Everyone thought he was crazy, but Jo van den Brand changed the course of his research group and bet on the right horse. Now that he has made it possible to measure gravitational waves, a lot more about the cosmos, which is still largely invisible, is clarified. “This is the most exciting time to be a physicist.”
14 September 2015. After 20 years of preparation, the time to finally measure something has almost arrived. Subatomic physicist Jo van den Brand awaits an ordinary work day with an endless series of major and minor tasks before the gravity interferometers go fully operational. But it won’t be another ‘check-list day’. While everyone lay sleeping, the meters sent an automatic e-mail bringing the news that somewhere far away in space something unusual had happened. And that turned everything the next day, and in de coming months, upside down. The project, barely on its way, already seemed to be a success. But for a long time, success seemed far from certain.
1995. The Faculty of Science was forced to cut its budget. When Van den Brand took over as Professor of the Subatomic Physics research group, the group’s continued existence hung by a single thread. “We were doing nuclear physics research, and I expanded the group’s activities to studying antimatter as well. Especially the support of the students, who had a deciding vote in the Faculty Council at the time, was what kept me from losing my research group”, Van den Brand confesses. Under his leadership, the research group focused on a broad, universal problem: the fact that the vast majority of the universe and its origins are impossible to study.
Dark matters & dark ages…
Everything we know about the universe is measured based on objects that emit electromagnetic radiation, such as light or radio waves. Scientists estimate that these objects make up for only one percent of all matter. The rest of the matter in the universe can only be inferred indirectly. “When astronomers talk about dark matter, they’re really just using a euphemism for: I have no idea what it is, but I need it, because otherwise my measurements don’t correspond to the laws of physics. Another problem is that just after the big bang, the universe was so compact and dense that light provides almost no information about that period. Scientists call this period before the formation of the first stars the ‘dark ages’.”
…And dark energy
In addition to the measurements using light and radio waves, Van den Brand wanted to create an alternative standard of measurement for astronomy, which could fill in the enormous gaps in our knowledge about the cosmos. That standard of measurement was to be gravity. If one could somehow measure the dynamic effects of gravity, then one would be able to gather knowledge about the most primary building blocks of the universe: space and time.
Van den Brand: “Space and time were formed during the big bang, and if you could measure them, you could obtain information about the early universe. And because you’re not dependent on light, you should be able to observe dark matter as well as dark energy, a hypothetical form of energy that could explain the mysteriously accelerated expansion of the universe.”
Clocks run slower
With his general theory of relativity, Einstein determined that space and time are actually two aspects of the same phenomenon. This is difficult to imagine in daily life, but one effect is that clocks run slower when they are near massive, compact objects, such as a star or a planet. If the clocks aboard GPS satellites were not constantly synchronised with those on earth, your navigation system would be kilometres off after just one day. This is because the satellites are in a high orbit around the earth, and up there time simply runs faster than here.
If space and time are just variations on the same theme, then the relativity of time should also apply to space as well. In other words: space is not straight and constant, but rather curved and dynamic. When large objects undergo changes, they create ripples in space similar to those caused when you throw a pebble into a pond. Those ripples – expanding and contracting space – are gravitational waves.
The great thing about gravity is that you don’t need light to observe it. Every object in the universe, whether light or dark, ‘betrays’ its presence by distorting the space around it. But there was one major drawback to measuring gravitational waves: they had a bit of a bad odour to them. In the late 1960s, a physicist at the University of Maryland, Joseph Weber, came up with an experiment to do just that, but no one was able to replicate his experiments. As a result, research into gravitational waves fell into disrepute.
2006. Despite Weber’s failure, Van den Brand joined a consortium that was willing to accept the challenge. “Shortly after I started, it became clear that I couldn’t focus on both space-time and antimatter. So I chose to focus on gravitational waves. Some people thought that was strange, because we had a good position at the VU with our research. It was a bit of a long shot, too, but we took it. I had to switch gears theoretically. I also spent years getting the funding arranged. The technical problems were huge, but all of the big problems in physics that I found challenging had to do with gravity. I simply followed my interests, even though many people didn’t understand my motivation.”
