After 100 years of searching, an international team of physicists has confirmed the existence of Einstein's gravitational waves, marking one of the biggest astrophysical discoveries of the past century. It's a huge deal, because it not only improves our understanding of how the Universe works, it also opens up a whole new way of studying it.

The gravitational wave signal was detected by physicists at LIGO on September 14 last year, and the historic announcement was made at a press conference this morning. Experts are already saying the discovery is a shoo-in for a Nobel Prize

Gravitational waves are so exciting because they were the last major prediction of Einstein's general theory of relativity that had to be confirmed, and discovering them will help us understand how the Universe is shaped by mass.

"Gravitational waves are akin to sound waves that travelled through space at the speed of light," said gravitational researcher David Blair, from the University of Western Australia. "Up to now humanity has been deaf to the universe. Suddenly we know how to listen. The Universe has spoken and we have understood."

What does that mean for us? Just think of all the breakthroughs that have come thanks to the discovery of x-rays and radio waves - now that we can detect gravitational waves, we're going to have a whole new way to see and study the Universe. 

But let's step back for a second here and explain what gravitational waves actually are. According to Einstein's theory, the fabric of space-time can become curved by anything massive in the Universe. When cataclysmic events happen, such as black holes merging or stars exploding, these curves can ripple out elsewhere as gravitational waves, just like if someone had dropped a stone in a pond.

By the time those ripples get to us on Earth, they're tiny (around a billionth of the diameter of an atom), which is why scientists have struggled for so many years to find them.

But thanks to LIGO - the laser interferometer gravitational-wave observatory - we've finally been able to detect them. The LIGO laboratory works by bouncing lasers back and forth in two 4-km-long pipes, allowing physicists to measure incredibly small changes in spacetime.

One 14 September 2015, they picked up a relatively big change in their Livingston lab in Louisiana, what you'd call a blip in the system. Then, 7 milliseconds later, they detected the same blip with their lab in Hanford, Washington, 4,000 km away, suggesting that it had been caused by a gravitational wave passing through Earth.

In the months since, researchers have been rigorously studying this signal to see if it could have been caused by anything else. But the overwhelming conclusion is that the blip was caused by gravitational waves - the discovery has statistical significant of 5.1 sigma, which means there's only a 1 in 6 million chance that the result is a fluke.

In fact, the signal almost perfectly matches up with what scientists predicted gravitational waves would look like, based on Einstein's theory. You can see the signal below, with the predictions overlaid:


So where did this gravitational wave come from? The physicists were able to trace the signal back to the merging of two black holes around 1.3 billion years ago. 

This event - which in itself is a big deal, seeing as no one had ever spotted a binary black hole merger before - was so massive that it significantly warped the fabric of space time, creating ripples that spread out across the Universe… finally reaching us last year.

"The discovery of this gravitational wave suggests that merging black holes are heavier and more numerous than many researchers previously believed," said LIGO researcher Eric Thrane, from Monash University in Australia. "This bodes well for detection of large populations of distant black holes … It will be intriguing to see what other sources of gravitational waves are out there, waiting to be discovered."

But this is just the beginning of what gravitational waves can teach us - several other gravitational wave observatories and detectors are scheduled to come online in the next five years, and they'll allow us to more sensitively detect gravitational radiation.

Just like we can currently listen to radio waves in order to find out what happened in the history of our Universe, we now have the ability to do the same with gravitational waves. And what's most exciting is that we can't even begin to predict right now what that could lead to.

The research has been published in Physical Review Letters.

You can see live updates from during the press conference below:

10am ET: Okay, the countdown is officially on! There's half an hour before the press conference kicks off, and 15 minutes until we have access to it. It's 2am here in Sydney, so apologies in advance for any typos during this live stream - never let a bad time zone get in the way of physics!

10.04am ET: While we're waiting, find out more about what the rumours are saying is going to be announced today - which is the first clear, unambiguous evidence that gravitational waves exist (something Einstein predicted 100 years ago). You can also watch this interview with physicist Lawrence Krauss, who first kicked off the rumours.

10.14am ET: Here we go, guys. Physics as we know it could be about to change forever…

10.23am ET: Let's all distract ourselves from the waiting game by watching this musical summary of the last unsuccessful search for gravitational waves, set to the tune of "The Circle of Life". Let's hope we're in for better news this time!

10.31am ET: France Córdova, the director of the National Science Foundation is welcoming us to the announcement.

10.35am ET: "Ladies and gentlemen, we have detected gravitational waves. We did it!" EEEEEK!!!!!!! This is it guys!!! I'm actually crying.

10.36am ET: This signal was seen on September 14 last year, and it was the result of two black holes that collided and merged around 1.3 billion years ago.

10.36am ET: More details are coming in fast, but right now let's be clear - gravitational waves have been detected, and it's about to open up a window on the Universe that we've never had before. It'll also change our understanding of how the Universe works. And it FINALLY proves Einstein right!

10.37am ET: We're watching a video of the two black holes spiralling around each other and eventually merging, triggering the gravitational waves. This is the first time a binary black hole merger has ever been seen.

10.38am ET: The black holes were about 30 times the mass of the Sun and accelerated to half the speed of light when they smashed into each other, just to give you a sense of how big the collision was!

10.39am ET: OK now we're seeing a simulation of the gravitational waves originating from the black hole merger, and then spreading out towards Earth where they very, very gradually make Earth wiggle like jelly.

10.40am ET: Don't panic, Earth isn't actually wiggling in any obvious way. We're talking about tiny, tiny changes that only LIGO could pick up. "We are trying to measure things one one-thousandth the diameter of a proton," said David Reitze, LIGO executive director.

