscillate, however, they must have mass.

Unless oscillation is the fundamental thing and mass is just a sometimes effect of oscillation... but then IANAP.

Re:oscillation

[Dragoniz3r]

Doesn't matter what we call the two things. We just know that in this case, one requires the other.

Re:oscillation

[Anonymous Coward]

When it says "oscillation" it's not talking about string theory. It's talking about one particle changing into a related but different particle and back again.

Re:oscillation

[Kongzilla]

Perhaps someone with more background than I have could explain this, since the argument for neutrinos having mass seems tenuous to me. Neutrinos are thought to have mass because they oscillate, presumably requiring the passage of time, which can only happen at sublight speeds. Yet photons are oscillating electromagnetic fields, and they have no mass and travel at the speed of light. Why do they get a free pass? For that matter, why is it that particles travelling at less than light speed must have mass? This always seems to be presented as a given; is there a line of reasoning behind it that I'm unaware of? Note: IANAP, though I have taken several courses at the undergrad level.

Re:oscillation

[Steve Max]

We say neutrinos have mass because a quantum superposition of states with slightly different masses oscillate in a very specific way; and we see the neutrino flavour changing in exactly that same way, with the same dependency on L/E (distance divided by energy). Since that is a direct effect of the different mass eigenstates moving at slightly different speeds for the same energy, it's very hard to get a theory that shows the same dependency without resorting to neutrino masses. Being not sure of what courses you've taken, I redirect you to the wiki for some more info and possibly more advanced links in your level of understanding.

Re:oscillation

[LarryRiedel]

photons are oscillating electromagnetic fields, and they have no mass and travel at the speed of light. Why do they get a free pass?

Having a spatial trajectory which looks like a propagating sine wave does not necessarily mean any oscillation or movement in the direction of time.

why is it that particles travelling at less than light speed must have mass? This always seems to be presented as a given; is there a line of reasoning behind it that I'm unaware of?

Maybe everything is moving at the same "light" speed through a 4D (Minkowski) space, and "mass" is the property which gives something the ability to move more (than zero) in the direction of forward in time.

How in the universe?

[MyLongNickName]

How could something have mass and so weakly interact with normal matter? My understanding is that most neutrinos pass through the earth unmolested.

(insert obligatory Catholic priest joke here).

I's thought that neutrinos being massless made this possible.

Re:How in the universe?

[Anonymous Coward]

Think about it this way.. how can something not have mass?

Re:How in the universe?

[rogeriomgatto]

That's how they managed to escape the priests... They avoid mass.

Re:How in the universe?

[pz]

How could something have mass and so weakly interact with normal matter?

Neutrinos are thought to have a very small mass. So exceedingly small that they barely interact with anything (they also have no charge, so they are even less likely to interact). But zero mass and really, really, really small but not zero mass, are two different things.

Re:How in the universe?

[Anonymous Coward]

No pudding for you. How could they have some pudding if they don't eat their mass :)

Re:How in the universe?

[hoytak]

Neutrinos only interact through the weak forces, which require them to be extremely close to other particles with which they interact. Such interactions also require the neutrino to have a lot of energy, since the force-carrying particles are quite massive. This is why all these experiments use neutrinos generated by very energetic reactions (accelerators, the sun, cosmic rays, etc.).

When I worked with BooNE, an experiment researching neutrino osculations, our detector was a 40 ft tank lined filled with clear, food-grade mineral oil and lined with photo tubes capable of detecting a few photons. The neutrinos were generated by bursts of protons crashing into a special block (I don't remember the material), and the byproducts at the given energy levels would be one type of neutrino. The interactions from different types of neutrinos would have different decays, which produced different signature rings of photons on the walls of the detector. In generating 10^9 + neutrinos, we only expected a handful of interactions.

Gravity is also on the table, but it's impossible to measure neutrinos based on that.

Re:How in the universe?

[dimeglio]

Photons are also massless and also interact with matter. Photons/electrons are also waves/particles which make them rather interesting. There might be different types of neutrinos. Some with mass, other with none. Since neutrinos are the results of a proton collision, the opposite - recreating a proton with a neutrino/strange quark collision might also explain this "mass-like" behaviour. Interesting nonetheless.

Re:How in the universe?

[BitterOak]

How could something have mass and so weakly interact with normal matter? My understanding is that most neutrinos pass through the earth unmolested.

(insert obligatory Catholic priest joke here).

I's thought that neutrinos being massless made this possible.

I'm not sure why this was modded flamebait (is a reference to our propensity to joke about the Catholic church flamebait?), but to answer the question, being massless has nothing to do with a particle's ability to interact weakly. Quarks can interact weakly (as well as strongly and electromagnetically) and they certainly have mass. The top quark, in fact, is quite heavy.

