Neutrino experiment affirms faster-than-light claim

http://blogs.nature.com/news/2011/11/neutrino_experiment_affirms_fa.html

by Rickasaurus • 15 years ago

253 120 15 years ago

blogs.nature.com

breadbox2• 15 years ago

To be precise, this latest experiment only ruled out one possible source of error (namely, bias in the detection of arriving neutrinos causing it to preferentially detect neutrinos at the forefront of the pulse). This doesn't affirm that the neutrinos actually exceeded light-speed.

But it is an important step towards understanding what's happening, and it's great that the OPERA group were able to put together this followup experiment so quickly.

jessriedel• 15 years ago

> This doesn't affirm that the neutrinos actually exceeded light-speed.

You might be thinking of "confirm". This certainly is an example of the OPERA group affirming their results.

> Affirm. v. 1. State as a fact; assert strongly and publicly. 2. Declare one's support for; uphold or defend.

compman775• 15 years ago

Take a look at definition 1 in your post.

sidcool• 15 years ago

Oops...I just posted this link on my Facebook account with the sensational heading "Foundations of physics shaken again". I will remove it.

espinchi• 15 years ago

Indeed, as stated by the internal communication note:

This test confirms the accuracy of OPERA's timing measurement, ruling out one potential source of systematic error. The new measurements do not change the initial conclusion. Nevertheless, the observed anomaly in the neutrinos' time of flight from CERN to Gran Sasso still needs further scrutiny and independent measurement before it can be refuted or confirmed.

lwat3• 15 years ago

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)

glimcat3• 15 years ago

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

rubidium• 15 years ago

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.

flatline• 15 years ago

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?

breadbox2• 15 years ago

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.

westbywest• 15 years ago

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.

nikcub• 15 years ago

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

baddox• 15 years ago

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.

lwat3• 15 years ago

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.

grannyg00se2• 15 years ago

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.

teamonkey• 15 years ago

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

EREFUNDO3• 15 years ago

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?

DanBC• 15 years ago

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.

Natsu• 15 years ago

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?

blackguardx• 15 years ago

They stopped that over ten years ago.

mbq2• 15 years ago

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)

bobds• 15 years ago

I think you mean causality.

dpark• 15 years ago

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.

stonemetal• 15 years ago

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.

bermanoid3• 15 years ago

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.

jarin• 15 years ago

I seriously cannot wait for the MINOS experiment :)

maeon3• 15 years ago

What is the difference between neutrinos and regular light photons? Do Neutrinos also exhibit the wave particle duality? Does this mean Albert Einstein was wrong, after all these years of assuming his "biggest blunder" was right?

fleitz• 15 years ago

Photons interact much more easily with matter. Photons are massless whereas neutrinos are believed to have mass. Also, photons mediate the electromagnetic force where as neutrinos only interact with the weak subatomic force.

neutronicus• 15 years ago

Photons are spin one, and mediate the electromagnetic interaction. They have zero mass and propagate at c.

There are actually three types of neutrino (and they spontaneously change from one type to another), they are all spin-one-half, and they interact with other matter only via the weak nuclear force, which has a much smaller effective distance than the electromagnetic force, so they don't interact very often. They have non-zero mass, but it is so small that we don't actually know what it is.

Everything in the universe exhibits the wave-particle duality.

archgoon• 15 years ago

>"biggest blunder"

Einstein's self professed "biggest blunder" was the cosmological constant. That term has never referred to the assumption of lorentz invariance.

davidjohnstone• 15 years ago

The last thing I heard about this was that the results could be explained by the researchers overlooking the relativistic motion of the GPS clocks, and when corrected for it, the results were actually another confirmation of special relativity. See http://www.technologyreview.com/blog/arxiv/27260/

That said, a brief search turned up this paper ( https://facultystaff.richmond.edu/~ebunn/vanelburg.pdf ) which argues that that explanation is faulty (i.e., the paper made a mistake, and when corrected, the original researchers' results stand).

(Disclaimer: although I once read a book on this stuff, I shouldn't be confused with an expert, and I have no idea who's right and who's wrong. But it is exciting.)

sliverstorm2• 15 years ago

I seem to remember when that theory was discussed, it was explained that GPS clocks already take into account relativistic motion. Or something like that, don't quote me, I'm not a physicist.

nobody314159262• 15 years ago

GPS onboard clock is corrected for relativity due to it's orbit height and speed so it's clock time is approximately correct

But measuring the simultaneity of an event between two different points with a moving clock is a lot trick.

