Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Atomic-S on 13/11/2013 08:07:58
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Given that neutrinos are now know to have a nonzero rest mass and therefore travel at somewhat less than the speed of light, there must be a reference frame in which a neutrino is at rest (with respect to a specific mode of its existence). That raises the interesting question of how neutrinos at rest behave. What happens when they encounter ordinary matter? What happens if they encounter a strong magnetic field?
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Neutrinos are thought to travel very close to the speed of light*, so a lot of their momentum may be due to their velocity.
Attempts to model the neutrino suggest that it might have the lowest rest mass (http://en.wikipedia.org/wiki/Neutrino#Motivation_for_scientific_interest) of any particle in the Standard Model.
This means that the energetic neutrino reactions by which we currently detect neutrinos would not occur.
To detect such slow-moving neutrinos, we would have to look for a very unstable isotope which can decay by the weak interaction if it strikes a slow-moving neutrino (eg moving at a relative speed of a walking pace, instead of at a walking pace less than the speed of light...).
Neutrinos don't respond to the electromagnetic force, so we can't store them in a magnetic bottle. Even if we had some way to slow down neutrinos to a walking pace, they would quickly fall out of the bottom our detector, using current technologies.
*But not faster than light, as suggested by an experiment at CERN & Gran Sasso in 2011.
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Given that neutrinos are now know to have a nonzero rest mass and therefore travel at somewhat less than the speed of light, there must be a reference frame in which a neutrino is at rest (with respect to a specific mode of its existence).
Yes. That is absolutely true.
That raises the interesting question of how neutrinos at rest behave. What happens when they encounter ordinary matter? What happens if they encounter a strong magnetic field?
Nothing should happen. The neutrino doesn’t have charge or a magnetic dipole moment. Therefore it behaves like any other particle with those properties.
Neutrinos are thought to travel very close to the speed of light*, so a lot of their momentum may be due to their velocity.
Any particle with a non-zero proper mass has a frame of reference in which they are at rest even if such a frame is not close to the Earth’s frame of reference. It’s this frame Atomic-S is referring to.
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It will be almost impossible to observe a neutrino at rest because of the uncertainty particle. particle accelerators accelerate particles at such a speed partly because it would be easier for the detectors to detect.
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Recent results from the Ice Cube experiment in Antarctica (reported in Science) show ultra-high energy neutrinos, approaching 1 Peta electron-volt (Pev). So far, the LHC can only reach energies of about about 7 TeV (0.7% of these energies).
These are very definitely not stationary neutrinos (in our frame of reference).
See http://arxiv.org/abs/1311.5238
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Given that neutrinos are now know to have a nonzero rest mass and therefore travel at somewhat less than the speed of light, there must be a reference frame in which a neutrino is at rest (with respect to a specific mode of its existence). That raises the interesting question of how neutrinos at rest behave. What happens when they encounter ordinary matter? What happens if they encounter a strong magnetic field?
Do you know what is De Broglie wavelenght? I'm sure you do. So a neutrino at rest will be described by a certain wavefunction with infinite wavelenght (or zero frequency) and then ... where would it be, to begin?
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This paper (http://indico.phys.vt.edu/getFile.py/access?contribId=4&sessionId=19&resId=0&materialId=slides&confId=21) suggests a neutrino De Broglie wavelength as low as 2mm, and suggests some ideas for detecting relics of the Big Bang.
Here is some speculation (http://www.cambridgeultrasonics.com/neutrinos/neutrinos.htm)that the De Broglie wavelength of red-shifted neutrinos (perhaps as much as 1.5m) could be larger than their separation (perhaps 1mm). This might produce a superfluid neutrino ocean of ultra-low energy neutrinos from the Big Bang?
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It will be almost impossible to observe a neutrino at rest because of the uncertainty particle.
The uncertainty principle is not different for neutrinos. No quantum mechanical particle is ever a rest
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That raises the interesting question of how neutrinos at rest behave. What happens when they encounter ordinary matter? What happens if they encounter a strong magnetic field?
The question about how they behave when they're at rest is vauge. What kind of behaviour can anything have when at rest do you have in mind? In any case quantum mechanical particle are never at rest since that'd mean they're not moving and that's mean we know their momentum perfectly (i.e. p = zero) and we can't know such a thing in QM. What did you have in mind anyway?
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Since neutrinos don't experience any appreciable friction, you would expect them to be in "free fall".
Neutrinos of cosmic origin, detected near the Earth's surface, would be expected to have a velocity at least as high as Earth's escape velocity (http://en.wikipedia.org/wiki/Escape_velocity#List_of_escape_velocities), or around 11 km/s.
