It's only arrogance if you're wrong. If you are correct, it's knowledge. If you're wrong, it's arrogance. Sadly, many employers do not understand this little bit of wisdom. [Jane Q. Public, 2012-10-25]
Jane, are you sure you want to use that criterion? Let's reminisce...
How do they know they were the same neutrinos they launched out? [Dr Max]
... they know the beginning ratio and ending ratio of the different types. If they are not the same, then some must have flipped (or rotated, or whatever language the neutrino guys use these days). [global_diffusion]
Not necessarily. They could be different neutrinos, caused by atoms in the way absorbing some neutrinos and emitting others. I am not sure but I suspect that is what GP [DrMax] was getting at. Rather than evidence of neutrinos actually changing from one type to another, it seems just as likely (more likely?) that intervening matter performed a conversion. Just as, say, a crystal or a gas can "change" a laser's color by absorbing photons and then emitting others of a different frequency, maybe matter is absorbing these neutrinos and emitting others with different properties. [Jane Q. Public, 2011-06-17]
Nonlinear crystals can change a laser's color by absorbing photons and then emitting others of a different frequency because photons are mediators of the electromagnetic force, so they interact with comparatively large (~10^(-10) m) electron clouds. But neutrinos only interact via gravity (irrelevant here) and the weak force which has a comparable range of ~10^(-18) m. Since the cross section determines how likely interactions are, neutrinos are roughly ten thousand trillion times less likely to interact with matter than photons. This is just an approximation, but experiments yield similarly tiny cross sections.
If neutrinos have to interact with intervening matter before hitting the detector, an extra interaction is involved. That's why Chris Burke pointed out that detecting neutrino flavor change due to an interaction with intervening matter would depend on the square of the interaction probability. Detection in the conventional flavor oscillation theory just depends on the interaction probability because it only involves a single interaction, so it's trillions of times more likely to explain the observed electron neutrino events.
In fact, that T2K paper acknowledged a much bigger source of noise on page 8: the muon neutrino beam was slightly contaminated by electron neutrinos. This contamination doesn't invalidate their results because it only explains ~1.5 out of 6 observed electron neutrino events.
Anyway, the processes that change a laser's color are given names like "second-harmonic generation" (where a crystal combines two photons into one, commonly used in green laser pointers) and "parametric down-conversion" (where a crystal splits one photon in two, commonly used as a source of entangled photons). To the best of my knowledge, these nonlinear processes only work in crystals, not in gases.
I haven't studied second-harmonic generation in depth, but five years ago I reviewed a quantum teleportation experiment that used a beta-barium borate (BBO) crystal to generate entangled photons via parametric down-conversion. Look at figure 1 on page 6 of the PDF or slide 12 of the powerpoint animation. Notice that the down-converted photons leaving the BBO crystal aren't collinear with the original UV pump laser beam.
That's because the down-converted photons are emitted in two cones which don't generally align with the pump photon, as shown in this diagram. Careful phase matching of the BBO crystal is required for the down-converted photons to leave in the same direction of the pump photon. For example, here's an experiment using collinear parametric down-conversion. Notice that they had to buy a BBO crystal that was likely periodically poled, then arrange it at exactly the right angle with respect to the pump beam in order to produce collinear down-converted photons. This is highly unlikely to happen naturally, as you suggest is happening with neutrinos.
Also, the total number of photons in the universe isn't conserved. That's why parametric down-conversion can turn one photon into two photons. But the total number of leptons is usually conserved, and the total number of baryons minus leptons is even more likely to be conserved. So the neutrino analogue of parametric down-conversion would increase the total number of leptons by +1 unless it also creates an antilepton (or destroys an existing lepton). Alternatively, it could create a baryon (or destroy an existing antibaryon, which seems unlikely) to keep B-L constant instead. Both possibilities seem to either violate conservation of energy or imply neutrino-induced radiation.
This would imply that the absorbing/emitting matter emitted it in exactly the same direction, which seems unlikely. [AlecC]
That's why I used the example of the laser: the photons are emitted in exactly the same direction, however unlikely you might think that is. [Jane Q. Public]
Here you've switched to a different topic: stimulated emission, which does happen in gases, and is collinear. But why is it collinear? Photons produced via stimulated emission are identical to the original photon not only in terms of direction, but also in terms of frequency, phase, polarization, and transverse and longitudinal spatial states. In fact, they're in exactly the same quantum state. As I've explained:
Bosons and fermions are both types of indistinguishable particles in quantum mechanics. Fermions have half-integer spin, like protons, electrons, antiprotons and positrons. Bosons have integer spin, such as photons and mesons. Some implications of this distinction can be deduced using nonrelativistic quantum mechanics, such as the fact that fermions obey the Pauli exclusion principle while bosons actually attract each other into the same state (Griffiths 1st ed p179). The connection between these statistics and spin is simply assumed in nonrelativistic quantum mechanics, but it can actually be deduced using relativistic quantum field theory.