Confusion• 15 years ago

I am a physicist and GPS indeed takes relativistic effects into account. GPS would not just be slightly wrong if it didn't: it would be entirely worthless. See for example [1].

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

bermanoid3• 15 years ago

That paper got some wide circulation for some reason, but it was an extremely simple criticism (six or seven equations, no derivations involving anything more substantial than distance = rate x time) by a computer scientist that simply misinterpreted the way the GPS synchronization was used (none of the physics was wrong in the paper, FWIW, the problem was that the author's claims about it having any connection to the OPERA experiment were completely unfounded).

IIRC someone from OPERA responded to questions about that paper by saying, basically, that it wasn't even worth debunking because they had real work to do, and publicly disproving every amateur with a theory would suck up all their time.

Arjuna• 15 years ago

This is an interesting paper on the topic: Determination of the CNGS Global Geodesy [1].

It discusses how the distance traveled by the neutrino beam was calculated. It covers GPS measurements, tidal effect considerations, the Sagnac effect [2], etc.

[1] PDF: http://operaweb.lngs.infn.it/Opera/publicnotes/note132.pdf

[2] http://en.wikipedia.org/wiki/Sagnac_effect

sliverstorm2• 15 years ago

I am hoping against hope...

rorrr• 15 years ago

The worst kinds of bugs are the ones that only happen in production, when you have some crazy set up with a load balancer, a CDN and/or Varnish, and a few app servers, high traffic, middle of the day, and a bunch of executives hovering. I have seen a crazy bug that happened only on one of the identical app servers. Turns out SVN export didn't perform correctly (still don't know why), and one of the files was messed up. That was not easy to find.

I have seen Apache ignore updated PHP files, and serving old code, which should never happen. This a real bitch to debug.

omarchowdhury• 15 years ago

Cool story, bro.

sfaruque• 15 years ago

I think you posted in the wrong comment thread...

EREFUNDO3• 15 years ago

Will this widen the gap between relativity and quantum mechanics? or will it actually help in finally resolving the disconnect between these two greatest and well tested theories? Particles defying general relativity is well known, but defying special relativity? I can see it going both ways.

hugh33• 15 years ago

On the offchance that it turns out to be really true, it will certainly point us in the direction of some interesting new physics, so it'll be a step in the right direction.

I'm still trying to keep my expectations down for now, though.

csomar• 15 years ago

I have very basic physic knowledge, and little time. I'm quite interested, however, to know how they synchronized their timers since the Neutrino speed is faster than light. Anyone has a short explanation or an article for that?

copper• 15 years ago

Roughly, they used gps signals to synchronize two accurate clocks, one each at the source and the destination.

For what it's worth, this part of the first paper is pretty accessible - at least, as to how they did it - it's more difficult to poke holes in how accurate it was :)

shin_lao2• 15 years ago

It's more likely they found a particle that travels back in time than a particle that goes faster than light.

moomin• 15 years ago

I think that's the same thing.

JonnieCache8• 15 years ago

Yep. Relativity says they are exactly the same thing.

ck22• 15 years ago

If quantum entanglement "pissed off" Einstein, I can only imagine his reaction to this.

loup-vaillant• 15 years ago

If I recall correctly, Einstein was pissed of by the so called "spooky action at a distance", namely non-local interaction. Note however that a many-world interpretation gets rid of that.

Now we have neutrinos that may travel faster than light. That would throw Special Relativity out the window, sure, but not the locality principle: those neutrino do not show infinite speed, unlike quantum entanglement under the Copenhagen interpretation.

ck22• 15 years ago

He was also upset that it appeared to violate relativity.

To his deathbed he believed in his alternate explanation that the particles were set opposite "at birth" and initiated that way until observation (if I understand that correctly).

So now we have at least TWO phenomena that appear to be "faster than light" - so get cracking scientists (and engineers) on a practical application for communications to probes that are light-hours or light-years away.

lobo_tuerto• 15 years ago

I wonder if us realizing speed of light isn't the cosmic limit for everything are like us again at realizing Earth isn't flat.

jgrahamc2• 15 years ago

I wrote to the lead author asking them to release the source code of the software that they used for the data analysis. I have yet to receive a reply, but it's pretty important to eliminate a programming error from this.

For example, there were small errors in the Met Office's climate change software that I detected. The scientific papers were correct, but the translation into code was not. This could have happened here and it would be better if they released the code.

http://blog.jgc.org/2010/02/something-odd-in-crutem3-station...

