archived as http://www.stealthskater.com/Documents/Susskind_01.doc [pdf] more Physics at http://www.stealthskater.com/Science.htm note: because important websites are frequently "here today but gone tomorrow", the following was archived from http://groups.yahoo.com/group/SarfattiScienceSeminar/message/4625 on December 18, 2003. This is NOT an attempt to divert readers from the aforementioned website. Indeed, the reader should only read this back-up copy if it cannot be found at the original author's site.
From: Jack Sarfatti
Typo-corrected 2nd draft. Also added excerpts from Lenny's "landscape" talk at John Brockman's Reality Club. See reference to Werner Erhard below in new art. Curiously introduced Brockman to Gary Zukav which is how Brockman became Gary's agent for "The Dancing Wu Li Masters". I also was the original source for the meetings Lenny had with Hawking and the others in Werner Erhard's attic described below.
On Wednesday, December 17, 2003, at 11:47 AM, Jack Sarfatti wrote:
> Note below my new "Blackett" formula for "charge" Q in the Calabi-Yau space, i.e. > Q = G*1/2h/cR > > R is a compactification scale "modulus" in the extra-dimensional generalized Kaluza-Klein space. > G* = e^phiG(Newton) > > See Saul-Paul Sirag's Nature paper on Blackett effect in astrophysics. > > My Commentary on Lenny's lecture http://physicsweb.org/article/world/16/11/8/1 in the context of my dialogues with Paul Zielinski and Harold Puthoff on "Metric Engineering: Making Star Trek Real" from my third book in the "Space-Time and Beyond" series now being written with full-color illustrations and cartoons. > > I examine Lenny's ideas to establish where mainstream cutting edge physics is these days in 2004 as a proper context to evaluate Hal's and my own fringe ideas relating to the UFO controversy. For the record, I suggested the problem for Lenny's first published physics paper at Cornell in 1963 on the problem of lack of a Hermitian operator for both time and wave phase in quantum theory. I had been working on that problem with George Parrent, Jr. (a student of Emil Wolf's) at Tech/Ops associated with Mitre on Route 2 near Boston. I also brought Johnny Glogower to Cornell with Phil Morrison's help. Johnny was part of Walter Breen's "Super Kids" group from Columbia University in a project allegedly funded by Eugene McDermott a co-founder of Texas Instruments. We were all "rebels". Lenny was a high school dropout. Johnny was a Quiz Kid, Westinghouse Finalist who flunked out of Brandeis. >
1 Excerpts from: Physics World http://physicsweb.org/article/world/16/11/8/1 Superstrings by Leonard Susskind Feature: November 2003
String theory is either a Theory of Everything (which automatically unites gravity with the other 3 forces in Nature) or a theory of nothing. But finding the correct form of the theory is like searching for a needle in a stupendous haystack.
As I sit down to write this article, I feel that I have taken on a task rather like trying to summarize the History of the World in 10 pages. It is just too large a subject with too many lines of thought and too many threads to weave together. In the 34 years since it began, string theory has developed into an enormous body of knowledge that touches on every aspect of theoretical physics.
String space - superstring theory lives in 10 dimensions, which means that six of the dimensions have to be "compactified" in order to explain why we can only perceive four. The best way to do this is to use a complicated 6- D geometry called a Calabi-Yau manifold in which all the intrinsic properties of elementary particles are hidden. Credit: A Hanson.
String theory is a theory of composite hadrons, an aspiring theory of elementary particles, a quantum theory of gravity, and a framework for understanding black holes. It is also a powerful technical tool for taming strongly interacting Quantum Field theories and, perhaps, a basis for formulating a fundamental theory of the Universe. It even touches on problems in condensed-matter physics and has also provided a whole new world of mathematical problems and tools.
All I can do with this gargantuan collection of material is to make my own guess about which aspects of string theory are most likely to form the core of a future physical theory perhaps 100 years from now. It will come as no surprise to my friends that my choice revolves around those things that have most interested me in the last several years. No doubt many of them will disagree with my judgment. So let them write their own articles …
String theory is considered to be a branch of high-energy or elementary particle physics. However, a high-energy theorist from the 1950s, 1960s or 1970s would be surprised to read a recent string-theory paper and find not a single Feynman diagram, cross-section, or particle decay rate. Nor would there be any mention of protons, neutrinos, or Higgs bosons in the majority of current literature. What the reader would find are black-hole metrics, Einstein equations, Kaluza-Klein theories, and plenty of fancy
2 geometry and topology. The energy scales of interest are not MeV, GeV or even TeV but energies at the Planck scale -- the scale at which the classical concepts of space and time break down.
The Planck energy is equal to ħ5/G where ħ is Planck's constant divided by 2n, c is the speed-of- light, and G is the gravitational constant, and it corresponds to masses that are some 19 orders of magnitude larger than the proton mass."
[JS:] There is actually a typo editor's error here, not Lenny's. The Planck energy is ħ c/Lp = ħ c/( ħ G/c3)1/2 = (ħ c5/G)1/2
This is the energy of the Universe when it was just 10-43 seconds old, and it will probably be forever out of range of any particle accelerator. To understand physics at the Planck scale, we need a quantum theory of gravity.
In the days when my career was beginning, a typical colloquium on high-energy physics would often begin by stating that there are 4 forces in Nature -- electromagnetic, weak, strong, and gravitational -- followed by a statement that the gravitational force is much too weak to be of any importance in particle physics, so we will ignore it from now on. That has all changed.
Today, the other 3 forces are described by the gauge theories of Quantum ChromoDynamics (QCD) and Quantum ElectroDynamics (QED), which together make up the Standard Model of particle physics. These quantum field theories describe the fundamental forces between particles as being due to the exchange of field quanta: the photon for the electromagnetic force, the W and Z bosons for the weak force, and the gluon for the strong force. In the string-theory community, however, the electromagnetic, strong, and weak forces are generally considered to be manifestations of certain "compactifications" of space from 10 or 11 dimensions to the 4 familiar dimensions of space-time. ... …
Why quantum gravity?
Elementary particles have far too many properties (such as spin, charge, color, parity, and hypercharge) to be truly "elementary". Particles obviously have some kind of internal machinery at some scale. Protons and mesons reveal their "parts" at the modestly small distance of about 10 -15 meters. But quarks, leptons, and photons hide their structure much more effectively. Indeed, no experiment has ever seen direct evidence of size or structure for any of these particles."
[JS]: This point-like structure may be from a huge space-warp effect depending on the momentum transfer from scattering probe to target from an exotic vacuum "dark matter" core of the spatially extended lepto-quarks where the effective gravity coupling at short range is 1040 times greater than Newton's.
The first indication that the true scale of elementary particles might be somewhere in the neighborhood of the Planck scale came in the 1970s. Howard Georgi and Sheldon Glashow (then at Harvard University) showed that the very successful (but somewhat contrived) Standard Model could be elegantly unified into a single theory by enlarging its symmetry group. The new construction was astonishingly compact, and most particle theorists assumed that there must be some truth to it. But its predictions for the coupling constants -- the constants that describe the strengths of the strong, weak, and electromagnetic interactions -- were wrong.
Georgi, along with Helen Quinn and Steven Weinberg (also at Harvard), soon solved this problem when they realized that the " ... coupling constants are not really constants at all. They vary with energy. 3 If the known couplings are extrapolated, they all intersect the predictions of the Unified Theory at roughly the same scale. …".
[JS] : This GUT scale is ~ Lp/(alpha) where Lp2 ~ hG/c3 and alpha ~ e2/hc ~ 1/137.
