Gravitational fields discovery making waves
In 1916, the inimitable Albert Einstein envisioned the existence of gravitational waves — the idea that gravity behaves like a field and disruptions in this field spread out like the ripples of a pebble tossed in a pond.
One hundred years later, an army of more than 1,000 physicists using some incredibly sensitive machinery has finally confirmed Einstein’s prediction, one of the central pillars of his general theory of relativity.
What they detected was the ripple of a gravitational wave caused when two black holes that had been spiralling around each other finally collided and joined together as one.
What’s perhaps most astonishing is that the ripple that was measured was sent out a billion years ago and just reached the earth, even though it’s been travelling at the speed of light all this time.
Dr. Cliff Burgess, a theoretical physicist who splits his time between McMaster University and Waterloo’s Perimeter Institute, explains it. (Some responses have been edited for length.)
What’s significant about the announcement?
Burgess: There are three things that are special about this. The one that has been in the press is probably the least interesting thing and that’s that these waves have been predicted to be there by Einstein 100 years ago. We know of essentially four forces and they all predict waves of some sort. We’d seen all the other ones and this was the one that was missing, so we could tick that box off. What’s more interesting is these black holes that send these waves, there’s no other way of seeing them, really. Most black holes are produced in isolation in the dark and the only way we’d ever see them is through these gravita- tional waves. The best thing is that this is the beginning of a new branch of astronomy. This is the first time that something has been seen using gravitational waves and they’ll be seeing more of these things. We have another way of looking at the universe. It’s not the end of the search, it’s the beginning of a new field.
Can you explain a bit more about gravitational fields?
Burgess: What we’d been taught in school about gravity is there’s a force acting on you due to the earth, let’s say, and it’s an instantaneous thing and it’s always there. About 100 years ago, Einstein in particular came to realize that a better way to think about it is that the earth is setting up a gravitational field. The field essentially applies a force to you. Imagine you’re the earth and you’re feeling the force of gravity due to the sun, let’s say. If someone instantaneously destroyed the sun, the way you and I would have thought of that is that instantaneously all the planets would stop feeling the attraction to the sun and then they’d start moving off in a straight line and stop orbiting. What really happens is that if someone destroyed the sun right now, we’d still actually feel the force attracting us to the sun for another eight minutes because a ripple goes out through the gravitational field. Until that ripple reaches us — and it’s travelling at the speed of light so it takes about eight minutes to get here from the sun — we still think we’re being attracted to where the sun was. It’s only when the ripple passes that we’d realize there’s no more sun there to be attracted to.
The signal that was measured originated a billion years ago. The scale of time and distance involved in astronomy and astrophysics almost seems incomprehensible, doesn’t it?
Burgess: You do get blasé about it because we talk about it a lot. But it is true — when you sit back and think about that, it really is phenomenal. It’s amazing that it’s just the same everyday rules of physics like we know about on earth and it seems to work everywhere.
Is this discovery worthy of a Nobel Prize?
Burgess: Three weeks ago if you’d have made a bet that they were going to win a Nobel Prize for this, you would have got some odds on it. Now, I would say it’s better than 90 per cent odds they’re going to get the prize this year. It does look very thorough and there’s very little doubt that they’ve seen what they said they were supposed to see.
What might come next because of this discovery?
Burgess: Not only do you learn about the black holes, but you learn about the space and time through which the wave travelled to get to you. So almost certainly people will be thinking about what that’s telling us about the structure of the universe as a whole. It will add to what we already know from studying the universe using visible light and electromagnetic radiation. There will be a whole bunch of directions people will take this because it’s very rare that you get a completely new family of things you can see and a new way of looking at the universe.
Einstein predicted this a century ago, before computers existed — just a chalkboard, a piece of chalk and his imagination. Does it astound you that he was able to come up with these mental visions of how the universe operates?
Burgess: Well, he was clearly a gifted man, right? (Laughs.) He had these two big theories — the special theory of relativity and the general theory of relativity. It’s probably true that with the special theory, someone would have gotten that if he hadn’t gotten it. Einstein’s genius was that he identified the important questions. It really is kind of striking that mathematics is the language that nature uses.
I would say … they’re going to get the (Nobel) prize this year. CLIFF BURGESS