Many would say that Albert Einstein was a pretty smart cookie. After explaining the photoelectric effect in 1905, which described light as individual packets of energy now known as photons, earning him the Nobel prize in 1921, he then theorised both special (1905) and general (1916) relativity, founding modern physics. Out of this came his famous equation E=mc2, establishing the idea that energy (E) and mass (m) can be interchanged via the speed of light squared (c2). So, all in all, a smart cookie.
However, physicists at the National Institute of Nuclear Physicists in Italy don’t seem to think so. Or at least that’s what the infamous result of their Oscillation Project Emulsion Tracking Apparatus (Opera) experiment, released in September 2011, told them. A subatomic particle called a neutrino travelled 60 nanoseconds faster than light should. After firing protons at a solid surface to break them up to produce pions (subatomic particles), which themselves rapidly decay into neutrinos and muons (more subatomics; it’s like Russian dolls for physicists), these neutrinos travelled over 450 miles to Cern in Switzerland, 60 nanoseconds faster than the 2.4 microseconds it would have taken light to get there. Opera published this striking result in arXiv on 22 September.
In an interview with Shaun Keaveny on BBC 6 music, Brian Cox said: “if right, it is a profoundly important discovery”. Modern physics has to be almost entirely rewritten, as according to E=mc2, no object with mass (including neutrinos) can travel at or faster than the speed of light. To make sense of that, the equation essentially says that mass and energy are not separate, but in fact different descriptions of the same thing. The result of this is that when you increase the speed of an object (increasing its energy), you also increase the mass that object has. Theoretically this means that a neutrino travelling at the speed of light would therefore acquire an infinite mass. Among many other issues, a neutrino with an infinite mass would produce a singularity (an object so massive that its gravitational pull could collapse the universe). On top of this already mind boggling problem, one of the weird consequences of relativity is that objects travelling extremely fast experience time more slowly than the world around them. Simply, this means that objects travelling faster than the speed of light could arrive at their destination before they had even left their starting point, tossing to one side what scientists call “causality”: the idea that every effect has a cause. Without causality, the universe becomes a very confusing place indeed.
Unsurprisingly, quite a few leading physicists have disputed the results. In November 2011 the accuracy of the measurements were questioned, but when the Opera scientists increased their accuracy by 3000 times, the result did not change. Another team of scientists called Icarus have measured the energy levels of moving neutrinos and said they simply don’t have enough energy (they would need 10 times the amount recorded) to travel faster than the speed of light. This is just one piece of a growing body of evidence that seems to contradict Opera’s result. Others have tried to explain the result of “faster than light” neutrinos by suggesting they took a short cut through another dimension. This Nature review article discusses this idea and many others around the results.
There is still no definitive conclusion over what this result means for physics, almost four months after the data was released. Laboratories in the US, Japan and at Gran Sasso itself will be repeating the experiment to see if the original results can be verified. Results of this sort of magnitude will cause ripples in the scientific community for quite some time. The last resistance to Einstein’s idea of light existing as photons ended in 1977, 72 years after he first put forward the idea. So for the moment, watch this space; with more scientific debate and experiments to come, it’s an exciting time to be interested in physics.
Here’s a short and snappy video explanation: