# Can neutrinos travel Faster Than Light **URL:** \ **Category:** Factual Questions\ **Created:** [September 22, 2011, 10:59pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266 "2011-09-22T22:59:06Z")\ **Posts on this page:** 20\ **Page:** 7
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [September 25, 2011, 3:50pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/121 "2011-09-25T15:50:12Z")
> [@Issac Asimov](#): > > The most exciting phrase to hear in science, the one that heralds the most discoveries, is not “Eureka” (I found it!) but “_That’s funny …_” > [@F.K. Richtmeyer](#): > > The whole history of physics proves that a new discovery is quite likely lurking at the next decimal place. > [@Frank Wilczek](#): > > In physics, you don’t have to go around making trouble for yourself, nature does it for you. > [@Sir Arthur Eddington](#): > > Not only is the universe stranger than we imagine, it is stranger than we can imagine. 🙂 ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [September 25, 2011, 4:20pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/122 "2011-09-25T16:20:36Z")
What I love is that the new exciting finding of the decade anyway (if confirmed) has not come out of the LHC but this relatively inexpensive project that was not looking for anything so major. How much did OPERA cost, compared to the LHC? One more quote. > [@Julius Comroe](#): > > Serendipity is looking in a haystack for a needle and discovering a farmer’s daughter. The word “serendipity” comes from the Persian tale of [“The Three Princes of Serendip”](http://en.wikipedia.org/wiki/The_Three_Princes_of_Serendip) as alluded to by [Horace Walpole](http://en.wikipedia.org/wiki/Horace_Walpole). And it, referred to by Walpole as “accidental sagacity”, plays a bigger role in science than many appreciate. Yeah, it might just be some technical error that they can’t find. _But_ if not then _whatever_ the explanation, it is definitely funny new trouble that strange nature has made for our imaginations to wrestle with. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 25, 2011, 5:05pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/123 "2011-09-25T17:05:10Z")
A follow-up question to my last post: Is there any good reason to believe c[sub]L[/sub] = c[sub]i[/sub], as opposed to c[sub]L[/sub] \< c[sub]i[/sub] due to quantum corrections (with c[sub]i[/sub] - c[sub]L[/sub] small)? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 25, 2011, 6:21pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/124 "2011-09-25T18:21:54Z")
> [@](#): > > Quoth **DSeid** : > To respond with more seriousness than you mayhaps intend - I reject the supernatural as explanations for how the natural world operates… And tachyons which can interact with normal matter are considerably more supernatural than gremlins are. Really, it doesn’t take much of a stretch of current knowledge at all to get gremlins. On the discussion of c, meanwhile: If one’s being pedantic, c refers to the fundamental speed limit of the Universe, and not necessarily to the speed of light. It appears that light does in fact travel at c, and at the very least travels at very close to it, but that’s an observation, not part of the definition. Even granting that, though, the best measurements of c probably do derive from measurements of the speed of light, since the speed of a particle should approach c as the ratio of its energy to its mass approaches infinity. Even if photons are massive, their mass is much, much smaller than their energy, so their speed is very, very close to c. In principle, you could measure c using _any_ particle, with any mass and energy, but the errors are much smaller in the case where the energy is much larger than the mass. ---
**Author:** ![Aji\_de\_Gallina](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aji_de_gallina/32/260_2.png) [@Aji\_de\_Gallina](https://boards.straightdope.com/u/Aji_de_Gallina)\ **Post date:** [September 25, 2011, 7:16pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/125 "2011-09-25T19:16:43Z")
> [@TriPolar](#): > > I’ve seen plenty of evidence that these gremlins exist. They frequently move my car keys from where I left them. One of their favorite tricks is to rip a hole in one of those cheap plastic grocery bags when there’s a bottle of soda in it. I don’t see why they wouldn’t mess with physicists measuring neutrinos. Are they the ones that constantly tangle the cables behind my computer? > [@DSeid](#): > > So you are fine with the concept as long as it stays out of the realm of science, that is the observable and subject to testable hypotheses? > > Really, I don’t get how you can accept so much of the weirdness that is physics and then freak out over this possibility. > > \*Worst \*case - perceived causality is a matter of reference frame: to some degree, at least for some particles, what is our future is their past and visa versa. Honestly, how is that so much more of a gamestopper than the spooky action at a distance of quantum entanglement? The problem with nteracting with Tachyons (should they exist) is that if can actually interact with them and their imaginary mass, all sorts of shit may happen. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 25, 2011, 7:28pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/126 "2011-09-25T19:28:03Z")
> [@Chronos](#): > > Even granting that, though, the best measurements of c probably do derive from measurements of the speed of light, since the speed of a particle should approach c as the ratio of its energy to its mass approaches infinity. Even if photons are massive, their mass is much, much smaller than their energy, so their speed is very, very close to c. This assumes that it is only their mass which slows them down. If they are massless, but slowed down because of vacuum polarization effects or what have you, I don’t think this argument holds. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 25, 2011, 7:37pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/127 "2011-09-25T19:37:23Z")