Space expanding or contracting
The idea of a measurement instrument for gravitational waves is that you emit a laser beam through a long tunnel. If the tunnel becomes shorter or longer due to a gravitational wave, then the laser beam will take more or less time to cover the distance. In order to measure that effect, you have to build two tunnels perpendicular to one another: the second tunnel acts as a control variable for the first one. Since the tunnels are both the same length, you can track a gravitational wave the moment a difference occurs in the time the laser beam takes to cover the same distance in both tunnels. If there is a difference, then one of the tunnels has become longer or shorter, which is only possible when space expands or contracts.
From a technical perspective, those tunnels are a nightmare: they have to be an absolute vacuum and completely free of vibrations, and they have to measure at nanosecond accuracy. Nothing can be allowed to disrupt a measurement. And the tunnels have to be long. Finally, such an instrument, called Virgo, was built not far from Pisa, Italy. It consists of two underground tunnels, each three kilometres long, with an extremely precisely polished, vibration-free positioned mirror at the end of each tunnel. Colleagues in America also built two more of these instruments to measure gravitational waves.
The project was also a nightmare from a social perspective. Van den Brand: “If you get results, you know that your colleagues will have many questions for you. So if we obtained a result, we wanted to be absolutely certain that it wasn’t a fluke.” For that reason, the two consortia decided to share their data. With only one instrument, you could obtain a reading caused by something as trivial as vibrations caused by an aircraft flying overhead. A measurement in two or more laboratories at the same time, however, would exclude such false readings. Another measure implemented was the creation of an ‘injection committee’: a group of researchers who would vibrate the mirrors at the ends of all of the tunnels with no warning. All of the analysts involved in the project had to learn how to differentiate true readings from false positives.
2010. The three complexes in Italy and the US went ‘live’, but measured nothing, even after a number of adjustments made the instruments more accurate. “But I wasn’t expecting much either”, says Van den Brand. “I knew that they probably wouldn’t be accurate enough initially. We wanted to measure gravity waves from two neutron stars colliding. We know that they usually occur in pairs, and that eventually they crash into one another, but the chance of being able to measure the gravitational wave from such a collision was just a few percentage points at most.”
2012. The consortium began construction of a correction that would make the instrument ten times as sensitive. Van den Brand was still sceptical, however: his long-term goal was focused on 2022, because only then would the design have sufficient sensitivity.
And there it was
2015. After the necessary adjustments, the running tests started. The test phase was scheduled to last until 14 September. “I opened my e-mail inbox, and there it was: an alert mail informing me that the laboratories had detected something. I thought: this can’t be true. I had prepared to wait for the long haul, and now here it was… during the testing phase.” On being asked, the injection committee declared that this time they weren’t the ones responsible for the reading. A lorry driving by? Fraud? The measurement was conducted in both American labs, as the one in Italy was offline at that moment, with an interval of less than a millisecond, as predicted. That ruled out lorries, rodents or earthquakes. And you have to be very clever to fool two laboratories at the exact same moment, when they are both armed to the teeth against fraud.
In the months that followed, Van den Brand and his colleagues wore themselves out trying to relegate their own measurement to the dustbin. But one by one, every possible alternative explanation was ruled out. Their conclusion: it really were gravitational waves. But where were they from? Clearly not two neutron stars colliding, because the signal for such an event would look very different. Eventually, after many complex calculations, the scientists determined that on 14 September 2015 they had measured gravity waves from two black holes colliding – an event that creates significantly larger ripples in space than a neutron star.
Impact becomes clearer
2017. More than a year after the publication of the scientific article about the 14 September event, the impact of their finding is becoming ever clearer. The article has been cited almost 1,500 times. In the spring of 2016, every science section was full of the discovery. It even lead to the creation of a completely new field of study: gravitational wave astronomy. The discovery was also food for science sociologists, who carefully observed the scientists as they worked together in order to determine why their collaboration went so smoothly.
For Van den Brand, however, the discovery’s importance for the field of physics matters most. “I think that it will only get more interesting once we’ve made our equipment a factor of 10 more accurate”, he remarks dryly. And then, with emotion: “After centuries of studying physics, our best theory about how the cosmos fits together doesn’t fit the observations at all. According to our theory, there should be matter and energy that we haven’t been able to observe until now. So either the theory is wrong, or we haven’t yet been able to observe the vast majority of the universe. Now we can find out. This is the most exciting time to be a physicist, I think. When I was at university, cosmology was virtually free of facts. It was just a bunch of wild ideas, without the opportunity to test them. And now… the big book of everything, about the creation of the universe… we’ll be writing that book over the next few decades. And we’ll only write it once. It’s fantastic to be a part of that.”