Re:How in the universe?

[BitterOak]

How could something have mass and so weakly interact with normal matter?

Neutrinos are thought to have a very small mass. So exceedingly small that they barely interact with anything (they also have no charge, so they are even less likely to interact).

The fact that they barely interact with anything has nothing to do with the fact that they are nearly massless. Photons are massless and they interact with anything that carries an electric charge. Electrons are much lighter than muons, but they are just as likely to interact with something. The only force that gets weaker as the mass goes down is gravity, which is by far the weakest of the fundamental forces.

Re:How in the universe?

[Anonymous Coward]

(insert obligatory Catholic priest joke here).
I's thought that neutrinos being assless made this possible.

Catholic priests wouldn't be able to bugger the neutrinos if the neutrinos were assless, but that's okay -- there are more than enough altar boys and Hatian orphans to go around.

Re:How in the universe?

[Snowhare]

It isn't their mass that makes them so unlikely to interact with ordinary matter. It is because they don't interact via the Electromagnetic or Strong Nuclear forces (at least not at the energies we are discussing here). Because we can't use gravity to directly detect them (or any other elementary particle) because of its incredible weakness, that leaves only the Weak Nuclear force, which is *extremely* short range. That short range means that a neutrino must pass *very* close to an electron or a quark to have any chance what-so-ever of interacting: Something like 10 to the minus 16th power meters. For comparison, a hydrogen atom has a diameter of around 10 to the minus 10th meters - or a million times larger.

A single *proton* has a diameter of around 10 to the minus 15th meters - or still 10 times larger than the distance in question.

So hundreds of neutrinos could pass directly through the very nucleus of an atom and *still* not interact with anything. And that is matter with a density more than a trillion times as dense as anything in your ordinary experience.

To neutrinos, other matter barely exists at all.

Re:How in the universe?

[Nimey]

Photons also interact with gravity - stellar masses and above can cause gravitational lensing.

Re:How in the universe?

[MichaelSmith]

neutrino osculations

You learn something new every day

Re:How in the universe?

[pz]

The fact that they barely interact with anything has nothing to do with the fact that they are nearly massless. Photons are massless and they interact with anything that carries an electric charge. Electrons are much lighter than muons, but they are just as likely to interact with something. The only force that gets weaker as the mass goes down is gravity, which is by far the weakest of the fundamental forces.

Good point, I should have been more expansive. There are definitely many more reasons that neutrinos are non-interactive.

Re:How in the universe?

[Anonymous Coward]

I's thought

What is that supposed to be in proper english?

Re:How in the universe?

[Barrinmw]

And then you can maybe get Weakly-Interacting Massive Particles that can interact with just the Weak Force and Gravity.

Re:How in the universe?

[Barrinmw]

Hey, my fiancee's father just got picked up to work on BooNe. Small world.

Re:How in the universe?

[justin12345]

I once read somewhere that the fundamental difference between something with mass and something without mass is that "at rest" (a purely theoretical state) an object with mass it would be stationary (that is to say absolute zero motion and temperature). An object without mass "at rest" would move at the speed of light. It would take an infinite amount of energy to accelerate an object with mass to the speed of light, and an infinite amount of energy to decelerate an object without mass to absolute zero.

I have no idea if there is any validity to this, and I can't recall where I read it, but I've always thought it was an interesting thing to think about. Perhaps someone can correct me or fill in the blanks.

Re:How in the universe?

[Anonymous Coward]

I thought that phenomenon was caused by the curvature in space-time, so IMHO it wasn't "interaction" per-se.

Re:How in the universe?

[Sulphur]

If a neutrino tunnels out of a black hole, does it radiate Hawkings?

Re:How in the universe?

[sjames]

You have mass. Now, tackle an elephant.

In a similar way, neutrinos have so little mass compared to even hydrogen that they don't really interact.

Re:How in the universe?

[ShakaUVM]

>>I thought that phenomenon was caused by the curvature in space-time, so IMHO it wasn't "interaction" per-se.

Gravity is just curvature of time-space.

Maybe.

The really interesting thing about photons, to me, is that time doesn't pass for them (because they're massless). So if you were a photon, would you experience all points in spacetime simultaneously?

Re:How in the universe?

[Anonymous Coward]

It's space itself that is bent by gravity. The photons just follow a straight path through space, they are not directly affected by gravity.

Re:How in the universe?

[Anonymous Coward]

Photons don't interact with gravity. Spacetime itself "interacts" (as it were) with gravity, and photons simply follow the curvature of spacetime.

Re:How in the universe?

