Mar 15 2012

Neutrino Communication

I do not envision a day anytime in the foreseeable future when the average person can take out a cell-phone sized communication device that operates using neutrino signals. Nor is Geordi La Forge’s visor, which can see neutrinos, ever to become a reality.  The problem with neutrinos is that they interact very weakly with matter. But perhaps this can also be an advantage. A group of University of Rochester researchers think so.

Neutrinos are nearly massless particles that travel at nearly the speed of light. (Reports of neutrinos traveling faster than the speed of light have been premature, and will likely not pan out.) As their name implies, they are electrically neutral. They interact with matter only through the weak nuclear force, which means they interact very little.  The so-called “mean free path” of neutrinos through solid lead is more than a light year. In other words – on average a neutrino would travel through more than a light year of lead before interacting with a nucleus.

Neutrinos are elementary subatomic particles that are created in nuclear reactions. Most of the neutrinos that pass through the earth come from our own sun. Occasionally we are bathed in a pulse of neutrinos from a distant supernova. Physicists have set up massive elaborate detectors in order to detect neutrinos. The Super-Kamiokande neutrino detector in Japan consists of large underground pool o f pure water surrounded by an array of detectors. The occasional neutrino will interact with a water molecule and result in Cerenkov radiation, which can be picked up by the detectors. Other neutrino detector designs use ice instead of liquid water, such as the IceCube Neutrino Detector in Antarctica.

So – if such massive and elaborate detectors are necessary in order to detect a tiny percentage of neutrinos, what does this mean for the prospects of using neutrinos as a communication medium?

“Of course, our current technology takes massive amounts of high-tech equipment to communicate a message using neutrinos, so this isn’t practical now,” said Kevin McFarland, a University of Rochester physics professor who was involved in the experiment. “But the first step toward someday using neutrinos for communication in a practical application is a demonstration using today’s technology.”

“Isn’t practical” is a massive understatement. We might say there are “non-trivial engineering hurdles;” a deliberately understated assessment frequently used for humor and irony. Physicists, however, like to prove that things are possible before they worry about whether or not they are practical. So some researchers using the Fermilab accelerator did a little experiment:

The message that the scientists sent using neutrinos was translated into binary code. In other words, the word “neutrino” was represented by a series of 1’s and 0’s, with the 1’s corresponding to a group of neutrinos being fired and the 0’s corresponding to no neutrinos being fired. The neutrinos were fired in large groups because they are so evasive that even with a multi-ton detector, only about one in ten billion neutrinos are detected. After the neutrinos were detected, a computer on the other end translated the binary code back into English, and the word “neutrino” was successfully received.

They used a massive accelerator to create the neutrinos and a massive detector  to read the signal – but it worked. In principle we can communicate using neutrinos, just don’t expect to see such a device at RadioShack anytime soon.

There are conceivable uses of neutrino communication that would be worth investing in multi-million dollar equipment on the part of large governments, like the US. Because neutrinos interact so weakly with matter, a neutrino signal could travel through any obstacle – the earth, other bodies like the moon, or any type of shielding. There would be no place without a clear signal (can you hear me now?).  NASA could therefore communicate with ships or bases on the far side of the moon. Or the military could communicate with submarines far beneath the ocean’s surface.

The potential applications would depend upon how compact the equipment can be made. Also, some communication may be one way only. A space ship may have a neutrino detector to receive signals, but not a way of generating a neutrino signal themselves.

In the end, it’s an interesting idea, better suited for now to science fiction or, at best, big government applications. We cannot predict what the future will bring. Scientists may figure out a way to generate or detect neutrinos that is much more efficient and practical. Or, we may discover some other way to communicate through matter, making neutrino communication obsolete before it ever is developed. Either way, it’s a cool thought experiment if nothing else.

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