What springs to mind when you think of Albert Einstein? Maybe it’s E=mc2, the snappy equation for special relativity, which he published in 1905. But there’s a lot more to Einstein, not least his theory of General Relativity. That’s Einstein’s theory of gravity, which he brought to the world in 1915.
Almost a century later, theoretical physicists are still exploring that solution, which has helped us to gain insight into the fundamental workings of the Universe.
“Einstein solved the problem of gravity and we are working on trying to understand the solution,” says Professor Peter Hogan, a theoretical physicist who specialises in General Relativity at UCD.
He describes General Relativity as a “fabulous theory” and one that has underpinned enormous advances: “It is the theory that predicts the existence of black holes, gravitational radiation and the Big Bang beginning of the Universe,” he says.
Professor Hogan, who is Associate Professor of Relativity Theory at the UCD School of Physics, has worked with some of the world’s leading relativists and has long-standing collaborations with colleagues in France, Japan, South Africa and the United States.
“I believe that if you work in science you need to test yourself by collaborating with the best people abroad,” he says. “It’s like a sportsperson who wants to compete at the highest level - they have to compete with the best people.”
With his collaborators, Professor Hogan has worked on Einstein’s theory in order to understand more about binary stars, or couplets of stars that orbit around a common centre of mass.
“One of the amazing things about General Relativity is it gives you a mathematical tool to model gravitational fields due to a binary star or a black hole or the gravitational field of the Universe,” says Professor Hogan.
“And if the source of the gravitational field is a binary star system, you could work out from the theory how those stars are moving.”
Professor Hogan has also used General Relativity to help shed light on dark matter, a mysterious substance that is thought to be behind the accelerating expansion of the Universe.
He and French collaborator Claude Barrabès demonstrated through their equations that dark matter is a product of gravitational shock waves colliding.
“You do that in General Relativity by solving Einstein’s equations and a solution gives you a way of modelling the gravitational field after the waves have collided,” says Professor Hogan. “And in that field we identified this dark matter.”
Keeping active in research is an important behaviour to model for students, he adds” “I see my job as teaching and studying.”
Professor Hogan’s most recent book, Equations of Motion in General Relativity (International Series of Monographs on Physics), is co-authored with Hideki Asada and Toshifumi Futamase and published by Oxford University Press.
Professor Peter Hogan was interviewed by freelance journalist Dr Claire O'Connell
