By Nury Vittachi
EINSTEIN'S BLANKET EXISTS. One of the biggest discoveries in modern science was announced this week. For 100 years, we’ve been pondering Einstein’s assertion that space was not just a place and time was not just a process, but both were aspects of something physicists call “the fabric of spacetime”.
We’ve long known that Einstein was right, but we’ve never been able to feel the threads that make up this mysterious “fabric” until now.
What happened? Physicists around the world are this week celebrating “the discovery of gravitational waves”. But I didn’t see a single media report that successfully explained what was actually discovered or what it means to our understanding of who we are and where we live.
So I’m going to try to do so, using the explanations, as much as possible, of scientists in history and the actual scientists doing the work.
NOT ABOUT GRAVITY
But first we need to define our terms. All the reports are about Gravitational Waves: these are not about gravity, and they are not about waves. That’s the problem.
Gravity, Sir Isaac Newton famously taught us, was a puzzling force that seemed to pull objects toward each other. Most people still think of it like that, and there’s nothing really wrong with doing so.
And we all know what waves are: it is our word for an up-down movement in a separate medium – a ripple flowing through water, for example.
(Gravitation as a force of relativity)
But Einstein showed that Newton’s view of gravity was an illusion. There is no “force” that exists in the way that most people envisage. Instead, reality itself is shaped by the objects within it, causing objects to seem to be pulled together. Einstein called this “curved spacetime”.
Physicists today use the word “gravitation” to refer to the new vision of reality we learned through Einstein’s theories of relativity.
And that’s something else that needs to be explained. When we talk about “the universe” we think of a big space with stars and planets in it. But Einstein (and physicists in general) mean something quite different: they use “the universe” to mean this version of physical reality as a whole.
A HUGE DUVET
Let’s stay with the fabric analogy, but to make it easier to visualize, let’s think of the universe as a huge duvet containing all of reality. Like a duvet, there is some space inside it, containing all sorts of stuff (feathers, padding, tiny bedbugs, etc). Also like a duvet, reality is not a straight-edged cube or rectangular monolith, but a thing with a relatively complex outer shape.
We live inside the universe (inside the duvet) and that is interesting enough for most of us – but for physicists, the ultimate goal is to reach up or down and actually touch the outer surface, or detect its presence in some way.
(The fabric of spacetime contains the universe)
EDGES OF REALITY
This week is the first time that we have really “felt the edges” of reality. It’s as if we have long known that reality is duvet-shaped, but this is the first time we have perceived the duvet’s outer cover, if you like. We have seen it and heard it. That’s why it’s such a big deal.
“It’s the first time the Universe has spoken to us through gravitational waves. Up until now, we've been deaf,” Prof Karsten Danzmann from the Max Planck Institute for Gravitational Physics, one of the team on the project, told reporters.
WAVES THROUGH A MEDIUM
The question of waves is important too. Waves are ripples which flow through a medium – a movement through water, for example. Take away the water, and the waves disappear too.
But the waves scientists detected this week are not movements through a physical medium in our universe–they are a ripple running through reality itself. To go back to our universe-as-a-duvet image, the ripples are not a wave flowing through the padding inside the duvet. They are ripples in the place we call reality: the duvet itself was manipulated and we have felt the results.
“The fact that we are sitting here on Earth feeling the actual fabric of the Universe stretch and compress slightly due to the merger of black holes that occurred just over a billion years ago: I think that's phenomenal,” Prof Sheila Rowan, who is one of the lead UK researchers involved in the project, told the BBC. “It's amazing that when we first turned on our detectors, the Universe was ready and waiting to say ‘hello’.”
(The reality in which we live is part of a malleable structure called spacetime)
TEARS IN SPACE
We also need to touch on the mechanics of the experiment. How did the Universe say “hello”, as Prof Rowan said? How did we detect the edges of reality?
The actual edges of the universe, if they exist, are too far away for us to reach out and touch.
But the universe (by which, remember, we mean “reality”) has huge numbers of tears in it – which we call “black holes”, a term coined by legendary physicist John Wheeler. In sci-fi books and movies, these are dangerous patches of space which suck in everything, from planets to stars to light itself.
None of that is true. Black holes do not suck anything. They do not pull at anything, nor do they draw things toward them.
Black holes are places where the fabric of time has been compressed so much that the reality in which we live is “damaged”, in a way of thinking. Think of a blanket (or our duvet) which has been scrunched up really hard in one particular place. It has been scrunched up so hard that the fabric is compressed and the cloth is torn—and that tear usefully teaches us something about the edges of reality.
(Black holes don't suck things in, but are "scrunches" in spacetime)
What scientists revealed this week, using a process called LIGO, which I won’t explain here, is that a billion years ago, two black holes (tears in the fabric of reality) came together causing a huge scrunch in the duvet: a scrunch so powerful that it caused a ripple in reality which we can feel today.
That was the ripple LIGO detected—and that’s why this week’s discovery is so important.
PROBING THE EDGES
But what’s really exciting is that the process worked, and that means we can continue to use it and find more about the edges of reality.
Team member Prof Gabriela González, from Louisiana State University, told the BBC: “Now that we have the detectors to see these systems, now that we know binary black holes are out there, we’ll begin listening to the Universe.”
We are feeling the edges of reality itself. And that’s pretty exciting.
Nury Vittachi writes about science for young people. His book on Einstein and the fabric of time was shortlisted for the Aurealis Award