> [@](#): > > This assumes that it is only their mass which slows them down. If they are massless, but slowed down because of vacuum polarization effects or what have you, I don’t think this argument holds. You may have a point here, and so it’s good to test with other low-mass particles, too: Gravitons are also believed to be massless, and so would be a good test case, although their energies will typically be far, far lower than those of photons. Still, though, the current result seems to be in conflict even with previous neutrino results. Honestly, vacuum polarization effects which slow down massive particles would also be a significant blow against special relativity, so I wouldn’t be eager to bet on that, either. But it’d be less of a blow than faster-than-c information-transfer, and there are in fact some current models which feature something like that. ---
**Author:** ![Wizard\_One](https://avatars.discourse-cdn.com/v4/letter/w/6a8cbe/32.png) [@Wizard\_One](https://boards.straightdope.com/u/Wizard_One)\ **Post date:** [September 25, 2011, 7:39pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/128 "2011-09-25T19:39:18Z")
Perhaps the neutrinos are tunneling during oscillation? As I recall, neutrinos passing through matter tend to oscillate at a greater frequency. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 25, 2011, 8:01pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/129 "2011-09-25T20:01:46Z")
Tunneling has nothing to do with this, and it’s unclear how flavor oscillation could cause this effect, either. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [September 25, 2011, 11:06pm UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/130 "2011-09-25T23:06:29Z")
> [@billfish678](#): > > It occurred to me these folks must have been excited as hell when they discovered this. > [@](#): > > Were thier results kept a secret till the announcement? were any rumors going around? Seems like a lot of time and many folks were involved here. And given the results that seems a recipe for someone, somewhere, sometime blabbing. When they first looked at the answer, I can assure you that the principle participants in the measurement all had their stomachs come up into their throats in terror, each worrying that he would be the one to look stupid when the error was found. The answer was known to the collaboration in March. It was kept secret for seven months as they checked and re-checked their work. Such secrecy isn’t too hard to maintain in a collaboration of this size. One to two month embargoes are commonplace, as one waits for the right conference to come around. Excitement would creep in for some, but not all, even after seven months of checking. They know as well as anybody how many single-point failures this measurement has, and even though they have checked everything as thoroughly as possible and they had no choice but to release the result (out of scientific honesty), many will feel anxiety about the result. On the other hand, some will have immediately seen the headlines in their mind and will have been excited for the inevitable publicity. And, some may now be willing to bet that this measurement will be confirmed by independent tests. Those folks are very exited. > [@Francis Vaughan](#): > > The question I have, is what part of the original experiment required such precision in measuring time and distance? I can see how they would probably need to window the detection of neutrinos to exclude background noise, but it seems that the level of precision in time/distance is significantly greater than needed. Indeed had it not been so, they would not have seen the difference in expected times in the first place. This level of temporal precision is not otherwise needed. The experimenters explicitly upgraded the geodesy and timing instrumentation to be able to make this measurement. > [@ZenBeam](#): > > How accurately has ci been measured, with the assumption that 1/sqrt(1-v^2 / ci^2) is the correct factor, but that ci might be greater than cL? [Precision tests of QED](http://en.wikipedia.org/wiki/Precision_tests_of_QED). These calculations involve the relativistic invariant _c_ all over the place. > [@DSeid](#): > > How much did OPERA cost, compared to the LHC? The OPERA detector cost in the $50M-$80M range. The CNGS neutrino beam (without which OPERA wouldn’t be very useful) cost in the $80M-$100M range. The LHC and its experiments cost about 30 times higher in total, although there are more than 30 times more scientists involved in the latter, so it sort of works out. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [September 26, 2011, 12:05am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/131 "2011-09-26T00:05:17Z")
Thank you for those figures. So, so far the possible explanations include: Error. Neutrinos can indeed accelerate to c and beyond. Two populations of normal matter interactive neutrinos are being produced, one that travels below c (normal-neutrinos) and one above c (tachyon-neutrinos). _c_L is actually less than _c_I whereas neutrinos can get closer to _c_I. Perhaps because some sort of refraction in a vacuum. Gremlins. And then a miracle occurred. (Or if this was organic chem, “an enzyme did it.”) Okay. So option one leads the pack. The hypothesis will be tested by repeating similar studies. If that hypothesis is falsified, then how does one go about determining which of the others is less unlikely and falsifying some of them? ---