[Anonymous Coward]

I don't think it is proven that electron neutrinos have any mass yet; what is proven is that there are differences in the masses of electron, muon and tau neutrinos. The lightest could still be massless

Re:How in the universe?

[John Hasler]

> So if you were a photon, would you experience all points in spacetime
> simultaneously?

You wouldn't "experience" at all.

Re:How in the universe?

[cowscows]

Supposedly if you took a hydrogen atom and scaled it up so that the single proton nucleus was the size of a basketball, the electron would end up as a tiny spec "orbiting" miles away. The proton is the center, and the electron forms the outer edge of the atom. But all of that space in between is empty. Even take a heavier atom, like lead and scale it up. You get more basketballs hanging out at the center, then a whole bunch of empty space, then a bunch of tiny electrons flying around. The heaviest, most dense material you've ever held in your hand was still mostly empty space.

In the everyday world, atoms generally don't interact by having their sub atomic particles bounce off of each other, various forces interact when they get close, and keep them from actually hitting each other. But a neutrino is basically immune to those forces, so unless it happens to actually hit another bit of subatomic mass, it just zooms on through all that empty space inside the atom and keeps on going.

And on a side note, when they say that a tablespoon or whatever of a neutron star weighs billions of tons, the reason why that is possible is because the gravity there has overcome all of the different forces that make atoms bounce off of each other, as well as the forces that hold the electrons so far from the nucleus. In a neutron star, that empty space is getting squeezed away.

Re:How in the universe?

[Steve Max]

You can't define a referential moving at "c", so you can't really describe a "rest referential" for a photon or any massless particle.

Re:How in the universe?

[ShakaUVM]

To put it another way, is it existing at all points along a line in spacetime at once?

Re:How in the universe?

[Anonymous Coward]

Gran Sasso is in Italy, so there are lots of priests there to chase after them.

Douglas Adams was right

[Fractal Dice]

We finally understood the universe, so it has been replaced with something even more perplexing.

Re:Douglas Adams was right

[vjoel]

We finally understood the universe, so it has been replaced with something even more perplexing.

This already happened long ago....

Shifty characters...

[WeatherGod]

I knew I couldn't trust 'em!

I thought -I- was a nerd....

[Anonymous Coward]

>> the first direct observation of a muon neutrino turning into a tau neutrino

Please forgive me in advance for asking, but why is this important?

I now know how people feel when I respond to their questions regarding computers, networks, etc.

Re:I thought -I- was a nerd....

[oldhack]

We've been observing only a third of neutrinos from the sun, and the speculation was that the rest were oscilliating into others not being detected, and that would be possible if neutrinos had mass, and that means one or the other symmetries in the standard model needs to be tweaked, and so on.

Get it? No, I don't get it either, but I'm no physicists.

Re:I thought -I- was a nerd....

[Brett Viren]

> Please forgive me in advance for asking, but why is this important?

Because it confirms part of our understanding of our universe. What more is there?

They explained this on NOVA a while ago

[NotSoHeavyD3]

Basically oscillations are repeated changes with respect to time. According to general relativity massless particles move at light speed and as a consequence do not experience the passage of time. So if neutrino's were massless they'd move at light speed and wouldn't experience time and therefore wouldn't be able to oscillate into different forms.

Re:They explained this on NOVA a while ago

[Spazmania]

Alas my humor remains too subtle...

Re:They explained this on NOVA a while ago

[TheLink]

> Alas my humor remains too subtle...

No matter. Give it some time and things might change.

Re:They explained this on NOVA a while ago

[jbengt]

According to general relativity massless particles move at light speed and as a consequence do not experience the passage of time.

Uh, wouldn't that depend on your point of view?

karma neutrino

[Anonymous Coward]

Karma karma karma karma karma neutriiiino!

Wait a second! Re:What if...

[eonlabs]

Does that fact that light is polarizable, has known frequencies of oscillation, and no mass (but has momentum), throw a wrench into all this claim that you need mass to oscillate? Probably not on these forums, but it still makes me pause to think about it.

Re:Wait a second! Re:What if...

[Steve Max]

Light doesn't oscillate in this way. A photon is a photon, and remains a photon. Electric and magnetic fields oscillate, but the particle "photon" doesn't. Neutrinos start as one particle (say, as muon-neutrinos) and are detected as a completely different particle (say, as a tau-neutrino).

The explanation for that is that what we call "electron-neutrino", "muon-neutrino" and "tau-neutrino" aren't states with a definite mass; they're a mixture of three neutrino states with definite, different mass (one of those masses can be zero, but at most one). Then, from pure quantum mechanics (and nothing more esoteric than that: pure Schrödinger equation) you see that, if those three defined-mass states have slightly different mass, you will have a probability of creating an electron neutrino and detecting it as a tau neutrino, and every other combination. Those probabilities follow a simple expansion, based on only five parameters (two mass differences and three angles), and depend on the energy of the neutrino and the distance in a very specific way. We can test that dependency, and use very different experiments to measure the five parameters; and everything fits very well. Right now (specially after MINOS saw the energy dependency of the oscillation probability), nobody questions neutrino oscillations. This OPERA result only confirms what we already knew.

