Sumanch via wikimedia commons. A faster than light particle would be invisible as it approached, but be seen in both directions after it passed

A new paper claims to demonstrate that neutrinos not only travel faster than the speed of light, but have the brain-twisting characteristic of “imaginary mass”, a property that means they actually speed up as they lose energy.

The phrase “extraordinary claims require extraordinary proof” has seldom been more appropriate, but Professor Robert Ehrlich, recently retired from George Mason University, believes he has that, with six different measurements from different areas of physics. All of these, Ehrlich claims in Astroparticle Physics, provide matching results that not only indicate that neutrinos have imaginary mass, but point towards the same value, making it less likely the readings are in error.

While the mere idea of imaginary mass sounds improbable to the non-physicist, it is a concept theoreticians have been tinkering with for some time. While imaginary numbers represent the square root of negative numbers, and have proven exceptionally valuable tools for physics, imaginary mass squared gives a negative mass value.

This just makes the concept sound even more improbable, but the idea actually falls fairly neatly out of the theory of Special Relativity. One of Einstein's key discoveries was the realisation that, for ordinary matter, mass increases with velocity. The formula is m2=m2 rest /(1-(v/c)2) where m is mass, v is velocity and c is the speed of light.

The conclusion that faster than the speed of light is impossible comes from the fact that, for an object with mass, traveling at the speed of light would make that mass infinite. Unless someone can work out how to get from traveling slower than light to faster than light without going through the speed of light it appears we are stuck with exploring the universe at a painfully slow pace.

However, in 1962 George Sudarshan pointed out that nothing in relativity theory prevented the possibility of particles that always travel faster than the speed of light. For these objects, dubbed tachyons, light speed would be a floor, not a ceiling.

This raised the question as to whether, if tachyons exist, we would be able to detect them. In 1985 it was suggested that neutrinos are actually tachyons. Most physicists paid little attention and went back to arguing about whether neutrinos have mass and travel slower than light, or are massless objects traveling at lightspeed. However, the claim has resurfaced several times since, most famously in the erroneous timing of neutrinos from Geneva to central Italy.

Ehrlich uses results from “Cosmic Microwave Background fluctuations, gravitational lensing, cosmic ray spectra, neutrino oscillations, and double beta decay.” From these he arrives at a mass that, besides its imaginary status, is less than a millionth that of an electron (m2νe=−0.11±0.016eV2), consistent with a speed only slightly above that of light.

Moreover, Ehrlich claims, “There are no known observations in clear conflict with the claimed result.” He also suggests three further tests that could be conducted to verify or disprove his conclusion, one of which is set to occur in 2015.