Yes, but what are neutrinos <i>for</i>?
Seven schemes for putting an elusive particle to use
Twenty-eight flashes of blue light may not seem like much to crow about. But for hundreds of scientists long in their pursuit, witnessing these faint flickers over the last two years has been a cause for celebration, because they mark the arrival of ghostly messengers called neutrinos from the far—and incredibly violent—corners of the universe. Last week, researchers reported in Science that IceCube, a novel observatory made of some 5,000 sensory orbs strung on 86 steel cables and buried more than a mile deep in the Antarctic ice, has been registering about one energetic neutrino originating from beyond our galaxy each month.
In fact, neutrinos, a type of elementary particle with no electric charge and very little mass, are all around us. Many trillions of them, produced in the sun’s nuclear core, zip right through our bodies every second of day and night. Luckily, they do no harm and leave no trace. That’s because neutrinos hardly ever interact with other particles: A typical neutrino can traverse the Earth, or even a light-year’s worth of lead, without bumping into an atom. Their severe reluctance to mingle makes neutrinos hard to pin down, so scientists have to build mammoth (and expensive) detectors like IceCube to trap just a few.
Why are neutrino hunters going to so much trouble? Neutrinos, produced in nuclear reactions and traveling at nearly the speed of light, zip away with little impediment, bringing scientists valuable information from the place of their birth. Neutrinos have already taught physicists a great deal about the subatomic realm, and given astronomers a way to test their calculations of the reactions at the scorching heart of the sun. Back in 1987, neutrinos were the first harbingers of the dramatic demise of a massive, bloated star in a satellite galaxy of the Milky Way. Soon, with more detections and better statistics, the IceCube researchers expect to pinpoint the cosmic particle accelerators, likely powered by black holes or dying stars, that propel energetic neutrinos like the 28 they have already nabbed.
That may be just the beginning. Some have suggested, with varying degrees of seriousness, that neutrinos could be used not only to probe the extremes of space but for more pragmatic, down-to-earth purposes. Their proposed schemes range from the perfectly sensible to the rather outlandish, and some require much better technology for producing and detecting neutrinos than is currently available. But if these visionaries turn out to be right, the esoteric and cagey neutrinos might be of interest not just for physicists chasing Nobel Prizes but also for nuclear monitors, mineral prospectors, and maybe even traders looking to make an extremely fast buck. Herewith, a brief guide to what neutrinos could help us do next.
FUTURE USES FOR NEUTRINOS
★ ★ ★ ★ ★ Expect it
★ ★ ★ ★ Likely
★ ★ ★ Could happen
★ ★ Don’t hold your breath
★ Only in science fiction
It has been over four centuries since astronomers have seen a supernova in the Milky Way. If a star explodes in the far side of the galaxy, interstellar dust would obscure our view—but the neutrinos would come through unhindered, with modern detectors giving us an unprecedented peek at the action.
Plausibility: ★ ★ ★ ★ ★ We have the technology, but nobody knows exactly when the next galactic supernova will occur.
Part of our planet’s internal heat comes from the decay of radioactive elements—but we don’t know exactly what fraction. Since radioactivity also releases neutrinos, measuring them could tell us how much uranium and thorium are in the Earth’s crust and mantle.
Plausibility: ★ ★ ★ ★ Scientists have already detected so-called geoneutrinos, and the next generation of neutrino detectors could help zero in on the answer.
There should have been equal amounts of matter and antimatter right after the Big Bang. But today’s universe consists overwhelmingly of matter. Physicists believe the behavior of neutrinos could reveal why.
Plausibility: ★ ★ ★ Likely to require decades of research.
Nuclear reactors and nuclear bombs release staggering numbers of neutrinos, so international monitors could rely on them for surveillance and help prevent proliferation.
Plausibility: ★ ★ ★ There are designs in hand and a prototype that’s been tested, but current detectors are unwieldy and difficult to deploy.
Some scientists have proposed that intense beams of neutrinos could be used to probe the Earth’s crust, sort of like how dentists use X-rays to scan teeth for cavities.
Plausibility: ★ ★ Need much stronger neutrino beams and much more sensitive detectors.
One researcher has suggested linking the world’s financial centers using encoded neutrino beams that take shortcuts through the Earth, giving high-frequency traders a time advantage of up to tens of milliseconds.
Plausibility: ★ Could be an interesting scenario for a Hollywood thriller.
Since neutrinos travel freely through space, proponents argue that they would make terrific messengers between advanced civilizations across the galaxy.
Plausibility: ★ Clever idea, but the energy cost of producing a sufficiently powerful neutrino beacon might be prohibitive.
Ray Jayawardhana is an astrophysicist and author of the new book “Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe” (Scientific American/Farrar, Straus & Giroux). He will be speaking at a Museum of Science author salon in Cambridge on Wednesday, Dec. 11.