Thursday, 16 November 2017

The Election Day Event

Today the LIGO and Virgo collaborations made their sixth announcement of a confirmed gravitational-wave detection. Once again the signal was from two black holes colliding — this time the black holes were each close to 10 times the mass of the sun, with the smaller object possibly as low as 5 solar masses, making this likely the lowest-mass binary-black-hole yet observed.

Monday, 16 October 2017

Kaboom! Two kinds of astronomy collide, and produce a burst of science

Holy crap! The LIGO and Virgo collaborations just announced their most incredible observation so far. After the first direct detections of gravitational waves from black holes colliding, that’s really saying something! And not just that — a string of other astronomical collaborations are part of it, making it even more incredible. If you have just heard the news, you may be in a whirl trying to make sense of it all. Even if you have spent the last two months scooping up all those scurrilous rumours, this may still be just too much. Hell, I have known about it since the observations came in on August 17th, and I am having trouble getting my head around it.

Ok. I need to calm down. Let’s take a step back, to the afternoon of August 17th (UK time).

Prelude


I was in the postdoc office, delivering a beautiful post-liquid-lunch soliloquy on the supremacy of binary black holes. All of the postdocs were listening intently, in that funny way they do, by looking directly at their computers and typing. The crux of my pontification was that so far the Advanced LIGO and Virgo detectors had found several gravitational-wave signals, but all of them were from the same kind of source: black holes colliding. For years people had been honking on about neutron stars, and how neutron stars spiralling together were going to be the prime LIGO source, and thumbing their noses at us binary-black-hole dreamers. And there was another crowd who were all worked up about “multi-messenger astronomy” — they hoped that gamma-ray satellites would observe a gamma-ray burst (which is an abstruse technical name for a burst of gamma rays) at the same time as we detected the gravitational waves from the neutron stars spiralling together. That would prove for the first time the hypothesis that neutron-star collisions are what produce short gamma-ray bursts. They were convinced that that was going to be what gravitational-wave astronomy was going to be all about.

No such luck. We had detected no binary neutron stars. There had been five months of the first LIGO-Virgo observing run, and then another almost nine months of the second observing run, and no neutron stars. Only black holes. Check out detections One, Two and Three. And just that Monday had come detection Number Four — black holes again.

Neutron-star fans were out of luck.

After a pleasant lunch, I was full of sympathy for them.

“They should stop calling it a gravitational-wave observatory!” I crowed. “They should rename it a black hole observatory!”

Some of the postdocs acknowledged this wisdom in their own special way, by putting on headphones.

The Big Moment


Five minutes later, Laura suddenly started yelling, “Send it! Send it!”

At first I did not pay much attention. She was on a conference call, and sometimes those things get a bit heated. Even when it comes to asking someone to send an email.

But she was not talking about emails. They were discussing whether to send a “circular”, an online notice to astronomers that we had found something interesting that they might want to point their telescopes at.

I now realised that three postdocs were yelling on three separate conference calls, and all of the rest were gathered around their desks.

Occasionally they tried to help me understand. There had been an alert that the Fermi gamma-ray satellite had found a gamma-ray burst. It was weak, so the gamma-ray people were unlikely to care much about it; they see these things all the time. Around the same time, the LIGO Hanford detector registered a binary-neutron-star signal. That sounds exciting, but the computer analysis codes had rejected it, because a confirmed detection needs a signal in at least two detectors, and the analysis codes decided that the Livingston detector data were poor, and there was no sign of a detection in Virgo. In other words, at first glance it might not sound interesting for gravitational-wave people, either.

But: any chance of a neutron-star detection is too good to pass up. Time to check by hand the data from Livingston and Virgo.

That was when I heard people periodically shouting “Koi fish!” around the room.

Laura explained to me, “A koi fish is a kind of glitch.”

I absorbed this information using the customary professorial response. “I know that.”

“There’s a great picture that just got sent around.”

(Yes, we were only minutes into this thing, and there was already a flood of emails, website links, data tables, and figures.)

