• 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?
• 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.

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.

• 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?

Source:TH