Leonard SusskindThe Cosmic Landscape

This is an excellent book, by a clear writer, who has big ideas, and expresses them well. I recommend reading this book, then reading a critic of String theory, Lee Smolin's The Trouble With Physics.Leonard Susskind is the original inventor of String Theory over 25 years ago, and has now merged its latest permutations with Inflationary cosmology to produce a theory of everything. Susskind throughout the book talks about how he spends much of his time trying to figure out how to explain esoteric ideas in physics to laymen. I have an undergraduate degree in physics, and have read perhaps a dozen books on cosmology, and was able to follow this book fairly well. I am a "layman" compared to Susskind, but have a much stronger astrophysics background than most "laymen", so take warning. Understanding this book is not as easy as falling off a log.His starting point is that Fine Tuning is a legitimate argument - that our universe is fine tuned to create life to a bizarre degree. I will not present his rationale for Fine Tuning. He for many years rejected the Fine Tuning claims, but became convinced himself when the Cosmological Constant was shown to be very small but positive. Since the possible range of the CC is huge, and anything but zero or very close to zero values will lead to very short-lived universes, or ones with no matter concentrations, many physicists assumed that the CC was somehow forced to be zero, by unknown physics laws. That it is not was startling to astrophysicists, and for Susskind this was the last straw to support a Fine Tuning argument.There are two ways we know of to get Fine Tuning, design or evolutionary selection. Selection requires multiple random options to select between, and because he rejects Design, this is where Susskind goes. He proposes the Anthropic Principle, in which virtually infinite universes are created, and only the very, very, very few which are habitable are ever observed by sentient life.To take you through his reasoning requires a peculiar journey through speculative physics. Inflation is what happens when the vacuum fluctuations of virtual particles in empty space sum up to a positive value. This positive term ends up producing a repulsion force against anything which has mass, meanwhile the virtual particles themselves DO have a mass, and the repulsion exceeds their gravitational attraction - which causes space to grow. The Cosmological Constant is the bulk term which describes the speed at which growth occurs. Since this new space is also filled with the same virtual particle field, mass is basically being created from nothing. The current Big Bang model is based on an initial high value of the CC, and then a drop down to our current very, very, very small but positive CC.String theory has an explanation for the CC, as well as for everything else. String theory started with an attempt to describe the behavior of quarks and other similar elementary particles. Some behave like elastic strings with masses at each end, and others like three strings linked like a Y, each with a mass at the end. This part of the theory is very solid. It was then extended to all the rest of physics. When one tries to explain the behavior of all the other elementary particles and forces using a similar model, a model CAN describe approximately our suite of particles and forces, but it requires 11 dimensions plus time (8 of these dimensions are rolled up rather than extended, which is why our universe looks 3-dimentionsla rather than 11-dimensional). Currently none of the models produced quite work out, so String Theorists have kept coming up with variations on the equations which can add features which might let them actually match our universe. As a minimum, they add things like shape, twist, flux, branes (string localizers) of various dimensions, shape for the branes, and singularities to the equations for each dimension. This produces a near infinite number of possible "String Theories", and a near infinite number of variables to dial to fit our world. Within the theory, the CC, fundamental forces, and elementary particles all could be different with a different set of dimensions, shapes, fluxes, branes, etc.One way to bring order to this is that not all possible combinations are stable. Basically, if there is an adjacent state which has a lower energy level (translates to a lower CC), frictional effects will lead a possible universe to drop to the lower state. What this means is that only local energy minima (valleys in a rough surface) are stable, and any universe that exists for any length of time must be in one of these en43ergy minima valleys.Susskind adopts the Eternal Inflation hypothesis of Alan Guth and Andrei Linde, and assumes that there is some initial stable high CC state. Quantum effects cause fluctuations in these String Theory properties, and if they lead to a lower energy state than the locally stable one, this fluxuation acts as a crystal seed for the spreading transition of the high CC region to the lower one. BUT, since the high CC region is inflating faster than the new lower one, the transition to the