This is something like the figure she showed me:

Signal plus "koi fish" glitch.
(Adapted from Fig.2 in the main LIGO-Virgo discovery paper.)

The big yellow splotch is the “koi fish” glitch — a patch of noise in the data that obscures any signal for a short time. But leading up to the glitch is the most incredible, perfectly clear signal any of us had ever seen: instantly recognisable to afficionados as a binary-neutron-star inspiral. The slowly rising line is the frequency of the gravitational wave increasing (“chirping”), as the two neutron stars orbit closer and closer, moving faster and faster. The full signal visible in the data was one hundred seconds long. ONE HUNDRED SECONDS! That’s over a MINUTE AND A HALF! The longest previous detection was the binary-black-hole signal GW151226, which lasted only ONE second! The movie illustrates the point best.

[Credit: LIGO/University of Oregon/Ben Farr]

Once the glitch was cleaned out of the data (you can read all about it in the paper), the combined data from all of the detectors added up to the loudest signal we have ever observed. (The signal was weak in Virgo because of the source's location in the sky. The fact that the signal was so weak in Virgo helped us to localise the source to somewhere over south-Eastern Africa.)

And of course there was also the gamma-ray burst. So we now know for sure that short gamma-ray bursts are indeed produced by colliding neutron stars.

Twenty minutes earlier I thought we were going to have to wait another five years, or longer, to answer that question, and most likely slowly and hesitantly, after a series of weak detections and “possible”, not completely certain, gamma-ray-burst counterparts. Now it was done.

A Rare Gift


I am a devoted disciple of black holes, yet I will gleefully admit that this was the most incredible detection so far. A few reasons:

Neutron-star mergers are still going to be rarer sources than binary black holes. We know this from the fact that in the last two years we have not observed any others. That is what made this observation so astounding: the two neutron stars were ten times closer than any of the black holes we have observed so far. Even the most evangelical and caffienated neutron-star lover never dared to suggest we would observe a signal this close; it would have been a joke. Only about 1 in 50 neutron-star detections will be this strong — so it could be a long while before we see anything like this again. (I explain this back-of-the-envelope estimate here.) That makes this a very rare and precious signal. Factor in that satellites will see the gamma-ray burst in only a handful of binary-neutron-star detections, and we see that it is a truly remarkable signal indeed.

When we observed binary black holes, we learned nothing new about the nature of black holes. We already knew from Einstein’s equations what the signals would look like. That was why we were confident that we had squeezed as much information as we could out of the signals: we could match the signals we had calculated against what we measured. In the case of black holes, the theory was well ahead of observations.

Neutron-star mergers are the other way around. People considered them a likely source of gamma-ray bursts, but no-one could confirm it with theoretical calculations. People have struggled to produce a gamma-ray burst from computer simulations of merging neutron stars for years, but without conclusive results. Even when they artificially cooked up the most promising conditions, they could only manage a hint of the beginning of a burst. This is because computer simulations of neutron-star mergers are much more difficult than for black holes — there is all that nuclear physics to take into account, for a start, and besides all of the extra (in some cases speculative) physics involved, calculating what is going on in every centimetre of ten-kilometre-wide objects takes a lot of computing power!

So now we have that ideal situation in science: the observations are guiding the theory. Combined gravitational-wave and gamma-ray measurements have nailed the question of the source of short gamma-ray bursts. Now it is for the theorists to catch up.

There was a huge amount of other information in these observations. I am not qualified to talk about the measurements from EM astronomers, but even from gravitational waves there was much more to do. One lovely example was to make good on Bernard Schutz’s thirty-year-old idea that we could use gravitational waves to measure the expansion of the universe. The calculation is not yet as accurate as those from conventional astronomy, but since the two current measurements disagree, this gives us hope that one day gravitational waves could nail this problem, too.

