Dr. Leonard Susskind discusses his most recent book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design
Does trying to understand modern string theory have you tied in knots? Have you ever wondered what a layman can learn from hadrons or the anthropic principle? Enjoy a lively program as Susskind explains the nuts and bolts of modern string theory and asks, "Can science explain the extraordinary fact that the universe appears to be uncannily, nay, spectacularly, well designed for our existence?"
Leonard Susskind is a theoretical physics professor at Stanford University in the field of string theory and quantum field theory. Susskind is widely regarded as one of the fathers of string theory for his early contributions to the String Theory model of particle physics.
Welcome every one to this evening's presentation of The Commonwealth Club. We aredelighted tonight to have as our special guest Leonard Susskind who is well known to allof us for his many writings in the area of Physics and particularly String Theory and ourfocus tonight would be around and about his latest book published this year, 'The CosmicLandscape'. Dr. Susskind will be presenting approximately 30 minutes of discussion andthen we are we will have an opportunity for you to bring questions up to me and I willtry to synthesize them and we can get as many of those questions as we can for forenlightening discussion on a very fascinating area about the the conceptual directionwhich physics is taking in its interaction with other philosophies and mathematicalcomponents of science. So I would like to turn it over to Dr. Susskind to start our program.First of all I want to say that Pluto is solar planet. For many people science meansmedicine, debates over global warming, endangered species, what I would call sciencewith a purpose, science to better the human experience. What I am going to tell you abouttoday is a very different kind of science, you could call it and I do call it selfish science.It's the kind that you do out of pure curiosity. This evening's subject is the universe andthe laws that govern it. Now I must tell you that the subject is extremely controversial.Every side is weighing in with heated angry opinions, sometimes I feel I am at the centerof a circular firing squad. To give you the flavor I would read some of the morecontentious public pronouncements. From the New York times, Cardinal ChristophSchoenborn Archbishop of Vienna, scientific theory such as the anthropic multiversehypothesis that try to explain away the appearance of intelligent design as the results ofchance now I think chance means probability and necessity, I think that means the lawsof mathematics and physics they are not scientific at all but as John Paul put it, they arean abdication of human intelligence an abdication of human intelligence. Then from afamous cosmologist on the edge website, decades from now I hope that physicists willonce again be pursuing their dreams of a truly scientific theory and would look back onthe current anthropic craze as millennium madness, where the cardinal sees atheism thefamous cosmologist sees religious hysteria.Again from the New York Times, famous experimental physicist who incidentallyhappens to be a friend of mine, Susskind that's me and the Landscape School have givenup. For them the reductionist's voyage that has taken Physics so far has come to an end.Since that is what they believe I don't understand why they don't do something else,macrame for example. So what's it all about academic tempest on a teapot or scientific revolution?Let's begin with a bit a history. William Paley is often credited with being the originatorof intelligent design. Sometimes towards the end of 18th century he raised the followingvery interesting question, suppose you are out on the beach and you came across a pocketwatch lying on the sand, you might very well ask how such an intricate object came intoexistence. One possible answer is that a billion billion billion atoms randomly cametogether and accidentally formed the watch. Paley dismissed this explanation saying thatit was incredibly unlikely and indeed it is. Like any sensible person he said that a watchmaker must have designed and created the watch for some purpose. Then he went onthe eye is a far more intricate object than a pocket watch. Surely it didn't just accidentallyappear on the forehead of some ancient animal by analogy Paley concluded that theremust have been an intelligent designer.Well we all know how that episode turned out; Charles Darwin who originally embracedPaley's idea incidentally became curious and eventually arrived at a completely differentconclusion. Darwin saw a pattern of evolution, mutation, competition and trial and errorwhich led to a branching tree of life that filled every niche. The explanation was notintelligent design but rather the impersonal unintelligent laws of Physics, Chemistry andProbability. Incidentally, Darwin's interest had nothing to do with medicine, endangeredspecies or how to genetically engineer a square tomato. He did it because he was curiousabout the world, how the world came to be the way it is. At the time it was pure selfish science.Fast forward a 100 years now 150 years excuse me. Physics and Cosmology are nowwrestling with questions about the universe, questions which closely parallel Paley's andDarwin's. The universe seems to be very, very special but in the ways that really bafflePhysicists. The universe is big, it could have been not bigger than an atom or evensmaller, it's full of chemicals and heat, it could have been cold and empty, it lasted longenough for evolution to take place. It could have collapsed in a big brunch excuse mebig crunch after an NOC may be it was a big brunch I don't know.Gravity is a million million trillion trillion trillion times weaker than theelectromagnetic forces in nature. We don't fully understand why. But if it were just a bitstronger the increased