Re:Wait a second! Re:What if...

[khayman80]

The explanation for that is that what we call "electron-neutrino", "muon-neutrino" and "tau-neutrino" aren't states with a definite mass; they're a mixture of three neutrino states with definite, different mass (one of those masses can be zero, but at most one).

Right above I speculated that it's not possible for a particle to oscillate between massive and massless eigenstates. Do you have a reference showing that one mass eigenvalue can be zero? I'm curious to see how a massive particle which travels at v at c is mandatory. I only got through two semesters of quantum using Sakurai in grad school; I'm hoping this point is also comprehensible with the Schrodinger equation and not full QED. (shudder)

Re:Wait a second! Re:What if...

[khayman80]

Well that got butchered. Change "I'm curious to see how a massive particle which travels at v at c is mandatory." to:

I'm curious to see how a massive particle which must travel slower than light can oscillate into a massive particle that must travel at exactly the speed of light. I'd always figured a superselection rule would prevent this sort of thing...

Re:Wait a second! Re:What if...

[Barrinmw]

Well, if it went from something with mass to something without mass, could it not use that energy from the mass to speed up to the speed of light? Sort of like how pair production causes light to become two particles traveling slower then the speed of light and then when they annihilate each other you get the photons traveling at the speed of light again?

Re:Wait a second! Re:What if...

[khayman80]

Well, if it went from something with mass to something without mass, could it not use that energy from the mass to speed up to the speed of light?

First, it's one thing to claim that electron-positron collisions produce gamma rays. This is a (generally) non-repeated event with a clear discontinuity in time. Before the discontinuity, particles travel slower than light. Afterwards, the products of the collision travel at lightspeed. But an oscillating particle varies smoothly and repeatedly between the two states so there's no clear discontinuity even though the physics of massless and massive particles are wildly different.

Second, I'm not suggesting such a superposition would violate conservation of energy. I'm struggling to put my objections in words. First, I grok quantum superpositions of electrons in different places or polarizations. But I don't think it's possible to have a quantum superposition of an electron and a proton because that would violate conservation of charge, mass, lepton number, and baryon number. (I believe this general idea is known as a superselection rule, which forbids certain superpositions.) In the same way, I'm trying to figure out if a superposition of a particle that defines the light cone and a particle that's constrained to move inside the light cone is meaningful. No conservation laws seem to apply, but I'm vaguely thinking that environmentally-induced superselection wouldn't allow such a superposition to exist for much longer than a Planck time.

Sort of like how pair production causes light to become two particles traveling slower then the speed of light and then when they annihilate each other you get the photons traveling at the speed of light again?

A photon can only produce a real electron-positron pair when it has at least twice the rest-energy of an electron and it hits a nucleus. Photons can't produce real particle pairs in free space because momentum and energy can't be simultaneously conserved without a third particle.

The fact that light travels slower in matter can be explained in many different ways. Some QED cartoons attribute this to the effective non-zero mass of a quasi-particle known as a polariton, which is composed of a photon and phonons in the material. Again, this doesn't happen in free space. Also, this example involves virtual particles but the oscillating neutrino is real (because it can be detected as a single particle.)

Re:Wait a second! Re:What if...

[Cyberax]

"A photon can only produce a real electron-positron pair when it has at least twice the rest-energy of an electron and it hits a nucleus."

Or another photon.

Re:Wait a second! Re:What if...

[Steve Max]

Mass eigenstates don't oscillate. n1 is always n1, unless you try to measure it, in which case its eigenfunction collapses into the interaction base (ne+nm+nt). That's quantum weirdness for you.

The interactions (production and detection) happen in the flavour base. The propagation happens in the mass base. This means you never oscillate "from massless to massive": you are created with a mixture of massive and massless states, which travel differently, changing the probability of each flavour.

Re:Wait a second! Re:What if...

[khayman80]

oscillate into a MASSLESS particle. Sheez.

Re:Wait a second! Re:What if...

[khayman80]

Mass eigenstates don't oscillate. n1 is always n1, unless you try to measure it, in which case its eigenfunction collapses into the interaction base (ne+nm+nt). That's quantum weirdness for you.

