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Comment by lwat | Hacker News Reader

So we're left with what, GPS errors? I've gone through their experimental setup and the timing looks foolproof. The only options left in my mind are

1) The distance between the labs is smaller than they think

2) Tachyonic neutrinos (not likely)

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2) Tachyonic neutrinos (not likely)

Another possibility that occurred to me (which is probably way off, and has likely already been trivially disproven by some simple experiment that I'm not thinking of at the moment) is that the "speed of light" that we tend to measure is actually a bit lower than the geometrical "c" that appears in equations (I'm not sure what the state-of-the-art is on measuring that geometrical quantity directly), because for some reason photons are slowed as they move through the vacuum (similar to how we can very easily slow photons by making them move through glass, except this would have to be via interactions with the vacuum or some other form of matter). It could be that the vacuum itself has an index of refraction for photons not quite equal to 1 due to some unknown interaction.

Neutrinos interact with almost nothing, so it's conceivable that they even if they have a small amount of mass and travel slower than geometrical "c", they could still end up going faster than photons because they slip through background interactions with ease.

Again, this is wild speculation, "c" is used all over the place, and if we had the wrong value for it, that would require a lot of coincidences, that this sort of vacuum index-of-refraction effect also had the side effect of making other measurements involving the speed of light (energy measurements, for instance - I would tend to think a discrepancy would be way more obvious here, involving, as they do, factors of c^2) come out looking correct, and that seems unlikely to me.

Then again, so much of what we directly measure is grounded in e/m interactions, so there's a chance (vanishingly small, as it is) that a fifth decimal place discrepancy in photon-in-vacuum-c vs. geometrical-c could escape notice because of the relative difficulty of directly measuring geometrical-c, especially if whatever vacuum effects that slow photon travel had other side effects that dunged up our energy measurements, too.

Neil deGrasse Tyson claims that another possibility is that of a new particle moving backwards through time.

Not that I understand that.

He said it in his recent "Ask me anything" session on reddit.

Well that's exactly what will happen when anything moves faster than light, it will travel backwards in time. The real question is where is it getting infinite energy to break the light barrier? or are neutrinos the only particles with mass that will not be dragged by the Higgs field?

He said a new particle though. So something other than the neutrinos themselves, I suppose?

It was a neutrino that was discovered moving faster than light at CERN, that is what I was referring to. Tyson also mentioned that it is likely a special type of neutrino already moving faster than light is the one being observed (tachyons). What they think we are seeing is a particle that has been moving faster than light but never accelerated to reach that speed, it has been moving at that velocity all the way since before the beginning of time itself.

A particle moving backwards through time === a particle moving faster than what we have currently established to be the speed of light

My understanding is that it isn't necessarily moving faster but is cheating by moving through a dimension that we can't even draw.

Feynman had particles moving backwards through time as an explanation for something. I'm not sure if he was being totally serious, or using it as an idea to move theory forward.

Anti-particles.

My knowledge of physics is only very basic but it's still fun to ponder these things. Do they need to factor in that the endpoints are rotating with the earth and the neutrinos are not?

At their latitude (~45 deg), the distance the earth travels in the 2ms it takes light to travel the distance is around 76cm (someone check my calc if you will).

They know the distance to within +-20cm, so the 76cm of Earth's rotation would be very significant (but not significant enough, again with my rough calculations, to bring these results back in line with c).

The distance is significant enough that to get an accurate measure of c over that distance you would have to take it into account. ie. it would be obvious

Since the rotation of the earth has to be factored in, does the earth's orbit around the sun need to be as well? How about the suns orbit around the Galactic center?

I suppose my question is - all things being relative, why aren't the neutrinos bound to the same frame as the emitter and detector?

You're thinking of the wrong kind of relativity. The neutrinos aren't "bound" to any frame. They just move from A to B. The (apparent) distance between A and B changes depending on the observer's frame of reference, as does the (apparent) time it takes them to get from A to B. The faster the observer goes, the shorter the apparent distance (Lorentz contraction) and the smaller the apparent time (time dilation) become. But the RATIO of the apparent distance from A to B to the apparent time it takes light to travel from A to B remains constant. So if the neutrinos are moving faster than light, they will appear to do so as measured from any frame of reference as long as you're consistent about using the same frame to measure time and distance. THAT is where it gets tricky because the GPS satellites that they use to establish both time and distance are all moving in different frames. You also have to take gravity into account because the emitter and detector are non-intertial frames.