pressure in the Sun would have caused it to burn out far too fast forus to be here. On the other hand, gravity is strong enough to hold us to the earth, to holdthe earth together and to hold on to its atmosphere. The universe appears to exist on theknife-edge of disaster. Disaster for us that is because its all just luck that things workedout so well, until recently most physicists would have said yes, none of it is so unlikelythat it couldn't all be accident. Most Physicists are reductionists, they believe that bigthings are made of smaller things, molecules are just collections of atoms, atoms areelectrons orbiting around nuclei, nuclei are globes of protons and neutrons and so forth.Part of the belief was that the smallest most basic objects are governed by impersonallaws of mathematics, laws that could not care less about our own existence. According tothat view life and the fine tunings that make it possible are mere co-incidences.But a number of things have happened during the last decade - things that are changing inthe minds of some of the best Physicists. Chief among them is the discovery of a singlenumber that is so absurdly unlikely that no one thinks it's accidental. The cosmologicalconstant or what the popular press calls the mysterious dark energy, not dark matter darkenergy, quite a different thing.In 1917, Einstein discovered that his own theory of gravity was ambiguous. Theequations left room for a kind of cosmic antigravity. A repulsive force that acts overbillions of light years which if it existed would relentlessly push every bit of matter awayfrom every other bit and Einstein called the strength of this antigravity force he called itthe cosmological constant. Eventually, Einstein soured on the idea, he called it his worstmistake and for the rest of his life he and everyone else assumed that the cosmologicalconstant was zero. Later astronomers concluded that Einstein was quite right. They saidthere is no cosmic antigravity. The Cosmological constant is zero or at least it's very,very small. How small? Astronomical observations require that at least the first 119decimal places of the cosmological constant all must be zero. 0.00000 I am getting tired a 119 zeroes.Almost all Physicists concluded that the antigravity term must be exactly zero eventhough they didn't know why. Later modern quantum Physicists added to the puzzle.They calculated that unless some fantastic cancellations took place the cosmologicalconstant should not be small at all. In fact according to the equations it should be so largethat it would easily blow up the earth, the atoms and molecules that make up the earthand even the elementary particles that make up atoms. Understanding why thecosmological constant is so close to zero became the biggest unsolved problem ofmodern physics. But no one ever found an explanation. The puzzle of dark energy is notwhy it exists, the puzzle is why is there so little of it.But then in 1987, one of the world's truly great physicists suggested an answer. It wasn'treally an answer, it was rather an observation. Steven Weinberg realized that if thecosmological constant were too large, galaxies, stars and planets could not have formedout of the primordial soup that was leftover from the Big Bang. And even more importantthere would be no us to look at the universe and ask questions about it. His point wasvery simple, the attraction of gravity is what caused lumps in the cosmic soup thatcondensed the galaxies and stars. If the cosmological constant were too strong theantigravity would interfere and prevent the stars from forming, no stars, no planets - no planets, no us.Weinberg was appealing to an idea that's called 'The Anthropic Principle', an idea thatoriginated with a number of British cosmologists. What the Anthropic Principle said isthis: "The laws of physics in cosmology must be such as to permit the existence ofintelligent observers." What an odd idea that the laws of nature must somehow care aboutus? The reductionists, physicists it seemed like putting the cart before the horse. Laws ofphysics determine determined by the existence of life that's upside down, they said.Life is a consequence of laws of physics, not the other way around. They looked on theAnthropic Principle with deep distrust, it sounded much too close to intelligent design.Weinberg himself disliked it. But he kept his mind open and asked how strong would theantigravity force have to be in order to prevent our own existence? What he discoveredwas quite amazing. If the cosmological constant just had one or two few zeros, a 118instead of a 119 there would be no us to ask about it. Amazingly, it seemed that theremight actually be a connection between the crazy fine tuning of the cosmologicalconstant and our own presence in the universe.Weinberg went further. He said that if the only reason that the cosmological constant isso small is to ensure the possibility of life, then there is no need for it to be any smallerthan a 119 zeros. He predicted that when the next digit would be measured the 120th, it would not be zero.Now Weinberg was and is considered one of the great scientists of the 20th century.Nevertheless physicists paid very little attention. The idea that the universe somehowcared about us was unacceptable. They wanted to believe that the laws of physics aredetermined by abstract impersonal equations. They wanted to believe that some deepmathematical principle made the cosmological constant exactly zero.So it was a tremendous shock. The scientific tsunami, when the next digit was measuredin the 120th decimal place, just as Weinberg predicted, the cosmological constant is not zero, its two.This is one of the most stunning reversals of fortune that I know of in science, think of it.10, 20, 30 zeros - only to be reversed in the 120th place. No one has an explanation exceptto say that if the cosmological constant were much different no one would be here to know it.The universe like