Distance is a curious concept, transient and refractive, warping and mutating according to scale and perspective.
The distance from your house to the shops, from New York to London, from one galaxy to another, all require not just different methods of measurement, but different ways of understanding what those measurements mean. The shop and your house, for instance, unlike two widely separated galaxies, are not belting away from each other at the speed of light.
Scaling up again, superstring theory – or plain string theory to its friends – predicts a potential infinity of universes, perhaps spread out like a cosmic quilt, perhaps cycling eternally from bang to crunch, perhaps happening simultaneously in a multidimensional overlay.
Here, distance, space, time – our quotidian grasp of these concepts, at least – collapse completely.
And it is here, on the edge of the known, that Brian Greene, particle physicist, leading string theorist, and professor at Columbia University, makes his living.
For Greene, though, there is still another concept of distance that sometimes occupies his mind, a concept that cannot be quantified, no matter how sophisticated the mathematics, and that will never be subject to experimental evidence, no matter how much juice is pumped into the Large Hadron Collider.
It is, nevertheless, a concept that gives rise to a powerful question. What is the distance between a New York scientist and a dead Algerian philosopher?
“I sort of re-read Albert Camus every few years,” he tells Cosmos from his office in New York.
“He has a hold on me in a very deep way, and his ability to weave deep philosophical questions together with the kind of human concerns that we all have, into what I find to be riveting stories, makes him a compelling thinker.”
Greene’s love for Camus isn’t the recently discovered intellectual regard of a smart guy in his 50s. It goes way deeper. It has occupied him for most of his life.
In terms of his research – from his doctorate describing Calabi-Yau shapes, the putative repositories of the six hidden dimensions string theory demands; to his present quest to uncover evidence of quantum gravity in data describing cosmic microwave background radiation – the image of Camus, Gauloises cigarette hanging from his lip, lurks beneath the equations.
For Brian Greene, Camus was the start of it all.
At the beginning of his best-known book, The Fabric of the Cosmos (2004), Greene describes his teenage discovery of Camus’ philosophical masterpiece, The Myth of Sisyphus, in his father’s bookcase. He was transfixed by the author’s opening line: “There is but one truly philosophical problem, and that is suicide.”
“I do consider physics to be in some sense a branch of existential philosophy,” Greene tells Cosmos.
“I would say there is a deep connection. The reason why I’m interested in physics, the reason why I’m interested in cosmology, is really to try to gain some insight into the very questions that Camus is asking. What is it that makes life worth living? What is it that drives the human spirit to explore as opposed to crawl back into the cave and crumble under the weight of existential angst?
“In essence, that is what Camus is asking. ‘What is it that makes life real? Why don’t we commit suicide?’”
String theory posits that the fundamental ingredients of the cosmos are not point-particles, but tiny one-dimensional strings, the varying vibrations of which determine material expression. One frequency produces an electron, another produces a quark, and so on.
Further, the cosmos comprises 10 dimensions, rather than the four that classical physics describes. The additional six are minuscule, curled up inside a multitude of Calabi-Yau shapes.
It is, to quote Greene’s Columbia profile, “a theory that purports to give us a quantum theory of gravity as well as a unified theory of all forces and all matter.”
It also, to quote astrophyicsist Neil deGrasse Tyson, makes claims that “continue to lie outside our current experimental capacity to verify its formalisms”.
It is a theory that thrives on head-spinning detail, and will ultimately stand or fall (or, more likely, adjust) on eventual experimental confirmation of its mathematical predictions.
That said, Greene’s existential approach gives rise to a position that may surprise.
“To me physics is more of a means to an end than an undertaking in its own right,” he says.
“I’m not that interested in this or that particle. I’m not that interested in how this or that particle smashes into others and creates a cascade of debris. These are vital elements of physics, but I’m interested only in so far as they can tell us something about the nature of reality, and, from that, why reality is worth being part of.”
It is a perspective that owes much to perhaps the only person whose influence on Greene’s young life was greater than that of Camus – his own father, an enthusiastic autodidact, polymath and, for a while at least, vaudeville performer.
“My father was not a traditionally trained academic thinker,” he says.
“He dropped out of high school in tenth grade. He went on the road to sing and perform and play harmonica and all those sorts of things, but deep inside the issues of science, the issues of philosophy, they captivated him.
“So he didn’t study them in school, he didn’t study them in a university – he never went to a university – but the ideas were with him all the time. When I was young we sat down and he taught me about atoms and molecules and protons and neutrons, and taught me about distant galaxies rushing away.