new lower one is slower than the growth of the old higher CC space, and the high CC universe never goes away, it just has infinite bubbles of lower CC inside it. Each of these likewise can spontaneously create new lower CC regions within them, each of which will continue creating infinite space a well.This view of the world - a inflating field of extremely high energy and high CC, with an infinite number of mini universes inside it that have bubbled out, is what Susskind calls his Cosmic Landscape. He proposes that our universe is one of these bubbles. To match the history of our universe, our bubble would have had to initially form near a trough leading to our valley, because inflation was initially high for a while (moving down a fairly level trough), then quickly dropped to our current rate.String Theory, and this Infinite Multiverse have been criticized as non-scientific. A recently published critical book on string theory is titled Not Even Wrong which is the ultimate dismissal in science. A claim which is untestable in principle is worse than wrong, it is not science, and useless. Susskind is defensive about this, and challenges what the definition of science is. He asserts that science is whatever scientists are doing - and in his world scientists engage in extensive speculative mathematics, with virtually no possibility of experimental tests. When people try to redefine science because what they are doing does not fit the definition is generally considered a fairly definitive failing, and was cited in the Intelligent Design court case as definitive proof that Intelligent Design is not science. It is not good news for Susskind that he is sharing the tactics of the ID movement.Scientific ideas to go through three steps: speculation, hypothesis, and theory. I don't think String Theory has quite mastered the hypothesis category yet, and the Landscape and Multiverse are still only speculations. A very legitimate critique is that the concepts just bring in too many free variables. Each one is another assumption, and anyone who has ever tried to fit a curve to data knows that once your free variables equal or exceed your data, then you have ZERO confidence in the predictive ability of the curve-fit.[Unfortunately only physical scientists and engineers ever fit anything other than straight lines to data. If anyone is interested, try putting three points not in a line on a piece of paper. A straight line will at best approximate them. But one can hit all the points with a wavy curve of almost any shape. But since a curve which comes in and goes off the top of the paper, and hits all the points fits the data as well as one that comes in off the bottom or either edge, there is no confidence in the predictive power of these curves. With the straight line, you have some confidence, and it is related to the number of data points minus the constants used to create the curve (2 for a line), divided by the number of data points. So the near infinite variables of string theory vs. only 100 or so fundamental constants and properties of our universe that the theory deals with gives zero confidence in the predictive power of that theory.]For my own interest, I have tried to spell out the major assumptions of Susskind in his Landscape fusion of String Theory and Inflation.1-8 There are 8 additional dimensions to space.9 The properties of everything are dependent on features of these 11 dimensions,10 The features include whether a dimension unrolls11 Also the shape of the dimension (number of holes)12 Also number of twists13 Also the flux value (integer) in each hole14 Also number of 1-D branes (termination surfaces for strings)15 Also number of 2-D branes16 Also number of 3-D branes17 Also number of 4-D branes18 Also number of 5-D branes (I don't think any go higher than 5 now, not sure)19 Whether any branes are negative (mentioned but not explained by Susskind)20 Shape of the branes21 Twist properties of the branes22 Number of singularities (different from black holes)23 TBD other mathematical structures24 Specific string properties which create the elementary particles and fundamental forces (not sure if these are set by all of the above or not)25 All of the above define the vacuum energy, and thus the cosmological constant (CC)26 A high CC creates an inflating universe27 Inflating universes can create mass and energy out of nothing, but it is all in balance, since gravitational energy is negative and exactly balances all the positive energy.28 Fluxuations in the vacuum energy create transitions to lower CC regions within the inflating space29 The "friction" transitioning from a higher to lower CC is released in the form of an elementary particle plasma (read hot Big Bang)30 There is a texture to the Landscape of vacuum energy states, and new bubbles of a CC will transition down the slope of this landscape until they reach a local minima, or valley.31 Only lower CC states can appear, not higher (not sure why)32 There is a continuing cascade to a zero CC level (string theory models can easily create negative CC, so not sure why things stop at zero, negative CC would be lower energy than zero, so