the eye seems to be very non-accidental. If William Pailey were alivehe would surely say that it must have been designed, fine-tuned for life by a cosmic tuner.Now the majority of physicists - scientists in general, reject intelligent designexplanations. Most would say something about it violating the scientific method. Nowpersonally, I don't believe in a rigid scientific method. Big paradigm shift always break the rules.Let me tell you why personally and this is a personal view of it, why I don't buy it? WhyI don't buy the intelligent design explanation of the universe? It has nothing to do withany antireligious bias. Frankly, I am too confused about the origin of the universe to haveany strong view. I am not a believer and I am not an atheist. I just don't know. Andbesides, I am prepared to accept the craziest explanation if it really explains. It's aquestion of curiosity. ID, Intelligent Design just doesn't do it for me. It doesn't satisfy myitch for an answer. When someone says there was a creator, I immediately think tomyself, what is the creator made of? Is it made of atoms and molecules? How manydimensions does the creator live in? Does the creator satisfy the rules of quantummechanics including the Heisenberg Uncertainty Principle? What are the laws by whichthe creator interacts with the rest of the universe? And finally what created the creator?That a billion, billion, billion, billion heavenly atoms just come together?Now theologians speak of first causes and prime movers and they say you are notsupposed to ask these questions. But I am afraid I was just born with a very strongcuriosity gene and I simply can't stop myself. I would call the theologians resistance tothese questions - an abdication of human curiosity. Darwin didn't buy it and neither do I.There is an answer that's gaining traction among cosmologists and theoretical physicists.And it does have Darwinian overtones.Let me go back to life for a moment. What does it take to explain the amazing existenceof a piece of machinery as subtle, fine-tuned and complex as a human being? The firstcondition is that there must be a huge number of biological possibilities. If there wereonly a handful of ways to rearrange the DNA molecule, it would be very unlikely thatany of them would be a blueprint for intelligent life.What makes biology interesting is the sheer diversity of possibilities. DNA is a ladderwith about a billion rungs. Each rung can be anyone of four base pairs. That means that amolecule of DNA can be arranged in four to the billion ways, four to the billion that is aninconceivably large number. Of course, only a tiny fraction of these designs lead to viablelife forms and an even smaller fraction the creatures which are complex enough to askquestions. But even a tiny fraction a four to a billion is still a very large number.Biologists call the collection of all possible life forms, not the life forms that do exists,but the life forms that could exists, they call it "The Landscape of Biological Designs".The landscape is such a big haystack that you can find almost any kind of needle in it,including intelligent needles. But it's not enough to have a lot of possibilities. Somethingmust turn those possibilities into realities. That's what Darwin figured it out. Startingwith a lot of carbon, oxygen and other elements, sunlight, random mutation and naturalselection created a diverse tree of life with every available niche eventually becomingfilled. A few remote branches of that tree just happened to have big enough brains to askquestions, that's all there is to it. There is no more.Now what of all - what is all of these have to do with the universe and especially withString Theory? Well, it's the properties of space. To our ordinary perception space isthree dimensional width, height and depth. But according to String Theory if you couldzoom in to the tiniest distances, a billion, billion times smaller than a proton, you woulddiscover that space had as many as seven extra dimensions or even more, dimensions thatare twisted up and curled into knots like immensely complicated tiny pretzels. Apparentlywhat I call "The Basement of The World". The distance scales vastly smaller thananything we have ever explored. String Theory says that the laws of physics are notunique. The microscopic geometry of space contains structures. Analogous to thebase pairs DNA molecules. These structures determine the properties of elementaryparticles, the forces of nature, and yes - the cosmological constant.The names for these fake base pairs are not adenine and cytosine and so forth. They areCalabi-Yau compactification manifolds, moduli fluxes, Euler numbers and Betti numbers- mathematical objects and there a lot of them. But just think of them as the hiddenmicroscopic DNA of a potential universe. That's the real message of String Theory. Notthe particles or little stands of energy. But that the properties of the universe aredetermined by a kind of super-microscopic DNA and like the biological landscape, thelandscape of possible universe designs is huge and very likely contains the blueprints fora world like ours. I should say very hopefully contains those blueprints.Again, it's not enough to have a lot of possibilities. What is the mechanism that broughtall of this diversity into existence? Surprisingly, physicists have a candidate it's called"Eternal Inflation" and it's based on something that most cosmologists and physicistsbelieve that universes can reproduce. There is surprisingly little controversy about thisvery provocative statement, universes can reproduce.The reproduction mechanism which incidentally is not sex has been understood since themid 1970s. A rapidly expanding universe is like an uncorked bottle of champagne.Bubbles appear as it expands and inside these bubbles the String Theory DNA isrearranged making it a little bit different than the parent universe. It's nothing less than acosmic mutation mechanism. These