“He didn’t know it in a deep academic sense, but he knew it from his own readings and that was enough to get a five-, six-year-old kid like me hugely excited about math and science. So he set me on this trajectory, for sure.”
Paternal influence did far more than ignite a spark, or even suggest a direction for Greene’s curiosity. It also provided, perhaps unconsciously, a working model for a life that encompasses both academic research and mass communication.
‘People have basically come to the realisation that there’s so much about black holes that we don’t understand.’
In parallel with his scientific career, Greene enjoys a second as a prolific, authoritative and, in recent years, experimental science communicator.
He is the author of three highly regarded and commercially successful books on cosmology – The Elegant Universe (1999), The Fabric of the Cosmos, and The Hidden Reality (2011).
He has also written a children’s book, Icarus at the Edge of Time, which in 2010 he adapted for film and stage, collaborating with the famous serialist composer Philip Glass. He has fronted documentaries, written innumerable newspaper articles, and enjoys a reputation as a science go-to guy on US television.
In 2008, with his wife, science journalist Tracy Day, he founded the World Science Festival.
This year’s festival, to be held in Brisbane in March, includes Greene’s latest theatre works, collaborations with, among others, Emmy Award-winning US composer Jeff Beal, and veteran actor-director Alan Alda.
If you’ve ever read The Fabric of the Cosmos – in its current Penguin reprint, a 569-page monster of densely packed nine-point type – you’ll be aware of the immense patience and generosity Greene brings to bear as an author.
Cosmology, string theory, and quantum mechanics are complex subjects, and Greene takes his readers gently through them, step by step, taking all the time he needs, often deploying characters from The Simpsons, Star Wars, The X-Files and even Gone With The Wind to explain the material.
His other books show equal patience (although, just quietly, the most recent benefits from the absence of Bart and Lisa), but the interesting thing is that nothing in the conditions of his academic tenure actually obliges him to write pop science.
The drive to do so, however, has been with him since he was a teenager – a fact he confirmed very recently when an office clean-out uncovered his letter of application to college.
“I re-read that statement written as a high school kid and in it, almost disturbingly, I’d followed the trajectory that I imagined that I might,” he laughs.
“I’d said I wanted to study the universe, study physics, but also bring the insights to a broad public.”
On reflection, he says, it was his father who showed that such a double-focus life was possible.
“I think that was always with me, because I was in a household where one of my parents was a performer – a thinker but a performer,” he explains.
“He was in many ways leading that kind of dual existence. He was a composer, so he would have long stretches of solitude where he would compose music, and then he’d have long stretches of being out there in the world, performing music.
“So in some sense it’s the same kind of thing for me.
“I’ve got long stretches of solitude when I’m working on the actual research, but it never feels like enough to me, and it never felt like enough to me to stop there.
“I’ve always felt driven to bring that material out to the world. It just felt so tragic to me, for these wondrous ideas to be largely inaccessible to a broad public that would be so excited to know about them if only they spoke the language.”
Greene’s skill as a science communicator lies only partly in his ability to explain the seemingly inexplicable.
It is aided in no small measure by carefully placed anecdotes, giving insight into the excitement and passion that suffuses theoretical physics.
One of these involves him bunny-hopping across the stage at the University of California, Santa Barbara, in celebration of Argentinian string theorist Juan Maldacena’s work on holographic parallel universes.
In another, he recalls asking the great American theoretical physicist John Wheeler, in 1998, what he thought the dominant theme in physics would be over the next few decades.
“He put his head down, as if his aging frame had grown weary of supporting such a massive intellect,” Greene wrote in The Hidden Reality. “He then slowly looked up and said a single word: ‘Information’.”
Almost two decades later, Cosmos asks him to answer the same question. He nominates two matters.
“I think Wheelers’ comment there was quite prescient,” he says.
“We are now living through an era in which ideas of information theory are playing a profound role in physics.”
This relates particularly, he explains, to continuing work on trying to understand the nature of black holes. It is an area of research that excites considerable passion.
“In the last few years people have basically come to the realisation that there’s so much about black holes that we don’t understand,” he says.
“Largely, it has to do with the following question: If something that contains information falls into a black hole – your iPhone, your iPad, an encyclopaedia, a book, your wallet – where does the information content go?
“Stephen Hawking, for a long time, simply said that the information is gone. It leaves the universe.