I think the model should not stop. This is a problem for the Landscape, because if high negative CCs are the innate end point of the Landscape, all the universes will eventually just puff out)33 Lot and lots of local minima exist (close to infinite, I think it depend on when you give up speculation on new arbitrary structures in the String Theory model)34 All these local minima are actually reachable from the particular high CC local minima of the Eternal Inflation field. (this assumption is one where the non-science accusation may be valid. Most of the minima will be vary far in properties from the starting condition, and the probability of a quantum fluxuation or tunneling effect reaching a distant state rather than the closest alternate state is vanishingly small. But by postulating an infinite multiverse of Eternal Inflation, it would not matter if one state had 200 orders of magnitude greater probability of being reached - all possible states will be populated with infinite numbers of bubble universes.)35 Anthropic Principle - life is rare and will only arise in an exotic very, very, few local minima which can support complex chemistry, and have long term stability. That is why our universe is exotic and unusually stable.36 Our universe had a CC that started in a nearly flat-bottomed trough that lead to our steep-sided valleyAs you can see, at just the major assumption level, this speculation/hypothesis is quite a doozy.It is science however, and there are a number of predictions made by these theories. The confirmed ones include:* Flatness of the universe* Homogeneity of the universe* Size of galactic and galactic cluster mass concentrationsThe unconfirmed ones include:* At the very largest mass structure level, we will see the effect of a higher CC as the universe settled into the bottom of the trough* A string theory model corresponds to our universe* A series of string theory models correspond to the trough leading to our current valley* Our universe has an edge with different properties, since it is continually transitioning high CC space around us into our low CC space (and we may be able to see a property variation, depending on how close we are to that edge. Note this is my own conclusion, not Susskind's)* Portions of our universe may or have already spontaneously dropped to a lower CC level. These regions would grow within our universe, and be observable.* Gravitons have zero mass, and behave like closed loop strings rather than strings with ends.There are also two predictions which currently are falsified:* Our CC is calculable and small based on string theory (the math sums up to infinity - in order to get a finite CC they throw out all numbers larger than a certain arbitrary value)* All the particles for which no rotational inertia has been observed to date (electrons, neutrinos, photons), actually have rotational inertiaSince the confirmations to date all are just part of the Big Bang with Inflation model, and really have nothing to do with either Eternal Inflation, String Theory, or the Landscape, all of these ideas are currently unsupported by any observations. Having two contradicting observations is also a problem - but a common one for hypotheses as they work out their bugs.I consider this hypothesis, however, to be the most coherent and complete materialist hypothesis I have ever seen for the formation of the universe. But please note what it includes:* by my count 36 major assumptions - most of which are not confirmable in any way* Another substrate to the universe other than the material, which is more fundamental, and from which the material emerged.* Assumptions with infinite properties* No explanation for where the original high CC Eternal Inflating space came fromCompare these features with the critiques of religious theories of the origin of the universe. The ill-defined infinite properties of God are criticized, as is the inability to explain God's origin, the complexity of assuming another substrate to the universe, and lots and lots of unconfirmable assumptions.I really liked Susskind's book. He is a clear writer, and both a clear thinker and a very big thinker. I suspect Susskind has gone wrong early in String Theory, and strings are not really applicable to electrons, neutrinos, and photons, based on their not having rotational inertia. The reason he thinks they must be strings is that otherwise the interactions between these particles and the string-based particles run into a summing-to-infinity problem. Since he is just ignoring a similar problem in calculating the CC, I didn't see why one was a convincing argument to him that that everything was strings, and the other summing to infinity problem is dismissible. Once this summing problem is readdressed, and an answer to it found, I suspect a simpler partial string and partial particle theory will replace String Theory, and I don't know if this Landscape concept would survive.Lee Smolin's The Trouble With Physics The Rise of String Theory, the Fall of a Science, and What Comes Next, provides a useful set of objections to counter Susskind's optimism over his Landscape theory. Smolin points out