The 50-year quest to find the particle that almost broke physics

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Physicists have made many world-changing discoveries, from the discovery of X-rays in 1895, which transformed medicine, to experiments in the 1920s that verified quantum mechanics and enabled modern computing. It isn't always useful in the real world for physicists to come up with new ideas. If there is one discovery that epitomizes the idea of curiosity-driven research with no eye on practical applications at all, it is the 50 year quest to find the neutrino.

There was a mystery surrounding a type of radioactivity. Physicists in the early 1900s used rudimentary detectors and dangerous substances to find evidence of decay. This was very worrying. One of the most tightly held laws of physics is the idea that the total amount of momentum in a system is unchanging. The first object in an atom is the atom. There are two objects after that, one of which is the atom. A simple two-body system that uses projectiles should have a predictable, unique value because of the law of conserved momentum. The two other types of radiation, alpha andgamma, obeyed the law, but in the case of alpha radiation the energies were random and unpredictable. Anyone who did an experiment like that couldn't get the data to come out.

The physicists had differing opinions on what was happening. Some contemplated throwing out the idea of momentum conserved, or at least sneaking around it by suggesting that on the tiny scales inside atoms, energy might only be conserved on average. Wolfgang Pauli was unable to put the mystery to rest. Pauli was known for his critical and rational approach, which earned him the nickname the "Scourge of God" He wasn't happy with the suggestion of physicist Peter Debye who told him not to think about beta decay at all It made the situation worse when Pauli came up with a theoretical solution. He admitted to doing a terrible thing. A particle can't be detected.

The neutrino was presented to other physicists in a letter by Pauli. He wondered if a tiny neutral particle was carrying the energy. He told his addressees that he didn't want to publish anything about it. It was almost impossible for these particles to show up in an experiment because of Pauli's predictions.

The theory of the new particle was submitted to the journal Nature. It was rejected because it was too far away from reality to be of interest to the reader. They were able to do it through quantities of lead so thick that it would be measured in a few years. If a particle can't be detected so it can't be verified, what use is it? It was mostly ignored by experimentalists for a long time.

The problem sat there for 20 years. The Los Alamos Laboratory in New Mexico decided to go after the elusive neutrino in the 1950's. He found a colleague who was willing to work with him. Cowan was more measured, less outgoing, but still a brilliant experimentalist. The core team of five gathered in a stairwell around a cardboard sign with a logo of a staring eye and the words "Project Poltergeist" on it. One of them held a broom in the air behind the sign. Their proposed experiment involved building an enormous tank, filling it with extremely well-filtered and prepared liquids, surrounding it in delicate electronics and hoping that they would be able to catch a particle that wasn't visible.

The results of the initial shoestring budget experiments were not very good, so they decided to move their experiment underground to avoid the effects of cosmic rays. The owner of the site allowed the physicists to set up their experiment in the basement. The name Project Poltergeist was changed to the Savannah River Neutrino Experiment in the late 1950's. The set-up had grown to a three-layer sandwich of liquid and detectors, its rectangular tanks weighing in at a staggering 10 tonnes. The detector was shrouded in layers of wax and concrete shielding while electronic cables carried signals to a trailer outside.

The experiment was on the river. After all the chemistry and electronics were worked out, it was all down to the collection of data. The researchers were filled with hope every time they saw the characteristic signal of two flashes 5 microseconds apart. Their eureka moment came slowly, but surely, until there was no doubt left. There were five times as many signals when the reactor was on as there were when it was off. Against the odds, they were able to design a system that could catch a few each hour and measure the interactions between the particles.

Twenty-five years after Pauli predicted a particle wouldn't be detected, the team achieved the impossible. They sent a telegram to Pauli, who interrupted the meeting he was attending at the particle physics laboratory in Switzerland to read it out loud. It's believed that Pauli polished off an entire case of champagne with his friends, which might explain why his reply telegram never made it to the two men. It said that everything came to him who knew how to wait.

The chargeless and almost massless neutrino is like a small particle that doesn't interact with anything. We have no use for the particles in our daily lives. The electron didn't seem to be useful at first, and its discovery wasn't aimed at telecommunications and computing Medical isotopes or to treat cancer weren't invented by particle accelerators. The discoveries weren't always intentional and no one was eagerly waiting for them. The knowledge we have gleaned from them is important and there are a few possible applications in the future.

The first use of neutrinos was for physicists. Experiments showed that our sun is one of many sources of neutrinos. A new field of astronomy was created in 1987 after multiple experiments detected a new type of particle. Our knowledge of nuclear physics, required for fusion reactor, which may provide abundant electrical energy on Earth in the future, was solidified by our understanding of how neutrinos form in the sun. One day, we may be able to use neutrinos to teach us how the particle accelerators work, as they may be able to give us a mechanism to copy in our own.

A new experiment called Watchman is being built in the Boulby mine in the north of England. A neutrino detector will be used in this project. The project could provide a unique contribution to global security by creating a reliable way to check whether a reactor complies with non-proliferation treaties. There is no way to hide a nuclear reactor from a detector like this.

There could be direct applications of neutrinos in the future. One day, neutrinos could become a kind of Cosmic messaging because of their ability to cover vast distances at almost the speed of light.

There is a system If there are any advanced civilisations out there living on one of the thousands of exoplanets that we have discovered, it is possible that they communicate with each other using neutrinos. The MINERvA experiment is a study of v-A interactions. The researchers sent a beam of neutrinos through half a mile of rock and were able to decode it again. This could be useful for submarine communication on Earth, for example, where radio waves are distorted by obstacles. They could communicate in a direct line through the center of the earth with the use of neutrinos.

It is fair to say that neutrinos are not ready to be used yet. We can't predict the future, but we can say that the outcome of our quest to understand them has contributed to our lives. The SNO observatory is located in a deep underground laboratory in Canada and has now been expanded and renamed SNOLAB. They mean it when they say that the laboratory is twenty times deeper than the Large Hadron collider. The air pressure goes up by 20 per cent as you descend in the lift, which feels a lot like descending in an airplane.

Particle physicists are not the only people in the lab. It opened up a lot of possibilities in other areas of science. The laboratory is so deep in the earth that it has a low level of background radiation from the sun. A broad research programme looking at the impact of low radiation levels on cells and organisms has been made possible by the stable underground facility. These experiments are helping biologists understand what the impact is when you remove the background radiation that has never been exposed to land-dwelling animals.

It's important because it could answer the question of whether radiation is always bad for cells and organisms, whether it always causes damage, or if there is a threshold level of radiation which is harmless or even beneficial to life. It's possible that evolution is influenced by radiation. The results seem to show that life needs less radiation. It has enormous implications not only for humans and our interactions with radiation, but also for our understanding of life elsewhere in the universe. We couldn't do this research without deep underground laboratories.

SNOLAB is one of the best places on the planet. Experiments on quantum computers are being planned. The time when a quantum bit can store information before it is lost is known as the decoherence time. It is possible that quantum computers will be underground in the future. This development work can only be done in the laboratories.

The neutrino has been described as a ghost, a messenger, a spaceship, and a little something. It began as an apology to save a basic law of physics and went on to lead to enormous payoffs in astronomy, geology and our most fundamental understanding of matter. We still don't know why neutrinos have a tiny mass, even though we've learned a lot about them.

The matter that makes up stars, galaxies and us is a billion times less abundant than the neutrino. Experiments and theorists alike have been driven to uncover its secrets due to it. The neutrino is one of the best sources of knowledge gaps in physics. We are yet to discover a lot about our universe.

The Matter of Everything: Twelve experiments that changed our world is available in the UK, Australia, and the US and Canada.