Moreover, this scale is close to the Planck scale. The implication of this was clear. The scale of the internal machinery of elementary particles is the Planck scale. And since the gravitational constant G appears in the definition of the Planck energy. To many of us, this inevitably meant that gravitation must play an essential role in determining the properties of particles.
The earliest attempts to reconcile Gravity and Quantum Mechanics (notably by Richard Feynman, Paul Dirac and Bryce DeWitt who is now at the University of Texas at Austin) were based on trying to fit Einstein's General Theory of Relativity into a Quantum Field Theory like the hugely successful QED. The goal was to find a set of rules for calculating scattering amplitudes in which the photons of QED are replaced by the quanta of the gravitational field (i.e., gravitons). But gravitational forces become increasingly strong as the energy of the participating quanta increases. And the theory proved to be wildly out of control. Attempting to treat the graviton as a point particle simply gave rise to far too many degrees of freedom at short distances.
In a sense the failure of this "quantum gravity" theory was a good sign. The theory itself gave no insight into the internal machinery of elementary particles. And it offered no explanation for the other forces of Nature. At best, it was more of the same: an effective (but not very) description of gravitation with no deeper insight into the origin of particle properties. At worst, it was mathematical nonsense.
Strings as hadrons
We all know that Science is full of surprising twists. But the discovery of string theory was particularly serendipitous. The theory grew out of attempts in the 1960s to describe the interactions of hadrons (particles that contain quarks such as the proton and neutron). This was a problem that had nothing to do with gravity. Gabriele Veneziano (now at CERN) and others had written down a simple mathematical expression for scattering amplitudes that had certain properties that were fashionable at that time. It was soon discovered by Yoichiro Nambu of the University of Chicago and myself (and in a slightly different form by Holger Bech Nielsen at the Niels Bohr Institute) that these amplitudes were the solution of a definite physical system that consists of extended 1D elastic strings.
For the 2 years that followed, string theory was the theory of hadrons. One of the spectacular discoveries made in this early period was that the mathematical infinities that occur in Quantum Field Theory are completely absent in string theory. However, from the very beginning, there were big problems in interpreting hadrons as strings. For example, the earliest version of the theory could only accommodate bosons, whereas many hadrons (including the proton and neutron) are fermions.
The distinction between bosons and fermions is one of the most important in physics. Bosons are particles that have integer spins such as 0, ħ, and 2ħ, whereas fermions have half-integer spins of ħ/2, 3ħ/2, and so on. All fundamental matter particles such as quarks and leptons are fermions, while the particles that carry fundamental forces (the photon, W, Z, and so on) are all bosons.
Fermionic versions of string theory were soon discovered and, moreover, they turned out to have a surprising symmetry called supersymmetry that is now totally pervasive in high-energy physics. In supersymmetric theories, all bosons have a fermionic superpartner and vice versa. The early 4 development of "superstring" theory was due to pioneering work by John Schwarz of Caltech, Andrei Neveu of the University of Montpellier II, Michael Green of Cambridge, and Pierre Ramond of the University of Florida. Much of the subsequent technical development was carried out in a famous series of papers by Green and Schwarz in the 1980s.
Another apparently serious problem with the string theory of hadrons concerned dimensions. Although the original assumptions in string theory were simple enough, the mathematics proved internally inconsistent (at least if the number of dimensions of space-time was 4). The source of this problem was quite deep but, strangely, if space-time has 10 dimensions, it contrives to cancel out. The reasons were not at all easy to understand, but the extraordinary mathematical consistency of superstring theory in 10 dimensions was compelling. However, so was the obvious fact that space-time has 4 dimensions -- not 10.
Thus by about 1972, theorists were beginning to question the relevance of string theory for hadrons. In fact, there were other serious physical shortcomings in addition to the bizarre need for 10 dimensions. A mathematical string can vibrate in many patterns (which represent a different type of particle). And among these are certain patterns that represent mass-less particles. But most dangerous of all were mass-less particles with two units of spin angular momentum ("spin-two"). There are certainly spin-two hadrons, but none that have anything like zero mass. Despite all efforts, the mass-less spin-two particle could not be removed or made massive.
Eventually, mathematical string theory gave way to QCD as a theory of hadrons, which had its own explanation of the string-like behavior of these particles without the bad side effects. For most high- energy theorists, string theory had lost its reason for existence. But a few bold souls saw opportunity in the debacle. A mass-less spin-two field might not be good for hadronic physics. But it is just what was needed for quantum gravity (albeit in 10-D). This is because just as the photon is the quantum of the electromagnetic field, the graviton is the quantum of the gravitational field. But the gravitational field is a symmetric tensor rather than a vector. This means the graviton is spin-two,rather than spin-one like the photon. This difference in spin is the principal reason why early attempts to quantize gravity based on QED did not work. a Theory of Everything
The mass-less spin-two graviton led to a radical shift in perspective among theorists. The focus of mainstream high-energy physics at the time was on energy scales anywhere from the hadronic scale of a few GeV to the weak interaction scale of a few hundred GeV. But to explore the idea that string theory governs gravity, the energy scale of string excitations has to jump from the hadronic scale to the Planck scale. In other words, with barely a blink of the eye, string theorists would leapfrog 19 orders of magnitude and therefore completely abandon the idea that progress in physics proceeds incrementally. Heady stuff. But also the source of much irritation in the rest of the physics community.
Another reason for annoyance was somebody's idea to start referring to string theory as a "Theory of Everything". Even string theorists found this irritating, but there is actually a technical sense in which string theory can either be a "Theory of E"verything or a "theory of nothing". One of the problems in describing hadrons with strings was that it proved impossible to allow for the hadrons to interact with other fields (such as electromagnetic fields as they clearly do experimentally). This was a deadly flaw for a theory of hadrons, but not for a theory in which all matter (including photons) are strings. In other words, either all matter is strings … or string theory is wrong. This is one of the most exciting features of the theory.
5 But what about the problem of dimensions? Here again, a sow's ear was turned into a silk purse. The basic idea goes back to Theodor Kaluza in 1919 who tried to unify Einstein's gravitational theory with electrodynamics by introducing a compact space-like 5th dimension. Kaluza discovered the beautiful fact that the extra components of the gravitational field tensor in 5 dimensions behaved exactly like the electromagnetic field plus one additional scalar field. Somewhat later in 1938, Oskar Klein and then Wolfgang Pauli generalized Kaluza's work so that the single compact dimension was replaced by a 2D space. If the 2D space is the surface of a sphere, then a remarkable thing happens when Kaluza's procedure is followed. Instead of electrodynamics, Klein and Pauli discovered the first "non-Abelian" gauge theory which was later rediscovered by Chen Ning Yang and Robert Mills. This is exactly the same class of theories that is so successful in describing the strong and electromagnetic interactions in the Standard Model.
[JS:] A 2-D Kaluza-Klein space has group structure of a 2-D sphere embedded in flat 3-D space with 3 rotation "charge" generators -- i.e. SU(2) group for the weak force with 3 charges. In general, we have N2 - 1 "charges" for the SU(N) internal symmetry gauge force group at a fixed space-time point where the "minimal coupling" local independence of phase rotations introduces the compensating spin 1 gauge force fields to restore the broken global symmetry. This force generator idea is re-expressed in the geometrodynamics of hyperspace.
