Albert Einstein in his office (Berlin, 1920)
As with many scientific theories, relativity is not easy to conclusively prove. But all of the evidence suggests Einstein was absolutely right. Clocks on the top of skyscrapers run just that tiny bit faster than clocks at the bottom because they’re further from the centre of the Earth and so spacetime is less warped.
In a phenomenon known as ‘gravitational lensing’, telescopic images of space sometimes show objects like galaxies as misshapen and distorted. That’s because the mass of other galaxies surrounding them warp spacetime, meaning that the image we get looks curved.
But one of the most significant pieces of evidence for general relativity was only announced in 2016 – more than 100 years after the theory was first published. That evidence comes in the form of something called ‘gravitational waves’.
Now if we think of space and time as a fabric, like the surface of a trampoline, massive events – like the collision of black holes – are going to create ripples in the fabric. If Einstein’s theory was right, we should be able to detect these waves: but we’d never quite managed it – until now.
In early 2016, scientists announced that they had used a giant laser known as LIGO (the Laser Interferometer Gravitational-Wave Observatory) to identify gravitational waves by pinpointing sub-atomic expansions and contractions as the ripples passed through spacetime.
LIGO works like a supremely powerful ruler: it bounces a laser beam back and forth between two mirrors placed 4km apart and measures the length of time the laser takes to make this journey.
Gravitational waves cause everything to change position, so if the laser beam moves out of synch then scientists know that a gravitational wave has rippled through its path, causing a sub-atomic shift.
The detection of gravitational waves is the piece de resistance of Einstein’s theory. Scientists have already used relativity to postulate the Big Bang and the expansion of the universe.
Relativity has helped us to theorise that 95% of the universe is made up of dark energy and dark matter. It’s even linked to machines like synchrotrons, which exploit electrons travelling at almost the speed of light.
Relativity has already given us so much. But now that we can detect gravitational waves, we can probe even deeper. We’re now able to study cosmic events like black holes and neutron stars in a level of detail that was previously unimaginable.
Just over a century on from its inception and Einstein’s relativity has fundamentally redefined our understanding of the universe. But Einstein’s greatest legacy is not just his revolutionary theories. His work inspired the many thousands of scientists that came after him to look further and to try and see things differently.
So physicists must continue probing, exploring and thinking: after all, from the cosmos to the quantum world, there’s still so much left to discover.