Thanks for taking the time to answer! You have helped me understand a few things better. However I also realise now that I phrased my question wrongly and should never have used the word "bound".

I also see now that I misread the grand-parent post. Of course these motions would not affect the measurements, and if they did, the rotation of the earth alone would be obvious.

By "frame of reference", I know you meant "inertial frame of reference", but of course the Earth moving around the sun and the solar system moving in the galaxy are not inertial. My weight is a bit stronger during the day than during the night because of the centrifugal force, isn't it?

I'm sure that the effects are tiny for the LHC, but are they accounted for at all?

> you meant "inertial frame of reference"

Actually no. The speed of light is constant in ALL frames of reference, whether inertial or not. The math just gets more complicated in non-inertial frames. (That's the difference between special and general relativity.)

UPDATE: it's actually a little more complicated than that. See http://en.wikipedia.org/wiki/Propagation_of_light_in_non-ine...

> I'm sure that the effects are tiny for the LHC

Actually, gravity is a pretty significant factor. See e.g.:

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps....

I'm pretty sure I remember that being on the list of things that were double-checked.

The sense I've gotten is that the most likely culprit is some sort of systemic error in the software somewhere, as that stuff is the most labor-intensive part of the experimental setup to analyze for errors.

While it may have been checked it doesn't seem to be mentioned in the paper http://arxiv.org/abs/1109.4897v2

I was explaining to a friend my understanding that the emitter and receiver for these neutrino experiments basically needed to be synchronized to a single, fictional (superluminal, etc.) frame of reference. I'm positive there are many factors going into how this is done.

3) Tiny stable wormhole or other anomaly under Alps (casualty saved, doubtful that it gives stable results)

4) High energy neutrinos spontaneously teleport themselves (casualty saved, new, very odd physics needed)

...

n) Subtle measurement problem (impossible to falsify until the result is replicated on independent setup)

How do either of those save causality? If you've got regular neutrinos traveling FTL, causality is broken. It doesn't matter if the particles travel FTL because they really have a measurable velocity FTL or because they somehow spontaneously teleport.

I think you mean causality.

Sure, thanks.

It's usually best to leave off the "look guys, I broke physics" until human error has been well and thoroughly ruled out.

Sure, I don't think anyone has suggested otherwise. However, the OPERA collaboration has done a heroic job checking everything they could think of. Thus the continued interest.

Physics, as I'm sure you know, has undergone many revolutions in its understanding of the world. This could be the start of a new one, or it could fizzle and be a quirky measurement error. In either case, highly worth following to see what happens.

If it's not a bit of partially-digested cheese, it might have to do with the interface between relativity and QED.

But while it's not unthinkable that relativity requires revision under some circumstances, it's one of the most thoroughly and repeatedly proven tenets of modern physics. It's going to require something much more definitive and reproducible to overturn that mountain. I wouldn't expect a positive answer to this inside ten years, but a negative answer could turn up any time since it depends on someone finds the bug in the gears.

If another lab using different equipment were to reproduce this result, that would give a positive result in less then 10 years?

That's one of the big steps which is necessary. It still leaves the questions of (a) funding, (b) how do you reproduce it and how long does that take, and (c) how do you explain it.

Many problems in science are considered to be "twenty year problems," by which we mean that they'll probably be solved eventually, but that it's unlikely to be any time soon. Many such problems go on for much longer without a solution despite significant progress (see also: fusion power plants). This isn't quite on that scope - but it could evolve into one if it actually ends up with a result which can be reproduced on command.

MINOS is already working on reproducing it (see article), and if they succeed it will be strong evidence that we're looking at something new.

I'm wondering: what do the involved scientists think might be the source of error? GPS timing (namely, the synchronization of the two remote clocks) sounds likely to me, because I was initially surprised that they could even hope to have sufficiently accurate chronography to detect such a small duration.

You should read the paper, they go through that in great detail. I'm not an expert but their clocks are being synchronized via two methods (GPS and fiber-optic connect) independently. They're pretty sure the timing is correct down to 1 nanosecond.

1) was my first thought since it was such a small time difference, but at C speeds the physical distance they would have to be off by is something like 20 meters. Off the shelf GPS units you can get for your car are accurate to around 3 meters, and the high end models are accurate to under 30 centimeters. It would have taken a major screw up for them to be off by 20 meters.

Doesn't the government add a small amount of variance to the GPS signal to limit its accuracy for non-military users? Or did they stop doing that?

They stopped that over ten years ago.

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