The future


GW170817 is going to be a goldmine of science for a while to come, and it should be clear from everything I have said that it will be a long time before we find a richer signal. That is a rock-solid prediction for the next year, because the LIGO and Virgo detectors will be switched off for another upgrade. When they switch back on in 2019, we may find one or two neutron-star mergers each year that coincide with gamma-ray bursts — but, again, it is unlikely that any of the signals will be as strong as GW170817. For that we may well have to wait until the next decade.

Or I could be wrong, and we get another surprise. It has happened before.



More Gravitational-Wave Stories

February, 2016:
The Discovery
How it Felt
How We Squeezed Out the Juicy Science

March, 2016:
Trying to Explain Gravitational Waves (Part I) (Part II)

June, 2016:
Book Review: Black Hole Blues
Detection Number 2 -- Black Holes Rule!
Rumours, Secrets and Other Sounds of Gravitational Waves

February, 2017:
One Year Anniversary (of being world famous)

June, 2017:
Detection Number 3 -- Nothing to see here: they are black holes
A hint of controversy

September 2017:
Detection Number 4 -- Virgo nails it

October 2017:
Did I just win the Nobel prize?

November 2017:
The Election Day Event

Tuesday, 3 October 2017

Woohoo! I just won the Nobel Prize!

Today I won the Nobel Prize in Physics. Yeah, I am pretty excited about it. To be honest, though, I was not surprised.

The prize was awarded for LIGO's first direct detection of gravitational waves, which we all know was the biggest scientific discovery of the century. That is not me showing off. That is what other people have said. It is such an undisputedly incredible achievement that all of us LIGO scientists can afford to be perfectly humble about it. We knew the Nobel was coming. We can take it in our stride. Hell, after all of those telecons of the Nobel Prize Acceptance Working Group, we were starting to get a bit sick of the whole thing.

Just a second. What is that you say? The prize is not for me? Nonsense. Take a look at the citation.

Wednesday, 27 September 2017

The Power of Three

Another day, another announcement of LIGO detecting gravitational waves from two black holes colliding. What's the big deal?

Wednesday, 2 August 2017

Time to promote Doctor Who

I have to confess that I enjoyed the latest season of Doctor Who. It gave me a wonderful sense of achievement. The Doctor himself has vindicated my life choices more thoroughly than I could ever have hoped. I once dreamed of being Doctor Who, but now he dreams of being me: a Professor at Cardiff University.

Monday, 10 July 2017

John Clarke

In these strange times, I offer you some comedy. Not my own, of course. No, we can do far better than that. I would like to tell you about Mr John Clarke.

John Clarke was a New Zealand-born comedian, who died in April. He died relatively young (68), and suddenly (he collapsed while out walking). The news sent me off to look up some of his material. Guess what? He was a genius.

Tuesday, 20 June 2017

The Irresistible Allure of Controversy

On June 13 a paper appeared on the preprint arXiv that brought into question LIGO's first detection of gravitational waves. Six days later one of my LIGO colleagues wrote a blog post highlighting errors that debunk the claim. His response was circulated amongst the LIGO and Virgo collaborations, and discussed within their many fascinating email lists, and officially approved as a response. As such, it is professional, polite, and to the point. This post, on the other hand, has not been circulated to my LIGO colleagues, or discussed in any mailing lists, or sanctioned by anyone. So any residual politeness is entirely my own fault.

Monday, 19 June 2017

Clive's Continuing Climate Confusion

When I was young, I do not remember my father shouting very often. He kept calm in the face of just about everything, even me as an argumentative adolescent. But sometimes he was faced with something so ridiculous, so nonsensical, so stupefying — a problem, a person, or a statement — that he had no calm response for it. It was just too stupid for him to comprehend. Then he would always yell the same thing: “Oh for crying out loud!” I guess he grew up in less profane times. Either that, or he was quoting Meat Loaf.

That is the first thing I thought when I checked up on Clive James’s latest writing, and found a teaser article to his latest effort: “Climate alarmists cop a Clive James savaging”. Oh for crying out loud!

I have not read the article itself; it is behind a paywall, and I will be damned if I am going to pay to see it. (I would be grateful if someone sent me a copy.) From The Australian’s gushing promo, I assume that it is much like all the others: complaints about climate-change activists, as if they are synonymous with the scientists, and not a word about the science itself.

