Gravitational waves and future astronomy

26 February 2016

Interview with

Lord Martin Rees, University of Cambridge, Dr Andrew Pontzen, UCL

Gravitational waves made a big splash around the world but why has their Man in the universedetection revolutionised astronomy and physics? Chris Smith put this to Andrew Pontzen and Martin Rees...

Martin - These gravitational waves are predicted by Einstein's theory and, in fact, they are the most distinctive and remarkable prediction of the theory and what is amazing is that the observations seem to fit extremely well with the calculations.  So it's a really strong vindication of Einstein's theory, about 100 years after he proposed the theory.

Chris - Are there any other things that we should do in order to validate, vindicate, and corroborate Einstein's predictions?

Martin - Well we still don't know exactly what shape these black holes are and how fast they're spinning and, of course, as astrophysicists, we'd like to know how the black holes got there.  What was the evolution that led to them so there's a great deal for astrophysicists to do.

Chris - We've heard a lot of people saying these gravitational ripples arrived from a billion light years away.  How do we know where those black holes were situated out in space?

Martin - The signal was detected in two detectors about 2,000 miles apart, and there was a slight time lag between the two detections and that tells you something about the direction because it tells you how much longer it took the waves to get from one to the other, going at the speed of light.  And if we had three detectors, we could do a kind of triangulation, but I think we should realise what amazing technology this is.  We're detecting this event, which happened millions of times further away than all the stars you see in the sky, and it's been detected by these instruments even though it's a tiny jitter in the mirrors that we heard about.  A very tiny effect - it's amazing technology.

Chris - 1/10,000 the diameter of a proton is the catchphrase they're citing.

Martin - That's right.  Another way they would present this is like measuring the diameter of a human hair at the distance of Alpha Centauri, the nearest star.  So it's amazing precision so it's the engineers who need far more credit than the theorists.

Chris - And Andrew - is it true to say then that in the past we've had some of our efforts at astronomy frustrated by light being interrupted on it's course to us by stuff like dust and other other materials, but these gravitational waves should pass straight through everything?  So we should, in theory not get them occluded by anything in way...

Andrew - Well, that's certainly true.  But I think there's an even bigger difference when you start observing the sky using gravitational waves, which is the kind of objects you're picking up are simply things you would never see with a traditional telescope...

Chris - So this really is a new vista?

Andrew - Oh yes. I mean, even now, we're talking about two black holes about 30 times each the mass of our sun merging.  If you just stop and think about what that actually means for a second, it's actually mind-blowing and...

Chris - I can tell you're excited.  So on a scale of one to ten where would you put this?

Andrew - Well... It's sort of... I mean it's a ten...

Chris - He's lost for words!

Andrew - Look it's a ten in terms of scientific significance.  In terms of my career, it's just a source of regret really because when I started, I had an opportunity actually to work on a PhD on gravitational waves.  And, at the time, I thought... oh come on, I mean these tiny things, they're never really going to be detected are they?  So I didn't and worked on something else and now I look like a bit of a fool.

Chris - Martin?

Martin - No, I would put it nine out of ten. In a way, the primordial gravitational waves, if we could detect them, would be even more exciting but they're very hard to detect.  So that would have been ten out of then.  I would give these nine out of ten but, because I'm an astrophysicist, I am not just interested in them as tests of Einstein's theory but as part of the evolutionary story of how stars form, evolve, and die. This is telling us about a new way in which stars end their lives.

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