Particles recorded moving faster than light

[K. A. Pital]

My, my! Bob and Alice come alive. iAnsible - changes everything. Again. *laughs*

That is so cool. I suspect that this could be significant. I think that sooner or later we'll have to develop a yet more refined theory.

[Molyneux]

My, my! Bob and Alice come alive. iAnsible - changes everything. Again. *laughs*

That is so cool. I suspect that this could be significant. I think that sooner or later we'll have to develop a yet more refined theory.

If it's true, then it definitely will be a shakeup...it really is an effort not to get my hopes up too high, though.

[PeZook]

Isn't media screaming about "overturning relativity" sensationalistic claptrap? There's a huge body of experiments and practical applications that confirm many predictions of relativity ; These won't go away. So we'll need a new, yet more refined theory to explain this, but just like with newtonian physics, relativity will continue to be used where these more precise predictions are not necessary.

[Simon_Jester]

Oh, absolutely. But if there turns out to be an FTL particle, especially one as mundane and 'boringly normal' as the neutrino*, then some of the really significant findings of relativity do get overturned. For one, we may have to rethink the way we treat causality; for another, there may be some pretty significant physics lurking in the background there that we just haven't seen yet- another theory with significance for how we understand the world that's on the same scale as relativity when it comes to its power to tell us things we didn't already know.

*Which is fairly well understood, or so we think
____________

The flip side of this- one way to cross-check this would be to check neutrino telescopes. We do have instruments for spotting bursts of cosmic-ray neutrinos, and if neutrinos can gain 60 nanoseconds on photons while traveling 700 kilometers, then over interstellar distances they might pull ahead by hours or days.

I'm not sure what the state of the field in neutrino observations is, or at least how good they are at that kind of cross-check. But I'm pretty sure we'd have noticed that, so if the results on Earth do turn out to include FTL neutrinos, someone's got some really hardcore explaining to do there- why wouldn't we see this FTL neutrino phenomenon over much longer interstellar distances?

[Surlethe]

One answer is that models of neutrino generation are wrong. For example, the neutrinos from SN1987A arrived (IIRC) a few hours before the light from the blast. If neutrinos were even traveling at 1.01c, they'd have arrived much earlier. Of course, if models of neutrino generation in stellar collapses are wrong, they might be generated well after the core collapse begins.

[Grog]

Sorry being stupid

[Hillary]

A question from a non-scientist. I thought that quantum physics largely didn't conform to Einstein's theories anyway - so why is this further example of such behaviour be of any greater significance?

[HMS Conqueror]

FTL neutrinos (and tachyonic behaviour generally) are already predicted by some quantum field theories. What effect they have on causality is not agreed, although physicists do cling quite hard to causality, more than pretty much anything else. And there aren't actually many other issues here. Spec. rel. does not, contrary to popular belief, state that nothing can move faster than the speed of light. It effectively states that it is impossible to accelerate a slower than light massive object to the speed of light or above (it would require an infinite amount of energy) - but if it starts off at that speed, there's no reason it can't stay there.

A question from a non-scientist. I thought that quantum physics largely didn't conform to Einstein's theories anyway - so why is this further example of such behaviour be of any greater significance?

QM has been reconciled with Spec. Rel., more or less. That is what Quantum Field Theory - the basis of all current understanding of particle physics - essentially is. General relativity, there is no clear unification. But remember that the problem is that any new theory must reproduce all the correct predictions of QM and Gen. Rel. - one can't be overturned, since in a certain range of validity, they are both firmly established experimentally.

[starslayer]

One answer is that models of neutrino generation are wrong. For example, the neutrinos from SN1987A arrived (IIRC) a few hours before the light from the blast. If neutrinos were even traveling at 1.01c, they'd have arrived much earlier. Of course, if models of neutrino generation in stellar collapses are wrong, they might be generated well after the core collapse begins.

There's an easy explanation for this actually; the neutrinos are all generated basically at the moment core collapse begins. It only takes a couple of seconds for the core to fall in on itself and compress into a hot proto-neutron star, but the shockwave takes much longer to tear the star apart. In fact, it stalls out at first- the initial rebound is not enough to blow the star apart. The big puzzle in supernova research is how and why the shockwave gets started again and blows up the star. The X-ray flash indicating the star has exploded doesn't become visible until much later than the neutrinos have all gotten away.

By the way, HMS Conqueror, I wouldn't say QM has been reconciled with SR "more or less." QFT is the unification of QM and SR.

[HMS Conqueror]

Despite the fact that it has been very successful in most respects, QFT has some incongruities (renormalisation, etc.). It's also not agreed which field theory describes the world, with, for instance, some predicting tachyonic neutrinos and others not. But for the purposes of this discussion, yes, QFT makes QM compatible with SR.

[K. A. Pital]

What if Lorenz symmetry falls apart at some threshold? I read about it, but I don't really understand the implications if it really happens. Some of the members more well-versed in physics could explain this?

