Riding g-waves into the early universe

Last week’s announcement by an international consortium of research bodies (NANOGrav) that there is now conclusive evidence of gargantuan gravitational waves coursing through the universe has confirmed a century-old prediction by Albert Einstein. The first discovery of gravitational waves was made by the LIGA research project in the US in 2017, for which the project’s founders won the Nobel Prize.

Gravitational waves are ripples in space-time caused by huge cosmic events, such as a clash of two black holes. Every cosmic event causes them, but bigger events cause bigger waves. LIGO’s signals were mostly in the frequency range of a few hundred hertz and were created by individual pairs of black holes or neutron stars that were up to 100 times as massive as our sun.

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But the gravitational waves now discovered have frequencies less than one-billionth of a hertz, and therefore bigger wavelengths, and emanate from thousands of pairs of supermassive black holes, each as massive as a billion suns, up to 10 billion light years away.

Everything about the universe is esoteric and beyond imagination, and humans can express them only in terms of their experience. Scientists have described the gravitational waves as a ‘hum’ reverberating across the universe, and as a huge choir or orchestra with each pair of black holes generating a different note, though we are receiving the sum of all the notes at once.

They hope the gravitational waves will help them to understand the state of the early universe after the Big Bang, and its subsequent evolution. There is also a view that they can lead to hypothetical phenomena like cosmic strings and wormholes. These waves give us a new, better and more subtle tool to observe the universe than all others we have. Some research institutes in India also had a role in the international effort.

It will take many years to analyse the data and decode the cosmic music that has been detected. Our knowledge of the universe has expanded over centuries, but we still do not know much about it and are blind people looking for a black cat in a dark room. It might be that we are too ambitious in thinking that we will comprehend it, but the very fact that we are part of it gives us reason to peer far and wide and into the past. Gravitational waves have excited the scientific community because they can take them to that time and space where no telescope, mathematical abstraction or poetic imagination has gone till now. Meanwhile, the European Space Agency has just launched its Euclid space telescope to ‘see’ what hasn’t been ‘seen’ thus far – dark matter and dark energy.