One may ask whether particles move in the extra dimensions. For example, can a particle that appears to be standing still in our usual 3-D space have velocity or momentum components in the compact dimensions? The answer is 'yes'. And the corresponding components of momentum define new conserved quantities. What is more, these quantities are quantized in discrete units. In short, they are "charges" similar to electric charge, isospin, and all the other internal quantum numbers of elementary particles. The answer to the problem of dimensions in string theory is obvious. 6 of the 10 dimensions should be wrapped up into some very small compact space. And the corresponding quantized components of momenta become part of the internal machinery of elementary particles that determines their quantum numbers.
6 > >Figure 1. There are an infinite number of ways to wind a string around an extra dimension. Each way is topologically described by an integer called the winding number, which can be positive or negative depending on the orientation of the string. The wound string is stretched along the compact direction, but from the point of view of ordinary 3D space it is located at a point and therefore looks like a particle. The winding number is simply a new kind of quantum number. String theory therefore has lots of possibilities for describing the complicated conservation laws and internal symmetries of elementary particles.
Life in 6 dimensions
Much of the development of string theory is therefore concerned with 6-D spaces. These spaces (which can be thought of as generalized Kaluza-Klein compactification spaces) were originally studied by mathematicians and are known as Calabi-Yau spaces. They are tremendously complicated and are not completely understood. But in the process of studying how strings move on them, physicists have created an unexpected revolution in the study of Calabi-Yau spaces."
[JS:] Recall that the classical gravity radius is proportional to M and the quantum radius is proportional to 1/M. That is, Rg = GM/c2
Rq = h/Mc
Therefore RgRq = Gh/c3 = Lp2 = 1 Bekenstein BIT.
We have a germ of a "duality" between "black holes" and quantum momenta
Rg = Lp2/Rq
Note also the Blackett empirical relation
e = G*1/2M
7 where for an electron
G* ~ 1040G
The "quantum momenta" p in the compactified extra-dimensions are "charges" Q (sources of the spin 1 gauge forces) where by the Blackett relation
Q/G*1/2 = M = h/cR
Q = G*1/2h/cR
R is a compactification scale.
G* = e^phiG(Newton)
In particular, it was discovered that a compactification radius of size R is completely equivalent to a space with size 1/R from the point of view of string theory. This connection -- which is known as T- duality -- has a mathematically profound generalization called mirror symmetry which states that there is an equivalence between small and large spaces (see box above). Mirror symmetry of Calabi-Yau spaces -- which are not only of different sizes but also have completely different topologies -- was completely unsuspected before physicists began studying quantum strings moving on them.
I wish it was possible to draw a Calabi-Yau space. But they are tremendously complicated. They are 6-dimensional -- which is 3 more than I can visualize. And they have very complicated topologies including holes, tunnels, and handles. Furthermore, there are thousands of them -- each with a different topology. And even when their topology is fixed, there are hundreds of parameters called moduli that determine the shape and size of the various dimensions. Indeed, it is the complexity of Calabi-Yau geometry that makes string theory so intimidating to an outsider. However, we can abstract a few useful things from the mathematics -- one of them being the idea of moduli.
The simplest example of a modulus is just the compactification radius R when there is only a single compact dimension. In more complicated cases, the moduli determine the sizes and shapes of the various features of the geometry. The moduli are not constants but depend on the geometry of the space itself,in the same way that the radius of the Universe changes with time in a manner that is controlled by dynamical equations of motion. Since the compact dimensions are too small to see, the moduli can simply be thought of as fields in space that determine the local conditions. Electric and magnetic fields are examples of such fields. But the moduli are even simpler. They are scalar fields (i.e. they have only one component) rather than vector fields. String theory always has lots of scalar-field moduli, and these can potentially play important roles in particle physics and cosmology.
All of this raises an interesting question. What determines the compactification moduli in the real world of experience? Is there some principle that selects a special value of the moduli of a particular Calabi-Yau space and therefore determines the parameters of the theory such as the masses of particles, the coupling constants of the forces, and so on? The answer seems to be 'no'. All values of the moduli apparently give rise to mathematically consistent theories. Whether-or-not this is a good thing, it is certainly surprising.
Ordinarily, we might expect the vacuum (or ground) state of the World to be the state of lowest energy. Furthermore, in the absence of very special symmetries, the energy of a region of space will depend non-trivially on the values of the fields in that region. Finding the true vacuum is then merely an 8 exercise in computing the energy for a given field configuration and minimizing it. This is -- to be sure -- a difficult task. But it is possible in principle. In string theory, however, we know from the beginning that the potential energy stored in a given configuration has no dependence on the moduli fields.
The reason that the field potential is exactly zero for every value of the moduli is that string theory is supersymmetric. Supersymmetry has both desirable and undesirable consequences. Its most obvious drawback is the requirement that for every fermion, there is a boson with exactly the same mass (which is clearly not a property of our World).
A more subtle difficulty involves the aforementioned fact that the vacuum energy is independent of the moduli. As well as telling us that we cannot determine the moduli by minimizing the energy, supersymmetry also tells us that the quanta of the moduli fields are exactly mass-less. No such massless fields are known in Nature and, furthermore, such fields are very dangerous. Indeed, mass-less moduli would probably lead to long-range forces that would compete with gravity and violate the Equivalence Principle -- the cornerstone of General Relativity -- at an observable level.
On the plus side, the vanishing vacuum energy that is implied by supersymmetry ensures that the cosmological constant vanishes. If it were not for supersymmetry, the vacuum would have a huge Zero- Point Energy density that would make the radius of curvature of space-time not much bigger than the Planck scale. A most undesirable situation.
[JS:] I have a different and much simpler explanation for the smallness of the cosmological constant in http://qedcorp.com/APS/EmergentGravity.pdf . Also the observational fact of "dark energy" with FRW Omega ~ 0.7 means that the cosmological constant is not exactly zero, which is a problem for the physics that Lenny is talking about.
Supersymmetry also stabilizes the vacuum against various hypothetical instabilities. It allows us to make exact mathematical conclusions. Indeed, T-duality and mirror symmetry are examples of those exact consequences.
9 Black Holes
Figure 2. Originally it was thought that there were five distinct string theories in flat 10- D space, each of which could provide a starting point for compactifications to four dimensions. SO(32) Type I theories are distinguished by having open as well as closed strings, where SO(32) represents the symmetry group of the theory. Type IIA and IIB theories have only closed strings. Closed strings have no ends and are like closed rubber bands with the topology of a circle, while open strings have 2 free ends that can move. Waves on open stings bounce back-and-forth between the ends. But waves on closed strings circulate endlessly around the string in one of two possible directions (hence the two versions of Type II string theory). Finally, there are 2 "heterotic" theories -- SO(32) heterotic and E8 x E8 heterotic -- which allow different kinds of waves to move in the 2 possible directions. It is now thought that the 5 different types of string theory are related to each other by deep symmetries such as T-duality, as if they were each the "classical" limit of a more fundamental theory called M-theory.
Throughout the 1980s and early 1990s, progress in string theory largely consisted of working out the detailed rules of perturbation theory for the 5 known versions of the theory which would allow theorists to arrive at actual solutions (Figure 2). These perturbative rules were generalizations of the Feynman diagrams of QED and QCD in which the "world-lines" of point particles are replaced by "world-sheets" that are traced out by moving strings. The study of world-sheet physics created a huge body of knowledge about 2D Quantum Field Theory. But it did not offer much insight into the inner workings of quantum gravity. At best, string theory provided an especially consistent way to introduce a small distance scale and thereby regulate the divergences that had plagued the older attempts at quantizing gravity.
