The Fabric of the Cosmos

When everything is probable.

not bad

Excellent book

Brian Randolph Greene (born 1963) is an American theoretical physicist and string theorist who is professor at Columbia University and chairman of the World Science Festival since co-founding it in 2008. He has participated in several PBS television specials, and has also written books such as  The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory , The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos , Icarus at the Edge of Time , etc.He wrote in the Preface of this 2004 book, “science is still struggling to understand what space and time actually are. Are they real physical entities or simply useful ideas? If they’re real, are they fundamental, or so they emerge from more basic constituents? What does it mean for space to be empty? Does time have a beginning? Does it have an arrow, flowing inexorably from past to future, as common experience would indicate? Can we manipulate space and time? In this book, we follow three hundred years of passionate scientific investigation seeking answers, or at least glimpses of answers, to such basic but deep questions about the nature of the universe.” (Pg. ix) He adds, “[This book] is intended primarily for the general reader who has little or no formal training in the sciences but who desire to understand the workings of the universe… Some of the material I cover is controversial. For those issues that remain up in the air, I’ve discussed the leading viewpoints in the main text. For the points of contention that I feel have achieved more of a consensus, I’ve relegate different viewpoints to the notes… I’ve striven for a balanced treatment.” (Pg. xi)In the first chapter, he suggests, “As we continue to gain facility with superstring theory and its extension M-theory, our cosmological insights will deepen, bringing both time’s origin and its arrow into ever-sharper focus. If we let our imaginations run wild, we can even envision that the depth of our understanding will one day allow us to navigate spacetime and hence break free from the spatio-temporal chains from which we’ve been shackled for millennia. Of course, it is extremely unlikely that we will ever achieve such power. But… deep understanding yields its own empowerment. Our grasp of the true nature of space and time would be a testament to the capacity of the human intellect. We would finally come to know… the silent, ever-present markers delineating the outermost boundaries of human experience.” (Pg. 20)He explains, “according to [Niels] Bohr and the Copenhagen interpretation of quantum mechanics … before one measures the electron’s position there is no sense in even asking where it is. It does not have a definite position… The electron has a definite position in the usual intuitive sense only at the moment we ‘look’ at it… when we measure its position… It’s not that the electron has a position and that we don’t know the position before we do our measurement. Rather, contrary to what you’d expect, the electron simply DOES NOT HAVE a definite position before the measurement is taken. This is a radically strange reality. In this view, when we measure the electron’s position we are not measuring an objective, preexisting feature of reality. Rather, the act of measurement is deeply enmeshed in creating the very reality it is measuring.” (Pg. 94)He states, “If two photons are entangled, the successful measurement of either photon’s spin about one axis ‘forces’ the other, distant photon to have the same spin about the same axis; the act of measuring one photon ‘compels’ the other, possibly distant photon to … take on a definitive spin value---a value that precisely matches the spin of its distant companion. And that boggles the mind… even though the two photons are spatially separate, their common origin establishes a fundamental link between them… the two photons are so intimately bound up that it is justified to consider them---even though they are spatially separate---as parts of one physical entity.” (Pg. 115-116)He says, “if the universe is spatially infinite, there was already an infinite spatial expanse at the moment of the big bang… In this setting, the big bang did not take place at one point; instead, the big bang eruption took place EVERYWHERE on the infinite expanse… it is as though there were many big bangs, one at each point on the infinite spatial expanse. After the bang, space swelled, but its overall size didn’t increase since something already infinite can’t get any bigger. What did increase are the separations between objects like galaxies… there is mounting evidence that the overall shape of space is not curved… the flat, infinitely large spatial shape is the front-running contender for the large-scale structure of spacetime.” (Pg. 249-250)He argues, “A common misconception is that the big bang provides a theory of cosmic origins. It doesn’t. The big bang is a theory… that delineates cosmic evolution from a split second after whatever happened to bring the universe