an Astrobiology Interview

For physics, this antagonism between small and large, quark and galaxy, has a possible deep resolution for string theorists in the geometry of space-time itself.

Higher dimensions than the three extended space coordinates and time provide the fabric for all matter, which is generated by vibrations of tiny energy loops -- a billionth of a billionth the size of an atom. One way to test these theories is using high-energy particle accelerators, as microscopes to probe the smallest distances in a global race to build the next big one (> 27 kilometers), the highest energy machine in the world.

A polymath and child prodigy in mathematics, Greene could multiply 30-digit numbers at the age of five. In sixth grade, Greene was so far ahead of his school in math that he had to find a tutor at Columbia University.

He entered Harvard in 1980 to major in physics, and with his bachelor's degree, Greene went to Oxford University, in England, as a Rhodes scholar. His best-selling book "The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory" (1999) was a finalist for the Pulitzer Prize in nonfiction.

For those curious about the frontiers of physics, as The New York Times Book Review indicated, the book "sets a standard that will be hard to beat". Both rigorous, visual and engaging, the scope of what is so deeply rooted in mathematics as modern cosmology becomes accessible through metaphor and analogy.

Many of the illustrations were taken from sketches made by Greene. His forthcoming three-part Nova special for PBS-TV begins this month [October 28th, 8-10 pm and November 4, 8-9 pm]. The exploration, also titled the "Elegant Universe" (which he co-wrote and narrates), carries the summation: "Eleven dimensions, parallel universes, and a world made out of strings. It's not science fiction, it's string theory."

As an innovative educator, Greene also occasionally defends the integrity of physics in filmography: he served as technical adviser and enjoyed a cameo role as himself in the film "Frequency," based on the novel premise of a solar storm providing a cross-time radio link connecting father and son across 30 years via the aurora borealis ("northern lights").

Not relying on time travel, but cross-time communication, the film, as Green explains, has an enigmatic twist that avoids many of the paradoxes of its Hollywood predecessors: "Time is far more subtle than our everyday experience would lead us to believe. In many ways, time may simply be a psychological construct for organizing the world. It is a device we scientists have found useful, but it may in fact be a dim approximation of something far more complex."

Astrobiology Magazine had the opportunity to talk with Greene about string theory, cosmology, and his forthcoming [February 2004] book, "The Fabric of the Cosmos: Space, Time, and the Texture of Reality".

Astrobiology Magazine [AM]: The line drawings and some specialized figures in "The Elegant Universe" came from sketches you did, correct?

Brian Greene [BG]: Yes, that's right.

AM: During the writing of 'The Elegant Universe', what kinds of writing habits worked best for you? For instance you mention in the forward to the book that Robert Malley [former Special Assistant to the President for Arab-Israeli Affairs and Director for Near East and South Asian Affairs at the National Security Council] encouraged you to 'put pen to paper'. You also mention some remarkable writing habits of Edward Witten (string theorist at Princeton's Institute for Advanced Study) as composing science papers directly on the computer keyboard. Are you someone who composes in particular places like a cafe or times like on airplane flights?

BG: I have to write at a computer. I find that I can't write any other way. Luckily, though, I find that I can write most anywhere as far as location goes.

AM: You've lectured in twenty (or more) countries on superstrings. Since science does not care about national borders, what is the most unusual or favorite place you've lectured?

BG: Well, I think Pakistan was probably my favorite place to lecture.

AM: Can you describe a particular defining moment in which you first got the insight that superstrings might offer a unifying path for physics?

BG: Michael Green [Cambridge], one of the co-inventors of the modern approach to string theory--gave a lecture at Oxford in 1984 in which he explained the theory's basic ideas. He made it abundantly clear that the theory had the potential to be a unified theory of all forces and all matter. It was convincing, and I've worked on the theory ever since.

AM: Is it aesthetically acceptable to describe one elegant goal of superstring theory as describing an infinite (or finite) universe without resorting to infinite quantities?

BG: We don't need the universe to be spatially finite or infinite--either possiblity is consistent with the theory. However, it is crucial that our equations describing the physical processes we measure (energies, probabilities in quantum mechanics, etc) all yield finite answers. Infinite answers in those context signal that the laws have broken down.

AM: One unique element of the style of 'The Elegant Universe' is an attention to whether a theory should be 'beautiful' or aesthetically appealing, and you have some family with a background in music. Do you think about superstrings at all in comparison to musical theories (frequencies, high and low notes, etc)? Any concepts that resonate between superstring theory and music?

BG: Well, the key idea of superstring theory is that what we think of as different particles are just different string vibrational patterns. So, in this sense, the particles of nature are the musical notes of strings--a rather significant resonance between physics and music.

AM: You played yourself--twice--in the movie, "Frequency". The movie is about a father communicating from 1969 with his son in the present on a ham radio, due to an unusual atmospheric aurora that bounces radio signals across time, not just space. You played Brian Greene being interviewed by Dick Cavett as both a younger and older man. Any reflections on either the interesting premise of the movie, or the adventures of being on the big screen?

Frequency, cross-time communication Credit: Frequency

BG: The movie, of course, was pure science fiction. But I was impressed how the writer (Toby Emmerich) and the director (Greg Hobblit, also co-executive producer of "Hill Street Blues", 1981) really tried to define a set of rules for their scenario and stick with them consistently.

As for my own role, well, it showed me how I'm going to look in 30 years!

