Father figure

Leonard Susskind: a Darwinian physicist

By Matin Durrani

He probably won’t like me for saying this, but Leonard Susskind of Stanford University looks a bit like Charles Darwin.

The reason I know is that Susskind – one of the father figures of string theory – flashed up a slide of the great man (Darwin that is) during a public lecture last night held as part of the University of Bristol’s centenary celebrations and the city’s Festival of Ideas.

It was uncanny: Susskind’s grey beard and thinning hair make him a dead ringer for Darwin, who was born 200 years ago this year. I wonder if anyone’s told him of the likeness before?

Attended by nearly 700 people packed into the university’s neo-gothic Wills Memorial Building, Susskind’s lecture was entitled “Darwin and the cosmic landscape”, in which he examined Darwin’s influence on physics.

Susskind’s thesis is that by putting forward the then radical idea of a natural explanation of the origins of life, Darwin “set the standard for what an explanation should be like”. In other words, as Susskind eloquently explained, by rejecting the idea that life was too improbable too have arrived by accident and that there must be some sort of grand designer, Darwin instead sought a scientific explanation for the existence of life.

As Susskind pointed out, there are four different base pairs on a DNA molecule (A, G, C and T) and with each molecule having typically 10^8^ base pairs, there must be 4 to the power 10^8^ different ways of arranging those base pairs. Genetic mutations allow different arrangements, which – eventually – leads to the “tree of life”.

But what’s all this got to do with physics? Well, string theory permits the existence of a “landscape” of about 10^500^ different universes. We live on one of these universes – the one that permits the existence of life. It’s essentially an anthropic argument – the world is fine-tuned so we’re here to observe it.

I won’t go into the details here, but you can find all you need to know about this subject in an article by former Physics World features editor Matthew Chalmers, who also rolled up at last night’s lecture and was one of several people to pop Susskind a question.

Susskind has also written about the landscape in his book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design, which fellow string theorist Michael Duff reviewed for Physics World in 2005.

After the lecture, I joined Susskind for dinner at the Bordeaux Quay restaurant on Bristol’s harbourside.

He was great company and recalled, over a pudding of chocolate tart, how he never wanted to write The Cosmic Landscape, but was persuaded to do so by legendary New York agent John Brockman who reckoned Susskind had a talent for writing. Actually, Susskind said he found his more recent book The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics much harder to write than his first.

Susskind has a knack for a good story and told me a great anecdote about the time he met Bristol-born Nobel laureate Paul Dirac in the US in the late 1960s when, as a fresh-faced physicist, he asked Dirac’s advice on how to solve a particular physics problem. I can’t remember all the details – and anyway it would never be as amusing if I told it — but suffice to say it was all about Schrodinger’s equation. No, honestly, it was funny.

Based at Stanford, Susskind seems to know pretty much everyone who’s anyone in US west coast physics, including former Berkeley Lab boss Steven Chu. Like most physicists, Susskind reckons Barack Obama has made a great choice in picking Chu as his energy secretary. (“Chu’s a great guy, really sharp.”)

Susskind also had some choice comments about another Stanford colleague — the Nobel laureate Robert Laughlin, who was famously recruited to lead and reform the Korea Advanced Institute of Science and Technology, but left under a cloud after just two years in charge.

As we left the restaurant, I asked Susskind if he fancied writing anything for Physics World. He wrote a feature for us a couple of years back on superstrings and did a small piece for our 20th anniversary issue last year. So we’ll see if he has something new up his sleeve.