This year marks the hundredth anniversary of Einstein’s theory of general relativity. With remarkable timing, the dedication ceremony of the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) Project was held on 19 May.
Advanced LIGO is a world-leading facility that will provide a revolution in our understanding of gravity and general relativity, and will enable transformative explorations of some of the best-kept secrets of the Universe, such as black holes.
Gravity may well be regarded as the first of the fundamental forces experienced by mankind. On Earth-sized scales it shapes our everyday life, but on the scale of the Universe it shapes the cosmos through the mysterious dark energy and dark matter.
Yet gravity provides the biggest challenge of this century for theoretical physics, because Einstein’s general theory of relativity is fundamentally incompatible with quantum mechanics. Since the dawn of time, the Universe has been broadcasting on its ‘gravity channel’ through a form of radiation known as gravitational waves, which are vibrations of space-time itself.
Gravitational waves are a fundamental prediction of general relativity. Their existence has been indirectly verified through the famous observations of radio pulsars in binary systems, for which Russell Hulse and Joseph Taylor were awarded the Nobel Prize in Physics in 1993. Their direct detection is a key and thus-far elusive confirmation of Einstein’s theory. Advanced LIGO aims precisely at capturing gravitational waves for the first time, and as a consequence it will allow us to listen to the unheard broadcast of the Universe on the gravity channel.
Einstein himself thought gravitational waves would be too weak ever to detect, but advances in technology have brought about a revolution in precision measurements that he could not imagine. Advanced LIGO consists of two kilometre-sized ‘rulers’ (one in Washington State and the other in Louisiana) that measure in real-time the continuous change in the space between ‘test masses’ (40kg mirrors), looking for fluctuations caused by gravitational waves. Ultra-stable laser beams are bounced between the mirrors, suspended four kilometres apart in high-vacuum tubes, measuring their separation to a precision of a thousandth of the size of an atomic nucleus.
In fact, gravitational waves are tiny fluctuations of space-time by the time they reach us on Earth. They are produced by catastrophic cosmic events such as colliding black holes or deadly explosions of stars. We also believe that the Universe produced these space-time ripples when it was much less than a second old.
Advanced LIGO will map directly the final minutes-to-seconds of the life of binary black holes and neutron stars when these compact objects orbit around each other at tens of per cent of the speed of light. It may eventually give us a snapshot of the infant Universe. This is a revolution that Einstein did not foresee.
LIGO is operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), with funding from the National Science Foundation. However, this is a truly international project. It has drawn on the expertise of 15 other nations, with particularly significant contributions from the UK Science and Technology Facilities Council (STFC), the Max Planck Society of Germany, and the Australian Research Council. A consortium of UK institutions (the universities of Glasgow and Birmingham, and the Rutherford Appleton Laboratory) received initial funding from STFC in 2003 to develop and build hardware for Advanced LIGO, which was successfully delivered in 2011. This has consolidated the position of UK scientists at the forefront of this emerging field and will allow them to play a leading role in the science coming from this world-leading project.
In fact, scientists at the universities of Birmingham, Cardiff, Glasgow and Sheffield have also had a central role in the last few years in developing sophisticated analysis methods that will be used to mine the Advanced LIGO data once the instruments go online later this year.
We do not know exactly when we will directly detect gravitational waves for the first time. It may take us a few years – we think it should happen by the end of the decade – but when we do, it will mark the dawn of a new era in fundamental physics and astronomy. And there will be surprises.
Professor Alberto Vecchio
Professor of Astrophysics, University of Birmingham