Neutrino communication more efficient than electromagnetic transmissions

May 22, 2008 08:38 GMT  ·  By
Simple sketch of the IceCube detector at the South Pole. The cylinder represents the AMANDA detector
   Simple sketch of the IceCube detector at the South Pole. The cylinder represents the AMANDA detector

The Search for Extraterrestrial Intelligence, or SETI for short, has been surveying transmissions that would hopefully turn out be a sign from ET for the last couple of decades or so, although nobody seems to be calling. Now scientists believe that this may have something to do with the fact that we're only looking at signals in the electromagnetic spectrum, which would not be such a logical approach for a more advanced alien civilization since electromagnetic radiation, like any form of light, can be blocked somewhere along the way by matter such as interstellar gas and dust, for example.

John Learned of the University of Hawaii on the other hand believes that the next logical step would be to try an interstellar communication system based on neutrinos. Neutrinos are subatomic particles belonging to the lepton group - also containing the electrons - of the fermion family, bearing zero electrical charge and unknown mass. Neutrinos present extremely low interactions with all normal matter, which is why they are extremely hard to detect and are believed to be one of the constituents of dark matter.

Neutrino detectors are extremely hard to build, require vast amounts of detecting material and even in such a configuration they can only detect a few particles per hour. Nevertheless, neutrino communication definitely has advantages over electromagnetic radiation. One of these advantages would be the fact that neutrinos cannot be easily affected by interactions with outer forms of radiation nor can they be easily stopped by normal matter.

Neutrino beams could be directional and sent in pulses, or even encoded. Such a communications beam would have to have an energy level of at least one million electron-volts so that they are not mistaken for other neutrinos occurring naturally in the universe. According to the researching team, a neutrino detector looking for an alien transmission using neutrinos should look for particles bearing an energy level of 6.3 petaelectron-volts, this being the "Glashow resonance" or the energy level where electrons interact with antineutrinos to create a W particle - a vectorial boson mediating the weak nuclear force.

An emitter could work in two ways to produce such neutrino particles. One would be by colliding electrons and positrons to create Z particles, but to produce a signal that would ensure that the message travels at least 3,000 light years would require an energy level of about 3 percent of that of the Sun's - impossible now, but likely in the future.

Alternatively, neutrino particles could be produced by firing protons at a target in order to obtain pion particles at energies of 30 PeV. The pions would then decay into muons and muon neutrinos, which can be later separated. The advantage of this second method it that the energy required is much smaller and could be obtained in the near future with the help of thermonuclear power plants, and both neutrino and anti-neutrino particles are produced, thus providing a means to encode messages.

Until then however, all we can do is listen to transmission that could hide such possible signals. The technology exists, but the detector volume would need to reach at least 1 cubic kilometer. The IceCube detector currently under construction at the South Pole should be able to detect neutrinos at 6.3 petaelectron-volts. If it does, then we'll know that we're not alone, since neutrinos at such high energy levels do not occur naturally in the universe.