Kip and Gravitational Waves

This story begins in 1915, during the First World War, when Albert Einstein, already recognized as one of the major physicists of his time, publishes the equations of his strange theory asserting that the space in which we are immersed can be deformed like hard rubber.

He also adds immediately that it could vibrate like the string of a violin or an iron rod, and in doing so transmit waves. Shortly after its publication, however, he changes his mind and writes an article rejecting the existence of such waves. Then he changes his mind again and writes a further article to say that, yes, they should exist after all.

For decades, physicists are confused and debate the reality or non-existence of gravitational waves. Richard Feynman subscribes to the idea that they are real. Others disagree: if space vibrates, we vibrate with it and yet do not notice it …

The matter is clarified only in the sixties, forty years after Einstein’s doubts: an Austro-English theorist called Hermann Bondi demonstrates that, theoretically, it is possible to boil a small saucepan of water with gravitational waves, and finally everyone is convinced. The theory predicts that space can transport vibrations similar to electromagnetic ones: ripples in space like those made by the wind on the surface of a lake.

Once this has been clarified, the question arises as to whether these waves can be observed in reality, actually running throughout interstellar space. An American physicist, Joe Weber, constructs an enormous metal cylinder with the idea that waves from space might cause it to vibrate – and he becomes convinced that he has witnessed precisely such vibrations. But he does not manage to convince anyone else, and ends up increasingly isolated and irascible. By now, though, research into the question is fully under way.

Italy is at the forefront of this research. Eduardo Amaldi, the father of the great Roman school of Physics, senses the importance and the viability of the enterprise and promotes the Italian line of research to detect these elusive waves. Prototypes of antennae are built in Italy – first in Frascati, then later in Legnaro near Padua. They pursue Weber’s idea, using large metal rods, but they also explore other ideas.

I remember as a young man, a young, aspiring student of physics, being shown by Massimo Cerdonio and Stefano Vitale in the physics department in Trento an oscillating tin with a superconducting ring inside it: the prototype of another idea for an antenna. Massimo Cerdonio went on to build the antenna at Legnaro; Stefano Vitale now leads the path towards the most spectacular international project of gravitational antennae envisaged for the future: LISA, a composite antenna made up of satellites in solar orbit …

But it finally became clear that the most promising technology for detecting the waves are the ‘interferometers’: two lasers at ninety degrees to each other which compare the lengths of two perpendicular arms. If a wave passes, one arm lengthens and the other retracts, allowing the wave to be seen.

One after another, in different countries, projects are launched to construct prototypes of similar antennae, but the sensitivity required from them is spectacularly high, way beyond the capacity of our available technology. We need to measure variations in length much smaller than an atom, over distances of kilometres. In the early nineties I was a young professor in America when Richard Isaacson came to Pittsburgh, where I was working. Richard was at the time responsible for gravitational physics at the National Science Foundation, the American agency that assigns funds for scientific research. He was in the process of making up his mind whether to invest funds in gravitational waves. The project that was being proposed aimed to detect waves within five to ten years. The two of us had dinner in a small Indian restaurant. He asked my opinion. I said that the science was sound and the project was fascinating, but like many others I was perplexed – the waves are weak, and before the technology will be capable of detecting them a considerable amount of time might have to pass. I asked him why he was convinced that it was possible to get there in a reasonable amount of time. His answer was cut and dried: faith in Kip Thorne. Kip is one of the best relativists in the world. He works at Caltech, is a world expert on black holes, neutron stars and other wonders of the universe where catastrophes of such extreme violence occur as to rock space and permit ripples of the events to reach us.

A few years later I meet Kip at a conference in India. We’re sitting next to each other on a bus that is returning us to the hotel after the conference dinner. I ask him what gives him the confidence to convince Isaacson that we could detect gravitational waves. Kip pauses for a while before answering, looking me straight in the eyes. The Indian night is rushing past us. He says, ‘Don’t you think that we should at least try?’ And I realize how high the stakes of a great poker hand in science are.

Kip now has a Nobel Prize. I reminded him of this conversation last year, after the detection had been made. His response was instant: it wasn’t thanks to him, he just put his faith in Rainer Weiss and Barry Barish, spectacularly gifted experimenters.

Twenty-five years have passed since my dinner with Isaacson; twenty since my conversation with Kip on an Indian bus. The poker game was an arduous one. It was the lifework of dozens and dozens of colleagues. We won.