Gravitational wave detection heralds a 'new era of cosmological observation'

The first gravitational waves - ripples in spacetime - have been detected, allowing physicists to explore the universe in a whole new way.

Physicists from Imperial’s community yesterday were celebrating as the LIGO (Laser Interferometer Gravitational-Wave Observatory) facility in the US announced it had detected the first gravitational waves.

Hayley Dunning sat down with theoretical physicist Dr Toby Wiseman from Imperial’s Department of Physics to ask what the discovery means.

Firstly, what is a gravitational wave?

Gravitational waves are ripples in spacetime – the fabric of the universe. Just like moving your finger in a pool creates waves in the water, objects moving in the universe create ripples in spacetime.

They were first proposed by Einstein 100 years ago as a consequence of his theory of general relativity. For the theory to work, space and time have to be dynamic, and gravitational waves are the manifestation of this. Finally, we now have proof that Einstein’s theory works just as he predicted.

Why haven’t we found them until now?

Gravity is an incredibly weak force. With just a schoolroom magnet you can lift a paperclip – the small force of the magnet is overcoming the entire gravitational force of the Earth. It takes a huge and violent event to create the kinds of waves we could detect on Earth – and we also need a seriously sensitive detector. Only now have these two things come together.

What exactly have the LIGO team detected?

The team believe they have seen waves from two huge black holes colliding 1.3 billion years ago, each 20-30 times the mass of the Sun. This is an incredibly energetic event, and the gravitational waves it gives off allow us to study the black event in very precise detail. For example, before they collided, the black holes were orbiting each other nearly one hundred times per second.

How does LIGO work?

As they pass by, gravitational waves actually change the distance between two objects by a minute amount, and it’s this change that LIGO measures. The pair of objects have to be free – that is not influenced by anything else, which is why the experiment is incredibly precisely designed.

Now that we can detect gravitational waves, what does this mean?

Gravitational waves open up a whole new way to look at the universe. It’s a new era of cosmological observation, where there are fundamental and dramatic new things to be discovered.

We can observe stars and other objects because they emit light and electromagnetic waves that we can detect, but some objects, like black holes and neutron stars, don’t emit these and have so far been undetectable, at least directly. It’s a beautiful new way to see black holes, and to study them.

What is the future for gravitational wave detection?

LIGO has been running in some form since 1992, but it’s most advanced incarnation only started up in September 2015. That the team have been able to detect gravitational waves already means that there are likely many more events we can study in the near future.

Additionally, the LISA (Laser Interferometer Space Antenna) mission, which launched its test phase in December 2015 with Imperial kit on board, will be able to hunt for more gravitational waves from its vantage point in space once it launches in 2034. Up there, there will be less interference from noise and seismic events so LISA will be much more sensitive to subtle shifts in spacetime.