The discovery of gravitational waves made by the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) observatories is undoubtedly the science discovery of the year. Albert Einstein was probably partying in his grave at the news, as it confirmed the theory of general relativity he drafted a century ago. However, these incredible findings could also highlight the theory’s shortcoming and introduce us to new, exotic physics.
Einstein first drafted his theory of general relativity in 1915, and its new outlook on gravity ultimately replaced Newton’s theory. Through general relativity, Einstein explained that space and time are not two separate entities, but an interwoven fabric called space-time. And massive objects curve space-time, which is what we know as gravity.
Many of Einstein’s predictions have been verified throughout the decades since Einstein first shared them with the world. But it wasn’t until 2015 that the first gravitational waves were detected. Gravitational waves are essentially ripples on a galactic pond. These waves are disturbances in the very fabric of space and time, caused by the motion of massive objects — namely two colliding black holes.
An illustration depicting LIGO's laser interferometer setup.
Decades in the making, the discovery was heralded as the ultimate confirmation of Einstein’s theory, but in an ironic twist, they may also be its undoing. A group of physicists studying the publicly-released data that LIGO has collected so far, claims to have uncovered wave “echoes that could contradict general relativity’s predictions.
Theoretical physicists Jahed Abedi, Hannah Dykaar and Niayesh Afshordi, published a new paper explaining that the group believes they have detected the first evidence of gravitational effects not explained by general relativity in the data.
The echoes will need further investigation (and peer review), as the researchers note they could disappear as more data comes in. If they continue to be observed, that would be huge. While Einstein’s theory has been successful for 100 years now, physicists have predicted that it could break down in extreme circumstances — like the heart of a black hole. If the echoes are confirmed, it would mean that relativity also fails at the edge of a black hole — known as the event horizon.
What does the event horizon look like? Right now, scientists can't say for sure.
According to general relativity, the event horizon is like the point of no return, and if anything that crosses that boundary, it will not be able to escape the black hole’s mighty gravity.
In this scenario, the event horizon would be practically invisible, meaning anyone who crosses wouldn’t even know until it was too late. However, if we assume quantum physics is correct, then the event horizon should not be an invisible border, but a cosmic firewall. This supposed ring of high-energy particles would incinerate any matter that passes by. If this is true, it’s a violation of Einstein’s theory.
So who’s right? Einstein and general relativity or is quantum theory the best explanation? Scientists are looking to LIGO for help.
Historically, there has been no way to directly view the event horizon of a black hole. That changed thanks to LIGO’s famous discovery. The waves recorded by the twin observatories were created when two black holes collided. Physicists proposed that if there was any sort of exotic phenomena, like a firewall, that the gravitational wave signatures would be followed by a series of echoes.
Afshordi’s team studied the three black hole mergers that LIGO has observed so far, and discovered that each observation was followed by echoes at the exact intervals their models predicted.
The echoes could be a statistical fluke, caused by random background noise. Only time and future observations will be able to tell with any certainty.
The LIGO team is also analyzing their data sets to see if they discover the same echoes.
