The life of the neutrino as we know it began amid personal chaos. Its existence was first postulated by Wolfgang Pauli, a brilliant but troubled Austrian physicist who at 20 wrote a definitive, 200-page book on Albert Einstein’s theory of relativity that Einstein himself admired, and at 25 proposed his “exclusion principle,” a fundamental statement on the behaviour of matter at the subatomic level that later earned him a Nobel Prize. Colleagues called him “God’s whip” and the “conscience of physics” for his ferocious skepticism and probing, often devastating questions. Yet he was also a prodigious drinker and carouser who, while lecturing at the University of Hamburg, was on intimate terms with the Reeperbahn, that city’s notorious red light district, and who suffered strange, haunting dreams.
The neutrino was perhaps Pauli’s least favourite of his contributions to modern physics. In the late 1920s, physicists examining the decay of radioactive materials such as uranium puzzled over a mysterious gap in the amount of energy they shed: they knew uranium emitted energy in the form of electrons, but when they added these electrons up they discovered that some energy was missing. Faced with this mathematical quandary, Pauli found himself forced in 1930 to accept the presence of an invisible and hitherto unknown neutral particle that could account for the loss—a ghostly spectre of the subatomic world. This was the neutrino. “It was the first time anyone ever postulated a missing particle,” says University of Toronto physicist Bob Orr. “Most people thought this was a really stupid idea.” Even Pauli himself called it a “terrible thing,” and he lamented that in proposing it he had “invented a particle that cannot be detected.” Indeed, he placed a standing bet—a case of champagne—on the notion that it never would be, outlining his ideas on the particle in a letter to colleagues that began: “Dear radioactive ladies and gentlemen.”
The improbable and bizarre dogged Pauli for the rest of his life, and have now caught up with his neutrino. Within months of penning that letter, Pauli’s marriage to Käthe Deppner, a Berlin cabaret dancer, collapsed. This, in combination with his mother’s suicide, sent him into a depressive tailspin, and he sought the treatment of Swiss psychiatrist Carl Jung. The two men became friends and embarked upon a joint obsession with the numeral “137,” both believing it a sort of code that would unlock the secrets of the universe. It is perfectly by accident that when Pauli died in a hospital of pancreatic cancer in 1958, he did so in room 137.
Therefore he was still alive in 1956, when physicists conducting tests at the Savannah River nuclear reactor in South Carolina managed to capture neutrinos for the first time, netting them in a vat of heavy water (it’s not clear whether Pauli shipped his American colleagues that champagne). Suddenly here they were—real neutrinos, however hard to discern and however puzzling.
Last Friday, that puzzlement deepened when physicists in Europe said they had repeated an experiment, conﬁrming controversial findings that were first reported in September in which neutrinos appeared to travel faster than the speed of light—an impossible result, according to our current understanding of physics, which says nothing can go faster than light.
In both instances scientists working on the so-called OPERA experiment at the European Organization for Nuclear Research (CERN) outside Geneva generated blasts of neutrinos and sent them south, through the rocky subterranean precincts beneath the Alps, then high into Italy’s Apennines mountains, where, near the city of L’Aquila, they popped up in a neutrino detector at the underground Gran Sasso National Laboratory—a distance, all told, of some 730 km. The latest OPERA findings appear to back those earlier results—the neutrinos arrived a shocking 60 billionths of a second or so faster than a beam of light.
Should that result hold up, physicists will either have to scrap Einstein’s theory of special relativity or accept a range of phenomena now confined to science ﬁction—for example, that an observer travelling past a swift-flying neutrino would witness the particle hurtling backwards in time and appear at its destination before beginning its journey. The confirmation, made by scientists working on the collaborative OPERA experiment, generated enormous international chatter among physicists, who remain skeptical of the results but who must nevertheless contemplate what it would mean if a faster-than-light, or “superluminal,” neutrino proves real. Such a development would upend everything we know about the concept of “causality,” opening up the possibility of time travel at the subatomic level, and even suggesting the existence of new, hitherto unknown dimensions. More than that, it might require us to contemplate the possibility of wormhole portals connecting a Geneva suburb with the mountains of central Italy. “It would be the most dramatic thing since Newton discovered universal gravitation,” says Orr.
Superluminal neutrinos would threaten to overthrow Einstein’s theory of special relativity, propounded in 1905, because in it Einstein established the speed of light as an absolute constant that’s fundamental to the workings of our universe. So far, special relativity has survived a century of scientific discovery and has become critical to our understanding of everything from astronomy to modern electronics—even to navigation systems like GPS. Its loss would be a major blow.
