Farewell to Reality (33 page)

So, how do superstring theory and M-theory fare?

Let's set aside for the moment the fact that all the small print in the contract for supersymmetry must be carried over to the contract for superstring theory. This means 100-plus undetermined parameters, muons transforming into electrons and other problems. If superstrings are supersymmetric, then the supersymmetry must be broken. There are plenty of ideas, but no real consensus about how this is supposed to happen.

One key characteristic of superstring theories is that they require hidden dimensions. The fact that the extra dimensions are hidden or cannot be experienced directly doesn't necessarily mean that they exert no influence in our more familiar three-dimensional world. It is believed that telltale signals of extra dimensions might be observable in the form of so-called Kaluza—Klein (KK) particles. These particles are the mass projections into four dimensions of momenta that are carried by particles moving in the hidden dimensions.
^*

KK particles are a bit like the sparticles of supersymmetry. For every standard model particle able to travel in the hidden dimensions (i.e. provided they are not confined to a D-brane), there should exist KK particles with the same properties of spin and charge but with different masses. Large hidden dimensions imply light KK particles. In fact, there is a lightest Kaluza—Klein particle (LKP), equivalent to the LSP, which has also been considered as a possible dark matter candidate.

It will probably come as no surprise to learn that there are no hard and fast predictions for the masses of these particles, as indeed there are few, if any, predictions for anything else. Instead the theorists throw their general ideas — sparticles, KK particles — over the fence and hope that the experimentalists at CERN's LHC will take them seriously and/or get lucky. So far there is no evidence from the LHC for
anything more than what looks very much like the standard model Higgs boson.

The theorists have embraced superstring theory, the dualities of M-theory, branes and braneworlds like kids in a toyshop. They have been busy trying to come to terms with all the subtleties and interrelationships established within the mathematical frameworks of the theories. In other words, they have been trying to figure out how to play with the toys. It seems that they have found it easier to build braneworlds than to attempt to make predictions that can be properly tested.

As Gordon Kane admits:

To be sure, the majority of research into string theory is not focused on how the theory connects to the real world; rather, most physicists are exploring questions at a more theoretical level. Such formal work is necessary, because … we need a deeper understanding to fully formulate the theory. Even the many theorists who are interested in how string theory connects to the real world don't typically think much about what it means to test the theory.
¹⁴

Despite the beauty and tightness of the structure, the theorists still haven't learned enough about it to enable them to predict the properties of even a single standard model particle. Yau again:

After some decades of exploring the Land of Calabi—Yau, string theorists and their math colleagues (even those equipped with the penetrating powers of geometric analysis) are finding it hard to get back home — to the realm of everyday physics (aka the standard model) — and, from there, to the physics that we know must lie beyond. If only it were as easy as closing our eyes, tapping our heels together and saying ‘There's no place like home.' But then we'd miss out on all the fun.
¹⁵

To date, thousands of papers and quite a few books have been published which explore the bizarre world of superstrings and M-theory. Most of these are concerned with the various esoterica of the theory and represent attempts to come to terms with its complex structure.

Nobody has yet found Dorothy's ruby slippers.

Richard Feynman was complaining about this situation as early as the late 1980s:

I don't like that they're not calculating anything. I don't like that they don't check their ideas. I don't like that for anything that disagrees with an experiment, they cook up an explanation — a fix up to say ‘Well, it still might be true.'
¹⁶

The mis-selling
^*
of the superstring programme

I don't actually mind that superstring and M-theory are more metaphysics than physics. More a modern fairy tale than a story of the real world. I don't mind that as many as 1,500 scientists have chosen to build careers in theoretical physics by chasing fantasies constructed on an arguably untenable structure of interconnected assumptions that now seem to have an ever-decreasing possibility of producing anything credible.
^**
It is perhaps tragic that in pursuing the theory, the search for scientific truth has been abandoned, if not betrayed. But it's a free world and I could argue that within the physics community no real harm is done.

My problem is that this is
not
how the theory is presented to the wider public.

Thus, the jacket blurb for Lisa Randall's
Warped Passages
reads:

Here she uses her experience at the cutting edge to reveal how the world is full of hidden, extra dimensions, far beyond our imaginations. She shows us how, in just a few years, we will be able to see them for the very first time — offering us a gateway into a whole new reality.
¹⁷

The jacket of Brian Greene's
The Fabric of the Cosmos
declares:

Here [Greene] reveals a universe that is at once more surprising, exciting and stranger than any of us could have imagined … It is a universe that exists in eleven dimensions, in which every single entity is composed of nothing more than tiny, vibrating pieces of string.
¹⁸

Okay, an author has a lot less control than you might imagine over things like book title, cover design and jacket copy, and publishers understand that caveats, maybes, could-be's and other qualifications can put off readers and get in the way of selling books. Both Randall and Greene are somewhat more circumspect in the main text of their books.

But here's no less an authority than Stephen Hawking, who, with Leonard Mlodinow, writes in
The Grand Design
:

M-theory is the unified theory Einstein was hoping to find. The fact that we human beings — who are ourselves mere collections of fundamental particles of nature — have been able to come this close to an understanding of the laws governing us and our universe is a great triumph. But perhaps the true miracle is that abstract considerations of logic lead to a unique theory that predicts and describes a vast universe full of the amazing variety that we see. If the theory is confirmed by observation, it will be the successful conclusion of a search going back more than 3,000 years. We will have found the grand design.
¹⁹

Hawking has something of a reputation for this kind of thing. When he was appointed Lucasian Professor of Mathematics at Cambridge University (the chair once held by Newton and Dirac), he used his inaugural lecture to declare that the unified theory — presumably the one Einstein was hoping to find — was close at hand in the form of supergravity based on eight supersymmetries. That was over thirty years ago.

