Dr Karl Explains Gravitational Waves, And What Einstein's Got To Do With Them

12/02/2016 1:08 PM AEDT | Updated 15/07/2016 12:51 PM AEST
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(AUSTRALIA & NEW ZEALAND OUT) Dr Karl Kruszelnicki in the Triple J studios, ABC Ultimo, 21 October 2004. SHD Picture by STEVE BACCON (Photo by Fairfax Media via Getty Images)

Waves that cause the literal fabric of space-time to ripple have been detected for the first time by a global collective of scientists, validating a prediction Albert Einstein made one hundred years ago.

But what is a gravitational wave? Why is it important? Was there ever any doubt that Einstein was a smart bloke?

Dr Karl Kruszelnicki is here to help.

Super massive black holes

The detection of these particular gravitational waves -- the ones announced today -- starts with two massive black holes that begin to orbit each other somewhere in space, drawn together by the gravity each exerts.

Both black holes have a mass thirty times that of the Sun, and they’re spiralling around each other at half the speed of light. As they accelerate they orbit each other about 250 times a second.

“Then they collide and turn into one big black hole and three solar masses get turned into energy. Three times the mass of the sun is vaporised and turned into pure energy,” Dr Karl told The Huffington Post Australia.

“Like a nuclear bomb -- matter gets turned into energy, but it’s not heat energy or light energy, it’s gravitational waves.”

The energy produced by the merging of these two black holes is prodigious -- and that’s what sends gravitational waves rippling through space-time.

“Just to give you an idea of how much energy that is -- our Sun, every second burns six hundred and twenty million tonnes of hydrogen. And when you add that up over the Sun’s entire life of ten billion years, that works out to less than one tenth of one per cent of the Sun’s mass.

“Instead of just having one tenth of one per cent of the Sun’s mass being turned into energy, you’re turning three times the mass of the Sun. And you don’t do it over ten billion years, you do it over a tenth of a second.”

In other words, this is serious stuff. We've got more to get to but for now, take a quick breather and enjoy this gratuitous gif of Kim Kardashian crying in a sauna.

Now, back to the discovery.

What’s Einstein got to do with it?

What’s especially noteworthy about the discovery announced on Friday is that it confirms a prediction made one hundred years earlier by Albert Einstein.

Einstein predicted the existence of gravitational waves as part of his 1915 general theory of relativity. Astronomers long suspected that they existed given observations they’d made about the way stars behaved, but until now they’d never been detected.


An artist’s impression of the gravitational waves

Dr Karl told HuffPost Australia it was incredible Einstein had predicted their existence at all.

“He said there should be gravitational waves. And when you think about this guy, by himself, thinking this all out with a pencil and paper and going further and further out on a limb and being right every time,” he said.

“He said you probably won’t even be able to measure it because first you need something really energetic and secondly, the size of the gravitational wave would be so small by the time it got to you you wouldn’t be able to measure it.”

Turns out there was something energetic enough -- just a casual two black holes colliding.

How did the waves get picked up?

Even though the black holes are massive, they’re so far away from us that by the time the gravitational waves reach Earth, they’re miniscule.

It takes a particular type of telescope to detect these waves, and on the 14th of September last year, both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors -- in Louisiana and Washington in the U.S -- independently observed the gravitational waves hitting Earth.

The way these telescopes work is that they emit stable laser beams that form a moiré pattern -- two identical patterns overlaid on one another.

When a gravitational wave passes through the detector, it shrinks one of the lasers by an infinitesimally small amount. But that shifts the moiré pattern, which is then detected by scientists.


An example of a moiré pattern

“This was done by inventing devices that are so sensitive that they measured the distance equalled to one billionth of a diameter of an atom,” Dr Karl told HuffPost Australia.

“Atoms are bloody small, you can’t see them. We’ve only recently been able to see them with electron microscopes, not the naked eye. But we can measure one tenth of a billionth of the diameter of an atom.”

We're nearly there. Here's Homer Simpson chasing squirrels around a tree.

Australia’s involvement

Australian scientists from The Australian National University (ANU), the University of Adelaide, The University of Melbourne, the University of Western Australia (UWA), Monash University and Charles Sturt University all contributed to Friday’s announcement.

Along with their involvement in research teams, these scientists helped build some of the super-sensitive instruments used to detect the gravitational waves.

“This is a watershed moment in the history of astronomy. LIGO's detection represents a whole new way of doing astronomy that can unlock the secrets of the universe. It has been a privilege to work with the international LIGO collaboration toward this discovery,” Monash University astronomer Dr Eric Thrane said.

Dr Helen Johnston, from the University of Sydney’s school of physics, told HuffPost Australia that Australian scientists are well positioned to help with further discoveries in the field of gravitational astronomy -- potentially helping to find where the black holes that cause gravitational waves are in the universe.

"There’s a big group in WA doing gravitational research … people at the Australian Square Kilometre Array Pathfinder (ASKAP), they’re really well set-up to help look for these black holes.”

gravitational wave

LIGO co-found Kip Thorne speaks at Friday's announcement

An exciting time for astronomers

The detection of gravitational waves will likely give rise to a new field of astronomy, scientists have said.

And using the discovery could help us look back at the earliest moments of the universe’s history.

“Where we try to look back in time we get blocked, as we get closer to the Big Bang, because there’s all this gas and dust in the way and we can’t see what’s happening back there. But gravity travels through it like it’s not there,” Dr Karl said.

He said beyond that, it was hard to predict what the discovery could lead to -- but serendipitous discoveries in the field of astronomy have helped along the invention of GPS, Wi-Fi, and the World Wide Web.

Dr Johnston said the fact we don't know what we're going to find is what's so exciting.

“Every time you invent a new field you turn up things you had no idea about. Most of science is known unknowns, but if you invent an entirely new field of astronomy that’s when you find out about things you had no idea were up there,” she said.

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