**Author:** ![Wizard\_One](https://avatars.discourse-cdn.com/v4/letter/w/6a8cbe/32.png) [@Wizard\_One](https://boards.straightdope.com/u/Wizard_One)\ **Post date:** [September 26, 2011, 12:29am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/132 "2011-09-26T00:29:39Z")
> [@Chronos](#): > > Tunneling has nothing to do with this, and it’s unclear how flavor oscillation could cause this effect, either. I can’t see how oscillation could cause it either, unless we’re deposing Newton. Because, without an error, the measurements show a particle with mass exceeding C, which would depose Einstein. Even if the neutrino had a fourth, massless flavor, it wouldn’t ACCELERATE. Hence the notion of tunneling… ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 26, 2011, 1:23am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/133 "2011-09-26T01:23:58Z")
Just thought I’d share a link to [Measurement of neutrino velocity with the MINOS detectors and NuMI neutrino beam](http://arxiv.org/abs/0706.0437). They found neutrino velocity faster than light some four years ago, but not at the level of accuracy of OPERA: > [@Abstract](#): > > A total of 473 Far Detector neutrino events was used to measure (v-c)/c = 5.1 +/- 2.9 x 10^-5 (at 68% C.L.). The Opera value falls within that range. The paper has _v_ \< _c_ allowable at the 99% confidence level: −2.4 × 10−5 \< (v − c)/c \< 12.6 × 10−5. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 26, 2011, 1:47am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/134 "2011-09-26T01:47:08Z")
> [@](#): > > Hence the notion of tunneling… Again, tunneling would do absolutely nothing to explain these results, since the neutrinos here aren’t passing through an energetically-prohibited region, and even if they were, tunneling is subject to the same speed restrictions as anything else. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 26, 2011, 2:00am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/135 "2011-09-26T02:00:08Z")
Regarding the possibility of “slow” photons, I thought that the way the laws of electromagnetism work dictate that photons HAVE to travel at the “true” C. > [@naita](#): > > If I’ve done the maths right and have the right information the neutrino discrepancy was 60 ns over the distance given, a 0.000025 in 1 difference from the speed of light. Applying that to 1987a’s distance of 168000 light years we get a difference of 4.2 years. So either the supralumial neutrinos result is wrong, or supernovas don’t send out neutrinos but 4.2 year old supernova remnants do, or neutrinos only go faster through planetary crusts. Was 1987a _ **exactly** _ 168,000 light years away? Add 4.2 light years and you get the same factor. The point of the experiment is that is the tightest test of both time and distance ever done. Which brings me to my wild-assed-guess: If the results are real, then it could be a manifestation of quantum gravity. Specifically, it could be the first measurement of something other than light traveling fast enough that uncertainty as to the boundaries of our local light cone become evident. ---
**Author:** ![Wizard\_One](https://avatars.discourse-cdn.com/v4/letter/w/6a8cbe/32.png) [@Wizard\_One](https://boards.straightdope.com/u/Wizard_One)\ **Post date:** [September 26, 2011, 2:05am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/136 "2011-09-26T02:05:41Z")
> [@Chronos](#): > > Again, tunneling would do absolutely nothing to explain these results, since the neutrinos here aren’t passing through an energetically-prohibited region, and even if they were, tunneling is subject to the same speed restrictions as anything else. The question is, were these neutrinos that were detected “early”, ones that interacted with matter while passing through the Earth? There is no true way to determine that. If they had, then they may have tunneled past interfering matter. Some of the tunneling research DID determine a higher than expected transit through the barrier. Of course, I WILL say that I don’t hold fast to tunneling causing the apparent increase in velocity, it’s about as likely as one of the rovers meeting Marvin the Martian. But, that was about the only thing I COULD think of that would cause an apparent superluminal travel of a particle with mass. I read through the paper, couldn’t see anything that they missed in THEIR attempt to shoot holes in the observations. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 26, 2011, 2:16am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/137 "2011-09-26T02:16:44Z")
> [@Lumpy](#): > > Was 1987a _ **exactly** _ 168,000 light years away? Add 4.2 light years and you get the same factor. The point of the experiment is that is the tightest test of both time and distance ever done. Which brings me to my wild-assed-guess: If the results are real, then it could be a manifestation of quantum gravity. Specifically, it could be the first measurement of something other than light traveling fast enough that uncertainty as to the boundaries of our local light cone become evident. The photons and neutrinos would both have to travel that extra distance. You wouldn’t have the photons traveling 168,000 light years and the neutrinos traveling 168,004.2 light years. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [September 26, 2011, 2:29am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/138 "2011-09-26T02:29:29Z")