I wonder if he has ever actually spoken with a climate scientist? As a media figure of some note, it is surely not that hard for him to get in touch with a few. I realise that he only lives in Cambridge, where first-rate scientists are hard to find, but surely he can manage someone?

I will not waste energy ranting more. Last time this happened, I had a long flight and a good book to help me deal with it. No such luck this time, so I will just re-post what I wrote then.


[March 23, 2016]

I take a dim view of most faiths, but faith in human nature is the worst of all, because I cannot seem to shake it off. My only consolation is that there is always a plentiful supply of indisputable evidence to nudge me away from delusion, at least for another few hours, like a diabetic taking a regular shot of insulin.

More correctly, it is my instinctive faith in the human intellect that needs -- and always gets -- a regular clobbering. 

Last week I was at a LIGO meeting in California. It was our first big meeting since we detected gravitational waves. With everyone delirious and disoriented from success, it was easy to find examples of fine minds going screwy. But it wasn't until the end, when I was packing to leave and catching up on my web browsing, that I got my real insulin shot for the week. 

It came from my old hero Clive James. Two years ago I used this wise old man of letters as an excuse to write a little about the workings of science, and in particular about scientific expertise. You see, I had admired Clive James for many years as an extremely clever and perceptive writer, not to mention a superb humorist, but he had more recently made a stand as a climate-change sceptic. I was all in favour of scepticism, but in the end, given a choice over what to do and what to support, surely the broad consensus of the expert scientific community took precedence? 

I wanted to believe that his view was merely a simple misunderstanding, which I suspected was common among many smart people who denounce climate-change science in the name of healthy scepticism and independent thought. That is why I wrote a long series of posts on the subject. (With only a few digressions…)

The alternative explanation, of course, was the fallible human intellect. An individual mind, no matter how sharp, cannot on every subject reach the truth alone. Not only had he made a mistake, but he was incapable -- and would always be incapable -- of seeing it. 

I did not want to believe that. I had to hold out a little hope. Clive could see the error of his ways at any moment. He had not written explicitly about climate change for the last year, so perhaps that moment had already come. He had instead had a huge late-career success with poetry, and more literary writings. In fact, I had his new book "Latest Readings" in my bag for the flight home. 

Then I checked his most recent Guardian column, and my hopes were dashed.

In an otherwise typically clever and insightful review of this year’s Oscars ceremony, he responded to Leonardo DiCaprio’s acceptance speech with a speech of his own. 

Along the way, he aired precisely the complaint I have against him, and of course put it much better: “People can harbour an irrational belief and still be rational in other respects. That’s what I would like my critics to think about me, so I strive to think the same about them.” 

Yes, that is exactly what I think about him -- but I can't let go of the possibility that it is not irrationality, just, once again, a misunderstanding. His argument against climate change never falls to the science, but to the stridence and closed-mindedness of the activists. On that point I have to agree with him. (He also has a rather odd argument about their poor grammar, but let’s not tumble down that rabbit hole.) If he mistakes the most extreme nut-job crusaders for the scientists, then of course he is going to conclude that the science is all wrong.

I did not open "Latest Readings" on the flight home. I thought it would be more instructive to watch a film I found that was called "Irrational man". It turned out to have nothing to do with science, but I thought it was delightful anyway -- when the romanticised sun-drenched college farce veered off into Dostoevsky territory (while remaining romanticised and sun-drenched), I was hooked. The director was good old Woody Allen, who is certainly very old but reputedly far from good, but I decided that loving the film was only a small variant on Clive's dictum: "People can harbour appallingly criminal sexual proclivities and still be admirable in other respects." Or something like that. 

As it happens, I had already postponed "Latest Readings" to read instead Alice Dreger's "Galileo's Middle Finger", which is all about science activism. What is wonderful about the book is that the author moves from the role of activist against researchers, to an advocate of researchers beset by attacks from activists, and then back again. On the way she decries the same activist tendency as James does: to see the cause as more important than facts, and to believe that the fight has to be won at all costs and by any means — including personal attacks on the enemy, aimed at destroying their careers, their personal lives, and their families.

