EXPERT REACTION: Gravitational waves discovered

The detection of gravitational waves by the LIGO consortium is one of the most significant discoveries in physics in the past century - confirming one of the key predictions of Einstein's Theory of General Relativity.

Much of the Universe is governed by this famous theory of Einstein's, and with him having published it 100 years ago, 2016 is a great time to prove Einstein right.

This discovery will also be the beginning of a whole new realm of physics - gravitational wave astrophysics.

The gravitational waves that have been detected are likely to have been produced by the merger of two black holes - and that is something we've not been able to see before.

The ability of ALIGO to detect gravitational waves from such dramatic events will allow them to be located in the universe and be followed up by telescopes, with any associated radiation providing vital additional information on these enigmatic objects.  

What's also really satisfying for me is the very strong involvement of Australian physicists and astrophysicists in the development of gravitational wave detectors and this very first detection - most notably David Blair's Group at the University of Western Australia and David McClelland's team at the ANU.

Even though gravitational waves are created by some of the most violent events in the Universe, such as black holes colliding, these ripples in space and time themselves are extraordinarily weak. When they pass though the Earth, the 4 km paths of LIGO’s lasers are stretched and squeezed my a minuscule amount, less than the width of an individual proton. It is astounding that LIGO has beaten down all of the other shakes and rumbles on this planet, allowing us to feel these tiny distortions. I now expect to be amazed about what it is going to tell us about the Universe.

It is extremely rare that scientists and engineers achieve breakthroughs as fundamental as this. A new window on the Universe has been opened overnight (If the rumours are correct).

Astronomers have exploited almost every wavelength of light from radio to optical to x-ray and even gamma-rays in pursuit of their science, but this is something very different. This is a new communication medium that allows us to explore gravity at strengths we've only ever dreamt of. Today's announcement is a scientific and engineering triumph, and I am thrilled for my Australian and international colleagues, many of whom have dedicated their entire careers for this moment. 

The thought that we can witness black holes merging at close to the speed of light, and in less than a minute releasing 1000s of times as much energy as the Sun does in its billion year lifetime, is the stuff of science fiction, and yet, reality. It is also confirmation of the predictive powers of Einstein's elegant theory, and the dawn of a new era in astronomy, that of gravitational wave astrophysics. It is a very exciting time to be a scientist.

Things we should never be entitled to see - colliding black holes, merging neutron stars, gargantuan collisions of galaxies - can now be routinely revealed to us. We are poised to discover whole new types of phenomena, and we will now receive entirely new insights on familiar objects. There have been many scientific highlights of physics and astronomy in recent years: the Higgs Boson, landing a probe on a comet, and an amazing fly-by of Pluto. But all this is dwarfed by what has been announced this week. A new era of science has begun. 

This is an immensely important discovery for physics and astronomy. Gravitational waves exert a powerful appeal. Back in 1915 Einstein proposed that space-time is a four-dimensional fabric that can be pushed or pulled as objects move through it.

If you run your hand through a still pool of water waves will follow in its path, spreading throughout the pool.

Now that we've caught these waves, we can use them to see the Universe in entirely different ways to what was previously possible.

Through the use of interferometry, which is the merging of two sources of light, LIGO is designed to measure changes between the two arms of each detector. The two giant detectors, which are located on opposite sides of the US, are then compared to confirm the findings.

The interferometer system includes a series of mirrors which are coated with multiple precisely controlled layers of optical materials to give the required reflective properties and lastly a top layer of gold, designed for thermal shielding.

The coatings, which were developed and applied at CSIRO, are among the most uniform and highly precise ever made. This precision ensures that LIGO’s laser remains clean and stable as it travels through the detectors.

We really are world-leaders in this area, and are thrilled to play a part in this discovery. 

For the first time, we’ve been able to observe a gravitational wave, created 1.3 billion years ago by the collision of two massive black holes. This observation confirms that gravitational waves do exist. It is a moment that will be remembered for 1,000 years.

Sensing for the first time these rumbles in space-time will go down as one the major events in the history of physics, made possible by a close-knit, world-wide collaboration using instruments whose sensitivities are approaching limits imposed by quantum mechanics.  And this is just the beginning

With this detection we have shifted from the realms of theory to the beginning of a new astronomy. Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location for multi-messenger astronomy

This verification of Einstein’s general relativity in the nonlinear strong gravity regime was done with massive instruments whose amazing sensitivities approach limits imposed by quantum mechanics - a fact Einstein would no doubt have found amusing*

(* In regard to quantum mechanics, Einstein is quoted as saying that “God does not play dice with the universe”  Of course his ‘God’ was the laws of physics.)

We built the most massive scientific instruments in the world and and made them so sensitive that they approach limits set  by quantum mechanics.  On September 14 last year,  they directly detected for the first time the weakest signals in the universe  – gravitational waves – generated in the most violent event yet recorded – the collision of two solar mass black holes.

The energy released in this binary black hole collision was equivalent  to 10 billion billion billion times the world’s nuclear arsenal.

What’s even more fascinating is that this event (BBH collision) did not (and does not) emit electromagnetic waves or neutrinos  – the only way to observe it was with spacetime change sensors  - our giant laser interferometers.

