Why Albert Einstein continues to make waves as black holes collide

In February, scientists claimed to have detected the energy released by two black holes colliding, and most rushed to applaud Einstein’s theory on the space-time continuum. But others are not convinced gravitational waves were registered.

A simulation of two black holes colliding, a process that is thought to cause grativational waves. Courtesy the SXS (Simulating eXtreme Spacetimes) project.
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As the new millennium loomed, a Gallup poll commissioned by CNN and USA Today found that Americans admired four people from the 20th century above all others.

The first three came as little surprise. Mother Teresa, Martin Luther King, Jr and John F Kennedy – most people could probably summarise their contributions to the world.

But at number four in the list was Albert Einstein – a name as instantly recognisable as his cartoonish, “mad scientist” image and a byword for genius in popular culture. But what did Einstein achieve that so many people admired? Some may have invoked his theories of relativity, or the T-shirt-friendly equation E = mc2.

But how many could have explained them in any depth, or known that his 1921 Nobel Prize was unrelated, that it was awarded for “his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect”?

In an interview in The New York Times in March 1944, Einstein asked: "Why is it that nobody understands me, and everybody likes me?"

The Gallup survey is evidence of what can be termed “the Einstein Theory of Gullibility”: that when it comes to that slippery thing we call genius, most of us happily accept that we have absolutely no chance of understanding what that genius entails.

More than 60 years after his death at the age of 76, Einstein is in the headlines once again. His name and work have been conjured up by scientists and journalists in seeking the great man’s posthumous endorsement for what has been described by some as “the most important scientific breakthrough of the century”.

On February 11, hundreds of scientists working on a decades-long, multibillion-dollar, multinational collaborative project in the United States collectively announced they had detected “ripples in the fabric of spacetime called gravitational waves, arriving at the Earth from a cataclysmic event in the distant universe”.

The event had been long predicted but never witnessed: a coming together of two black holes, 1.3 billion light years away from Earth, which had been slowly orbiting and drawing inexorably closer for billions of years.

According to the Laser Interferometer Gravitational-Wave Observatory (Ligo) Scientific Collaboration, in the final few minutes this dance accelerated dramatically until, “during the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single, more massive, black hole”.

The resulting release of energy was emitted as a burst of gravitational waves, and it was these that Ligo observed. The detection of these faint waves on Earth up to 1.3bn years later – an observation made on September 14 last year – “confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos”, said Ligo. “The field of gravitational wave astronomy is now a reality.”

Conveniently, the discovery happened exactly “100 years after Einstein’s prediction”.

It was, said the director of the White House Office of Science and Technology Policy, which has invested US$1 billion (Dh3.67bn) in the project, “one of history’s greatest scientific discoveries”.

Cue unquestioning celebratory headlines around the world. In the ensuing excitement, even US president Barack Obama found time to Tweet “Einstein was right!”.

Only, he wasn’t. Einstein believed in neither gravitational waves nor black holes.

While there are few theoretical or experimental physicists who would dispute Einstein’s immense significance to their field – his 1915 general theory of relativity nailed gravity and is the foundation of all modern astrophysics – a handful of scientists outside the Ligo magic circle have expressed scepticism about the discovery.

Dr Natalia Kiriushcheva, a theoretical and computational physicist at the University of Western Ontario (UWO), Canada, says that while it was Einstein who initiated the gravitational waves theory in a paper in June 1916, it was an addendum to his theory of general relativity and by 1936, he had concluded that such things did not exist. Furthermore – as a paper published by Einstein in the Annals of Mathematics in October, 1939 made clear, he also rejected the possibility of black holes.

Regardless, on news of the discovery last month, Rainer Weiss, an MIT (Massachusetts Institute of Technology) physics professor, who was among those who proposed the Ligo project in the 1980s, said: “It would have been wonderful to watch Einstein’s face had we been able to tell him.”

It surely would, says Dr Kiriushcheva. Were Einstein alive today, she says: “I think he would be very sceptical about this discovery, and would analyse very, very carefully what they have been doing.”