Personally, I found the whole enterprise dry, overly technical, and -- above all -- disappointing. I felt that a quantum theory of gravity should profoundly affect our views of space-time, Quantum Mechanics, the origin of the Universe, and the mysteries of black holes. But string theory was largely silent about all these matters. Then in 1993, all this began to change. And the catalyst was the awakening interest in Stephen Hawking's earlier speculations about black holes.
The starting point for Hawking's speculations was the thermal behavior of black holes, which built on earlier work by Jacob Bekenstein of the Hebrew University in Israel. Rather than the cold, dead objects that they were originally thought to be, black holes turned out to have a heat content and to glow like blackbodies. Because they glow they lose energy and evaporate, and because they have a temperature and an energy, they also have an entropy. This entropy S is defined by the Bekenstein- 3 Hawking equation: S = AkBc /4 ħG, where A is the surface area of the horizon and kB is Boltzmann's constant.
10 After realizing that black holes must evaporate by the emission of blackbody radiation, Hawking raised an extremely profound question. What happens to all the detailed information that falls into a black hole? Once it falls through the horizon, it cannot subsequently reappear on the outside without violating causality. That is the meaning of a 'horizon'. But the black hole will eventually evaporate, leaving only photons, gravitons, and other elementary particles as products of the decay. Hawking concluded that the information must ultimately be lost to our world. But one of the fundamental principles of Quantum Mechanics is that information is never lost, because the information in the initial state of a quantum system is permanently imprinted in the quantum state.
Hawking's view was that conventional Quantum Mechanics must be violated during the formation and evaporation of the black hole. He rightly understood that if this is true, the rules of Quantum Mechanics must be drastically modified as the Planck scale is approached. The importance of this for particle physics -- particularly for unified theories -- should have been obvious. But initially Hawking's idea generated little interest among high-energy theorists apart from myself and Gerard 't Hooft at the University of Utrecht. We were convinced that by modifying the rules of Quantum Mechanics in the way advocated by Hawking, "all hell would break loose" such as causing empty space to quickly heat up to stupendous temperatures and energy densities. We were sure that Hawking was wrong. By the early 1990s, however, the issue was becoming critical -- especially to string theorists. String theory by its very definition is based on the conventional rules of Quantum Mechanics. And if Hawking was right, the entire foundation of the theory would be destroyed.
[JS:] I tend to disagree with Lenny and t'Hooft that the unitarity of micro-quantum theory is an absolute. P.W. Anderson's "More is Different" suggests otherwise. Think of the relation between Special Relativity and General Relativity -- similarly with micro- quantum theory and MACRO-quantum theory of superfluids.
4-D space-time is a non-dynamical absolute in Special Relativity. It acts on mass- energy without any direct reaction of mass-energy back on it. This is because the string tension is infinite in that limit. Special Relativity is action without reaction. General Relativity corrects that by giving a finite value to string tension. How? Because General Relativity emerges from a Macro-quantum theory as shown in http://qedcorp.com/APS/EmergentGravity.pdf . The finite string tension in Ed Witten's sense of "alpha'" is actually a quantum h effect added to G and c.
Similarly as shown by Bohm and Hiley in The Undivided Universe p. 30 & 14.6, micro-quantum theory is like Special Relativity because the quantum BIT "pilot wave" is a non-dynamical absolute. It acts on the IT "extra variable" without any direct reaction of IT back on its quantum BIT.
That is, in Wheeler's terms micro-quantum theory is
IT FROM BIT .
In contrast, MACRO-quantum theory adds to that
BIT FROM IT .
Micro-quantum theory is linear and nonlocal in configuration space for entangled composite systems with unitary time evolution and a probability interpretation in Lenny's sense, but with "signal locality" in a detente "passion at a distance" (A. Shimony) with retarded causality. 11 In contrast, Macro-quantum theory with superfluid signal "generalized phase rigidity" (e.g. string tension) is nonlinear (Landau-Ginzburg eq.) and local in ordinary (hyper) space with non-unitary time evolution and a complete breakdown of the Born probability interpretation. Also it allows "signal nonlocality" violating retarded causality. Micro-quantum theory still works for the "normal fluid" noisy component.
Over the last decade, the apparent clash between standard quantum principles and black-hole evaporation has been resolved, favoring -- I should add -- the views of 't Hooft and myself. The formation and evaporation of a black hole is similar to many other process in Nature in which a collision between particles gives rise to a very rich and chaotic spectrum of intermediate states. In the case of a black hole, the collisions are between the original protons, neutrons, and electrons in a collapsing star. Roughly speaking, a black hole is nothing but a very excited string with a total length that is proportional to the area of its horizon.
[JS:] Already in 1973, I published a paper in Herbert Frohlich's "Collective Phenomena" that the Regge string hadronic trajectories showed that the hadronic resonances were tiny black holes in Abdus Salam's strong short-range "f-gravity" with G* ~ 1040 G(Newton).
Spin ~ G*E2/hc5 + intercept
G*/hc5 ~ (String Tension)-1
G*/hc5 ~ (1 Gev)-2 UNIVERSAL SLOPE (micro-geometrodynamics)
The decay of the hadrons would be like Hawking radiation. Abdus Salam invited me to work with him at Trieste because of this paper. We now see that this idea that I had before its time was essentially on the right path. [StealthSkater note: With all due respect and admiration for Dr. Sarfatti, as the past recipient of one his notorious CIA ("Crackpot Identification Agency") e-mails, let me ask which of the following phrases/words does not describe him: brilliant; self-promoting; sometimes arrogant and deaming; not afraid to go out on a theoretical limb; humble]
During the collision or collapse process, all the energy of the initial state goes into forming a single long, tangled string. And the entropy of the configuration is the logarithm of the number of configurations of a random-walking quantum string.
The correspondence between string configurations and black-hole entropy was checked for all of the various kinds of charged and neutral black holes that occur in compactifications of string theory. In most of the cases, the entropy of the string configuration could be estimated. It agreed with the Bekenstein-Hawking entropy to within a factor of order unity.
But string theorists wanted to do better. The Bekenstein-Hawking formula for the entropy of a black hole is very precise: the entropy is 1/4 of the horizon area (measured in Planck units) for every kind of black hole be it static, rotating, charged, or even higher-dimensional. Surely the universal factor of a quarter should be computable in string theory? The key to a precise calculation was obvious. Certain black holes called extremal black holes -- which are the ground states of charged black holes that carry electric and magnetic charges -- are especially tractable in a supersymmetric theory. The only problem was that in 1993 no one knew how to build an extremal black hole out of the right type out of strings. This had to wait a couple of years for the discovery of entities called D-branes.
12 Brane World
In 1995, Joe Polchinski of the University of California in Santa Barbara electrified the string-theory community with a major discovery that has subsequently impacted every field of physics. As we have seen, T-duality is the strange symmetry that interchanges the Kaluza-Klein momenta and winding numbers of a closed string (see Figure 1). But what happens to an open string? Obviously the idea of a winding number does not make sense for such a string. What actually happens to open strings under T- duality is that the free ends become fixed on surfaces called D-branes.