bubbles expand and eventually it grow to becomenew universes which in turn bubble and produce new offspring. Although themechanism is not the same as Darwinian evolution, the effect is nevertheless to fill everyniche. A vast multi-verse a multi-verse or bubble universes that's what many physicistand cosmologist see ahead of us.Where do we live in this enormous multi-verse? The one thing that we can be sure of isthat we live in one of the rare spots where life is possible. According to this view, theuniverse is not designed; it's simply very - very big and very - very varied. And we livein a very atypical branch of it, where life just happens to be possible. That's it. There isno more explanation, nor is there need for any. It's ironic that the dream of it - a uniquemathematical universe, a universe which could be no other way, is suddenly under attackfrom our own favorite mathematical theory. But it's the lack of uniqueness. Theenormous diversity of possibilities, that's the real strength of String Theory. Without it,we could never explain the special condition - the special co-incidences that allow our own existence.Let me come back now to the Anthropic Principle. As I said, Physicists have been veryreluctant to consider it. Partly they misunderstood it making up at something more that itreally is. I find it very helpful to tell a story that explains just how ordinary the AnthropicPrinciple is. Ordinary but not trivial. I will read it to you. It's the story of the parable ofthe big brained fish. Once up on a time on a planet completely covered by water,there lived a race of big brained fish. Their big brains made them very smart and alsovery curious. In time, their questions about the nature of water, and other things becamevery sophisticated. The most brilliant of them - among them were called fishysicists. Thefishysicists were wonderfully clever and in a few generations they came to understand agreat deal about the nature of water. One thing stumped them. Why was the temperatureof their fluid environment in the narrow range in which water is liquid and it is a narrowrange? Nothing they knew could explain it.Now closely allied with the fishysicists were another group the codmologists who wereinterested in what if anything might lie above the surface. Among the codmologists, therewas a school that held a very radical idea. If the temperature were too high, they wouldbe boiled, boiled fish that is. If too low, they would be frozen fish. The temperature hadto lie in the liquid range or else there would be no fish to even ask questions. They calledit the Anthropic Principle. Garbage said the fishysicists, its putting the cart before thehorse. It's not science, its religion, it's giving up and besides, if we agree with you,everyone will laugh at us and take away our funding.Now a small number of codmologist held to a very particular version of the AnthropicPrinciple. They believed that a stupendously big space existed beyond the upper waterboundary. In this very big space, there might be many other bodies similar in some waysto their own water world, but different in other ways. Some worlds would beunimaginably hot. So hot that hydrogen nuclei might even fuse to form helium and thenperhaps grow even hotter. Other worlds would be cold the frozen nitrogen would exist.Only a tiny fraction of the bodies would be a temperature conducive to the formation offish. Then there would be no mystery why the temperature was fine-tuned, as every angleknows most places are fishless. But here and there conditions are just right and that'swhere the fish are. The end.Of course the codmologist got it right. The reason the temperature was between freezingand boiling, is because if it's weren't, there would be no fish. But the ordinaryastronomical universe is big enough and varied enough that there are many places wherethe conditions for fish are right.The parallel is obvious. A multi-verse vastly bigger than we ever imagined and vastlymore diverse and life exists in the rare places where it can. And that means in the tinyfraction, where the cosmological constant is small enough to allow stars and planets toform. But there is one very disturbing difference. The fish can build a pressurized waterfilled submarine and travel to the surface where they could look out and check if thecodmologist were right. They have to bring a telescope with them. But we will never lookout at the multi-verse and directly see how the universe is. It's not just the technological problem.According to our best understanding, those other worlds are receding away from us sofast that their light can never reach us. They are forever hidden behind an eternal cosmichorizon. For some people, this makes the notion of a multi-verse metaphysicalspeculation and not science. They may be right. But others including me see itdifferently. Curiosity makes us ask, "What's out there beyond the horizon? Is theuniverse enormously big? But everywhere the same, or is it of a highly varied multiverse?" At the moment, the highly varied multi-verse has the advantage. It's the onlyanswer on the table. The only known explanation for the 119 zeros. Still, no one knowsfor certain what this what the future will bring, other explanations may turn-up,surprises and reversal of fortune or what make science so exciting? But to me, not askingwhat's beyond the horizon seems like another abdication of human curiosity. But twothings seem certain to me. First is that we won't find out unless we try. And the second isthat having opened up these questions somewhat against our own will, we will not goback to business as usual. Pandoras box is been opened and the questions that leaped out will not quietly climb back in.Finally, I want to express my continued amazement and delight, and finding that I live ina cultural universe that understands the importance and value of selfish science. Eventhough I am sometimes, I had a lot's to explain it to myself. Thank you.