Why, after millions of years of steadily lighting the cold darkness, does a supergiant star suddenly explode in a blinding blaze of glory brighter than 100 billion stars? What exotic objects in deep space are firing out particles at by far the highest energies in the universe? And perhaps most mind-bending, why does the universe contain any matter at all? These mysteries have vexed astrophysicists and particle physicists for decades. The key to solving all three deep conundrums is itself one of the greatest enigmas of physics: the neutrino.
The universe is awash in these peculiar, nearly massless, subatomic particles. Created in tremendous numbers right after the Big Bang, and constantly churned out in stars and other places by radioactive decay and other reactions, trillions of these ghostly particles sail right through stars and planets, including our own.
Carrying no electrical charge, neutrinos are attracted neither to protons nor electrons, so they don’t interact with electromagnetic fields. They also don’t feel a powerful force that operates on tiny scales, known simply as the strong force, which binds protons and neutrons together in an atom’s nucleus.
Neutrinos are more aloof than supermodels, rarely interacting meaningfully with one another or with anything else in the universe. Paradoxically, it is their disengaged quality that earns them a crucial role both in the workings of the universe and in revealing some of its greatest secrets.
Neutrino physics is entering a golden age. As part of one experiment, neutrinos have recently opened a new window on high-energy sources in deep space, such as black holes spewing out particles in beams trillions of miles long.
Another astronomy experiment deep underground in a Japanese mine will use neutrinos to learn the average temperature and energy of ancient supernovae to better understand their typical behavior. And physicists are using computer modeling to close in on the neutrino’s critical role in triggering the kind of supernovae that distribute essential elements like oxygen and nitrogen.
Beyond expanding the role of neutrinos in astronomy and uncovering their role in astrophysics, physicists are still trying to discover some of the neutrino’s basic properties. Some researchers, for instance, are trying to pin down the particle’s possible masses.That fundamental information would influence theories that explain the masses of other particles.
By determining yet another elusive fundamental property of neutrinos, researchers also hope to answer one of theoretical physics’s great riddles: why all the matter and antimatter created by the Big Bang didn’t cancel each other out and leave nothing but energy. At the dawn of the universe, for every particle of matter, such as an electron, there was an anti-electron; for every quark (a fundamental constituent of matter), there was an antiquark, explains physicist Chang Kee Jung of Stony Brook University. When these opposites meet, they should annihilate each other, creating pure energy.
So why is any matter left? The most plausible solution, leading physicists like Jung say, hinges on the theory that today’s neutrinos, which have barely any mass, once had superheavy partners. These neutrino cousins, 100 trillion times more massive than a proton, formed in the tremendous heat that existed right after the Big Bang. They had the special androgynous ability to decay into either matter or antimatter counterparts. One such overweight particle might have decayed into a neutrino plus some other particle — like an electron, for instance — while another superheavy neutrino might have decayed into an antineutrino and another particle.
For this theory to explain why matter exists, those early superheavy neutrinos would have had to decay more frequently into particles than antiparticles. Physicists at neutrino detectors such as NOvA in Minnesota, in addition to trying to determine the masses of the neutrino, are studying whether today’s lighter neutrinos switch from one type (or “flavor”) to another at a different rate than antineutrinos. The same theory that could explain this behavior in today’s light neutrinos could also explain the inclinations of superheavy neutrinos at the dawn of time. If the superheavy neutrino theory is correct, then these primordial particles are the “supreme ancestor” from which every particle in the cosmos descended.
Neutrino-related discoveries have already earned three Nobel prizes, and the path-breaking experiments underway could well earn more tickets to Stockholm. The seemingly superfluous neutrino couldn’t be more essential to our understanding of the cosmos, or less concerned with its profound importance.
The Ice Telescope Cometh