Are Neutrinos Faster Than Light?

[Kahsi]

neutrinos and their speed

Hi.

Physicists detected the first neutrinos from a supernova in 1987 when a star collapsed some 150 000 light-years away in the Large Magellanic Cloud, the galaxy nearest to the Milky Way. Two huge underground experiments — the Kamiokande detector in Japan and the IMB experiment near Cleveland in Ohio, USA — detected neutrinos from supernova 1987A a full three hours before light from the explosion reached Earth.

http://hitoshi.berkeley.edu/neutrino/neutrino.html

Doeas this mean that neutrinos are faster than light?

 

[marlon]

Doeas this mean that neutrinos are faster than light?

Not at all, why would you think that ?

they move at a speed very close to the speed of light though

marlon

 

[Kahsi]

I just got confused because the neutrinos arrived 3 hours before the light.

 

[marlon]

I just got confused because the neutrinos arrived 3 hours before the light.

This just implies that the neutrino's were emitted PRIOR to the actual explosion.


EDIT : i need to be more exact : the neutrino's came out at the time of the explosion, it's the EM-radiation that 'came later' .

regards
marlon

 

[Meir Achuz]

Neutrinos get out of the supernova faster than light, because the photons react more strongly with the matter in the supernova. That is the simple explanation.
The details get more complicated and speculative.

 

[mathman]

Neutrinos came out at the time of the explosion. Gamma rays come out later - they are born afterwards.

 

[Kahsi]

Ah, thank you guys. May I ask one last question? I can't find a proper explanation of what a "right-handed" and a "left-handed" neutrino is.

 

[marlon]

Ah, thank you guys. May I ask one last question? I can't find a proper explanation of what a "right-handed" and a "left-handed" neutrino is.

Here is all you need

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html#c1

marlon

 

[marlon]

Neutrinos get out of the supernova faster than light,

That is not true. Neutrino-velocity does not exceed the speed of light

because the photons react more strongly with the matter in the supernova.

I don't even know what this means and where you got such info

That is the simple explanation.

marlon

 

[Meir Achuz]

RH and LH for particles are defined by convention.
The convention is that if the helicity (component of the spin in the direction of the momentum) of the particle is positive, it is called RH, and v-v.
This applies to all particles. For the photon, this elementary particle definition turns out to be opposite to the optical designation of RH and LH circular poariztion.

 

[Kahsi]

Thank you once again. A very useful link. I suspected that it had something to do with the rotation. :shy:

 

[Meir Achuz]

The neutrinos and photons diffuse out of the supernova. The diffusion time depends on their interaction. This knowledge is acquired by reading papers, going to conferences, and working things out.

 

[marlon]

RH and LH for particles are defined by convention.

No it is not. The reason for the specific left-handedness of neutrino's has to do with parity conservation in beta decay. same goes for the anti-neutrino.

This applies to all particles.

No it does NOT.

here is a quote from the site i gave :

This "left-handed" vs "right-handed" characterization is not meaningful for other particles, like electrons. An electron could have spin to the right and be traveling right and therefore be classified as right-handed. But from the reference frame of someone traveling faster than the electron, its velocity would be to the left, while its spin would be unchanged. This would mean that the electron is a left-handed particle with respect to that reference frame.


Meir, this is not the first post where you supply erroneous information. you are going to have to be more careful in the statements that you make.

marlon

 

[marlon]

The diffusion time depends on their interaction. This knowledge is acquired by reading papers, going to conferences, and working things out.

Since you have been working things out. Please prove me that neutrino's exceed the speed of light at any time ?

marlon

 

[Meir Achuz]

Two simple things and then I'm outerhere.
1. LH is not a Lorentz invariant, but does describe the helicity state in any given frame.
2. The key word is "diffusion".

 

[marlon]

Two simple things and then I'm outerhere.
1. LH is not a Lorentz invariant, but does describe the helicity state in any given frame.
2. The key word is "diffusion".

I really don't think that you know what you are talking about. I have one question for you : why do you think that elementary particles are massless ? What is the difference between parity and intrinsic parity ?


Ofcourse, LH is not Lorentz invariant, that is my entire point. this also proves you wrong because this property cannot be valid for all particles then.


marlon

 

[marlon]

And what is this nonsense about diffusion ?

marlon

 

[dextercioby]

Scattering would be a better name for the processes in which a photon is involved in a hot dense stelar plasma.I think he would refer,in analogy,to the same kind of processes that occur in our sun and how a photon born in the core would need ~5000 yrs to reach the surface...

Daniel.

 

[juvenal]

I really don't think that you know what you are talking about. I have one question for you : why do you think that elementary particles are massless ? What is the difference between parity and intrinsic parity ?


Ofcourse, LH is not Lorentz invariant, that is my entire point. this also proves you wrong because this property cannot be valid for all particles then.


marlon

Marlon - he never claimed that the helicity was Lorentz invariant. However, you can define a helicity for any particle in some given frame, and experimentalists/phenomenologists DO use the concept of helicity even with massive particles. For example, in the pion decay to lepton neutrino, one talks about helicity suppression as being the reason for the muon channel being favored over the electron channel. p 266-7 of Halzen and Martin is a reference for this.

