Physics Nobel Prize for former Leiden Lorentz Professor
The 2017 Nobel Prize in Physics has been awarded to Rainer Weiss, Barry Barish and Kip Thorne for their work on the measurement of gravitational waves. Leiden physicist Jan Willem van Holten explains why this is such an important discovery. ‘A new branch of astrophysics is born.’
Jan Willem van Holten is extraordinary professor in Theory of Supergravity and Cosmology. Gravitational waves are a phenomenon of his own research area—general relativity—which he teaches to physics students in Leiden. One of the Nobel Prize winners, Kip Thorne, was a Lorentz Professor in Leiden in 2009.
Vibrations in spacetime
‘Almost everything we know about the cosmos, we know thanks to observations with radio telescopes, visible light telescopes and X-ray telescopes, on Earth and onboard satellites. With those, we can see planets, stars, comets and gas clouds. We can also look at the afterglow of the Big Bang; the cosmic microwave background that consists of microwaves. Einstein predicted in 1916 that there should be vibrations in the gravitational field, which travel at the speed of light: 300,000 km/s.’
Geometry of space
‘The special thing about gravity, is that according to Einstein’s theory of general relativity, gravity is nothing but the geometrical shape of space. It is the curvature of space which bends the path of planets and stars; not some kind of magical attractive force. That curvature emerges in any place where mass is present. This is how our Sun curves space in our part of the Universe, and keeps planets orbiting around it. Gravitational waves are actually waves in the geometry of space which are emitted by moving objects such as stars. Those waves make distances between two points in space periodically larger and smaller.’
‘We are talking about a tiny effect. Einstein himself thought that we would probably never measure them. Yet, Rainer Weiss, Barry Barish and Kip Thorne managed to do it, with the LIGO detectors in the United States. There, laser beams echo between two mirrors that are 4 kilometers apart. When that distance gets a little bit bigger, the beam travels for a longer time. And vice versa, when the distance gets smaller, the laser will arrive faster. If you take two of those beams, perpendicular to each other, and the travel times differ even slightly, they won’t arrive at the exact same time. That difference has now been measured, both in the detector in Louisiana and in Washington. This proves the existence of gravitational waves. You can also see that the phenomenon is periodical, from which we are able to deduce the frequency and wavelength of the waves.
‘The three winners of the 2017 Nobel Prize have made this breakthrough possible. Rainer Weiss was the first to think of measuring with laser beams. Kip Thorne, who was a Lorentz Professor in 2009 in Leiden, has done a great deal of work in giving shape to the theory of gravitational waves. Barry Barish has lead the project in the right direction and was responsible for the realization of the LIGO instruments.’
New branch of astrophysics
‘With this discovery, a new branch of astrophysics is born, which doesn’t need telescopes, but gravity antennas. In August of this year, a gravitational wave from merging black holes hit Earth again, and that one was in addition measured by the European Virgo detector. In the future we hope to detect many more gravitational waves from objects in the Universe, and perhaps even from the Big Bang.’