Faster than light neutrino result flawed, loose cable to blame

Tracks made by neutrinos in an experiment at CERN. Credit: CERN

Remember last September’s Italian experiment that supposedly detected faster-than-light neutrinos?  Neutrinos, which come in several varieties, are neutral subatomic particles that have a very minute mass and rarely interact with matter. When hydrogen is fused into helium in the sun’s core to produce the light and heat that make Earth a pleasant abode, zillions of neutrinos are created in the process. Most pass right through the sun, speed outward and fly right through the planets as if they weren’t even there. 50 trillion electron neutrinos zip through your body every second!

When the Italian team discovered that their neutrinos completed the journey from CERN Laboratory near Geneva, Switzerland to Gran Sasso Laboratory near Rome 60 nanoseconds faster than a beam of light, even they were skeptical of the result and encouraged others to repeat their experiment. According to one of the key tenets of Einstein’s Theory of Relativity, no material object in the universe can travel faster than the speed of light.

The Gran Sasso National Laboratory is located nearly a mile below the surface of Gran Sasso mountain some 60 miles from Rome. The massive array detects tiny particles called neutrinos. Credit: Paolo Lombardi INFN-MI Rome

And indeed a flaw in the experiment was uncovered this week. Come to find out that a loose cable between a GPS receiver and a computer was to blame. The GPS was used to synchronize the start and arrival times of the neutrinos. When the cable was tightened, the 60 nanoseconds difference disappeared. An additional nail-in-the-coffin was delivered by another group of experimenters working in the same lab in a repeat of the experiment. They failed to detect the radiation that would be emitted by particles traveling faster than the speed of light.

The sun produces trillions of neutrinos as it cooks up hydrogen in its core. Photo: Bob King

One more interesting sidelight about neutrinos. Lest you think they all get away without turning everything and everybody into Swiss cheese, scientists have built special neutrino detectors like Super Kamiokande in Japan to spot their tracks. Detectors there pick up tiny flash of blue light when a neutrino has a rare interaction with a water molecule in a stainless steel tank filled with 50,000 tons of ultra-pure water. Besides being useful for studying the sun’s neutrino output, Super Kamiokande can also detect neutrinos shot out when a star collapses and explodes as a supernova. Because they travel at nearly the speed of light, they escape the star before anything else, giving astronomers a heads-up on what’s happening inside the explosion. Pretty cool.

Einstein can still rest comfortably in his grave that the speed of light – at least for the time being – will remain the ultimate speed limit in the universe. I encourage you to check out the full story for more information.  And before we leave the subject, here’s a  joke I think you’ll enjoy:

“We don’t allow faster than light neutrinos in here”, said the bartender. A neutrino walks into a bar.

* Source for some of the info in today’s blog comes from space.com

4 Responses

  1. Travis Kitch

    Ahhhhh, so that’s what happened. I, too, remember when that puzzling result was published. On a related note, and please, Bob, correct me if I am wrong, but is there not a neutrino detector near Sudbury, Ontario, deep under ground? How many other neutrino detectors have been built?

    Thanks as always,

    1. Profile photo of astrobob

      Hi Travis,
      Looks like there are about a half dozen working detectors including one at the South Pole, called IceCube, one here in my state of Minnesota in Soudan called MINOS (I’ve been to this one) and yes, there is one in Sudbury deep in a mine there, too!

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