[Beowulf]

Oh, absolutely. But if there turns out to be an FTL particle, especially one as mundane and 'boringly normal' as the neutrino*, then some of the really significant findings of relativity do get overturned. For one, we may have to rethink the way we treat causality; for another, there may be some pretty significant physics lurking in the background there that we just haven't seen yet- another theory with significance for how we understand the world that's on the same scale as relativity when it comes to its power to tell us things we didn't already know.

*Which is fairly well understood, or so we think
____________

The flip side of this- one way to cross-check this would be to check neutrino telescopes. We do have instruments for spotting bursts of cosmic-ray neutrinos, and if neutrinos can gain 60 nanoseconds on photons while traveling 700 kilometers, then over interstellar distances they might pull ahead by hours or days.

I'm not sure what the state of the field in neutrino observations is, or at least how good they are at that kind of cross-check. But I'm pretty sure we'd have noticed that, so if the results on Earth do turn out to include FTL neutrinos, someone's got some really hardcore explaining to do there- why wouldn't we see this FTL neutrino phenomenon over much longer interstellar distances?

A possibly not crazy possibility: neutrinos have a complex rest mass, and as they oscillate to the other flavors, they change speeds. At least one flavor is FTL, and at least one is STL, so that when you average it out over interstellar timescales, they end up barely STL, or lightspeed, and so the supernova neutrino problem... isn't.

[starslayer]

At department coffee today, our particle astrophysics guy talked about the OPERA results. According to him, there's really no understanding of where this result will lead if it holds up. He said that based on previous happenings in neutrino physics, this result probably will go away, as most of us expect. There's no complete consistent model of neutrino properties yet; some models have neutrino speeds increasing with energy (what one would naively expect), some have no velocity dependence on energy, and some have neutrino velocities decreasing with energy. There's variation in all of those, too, so some models have neutrino velocity depending strongly on energy, and some not so much, etc. If this result had instead been a 60 ns delay, it would have implied a neutrino mass of 100 MeV! For comparison, most other experiments have constrained neutrino masses to an eV or less, and it is consistent with previous experiments for at least one flavor of neutrino to have zero mass.

The neutrino energy during the OPERA experiment was a few GeV, and the 1987A neutrinos were at 10's of MeV, he said. The 1987A neutrinos were also basically coincident with the initial photons from the supernova according to him, so the speed difference from that data point is miniscule. However, no one has any real clue how neutrino speed might depend on flavor. Hence the comment that the community hasn't the foggiest where this result will lead if it holds up.

The OPERA group also did their analysis in an interesting way. Instead of looking at their data and analyzing it one step at a time, they completely developed their analysis script before ever even seeing the data, essentially doing a "blind" analysis. They did this by simulating the outcome of their timing experiment using the Monte Carlo method (essentially, they made a bunch of random simulations of the outcome), and developing their analysis code based on those "results." They wanted to avoid massaging their data until they got an expected result or something like that, which I think they succeeded in doing.

Edited to correct an inaccuracy.

[Chirios]

Oh, absolutely. But if there turns out to be an FTL particle, especially one as mundane and 'boringly normal' as the neutrino*, then some of the really significant findings of relativity do get overturned.

Are you sure about that? I mean, let's ignore for the moment that there's a huge chance that there's either something wrong with the way that they measured the time, or with the equipment itself, aren't there multiple ways that the neutrino's would be able to "appear" faster than light without travelling faster than light locally?

FTL neutrinos (and tachyonic behaviour generally) are already predicted by some quantum field theories. What effect they have on causality is not agreed, although physicists do cling quite hard to causality, more than pretty much anything else.

Probably cause if you get rid of causality you get rid of physics... and most of science besides.

[starslayer]

aren't there multiple ways that the neutrino's would be able to "appear" faster than light without travelling faster than light locally?

Not in this case. Here they directly measured the time the neutrinos took to cover the distance. Apparent superluminal motion in stuff like astrophysical jets is an optical illusion arising from relativistic beaming; however, if you were to have two stations in the jet itself directly measure the time it takes for a given particle to move between them in the jet, they would record an STL time.

[Surlethe]

Probably cause if you get rid of causality you get rid of physics... and most of science besides.

Why?

[Napoleon the Clown]

Because every time a theory is proven to be incorrect it completely destroys everything we know about physics. Remember that time they showed that the sea-level gravity on Earth is not exactly 1 g and all gravity on Earth disappeared?

Okay, enough being a sarcastic ass to Chirios.

If this turns out to be a true case of particles exceeding c it will mean causality is wrong. That is not to say that everything it says is completely and totally incorrect. Scientifically speaking, if a theory has even one part of it proven to be incorrect the entire theory is considered to be wrong, much like a true or false question. That is not to say that specific portions of it are not correct. Just that we need to take into account the new information and formulate a theory that more precisely expresses the concepts and ideas behind it.

A neutrino moving faster than light just means that there are objects with rest mass that are capable of surpassing the speed of light. It does not automatically mean that any object with mass can exceed c. Neutrinos behave in a way that the matter people are familiar with does not. Those on the forum better versed in physics, especially the fields dealing with neutrinos, are going to be more able to even formulate proper hypotheses on the matter than I can. My understanding is above layman understanding but is far from the understanding one would achieve by obtaining a degree.