Do the authors of best-selling books about superstring theory actually believe in it? When asked directly at the Isaac Asimov Memorial Debate at the American Museum of Natural History in New York
City, which took place on 7 March 2011, Greene replied: ‘If you asked me, “Do I believe in string theory?”, my answer today would be the same as it was ten years ago: No.'
²⁰

He went on to explain that he only
believes
ideas that make testable predictions. But he insists that, despite the conspicuous absence of testable predictions from superstring theory, it remains one of the best bets for providing a unified theory.
^*

Greene's honesty is commendable. However, we might conclude that the continued publication of popular science books and the production of television documentaries that are perceived to portray superstring theory or M-theory as ‘accepted' explanations of empirical reality (legitimate parts of the authorized version of reality) is misleading at best and at worst ethically questionable.

^*
If we recall that QED, the quantum field theory of electromagnetism, is based on the circular U(1) symmetry group, then we might get some sense of the strong connection between ‘circularity' and electromagnetism.

^*
Remember that mesons are formed from quark—anti-quark pairs.

^*
Not to be confused with the 10 space-time dimensions of the theory.

^*
Heterotic superstring theories are hybrids of Type I and bosonic superstring theories.

^*
Apparently this was the only time that all three were available.

^*
Perhaps it is more correct to say that the theorists would prefer a universe like this because it is one that they can develop a theory to describe.

^*
The ‘D' derives from Peter Dirichlet, a nineteenth-century German mathematician.

^*
I'm reminded of the mice in Douglas Adanis'
Hitchhiker's Guide to the Galaxy
. They are not mice, in fact. They are projections into our dimensions of super-intelligent. pan-dimensional beings.

^*
Mis-selling happens when a salesperson misrepresents or misleads an investor about the characteristics of a product or service (or theory), leaving out certain information or distorting the description to imply a need that doesn't exist.

^**
A recent estimate by Russian-born theorist Mikhail Shifman, an early proponent of SUSY, puts the number of high-energy physics theorists at somewhere between 2,500 and 3,000. He thinks of them as a ‘lost generation', writing: ‘During their careers many of them never worked on any issues beyond supersymmetry-based phenomenology or string theory. Given the crises (or, at least, huge question marks) we currently face in these two areas, there seems to be a serious problem in the community.' See M. Shifman, arXiv, pop-ph/1211.0004v3, 22 November 2012.

^*
Of course, this is a matter of opinion. Unfortunately I haven't been able in this book to tell you about alternative approaches to unifying general relativity and quantum theory. Unlike superstring theory, loop quantum gravity assumes no ‘background' spacetime but rather generates the geometric framework of spacetime from within the theory, as does general relativity. The theory has made no immediately testable predictions, but clearly illustrates that the superstring programme is not the only game in town. Loop quantum gravity is the preserve of relativists, however, not particle theorists, and for this reason is less fashionable. I recommend Lee Smolin's popular books
Three Roads to Quantum Gravity and The Trouble with Physics
, and Carlo Rovelli's more specialist book
Quantum Gravity
(see the bibliography).

9

Gardeners of the Cosmic Landscape

Many Worlds and the Multiverse

Time and again the passion for understanding has led to the illusion that man is able to comprehend the objective world rationally by pure thought without any empirical foundations — in short, by metaphysics.

Albert Einstein
¹

SUSY, superstring theories and M-theory are relatively well-developed ingredients or candidates for a grand unified theory or a theory of everything. They seek to provide solutions for a number of the problems in the authorized version of reality: to offer a rationale for the masses of the three generations of elementary particles (in terms of string vibrations); to resolve the hierarchy problem; to provide dark matter candidates and finally to reconcile quantum theory with general relativity.

We can judge for ourselves how successful we think they have been at addressing these problems. They certainly cannot be considered as accepted components of the authorized version of reality. And there is a sense that, as more proton—proton collision data are collected at the LHC, at least some of the chickens may be about to come home to roost.

Of course this is disappointing. It would have been marvellous if the LHC had turned up signals that could have been interpreted as sparticles or mysterious Kaluza—Klein particles, shadowy projections of particles lurking in hidden dimensions. But although it is still relatively early days, the data appear to be telling us that this is probably not how nature works.

However, the fairy tales seem set to continue, and probably for some time to come. There appears to be just too much at stake. Too
much effort has been expended for SUSY, superstring theories and M-theory to be given up lightly. And although the mathematical structures themselves might be tight, the network of largely unfounded assumptions on which the structures are based offer just too much freedom and flexibility. It seems that no amount of experimental data will be sufficient to close off all the ‘work-arounds', the patches that allow the theorists to declare that, well, it might still be true.

But if we think superstring theorists have lost contact with reality and are indulging in the kind of metaphysics that Einstein warned us about in the quotation above, then we might need to prepare ourselves for a bit of a shock. The problems that SUSY, superstring theories and M-theory seek to address pale almost into insignificance compared with one of the most fundamental problems inherent in contemporary physical theory — the quantum measurement problem.

Seeking to resolve this problem has produced metaphysics on the very grandest of scales.

Von Neumann's ‘projection postulate'

The first theorist carefully to articulate the mechanism (and hence the problem) of quantum measurement was the Hungarian mathematician John von Neumann. In his book
Mathematical Foundations of Quantum Mechanics,
first published in Berlin in 1932, he noted that the equations of quantum theory offer a perfectly respectable description of the time evolution of a quantum wavefunction which conforms entirely to our classical expectations. The wavefunction develops ‘linearly', its properties and behaviour at each moment closely, smoothly and continuously connected with its properties and behaviour just a moment before. The time evolution is completely
deterministic.