Scientists have finally learned the mass of the tiniest elementary particle, the neutrino. Find out what this means for future studies.
In high school, I discovered an obscure Canadian progressive rock band called Klaatu. Their only real claim to fame was an urban legend that they were really the Beatles in disguise. When people found out that wasn’t true, they faded into obscurity. Although. they did release five albums and their song Calling Occupants became a hit for the Carpenters.
What attracted me to Klaatu was their science fiction motif. Their lyrics brought together cosmological ideas as we understood them then, with philosophical thoughts that helped me find a semblance of meaning in those days of typical teenage angst. What brings Klaatu to mind today is the title of one of their songs. I’m thinking of their track Little Neutrino
The smallest particles, having little or no mass
The song itself was haunting and mysterious in a progressive rock kind of way. More importantly, though, I had no idea what a neutrino was. As always, the lyrics made more sense once I found out what they were talking about. All I really needed to know to get those lyrics was that neutrinos were the smallest of all the known particles, having little or no mass.
Wolfgang Pauli first proposed neutrinos. He believed the hypothesis of neutrally charged subatomic particles explained certain kinds of radioactive decay. At first, he called them neutrons. He asserted that this “neutron” was released along with the electron during what is now known as beta decay.
Particle physics got confusing in 1932, when James Chadwick discovered the kind of neutron we learned about in high school. His idea of a neutron had much greater mass and it stayed in the nucleus of the atom along with the protons. Enrico Fermi came up with the term neutrino to distinguish between the two kinds of particles. Like the term “big bang”, “neutrino” came about half-jokingly. It started with a light-hearted conversation with Fermi’s colleague Edoardi Amaldi. It is Italian for “the little neutral one”.
They detected neutrinos in a gold mine.
According to Fermi, during beta decay, a neutron breaks down. This leaves a proton behind and releases an electron and a neutrino. The scientific community did not accept his theory at first. Even so, later experiments vindicated him. By 1956, a team of researchers detected Fermi’s proposed neutrino particle. The team received the Nobel Prize for Physics in 1995. In 1965, another research team proved that neutrinos exist in nature. They detected them in the depths of a South African gold mine.
As mentioned above, scientists believed that neutrinos had little or no mass. Then, in 1998, a team of researchers proved that neutrinos do have a minute mass. This was another Nobel prize winning achievement in 2015. Even so, the Standard Model in nuclear physics still does not assign a specific mass to the neutrino.
We’ve reached a stage in our understanding of cosmology where it challenges us at the level of the very large and the very small. Which brings us to a discovery that researchers at University College London. Universidade Federal do Rio de Janeiro, Institut d’Astrophysique de Paris and Universidade de Sao Paulo have just announced. The team published their results in the journal Physical Review Letters last week.
Largest objects can tell us about the smallest objects
As Professor Ofer Lahav, a co-author of the study said, “It is impressive that the clustering of galaxies on huge scales can tell us about the mass of the lightest neutrino, a result of fundamental importance to physics.” The largest objects in the universe can tell us about the smallest objects in the universe when we learn to work across disciplines.
I learned from that 70s progressive rock song that neutrinos were unimaginably small. What these researchers have determined is almost impossible to grasp. They have concluded that a neutrino’s maximum mass is six million times less than an electron. Its minimum mass may well be zero. To put this in perspective, an electron has roughly 2,000 times less mass than a neutron. Doing the math, we find that a neutrino is 12 billion times smaller than a neutron. When Fermi and Amaldi called it ‘the little neutral one”, they made the understatement of the century.
The methodology behind this study gives us some telling insights into how scientists will work in future studies. The team took an interdisciplinary approach, combining discoveries from cosmology and particle physics and powering their work with the latest computing tools.
Half a million computing hours
They collected data on 1.1 million galaxies to measure the rate of expansion of the universe. Then they applied the latest discoveries from particle accelerators to determine what the expansion constraints would be. This required computing power that has never been available before. The data crunching took half a million computing hours to complete. My laptop would take 60 years to get this done.
Knowing the maximum mass of a neutrino is an important piece of the puzzle in working out the story of the universe and our place in it. In earlier stories, we have touched on the mysteries of dark matter and dark energy. Projects like the Dark Energy Spectroscopic Instrument (DESI) and Euclid will be more effective as a result of this discovery. We will never be able to tell our new, science-based creation story until we have explained what dark matter and dark energy are and how they work. The neutrino’s mass may be the key that unlocks that mystery so that we can learn more.
We always have more to learn if we dare to know.
University College London
Upper Bound of Neutrino Masses from Combined Cosmological Observations and Particle Physics Experiments
The 5 Big Questions We Need Cosmology to Answer