Indeed, they would be expected to have a velocity at least as high as the escape velocity from the Solar System, at around 42km/s (or the escape velocity from the Milky Way, which is over 520 km/s).
"Stationary" is a relative term.
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Do you know what is De Broglie wavelenght? I'm sure you do. So a neutrino at rest will be described by a certain wavefunction with infinite wavelenght (or zero frequency) and then ... where would it be, to begin?
A valid point. My concern then would be with respect to neutrinos having very low kinetic energy, which can be referred to as "rest" only in an approximate sense. We could contemplate, for example, the effect of a neutrino that was not strictly at rest but whose wavelength was compatible with having it within a one liter container.
Actually, to make the subject more meaningful, we should contemplate not the presence of one neutrino but a macroscopically significant number of them in the 1 liter container. Say 1024 of them. Of course, that would create a problem due to the half-integer spin, which would invoke the Pauli exclusion principle and not allow any two of them to occupy the same state. The longer wavelengths would quickly be claimed, and most of them would have to exist in much shorter wavelengths, which means significantly higher kinetic energies (although still well below that of those typically encountered). Probably we ought to be thinking more , however, in terms of a more reasonable number of them, such as 1012 particles per liter. Were that achievable, what would the environment thus created be like?
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It would seem on the basis of http://www.cambridgeultrasonics.com/neutrinos/neutrinos.htm that the question of low-energy neutrino behavior, particularly in large groups, is quite significant.
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Estimates suggest that as a relic of the Big Bang (http://en.wikipedia.org/wiki/Neutrino#Big_Bang), there are around 56 low-energy neutrinos of each type per cm3, or about 170,000 relic neutrinos per liter.
This is a long way short of the 1024 that you would like for your experiment.
Solar Neutrinos (http://en.wikipedia.org/wiki/Neutrino#Solar) are estimated at 6.5×1010 per cm2. Since these high-energy neutrinos travel at almost the speed of light, they will be spread out over 3x108 meters, or an average of 5mm apart. This suggests a density of around 2000 solar neutrinos per liter. This won't help achieve the densities you want.
Since we currently have no way to focus or reflect neutrinos, I don't see how you will get higher densities, short of a supernova or a nuclear explosion - and these tend to be high energy neutrinos with short wavelengths.
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It would seem on the basis of http://www.cambridgeultrasonics.com/neutrinos/neutrinos.htm that the question of low-energy neutrino behavior, particularly in large groups, is quite significant.
I don't understand very well the connection between ultrasound technology and the properties of low-speed neutrinos.
Maybe you are working in that field?
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While there have been proposals to use neutrinos for telecommunications (eg to communicate with submarines deep underwater), this is not a mainstream technology today. I work with photons & electromagnetic waves, which are much easier to handle...
I suspect that there is not a strong link between neutrinos & ultrasonics, either...
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Ah, ok, thank you. But my question was for Atomic-S [:)]
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The relation between ultrasonics and neutrinos is, according to the cited article, that theory indicates that neutrinos may be capable of collectively forming a medium in which wave action is possible that resembles that associated with sound. Of particular interest is the theory that neutrinos could form a Bose-Einstein condensate, which has interesting behavioral characteristics similar to those of superfluid helium. Waves of such a medium are of interest, in particular if such collected neutrinos may account for a number of the properties of matter which are currently the object of investigations regarding string theory and the like.
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Since we currently have no way to focus or reflect neutrinos, I don't see how you will get higher densities, short of a supernova or a nuclear explosion - and these tend to be high energy neutrinos with short wavelengths.
If we had just launched from a star at nearly the speed of light when suddenly it went supernova, we would encounter a lot of low-energy neutrinos because there would be a lot of them and we would be moving at about the same speed as them. That would allow experiments to be conducted with them during a very brief time interval.
Of course, this method is somewhat impractical at present.
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The relation between ultrasonics and neutrinos is, according to the cited article, that theory indicates that neutrinos may be capable of collectively forming a medium in which wave action is possible that resembles that associated with sound. Of particular interest is the theory that neutrinos could form a Bose-Einstein condensate, which has interesting behavioral characteristics similar to those of superfluid helium. Waves of such a medium are of interest, in particular if such collected neutrinos may account for a number of the properties of matter which are currently the object of investigations regarding string theory and the like.
Yes. My question was rather different, I tried to be ... diplomatic.
What I mean is: Why does a company which studies ultrasounds for practical applications, writes papers about ... imaginary properties of extremely elusive objects as neutrinos? [:)]
(If you are involved in such research, I hope not to have been unkind).
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