Yeah I get that, although my phrasing and editing have been poor. I'm simply uncomfortable with the idea of a superposition of massless and massive particles. This post's 2nd paragraph summed up my feelings on the matter. And I really do mean to say "feelings"-- it's been years since I touched quantum mechanics, and none of that was based on relativistic hamiltonians (except for fine structure, of course). I couldn't spinor my way out of a paper bag.

The interactions (production and detection) happen in the flavour base. The propagation happens in the mass base. This means you never oscillate "from massless to massive": you are created with a mixture of massive and massless states, which travel differently, changing the probability of each flavour.

Okay, this makes sense and doesn't really bother me for natural neutrinos which are wildly ultrarelativistic even for the most massive eigenstate allowed by experiment. But suppose we could artificially create neutrinos with extremely low energies? Then the massive eigenstates would travel so differently than the massless eigenstates that it my head hurts just thinking about it. It might be possible to contain the slow-moving massive eigenstates, but the massless ones would still fly off at lightspeed, albeit with less energy. One part of the superposition would be in the lab, and the other part would be heading to the stars...

Example: Relativity vs Newton

[syousef]

If two theories explain the same data equally well, the simplest is more likely.

Is that really the case? That seems like it's a very hominid-centric assumption. I can't think of any counter examples but it seems very naïve to assume that the nature of the Universe would be simple...? Though, perhaps my understanding is limited.

Well it's VERY difficult to detect relativistic effects at human walking speed but they are still there. So you could create a whole stack of data that supports Newtonian physics over Relativity on that basis, but Relativity, though more complex is a more accurate description of the Universe.

When something doesn't fit your model, more experimentation and experience is needed, and most importantly you may need to do DIFFERENT experiments to determine whether a simpler or more complex theory is more accurate.

Re:Example: Relativity vs Newton

[OeLeWaPpErKe]

The problem with that process is that it assumes 2 very big axioms :
1) the universe follows mathematical laws (and the implication that our idea of mathematics is correct, which is extremely unlikely since it's known to be flawed, specifically mathematics is not correct when dealing with the extremely large (ie. infinite or more), or the extremely small (ie. 1/infinite). The existence of real numbers, however, is dependant on a known-inconsistent axiom)
2) the laws are not chaotic (also a questionable assumption since many laws are chaotic, e.g. gravity is chaotic : you can make short term predictions very easily, but long-term predictions are utterly impossible for anyone except God (ie. you need to be omniscient), like climate, just google "3 body problem" for a demonstration)

Re:Example: Relativity vs Newton

[t0rb3n]

The existence of real numbers, however, is dependant on a known-inconsistent axiom.

And which one would that be? Such axiom would not be used in maths... if you're referring to the axiom of choice, it's certainly not inconsistent, but rather undecidable.

Re:Example: Relativity vs Newton

[Anonymous Coward]

the universe follows mathematical laws (and the implication that our idea of mathematics is correct, which is extremely unlikely since it's known to be flawed

However there's no counter-evidence that the universe doesn't follow mathematical laws. What would that even mean? That the universe isn't true?

Robust result?

[harryjohnston]

Offhand, this doesn't seem like a very robust result - we're only talking about a single observation, after all. Does the equipment allow them to determine the source of the observed tau neutrino? How can they be sure that it came from the muon neutrino stream from CERN rather than being random background?

There's also no mention of a control, e.g., another tau neutrino detector close to the same muon neutrino source. Even if there was, is a single detection versus no detections statistically significant?

Re:Robust result?

[Brett Viren]

Your questions are not well addressed by the press release. There are two items that are missing: There are no tau neutrinos in the beam to begin with so any that are found are best explained by oscillation. The signature for a tau neutrino interaction, in this case, is a "kink" in the track produced from the outgoing tau traveling for some distance and then decaying to a muon. This signature reduces the background to negligent levels. And, yes, if background is small enough then even a single event is statistically significant.

Re:Robust result?

[harryjohnston]

But has the background actually been measured? Or is this an assumption based on theoretical grounds?

Re:Robust result?

[Brett Viren]

With Monte Carlo simulations the background has been estimated (http://arxiv.org/abs/0910.3468) to be 10%.

How measure no charge, no mass?

[LongearedBat]

Okay, so neutrinos have a tiny mass. But if a particle has actually no mass and no charge, how could one find out that it even exists? (Just curious.)

Re:How measure no charge, no mass?

[Anonymous Coward]

Photons are masless and chargeless, right?

Re:How measure no charge, no mass?

[John Hasler]

Photons have no rest mass and no charge. They aren't hard to detect.

Still not right

[Roger W Moore]

Something PROVEN TO BE missing from the Standard Model? Was shocking when it was first shown by SNO and SuperK 10 years ago.