[HMS Conqueror]

I'm sure if there is no more causality people will still assume it when deciding whether to wake up in the morning, but it does rather pull the rug from under the whole project of trying to rationally understand the universe. I would probably bet against causality violation, even if these neutrinos really are FTL, but it's still genuinely concerning.

[starslayer]

but it does rather pull the rug from under the whole project of trying to rationally understand the universe.

Why? And if these neutrinos are FTL, it is a causality violation according to some frame, which is all it takes for causality to be violated.

[Surlethe]

I'm sure if there is no more causality ... it does rather pull the rug from under the whole project of trying to rationally understand the universe.

Why? You're just restating Chirios' point without explaining.

[HMS Conqueror]

If effect doesn't necessarily follow cause, the entire predictive nature of the scientific method ceases to function. It also would seem to imply the possibility of paradoxes. If you still don't understand why it should be a big deal, the wikipedia page should be your next port of call.

[Surlethe]

Again, you restate the claim, except substituting the definition of "causality." Be careful of amphiboly on "follow."

[D.Turtle]

To go a bit further as to why the following is not true:

If effect doesn't necessarily follow cause, the entire predictive nature of the scientific method ceases to function. It also would seem to imply the possibility of paradoxes. If you still don't understand why it should be a big deal, the wikipedia page should be your next port of call.

Uncountable numbers of "experiments" are done every single second that support our current understanding of causality (and physics). Now, it is possible that this understanding is untrue or inaccurate in very, very specific cases. However, the over all effect will still (have to) be that the vast majority of all "experiments" act like our current understanding of causality, etc expects them to. After all, if this wouldn't be the case, we would have found lots of things acting counter to our current understanding of physics.

As an example: Newtonian physics is close enough as to be very accurate for the vast majority of happenings in our "normal" world. There are fringe cases where Newtonian physics break down and deliver obviously untrue results. This is where relativity and quantum mechanics jumps in. However, relativity and quantum mechanics still has to deliver results that jive with what Newtonian physics predicts in the vast majority of the "normal" world - as those measurements were made for a long, long time and held true. Simply because we discover they don't apply in other specific cases, does not mean that Newtonian physics suddenly delivers completely wrong results in the "normal" world.

[Pinjar]

Unfortunately I am another layman. I don't really have a clue what is going on but would like to understand.

The speed of light in a vacuum has been mentioned and my first thought was why do we assume that we know what the speed of light is? Has the speed of light ever been determined from first principles? Or has it only been measured?

I have read a number of popular science books that describe even empty space as a frothing quantum sea. Are they hopelessly out of date with current thinking?

It seems to me that if neutrinos don't interact all that much with other things that they would get from A to B faster than a beam of light would progress from A to B even though the beams photons were moving faster than the neutrinos.

Though I suppose from the photons perspective they only exist when they interact with something else and the neutrinos exist all the time so could a beam of light even propagate in a true vacuum?

Totally off base? I suppose they have already though of all this and I am hopelessly behind the times or have completely misunderstood.

[starslayer]

In order:

1. The speed of light has been measured to very high precision, and is in fact how we now define the length of a meter. If you doubt this measurement at all, you can get an approximate result using a chocolate bar and a microwave oven.* It has never been determined from first principles, at least not in terms of things that are not themselves measured fundamental constants.

2. No they are not. The quantum foam is a relatively recent idea from the last 20-30 years, as I recall.

3. Through matter, yes. You are correct in that since photons readily interact with atoms, in most matter they quickly interact with one and are absorbed or scattered. Thus, a wavefront of photons moves more slowly through matter than a similar one of neutrinos, and both move more slowly through matter than they would through a vacuum. However, in between interactions, the individual photons which make up the wavefront are moving at c, their speed in a pure vacuum. This is because the space between atoms is just as empty as that in a pure vacuum - it's just that in a solid, for example, there's a lot more stuff taking up some of that space.

4. Yes, light can propagate through a true vacuum. As I noted above, it does so all the time, since the space between atoms in bulk matter basically is a true vacuum anyway. Whether they "experience" the passage of time is not clear, since the equations all diverge as you get close to the speed of light for things with mass. From our perspective, which is really what matters in this case, the photons exist when they exist (sounds tautological, I know, but I'm having trouble coming up with some good wording for this), not just when they hit something.

*To measure the speed of light using a microwave, remove the turntable and put the chocolate bar in the middle of it, aligned parallel to the back of the oven. Open the door and turn the microwave on for, say, 30 seconds or so. You may have to experiment to find the right amount of time. What you want is for some portions of the chocolate bar to melt (there should basically be even stripes of semi-melted chocolate if you've done this correctly). Measure the distance between the middle of one melted band and the next one over; this is the wavelength of the microwaves. Now read the frequency off the back of the microwave and multiply those two numbers together, since from wave mechanics, the speed of any wave is just wavelength*frequency. You should get about 300 billion cm/s, which is the speed of the microwaves. Since microwaves are a form of light, and air has an index of refraction very close to one (i.e., from light's perspective is actually close to a vacuum), you have just measured c.