>Figure 3. D-branes are surfaces that "live" in string theory, and they come in various dimensions. D2-branes, for example, are 2- dimensional and can also be called membranes. D0-branes are particle- like, and D1-branes are string-like. Higher- dimensional objects can exist as well. D-branes are essential for making string theory mathematically consistent and have far-reaching implications for a theory of quantum gravity
D-branes come in various dimensions. 2D branes, for example, can also be called membranes. They have an energy or mass per unit surface area and are localized physical objects in their own right. In a sense, they seem to be no less fundamental than the strings themselves. To an outsider, D-branes may seem to be arbitrary additions to the theory. But they are not. Their existence is absolutely essential to the mathematical consistency of the theory. In addition to allowing T-duality to act on an open string in Type I string theory, they are necessary for implementing the deep dualities that link the 5 different kinds of string theory together.
But from the point-of-view of black holes, the importance of D-branes is that you can build extremal black holes from them. In fact, just by placing a large number of D-branes at the same location, you can build an extremal supersymmetric black hole. And because of the special properties of supersymmetric systems, the statistical entropy of that black hole can be precisely computed. The result -- which was first derived by Andrew Strominger and Cumrun Vafa at Harvard in 1996 -- is that the entropy is equal to exactly 1/4 of the horizon area in Planck units! This suggested that the microscopic degrees of freedom implied by the Bekenstein-Hawking entropy are the degrees of freedom describing strings. It was a major boost for the superstring community.
At about the same time as D-branes were discovered, another very important development took place. As I mentioned, the coupling constant of string theory is not really a constant at all and in many respects it is very similar to the compactification moduli. String theorists took a surprisingly long time to make the connection. But it turns out that 10-D string theory is itself a Kaluza-Klein compactification of an 11-D theory that became known as "M-theory".
13 M-theory appears to underlie all string theories (Figure 2). The 5 different versions of string theory are just different ways of compactifying its 11 dimensions. But M-theory is not itself a string theory. It has membranes but no strings. And the strings only appear when the 11th dimension is compactified. Furthermore, the momentum in the compact 11th direction (the Kaluza-Klein momentum) is identified as the number of D0-branes (i.e., zero-dimensional branes or "points") in a particular type of string theory.
This connection between Kaluza-Klein momentum and D0-branes led to another breakthrough. In 1996, myself, Tom Banks, Steve Shenker (at Rutgers University), and Willy Fischler (at the University of Texas) realized that M-theory could be cast in a form no more complicated than the quantum mechanics of a system of non-relativistic particles (i.e., D0-branes). The resulting theory -- which is called Matrix theory -- is an exact and complete quantum theory that describes the microscopic degrees of freedom of M-theory. As such, it is the first precise formulation of a quantum theory of gravity.
Duality
Matrix theory was just one example of how D-branes can be used to formulate a theory of quantum gravity. Soon after its discovery, Juan Maldacena (who is now at the Institute for Advanced Study (IAS) in Princeton) came up with a new direction to explore. Ed Witten of the IAS and others had previously shown that D-branes have their own dynamics. But it turned out that the fluctuations and motions of a D-brane can be quantized in the form of a gauge theory that is restricted to the D-brane itself. The theory that lives on a coincident collection of D3-branes, for example, is a supersymmetric non-Abelian gauge theory. In other words, it is a supersymmetric version of QCD -- the theory describing quarks and gluons. In a sense, string theory is returning to its roots as a possible description of hadrons (See Physics World, May 2003, pp35-38).
Figure 4. Anti-de Sitter space is a solution to Einstein's field equations that is negatively curved everywhere. It is analogous to the geometry of Eschers's "Angels and Devils" in which you have to imagine that all the angels and devils are the same size, but that they are distorted due to the negative curvature of space (in the same way that Mercator's projection of the globe misrepresents the area of continents away from the Equator). This figure depicts anti-de Sitter space at an instant; the vertical dimension is time. The geometry is bounded by the surface of the cylinder and the holographic principle states that quantum gravity in the interior of the space is described by a quantum field theory (such as QCD) on the boundary.
Maldacena realized that in an appropriate limit, the theory of D3-branes should be a complete description of string theory not just on the branes, but in the entire geometry in which the branes are embedded. A gauge theory would therefore also be a description of quantum gravity in a particular background space-time. This space-time is called anti-de Sitter space which, roughly speaking, is a 14 "universe inside a cavity". The walls of the cavity behave like reflecting surfaces so that nothing escapes it (Figure 4).
This "duality" between Quantum Field Theory and Gravity is an exact realization of what is called the holographic principle. This strange principle -- formulated by 't Hooft and myself -- grew from our debate with Hawking regarding the validity of Quantum Mechanics in the formation and evaporation of black holes.
According to the holographic principle, everything that ever falls into a black hole can be described by degrees of freedom that reside in a thin layer just above the horizon. In other words, the full 3-D world inside the horizon can be described by the 2-D degrees of freedom on its surface. Even more generally, it should be possible to describe the physics of any region of space in terms of holographic degrees of freedom that reside on the boundary of that region. This leads to a drastic reduction of the number of degrees of freedom in a field theory. Most theorists found it very hard to swallow until Maldacena's work came along. Maldacena's duality replaces a gravitational theory in anti-de Sitter space by a field theory that lives on its boundary in a very precise way. In other words, the 3 + 1 dimensional boundary field theory is a holographic description of the interior of 4 + 1 dimensional anti- de Sitter space.
The D-brane revolution has been very far reaching. Matrix theory and the Maldacena duality are both formulations of quantum gravity that conform to the standard rules of Quantum Mechanics and should therefore lay to rest any further questions about black holes violating these rules.
Googles of possibilities
I would like to end by discussing the future of string theory not as a mathematical subject, but as a framework for particle physics and cosmology. The final evaluation of string theory will rest on its ability to explain the facts of Nature and not on its own internal beauty and consistency. String theory is well into its 4th decade. But so far, it has not produced a detailed model of elementary particles or a convincing explanation of any cosmological observation. Many of the models that are based on specific methods of compactifying either 10-D string theory or 11-D M-theory have a good deal in common with the real World. They have bosons and fermions, for example, and gauge theories that are similar to those in the Standard Model. Furthermore, unlike any other theory, they inevitably include gravity. But "the devil is in the details". And so far, the details have eluded string theorists.
It is possible, of course, that string theory is the wrong theory. But I believe that would be a very premature judgment. And probably incorrect. The problem does not seem to be a lack of richness but rather the opposite. String theory contains too many possibilities. For most physicists, the ideal physical theory is one that is unique and perfect in that it determines all that can be determined and that it could not logically be any other way. In other words, it is not only a 'Theory of Everything', but it is also the only 'Theory of Everything'. To the orthodox string theorist, the goal is to discover the one true consistent version of the theory, and then to demonstrate that the solution manifests the known laws of Nature such as the Standard Model of particle physics with its empirical set of parameters.
But the more we learn about string theory, the more non-unique it seems to be. There are probably millions of Calabi-Yau spaces on which to compactify string theory. Each space has hundreds of moduli and hundreds of subspaces on which branes can be wrapped, fluxes imposed upon, and so on. A conservative estimate of the number of distinct vacua of the theory is in the googles -- that is, more than 10100. The space of possibilities is called the "Landscape". And it is huge. To mix metaphors, it is a
15 stupendous haystack that contains googles of straws and only one needle. Worse still, the theory itself gives us no hint about how to pick among the possibilities (see "The String-Theory Landscape").
This enormous variety may, however, be exactly what cosmology is looking for. A common theme among cosmologists is that the observed universe may merely be a minuscule part of a vastly bigger Universe that contains many local environments (or what Alan Guth at MIT calls "pocket universes"). According to this view, so many pocket universes formed during the early inflationary epoch (each of which with its own vacuum structure) that the entire landscape of possibilities is represented. The reasons for this view are not just idle speculation, but are rooted in the many accidental fine-tunings that are necessary for a Universe that supports Life. Thus, it may be that the enormous number of possible vacuum solutions -- which is the bane of particle physics -- may be just what the doctor ordered for Cosmology.
