THE SPEED OF LIGHT CAN BE EXCEEDED! Fuckn' hell!

[mistermack]

The other question I haven't seen answered is, do neutrinos ALWAYS travel at the speed of light, ( or slightly faster ) or have they been observed travelling slower?

'Kin ELL' !!!

Most neutrinos passing through the Earth emanate from the Sun. About 65 billion (6.5×1010) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.[3]

I didn't think there were so many of the little buggers.

Fortunately for anyone that lives on the Earth, the vast majority of them pass straight through the planet and out the other side without interracting with anything in it. They're like ghost particles.

Aha, but CAN WE LIVE WITHOUT THEM? That would be a bugger, if we couldn't.
They may do something we don't know about.

To answer my own question, having read down a bit, they do always travel at or around c, never measurably less. In fact, according to wiki, their speed was measured at 1.000051(29) c before this announcement, but that was inside the margin of error, and not recognised as significant.

[Warren Dew]

If the speed discrepancy was bigger, I'd be a lot more excited.
But why would tachyons only move so close to the speed of light. Why not double, or treble the speed?

Tachyons move closer to the speed of light, which is to say slower, the larger their energy relative to their rest mass. These were high energy muon neutrinos. If the neutrinos are tachyons, we just need to figure out how to generate lower energy neutrinos to see them go faster.

Of course, that's not the only possible explanation. Possibly it's the higgs boson that is a tachyon, and not the neutrino, in which case perhaps there's a transformation into a higgs boson within the 18m thick, high density hadron stop, which might stabilize a tachyon if you believe in tachyon condensation in a vacuum. A high energy for a muon neutrino is probably a low energy for a higgs boson, so the stabilized tachyonic higgs boson would travel through the tachyon stop much faster than light - which would neatly account for the 60 ns, assuming the neutrinos themselves travelled at "only" the speed of light.

This is all assuming some form of the tachyon explanation is correct, of course.

[mistermack]

It's actually at odds with what Wikipedia says. The lower-energy neutrinos from Supernovae arrive on Earth at almost exactly the same time as photons, when they should arrive years earlier if they were low-energy Tachyons :

For instance, photons and neutrinos from SN 1987A were observed to have an agreement in transit time to about 1 part in 450 million, with even this difference being accounted for by light being impeded by the material of the star early in its journey. The OPERA results, in contrast, suggested that neutrinos were traveling faster than light by a factor of 1 in 40,000,[nb 4] i.e. that neutrino speed is 1.0000248(28) c. Had neutrinos from SN 1987A traveled faster than light by this factor, they would have arrived at Earth several years before the photons; this was not observed to be the case.[nb 5][34] However, neutrinos from the supernova had orders of magnitude less energy than the neutrinos observed in the OPERA experiment, as the authors point out.

Of course, they weren't saying that the neutrinos might be Tachyons. The evidence of the Supernovae does seem to point in the opposite direction.

[Warren Dew]

That wikipedia article doesn't take into account the difference between electron neutrinos and muon neutrinos.

[mistermack]

That wikipedia article doesn't take into account the difference between electron neutrinos and muon neutrinos.

No, not in the bit that I quoted. It's a bit unclear on the subject.
It says this earlier on the page :

There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. Each type also has a corresponding antiparticle, called an antineutrino. Electron neutrinos (or antineutrinos) result when protons decay, through beta decay, to neutrons, or vice versa. Interactions involving neutrinos are mediated by the weak interaction.

Obviously nobody knows if they are Tachyons or not, but the neutrinos from the Supernova were undoubtably travelling AT the speed of light. They arrived only hours before the photons, and even that difference was expected :

Neutrino emissions

Approximately three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is due to the neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface). At 7:35 a.m. Universal time, Kamiokande II detected 11 antineutrinos, IMB 8 antineutrinos and Baksan 5 antineutrinos, in a burst lasting less than 13 seconds. Approximately three hours earlier, the Mont Blanc liquid scintillator detected a five-neutrino burst, but this is generally not believed to be associated with SN 1987A.[6]

Although the actual neutrino count was only 24, it was a significant rise from the previously-observed background level. This was the first time neutrinos emitted from a supernova had been observed directly, which marked the beginning of neutrino astronomy. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in neutrinos. The observations are also consistent with the models' estimates of a total neutrino count of 1058 with a total energy of 1046 joules.[8]

The neutrino measurements allowed upper bounds on neutrino mass and charge, as well as the number of flavors of neutrinos and other properties. [6] For example, the data shows that within 5% confidence, the rest mass of the electron neutrino is at most 16 eV. The data suggests that the total number of neutrino flavors is at most 8 but other observations and experiments give tighter estimates. Many of these results have since been confirmed or tightened by other neutrino experiments such as more careful analysis of solar neutrinos and atmospheric neutrinos as well as experiments with artificial neutrino sources.