three important facts that Susskind left out. The first is that before String Theory, there were about a dozen attempts to unify quantum gravity and general relativity -- all of them were mathematically consistent, but every one made predictions that were tested and falsified. Susskind is advocating that Physics be judged by mathematical consistency rather than experiment, but if we had not tested previosly, we would now be using one of those falsified theories rather than String Theory.The second point is that the hidden dimensions of String Theory are unstable. Quantum fluxuations cause them to spontaneously collapse, or inflate to infinity like our three conventional dimensions. The ONLY way String Theory can lock them down so they are stable AND hidden is if they have a more complex shape than just being rolled into a tube. String Theory has a prediction -- hidden dimensions will unroll -- that is disproven by observation. What Susskind did not describe was the special case for these extra dimensions, which is the only way they could be stable, is that each must have at least two holes in it, and that each hole must have one or several charged Branes wrapped around the surface (basically a pretzel shape is the least complex stable shape). Only then will they stay stable and hidden. This is a bizarre kluge to the theory that makes it effectively absurd.The third point is that String Theory for most of its history predicted a negative or zero cosmological constant. Theorists worked with the zero CC versions until a small positive CC was discovered. Then they found a way to further kluge the theory. That is what the negative branes were invented for. Branes are an imagined surface or shape (can be from 1 to 5 D) that the ends of strings must stay connected to. They were first imagined in 2-D as membranes, then expanded into more Ds, and called D-branes, or just Branes. A negative brane was never explained by Susskind, and I suspect it is just a mathematical artifact to somehow bring the vacuum energy to a positive value. The addition of them to String theory is another patch to deal with a contrary observation.Smolin points out that good theories are usually quickly confirmed by observations, and they suggest all sorts of new and surprising things which then advance physics in other areas. The theories that have been discarded in physics are the ones which try to be kluged up with special cases to deal with one embarrassing observation after another. This looks to me to be the case with String Theory. Smolin started his book with 5 big questions that faced physics 30 years ago, when String Theory first became the dominant idea in theoretical physics, and that NONE of these have been solved in the last 30 years. He thinks it is due to physics departing from testability, and embracing a theory which is infinitely klugable and non-falsifiable -- and as a result the experimentalists have been starved of viable theories to test to advance our understanding of these issues.Smolin is as good and clear a writer as Susskind, and he has a better case, since he does not try to hide embarrassing facts, nor attack the principle of experimental confirmability at the core of science. Reading the two together, Smolin blows Susskind out of the water -- String Theory is a dead end. Despite this judgement, I still reccommend the book as very enjoyable and thought provoking.

Suskind's accessible, lucid, and lively science writing rivals Hawking. When he is recounting stories of meeting colleagues at universities or conferences, his writing is as engaging as a novelist's writing. This book on a String Theory take on the Anthropic  principle is not only useful and needed, but is very enjoying to read due to Suskind's prose.Suskind offers in the beginning a very clear explanation of the Feynman diagram to be used as a tool for explaining particle physics. He also provides a brilliant account of the significance of the cosmological constant to the fine tuning of the universe. If the constant were negative, galaxies and stars would collapse leading to a collapse of the universe. If it is an order of magnitude greater than the 123 decimal places of the value for this universe,  the repulsive force would prevent the forming of galaxies and star systems.Suskind uses the notion of "landscape" to set up his treatment of the fine tuning problem.  