Further information
T-duality
In a single compact dimension, there are 2 kinds of quantum numbers: momentum in the compact direction and the winding number. Both of these are quantized in integer multiples of a basic unit, and each has a certain energy associated with it. In the case of momentum, for example, the energy is just the kinetic energy of motion in the compact direction. The energy of a particle with n units of compact momentum is equal to n/R, where R is the circumference of the compact direction. Note that the energy grows as the size of the compact space gets smaller. On the other hand, the winding modes also have energy which is the potential energy needed to stretch the string around the compact coordinate. If we call the winding number m, then the winding energy is equal to mR. In this case, the energy decreases as the size of the compact direction decreases.
The surprising thing is that the spectrum of energies is unchanged if we change the compactification radius from R to 1/R and at the same time interchange the Kaluza-Klein momentum and winding modes. In other words, just by looking at the spectrum of energies, you could never tell the difference between a theory that is compactified on a space of size R or on one of size 1/R. As you try to make the compactification scale smaller than the natural string scale (i.e., the size of a vibrating string), the theory begins to behave as if the compactification radius was getting bigger. Physically, the smallest compactification value of R is the string scale. But from a mathematical viewpoint, 2 different spaces -- one large, the other small -- are completely equivalent. This equivalence is called T-duality.
Author
Leonard Susskind is in the Department of Physics, Stanford University, 382 Via Pueblo Mall, CA 94305-4060, U.S., e-mail [email protected]
Further reading J Maldacena, 1999. "The large N limit of superconformal field theories and supergravity", Int. J. Theor. Phys. 38 1113-1133 J Polchinski, 1995. "Dirichlet-branes and Ramond-Ramond charges, Phys. Rev. Lett. 75 4724-4727 J Polchinski, 1998. String Theory (volume 2): Superstring Theory and Beyond (Cambridge University Press) J H Schwarz et al. 1981. Superstring Theory (volume 1): Introduction (Cambridge University Press)
16 A Strominger and C Vafa ,1996. "Microscopic origin of the Bekenstein-Hawking entropy", Phys. Lett. B 379 99-104
The official string theory website: http://www.superstringtheory.com
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[JS:] Here's Lenny from http://www.edge.org/
What we've discovered in the last several years is that string theory has an incredible diversity -- a tremendous number of solutions -- and allows different kinds of environments. A lot of the practitioners of this kind of mathematical theory have been in a state of denial about it. They didn't want to recognize it. They want to believe the Universe is an elegant universe. But it's not so elegant. It's different over here; it's that over here. It's a Rube Goldberg machine over here. And this has created a sort of sense of denial about the facts about the theory. The theory is going to win. And physicists who are trying to deny what's going on are going to lose. [StealthSkater note: There are other competing theories out there such as Loop Quantum Gravity which don't need all of the extra dimensions. So far, ingenious experiments design to search for these Planck-scale dimensions without using conventional particle accelerators have turned up nothing as of 2005. Perhaps when the upgraded CERN accelerator goes on line around 2007, it can detect the so-called "s-particles" which would be a good sign of supserstrings.] The Landscape
A Talk with Leonard Susskind The Reality Club: Responses by Paul Steinhardt, Lee Smolin, Kevin Kelly, Alexander Vilenkin, Lenny Susskind Leonard Susskind Edge Video DSL+ | Modem
Introduction
The beginning of the 21st Century is a watershed in modern Science -- a time that will forever change our understanding of the Universe. Something is happening which is far more than the discovery of new facts or new equations. This is one of those rare moments when our entire outlook, our framework for thinking, and the whole epistemology of Physics and Cosmology are suddenly undergoing real upheaval. The narrow 20th Century view of a unique Universe -- about 10 billion years old and 10 billion light-years across with a unique set of physical laws -- is giving way to something far bigger and pregnant with new possibilities.
Gradually physicists and cosmologists are coming to see our 10 billion light-years as an infinitesimal pocket of a stupendous Megaverse [SS: or Multiverse]. At the same time, theoretical physicists are proposing theories which demote our ordinary laws of Nature to a tiny corner of a gigantic landscape of mathematical possibilities.
17 [JS:] I have used the term "landscape" for the Bohmian BIT "quantum pilot wave" with the "IT" "extra-variable" as the "system point" rolling on the landscape, in sense of "complexity theory" (The Quark and The Jaguar, Murray Gell-Mann) for many years now. Indeed, there is even an animation of the idea made by Paul Zielinski in upper left- hand corner of http://stardrive.org/title.shtml .
Micro-quantum theory is an absolute non-dynamical BIT landscape with the IT extra-variable ("hidden variable") as a passive test particle. Macro-quantum theory is when the IT gets so "heavy" that is distorts what it is rolling on with 2-way nonlinear "Landau-Ginzburg" spontaneous self-organization. Heisenberg, of course, used "potentia". And in that same vein, so do other Pundits use "possibilities" to describe the BIT field of quantum theory.
This Landscape of possibilities is a mathematical space representing all of the possible environments that theory allows. Each possible environment has its own laws of physics, elementary particles, and constants of Nature. Some environments are similar to our own corner of the landscape but slightly different. They may have electrons, quarks, and all the usual particles. But gravity might be a billion times stronger. Others have gravity like ours, but electrons that are heavier than atomic nuclei. Others may resemble our World except for a violent repulsive force (called the 'cosmological constant') that tears apart atoms, molecules, and even galaxies. Not even the dimensionality of space is sacred. Regions of the Landscape describe worlds of 5,6,…11 dimensions. The old 20th Century question "What can you find in the Universe?" is giving way to "What can you not find?"
The diversity of the Landscape is paralleled by a corresponding diversity in ordinary space. Our best theory of cosmology (called inflationary cosmology) is leading us -- sometimes unwillingly -- to a concept of a Megaverse, filled with what Alan Guth (the father of Inflation theory) calls "pocket universes". Some pockets are small and never get big. Others are big like ours but totally empty. And each lies in its own little valley of the Landscape.
Man’s place in the Universe is also being reexamined and challenged. A Megaverse that diverse is unlikely to be able to support intelligent Life in any but a tiny fraction of its expanse. Many of the questions that we are used to asking (such as "Why is a certain constant of Nature one number instead of another?") will have very different answers than what physicists had hoped for. No unique value will be picked out by mathematical consistency, because the Landscape permits an enormous variety of possible values. Instead the answer will be "Somewhere in the Megaverse, the constant is this number. And somewhere else, it is that. And we live in one tiny pocket where the value of the constant is consistent with our kind of Life. That’s it! There is no other answer to that question."
The kind of answer that this-or-that is true because if it were not true, there would be nobody to ask the question is called the Anthropic Principle. Most physicists hate the Anthropic Principle. It is said to represent surrender and a giving-up of the noble quest for answers. But because of unprecedented new developments in physics, astronomy, and cosmology, these same physicists are being forced to reevaluate their prejudices about anthropic reasoning. There are 4 principal developments driving this sea change. Two come from theoretical physics, and two are experimental or observational.
On the theoretical side, an outgrowth of inflationary theory called eternal inflation is demanding that the world be a Megaverse full of pocket universes that have bubbled up out of inflating space like bubbles in an uncorked bottle of Champagne."