Because photons have spin 1 and are thus bosons, they attract other photons into the same state. Griffiths derives Einstein's "B coefficient" governing stimulated emission on p311 of the 1st edition; this derivation depends on the fact that photons are bosons. However, neutrinos have spin 1/2 and are thus fermions, so the Pauli exclusion principle prevents them from occupying the same quantum state as other neutrinos. Therefore, stimulated emission of individual neutrinos is impossible.
Not necessarily. They could be different neutrinos, caused by atoms in the way absorbing some neutrinos and emitting others. ... [Jane Q. Public]
It's not entirely an oversimplification to say "that won't happen" - solar neutrinos pass straight through the Earth for example. (See the Wikipedia page) [Tim C]
Do they? Or do they often collide with atoms and experience the same kind of "conversion"? As far as I know, nobody has performed any experiments to find out. The very idea that they might change from one form to another is very recent. [Jane Q. Public]
Sure, if 1957 fits your definition of "very recent".
Do they? Or do they often collide with atoms and experience the same kind of "conversion"? As far as I know, nobody has performed any experiments to find out. The very idea that they might change from one form to another is very recent. [Jane Q. Public]
I guess just over half a century is 'very recent' by some standards, but I'd say probably not by the standard of "recent enough for me to assume no experiments have been conducted." [Chris Burke]
This was the first experiment of this kind to be performed, as you well know. Those others you mention over that last century are not relevant to my comment. Tell me: when was the last other experiment performed to find this evidence about the third leg of the oscillation? What's that you say? Never? Wow. How about that. [Jane Q. Public]
You originally wrote "change from one form to another" which isn't flavor-specific and thus refers to neutrino oscillation in general. Here you seem to be asserting that "change from one form to another" means "change from muon neutrino to electron neutrino which is controlled by theta_13". Even if that's what you originally meant, you still need to redefine "Never" to mean the papers published in 1992, 2001, 2002, 2003, 2003, 2003, 2005, 2006, 2007, etc.
I think it'd be Nobel prize material if one found neutrino-stimulated neutrino emission, as that is what you're alleging. I'm not saying it's impossible, just that IIRC my undergrad physics at all, it'd be a big discovery. [tibit]
Bigger than, say, neutrinos spontaneously, and without obvious cause, changing from one form to another? I don't see why. In fact, I think it is the more likely explanation. It fits Occam's razor a hell of a lot better, because you don't have to assume some kind of spontaneous process from a cause unknown. [Jane Q. Public]
This still begs the question: they are claiming that this is a "new type" of neutrino oscillations. So what causes the oscillations? So far I have yet to see an explanation, anywhere. [Jane Q. Public]
You are saying that the cause of this oscillation is known? If so, can you enlighten us, or at least link to an explanation of this behavior? Because everything I have read about it so far says that (a) this is the first time it has been observed, and (b) the cause is unknown. [Jane Q. Public]
You tell me: what is the most likely hypothesis for why this happens? Not how... stop getting that confused. I asked why. What is the cause behind neutrino oscillation? I will patiently wait for at least one, or hopefully at least three hypotheses about the cause of these theoretical oscillations. I don't want to hear any garbage about waveforms and probability. That's a how. I asked for a why. ... Come back when you can explain to me some hypotheses for the cause of neutrinos oscillating. NOT an equation (still very much speculative, at that) purporting to describe how. [Jane Q. Public]
Dismissing wave functions and probability as "garbage" isn't a very productive approach to learning quantum physics. The cause of neutrino oscillation is that a neutrino's wave function interferes with itself, because neutrino propagation eigenstates aren't identical to the flavor eigenstates involved in neutrino detection, and propagation eigenstates with different masses have different wavelengths. As a result, flavor detection probabilities vary spatially.
Thanks for the mention of MSW Effect. The idea of coherent forward scattering is something that I mentioned myself earlier, but I was merely speculating about the possibility, without actually knowing about it. [Jane Q. Public]
... I only mentioned the possibility that coherent scattering might exist, in a completely different comment that did not directly bear on the first one. And, as it turns out, coherent scattering does exist. But the possibility that it is the actual cause of the results of this experiment are, admittedly, near nil. The point of that comment was only that coherent scattering should be possible... and it turns out that it is. [Jane Q. Public]
No, you made a vague reference to parametric down-conversion which isn't naturally collinear and seems to either violate conservation of energy or imply radiation if it could happen with neutrinos. Then you made a separate vague reference to stimulated emission which doesn't work with fermions like individual neutrinos. Saying the word "laser" isn't the same as saying that "coherent scattering should be possible" because MSW effect (i.e. coherent forward scattering) is analagous to refraction, not to a laser. Just because a laser emits coherent light doesn't mean you get to reinterpret your previous statements like those of Nostradamus.