“That created terrible problems, because our understanding of quantum physics doesn’t allow information to just simply disappear.”
‘We used to think that physics is solely the study of phenomena whereby a force is exerted here and an influence is also felt here.’
Physicists Leonard Susskind and Gerard ‘t Hooft, among others, pursued the issue. They suggested, at length, that when information enters a black hole it is copied and stored on the hole’s two-dimensional surface at a density of one bit (one yes-no question) per Planck length (10-33 centimetres). Greene and his fellow string theorists attacked the problem from a different angle and reached the same conclusions.
Information in a black hole is not destroyed, but conserved. Two-dimensional storage describes three-dimensional objects.
Given that the space inside a black hole is governed by the same principles as the space outside it, the possibility that our three-dimensional reality is in fact the result of a two-dimensional projection – much like a hologram – was bolstered.
“People struggled with that for a long time, and now it’s really come to a head with our proposals of how the information would not get lost,” says Greene.
“Stephen Hawking agrees with me now. He has his own version, in fact.”
But where Wheeler saw just one central focus for physics, Greene adds a second.
“Another dominant theme is the notion of non-locality,” he says.
The best illustration of the term is the experimentally verified phenomenon in which two sub-atomic particles, entangled and then separated, exhibit simultaneous change, regardless of the space between them.
Einstein famously derided the idea as “spooky action at a distance”, but it has long since been accepted as uncontroversial in particle physics.
“We used to think that physics is solely the study of phenomena whereby a force is exerted here and an influence is also felt here,” says Greene.
“But quantum physics has taught us that there are certain kinds of non-local effects. And as we study gravity and information we’re finding that gravity also seems to have a deep non-locality embedded within it.”
Indeed, non-locality related to quantum gravity is, to slip into the vernacular, so hot right now, with several teams around the world working towards experimental validation of the idea.
One team, for example, led by Alessio Belenchia at Italy’s Scuola Internazionale di Studi Avanzati (SISSA), in December 2015 published in Arxiv an overview of several past experiments testing non-locality and quantum gravity, highlighting in particular mysterious “spontaneous periodic squeezing that cannot be generated by environmental effects”.
The paper predicted the rapid development of “table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology”.
And testing – the gathering of evidence, the repetition of method and result – is of course the bedrock validation of the scientific method.
It is an issue that sits sometimes uneasily in the field of string theory, not least because, as deGrasse Tyson pointed out, many of its predictions, such as multiple universes, currently lie beyond empirical proof.
It is not a matter that unduly depresses Greene.
“To me, what makes life worth living as a physicist is the possibility that we are developing ideas that future generations may be required to ultimately verify,” he says.
“How thrilling would it be, if, through the power of human thought, we were able to come up with radically new pictures of reality that future generations finally are able to confirm?”
In the meantime, string theory enjoys a robust predictive power, which provides at least indirect evidence that Greene, Hawking, Maldacena and their colleagues are on the right track.
‘If string theory’s wrong, I’d like to know right now. I’d like to have known 20 years ago.’
Greene remains hopeful, too, that it won’t be long before the Large Hadron Collider throws up evidence of the super-symmetric particles – “partners” that pair every electron with a “selectron”, every quark with a “squark”, and so on – that string theory demands.
He cites other possible forms of evidence, including the creation of miniature black holes (with a consequent loss of energy presumed to have shunted into other dimensions), and, his own meticulous search for subtle signatures in the cosmic microwave background radiation.
“Collectively there are a number of ways that I think you get strong hints that string theory is going in the right direction,” he says. “But failure to see any of them will not rule the theory out.”
He has no time for critics who suggest that absence of evidence in string theory is strong evidence for continuing job security.
His counter-argument echoes Jean Paul Sartre’s assertion that “Man is not the sum of what he has already, but rather the sum of what he does not yet have, of what he could have.”
Says Greene: “I think that you go around once in life, and who would ever want to spend that time working on something that’s not right, that’s wrong, that’s a total waste of time?
“So if string theory’s wrong, I’d like to know right now. I’d like to have known 20 years ago.
“We want to rule the theory out. I would be thrilled if string theory is wrong. I would be thrilled if we could learn that right now. Then I could move on to something else that might be right.”
At which point, somewhere in the shadowlands of the imagination, Albert Camus hitches up his coat collar, drags on his Gauloises, gives a quiet chuckle, and heads off to the wine bar.
Dr Brian Greene will be visiting Australia in March, 2016. Information and tickets are avialable here.