So there can't be any real doubt that THOSE neutrinos travelled at exactly c.

[Warren Dew]

So there can't be any real doubt that THOSE neutrinos travelled at exactly c.

I think actually most physicists doubt that those neutrinos travelled at exactly c - the most common opinion seems to be that neutrinos travel at a microscopically tiny amount slower than c, as required if they have rest mass. They could travel at an equally tiny amount faster than c and we still wouldn't know it. It is true that they travelled much closer to c than the OPERA measurement.

[JimC]

So there can't be any real doubt that THOSE neutrinos travelled at exactly c.

I think actually most physicists doubt that those neutrinos travelled at exactly c - the most common opinion seems to be that neutrinos travel at a microscopically tiny amount slower than c, as required if they have rest mass. They could travel at an equally tiny amount faster than c and we still wouldn't know it. It is true that they travelled much closer to c than the OPERA measurement.

And that is the critical point, I think. It is still a fair bet that the OPERA results will turn out to be the result of a tiny error somewhere along the line...

If not, then neutrinos have very different behaviours depending on their energies...

[mistermack]

So there can't be any real doubt that THOSE neutrinos travelled at exactly c.

I think actually most physicists doubt that those neutrinos travelled at exactly c - the most common opinion seems to be that neutrinos travel at a microscopically tiny amount slower than c, as required if they have rest mass. They could travel at an equally tiny amount faster than c and we still wouldn't know it. It is true that they travelled much closer to c than the OPERA measurement.

Yes, the word "exactly" is not really appropriate I suppose. I meant that the difference was unmeasurable and undetectable, even over the distance of 168,000 light years. Even the words "microscopically tiny" don't do justice to the amount of difference.

In comparison to a difference that apparently CAN be detected and measured in a short distance here on Earth.

The difference between the two results is gigantic, and I think it really would have fundamental implications for relativity and causality.

That's why Jim Al-Khalili was promising to eat his shorts live on TV if it turned out that the results were correct.

It's funny how on the day of the announcement, it was the biggest thing in physics for 100 years, and yet a few days later, it's faded away in the news entirely.

Re the point you made about the difference between electron and muon neutrinos, would they not be oscillating between the two, en route from a supernova?
And if they can oscillate, I wouldn't have thought that the different flavours could have different speeds, without some sort of energy input/release?

[Warren Dew]

Re the point you made about the difference between electron and muon neutrinos, would they not be oscillating between the two, en route from a supernova?

As best I can tell, neutrinos oscillate in vacuum only until the eigenstates - basically the neutrino flavors - decohere. That would happen soon after leaving the supernova, so there would be no oscillation for the vast majority of the trip from a supernova to earth. If the different flavors of neutrino from supernova 1987a traveled at different superluminal speeds, they would have hit the earth in bursts possibly years apart. Unfortunately, we likely wouldn't have been able to observe any earlier bursts that might have occurred.

And if they can oscillate, I wouldn't have thought that the different flavours could have different speeds, without some sort of energy input/release?

I think that's where decoherence comes into play, although I'm not sure. The oscillation comes about because of differences in rest mass, so with the same total energy, the different flavors should travel at different speeds even if the masses are positive and the neutrinos subluminal.

[mistermack]

I suppose this is what they mean when they say that this supernova was the start of neutrino astronomy.

If the neutrinos arrive at the same time as the light, it's easy to associate the two, but if there is a significant gap, you would have to be able to pinpoint the source very accurately to confidently say that the light and neutrinos came from the same event.
I don't know if it's possible to accurately detect where the neutrinos come from.
If they don't respond to mirrors and lenses as light does, I don't see how you can focus your detector on any part of the sky.
I suppose that before this result from the Cern/Italy experiment, it was assumed that the neutrinos would always arrive WITH the light, but now they are maybe beginning to think again.

