Tekst: Jake Gordin
This is not too surprising given the reputation of the enterprise: it’s thought to be difficult to comprehend, given the slew of jargon and the association with mathematics. Science also underpins the functioning of the modern world. The ubiquity and complexity of science is likely a reason why the successes of science are taken for granted.
What I’d like to talk about here is an example of a recent scientific discovery: the detection of gravitational waves. This discovery had no right at all to be possible to achieve – and yet, in 2016, it was done.
To understand why the detection was so astounding, we need to understand what gravitational waves are, and to understand that we begin with Einstein. Einstein’s fame in popular imagination doesn’t extend beyond his crazy hair and equally famous equation, E=mc2. His main scientific achievement, however, was developing his own theory of gravity, called The General Theory of Relativity – or just ‘general relativity’.
The Wave Approaches
This theory replaced the theory of gravity put forward by Isaac Newton. Newton’s theory of gravity is the one we learn in high school; it’s what we often think of when we hear the word “gravity”. One important prediction made in 1933 was that gravitational waves exist. To understand what a gravitational wave is, imagine a regular water wave that forms in the ocean. There’s nothing distinct about a wave from the water that makes up the ocean; a wave is simply a part of the water that’s been rearranged in some way.
Things in outer space don’t float in water, but they do exist in something called spacetime. The name is an “on-the-nose” kind of descriptive one: space and time exist together, and when one changes, so does the other. A key insight Einstein had is that spacetime is dynamic. It can change shape, much like water. Einstein conceptualised gravity as being caused by changes in spacetime. Gravitational waves are small ripples in spacetime, bumps that move along, like waves in the ocean. What causes them? Everything, any movement within spacetime, disturbs spacetime.
The effects of gravitational waves are, however, really small. Einstein himself didn’t expect them to be discovered ever, let alone in his lifetime. Only something as extreme as a black hole collision – objects with an incredibly strong gravitational field – could produce a wave strong enough to be detected.
Detection
We now fast forward a bit from 1933 to the 1960s. At this point in time, general relativity had become established as the de facto framework for understanding how gravity works. Gravitational waves had not yet been detected. Physicists worked on prototype designs for building an experiment that could detect them; several still campaigned for funding to construct such an ambitious project.
The basic idea of the experiment was this: gravitational waves are ripples in spacetime. Therefore, when they pass through something, that thing will be stretched and squeezed. This is similar to a water wave that rises up from out of the ocean, like something has pushed the water together at the bottom, forcing it up. But since we exist in spacetime, not outside of it, anything caught in that wave will be pushed together and thinned too. This squeezing effect is of course tiny – you’d never notice if a wave passed through you.
However, if you take two very long tubes and put them perpendicular to each other in an «L» shape, and shoot a laser beam down the tubes, hit them off mirrors, and time how long it takes for the laser to come back. If the tubes are the same length, the lasers will bounce off the mirrors and come back at the same time.
A gravitational wave passing through would make the one tube shorter, and not the other. This is because the tubes are at a 90o angle: the wave’s passing through the tube in line with it will be squeezed and pushed up, and so will thin. But the tube that is perpendicular to the wave will be squeezed side to side, but not top to bottom; it will be thinner, but not shorter. If a wave passes through, the laser beam in one tube would be out of sync with the other, and you wouldn’t see them return simultaneously.
This is a very simple outline of how the gravitational wave experiment works. The reality of building such a machine, considering how weak gravitational waves are, and the fact that you have to isolate all sorts of possible interference – traffic, earthquakes, storms – is very different. The machine needs to be huge – the length of each tube of the «L» is about 4 kms. The laser beam needs to be very stable; the mirrors must be very smooth. Such an experiment is a remarkable feat of engineering, and is very expensive to construct.
It took another 30 years to go from conceiving of ways to detect gravitational waves to securing funding. By 2002, however, LIGO was built: the Laser Interferometer Gravitational-Wave Observatory. After an unsuccessful detection run from 2002 – 2010, LIGO could in 2016 report that they had observed the first direct detection of gravitational waves.
What it means for us
I think it’s important to stop and take note of the enormity of what was accomplished back in 2016. It’s possible to get a bit lost in the headiness of it all and think the detection of gravitational waves is something scientists just do. They have some fancy maths formulae, they build things to detect other things; then the predictions come true, and all is well with the world. But taken as a complete narrative, the detection of gravitational waves in 2016 was nothing short of absolutely absurd.
When Einstein predicted the existence of gravitational waves, take note of what this really means: he scribbled down some Latin and Greek letters. He claimed only on the basis of those letters, those marks of pencil on paper, that in the real world spacetime itself could ripple and produce waves. Years later, after Einstein had died, other smart, talented people took those scribbles very seriously and convinced the US government to spend millions of dollars to build an enormous facility. The goal was to measure if a passing gravitational wave changed the length of a tube to a degree of precision on a scale smaller than an atom. And in 2016, there it was, exactly as Einstein predicted.
More extraordinarily: Einstein thought black holes were theoretical. He didn’t even know about lasers. But people believed the equations, those abstruse markings on paper – symbols that, when translated, say something profound about the fundamental nature of the universe we live in.
It’s in this way that science is underrated. Einstein was a genius of course – he was working on a level of abstraction that reached so far ahead of his time – but the fact that his theoretical insights could give us any insight into the behaviour of things as removed from our everyday experience as «spacetime» or «gravitational waves», is unreasonable. It should be much harder for us to know anything about objects as bizarre as black holes, and much more challenging for us to detect things as elusive as gravitational waves.
We should not take this for granted, either in physics or in any other part of science. We similarly take medicine for granted. For example, all the chemistry and biology that went into figuring out things about the immune system, that it exists at all, and that it can be hindered or aided by things we do, are now basic medical facts. Likewise for technology: the use of quantum physics, the understanding of electrons and materials and how we can manipulate them to build things like computers. These things weren’t known by humans at all just 100 years ago.
This connection between very abstract things – like black holes so far away from us, gravitational waves, and the fact that spacetime is a thing – and more tangible, real things, like a huge facility built to measure the real consequences gravitational waves have on earth, has no right to be as clear as it is. Our universe is filled with objects so complex, and the ideas and concepts we’ve developed to try and make sense of what’s out there beyond our planet are equally so. The cause of wonder – why the success of science borders on the miraculous – is that despite the complexity around us, our universe is indisputably knowable.