The topics make up a far larger and more dangerous city of science than the cosy village of gravitational waves that I live in — medical interventions of intersex children, transgender issues, societal versus biological causes of rape, and controversial studies of indigenous peoples. My view that controversy and political shenanigans are rife in my field is now revealed as laughable compared to the adventures that Dreger describes. Arguments over the false-alarm rate of a gravitational-wave signal can become heated, but no-one is ever labeled in national headlines as a rape apologist or accused (in The New Yorker, no less) of implementing a campaign of Nazi eugenics. No embattled gravitational-wave astronomer has ever told me, as one researcher told Dreger, "Things were so bad that the police told me to take some precautions, like checking my car for car bombs every morning."

Dreger argues for activism based on evidence, with the goal of reasoning with the “enemy” and, if the evidence accumulates differently to how you expected, then perhaps also conceding to them. That approach relies on just the kind of rationality that I refuse to have faith in, but just because it is not infallible doesn’t mean that it never works. Sometimes it does, and it is surely better than ignoring or suppressing facts, or behaving like a shit. 

Dreger and friends display an admirable enthusiasm for charging headlong into political minefields. Put another way, when she sees the intellectual equivalent of an innocent hiker being savaged by wolves, instead of running away with barely a pause to take a selfie, she strolls in and tries to pull them off. She makes clear that this is just as dangerous as it sounds, and not all of the battle scars are scars of victory. 

The book is a thoughtful, spirited, and very personal defence of a scientist's right -- indeed, obligation -- to ask and then try to answer any damn question they want. The argument appears again and again, but never more powerfully than when Dreger experiences a euphoric epiphany and asks, "Is there anything too dangerous to study? Should there be any limits? What if, in order to prove how important truth-seeking is, we made a point of studying the most dangerous ideas imaginable?" And a few lines later, "What if we came together in the ivory towers, barricaded the doors, and looked at the skies?"

Dreger’s book does not include any examples of scientists who think that climate change is a sham, and have been hounded from their jobs as a result. Perhaps Clive James will have to write about them himself. If he did, and if they were for real, I would echo his support of them — we need dissenting opinions, and we should welcome data that challenge our views. If the facts are going to eventually overturn the current consensus view, then I hope that they are uncovered as soon as possible. But for now all we can do is act on the facts we have. To refuse to accept them just because some of the people who voice them are tossers -- that truly is irrational. 

Thursday, 1 June 2017

Nothing to see here: they are black holes

The latest news from LIGO: another observation of two black holes colliding. This one dates from January 4th.

The black holes were approximately 20 and 31 times the mass of our sun. For the record, this similar to the first binary we found back in 2015. The main difference is that the new binary was almost twice as far away (or less favourably inclined to us), so the signal was about half as strong, making our measurements about half as accurate.

That doesn't sound very exciting, does it? The same thing again, but half as informative. Did we learn anything interesting?

Friday, 17 February 2017

How I saved the world with gravitational waves

Are you filled with hopeless dread, now that the forces of bigotry and fear have been unleashed on humanity at unprecedented levels via individuals of incomprehensible incompetence and stupidity? Is it no consolation whatsoever that moronic despots are already the norm in many parts of the world, and the only novelty is that suddenly the blundering malevolence is so close to home? Do you wish that you could hide from it all? 

Perhaps you envy us scientists, who can escape into the endless funhouse of pure intellectual exploration?

Tuesday, 24 January 2017

Fake News Flash!

Oh, the humiliation! The guilt! The shame! It is all weighing on me too much, and I have to confess.

Last weekend I spread a piece of fake news.

Wednesday, 18 January 2017

Lest We Forget: 2016

What an instructive year 2016 turned out to be!

We learned nothing new, of course — I am hard-pressed to name any year when that happened. But it was a great year for reminders.