The ANU designed, constructed, installed and commissioned the lock acquisition subsystem.  This crucial subsystem initially fixes the interferometer mirrors with respect to each other.  Once this has been established, mirror separations induced by a passing gravitational wave can then be read out from the change in the laser light leaving the interferometer.

With skilled craftsmen in our workshop, we also built, installed and commissioned 30 small optics steering mirrors for routing the signal beam around the interferometer and into the photo-detectors where the optical signal is turned into a voltage.

When I first heard of GW150914 from one of my post docs, I thought it was probably a blind injection. When I was informed that this was not the case, the excitement was palpable and my group monitored "the chatter" 24/7. Once a signal was confirmed, I was overwhelmed by the enormity of what our international collaboration of over a thousand scientists and engineers had achieved. Waves in spacetime really do exist. They do propagate over astronomical distances. And they can be detected – they do detectably modulate the optical path of our interferometers.

Twenty five years ago, the idea of building giant optical sensors limited by quantum mechanics to detect the weakest signals in the universe to help us understand it in a new way, drove me to initiate an Australia-wide collaboration.  We are now at the dawn of that new era and I am proud to have Australian technology in the Advanced LIGO detectors.

Whilst a new field of astronomy is the most enduring outcome of all our work, the brilliant young scientists and engineers we have produced and the contributions they will make to science and technology will also be long lasting.

Detection may not change my work but it will change the Australian physics and astronomy community’s view of my work.   Thankfully, we will never again have to address the damning remark - 'but what if gravitational waves cannot be detected?'.

This event did not generate light or neutrinos so the only way to observe it was through its gravitational wave emission. We have now unlocked the door to major processes and components of our Universe which only have a gravitational wave signature.

Einstein’s General Relativity has been a highly successful theory passing all tests conducted in our Solar System in the weak gravity regime. With the detection of gravitational waves from this binary black hole merger, it has passed with flying colours its first test in the strong gravity regime which is a major triumph.

We now have at our disposal a tool to probe much further back into the Universe than is possible with light, to its earliest epoch.

The University of Adelaide developed and installed ultra-high precision optical sensors used to correct the distortion of the laser beams within the LIGO detectors, enabling the high sensitivity we needed to detect these minute signals. We’ve been assisting with the assembly and operation of the detectors and one of our PhD students, Elli King, was working at the LIGO Hanford Observatory when the gravitational wave was discovered. She was part of the team that conducted the exhaustive checking to make sure that signal was genuine.

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 Advanced LIGO detectors are a technological triumph and the discovery has provided undeniable proof that Einstein’s gravitational waves and black holes exist. I have spent 40 years working towards this detection and the success is very sweet. We are on the threshold of a potential revolution in which gravitational astronomy could dramatically change our understanding of the universe and its evolution.

At the University of Melbourne we analyse LIGO data on massive supercomputers to hunt for persistent signals from neutron stars, some of the most extreme objects in the Universe. This is a huge computing challenge.

The discovery confirms Einstein's prediction that gravitational waves exist, validating one of the pillars of modern physics. It confirms that black holes exist and orbit each other in binary systems, teaching us important lessons about how stars are born and live their lives.

It is incredibly exciting to be participating as scientific history is being made. Every aspect of this research is 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.

Humanity is at the start of something profound and perpetual. We now have a new way of looking at the Universe and we will never stop looking. Gravitational waves are neither scattered nor absorbed by the material they pass through, so they let us peer right into the heart of some of the most extreme environments in the Universe, like black holes and neutron star, to do fundamental physics experiments under conditions that can never be copied in a lab on Earth.

The possibilities are endless.

University of WA was involved in stabilising the detectors to enable continuous operation. We ran an independent analysis of the data to verify the signals, and we searched the sky with our Zadko robotic telescope to see if there was any explosion visible in light.

Gravitational waves are akin to sounds that travel through space at the speed of light. Up to now humanity has been deaf to the universe. Suddenly we know how to listen. The universe has spoken and we have understood!

We have just passed through the threshold from being deaf to the universe, to being able to hear and understand. This is the tip of an iceberg. A whole new spectrum is open to us.

This is like Heinrich Hertz’s first detection of radio waves.  He never guessed  that it would revolutionise life in the next century.

We have opened a whole new frontier by creating exquisite and almost unimaginable technologies that have allowed us to measure vibrations as small compared with atoms as atoms are compared to people.

By measuring the smallest amount of energy ever measured, we have detected the most powerful explosion ever observed in the universe, in which three times the  total mass energy of the sun was emitted in pure explosion of gravitational energy in a time of less than one tenth of a second.

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.

The discovery of this gravitational wave suggests that merging black holes are heavier and more numerous than many researchers previously believed. This bodes well for detection of large populations of distant black holes – research carried out by our team at Monash University. It will be intriguing to see what other sources of gravitational waves are out there, waiting to be discovered.

Charles Sturt University has contributed to detector characterisation, validation of the calibration of the instruments and development of the detection pipeline for the stochastic background of gravitational waves.

This discovery is the first direct detection of gravitational waves, predicted in 1916. It is a further confirmation of the validity of general relativity as the correct theory of gravity.

The most exciting thing is that it opens the door to a new window on the Universe. In the same way that radio astronomy led to the discovery of the cosmic microwave background, the ability to 'see' in the gravitational wave spectrum will likely to lead to unexpected discoveries.

This detection marks the beginning of the age of gravitational wave astronomy.