In Einstein’s absence, Dr Kiriushcheva and Sergei Kuzmin, a UWO maths professor who shares her scepticism, have been doing just that.

In the process, they are going up against an institutional behemoth – something Einstein, a singular individual who abhorred “herd nature”, would doubtless have approved of.

Founded in 1997 for the sole purpose of proving the existence of and detecting gravitational waves, Ligo embraces about 1,500 scientists from dozens of institutions across 15 countries, including the US, Britain, Korea, Australia, Germany, India and Russia.

Proof of the bankable value of the discovery came on February 17, less than a week after the announcement, when the Indian government gave the go-ahead to a four-year-old proposal to build India’s own Ligo observatory.

Nevertheless, says Dr Kiriushcheva, it is the job of scientists to be sceptical – and, she insists, there is plenty about the Ligo project that invites scepticism.

The Ligo Scientific Collaboration relies primarily on two unique pieces of equipment more than 3,000 kilometres apart in the US: one in Livingston, Louisiana, and the other up in the north-west, in Hanford, Washington.

Each of these identical “laser interferometers” consists of two 4km long tunnels, set at 90 degrees to each other. A laser beam is split and fired through the two tunnels, bouncing off a mirror at the end and then back to a mirror at the start. The distance each beam travels is precisely the same – until, in theory, a passing gravitational wave, minutely distorting space as it passes at the speed of light, affects the length of first one and then the other.

On the repeated cycle of this distortion alone, the Ligo scientists claimed that they had not only detected gravitational waves for the first time, but that the waves had originated from the never-before-witnessed merger of two black holes, 1.3bn light years away from Earth – an event that happened at about the same time as the first plants grew on Earth.

The distance between the two detectors meant that the wave was picked up by the Livingston observatory seven milliseconds before its counterpart in Hanford, which gave the scientists a rough idea of the direction in the universe from which it originated.

Now it remains only for the Nobel Foundation to figure out who among the 1,500 inhabitants of the Ligo village should be awarded the next Nobel Prize for physics.

But, according to the Ligo paper, the observations were made by the twin observatories on September 14, 2015. The problem with this, says Dr Kiriushcheva, is that this was four days before the detectors began their first “observing run”.

There is no mention of this in the discovery paper.

Ligo’s twin observatories, fitted with upgraded detectors, had undergone a five-year rebuild and, according to the organisation’s records, did not start their “first official ‘observing run’” until 8am on September 18, 2015 – four days after the historic detection of gravitational waves.

In the weeks leading up to the run, both interferometers had been “operating in engineering mode” as technicians had been “work[ing] to refine the instrument to prepare it for official data collection duties”.

Surely this meant that, by Ligo’s own terms, optimal conditions for the experiment were not in place when the waves were detected?

Not so, says Peter Shawhan, a professor at the University of Maryland and a Ligo spokesman.

"The last actual adjustments to the detectors were made on September 11, so we have stable, well-calibrated data from September 12 onward," he told The National.

Ligo had "decided not to write about that detail" in the main paper but it was "described briefly" in a companion paper – Characterisation of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914 – which went unreported amid the global acclaim.

One detail that was mentioned in the main paper, though only in passing, was the curious fact that the historic detection was made while Ligo’s companion Virgo detector, a collaboration between the Italian and French governments and located just outside Pisa, was offline, undergoing its own upgrade.

This seems remarkable: the whole point of having multiple detection centres, as widely separated as possible, is to corroborate and increase confidence in any detection.

“We have [our own] two widely-separated Ligo detectors, and checking for consistency between them is absolutely crucial for the analyses we do,” says Prof Shawhan.

“But you are right, we would have liked to have Virgo running too, and seeing the signal in three detectors would give us even greater confidence.”

Yet it seems this wasn’t the only part of the global detection system not in place when the gravitational waves were reported.

