Monday, 17 February 2014

Some light history of black holes

My research is on black holes. So how about a story or two about black holes?

There are two famous solutions to Einstein's equations that describe black holes. The first was worked out by Karl Schwarzschild only months after Einstein completed his general theory of relativity, in 1915. Keen students of history will realise that this was during the First World War, and sharp-eyed etymologists will guess that Schwarzschild was German. So, yes, he managed to work out the first really big-deal solution of Einstein's equations while fighting in the First World War.

Although it is surely completely untrue, I like to imagine young Karl hunched down in the trenches, barely able to see in the gloom of smoke, and barely able to hear over the erratic BANGs and RAT-TAT-TATs of battle, and with his papers spattered with mud and blood from the debris that occasionally rains down into the trench, scrawling away at his calculations. You can be sure that in my vision he is writing with a blunt pencil, and the man who borrowed his sharpener two weeks ago just went Over The Top and never came back.

"Jesus Christ! Where have I lost a minus sign?"

All the other soldiers think he has gone mad. But they do still give him cigarettes.

The next day he is clearly at a very different stage of madness: all grins, and just bubbling with joy.

"What's got you?" they ask. (I leave it to the reader to translate this dialogue into German, and correct my one-century-displaced colloquialisms.)

"Yesterday I made a major scientific discovery!"

"Oh yeah?"

"I finally solved Einstein's new equations of gravity for the space-time metric of a spherically symmetric star. I sent it off to a journal in a dispatch last night. Isn't that fantastic?"

"Um. Yeah. Good for you."

"Now I can relax and get on with contributing to the war effort. What's happening today?"

"We're going over the top."

And that is the last we hear of Schwarzschild [1].

Karl's solution can describe the most basic kind of black hole, which just sits there in space. The next important black-hole result described a rotating black hole, which might sound like only a minor step up in complexity, but it took almost 50 years for anyone to work out. (When physicists say that Einstein's equations are difficult, they are not trying to be funny. You can always tell when physicists are trying to be funny. It is very uncomfortable.)

The rotating solution was worked out by Roy Kerr in 1963. Kerr happens to be from New Zealand, just like me, which I have to say is a far greater source of national pride than the All Blacks. Pulling out of your hat one of the two most important solutions of arguably the most difficult and mind-bending physical theory of the 20th century strikes me as just a tad more impressive than carrying a ball around a field while grunting [2].

I am not telling you about the Kerr solution because of the amazing physics it predicts. That was just a bit of background to what I think is a wonderful example of just how perversely interesting the behaviour of scientists can be.

Before I tell that story, I have another little story, which I think illustrates just what an impressive achievement the Kerr solution was. I was once at a conference in Argentina (ah, the jet-setting life of the scientist!), and I was walking behind two big-shots on the way to lunch, listening to them talk [3]. You should understand that these were senior Professors, big names, great minds, leaders in the field. And I heard one of them whisper to the other, "Have you ever worked through the derivation of the Kerr solution?"

"Fuck, no!"

"Me neither."

Anyway, here is the story I really wanted to tell.

Kerr came up with his solution in 1963. Needless to say, many others had been trying to solve the same problem, and some had got quite close. But close is not good enough. Kerr will be remembered, and the rest will not. One of them (I have forgotten who) recently gave a talk at a conference. During his talk he paused to tell a joke. Now, I warned you earlier about physicists trying to make jokes. He told us it was a story he had never told before. He did a long build-up, all about a cute solution of Einstein's equations that he once worked out, which aficionados of the theory in his audience were familiar with. Then came the punchline.

"I sent it off to the journal, who sent it to someone to referee. He realised that if he changed a few minus signs, he would have the solution for a rotating black hole. So he wrote that up, and become the most famous relativist after Einstein."

I told you it can be uncomfortable. For anyone not paying attention to the subtle subtext of that punchline, the guy was saying, "I was robbed! It should have been me!" And he was saying it FIFTY YEARS after the Kerr solution was published. So this guy, who had done a number of other notable things and was a renowned physicist, had been bitter and twisted about not finding the Kerr solution for half a century. It is easy to see why he got so wound up about it, but you also have to wonder if there was not some way he could get a bit of perspective. At least he was not blown up in the trenches in the First World War!

In the course of relating this story to another venerable scientist, I realised a comforting lesson about the mental-health dangers of life at the top. "We should count ourselves lucky to be mediocre," I said.

"Speak for yourself!" he snapped back. Then he walked away, and has not spoken to me since.

1. I just checked, and "completely untrue" is not the half of it. Schwarzschild did indeed serve in WWI, although he was not a young man. He was a distinguished and successful scientist who joined the army at the age of 40. He died of a rare skin disease called pemphigus in 1916, a year after he worked out the Schwarzschild solution. I learnt all this from wikipedia, so it must be true. Nonetheless, when the epic story of Einstein's general theory of relativity is finally turned into a major Hollywood blockbuster, I expect that it is my version that will make the cut. [return]

2. I understand that this is unfair, and that rugby is a game that requires great skill and physical strength, agility and endurance. It is especially unfair, considering how terribly under-appreciated is the great cultural contribution of our sportsmen. I apologise, guys. Now please let me take my head out of the toilet bowl. [return]

3. I am afraid lunch did not include Argentinian steak. At least, not that day. [return]


  1. This is very entertaining. I hope you're saving the best stuff for the popular science book that will make your fortune, though you'll have to spit every time you admit it.

    1. I was assuming that anything written while I have only five readers can be safely recycled.

  2. I've got to know: have I stayed in the house of the self-assuredly non-mediocre scientist with whom you have not spoken since?

    1. No, but you have met him. Drink coke, play again.

    2. Unfortunately that pretty much opens us up to the wider universe of arrogant scientists. Even narrowing down to those I have met, it would still be quite a challenge.

    3. You also have to filter for potential artistic license.


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