i take it you’ve read today’s XKCD. 
I only wish I followed such things closer, but: (A) Isn’t Einsteins work predicated on the assumption all matter has mass? And, (B), didn’t he not like the idea proposed by his contemporaries that some subatomic particles sometimes have mass and sometimes don’t? And, in work after his lifetime, haven’t such subatomic particles been theorized to exist based on results from greater and greater studies with particle accelerators? If so, isn’t it possible scientists simply seeing the behavior of a massless particle that many always believed existed from all their theortical work?
As others have mentioned, I don’t see how this affects causality. It’s not as if the neutrinos arrived before they had left. Could some kind person explain this for me?
The practical application is that the answer might be “not yet” instead of “not ever”. If c is not an absolute limit as we believed, we might be back to incremental advances. If this one was only 7.4km/s faster than c, maybe it’s possible to get it up to 7.5km/s faster than c. And if we can get 7.5km/s faster than c, maybe we can get to 7.6km/s faster. And so on.
While a very healthy dose of skepticism is of course justified, even with their six sigma claim, this would not, if I understand things at all correctly, “overturn” anything necessarily. “Tachyons” have always been a theoretical possibility within the current framework. This could merely provide some evidence that they are creating both neutrinos and tachyon-neutrinos, two populations one of which always travels below the speed of light and one that always travels above. Now that would be exciting but not “overturning.”
The webcast of the OPERA collab’s talk at CERN is live now…
If we do not have causality, we might have been buggered already, and we just don’t know it yet.
I remember reading some guy’s case a while back that the speed of light has been slowing down.
Maybe it appears that they go faster than “c” becasue they haven’t measured “c” that accurately for a while.
Not saying I have bought into such an idea, just throwing out crazy ideas like everyone else.
Let’s suppose for the sake of answering your question that the neutrinos in the OPERA experiment really did exceed c, the universal speed limit, by 7.5 km/s. In this case, covering a distance of 730 km, that would mean they arrived after they left the emitter at CERN. But, it also means they have the potential ability to arrive before they are emitted. Take a gander at this: space-time diagram. This is the standard way to plot causality in a handy graph. In such a graph, the units of distance and the units of time are equal, like 1 light-year and 1 year, so that a light ray traveling at c makes a perfectly 45 degree diagonal line. Anything going faster than c has a shallower slope.
So imagine that there’s another line on that graph, slightly shallower than the yellow light ray, connecting two points E (emitter) and D (detector). E and D have their own space-time trajectories, called world-lines. Since E and D themselves are “at rest” (they have no relative velocity) their world-lines are just vertical lines at two points in space (on the x-axis). Now here’s the twist. If I accelerate the detector D, then it experiences less time than does E. That shifts E’s spacetime coordinate forward compared to D. Suppose I accelerate D dramatically, to .99999c. Now it’s way “behind” E in relative time elapsed. And there’s still a shallow slope line connecting them, because the neutrinos still go from emitter to detector. Only now, the slope of the neutrino line is so shallow, its slope is negative. The neutrinos have arrived before they departed.
Bottom line: Even if we have FTL neutrinos in the OPERA results, they did not travel backwards in time. But according to the mechanisms and methods of Special Relativity, FTL travel opens the doorway to, or is equivalent to, breaking causality.
I hereby propose we refer to the ones traveling faster than c as Porsche neutrinos.
But they did arrive before they left — in some reference frame.
It’s a principle of relativity that if you see anything travelling faster than light, there is another reference frame in which you would see it travelling backwards in time.
Yeah, I used the causality violation created by those neutrinos to read today’s XKCD yesterday. 
Nah. Clearly the car to allude to would have to be a DeLorean.
**I mistakenly cited the difference’s margin of error rather than ****the difference itself **
**in the last sentence above. The actual number ****4.14 ± 0.97 years is pretty much exactly **
calculated in post #30 by naita, who deserves to be repeated, admiringly, in full:
Another member may also be on to something:
**Maybe one of our specialists can comment ****on the ****following paper: **
Hypothesis of Tachyonic Neutrinos
**I think naita addressed the following in his post #30, quoted above: **
If I understand this correctly neutrinos moving faster than c implies a breaking of Lorentz covariance. So if true the physics 1 observer sees would not be equivalent to another in a different frame of reference and there would be no way to transform the reference frames to make them line up.
So, if this is true, does that means there would have to be some sort of fixed background field (like Newton’s old Tinkertoy clock framework) that these particles would have to exist within?
:smack:
I sit corrected.
The problem with tachyonic neutrinos is that they should travel faster the less energy they have, meaning that the 1987A neutrinos should have appeared here even more earlier – this seems to me to rule out the idea that neutrinos may travel faster then ‘c’, where I here mean ‘the speed of a massless particle’, or ‘the speed limit of special relativity’.
As for two speeds of neutrino propagation, I’m also not certain how that could be made to work – neutrinos oscillate into one another, meaning that one kind of neutrino becomes another kind, so even if different neutrinos move at different speeds, these effects should even out.
So then there’s the idea left that neutrinos travel faster than light, because light travels slower than c, i.e. because the photon is massive; but if that were the case, then light at different energies should travel at different speeds, and there are really good bounds on that happening…
The bottom line for me then is, if this is a real effect, I can’t see any way to fit it into established physics.
I just watched the CERN seminar presenting the results. They are very serious about the result, and have done a very careful job accounting for the systematics, including multiple independent checks of their experimental timing chain by different metrology companies. The geodesy measurement was performed twice (apparently by the same team, it wasn’t made clear). That doesn’t mean they didn’t make a mistake somewhere, but if they did, it’s a subtle one. I for one am very much looking forward to future experiments to either confirm or not the result.
Maybe a silly question, but was anyone looking for neutrinos from 1987a 4 years before the light arrived on earth? We didn’t have any idea there would be a super nova until the light arrived. Could 1987a have created different types of neutrinos, some types which exceeded light speed?