In a September 18 press release that announced the start of the Ligo detectors’ first official observing run – four days after evidence of gravitational waves was recorded – much was made of a worldwide network of conventional observatories on standby to validate any apparent detection.

“Today,” Ligo announced, “the broader astronomical community has been added to the team.” This meant Ligo would “be able to notify any number of 74 astronomical observatories around the world, who have agreed to, at a moment’s notice, point their telescopes to the sky in search of light signals corresponding to possible gravitational wave detections”. But there was no mention of this network in the discovery paper. The simple reason, says Prof Shawhan, was, “as you guessed, on September 14 we were not ready to promptly share an event candidate with the astronomers”.

He downplayed the significance of telescopes in confirming Ligo detections. “We would,” he says, “love it if the astronomers are able to find a counterpart, but we do not necessarily expect there to be a detectable counterpart for every gravitational wave event.”

There are other black holes in the Ligo universe, says Dr Kiriushcheva and other scientists, who are raising questions about an event that took place five years ago, shortly before the twin US detectors were closed for their upgrade.

On September 16, 2010, a false signal – a so-called “blind injection” – was fed into both the Ligo and Virgo systems as part of an exercise to “test ... detection capabilities”. At the time, the vast majority of the hundreds of scientists working on the equipment had no idea that they were being fed a dummy signal.

The truth was not revealed until March the following year, by which time several papers about the supposed sensational discovery of gravitational waves were poised for publication.

“While the scientists were disappointed that the discovery was not real, the success of the analysis was a compelling demonstration of the collaboration’s readiness to detect gravitational waves,” Ligo reported at the time.

But take a look at the visualisation (www.ligo.org/news/blind-injection.php) of the faked signal, says Dr Kiriushcheva, and compare it to the image apparently showing the collision of the twin black holes, seen on the second page of the recently-published discovery paper (tinyurl.com/h3wkvmo).

“They look very, very similar,” she says. “It means that they knew exactly what they wanted to get and this is suspicious for us: when you know what you want to get from science, usually you can get it.”

The apparent similarity is more curious because the faked event purported to show not a collision between two black holes, but the gravitational waves created by a neutron star spiralling into a black hole. The signals appear so similar, in fact, that Dr Kiriushcheva questions whether the “true” signal might actually have been an echo of the fake, “stored in the computer system from when they turned off the equipment five years before”.

Prof Shawhan admits that “most of us who saw the signal early on September 14 [last year] assumed that it must be a blind injection since it was so beautiful”.

But “the blind injection team had not started the active period for that yet, and double-checks of all channels confirmed that there was no injection, either intentional or unintentional”.

Besides, he says, although the two images “do look visually similar, if you look closely you can see that the timescales are different”.

The fake signal from 2010 rises from a frequency of about 90 to 256 hertz in 0.25 seconds, a jump that takes the September 2015 signal only about only 0.02 seconds to achieve. That, he says, “tells you that the 2015 event corresponds to a binary [event] with larger masses”.

For Dr Kiriushcheva and her colleagues, perhaps the biggest question mark hanging over the Ligo findings is that for any scientific experiment to have full credibility, its results must be independently repeatable – clearly impossible when only Ligo and its scientists have access to the necessary funding and equipment.

Prof Shawhan says that “the results have been replicated in some sense; although it may look like one result from the outside … we rely on two independent detectors each observing the same event in a consistent way.

“We also have found the event using multiple independent data analysis algorithms executed by different people within our collaboration … this gives us the confidence to claim that we have unambiguously detected a gravitational wave signal.”

The questions raised by Dr Kiriushcheva and her colleagues are all good ones, he says, and “some continued scepticism is fine. But we have presented everything we know about this event and we hope to be able to report on additional events in the future”.

Watch that space.

In the meantime, regardless of where he stood on the issue of gravitational waves, were he still alive today, “continued scepticism” is something Einstein would doubtless have approved of.

After all, as he once said: “The important thing is to not stop questioning. Curiosity has its own reason for existing.”

Jonathan Gornall is a regular contributor to The Review.