Indeed, the original OPERA findings were so astonishing that physicists worldwide dismissed them as fantastical, reflective of some underlying error in the experiment. Even some scientists in the OPERA collaboration (these endeavours have grown so complex and costly that large groups are increasingly the norm) refused to sign the draft paper drawn up after the experiment—an unusual display of internal dissent. An OPERA spokesman has reportedly said that all 200 of the participating scientists from 13 countries signed the draft following the second experiment, which improved upon the first by ruling out what critics felt must be the source of the September results: the bursts of neutrinos emanating from CERN were so long that the margin of error could have explained the perplexing results. And still there is skepticism (despite what the OPERA spokesman claims, the neutrino rumour mill among physicists over the past weekend held that, while scientists who did not sign the OPERA draft in September did sign the second, others who signed in September have now opted out).
For many physicists, the prospect of a superluminal neutrino is too much. “The most likely hypothesis was originally, and still is, that the experiment is wrong,” says Lee Smolin, a theoretical physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Ont., and the author of The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next. “Of course, the experiment has the last word. If it is true it’s the most important experiment of our lifetimes.”
Still, bearing all the caveats against ditching Einstein in mind, it must be said that of all the creatures of the subatomic world, the neutrino is the most likely candidate to change how we think about the universe. We know less about it than any other particle, so mysterious, hard to observe, and strange is it. They are invisible, nearly weightless, shape-shifting things that, unlike electrons, their subatomic cousins, have no electric charge. Neutrinos therefore have little impact on the things they meet upon their travels—so feeble are their interactions with matter that they can pass through lead as easily as moonlight through a window. Generated by the decay of radioactive elements or nuclear reactions—such as occur during supernovas and in the core of the sun—they are likely among the most numerous subatomic particles in the universe and are constantly streaming down upon us, then through us like ghosts.
They have long been thought fast—just a hair slower than light, according to previous orthodoxy, as well as according to measurements taken during a shower of neutrinos that rained down upon Earth in 1987 as a result of a distant supernova.
Neutrinos can be as new as those generated in nuclear energy reactors or as old as the Big Bang itself, which scattered remnant neutrinos across the cosmos. All this makes understanding them crucial to our understanding of how the sun’s innards work, how stars die, and how the universe was born. “There’s all sorts of things that we don’t understand about the cosmos,” says Mark Chen, a neutrino physicist at Queen’s University and director of the SNO+ experiment at the Sudbury Neutrino Observatory in northern Ontario. “In our quest to understand the fundamental laws of nature, neutrinos play a big role despite their small size.”
Yet they’ve remained maddeningly unknowable. “You need to produce astronomical quantities of them if you want to see any,” says University of Toronto experimental particle physicist Pierre Savard, who works on the ATLAS particle physics experiment at CERN. Herein lay the major hurdle for the OPERA scientists, who have toiled for two months to rework their experiment and test their earlier result. In both cases the experiments began with the OPERA group at CERN shooting photons—particles of light—into the great coil of the complex’s particle accelerator. Carefully aimed into Italy, the photons then collide with a graphite target to produce a shower of charged particles, which in turn decay into neutrinos. These particles continue on the same trajectory through the Earth to the Gran Sasso lab, where some leave traces of their arrival in bricks of photographic emulsion film interwoven with lead plates. Because scientists must bombard Gran Sasso with copious quantities of neutrinos just to capture a handful, measuring their speed is like clocking the departure and arrival of a herd of cats (with all the headaches of measuring down to the billionth of a second and of synchronizing watches between Geneva and Gran Sasso). Now the cats have been corralled and the results are the same—that the neutrinos arrived in Gran Sasso sooner than light could. Sooner, in other words, than they really should have.
In conversation, physicists wondering at the experiments from afar are almost too abashed to discuss what it would mean were the findings corroborated or refuted—as they may soon be at the Fermilab in the American Midwest. Dump relativity? “That would have serious impacts on your and my ability to even speak,” says physicist Charles Dyer, of the University of Toronto. “If special relativity is incorrect then issues of causality would raise their ugly heads—we could do some very fancy things, like going back in close time, and we could have statements like ‘A’ and ‘not A’ being both true at the same time.”
Yet it may also turn out both that the experiment’s results are correct and that neutrinos are still sticking to Einstein’s speed limit. “Another possibility,” says Savard, “is invoking extra dimensions of space. Maybe the neutrinos are not necessarily going faster than the speed of light, but taking shortcuts.” Savard stops himself, exclaiming of the OPERA experiment: “It’s an interesting result, but we will need much stronger experimental confirmation before we start speculating as to what this could mean.” Chen, the Queen’s prof, who is on sabbatical at Oxford, is less circumspect—and almost giddy. “Maybe neutrinos are travelling through wormholes and other dimensions—taking a shortcut—so then by travelling through this wormhole, not only can you violate causality but it enables you to travel in time and generate effects before their cause. So all of that science fiction is connected to this observation. And that’s what makes it fun.”
Wolfgang Pauli’s “terrible thing,” the poor neutrino, sure has travelled far.