18 [JS:] I have used that same image independently. I think it is in my book Space-Time and Beyond II. Of course, it's obvious that I used it because Rashi de Troyes 1040-1105 was a vintner in Champagne in the South of France at the time alluded to in "The Da Vinci Code" and other books in a similar vein.
At the same time, string theory -- our best hope for a unified theory -- is producing a landscape of enormous proportions. The best estimates of theorists are that 10500 distinct kinds of environments are possible.
Very recent astronomical discoveries exactly parallel the theoretical advances. The newest astronomical data about the size and shape of the Universe convincingly confirm that inflation is the right theory of the early Universe. There is very little doubt that our Universe is embedded in a vastly bigger Megaverse. [StealthSkater note: But superstring and brane theory were used to propose an alternative model to the Inflationary phase of the Big Bang. Called "Ekpyrotic", it describes how our 4-D Universe was created in a "Big Bang" that resulted from the slow collison of 2 infinitely- long 5-D branes in the Multiverse/Megaverse. This model produces the same results as the earlier Inflationary model but without the need for magnetic monopoles and gravitational waves (which have never been seen). Archived at => doc pdf URL ]
But the biggest news is that in our pocket, the notorious cosmological constant is not quite zero as it was thought to be. This is a cataclysm. And the only way that we know how to make any sense of it is through the reviled and despised Anthropic Principle.
[JS:] I have an explanation of precisely this problem in http://qedcorp.com/APS/EmergentGravity.pdf http://qedcorp.com/APS/StarGate1.mov
I don’t know what strange and unimaginable twists our view of the Universe will undergo while exploring the vastness of the Landscape. But I would bet that at the turn of the 22nd Century, philosophers and physicists will look back nostalgically at the present and recall a golden age in which the narrow provincial 20th Century concept of the Universe gave way to a bigger better Megaverse, populating a Landscape of mind-boggling proportions.
... the only real physics problem that has been solved by string theory is the problem of black holes. It led to some extremely revolutionary and strange ideas.
Up to now string theory has had nothing to say about Cosmology. Nobody has understood the relationship between string theory and the Big Bang, inflation, and other aspects of cosmology.
The Landscape (Leonard Susskind)
What I mostly think about is how the World got to be the way it is. There are a lot of puzzles in physics. Some of them are very, very deep. Some of them are very, very strange. And I want to understand them. I want to understand what makes the World tick. Einstein said he wanted to know what was on God's mind when he made the World. I don't think he was a religious man, but I know what he means.
19 The thing right now that I want to understand is why the Universe was made in such a way as to be just right for people to live in it. This is a very strange story. The question is why certain quantities that go into our physical laws of Nature are exactly what they are and if this is just an accident. Is it an accident that they are finely tuned, precisely (sometimes on a knife's edge) just so that the World could accommodate us? [StealthSkater note: in 2005, this is an argument that is ongoing regarding Evolution vs. Intelligent Design. Perhaps there is a hybrid model that makes use of both concepts. One in which a Creator built the gameboard and dice; made a few fundamental rules; and then stepped back to watch how the game unfolded. Contrary -- but possibly parallel to this -- is the question did God create the Universe, or does he merely rule it?]
For example, there is a constant in Nature called the cosmological constant. And it is a certain number. If that number differed by the tiniest amount from what it really is, the Universe could not have been born with galaxies, stars, planets, and so forth. Is it an accident that the number was exactly right to be able to form the Universe as we see it? Or is it some feature of the way the Universe works that makes it necessarily create Life?
The question is whether our environment in a bigger sense (in terms of the laws of Nature that we have), the elementary particles, the forces between them, and all those kinds of things are environmental things which are contingent in our particular region of the Universe or are exactly the same throughout the whole Universe. If they're contingent, that means that they may vary from place-to-place or they may vary from one thing to another thing to another thing. If that were the case, then we would answer some subset of the questions that we're interested in by saying "things are the way they are because if they were any other way we couldn't live here. The environment has to be right for us to exist."
On the other hand, if everything is the same all across the Universe from beginning -to-end, then we don't understand why things are tuned in the way that allows us (with knife-edge precision) to be in an environment that supports Life. This is a big controversy that's beginning to brew in physics: whether the laws of Nature as we know them are simply derivable from some mathematical theory and could not be any other way, or if they might vary from place-to-place. This is the question that I would like to know the answer to.
In the United States, the cosmologists don't like the idea of the Anthropic Principle at all. In England, they love it. I was very surprised to find out when I started talking about this that the physicists (like myself, people who are interested in theoretical, mathematical questions in physics) are rather open to it in the United States, but the cosmologists are not. This idea originated to a large extent among British cosmologists (Martin Rees being one of them, John Barrow being another one). There's also Andrei Linde (who is a Russian but of course lives in the United States) who was one of them as was Alexander Vilenkin. But that's not the crowd that I'm addressing my remarks to.
The crowd that I'm addressing are the high-energy physicists, the string theorists, and includes the Brian Greenes, the Ed Wittens, the David Grosses, and so forth. The reason is because over the last couple-of-years, we've begun to find that string theory permits this incredible diversity of environments. It's a theory which simply has solutions which are so diverse that it's hard to imagine what picked one of them in the Universe. More likely, the string theory universe is one with many different little patches of space that Alan Guth has called "pocket universes". Of course, they're big. But there are little patches of space with one environment, little patches of space with another environment, etc.
Mostly physicists have hated the idea of the Anthropic Principle. They all hoped that the constants of nature could be derived from the beautiful symmetry of some mathematical theory. And now what people like Joe Polchinski and I are telling them is that it's contingent on the environment. It's different over there, it's different over there, and you will never derive the fact that there's an electron, a proton, a 20 neutron, whatever with exactly the right properties. You will never derive it because it's not true in other parts of the Universe.
Physicists always wanted to believe that the answer was unique. Somehow there was something very special about the answer. But the myth of uniqueness is one that I think is a fool's errand. That is, some believe that there is some very fundamental, powerful, simple theory which -- when you understand it and solve its equations -- will uniquely determine what the electron mass is, what the proton mass is, and what all the constants of Nature are. If that were to be true, then every place would have to have exactly the same constants of Nature. If there were some fundamental equation which, when you solved it, said that the World is exactly the way we see it, then it would be the same everywhere.
On the other hand, you could have a theory which permitted many different environments, and a theory which permitted many different environments would be one in which you would expect that it would vary from place -to-place. What we've discovered in the last several years is that string theory has an incredible diversity -- a tremendous number of solutions -- and allows different kinds of environments. A lot of the practitioners of this kind of mathematical theory have been in a state of denial about it. They didn't want to recognize it. They want to believe the Universe is an elegant universe. But it's not so elegant. It's different over here. It's that over here. It's a Rube Goldberg machine over here. And this has created a sort of sense of denial about the facts about the theory. The theory is going to win, and physicists who are trying to deny what's going on are going to lose.
These people are all very serious people. Davis Gross, for example, is very harshly against this kind of view of diversity. He wants the World to be unique. And he wants string theorists to calculate everything and find out that the World is very special with very unique properties that are all derivable from equations. David considers this anthropic idea to be giving-up the hope for uniqueness. And he quotes Winston Churchill when he's with young people when he says, "Nevah, nevah, nevah, nevah give up."