All Opera will hopefully eventually show is that the ALREADY DISCOVERED neutrino oscillations convert muon neutrinos into predominantly tau neutrinos....and yes I use the future tense. One axiom of particle physics is that you never, ever believe single events because the statistics are simply too low to be certain that there is not a background fluctuation (no matter how low you think your backgrounds are - suppose you missed something?).

It actually is true!

[Roger W Moore]

However the effect is due to General Relativity and is amazingly tiny. GPS satellites have to include corrections of ~nanoseconds due to the Earth's gravitational field i.e. 20+ orders of magnitude larger than a human. So even scaled over a human lifetime the effect will be almost unmeasureably tiny.

Re:It actually is true!

[Mattskimo]

Fat people *do* live shorter lives, but relativity has very little to do with it.

Careful

[Roger W Moore]

...only with big mixing angles, unlike the almost-zero angles in the quark sector's CKM matrix.

Careful - you are confusing quark mixing with CP violation. The complex phase which gives CP violation in quark mixing is almost zero, the actual quark mixing angle is quite significant. For example the Cabibbo mixing angle for udsc mixing is ~13 degrees.

Re:Careful

[Steve Max]

~13 degrees is small, compared to the two main angles in the PMNS matrix (ok, \theta_13 is smaller, but the atmospheric and solar angles are really big). In fact, CKM angles are so big that you can treat the matrix as an identity matrix with a perturbation; in the neutrino sector, the mass and flavour eigenstates are so different that this type of treatment is meaningless.

Re:Careful

[Steve Max]

Proofreading is a good idea, people should do that... Of course I meant CKM angles are so SMALL that you can treat it as an identity matrix plus a perturbation.

Re:Careful

[Roger W Moore]

~13 degrees is small, compared to the two main angles in the PMNS matrix

Small, yes, almost zero (which is what you originally said) no. Meson decays involving off-diagonal terms of the CKM (which can be as large as 0.22), while suppressed, are still easily observed. The mixing certainly seems to be a lot larger in the PMNS matrix but the quark mixing is still very much non-negligible. What will be very interesting is to learn whether there is a CP phase and if so what that is.

Oscillation and the conservation of energy?

[SigNick]

1. If an electron neutrino can spontaneously transform to a tau neutrino with higher mass, where exactly does the required energy come from? Alternatively, when a tau neutrino transforms to an electron neutrino, where does the extra energy disappear?

2. If neutrinos have mass, then they are restricted to speeds below c. If they are accelerated to near c, then according to the relativistic energy-momentum equations they should have colossal mass, not miniscule (just like electrons, for example). Is there any evidence of observing neutrinos with huge energies?

The Wiki article about neutrino oscillation paints the picture that the oscillation is a pseudo-illusionary quantum mechanical effect, and therefore questions like the two above are meaningless. Smells more like handwavium to me.

Could a real physicist push back the veil of shadows one bit? Pretty please? =)

Re:Oscillation and the conservation of energy?

[volpe]

If they are accelerated to near c, then according to the relativistic energy-momentum equations they should have colossal mass, not miniscule

(ob-IANAP)
"Mass" means "proper mass" (or "rest mass"). The concept of "relativistic mass" (i.e. calling it such) has been out of vogue for more than 40 years.

Re:Oscillation and the conservation of energy?

[Anonymous Coward]

2. The relativistic mass of the neutrino must be small enough that it's effect at high energies (excepting the oscillation just found) hasn't been observable. Relativistic effects are similar for something with no mass and something with extremely little mass.

Re:Oscillation and the conservation of energy?

[Brett Viren]

> 1. If an electron neutrino can spontaneously transform to a tau neutrino with higher mass, where exactly does the required energy come from? Alternatively, when a tau neutrino transforms to an electron neutrino, where does the extra energy disappear?

It is not yet known which neutrino has the higher mass. Also, when we say electron-, muon- or tau-neutrino we are speaking of weak-eigenstates, something that is well defined at the point of interaction (only). These do not even have a definite mass (they are not mass eigenstates) although they do have a mass expectation value (average, expected mass). Instead they are a super-position of the 3 mass eigenstates. This superposition changes as the neutrino wave packet propagates. This is because each mass eigenstate propagates independently and since energy must must be conserved, each mass eigenstate will travel at different speeds. This propagation then leads to oscillations, or the mixing of weak eigenstates. If the neutrino wave package is detected later, one may see an outgoing electron, muon or tau even if one starts, in the case of OPERA, with a muon-neutrino (and the neutrino energy is at least high enough to produce the outgoing lepton mass).

> 2. If neutrinos have mass, then they are restricted to speeds below c. If they are accelerated to near c, then according to the relativistic energy-momentum equations they should have colossal mass, not miniscule (just like electrons, for example). Is there any evidence of observing neutrinos with huge energies?

