Wednesday, October 5, 2011

Faster Than a Speeding Photon

I've been avoiding posting about this story because I'm not sure I'm totally on board with the results. But to say it has caught the news media and Internet on fire would be an understatement. So I've decided to go for it: Let's review the paper about neutrinos going faster than the speed of light.

Physics, especially particle physics, can get really complicated really fast. So, I think, to understand the significance of this finding you have to know some basics about fundamental particles. For that I suggest you go back and read my So Quarky post from back in 2010. Neutrinos are one of these fundamental particles belonging to the class of particles called leptons. They have no charge which means they are not affected by the electromagnetic force; they are only affected by the weak subatomic force. They are able to pass through large amounts of matter without being affected. Since it has mass, although extremely tiny, it is affected by gravity but that is the weakest of the forces. Neutrinos come from several sources. Most of them are left over from the big bang and make up part of the cosmic microwave background while others are produced in stars, beta decay, etc. We can also generate them in physics laboratories by colliding high energy particles into fixed or moving targets.

The speed of light is 299,792,458 meters per second (186,282 miles per hour). According to Albert Einstein's theory of special relativity, the speed of light (c) in a vacuum as a physical constant, a maximum speed at which all energy, matter, and information in the universe can travel. The speed of light is the speed of light no matter the motion of the source or the inertial frame of reference of the observer. It is the ultimate limit, the fastest a particle can move. So what happens when an experiment records a particle going faster than the speed of light?

The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) lies 1,400 meters underground in the Gran Sasso National Laboratory (LNGS) in Italy. It was designed to "perform the first detection of neutrino oscillations in direct appearance mode in the νμ→ντ channel, the signature being the identification of the τ− lepton created by its charged current (CC) interaction." Um, ok. In addition to this main goal, OPERA is also suited accurately determine neutrino velocity though the measurement of the time of flight and distance from the source. CERN (the European Organization for Nuclear Research), 730km away, fires a beam of neutrinos through the earth to OPERA, a 2.43-millisecond trip for a photon. A total of 16111 events were collected over three years. They found that, on average, the neutrinos arrived 60 nanoseconds faster than expected if they were traveling at the speed of light.


Now take a couple of logical steps past that. If neutrinos go faster than the speed of light (even a little bit) then are we getting into the realm of tachyons and time travel? Possibly.

But wait...don't throw Einstein's theories out the window and don't start building that time machine just yet.

The big question now is whether these scientists have actually discovered particles going faster than the speed of light or if there is some type of error in their experiment that is making the velocity look artificially short. After all, this is an extremely sensitive measurement. We're talking unreacting particles that are lighter than an electron and time measured in nanoseconds. Right now there are all sorts of responses being talked about an published on this topic.

The consequences of these results would be huge, and one of the things I like about this experiment is the way in which it was presented. They didn't just announce "We've broken the speed of light!" The authors put the information out there -- here are our results -- asking scientists to independently confirm or deny these results and/or offer up explanations as to why these results were obtained.

What do you think?

Here is the prepublished paper:
Adam, T. et al. (2011) Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. High Energy Physics - Experiment ( arXiv:1109.4897v1)

I also recommend reading through a few of these articles as they offer some great views from other physicists:
Science Magazine: Neutrinos Travel Faster Than Light, According to One Experiment
Nature News: Particles Break Light-Speed Limit
The Guardian: Faster Than Light Particles Found, Claim Scientists
Scientific American: Faster-Than-Light Neutrinos? Physics Luminaries Voice Doubts
The New York Times: Tiny Neutrinos May Have Broken Cosmic Light Speed
Wired Science: Can Neutrinos Move Faster Than Light?
New Scientist: Faster-Than-Light Neutrinos? New Answers Flood In

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