I had previously been under the impression that neutrinos were utterly massless, but I keep reading in the discussions of this experiment that they are “nearly” or “virtually” massless. But if they have mass they are not (as I understand it) allowed to travel at light speed as that mass would have to be infinite at that speed - can anyone correct my thinking here? > [@Keeve](#): > > Ever since this story came out, I’ve been considering the idea that we’ve been mistaken about the Cosmic Speed Limit. We had thought that the Cosmic Speed Limit was the speed of light, and that nothing, not even neutrinos, could go faster than that. Now it seems that the actual Cosmic Speed Limit is not that of light, but of neutrinos. Light (in other words: photons) is pretty fast, but just a wee bit slower than neutrinos. And because the Speed Of Light and the Speed Of Neutrinos are so damn close to each other, no one noticed the error until now. > > I think the above was proposed by a few other posters as well, but I used more words than they did. And I avoided using “c”, because it has two different meanings — speed of light, and cosmic speed limit — which used to mean the same thing, but now it seems that they might be different. > > Anyway, what is the argument AGAINST what I just wrote? If I understand the thread correctly, the argument against is this: If the speed of photons is even a tiny bit slower than the cosmic speed limit, then the photons can’t have zero mass. And they can’t even have a tiny nonzero mass, because that would have shown up long ago. > > So I guess my real question is this: What makes us so sure that photons really do have no mass at all? Is it merely a conclusion derived from the presumption that the speed of light is indeed the cosmic speed limit, in which case it is circular logic and wrong? Or do we have any experimental data proving photons to be massless? As I understand it: the cosmic speed limit (CSL) is _not_ defined by the speed of light. Rather, light (being massless) travels as fast as the CSL allows it to. Now if it is determined that light has some minuscule mass then it would not be allowed to travel at the CSL, as its mass would need to be infinite. That said, I’m sure light having mass would throw up as many problems as superluminal neutrinos would, but that’s way out of my league. Could that remove the need for positing dark matter? ---
**Author:** ![Wizard\_One](https://avatars.discourse-cdn.com/v4/letter/w/6a8cbe/32.png) [@Wizard\_One](https://boards.straightdope.com/u/Wizard_One)\ **Post date:** [September 26, 2011, 5:47am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/139 "2011-09-26T05:47:25Z")
> [@Askance](#): > > I had previously been under the impression that neutrinos were utterly massless, but I keep reading in the discussions of this experiment that they are “nearly” or “virtually” massless. But if they have mass they are not (as I understand it) allowed to travel at light speed as that mass would have to be infinite at that speed - can anyone correct my thinking here? > (/QOUTE) > > You understand incorrectly. Neutrinos come in three flavors. Each, with its own mass. > Neutrinos oscillate between flavors. > > (QUOTE) > As I understand it: the cosmic speed limit (CSL) is _not_ defined by the speed of light. Rather, light (being massless) travels as fast as the CSL allows it to. Now if it is determined that light has some minuscule mass then it would not be allowed to travel at the CSL, as its mass would need to be infinite. > (/QUOTE) > > Photons do NOT have mass, per repeated observations, hence travel at maximum velocity. > > (QUOTE) > That said, I’m sure light having mass would throw up as many problems as superluminal neutrinos would, but that’s way out of my league. Could that remove the need for positing dark matter? BOTH would throw a trainload of monkey wrenches into ALL physics. To the point where a LOT of things that work today would not work under THOSE physical laws, as suggested. Hence, the GREAT excitement. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 26, 2011, 6:00am UTC](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266/140 "2011-09-26T06:00:41Z")
> [@](#): > > Quoth **Lumpy** : > Regarding the possibility of “slow” photons, I thought that the way the laws of electromagnetism work dictate that photons HAVE to travel at the “true” C. Which means that if photons are massive, or for some other reason travel at less than c, it would imply that our understanding of the laws of electromagnetism are incomplete. That’s another thing I wouldn’t bet on, but it’s certainly possible. **Askance** , it was long believed that neutrinos were massless, but neutrino flavor oscillation (which has now been observed, and is pretty conclusively established) can only work if they have mass (or at the minimum, that at least two of the three varieties have mass). We know very little about what the masses are, though, beyond the fact that they’re very small: All of them are less than about 1 eV, and at least two of them are greater than about 10[sup]-5[/sup] eV. Note that, for most purposes, neutrinos having a very small mass produces experimental results that are almost the same as we would expect if they were massless. The same is true for photons, incidentally: A photon with very small mass would produce experimental results very similar to a truly massless photon. For any given experiment, there is some sufficiently small mass such that photons of that mass would be experimentally indistinguishable from massless ones. What this means is that we can never actually experimentally prove that photons are massless: All we can do is set upper bounds on what the mass can be. IIRC, the current upper bounds on the photon mass are somewhere in the vicinity of 10[sup]-6[/sup] eV: That is to say, we know that if they do have mass, it must be less than that. Neither the mass of neutrinos nor of photons could possibly account for all of the dark matter. Neutrinos are a part of it, but current measurements seem to show that they’re only a small part of it. And photons are certainly not enough to be even worth mentioning. [Previous page](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266.md?page=6) [Next page](https://boards.straightdope.com/t/can-neutrinos-travel-faster-than-light/597266.md?page=8)