As for the diffusion, I think that all he was saying was that photons interact more with matter than neutrinos since neutrinos can only interact weakly while photons can interact via EM.

 

[SpaceTiger]

I would say both marlon and Meir Achuz are right in their answer to the poster's question, but it depends on how you look at it. In the initial core collapse, both neutrinos and photons will be created, but each will take a different time to escape from dense core of the supernova. Neutrinos have smaller interaction cross sections than photons (in every case that I'm aware of), so they'll escape the core more quickly than neutrinos. This is what Meir Achuz means when he says that they come out faster than the light, he doesn't mean that they're actually moving faster than light. Also, as he said, this can be thought of like a diffusion process, just like photons in the sun. However, the photons we're seeing after those three hours actually experienced their final scattering well after the neutrinos, so it could be said that marlon is right in asserting that the photons were created after the neutrinos. It's mostly a semantic point, though.

Anyway, fun fact about supernovae: most of the EM radiation we see is from radioactive decay of nickel-56 and cobalt-56.

 

[marlon]

Marlon - he never claimed that the helicity was Lorentz invariant.

No, i never said he did. point is that helicity is NOT a universal property of all particles, which he claimed.

marlon

 

[marlon]

In the initial core collapse, both neutrinos and photons will be created, but each will take a different time to escape from dense core of the supernova. Neutrinos have smaller interaction cross sections than photons (in every case that I'm aware of), so they'll escape the core more quickly than neutrinos.

Well, that is indeed very true but i would never formulate this is as 'moving faster then light' (if that is what was originally meant).

regards
marlon

 

[juvenal]

No, i never said he did. point is that helicity is NOT a universal property of all particles, which he claimed.

marlon

He did not. You are misinterpreting his post.

RH and LH for particles are defined by convention.
The convention is that if the helicity (component of the spin in the direction of the momentum) of the particle is positive, it is called RH, and v-v.
This applies to all particles.

There is nothing in this person's post which is wrong in my view. In a given Lorentz frame, I can call an electron or muon left-handed or right-handed. And practicing experimentalists/phenomenologists do this all the time. That's what he means by "This applies to all particles". He did NOT mean "A muon or any massive particle has a fixed helicity in all frames".

The only possible quibble you could have is that he did not say explicitly say "in a given Lorentz frame", but that is implicit anyhow since he mentioned momentum.

 

[marlon]

The only possible quibble you could have is that he did not say explicitly say "in a given Lorentz frame", but that is implicit anyhow since he mentioned momentum.

Are you his lawer ?

I still don't agree for two reasons :

1) LH and RH are defined by convention. This is untrue because this implies that LH and RH are 'fixed' values, which is not the case. The determining factor is conservation of helicity. Point Final...That's what i should have read in that post.

2) About the 'applying to all particles' i say this : you interpreted that your way, i interpreted it my way. It is very possible that my interpretation is wrong however that clearly proves there must be something missing in the actual explanation. There should have been a clear distinction between parity and intrinsic parity. Besides, the same goes for 'moving faster then light'
Now, i don't want to continue a discussion that has degenerated into semantics, so why don't we just drop it, ok ?

marlon

 

[Meir Achuz]

I would like to thank a number of the contributors to this thread.
We do have to keep our cool when discussing hot matter.
I do want to add one bit from memory. Of course, the optical signal was not seen until that fellow in South America decided to look through his telescope.
The difference in times for the neutrino burst and the emission of photons depends on theoretical extrapolations of the light curve from the supernova, and so is speculative.

Astrophysics, abstract
astro-ph/9711196
From: Georg Raffelt [view email]
Date: Tue, 18 Nov 1997 13:17:08 GMT (59kb)

Photon Dispersion in a Supernova Core
Authors: A.Kopf (MPA Garching), G.Raffelt (MPP Munich)
Comments: 8 pages, REVTEX, 7 postscript figures included
Report-no: MPI-PTh/97-73
Journal-ref: Phys.Rev. D57 (1998) 3235-3241

While the photon forward-scattering amplitude on free magnetic dipoles (e.g. free neutrons) vanishes, the nucleon magnetic moments still contribute significantly to the photon dispersion relation in a supernova (SN) core where the nucleon spins are not free due to their interaction. We study the frequency dependence of the relevant spin susceptibility in a toy model with only neutrons which interact by one-pion exchange. Our approach amounts to calculating the photon absorption rate from the inverse bremsstrahlung process gamma n n --> n n, and then deriving the refractive index n_refr with the help of the Kramers-Kronig relation. In the static limit (omega --> 0) the dispersion relation is governed by the Pauli susceptibility chi_Pauli so that (n_refr)^2-1 approx chi_Pauli > 0. For omega somewhat above the neutron spin-relaxation rate Gamma_sigma we find (n_refr)^2-1< 0, and for omega >> Gamma_sigma the photon dispersion relation acquires the form omega^2-k^2=(m_gamma)^2. An exact expression for the "transverse photon mass" m_gamma is given in terms of the f-sum of the neutron spin autocorrelation function; an estimate is (m_gamma)^2 approx chi_Pauli T Gamma_sigma. The dominant contribution to n_refr$ in a SN core remains the electron plasma frequency so that the Cherenkov processes gamma nu <--> nu remain forbidden for all photon frequencies.