AM: For the book, you interviewed the eminent John Wheeler, who in addition to being Richard Feynman's adviser at Princeton, wrote the definitive modern book on gravity--the big black book. His quote on gravity was: "mass grips space by telling it how to curve area, space grips mass by telling it how to move." Wheeler is also gifted with an uncanny ability to coin a phrase, having named 'black holes', 'quantum foam', and other key terms for describing cosmology. Do you have a favorite, concise phrase that circulates about superstrings?

BG: "It don't mean a thing, if it ain't got that string."

AM: The quest for the ultimate theory is not about experiments today, nor about stitching together a set of findings, but about a framework to describe the universe in a unified way, from small (quantum effects) to large (gravity)--subatomic to galactic. Does the superstring community look to an energy range where the first predictions might be accessible to test?

BG: If some recent ideas are correct, it just might be possible to catch glimpses of string theory in the new accelerator being built at CERN (the Large Hadron Collider, Center for European Research Nucleare, Geneva, Switzerland).

It should start running in 2007.

AM: There is a favorite 'zoom' illustration to show the increasing scales of the universe, which usually travels about forty or so changes in magnification by powers of ten. Is there a way to illustrate the superstring frontiers in a range of such scale factors?

BG: Well, strings are--in their most conventional incarnation--about 20 orders of magnitude smaller than atoms. So, after reaching atoms, you need 20 more magnifications by powers of 10 to get to strings.

AM: A prototype string may be on the order of 10-33 centimeters in length. Are there prototype ways to describe the size of the curled-up dimensions as a kind of compartment? Can these dimensions reach up to a millimeter (if they contain gravity) and still not be detectable?

BG: The conservative incarnation of extra dimensions imagines them also being on the order of 10-33 centimeters. However, in the last few years we've realized that such dimensions could be as large as a tenth of a millimeter and still be consistent with observations. (I discuss this in more detail in an upcoming book.)

AM: How many curled-up dimensions beyond three extended space coordinates and time are contained in the superstring universe? Does more than eleven total give rise to a forbidden universe of massless particles?

BG: String theory seems to limit the maximum total number of spacetime dimensions to 11. Any more than that, and it is very hard to make sense of string theory's equations.

Elegant universe of Einstein, unifying natural forces Credit: Einstein archives

AM: You described the absurd state of infinite energy, density and temperature as a signal that the standard and inflationary cosmological models have broken down. Would you see one of the strengths of superstrings as a way-out of this initial condition, to avoid the infinite extremes?

BG: I hope so. This is what I'm working on now: trying to tie string theory and cosmology together. It is an exciting field of study but there are many difficult problems still to solve.

AM: Among the many analogies for curled-up dimensions, what does the hologram (three perceived dimensions in a two-dimensional plane) offer to imagine the higher dimensions and their relation to what we anthropically can even imagine?

BG: I'm not sure holograms are a particularly good metaphor for curled-up dimensions, but recent work in string theory does offer the possibility that our entire universe is much like a hologram. The idea is that what we see is but a holographic projection of laws that exist and fundamentally operate on a distant bounding surface.

It is a strange idea, but it just might be right.

AM: Astrobiologists rely on liquid water as a key ingredient (and assumption) to define a planet's habitability. From the view of a cosmologist, you describe the apparent 'stiffness' of physical laws as they might make possible (or extinguish) life: a conservative, order-of-magnitude change in electromagnetic strength, and life disappears from the fate of the universe itself, along with oxygen, intelligence or a single quark. Is there a case where superstrings (or physics) has to apply an anthropic principle, if a quantum mechanically consistent picture includes all forces, all matter and lastly, conditions for intelligent life?

BG: This is a much debated question. I hope that we do not need to rely on anthropic reasoning. To me, it is as close to "giving up" as science can get. But we just don't know--it could be that there really are many possible (or real) universes, and so trying to explain why ours is the only universe might be a fool's errand.

AM: One part of an elegant theory of the universe historically has relied on the laws of physics being the same everywhere. Andre Linde has a concrete proposal for the multiverse, or alternative universes, where the laws may differ and never contact. Was it an assumption that drove Einstein's quest for unification, that physics work the same from small to large and everywhere in between? Do superstrings have a contribution to make in understanding the different paths a multiverse might arrive?

BG: String theory, with our current understanding, seems to admit the possibility of many different universes, with vastly different properties. Our hope is that better understanding will show why our universe is somehow special, or picked out by the equations themselves.

Whether we will succeed in this undertaking is anybody's guess. If we fail, we might have to resort to anthropic type reasoning, but many of us view that as a last resort.

AM: There are fifteen or so international space missions for finding 'rocky worlds' that qualify as habitable. Are there any elegant, but exotic scenarios to accelerate either communication or even travel to a star more than fifty or a hundred light years away?

BG: The only way to accelerate such travel that I know of, in principle, involves wormholes--shortcuts through space. But it is unlikely that they really exist, and even if they did, it is unclear whether they'd be sufficiently stable for us or our signals to pass through. So, I would not take it too seriously on a practical level. But theoretically, speaking, they are very interesting probes of space and time.

AM: Other than the PBS series on "The Elegant Universe", any other plans for future projects?

BG: Well, I have this new book coming out in February, "The Fabric of the Cosmos: Space, Time, and the Texture of Reality".

Related Links
The Elegant Universe: An excerpt online
String Theory Web Site
Superstrings
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