You're trying to draw a distinction between the MSW effect in matter and neutrino flavor oscillation in vacuum that simply doesn't exist in our universe. The MSW effect is analagous to the way a prism separates white light into a rainbow, which is an example of dispersion. A prism's index of refraction is wavelength dependent, so photons with different wavelengths travel through it at different speeds.
Electron neutrinos interact with electrons in matter via W bosons, but muon and tau neutrinos don't. This is a kind of dispersion where electron (anti-)neutrinos travel slower(faster) in matter than muon or tau neutrinos because they have different effective masses. Both vacuum and MSW oscillations occur because a neutrino's flavor (detection) eigenstates are rotated with respect to its propagation eigenstates, which travel differently because they have different masses. If we lived in a universe where all neutrinos were massless, neutrino oscillation wouldn't happen in vacuum, but the MSW effect would still cause neutrinos to oscillate in stars.
But we actually live in a universe where neutrinos have very small but non-zero masses, so the same physics that explains the cause of the MSW effect (where neutrinos oscillate in stars) also explains the cause of neutrino oscillation in vacuum. For example, Boris Kayser derives functionally identical Hamiltonians for vacuum and MSW oscillations in equations 25 and 37.
I am curious ... What is the proposed mechanism by which these neutrinos oscillate? If flavor is a measurable property, then how can they "spontaneously" change? [Jane Q. Public]
... I am still left, however wondering not how neutrinos oscillate, but rather the why. What causes them to oscillate in the first place? I understand about spontaneous propagation and destruction of virtual particles, for example, and to me that needs little explanation, because it's all probability and there is no -- or very little anyway -- net gain or loss. Things aren't changing properties, on average... just form. But it seems to me that this neutrino oscillation is different. There is a macroscopically measurable difference of properties, and so I have a hard time accepting that it is merely probability "driving" the neutrino oscillations. [Jane Q. Public]
A few years ago, I mentioned that virtual particles can explain why light slows down in materials, which is related to the MSW effect. But I also said that "I couldn't spinor my way out of a paper bag" so here's a simpler analogy for understanding the cause of neutrino oscillations.
Consider the famous double-slit experiment which is performed in freshman physics classes. Photons actually go through both slits, then interfere with themselves to cause a counterintuitive oscillatory pattern on the screen. Neutrinos interfere with themselves too, which causes a similar pattern of neutrino flavor oscillations. Both patterns exist because of wave function interference, which makes the resulting detection probabilities vary spatially.
In other words, by questioning the long-established cause of neutrino flavor oscillation, you're also questioning basic quantum theory.
Well, since it [a neutrino] isn't subject to magnetic or electrical forces, it basically has to slam into the nucleus ... it needs to get close enough to another particle - by coincidence - for the weak force to start having a decent effect on them. [OeLeWaPpErKe]
You are saying, in effect, that radioactivity is unlikely. And statistically, it is, I suppose. All I am doing is speculating. So far, I have not seen anybody (aside from a commenter here who so far has given no evidence) that there is a cause known for this "oscillation". I am simply guessing -- no more than that -- at a possible cause, rather than assume it is somehow spontaneous. [Jane Q. Public]
It's odd that you mention radioactivity, because that's a spontaneous, macroscopically measurable difference in the properties of a nucleus, and it's "driven" by mere probability. Just like neutrino flavor oscillation.
... at this time any real evidence is still waiting to show up. And I will be happy to accept that evidence, if it was responsibly gathered. Until then, I am entitled to my opinion as to what is more likely. [Jane Q. Public]
The skeptic looks for potential causes for an observation, rather than accepting that it happens spontaneously or through "mysterious" processes. If the cause is unknown, then speculation as to the possible cause is not only called for, but necessary. Further evidence will not be forthcoming until those speculations are tested. I do not claim to be as qualified to speculate on the matter as professional physicists; nevertheless, in an absence of explanation I still have a right to speculate. [Jane Q. Public]
Freedom of speech gives you the right to speculate either way, but your frequent rants about physics would be more credible if you:
- Recognize that "absence of explanation" should read "absence of explanation that I've learned about."
- Try to understand the conventional explanation instead of pretending it's absent.
... this looks like a definitive on-point source, from LBL by a FNAL author. Enjoy! [singlercm]
Thank you for that link. I now see how, theoretically anyway, it could be a probabilistically-determined superposition. That clears up a lot. [Jane Q. Public]
No, it really is a superposition, not just in theory but later confirmed by the experiments shown in figure 13.2 of that paper and many more. You're just manufacturing unwarranted doubt about yet another topic in physics.