The Best Australian Science Writing 2012 Read Online Free PDF Page B

faster-than-light travel by a subatomic particle known as a neutrino, with some going as far as claiming ‘Einstein was wrong: relativity theory busted.’ Startling stuff. If it’s true, then time travel – the stuff of science fiction – may be for real. The scientists responsible for the experiment and analysis let slip that they have some preliminary data that suggests that these particles travel faster than light, but they seem to be the only ones not jumping to conclusions just yet. The team at the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) in Gran Sasso, Italy – a laboratory sheltered from cosmic rays 1.4km beneath Gran Sasso, the highest peak of the Apennines – regularly detects neutrinos emitted from the Large Hadron Collider (LHC) in Switzerland, 730km away. Neutrinos, which are electrically neutral subatomic particles, are indifferent to the presence of trivial things such asEarth and zip through without so much as a passing interest. Owing to their small mass they should do so at approximately the speed of light ( c ), the speed light travels in a vacuum, known quite well to be 299,792,458 metres per second.
    Using GPS timing and position data, the OPERA team claims to know the distance between the point at which neutrinos are emitted from the LHC and the point at which they are detected in Italy to a precision that allows them to predict the neutrino’s arrival time to within 10 nanoseconds (a nanosecond being a billionth of a second).
    What they claim to have found, though, is neutrinos arriving 60 nanoseconds (0.00000006 seconds) early. If accurate, this would be a six standard-deviation result – enough to convince physicists that something is genuinely awry. The scientists concerned have released the findings to the scientific community in the hope that, if something has been overlooked, it will be picked up by their peers. The peer-review process is usually quite efficient at eliminating likely sources of error, and in this case there are plenty of possibilities. But on the face of it, it seems the OPERA team has been very careful.
    There’s the issue of knowing the exact positions of the source and detector to within the quoted uncertainty – keeping in mind that in the extra 60 nanoseconds the neutrinos are supposedly travelling, they will cover a total of 18 metres. This means knowing those two positions – and the geodesic distance between them (the ‘straight’ line they follow is actually a straight line in curved space thanks to General Relativity and the mass of the Earth) – to within 3 metres out of 730,000 metres. Though traditional civilian-grade GPS has an accuracy of about 15 metres, the OPERA experiment used the top-of-the-range technology known as ‘carrier phase tracking’, which offers better than 1 centimetre accuracy over 730,000 metres. However, it still requires the GPS antenna to be above ground, so one also needs to take intoaccount the timing for signals to travel along wires to the underground experiments. For this purpose, the OPERA scientists also made use of a cesium atomic clock. Overall, the accuracy they achieved was 20 centimetres out of 730,000 metres – well within the required range.
    Presuming for now all the possible sources of error are accounted for, what would this result mean? Time-travel seems to be the go-to topic when faster-than-light particles are mentioned, but don’t hold out hope for a TARDIS just yet.
    If a particle is able to travel faster than c , a few odd things happen. Critically, it breaks special relativity , which states that there’s an absolute speed limit – the speed at which massless particles travel – that doesn’t depend on relative motion. One practical aspect of special relativity is that the concept of ‘simultaneity’ – two things happening at the same time – is frame-dependent. If two events occur at the same