I'll ring you back on the mobile

ON A normal day physicists from the MINERvA collaboration based at Fermilab, America's main particle-physics facilty, near Chicago, study neutrinos in the hope of unlocking the mysteries of the universe. In their spare time, though, they decided to test an idea that is (slightly) more down to Earth. 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.