Ed Witten dislikes this idea intensely. But I'm told that he's very nervous that it might be right. He's not happy about it, but I think he knows that things are going in that direction. Joe Polchinski -- who is one of the really great physicists in the World -- was one of the people who started this idea. In the context of string theory, he was one of the first to realize that all this diversity was there and he's now fully on-board. Everybody at Stanford is going in this direction. I think Brian Greene is thinking about it. Brian moved to some extent from hardcore string theory into thinking about cosmology. He's a very good physicist. There were some ideas out there that Brian investigated and found that they didn't work. They were other kinds of ideas -- not this diversity idea -- and they didn't work. I don't know what he's up to now. I haven't spoken to him for all of a month. Paul Steinhardt hates the idea. Alan Guth is certainly very susceptible. He's the one who coined the term "pocket universes".
The reason that there is so much diversity in string theory is because the theory has an enormous number of what I call "moving parts" -- i.e., things you can tinker with. When you build yourself an example of string theory as in Brian's book, it involves the geometry of these internal compact spaces that Brian became famous for studying. There are a lot of variables in fixing one of them, and a lot of variables to tinker around with. There are so many variables that this creates an enormous amount of diversity. ~~~ ... I was just incredibly excited. I figured, "Okay, here I am. I'm going to be a famous physicist. I'm going to be Einstein, I'm going to be Bohr, and everybody's going to pay great attention to me," so I wrote up the manuscript. 21 .... Now the Physical Review Letters is a very pompous journal. They said that they would only publish the very, very best. What usually happens when people start getting that kind of way is that they wind up publishing the very worse. Because when standards get very, very high like that, nobody wants to bother with them. So they just send it to someplace where it's easy to publish."
[JS:] Bravo Lenny! :-) ... And how did it came back? Well, they said, "This paper is not terribly important, and it doesn't predict any new experimental results. I don't think it's publishable in the Physical Review."
Boom! I felt like I had gotten hit over the head with a trashcan. I was very, very deeply upset. The story that I told Brian Greene for his television program was correct: I went home, I was very nervous, and very upset. My wife had tranquilizers around the house for some reason, and she said, "Take one of these and go to sleep." ...
I met Hawking and Gerard ‘t Hooft in the attic of Werner Erhard's house in San Francisco. Erhard was a fan of Sidney Coleman. Dick Feynman, myself, and David Finkelstein were his gurus."
[JS:] That was my doing. I promoted Finkelstein to Werner when I invited David to Esalen in 1976. That story is in Gary Zukav's Dancing Wu Li Masters. Gary was my roommate in San Francisco's North Beach at 372 Green Street.
And of course, we didn't give a damn about his silly business. But we loved his cigars, we loved his liquor, we loved the food that we got from him, and he was fun. He was very, very smart."
[JS:] Yeah Lenny, tell me about it! I created the space for you and the others to get there. ;-)
Hawking came and told us his ideas about black holes. And one of the things he told us was that things which fall into the black hole disappear from the Universe completely and can never been returned -- even in some scrambled form. Now, information is not supposed to be lost. It's a dictum of physics that information is preserved. What that means is that in principle, you can always take a sufficiently precise look at things and figure out what happened in the Past -- infinitely accurately -- by running them backwards.
Hawking was saying that when things fall into a black hole, they are truly lost and you can never reconstruct what fell in. This violated a number of basic principles of Quantum Mechanics, and ‘t Hooft and I were stunned. Nobody else paid any attention, but we were both really stunned. I remember ‘t Hooft and myself were standing, glaring at the blackboard. We must have stood there for 15 minutes without saying a word when Hawking told us these things. I was sure that Hawking was wrong. ‘t Hooft was sure that Hawking was wrong. And Hawking was absolutely sure that he was right in saying that information was lost inside black holes.
For 13 years I thought about this -- continuously, pretty much -- and at the end of that 13 years, I began to suspect that string theory had in its guts a solution to this problem. And so I became interested again in string theory. I didn't remember anything about it. I had to go back and read my own papers because I tried reading other people's papers … and I couldn't understand them."
[JS]: I know the feeling. :-)
22 In the intervening years, powerful mathematics was brought to bear on the theory. I found it rather dry since it was rather completely mathematics with very little of an intuitive, physical picture. The main things that happened were that -- first of all -- 5 versions of it were discovered. Tricks were discovered about how to get rid of the extra dimensions. You don't actually get rid of them, you curl them up into little dimensions. You can read all about that in Brian Greene's book The Elegant Universe. That turned out to be a good thing.
John Schwarz, Michael Green, and a few other people worked out the very difficult mathematics in great detail. They demonstrated that the theory was not inconsistent in the ways that people thought it might be. When they showed that the mathematics was firm, Ed Witten got very excited. And once Ed walked into it, well … He's a real mathematical powerhouse and dominated the field very strongly. Witten has written many famous papers. But one of his key papers -- which may have been the most important one -- was written in about 1990. He and collaborators around him worked out the beginnings of a mathematics of these Calabi-Yau manifolds which are tiny, curled-up spaces that are very well- explained in Brian Greene's book.
Ed is also a physicist. And he had a lot of interest in trying to make this into a real theory of elementary particles. He never quite succeeded, but he discovered a lot of beautiful mathematics about it. I found a lot of it rather dry because it was not addressing physics questions the way I enjoy addressing them. It was just a little too mathematical for my taste. My taste leans less toward the mathematical and more toward the pictorial. I think in terms of pictures.
I wasn't really following the subject too closely at that point. I was still interested in black holes, and it wasn't until about 1993 that I began to suspect that there were ingredients in string theory that could resolve this puzzle of Hawking's. So at that point, I really got into it. I started to think about the connection between string theory and black holes.
String theory was a theory of gravity. When you have gravity, you can have black holes. And so string theory had to have black holes in it, and therefore it should have a resolution of this problem. Over a period of a couple of years, it did have a resolution. It did, in fact, turn out that Hawking was wrong. That is to say, he was wrong in a great way. When a person puts a finger on a problem of that magnitude -- independently of whether they got it right or they got it wrong -- they have a tremendous impact on the subject. And he has had a tremendous impact. I developed some simplified ways of thinking about it that demonstrated that black holes did not lose information, that things don't fall into the black hole and disappear, that they eventually come back out. They are all scrambled up, but nevertheless they come back out. I began writing papers on that. And my paper -- which said that stuff does not get lost inside a black hole in string theory -- stimulated the string community to start thinking about black holes. There was an eruption of papers -- mine, Joe Polchinski's, Andy Strominger's, Cumrun Vafa's -- that really nailed that problem down.
And black holes have been solved. Black holes have been understood. To this day, the only real physics problem that has been solved by string theory is the problem of black holes. It led to some extremely revolutionary and strange ideas. Up to now, string theory has had nothing to say about cosmology. Nobody has understood the relationship between string theory and the Big Bang, inflation, and other aspects of cosmology. I frequently go to conferences that often have string theorists and cosmologists. Usually the string theory talks consist of apologizing for the fact that they haven't got anything interesting to tell the cosmologists. This is going to change very rapidly now because people have recognized the enormous diversity of the theory. [StealthSkater note: I beg to differ, but black holes have not been solved. That is, what they fundamentally are is still up for debate. Perhaps their effects are what Prof. Susskind is referring to. New models are replacing the hard-to-believe point-like singularities of infinite density with something called "Gravastars" => doc pdf URL ] 23 People have been trying to do business the old way. With string theory, they were trying to do the things that they would have done with the earlier theories, and it didn't make a lot of sense for them to do so. They should have been looking at what's really unique and different about string theory -- not what looks similar to the old kind of theories. And the thing which is really unique and very, very special is that it has this diversity that gives rise to an incredibly wild number of different kinds of environments that physics can take place in.
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