They might be looking back at earlier neutrino bursts and trying to find ways to tie them in to sn1987 a.
I can't imagine a technique for doing that though.

[Xamonas Chegwé]

OK - idle thought experiment on neutrinos No. 376

Feel free to shoot me down in flames but i think this might just fly...



What if neutrinos are not affected by gravity? Could that explain the anomalous measurements? As far as I can find, there is no real evidence that they are affected by gravity - it is just sort of assumed that they are because... well.. everything else is! I mean, if light, which is massless, is affected by the presence of matter, surely neutrinos, which may have a little bit of mass, perhaps, MUST be influenced by gravity too, right?

Let's look at what it would mean if they were not. It would mean that all of general relativity would not apply to neutrinos: no curvature of space by massive bodies, no slowing of time close to a gravity well, etc. This would make neutrinos appear to be exceeding c when their speed was measured close to a massive object - like the Earth, for example, because, for them, time would be moving faster and they would not need to travel in a curved trajectory to allow for GR!

This would also explain the fact that neutrino bursts from supernovas do not arrive years before the light does. Simply put, once the particles (both photons and neutrinos) have left the vicinity of the nova, both are travelling through clear space with negligible gravitational influence - hence their observed speeds are both c, near as damn it. A slight lag in the arrival of light from novas has been observed and has been put down to the light being slowed by having to pass through a matter-rich soup close to the nova - matter which the majority of neutrinos would simply slip through - thus light gets off to a slow start. but, another explanation for this phenomenon is that light is initially slowed by the intense gravitational field of the neutron star formed during the nova, whereas neutrinos, not being subject to gravity, just whizz along as normal.



Like I said, this is just a thought experiment. Perhaps the influence of gravity on neutrinos has already been proven. Perhaps the differences in time and curvature would not account for the speeds measured. Perhaps I drink too much! But I would be interested to hear what others think about this.

[JimC]

I don't think light is slowed as it moves directly out of a gravitational well - it still travels at c, but is redshifted...

However, the business of following the curve of a space-time geodesic as you pass laterally by a strong gravitational field may be a different matter...

I actually liked your earlier idea more - that neutrinos, unaffected by the chaotic particle soup that pops in and out of a vacuum due to quantum fluctuations, travel at "true c" in space, whereas light has its speed reduced to fractionally under "true c" by an effect akin to (but very tiny) the changes it experiences going through glass etc.

[Xamonas Chegwé]

I don't think light is slowed as it moves directly out of a gravitational well - it still travels at c, but is redshifted...

Time is slowed in a gravity well - which affects velocity. That is why satellite clocks have to be fine-tuned to keep in synch with clocks on Earth, which run slightly slower.

The speed of light in a gravity well (and in a vacuum) is measured at c by an observer within the well. However, for an observer outside of that well, light will be observed slowing as it passes through it due to the local slowing of time. See this article on Shapiro Time Delay.

If neutrinos somehow manage to be unaffected by gravity, this effect would be negated and they could appear to travel faster than c within a gravity well! However, whether the measured speed of the OPERA neutrinos is in keeping with this effect would be interesting to know.


And I quite like both theories. They are quite possibly both a pile of bollocks but, as thought exercises alone, they were fun.

[Warren Dew]

The speed of light in a gravity well (and in a vacuum) is measured at c by an observer within the well. However, for an observer outside of that well, light will be observed slowing as it passes through it due to the local slowing of time. See this article on Shapiro Time Delay.

The section on neutrinos in that article says they are affected the same way light is.

[Xamonas Chegwé]

The speed of light in a gravity well (and in a vacuum) is measured at c by an observer within the well. However, for an observer outside of that well, light will be observed slowing as it passes through it due to the local slowing of time. See this article on Shapiro Time Delay.

The section on neutrinos in that article says they are affected the same way light is.

It does - but without much corroboration. It just says that the observed results are within 10% of what would be expected - not the most accurate example of observation matching prediction!

It also says that this is consistent with recent estimates of neutrino mass - again, something that has yet to be verified and could skew results.

I am not arguing that I am right as much as I am arguing that ruling out any not-completely-batshit theory is a little premature at this stage (because the idea of something being able to ignore gravity is just about as bonkers as something travelling faster than c but that appears to have been observed - so all bets are off!)