 

[DrChinese]

The fact that neutrinos arrive before photons - after a supernova - is one of the things that clearly demonstrates the existence of neutrinos (in case you had any doubt).

As mentioned above: neutrinos created in a star will see the star as essentially transparent. To a photon created within a star, the star is essentially opaque. The speed of a neutrino through a star far exceeds the speed of light within a star. (Analogy: the speed of light in a vacuum exceeds the speed of light within water.) When the supernova occurs, the neutrinos leave the star before the main photon burst starts because the photons are being scattered. So the neutrinos arrive earlier, which is an experimental fact.

The speed of light in a vacuum of course is equal to the speed of a neutrino in a vacuum.

 

[Creator]

Neutrinos get out of the supernova faster than light, because the photons react more strongly with the matter in the supernova. That is the simple explanation.
The details get more complicated and speculative.

I thought you were going to bring up the nature of the neutrino measurement which also adds to the speculation.


It is a not-so-commonly realized fact that it is NOT the neutrino mass that is measured experimentally; rather, it is the mass squared term that is measured, and it is turns out almost always to be negative; in other words, negative mass squared, This negative mass squared can be referred to as 'imaginary' and thus can be used to imply superluminal velocity. Thus the supernova 1987A neutrino-preceeding-photon observation can equally be regarded as evidence to support superluminal neutrinos.

http://arxiv.org/PS_cache/hep-ph/pdf/9712/9712265.pdf

Just thought you guys ought to know.

Creator

--Give me ambiguity or give me something else.--

 

[Nereid]

Anyway, fun fact about supernovae: most of the EM radiation we see is from radioactive decay of nickel-56 and cobalt-56.

Where could we find out more on this topic, SpaceTiger?

Also, what's the main source of light for Type Ia SN?

 

[SpaceTiger]

Where could we find out more on this topic, SpaceTiger?

Well, this seems to be a decent site on all such things, but is fairly simplistic. For more details, you could look http://www.nd.edu/~kkrisciu/supernovae.html .

Keep in mind that what I know is from colloquia, conversations, and the sum of many textbooks, so I'm not particularly well-versed in quality internet resources for this kind of information. If anyone has some better suggestions, please jump in. The above both look respectable, however.

Also, what's the main source of light for Type Ia SN?

Same deal, most of the light comes from radioactive decay.

 

[Creator]

I thought you were going to bring up the nature of the neutrino measurement which also adds to the speculation.


It is a not-so-commonly realized fact that it is NOT the neutrino mass that is measured experimentally; rather, it is the mass squared term that is measured, and it is turns out almost always to be negative; in other words, negative mass squared, This negative mass squared can be referred to as 'imaginary' and thus can be used to imply superluminal velocity. Thus the supernova 1987A neutrino-preceeding-photon observation can equally be regarded as evidence to support superluminal neutrinos.

http://arxiv.org/PS_cache/hep-ph/pdf/9712/9712265.pdf

Just thought you guys ought to know.

Creator

--Give me ambiguity or give me something else.--

Oh yea, and here's another article by Craemer along the same line as my previous post. I always liked his 'alternate view'.
It's a bit less technical for those needing simplicity. :uhh:

http://www.npl.washington.edu/AV/altvw93.html

Creator

 

[ADeAngelis]

Smells bad, and inconsistent with SN1987A…
There had been a delay of ~3h between the neutrinos and the gammas in SN1987A (it had been explained by astrophysical reasons, though). If one however interprets it as physical, takes the distance of the SN (168000 ly) and rescales it to the distance between CERN and Gran Sasso, one would expect at GS a delay of

Dt ~ 10000 s * (700e3/(168000*3e7*3e8)) ~ 5 ps

which is 1 millimeter… It is true that the SN neutrinos where in the MeV, but it looks strange that something dramatic happens between the MeV and the GeV…

Alessandro De Angelis

PS – People had claimed and then withdrawn, in the case of the SN1987A, a neutrino detection 1 day before – and also speculated about neutrinos being tachions; this would make however 50 ps, still not enough…

 

[gvk]

Do you mean this
http://arxiv.org/ftp/arxiv/papers/1109/1109.4897.pdf?

 

[gvk]

DrChinese
"The speed of light in a vacuum of course is equal to the speed of a neutrino in a vacuum."

Today in 2011, not all physicists think so (the above is article from Gran Sasso National Laboratory which just appeared in ArXiv.org).

This is a serious attempt to crash our fundamental basis. My impression, there is some experimental miss-interpretation, but how big team of good physicists in respectable Lab can make such conclusion, this is out of my mind.

 

[jtbell]

DrChinese
"The speed of light in a vacuum of course is equal to the speed of a neutrino in a vacuum."

Today in 2011, not all physicists think so (the above is article from Gran Sasso National Laboratory which just appeared in ArXiv.org).

Note the date on Dr. Chinese's post.

Please confine further discussion of the OPERA results to the existing thread:

https://www.physicsforums.com/showthread.php?t=532620