Ringing the neutrinophone
For years theorists have mused that neutrinos’ signature unwillingness to interact with matter might be harnessed to dispatch messages directly through the Earth’s core, to submerged submarines or even across galaxies, which are impervious to traditional electromagnetic signals. In a paper just submitted to Modern Physics Letters A, MINERvA’s boffins demonstrate that such proposals, though wacky, are not completely outlandish.
MINERvA uses a beam of neutrinos sent from Fermilab’s accelerator, the Main Injector, to a detector roughly 1km (0.6 miles) away. The beam is created by smashing pulsed bunches of trillions of protons into a graphite target. For a week before the start of a maintenance break, however, it runs at half its typical intensity, not ideal for MINERvA’s day job, but just dandy for the communications test. (The data collected are nonetheless used for MINERvA's everyday research.)
The detector (pictured above) is hidden underground to ensure that the rare events observed in it are due to neutrinos and not cosmic rays, which do not penetrate rock. As a result, the experiment’s neutrinos must travel 240 metres through the Earth’s crust, precisely the sort of thing the theorists envisaged.
The message, which read "neutrino", was transcribed into a string of "0s" and "1s" using the standard code employed in digital communications. The beam was then tweaked so that a pulse created using a full bunch of protons corresponded to a "1", while one with no protons signalled a "0". The pulses were separated by 2.2 seconds and the message was repeated in cycle for about two hours.
At the receiving end, each "1" translated into an average of 0.8 neutrino events registered in the detector; a "0", naturally, translated into none. This was enough to reconstruct the message accurately.
Practical neutrino-phones are, of course, a long way off. For a start, the data-transmission rate, at a piddling 0.1 bits per second with a bit error rate of 1%, leaves a lot to be desired, though it could be improved with a more intense beam, which would anyway be required to send messages over long distances. A bigger problem is that MINERvA’s detector, at 5 metres long, 3.5 metres high and weighing 170 tonnes, is not exactly portable. And the Main Injector is many times heftier still. All the same, who said fundamental physics has no real-world applications?