JonnieCache8• 15 years ago

I find it very strange that the source code is not routinely released in these circumstances. What possible reason is there for not doing so? The code and the ideas within have no direct commercial value, surely?

At the very least it should be as available as the papers themselves.

jamesrom• 15 years ago

The only advantage I can see is that when the theory, formulas and algorithms are published, not the specific implementation itself, it forces people who want to who want to verify your work to write their own implementation. It kind of makes sure that a bug in your own implementation doesn't pollute the results of those trying to verify your work.

hugh33• 15 years ago

What possible reason is there for not doing so? The code and the ideas within have no direct commercial value, surely?

Laziness, lack of time, and the fact that most scientific code is not suitable for public consumption. For instance, my code includes error messages such as "What the fuck????" and "This never happens" which I'd need to take out in order to prepare it for publication.

In addition, there's the assumption that source code is a pretty trivial implementation detail; we publish the algorithm but not the details of the implementation, just as the experimentalist tells us what he built but doesn't tell us what brand of screwdriver he used to build it.

jonhendry16• 15 years ago

Biology researchers don't get to reuse the other guy's mice, why should they reuse their code? As long as the paper describes the algorithms used, anyone should be able to duplicate the work using their own preferred implementation.

Also, a lot of the code may well be specific to the apparatus used, which may be unique to a lab, consisting of custom-built hardware.

hugh33• 15 years ago

If I were involved in this project, I'd be sitting around saying "please don't let it be my fault, please don't let it be my fault".

Somewhere, somebody screwed up... and if the problem is in my code then I want to find it and correct it myself, rather than have it found and corrected by some random stranger who emailed me, and will then post the bug all over the internet so the world can point and laugh at the exact line of my source code that sent the world on a wild goose chase for FTL neutrinos.

So I don't blame this guy for not sending you his source code.

jgrahamc2• 15 years ago

I don't blame him either. Random British guy writes to you in French and ask for your source code. Sure I'd be skeptical too (although personally I err on the side of releasing all my code).

The problem is that suppose it is a bug and suppose the code is being kept behind so they can find the bug themselves. A huge amount of time and money is wasted whereas a programmer could look at the code and compare with the paper pretty quickly.

Also in the case of high-energy physics its not exactly easy to duplicate experiments because of the eye-watering cost of the equipment.

mattheww• 15 years ago

Asking for the source code of the OPERA analysis is similar in scope to asking for the source code to gmail. Unless you made a very specific request and explained how you would be qualified to review it, I doubt they are taking you very seriously.

Furthermore, I doubt anyone at OPERA is in a position to even fulfill your request. The minimum number of separate systems with exclusive sets of code is three, and probably more than ten.

However, physicists do make extensive use of unit tests, so that may be some consolation.

tripzilch• 15 years ago

> However, physicists do make extensive use of unit tests, so that may be some consolation.

Ehm, well some do. And those that do, endlessly complain about most of them that don't.

Fact of the matter is, most physicists aren't trained in proper software engineering methods. Quite a few, but not nearly a majority are very interested in computers and computing so they may pick up a thing or two or actually bite their teeth in doing things the right way, and then there's most of them who love Physics for being Physics and Science for Science and see the computer as just another tool next to their pencil and paper, and just "get things done" and screwed be the next PHD that has to pick up on their research.

At least, that's what I hear from a friend doing a PHD involving analysing huge datasets coming from apparatus measuring high energy cosmic particles.

Of course the LHC is a much more prestigious project, so you might expect somewhat higher quality, but you can't change the culture. Physicists are generally not Software Engineers.

jonhendry16• 15 years ago

It's simple. For programmers, code is king. For scientists, data is king. Code can be recreated. Data is irreplaceable, so that's what is important, along with method.

ajuc4• 15 years ago

Data depends on the code. You can't write neutrino arrival time to file on hard disk without some code in between the equipment and the file. That code can be wrong, too.

Some code has to be trusted, and scientists can't check every assumption every time, so I don't blame them. But why don't they allow others to check the code? It's the opposite of scientific method.

dean• 15 years ago

Putting my tester's cap on, would it be feasible to have OPERA repeat the experiment with photons, instead of neutrinos? Presumably, if that experiment showed that photons travel faster than light (i.e., light travels faster than light), it would prove that there had to be an error in the experiment.

Neutrino experiment affirms faster-than-light claim

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