Well, particle masses do not change with speed. One can couch relativistic equations into an effective mass, which does increase with speed. But, in any case, only (rest) mass differences matter in neutrino oscillations (differences of squares of masses, actually).

Experiments like IceCube look for and see incredibly and not fully explainable high energy neutrino interactions.

Re:Oscillation and the conservation of energy?

[Janek Kozicki]

the mass is a scalar, so it cannot change in Lorentz transformations. Scalars are not subject to change in Lorentz transformations. Therefore it's mot mass that increases, but momentum, you know p=m*v. Velocity is a vector, and in fact that vector is the value that makes momentum going to infinity. It seems as if mass was increasing, but in fact it is momentum increasing. But also it is not velocity strictly increasing to inf, because velocity isn't going to infinity either. I'd need to show you the derivation of that to show exactly that it's momentum that increases to inf and not per se mass or velocity. But I'm in hurry, search yourself for more.

About the conservation of mass/energy during neutrino oscillations I noted the question down, and will talk about that with friend professor, who works with neutrinos, when I meet him next time.

Re:Oscillation and the conservation of energy?

[Young Master Ploppy]

I'm not a "real" physicist - but I did study this at undergrad level, so here goes:

Heisenberg's Uncertainty Principle ( http://en.wikipedia.org/wiki/Uncertainty_principle ) states that there must always be a minimum uncertainty in certain pairs of related variables - e.g. position and momentum, i.e. the more accurately you know the position of something, the less accurately you know how it's moving. Another related pair is energy and time - the more accurately you know the energy of something, the less accurately you know when the measurement was taken.

(disclaimer - this makes perfect sense when expressed mathematically, it onlysounds like handwavery when you translate it into English, as words are ambiguous and mean different things to different people)

Anyway, this uncertainty means that there is a small but non-zero probability of a higher-energy event occuring in the history of a lower-energy particle (often mis-stated as "particles can borrow energy for a short time, but check the wiki page for a more accurate statement). It sounds nuts, I know, but it has many real-world implications that have no explanation in non-quantum physics. Particles can "tunnel" through barriers that they shouldn't be able to cross, for instance - this is how semi-conductors work.

By implication, there is a small probability of the neutrino acting as if it had a higher energy, and *this* is how neutrino-flipping occurs without violating conservation of energy.

Re:Oscillation and the conservation of energy?

[John Hasler]

> 1. If an electron neutrino can spontaneously transform to a tau neutrino
> with higher mass, where exactly does the required energy come from?
> Alternatively, when a tau neutrino transforms to an electron neutrino, where
> does the extra energy disappear?

Think of it as oscillating between a higher rest-mass state moving slower and a lower rest-mass state moving faster (yes, I know that isn't "really" what happens). The momentum doesn't change.

> 2. If neutrinos have mass, then they are restricted to speeds below c. If
> they are accelerated to near c, then according to the relativistic energy-
> momentum equations they should have colossal mass...

Only "colossal" relative to their rest mass, which is miniscule even by the standards of particle physics.

Re:Oscillation and the conservation of energy?

[Anonymous Coward]

!?!?

G.M. Wang, E.M. Sevick, E. Mittag, D.J. Searles & Denis J. Evans (2002). "Experimental demonstration of violations of the Second Law of Thermodynamics for small systems and short time scales". Physical Review Letters 89: 050601/1–050601/4. doi:10.1103/PhysRevLett.89.050601

Re:Oscillation and the conservation of energy?

[Anonymous Coward]

It all comes down to quantum effects from having different eigenstates in different bases.
Start off by thinking between the difference of cartesian coordinates and polar coordinates. A particle in a plane can have a certain x coordinate, 42 or something. It could be oscillating up and down, if you'd measure the x-value, it'd stay 42, no matter what you do.
If, on the other hand, you look at the particle from pole coordinates, you'd see it's r-coordinate oscillate, because it's moving up and down in a straight line, and the distance to the origin isn't staying a constant.

Now quantum mechnically, if you'd measure that particle's r-coordinate, you'd collapse it's wave function, and force it to have a specific r-coordinate. That way it would stay a constant distance from the origin, and perhaps start turning in a circle. This, in turn, will cause it's x-coordinate to fluctuate.
It's a little trickier in real life, because it works with probabilities rather than fixed outcomes, but the idea is roughly the same.

Now a similar thing happens with these neutrino's. You can look at them in two different bases with different eigenvalues. Either the mass eigenstates, or the flavor eigenstates. When a neutrino travels, it should have a constant energy (as you pointed out correctly), so it's mass is constant (though very very small). This doesn't quite overlap with the flavor eigenstates however, So they will start to oscillate between flavors: electron, muon, tau.
But then, when a neutrino encounters a neutron, it can split that neutron into a proton and a charged lepton. Which lepton depends on the flavor: either electron, muon, or tau. But this reaction forces the neutrino to pick a specific flavor. What flavor that will be depends on where it is in it's oscillation cycle. Each flavor will have a specific probability of appearing.

