Thursday, September 22, 2011

Neutrinos Behaving Badly

The OPERA Collaboration has announced what they claim is a 6-sigma measurement that neutrinos move faster than the speed of light in a vacuum (see stories by Nature and the BBC).  OPERA is an Italian experiment designed to measure neutrino oscillations in a stream of the elusive sub-atomic particles coming from CERN.  To date they have detected the arrival of over 16,000 neutrinos (which is quite a few considering how hard it is to stop a neutrino) and now they claim that they have good evidence that those particles move just a hair faster than what was thought to be the universal speed limit.

The OPERA folks are being very cautious with their claims and the point out that this could simply be some systematic error for which they haven't accounted.  Interestingly, Nature is reporting that there was some evidence for similar speeding neutrinos at the MINOS neutrino experiment, but that the distance from Fermilab (where the neutrinos were being made) to the MINOS detector wasn't know to sufficient precision to be able to make such a claim.

So what does this mean?  The joke that half of all 3-sigma results are false rings in my ears.  If I had to bet, my money would be on some sort of error or some effect of a previous theory that accounts for the apparent effect.  I guarantee that there will be a lot of very smart experimentalists thinking about systematic errors in measuring neutrino speeds and that there will be a whole slew of papers from theorists showing that super-luminal neutrinos are predicted by their brand of quantum gravity, super-symmetry, or f(R) theory of gravity.  What does it mean if this is true?  Well, we can start by going back to the drawing board on relativity.

UPDATE:  The paper is up on the arXiv here.  I am not a particle physicist, but it looks like they have done a very nice, careful job in not over-selling their result.  The measured velocity was about 7430 +/- 1740 m/s faster than the speed of light.

One other interesting note:  When the famous supernova 1987A went off in our friendly neighborhood Large Magellanic Cloud, neutrino bursts were measured at three different detectors around the globe about 3 hours before the first light from the supernova was seen.  This is generally explained because 1987A was a core-collapse supernova and while the neutrinos it produced could simply stream outward through the outer layers of the collapsing star, the light could not and therefore was delayed slightly.  That supernova was about 168,000 light-years away.  Assuming that neutrinos actual do travel faster than light by the amount measured by the OPERA team, those neutrinos should have arrived 4 years prior to the first light from the supernova.  Things like this are why most physicists are looking for a problem with the experiment rather than throwing relativity out the window.


  1. "What does it mean if this is true? "  

    Man would that be a paradigm changer.  For an entire century physics has progressed forward on the fundamental assumption (which has a tremendous amount of experimental support lest anyone forget) that nothing can travel faster then the speed of light.  If that is false, that changes everything:

    1.  Casualty goes out the window since if there are superluminal particles the claim goes causality is gone.

    2.  Every particle physicist "knows" that a faster then light particle is a tachyon that makes the vacuum unstable destroying physics and hence tachyons are to be avoided like the plague.  

    Unless... Unless there is something tricky going on like the particles are taking a short cut through higher dimensions that light isn't and so get their faster or some other crazy idea.

    So anyways, *assuming* this is correct, this will change physics fundamentally in big ways.  Which is why most people are probably going to think something is wrong with their measurement.

  2. Wow! I'm very intrigued. I really wish I understood it all better. I wonder if I'd have time in life to get a PhD in particle physics too.

  3. I'm going to go with systematic error on this one, not because I have any special insight into how the universe works, but because I know from personal experience that it is more likely to be a matter of, "Well did you think about accounting for such and such effect?"

    "Uh, no we didn't think that was necessary since it will only affect blah, blah, blah, when blah, blah, blah under 3 sigma type 4 conditions when the synaptocrypticbioetheric bottom tau mode dangle arm is set to receive florogrammeter Sperven bearing type sinusoidal replenerations."

    "Did you ever actually measure that?"


    "Well, try measuring it."

    [Tinkers around in the lab with the equipment. Makes measurements.]

    "Well what do you know! It does make a difference! Who would have thought?"

    That type of scenario is most assuredly more likely than the possibility that we have finally found a tachyon.

    The first key is replication. The second is let it sit for a while and get a lot of people to look at it and make sure we didn't over look something, and then finally consider other theories and ideas. The reason for a measure of caution is because the results would imply a violation of causality, and up until now (as in the entity of known human existence) has amply proved that causality holds. It's a bit like tossing out gravity because someone observed an object levitating in a lab.

    But if it does hold up under scrutiny and can be replicated, wow that would be so cool!

  4. thanks for posting...


To add a link to text:
<a href="URL">Text</a>