It has been an exciting twelve months for those of us working on Einstein’s theory of gravity, general relativity. In November 2015 we celebrated the centenary of the publication of Einstein’s general relativity paper. Just a few months later, we learnt that one of the great predictions of his theory, gravitational waves, had been discovered by the LIGO experiment.
Gravitational waves are ripples in spacetime. Whenever heavy objects accelerate they produce gravitational waves, just as boats cause ripples as they move through water. However, these ripples in spacetime are extremely small. The gravitational waves produced in our Solar system are so small that they would only ripple the surface of the Earth by sub-atomic distances. Experiments like LIGO aim to detect gravitational waves produced by some of the most violent and energetic processes in the Universe.
Black holes are one of the best candidates for gravitational wave observations. A black hole is an object that is so small and heavy that not even light can escape from its intense gravitational field. Black holes have been a staple of science fiction for at least fifty years but were actually found as mathematical solutions of Einstein’s equations much earlier – in 1916, soon after the theory of general relativity was published.
Whenever two black holes crash into other, they merge to form a larger black hole. The process is so violent that huge amounts of gravitational waves can be produced during the merger. In September 2015 LIGO observed gravitational waves from a collision between two black holes that occurred around a billion years ago. In just a few milliseconds gravitational waves with three times the energy of our Sun were produced.
Astronomers still don’t know how many black holes exist and how often they collide with each other since black holes cannot be seen with standard telescopes. Following its first detection, LIGO has seen gravitational waves from other black hole collisions and LIGO’s detections will help astronomers to understand how many black holes there actually are.
Whenever scientists give talks about black holes, we are always asked what would happen if you fall into a black hole – perhaps because black holes are so often used as a plot device in science fiction movies! According to Einstein’s theory, astronauts in a spaceship would not realise that they have fallen into a black hole until they are already deep inside.
However, in recent years Einstein’s description of the black hole surface has been challenged as it disagrees with quantum physics. There is an emerging consensus amongst scientists that the region inside the black hole is rather different than Einstein’s theory would suggest. We’re still not sure what would happen if you fall into a black hole – some people suggest that you would be immediately burnt to pieces by a firewall while others believe that your spaceship would get trapped for a long time but you might eventually escape.
We can’t measure what happens when objects fall into real black holes as we are too far away from the nearest black holes so this whole discussion may seem rather esoteric. However, thought experiments like these are important in understanding the structure of black holes, which in turn relates to how they form and how many there are.
The theory of black holes also turns out to be very relevant for understanding quantum physics in extreme circumstances. Companies such as Intel are currently developing the first quantum computers – computers that use quantum effects to process information faster than ordinary computers. Black holes are the very best quantum computers that can exist in Nature. The study of black holes can hence teach us lessons relevant to building desktop quantum computers.
On October 11 we celebrate Ada Lovelace Day. Ada Lovelace developed programmes for a computer in the nineteenth century, long before computers were actually built. Theoretical physics working on black holes are very much following in Ada’s footsteps, in carrying out thought experiments long before we can realise them experimentally.
These days science is an international endeavour and diversity of researchers’ backgrounds is crucial to progress. Unfortunately theoretical physics is a field where gender diversity is still very poor- barely 10% of theoretical physicists are women. Ada Lovelace Day is a day to celebrate women’s contributions to science but it is also a time to reflect on why gender diversity is still so poor.
Women leave science for many different reasons, not least the difficulty in combining work and home life, yet all research studies show that a diverse and inclusive workforce is absolutely essential in driving innovation. In theoretical physics it is manifest that the biggest breakthroughs have come from scientists who have very original ways of thinking and unique viewpoints on science. By excluding women we are reducing the chance of major advances. Ada Lovelace Day is a reminder that we all need to work on changing the culture of science so that everybody can thrive and progress is maximised.
This content was written by Professor Marika Taylor. Marika is Professor of Theoretical Physics at the University of Southampton. Visit her staff page to learn more about her work and find her on Twitter: @taylor_marika