An explanation of relativity from Trevor Rayment, director of physical science at the Diamond Light Source

The year 2016 is an important one for both science and society. It marks the centenary of an event that redefined our understanding of space, time, gravity and the fundamental physics governing our world: Einstein’s theory of general relativity.

Most of us have heard of relativity, but the abstract nature of the theory can make it difficult to grasp. We might ask ourselves why relativity matters, how does it actually influence our lives?

In fact, the impact of Einstein’s work reverberates in profound ways. Relativity has allowed us to better understand and explore the cosmos, helping scientists to develop theories on the origins of the universe.

It also has practical applications. Our understanding of relativity has allowed us to make huge strides in engineering and innovation. From GPS, to nuclear power, to televisions, much of the technology we take for granted has its roots in Einstein’s theory.

But what exactly is the theory of relativity? Well it’s essentially two different theories rolled into one. The first, special relativity, rocked the foundations of physics when it was published in 1906, by proving that light travels at the same speed no matter what.

Why did this matter? Because up until that point, scientists generally believed that the speed of light varied and that time itself was fixed – so that no matter how fast you moved, time would work in the same way.

But Einstein showed that, because the speed of light is always the same, the rate at which time elapses is relative to the speed at which one moves through space. For objects that are moving fast, time actually slows down.

The implications of special relativity were huge – essentially it demonstrated that time as we knew it did not exist. But Einstein didn’t stop there. In 1916, he revealed the second part of his theory: general relativity.

Back in the 17th century, Isaac Newton predicted the existence of gravity, but he didn’t understand how it originated. In 1916, Einstein cracked the code. He discovered that mass causes spacetime to warp, creating a gravitational pull.

Imagine a trampoline with a bowling ball in the centre. The mass of the ball warps the fabric of the trampoline so that smaller objects – say, a marble placed on the outside – will fall towards the middle. Earth is a massive object, and so it warps the fabric of spacetime, drawing matter towards its centre. This is the source of gravity.

Einstein’s theory of general relativity has amazing implications. Clocks run faster at the top of buildings than at the bottom, because they’re further from the centre of the Earth, meaning time is less warped.

Relativity has helped define our understanding of the universe and its story through time. Using calculations supported by relativity, scientists have determined that the universe is expanding from a sudden climactic beginning: the big bang. We’ve also used this theory to postulate that 95 per cent of the universe is made up of dark energy and dark matter.

Together, Einstein’s theories of special and general relativity reshaped our fundamental understanding of the world around us.

They’ve also delivered a variety of practical advances, from the electromagnets that power our computers, smartphones and MRI machines, to the synchrotron light sources that support research into medicine, engineering, nanotechnology and more.

On the centenary of the theory’s publication, we can look back at how far we’ve come and how much possibility still lies ahead of us. This was truly Einstein’s great gift to the world – from gravity, space and time down to quantum mechanics, relativity can help us to grasp the exquisite complexity of the universe.