Are Neutrinos Faster Than Light?

Neutrinos travel faster than light! The science world is agog at this unexpected announcement from CERN  in Switzerland. This result has to be verified, for if true it seems that one of science’s central tenets is wrong!

Image of sn1987a_

An eerie, nearly mirror-image pair of loops of red luminescent gas frame the expanding debris of a star seen as a supernova explosion in 1987. Neutrinos emitted by this explosion did not travel faster than light. (Image Credit: Dr. Christopher Burrows, ESA/STScI and NASA)


It’s all Einstein’s fault of course. Albert Einstein (1879-1955) came up with the theory of relativity that established the speed of light as the cosmic speed limit. Actually Einstein had two theories of relativity, it is the earlier one, ‘special relativity’ published in 1905 under the snappy title “On the electrodynamics of moving bodies”, that lays down the problems with faster than light (FTL) movement. Some of the implications of Einsteinian relativity may seem crazy, for example the idea that  time slows down around bodies approaching the speed of light, but this seems to be how the Universe works. Remember, reality has been around since long before we showed up. Experiments have proven relativity’s predictions. Atomic clocks flown around the world on jet planes have been found on landing to have run slightly slower than identical clocks ticking away back home in the lab.

So what are neutrinos? Neutrinos are strange ghostly little particles; they have an extraordinary ability to pass straight through matter. It is has been claimed that a neutrino would have a 50% chance of passing unhindered through a block of lead 50 light years thick! Vast numbers of neutrinos are created in the core of the Sun and other stars as a by-product of the energy-creating fusion reactions.  The neutrinos zip through the Sun’s outer layers in just over a couple of seconds and escape into space. A small portion of them reach Earth just over eight minutes later. Detecting them gives us nearly instant news on what is going on inside the Sun. Neutrino astronomy is a small but important branch of our science.

In the now famous OPERA (Oscillation Project with Emulsion-tRacking Apparatus) experiment (which was actually intended to investigate the difference between sub-types of neutrino) the European scientists directed a beam of neutrinos through the Earth from CERN (European Centre for Nuclear Research) to the Gran Sasso Laboratory 730 km (453 miles) away in Italy. There the beam strikes a detector, composed of 150 000 bricks of alternating lead plates and photographic  plates. If you divide the distance between those two points by the time it takes for the neutrinos to travel, you get their speed. It appears that the neutrinos arrived 0.000 000 06 seconds (60 nanoseconds) earlier than the 2.3 milliseconds taken by light. It is a tiny discrepancy, suggesting the neutrinos travelled at 1.000 02 times the speed of light but very disturbing to scientists. The researchers at OPERA have been careful to show that they have accounted for every conceivable source of error but almost certainly there is a problem with their experiment.

In 1987 we observed an exploding star, a supernova, in the Large Magellanic cloud. This cataclysmic event blasted out an abundance of neutrinos, easily detected here on Earth over 168 000 light years away. If neutrinos can travel faster than light, the neutrinos from Supernova 1987A would have got to Earth before the light of the explosion itself. If they travelled at the speed observed by the OPERA researchers, the neutrino detectors on Earth would have seen them four years before the supernova was visible.  This did not happen; in fact the neutrinos from the supernova arrived three hours before the light! This does not mean the neutrinos outraced the supernova’s light, rather they had a head start. So dense is the core of an exploding star that it takes an appreciable time for the photons of light to force their way out and into space.  This lag between the arrival of neutrinos and light from a supernova had been predicted in advance. This observational evidence is one strike against the results from CERN, but there is a deeper philosophical reason not to take them at face value.

A central tenet of modern science is the concept of “causality”, the idea that cause precedes effect. I spill a cup of hot coffee on to my lap and I yell out, the yell (effect) comes after the spill (cause), everyone who observes this minor disaster agrees on the sequence. So far so simple. However this is vital: causality is the philosophical glue which holds science and technology together. Imagine a machine, made of three subcomponents, A, B and C, which act in sequence to do a task at the press of a button. So I press the button, starting component A, A does its stuff, starts off B …all the way through to C and the desired outcome. How could such a thing be designed in a world without causality where C sometimes is activated before A, which happens before the button is pressed? If anything can move faster than the speed of light causality collapses and so does the whole, carefully-assembled edifice of science

What is more if FTL communications are possible, then it would be possible to observe a distant event occurring and transmit this information back to the site where it occurred before the event happened.  What if the event is something important and the fore-knowledge prevents it?  (“Don’t let the President go to Dallas!”)

Paradoxes like this are common in works of science fiction but are impossible to fit into a logical and consistent universe. FTL is functionally equivalent to time travel into the past, opening a horrendous can of worms.  This is the deeper reason why FTL travel is impossible and why I am sceptical of this report from CERN. Please prove me wrong!