Who’s afraid of neutrinos?

Who’s afraid of neutrinos?

The India-based Neutrino Observatory would greatly advance scientific research

Which one of us would not have applauded Galileo in January of 1610 when he trained his telescope for the first time on Jupiter and observed four dots alongside it? Within days he noticed that the dots seemed to be going around Jupiter... they were its four largest moons!

Today, very large telescopes send us iconic images of distant galaxies and of faint remnants of the light produced by the Big Bang. The light from the moons of Jupiter was always falling on earth. It took a telescope to detect it because it was so feeble and could not be seen with the naked eye. Interesting things, telescopes. They observe something that is already there. They do not produce what they observe.

Just like light

There are two other things that, like light, can travel great distances in the universe, and therefore can be usefully observed. The first of these are gravitational waves. Predicted by Einstein’s famous theory, these waves travel at the speed of light and are produced when very heavy objects such as black holes collide. Gravitational waves were first detected in September 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO). As the waves passed, LIGO measured that they expanded and contracted the earth a tiny bit for a fraction of a second. The measurement told us that the colliding black holes were 30 times the mass of the sun, 1.3 billion light years away, and during the collision, the mass of three suns just vanished to produce the energy of the gravity wave that spread across the universe. However, LIGO did not produce the waves that it observed.

They were produced by cataclysmic events, and we wouldn’t want to be anywhere near them, but observing them through LIGO is like receiving a postcard from that collapsing, tragic part of the universe that even light cannot escape from.

The only other particles that can zip through the universe at speeds very close to that of light are called neutrinos. The biggest nuclear reactor that most life on earth derives energy from is the sun. Like all nuclear reactors, in addition to giving out energy (heat and light), the sun also emits neutrinos. We have all seen sunlight. Can we also observe the billions of neutrinos the sun emits every second?

00:00

00:23

In the mid-1960s, when solar neutrinos were observed through the first neutrino telescopes, it quietly unleashed one of the biggest revolutions in our knowledge of the laws of physics that govern the universe. Raymond Davis and John Bahcall detected that only half the neutrinos that the sun was emitting towards the earth were actually reaching us.

The reason? As they travelled the distance from the sun to the earth, the neutrinos were changing from electron-neutrino type that the sun was emitting to muon-neutrino type, and thus escaping detection. All the laws and forces of nature that we know of, other than gravitation, are described by what physicists call the Standard Model. It predicted that neutrinos, which come under three types or flavours — tau-neutrino, electron-neutrino and muon-neutrino — would not oscillate from one flavour to another. The discovery that they do meant that the Standard Model or the basic laws of physics had to be further modified. Thus, through the neutrino detectors we are actually observing the fundamental laws of physics at the cutting edge.

ALSO READ

Union Cabinet clears LIGO-India gravitational wave observatory

The proposed India-based Neutrino Observatory (INO) aims to observe muon neutrinos that are continuously produced in the atmosphere when cosmic rays strike the earth. Since every type of matter particle has an anti-matter partner particle associated with it, there are also anti-neutrinos that the INO can observe. Anti-neutrinos also come in three flavours and can oscillate from one to the other. An important question in the mystery of trying to piece together the laws of physics is: do anti-neutrinos oscillate or flip their flavours at exactly the same rate as neutrinos do, or are there slight differences in their rates? In other words, do laws of physics treat matter and anti-matter exactly the same way as far as the neutrinos are concerned or do they treat them differently?

While the INO will not by itself provide an answer to this question, its measurements will — by determining the order of the neutrino masses and thereby help other neutrino experiments that are already under way or being built in other parts of the world. The INO, by observing the rates at which neutrinos and anti-neutrinos oscillate, will make a substantial contribution to the quest to unravel the secrets of the ultimate laws of physics.

Nothing to fear

Unfortunately, some activists and political parties in Tamil Nadu have made baseless allegations that the INO, which is just like a telescope, causes radioactivity and have compared it with the dangers of having a nuclear power plant or radioactive material in the neighbourhood. This cannot be true since the neutrinos, whether they are naturally occurring in the atmosphere or from the sun, or are emitted by far away man made nuclear reactors and sent in beams of neutrinos with few GeV energy, are very feeble and weakly interacting particles that we can’t even see or feel without the help of an observatory. Beams of neutrinos are being sent to the NOvA neutrino detector in the U.S. and to the T2K neutrino detector in Japan every day. Moreover, being the lightest matter particles, the neutrinos do not decay into any other particles, as everything else is heavier — so they are not like uranium which decays radioactively into smaller atoms. All the INO would do is to provide the lens to observe neutrinos as they are too feeble or faint to be detected by the naked eye. It does not create a radiation hazard or put us in harm’s way. While we should ensure that the tunnel is dug with proper environmental safeguards and the project has various clearances, raising the spectacle of radiation hazards and comparing it with nuclear or thermal power plants is spreading false fears and is unscientific.