10.41am ET: Reitze compares it to trying to measure the distance between the Sun and its nearest star - LIGO is capable of measuring that to the level of about the width of a human hair. Impressive!

10.42am ET: "This was a scientific moonshot… and we did it, we landed on the Moon." YES!

10.43am ET: OK so now we're getting more information from LIGO spokesperson Gabriela González on the discovery itself. We'll also provide you guys with some more information on what this all means shortly.

10.44am ET: The LIGO team was able to measure the tiny gravitational wave by using two laboratories at the same time - one in Livingston, Louisiana, and one in Hanford, Washington. The waves are so small that if you only saw the tiny distortion in one lab, you wouldn't be able to believe they were real, explains González.

10.45am ET: So here's the smoking gun. These are the signals picked up, first by the Livingston lab and, 7 milliseconds later, by Hanford in September 2015.

The changes they spotted were only a very small portion of the diameter of a proton, but the amazing thing is they pretty much EXACTLY match up with the predictions scientists made of what gravitational waves would have looked like (overlaid below).


10.46am ET: The unit of measurement here is strain - which means strain in the spacetime, which is pretty incredible to think about in itself.

10.47am ET: The gravitational waves we've spotted originated more than 1 billion light years away, "when multicellular life here on Earth was just beginning to spread," as González explains.

10.50am ET: OK, wow. Now they're playing us the actual sound that the gravitational wave produced! This is incredible. We are LISTENING TO GRAVITATIONAL WAVES. What is this life?!

10.50am ET: With new observatories coming online next year, we'll be able to better map and track where gravitational waves are coming from.

10.51am ET: "This is just the beginning, we've discovered gravitational waves from the merger of black holes. It's been a very long road, but this is just the beginning. It's the first of many to come… now that we know binary black holes are out there, we'll begin listening to the Universe."

10.56am ET: Physicist Rainer Weiss is giving us more details on the discovery and the sensitivity of the LIGO laboratory. It's absolutely mind blowing that LIGO was able to pick up such tiny changes with such incredible accuracy.

10.57am ET: So how does LIGO work? Basically, the physicists fire light from lasers into two L-shaped pipes, and this light is bounced back and forth by a set of mirrors. Any tiny ripples in spacetime will cause slight timing changes in this laser light, and the LIGO detectors are able to pick that up.

10.59am ET: Ooooh Weiss having a dig at theoretical physicists. Burn!

11.01am ET: Oh man, it's wonderful to see all the scientists involved hugging and cheering. This is such a huge day, and it's involved so much hard work from so many researchers.

11.04am ET: The detection of the gravitational waves will be published today in Physical Review Letters, with more papers to come.

11.06am ET: OK now we're seeing a simulation of how the gravitational waves actually originated from the merging of two black holes. The total power output in gravitational waves during the brief collision of these black holes was 50 times greater than all of the power put out by all of the stars of the Universe put together. Whoa.

11.07am ET: Because the collision was so short, the energy released wasn't quite that much, just the equivalent of taking three suns and annihilating them, NBD.

11.07am ET: We're now going to be able to try to detect gravitational waves from a whole lot of other astronomical events. "LIGO has opened a new window onto the Universe," says Kip Thorne, LIGO co-founder.

11.08am ET: What's really exciting about this, is that it gives us a whole new way to view the Universe - just like the discovery of radio waves. "I think we can be rather sure that we'll see big surprises - perhaps even bigger surprises through the gravitational wave window than through the radio and x-ray windows," said Thorne.

11.10am ET: "Wow, Einstein would be beaming right now, wouldn't he?" YES, Córdova, he would!

11.13am ET: Okay, while we're doing the official thank yous, we're going to get stuck into the paper that's just been released to get you guys some more details above.

11.15am ET: It's question time! 

11.16am ET: Did the researchers think the result was too good to be true? Absolutely. That's why it took so long for them to make the announcement after the signal was discovered in September.

11.22am ET: Good question: Do we expect to see many more gravitational waves, or did we luck out and spot a once-in-a-decade event? Short answer: Yes! Physicists should be able to see a few more signals this year, and they're going to be able to increase the sensitivity of the interferometers to hopefully get more readings.

11.29am ET: A few great questions into what happens next. One exciting development is the launch of LISA - the Laser Interferometer Space Antenna Project - which is a space-based gravitational-wave observatory. That's important, because LISA will be able to listen to gravitational wave signals without any background noise from Earth.

11.30am ET: Apparently about 90,000 of us are watching this stream live. F*ck yeah, science!

11.31am ET: Another fun fact, Kip Thorne was a scientific consultant on Interstellar. So who's excited for Interstellar 2?

11.32am ET: We're skimming over a lot of questions here because there's a whole lot of detail being shared. But the overwhelming message you need to know is that this is just the beginning. The interferometers are going to get more sensitive, and are going to be able to pick up lower frequencies, which means we'll be able to much better understand these gravitational waves in the future.

11.33am ET: Nice question: What does this mean for us here on Earth? Does this bring us further in the science of time travel? "It brings us a much deeper understanding of how spacetime behaves when it is extremely warped," says Thorne. "I don't think it's going to bring us any closer to being able to do time travel. I wish it would, but that's a different direction." Damn, sorry guys.

11.37am ET: Okay, the webcast is wrapping up now. With all the updates, we haven't had the chance to tell you guys just how overwhelmed, happy, and excited we are about this news. Science is always awesome, but this is one of the biggest things that's happened since ScienceAlert first launched eight years ago, and writing this now is just mind-blowing (and that's not just the early morning talking). Thank YOU all for watching and getting excited with us. We wouldn't be able to do it without you.

The press conference streamed live here: