• Question: Is there a way to explain the faster-than-light particles that were recently observed at the LHC?

    Asked by supercritialsunil to Ben, Jony, Katharine, Mark, Peter on 16 Nov 2011. This question was also asked by breem001.
    • Photo: Ben Still

      Ben Still answered on 16 Nov 2011:

      So the particle, neutrinos, were actually a part of an experiment called OPERA. Neutrinos were fired from CERN (where the LHC also lives) to an underground cavern under a the Gran Sasso mountain in Italy. They said the neutrinos arrived 60±10 nano-seconds (ns=billionths of a second) before light would.

      The surprising thing is that 60ns is much larger than the error of 10ns quoted, some believe that the errors should be larger and this would account for the difference in arrival time of the neutrinos. There are, as there always is, lots of theories which also claim to explain the difference; quantum gravity, certain string theories.

      If you want to read more check out my series of blog posts starting from http://bit.ly/NuBlogFTL

    • Photo: Katharine Schofield

      Katharine Schofield answered on 16 Nov 2011:

      Well, I reckon there will be a way to explain this odd experimental result, but I don’t have any theories myself about what that might be. There are lots of physicists working furiously to try to figure it out though.

    • Photo: Jony Hudson

      Jony Hudson answered on 16 Nov 2011:

      I’d really love it if this result holds up 🙂 It would be great for something really unexpected to pop up, and to have to rebuild a load of our theories.

      The honest truth is, at the minute nobody has any real idea how to explain it! People are checking to see if the experimenters made any mistakes – it’s a very complicated experiment, so it’s possible.

      The best thing would be if a different team could repeat the experiment. That would be really helpful information.

    • Photo: Mark Basham

      Mark Basham answered on 16 Nov 2011:

      hi supercritialsunil

      I really hope the results hold up too, there are plenty of theory about which don’t have experimental evidence to back them up. This may be the start of a new set of experiments which can be used to prove or disprove some of these theory’s.

      In a way the worst thing that could happen is they work out that it was an error in the measurement.

    • Photo: Peter Williams

      Peter Williams answered on 16 Nov 2011:

      lots. see my answer here http://ias.im/63.428 – cut and pasted below…

      They’ve done exactly the right thing. They tried to find the discrepancy, but haven’t yet. So they’re asking the whole scientific community to check over their results. There are many things that could in principle explain the difference – remember this is only 20 nanoseconds, the time it takes light to travel about 7 meters – so equivalently a mistake in the distance between the source and detector of about that. For example, a mistake in the way GPS has been used to calculate that distance is being investigated. Another possible explaination is at the source – they monitor the current profile of a bunch of protons hitting a target, but this is not generating the neutrinos that fly from CERN to Gran Sasso, the target generates a whole bunch of stuff, some of which are things called pions, these decay to muons which in turn decay to neutrinos. So this is a pretty complicated chain of events – perhaps this process is not sufficiently understood.

      An independent experiment in the US called MINOS wll be performing their own test of the result later this year. So that’s one to watch.

      Also bear in mind that there are other effects that would happen if neutrinos are superluminal (faster than light) that have NOT been observed. Chiefly something called Cherenkov Radiation. This is like a sonic boom, but in light rather than sound. When we talk about the speed of light, we generally mean the speed of light in a vacuum. But light slows down in dense media – this is how lenses work. If a particle enters a material faster than the speed of light in that material then it quickly loses energy and emits light to get rid of that energy – called Cherenkov Radiaition after the guy that discovered it. Here is a picture of the spent nuclear fuel pool at La Hague in France (there is a smiliar one at Sellafield) http://s3.amazonaws.com/files.posterous.com/dougv/6VIfSDonKx0ywWTeXAeGmEcggy6pW4qdVvltla61Fgz5MfZ0PQdijxVNgmWU/spentfuelpool.jpg?AWSAccessKeyId=AKIAJFZAE65UYRT34AOQ&Expires=1321442343&Signature=7wH2fG2Ztt2rj3KP7I1BnxSmRPE%3D – this is a pool of water where they store spent reactor fuel, The rather pretty (or eerie if you are anti) blue glow is Cherenkov radiation. In this case the particles that is undergoing the sonic boom are neutrons, the speed of light in the water is slower than they are moving. But in principle the same would happen with neutrinos in the OPERA detector. But it doesn’t – so that’s inconsistant with their measurement of superluminal speeds.

Comments