This is what they measured here, they started with a neutrino beam that contained no tau neutrino's to start with, but they were in a flavor eigenstate when they were created, no mass eigenstate. Having to travel with a certain energy, they had to collapse into a specific mass, and started oscillating between flavors. Upon arrival, after oscillating, they encountered particles were forced to choose flavor again to interact, and one of them picked "tau".

I hope I cleared things up instead of confusing you more :)

Re:Oscillation and the conservation of energy?

[marcosdumay]

Anyway, you shouldn't be able to measure that energy lend over time. Every time you look at, the energy must appear to be conserved, all you can measure are consequences of the particle having extra energy on the past, but not anymore. So, the uncertainty principle can't explain the neutrino changing. It is probably better explained by it losing some kynetic energy (then, what happened to momentum, did it interact with matter?).

Re:Oscillation and the conservation of energy?

[uninformedLuddite]

Could a real physicist push back the veil of shadows one bit? Pretty please? =)

What? And show the world where all the dark matter and gravity waves have been hiding?

So it is actually Transformers at work

[Anonymous Coward]

Decepticons are the smaller, massless, naughty, hidden, rare-to-find ones and Autobots are the nice particles that behave well - like Bumblebee and Optimus Prime.

Once in a while, Fallen or Megatron is raised from the dead with the All Spark (String theory / God particle?) and that is when the whole belief or theory needs to be changed - which brings great new understanding.

Is that a good continuation of the analogy?

Because, after all, the particles are essentially transforming and otherwise hidden in plain sight.

What about the mass

[Anonymous Coward]

What I understand that the different states of the neutrino can be interpreted as eigenvectors of its state function. The resulting mass prediction had quit a broad range. Is the mass better defined now that we have observed the oscillation? Also, if a neutrino has mass and spin, wouldn't it (very weakly) react to a magnetic field??

How science is viewed by the Normals

[ProteusQ]

This reminds me of the /. post a few days ago about those who are ignorant of science and proud to be so. This is how I think some of them might perceive this situation:

Last week, a Normal would have been told by Those Who Do Science that a neutrino has no mass, and that is the end of the matter. A non-physicist has nothing to contribute to the discussion. Persistent disagreement amounts to sheer ignorance, so keep quiet.

But now, it would appear that either neutrinos have mass or the Standard Model is wrong. Science has revealed its own ignorance. Everyone who was wrong last week is right this week. But the message to the Normals remains the same: it doesn't matter that we were wrong last week; eventually, We Who Do Science get it right. You still have nothing to say. Keep quiet.

The Normals perceive the above and conclude that it's hypocrisy. Hence, they can ignore science and be proud that they are smart enough to avoid hypocritical know-it-all's.

BTW: Yes, this is post if Offtopic, but it's not Flamebait or Troll. I'm not agreeing with this POV; I'm passing on my perception of it. And how else can one discuss the interrelationship between topics without being regarded as Offtopic in regards to one post or the another?

I wish I had an answer of how to fix the above problem. Eliminating arrogant PhD's would be helpful, but that would leave all of the arrogant Normals -- and the rest of us aren't free from shocking amounts of arrogance at times, either. We could use another Sagan to highlight that math+science is a process that anyone can join in on once the ground-rules are mastered. However, it would me imperative that the next spokesperson not be hostile to religion -- the Normals are hypersensitive to this issue, and getting in their face about the matter only increases the alienation. [Not saying that Sagan was hostile to religion -- just saying then next spokesperson cannot be.]

Re:How science is viewed by the Normals

[John Hasler]

> Last week, a Normal would have been told by Those Who Do Science that a
> neutrino has no mass...

Where did you get that idea?

Re:How science is viewed by the Normals

[david mitchell]

Best off-topic post in the thread so far, thanks! And may I point out that many of the hypersensitive alienated Normals are armed?

--

Re:How science is viewed by the Normals

[devent]

> I wish I had an answer of how to fix the above problem.

How about teaching in school what science is and what a theory is all about?

A theory can't be right or wrong, a theory can only get the right or wrong predictions in a limited model. For example, the Newtons Gravitation theory have right predictions if the masses are travelling at very slow speeds but fails at speeds near the speed of light. So the SM is neither right nor wrong, but you will get some right predictions and some wrong predictions. So far the SM had only right predictions.

That is what the ID or Creationists don't get. ID is not a theory, because you can't tell if the prediction is right or wrong.