Remember that Neutrino Discovery at CERN?

Several months ago, CERN announced that their neutrino experiments had shown that neutrinos might be traveling faster than the speed of light.  I wrote about it at the time and mentioned that I didn’t think it likely.  It turns out that their result was actually due to a loose fiber optic cable.  Once it was tightened down properly, the neutrino travel time increased by something like 60 nanoseconds and the problem of FTL neutrinos was solved.  I’m a little bit disappointed in those guys at CERN.  If I had gotten an experimental result that required me to throw out 100 years of well-established experimental and theoretical physics, I’d be checking out my test setup.  Thoroughly.

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3 Responses

  1. Darn. FTL neutrinos would’ve been a really cool spin on the universe. Oh well.

  2. eh, what about the studies going on at the South Pole? We had the guy speak about the experiments going on there and it was stated that neutrinos travel faster than speed of light which is how they pass so easily and quickly through earth…

    • Not to sound like a know-it-all, but that guy is mistaken. Neutrino interactions have nothing to do with their velocity.

      The reason that neutrinos pass so easily through matter, including the Earth, is because they only interact with matter via gravitational and electroweak forces. That’s what made it so difficult to finally detect them. They do not carry a charge and they don’t have a magnetic moment, so they don’t get deflected by the magnetic field of the Earth (to be perfectly complete, they probably do have a magnetic moment, but it is miniscule and not worth mentioning).

      Most physicists have accepted the idea of a massive neutrino, although this is a relatively new idea. There are three different types or flavors of neutrinos. It turns out that neutrinos undergo something called flavor mixing, where they spontaneously change from one flavor to the next. This was a really big deal about 10 years ago and Nobel prize was awarded for its discovery, because it led to the conclusion that neutrinos had to have mass. But, since the mass is so tiny, the gravitational force on a neutrino, even by something as huge as the sun, is negligible. That’s part of the reason why neutrinos pass so easily through matter.

      The real reason that neutrinos pass through matter so easily is because they only interact with matter via something called the electroweak interaction; it’s the fundamental force which is involved in the beta decay you probably learned about in general chemistry. Weak interactions between neutrinos and matter do not occur too often because the range of the weak force is so small. That’s why you have to build special detectors deep underground and fill them with heavy water in order to start seeing neutrino interactions.

      I’ll post a picture in my original post so you can see what a neutrino detector looks like. They’re rather fascinating and it makes it really obvious why it took us something like 70 years to actually detect them.

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