How to get your mind around gravitational waves, space-time 'chirps' and black holes

Friday, 12 February 2016

A century ago, Albert Einstein predicted the existence of gravitational waves in his general theory of relativity.

Until the LIGO Scientific Collaboration announcement on Thursday, the waves were a theory.

Scientists from the Laser Interferometer Gravitational-wave Observatory (LIGO) detected the waves - distortions, or ripples, in the fabric of space-time caused by energetic processes in the Universe, such as the collision of two black holes.

Essentially, the discovery opens a window to the sounds of the Universe and LIGO have been listening.

**READ MORE: 

* [Scientific milestone for Einstein's prediction of gravitational waves

](http://www.stuff.co.nz/world/americas/76814468/einsteins-gravitational-waves-detected-from-black-holes-in-scientific-milestone)* Kiwi black hole expert wins big**

We need to get a few things out in the open first.

First of all, it's difficult to understand, let alone explain, the fabric of space-time, gravity and black holes, so suffice to say it's important and represents a groundbreaking 'Einstein was right!' moment.

It'll go down as one of the most important discoveries in physics for 100 years.

Let's get started, shall we?

Think of the waves scientists have detected as a bit like listening to the sounds of the Universe travelling at the speed of light.

Or, to put it another way, it's the sound of two black holes colliding.

**Woah, back up a little.

**And remember Newton.

Sir Isaac was a forward-thinking kind of man and theorised gravity as a force that attracted objects like the Earth and Moon.

**And Einstein?

**Don't be silly, everyone has heard of Einstein.

Here's some background.

This bit is important. Einstein predicted that waves formed when energy and matter changed space and time (that's the effect often compared to a rock in a pond or a bowling ball in the centre of a trampoline).

Objects follow the 'paths' in space-time created when mass distorts.

Gravitational waves can't be seen but the theory suggested effects would mean an observer would see distances between cosmic objects change. Since the effects are so tiny, the scientists need to observe massive objects, so think black holes. They're massive.

Scientists have caught a glimpse of the distortions created in space-time.

**What's it got to do with New Zealand?

**Everything!

There were quite a few Kiwis involved and the announcement has astronomers, physicists and mathematicians jumping up and down.

New Zealanders involved in the LIGO work included University of Auckland Department of Statistics associate professor Renate Meyer.

She said the discovery was truly momentous.

'LIGO has opened a new window to study the Universe and the forces that govern it.

'It can see events, such as colliding black holes and supernovae that are not observable with electromagnetic-based telescopes.'

University of Canterbury alumnus Dr Ra Inta, a researcher at Texas Tech University, said some of the more violent events in the Universe could be heard.

'This detection is a historical event, kicking open a completely new window to astronomy.

'In this sense, observing gravitational waves is more like listening to the Universe than looking at it.'

What's space-time?

Space-time, a mathematical modelling system, is viewed as the fabric of the universe. Everything lies within it and it is subject to distortion by mass.

The larger the mass, the greater the distortion.

**Why are you making my brain hurt?

**It's important to try to understand the ebb and flow of gravitational effects.

To think about space-time, imagine the Earth and the much larger Sun are sitting on a 'surface', let's go for the old trampoline analogy, with the Sun in the centre.

The mass of the Sun distorts the space (and the time) around it, more so than the Earth distorts space-time, and leads to our planet following the more pronounced distortions of the larger object and orbiting the Sun.

This is gravity (albeit a simplified analogy).

**Next, imagine any old ripple.

**Some cheeky scientist has lobbed a black hole onto our trampoline, creating a ripple.

So, the effect of black holes colliding would lead to a wave causing a minute distortion, a ripple on a subatomic level, in a manner analogous to the way the Moon's pull affects tides on Earth. That's what LIGO measured.

What's the big deal?

It's useful to imagine, for a moment, that scientists failed to discover gravitational waves.

Let's go back to Einstein's theories, which form the basis of modern physics. Gravitational waves, hitherto unobserved, were always part of the mathematical mix used to described the world and the Universe.

If the waves didn't exist that would mean the ways in which scientists have been describing our Universe for a century would need to be reimagined.

Essentially, physics would be overturned and it'd be back to the drawing board.

**Scientists have found a new way of 'listening' to the Universe.

**University of Canterbury professor of physics David Wiltshire said LIGO was able to listen without being limited to the electromagnetic spectrum.

'It is a moment in history every bit as important as when Galileo first pointed his telescope at the stars and planets, or when the first radio, X-ray, infrared or gamma ray telescopes were first turned on by 20th century astronomers.

'We have now made a measurement so sensitive it's like measuring the width of a human hair at the distance of Alpha Centauri.'

Here's University of Adelaide head of physics associate professor Peter Veitch:

'Our current model of the universe is derived largely from information carried by electromagnetic waves emitted by only a small component of the universe.

'The gravitational wave LIGO detected was emitted by objects we can't see. Now we will be able to eavesdrop on the violent dark side of the universe. Who knows what else we will find now that we can both look and listen to the universe?

'The LIGO detectors are a technological triumph and the discovery has provided undeniable proof that Einstein's gravitational waves and black holes exist.'

Oh. Right. How did they detect the waves again?

Everything around us and inside us is being stretched and squeezed and vibrated and the team was able to listen for gravitational waves that are part of the overall cosmic mix.

Simultaneously, two laser interferometers detected a signal that was characteristic of two black holes crashing into each other.

**An interferometer?

**Essentially, two huge tunnels, four kilometres long at right angles to each other. A laser beam is sent down each tunnel and bounced back using mirrors. Detecting changes in the returning beams back at the start point led to the discovery of gravitational waves.

**That's some piece of kit.

**The next step is putting an interferometer in space.

**OK, so tell me more about the waves.

**Probably the easiest way to work towards an understanding is to think of sound waves.

When two snooker balls collide they produce sound waves, an audible clink. When two black holes collide, they produce an inaudible space-time gravitational wave, which can be heard when it's converted to an audio wave as a 'chirp.'

It's a big deal.

It opens the door for, potentially, a new branch of physics. By being able to observe the information from gravitational waves, physicists can apply new information to astronomy, astrophysics and theoretical physics.

A new physics?

The doors could open for new discoveries, or confirmation of theories, in the study of dark matter and dark energy.

University of Melbourne professor of physics Andrew Melatos said every aspect of the research was elegant and beautiful.

'The LIGO detectors are genuine marvels of precision engineering.

'Einstein's theory of relativity, which predicts the existence of gravitational waves, brings together the concepts of geometry and gravity in a wonderfully inspiring way.

'The sources that LIGO detects, like black holes, are the home of some of the most fascinating physics in the Universe. It is very exciting to think that we now have a new and powerful tool at our disposal to unlock the secrets of all this beautiful physics.

'The possibilities are endless.'

Dark matter?

That's enough for today.