Landscape is the idea of the variation of the environments of the universe. Each environment has its own constants, laws of physics, and particles based on the fields it has. For instance, if the Higgs field is different, the mass of the elementary  particles and the laws of physics would be different. Variation of fields would offer a diversity of multidimensional landscape in the universe or the "megaverse". The universe features a variation of environments of different vacuum energies. Some of them can be like ours while many aren't. This richness of the landscape variation is how Suskind sets up the problem.To introduce String Theory, Suskind recounted the interesting story of how he got started on String Theory. He was looking at Veneziano's S Matrix equation on Hadrons collision that Hector Rubenstein introduced to him. He was not at all interested in the particle physics surrounding S matrix  but found the equation oddly looked like about harmonic oscillator. Later he saw that the equation depicts two open end strings colliding with the ends featuring a quark and anti-quark. He called the string "rubber band" because of elasticity. So String Theory started out as a theory about hadrons. Initially there are the baryons string configurations with three strings joined at one end while a quark is on the other end. There is also the simpler meson configuration with a quark and anti quark on each end of the string. When a string replaces a particle in a Feynman diagram and traces out a time elapsed history, a sheet resembling a cylinder results which is called a "world sheet". That is the origin of how the interesting Calabi Yau manifold geometry evolves into many shapes and configurations. String Theory connects with and utilizes General Relatvity's compactification of space to account for how extra dimensions can be compactified. For instance, the cylindrical world sheet seen in a very small scale would appear like a line thereby compactifying 2 dimensions to 1 dimension. Further, using Kaluza-Klein theory of extra dimensions of space being rolled up, String Theory adds 6 more rolled up dimensions to make up 9 dimensions plus time to be the 10th dimension. The distance around a compactified surface is called the compactification scale, which fixes the charge and mass of the particles. In other words, the scale of the surface would vary the laws of physics. Recall that the quantised vibration features of the strings determine the kinds of particles there are.In 1995, Witten introduced a M theory that modified the String Theory into a version that utilizes membranes instead of string. Membranes are the sheets version of strings. A string in a one dimensional space which is just a 1-brane. The 10 space directions of M theory feature 9-branes.  As indicated above, there are 6 dimensions rolled up in the initial 3 spatial dimensions in String theory. The variations of the Calabi Yau manifolds that can result from the branes offer 10 to the 500 environments ot vacuums for String Theory.  The landscape offering these environments are the possibilities that megaverse can take shape literally. How do these possibilities get actualised into pockets of multiverses to constitute the megaverse? It is by  mestability of the vacuums and space cloning which use eternal inflation as the driving mechanism.  Metastability refers to the idea that properties of vacuums that can spontaneously changed into pockets of actual miniverse populating the landscape each of which with a unique own cosmological constant. Space cloning is the replicating of empty space by a bubbling process filling the gap. This cloning process grows exponentially through an inflation process that eventually actualises pockets of miniverse. With pockets of miniverses each with different cosmological constant which produces its own laws of physics and particles, the finetuning of the anthropic principle is easily explained. In a cosmic landscape of possibilities populated by a megaverse of actualities, one of the actualities or miniverses would have the proper cosmological constant and associating law of physics like our observable universe that has the galaxies, stars, and planets to sustain life. It is in effect disarming the notion of fine tuning. Among all the pocket universes,  at least one of them would work. Suskind thinks String Theory is powerful to address the anthropic principle because it has the wealth of numerous Calabi Yau manifolds to offer the millions of vacuum possibilities to be populated into pocket miniverses, thereby showing fine tuning is no more than an actual pocket miniverse among many that has the right working condition.  Suskind did an excellent and lucid job in elaborating this approach.

Well, you must have a little more than a light scientific culture. What I mean is that even though Susskind tries to explain in plain english things are far more complicated than it seems.

Its highly addictive - be warned finished any other book you have - cos once you pick this one up you will not want to stop reading it.This guy was there when it all happened, worked with the greats, and still manages to explain to me (a complete mathematical moron) exactly what theories we have come up with about the way the universe works.It is a book I will read again and again.

Leonard's books a always excellent. I look forward to the day when I actually understand one! Makes far more sense that the unrealistic no dimension point like particles (which somehow change from that state to pure energy and back) of non-string theory.

Didn't realise it was coming from a library in Boston! and still had all the labels on it? Oh well, the receiver of this gift was still happy with the giftThanks

Fantastic book. I really enjoy all of Susskind's presentations of physics (e.g. youtube videos) and the book is just as much fun. Well written, easy to understand, yet not so simple as to be boring.