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A network of light sensors in Siberia is on the lookout for brief, mysterious flashes in the sky.
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Deep in the Siberian taiga, there are a hundred light traps: each about the size of a small table, but together they cover a square kilometer. At night, these traps gaze at the sky, catching faint flashes of light born when cosmic particles slam into the atmosphere. The setup is called TAIGA-HiSCORE, and it usually works as a giant "eye" for such particles.
But this eye has a rare feature: all the traps are synchronized to within one billionth of a second. Thanks to this, the array can spot not only ordinary particles but also extremely short flashes of light — lasting just a few billionths of a second. Such flashes could come from distant cosmic objects that no one has seen yet.
Synchronizing a hundred traps to nanosecondprecision is like having a hundred photographers across a city press their shutters within less than the time of one sound wave oscillation.
The scientists tested the method on an artificial Earth satellite: the array caught its signal, so the technique works. Then they reviewed data from the winter of 2018–2019 and found one pair of flashes that could have come from a single source. But the probability that it was just a random coincidence from ordinary particles turned out to be no less than ten percent. That's too high to confidently claim a new phenomenon.
But now we know the limit: flashes brighter than a certain threshold and longer than five nanoseconds occur no more than two thousandths of an event per square degree of sky per hour. That's like saying that in a big city, you'd see no more than one such flash per hour over an area of a few football fields.
For now, the mystery remains: the sky is silent, but the traps are ready. Every clear night, a hundred light eyes in the taiga keep looking up, and maybe one day they'll catch a real flash from deep space.
The hundred light traps of TAIGA-HiSCORE are synchronized more precisely than the clock in an ordinary smartphone: the difference between them is less than one billionth of a second.