into existence, but it says nothing at all about time zero itself… It tells us nothing about what banged, why it banged, how it banged, or, frankly, whether it ever really banged at all. In fact… the big bang presents us with quite a puzzle… gravity is an attractive force… So what could possibly be responsible for the OUTWARD force that drove space to expand? It would seem that some kind of powerful repulsive force must have played a critical role… but which of nature’s forces could that possibly be?” (Pg. 272)He suggests, “[we need] a theory that can overcome perhaps the greatest obstacle theoretical physics has faced during the last eighty years: a fundamental rift between general relativity and quantum theory. Many researchers believe that a relatively new approach called superstring theory may have accomplished this, but if superstring theory is right, the fabric of the cosmos is far stranger than almost anyone ever imagined.” (Pg. 323)But he acknowledges, “bear in mind that no one has ever seen a string and… it is likely that no one ever will. Strings are so small that a direct observation … would require resolving power nearly a billion billion times finer than our current technology allows. Some scientists argue vociferously that a theory so removed from direct empirical testing lies in the realm of philosophy or theology, but not physics. I find this view shortsighted… While we may never have technology capable of seeing strings directly, the history of science is replete with theories that were tested experimentally through indirect means.” (Pg. 352)He points out, “But the quantum mechanical equations of string theory don’t work in four spacetime dimensions, nor in five, six, seven, or 7,000. Instead… the equations of string theory work only in ten spacetime dimensions---nine in space, plus time. String theory DEMANDS more dimensions. This is a fundamentally different kind of result… Prior to strings, no theory said anything at all about the number of spatial dimensions in the universe… Now, for the first time, string theory provided equations that PREDICTED the number of space dimensions.” (Pg. 366-367)He admits, “the code of the cosmos may well be written in the geometry of a Calibi-Yau shape… The question, then, is which Calabi-Yau shape, if any, constitutes the extra-dimensional part of the spacetime fabric… the question remains unanswered… The equations don’t even determine the size of the extra dimensions. Since we don’t see the extra dimensions, they must be small, but precisely how small remains an open question. Is this a fatal flaw of string theory? Possibly. But I don’t think so… the exact equations of string theory have eluded theorists for many years and so much work has used APPROXIMATE equations.” (Pg. 372) He adds, “String theory, at least in principle, allows all particle properties to be determined by the theory itself. No one has accomplished this, but as emphasized, string theory is still very much a work in progress. In time, researchers hope to realize fully the vast potential of this approach to unification.” (Pg. 374)He observes, “with the new insights of the unified M-theoretical framework, [Edward] Witten was able to … demonstrate that one space dimension had been overlooked [by string theory] all along. Thus, Witten showed that the five ten-dimensional frameworks that string theorists had developed for more than a decade were actually five approximate descriptions of a single, underlying eleven-dimensional theory. You might wonder whether this unexpected realization invalidated previous work in string theory. By and large, it didn’t. The newfound tenth spatial dimension added an unanticipated feature to the theory, but is string/M-theory is correct, and should the tenth spatial dimension turn out to be much smaller than all others… previous work would remain valid.” (Pg. 383)He asserts, “Earlier, we required the extra dimensions of string/M-theory to be tightly curled up. The reason, clearly, is that we don’t see the extra dimensions and so they must be hidden away. And one way to hide them is to make they smaller than we or our equipment can detect… there is an alternative explanation for why we’re not aware of the extra dimensions. It is not necessarily that the extra dimensions are extremely small. They could be big. We don’t see them because of the way we see. We see by using the electromagnetic force, which is unable to access any dimensions beyond the three we know about.” (Pg. 392-393) Later, he adds, “Right now, right next to you… there could be another spatial dimension---a dimension beyond left-right, back/forth, and up/down, a dimension that’s curled up but still large enough to swallow something as thick as this page---that remains beyond our grasp.” (Pg. 400) But he adds, “if the braneworld scenario is correct, upcoming accelerator experiments DO have the potential of confirming string theory.” (Pg. 428)Anyone interested in string theory, M-theory, and its cosmological implications will likely be interested in this book.