The Elegant Universe: 25th Anniversary Edition

Brian Greene’s The Elegant Universe is being reissued today, in a 25th anniversary edition. It’s the same text as the original, with the addition of a 5 page preface and a 36 page epilogue.

The initial excitement among some theorists in late 1984 and 1985 that string theory would provide a successful unified theory had died down by the early 1990s, as it had become clear that this was not working out. This didn’t stop the theory from continuing to be sold to the public in hype-heavy books such as Michio Kaku’s 1995 Hyperspace. Interest in string theory among theorists was revived in the mid-nineties by the advent of branes/dualities/M-theory. The publication of the The Elegant Universe in 1999 brought to the public the same hyped story about unification, together with the news of the new “M-theory”. The book was wildly successful, selling something like 2 million copies worldwide. A 3-hour PBS special based on the book reached an even larger audience.

From the beginning in 1984 I was dubious about string theory unification, and by the late 1990s could not understand why this was dominating physics departments and popular science outlets, with no acknowledgement of the serious problems and failures of the theory. From talking privately to physicists, it became clear that the field of particle theory had for quite a while become disturbingly tribal. There was a string theory tribe, seeing itself as embattled and fighting less intelligent other tribes for scarce resources. Those within the tribe wouldn’t say anything publicly critical of the theory, since that would not only hurt their own interests, but possibly get them kicked out of the tribe. Those outside the tribe also were very leery of saying anything, partly because they felt they lacked the expertise to do so, partly because they feared retribution from powerful figures in the string theory tribe.

At some point I decided that someone should do something about this, and if no one else was going to say anything, maybe I needed to be the one to do so. My unusual position in a math department pretty well insulated me from the pressures that kept others quiet. I’ve told the story of the article I wrote starting at the end of 2000 here. It was put on the arXiv in early 2001 and ultimately published in American Scientist. Looking at it again after all these years, I think the argument made there stands up extremely well. While there was no direct reference to the Greene and Kaku books, there was:

String theorists often attempt to make an aesthetic argument, a claim that the theory is strikingly “elegant” or “beautiful”. Since there is no well-defined theory, it’s hard to know what to make of these claims, and one is reminded of another quote from Pauli. Annoyed by Heisenberg’s claims that modulo some details he had a wonderful unified theory (he didn’t), Pauli sent his friends a postcard containing a blank rectangle and the text “This is to show the world I can paint like Titian. Only technical details are missing.” Since no one knows what “M-theory” is, its beauty is that of Pauli’s painting. Even if a consistent M-theory can be found, it may very well be a theory of great complexity and ugliness.

The subject of string theory and the state of fundamental physics was complicated and interesting enough that I thought it deserved a book length treatment, which I started writing in 2002 (the story of that is here). The book I wrote was not a direct response to The Elegant Universe, but was an alternative take on the history and current state of the subject, trying to provide a different and more fact-based point of view.

During this time, Kaku came out with his own M-theory book, Parallel Worlds, published in 2004. Also in 2004, Greene published a follow-up to The Elegant Universe, entitled The Fabric of the Cosmos, which was the basis several years later of a four-hour Nova special.
Over the last twenty-years there’s been no let up, with Kaku’s latest The God Equation, yet another hype-filled rehash of the usual string theory material. Greene regularly uses his World Science Foundation to do more string theory promotion, most recently putting out “The State of String Theory”, where we learn the subject deserves an A+++.

In recent years I’ve often heard from string theorists who feel that their research is getting a bad name because of the nature of the Greene/Kaku material. They see this hype as something that happened long ago, back before they got into the subject, so ask why they should be held accountable for it. When asked why they won’t do anything about the ongoing hype problem, it becomes clear that string theory tribalism is still a potent force.

Turning to the new material in this new edition of the book, much of it is the usual over-the-top hype, although often in a rather defensive mode:

the past twenty-five years have been such an astonishingly productive period that exploring progress fully could easily fill an entire book on its own… The fact is, the past twenty-five years have been jam-packed with discoveries in which string theorists have scaled towering problems and dug deeply into long-standing mysteries… the decades of rich development in string theory carried out by some of the most creative, skeptical and discerning minds on the planet is the most readily apparent measure of the field’s vitality. Scientists vote with their most precious commodity — their time. By that measure, and correspondingly, the measure of vibrant new ideas that have opened stunning vistas of discovery, string theory continues to be a source of inspiration, insight, and rapid progress.

While some scientists have left the field

others, indeed so many others that string theory has been berated by for attracting too many of the highest-caliber scientists, have found that the pace of new theoretical discoveries and novel physical insights is so rapid and thrilling that they are propelled onward with vigor and excitement.

The epilogue mostly deals with three topics. The first is the failure to find SUSY at the LHC, which Greene explains is perfectly compatible with string theory, and that, even before the LHC turned on:

there were theorists at that time who emphasized that string theory seems to favor superheavy superpartners, far too massive for the Large Hadron Collider or even any remotely realistic next-generations colliders to produce.

He acknowledges that at the present time string theory predicts nothing at all about anything, that even if we had a Planck scale collider:

We would still need to understand the theory with greater depth to make detailed comparisons between calculations and data, but in that imagined setting experiment would guide theorizing much as it has across a significant stretch of the history of physics.

The second topic is the string theory landscape and the anthropic multiverse “prediction” of the CC, with about ten pages devoted to explaining that

the dark energy has its measured value because if its value had been significantly different, we would not be here to measure it.

The final topic, taking up twelve pages, is AdS/CFT. The conclusion is that:

We now have powerful evidence that — shockingly — string theory and quantum field theory are actually different languages for expressing one and the same physics. In consequence, the experimental luster of quantum field theory casts a newfound experimental glow on string theory.

No more “what is M-theory?”, instead we’re told that the question “What is the fundamental principle underlying string theory?” gets answered by:

the new lesson seems to be that quantum mechanics already has gravity imprinted into its deep structure. The power of string theory is that its vibrating filiaments allows us to more easily see this connection.

The last section is “A Final Assessment.” No A+++, but:

In the arena of unification, both in terms of showing that gravity and quantum mechanics can be united as well as demonstrating that such a union can embrace non-gravitational forces and matter particles too, I give string theory an A. String theory surmounts the difficult mathematical hurdles that afflicted earlier work on unification and so, at least on paper, establishes that we have a framework in which the dream of unification can be realized.
In the arena of experimental or observational confirmation, I give string theory an incomplete.

One thing I was looking for in the new material was Greene’s response to the detailed criticisms of string theory that have been made by me and others such as Lee Smolin and Sabine Hossenfelder over the last 25 years. It’s there, and here it is, in full:

There is a small but vocal group of string theory detractors who, with a straight face, say things like “A long time ago you string theorists promised to have the fundamental laws of quantum gravity all wrapped up, so why aren’t you done?” or “You string theorists are now going in directions you never expected,” to which I respond, in reverse order “Well, yes, the excitement of searching into the unknown is to discover new directions” and “You must be kidding.”

As one of the “small but vocal group” I’ll just point out that this is an absurd and highly offensive straw-man argument. The arguments in quotation marks are not ones being made by string theory detractors, and the fact that he makes up this nonsense and refuses to engage with the real arguments speaks volumes.

Note: after tomorrow I’ll be on a short vacation for a while in San Francisco and dealing with blog comments might take longer than usual.