Farewell to Reality (37 page)

Into this vacuum a number of new theoretical structures have been introduced. They offer potential solutions for some of the problems but they are inevitably motivated by the theorists' instincts and their mathematical and personal preferences. The theories are constructed on a network of assumptions that we are obliged to accept at face value.

So, superstring theory is founded on the assumption that elementary particles can be represented by vibrations in one-dimensional filaments of energy. To this we add the assumption that there exists a fundamental spacetime symmetry between fermions and bosons. As the theory then demands a total of nine spatial dimensions, we assume that six dimensions are compactified into a Calabi—Yau space. There is no experimental or observational evidence for any of these assumptions.

In a separate series of developments, the quantum measurement problem is resolved by assuming that all the different possible outcomes of a measurement are realized in different equally real worlds which either split from one another or exist in parallel. Eternal inflation is a characteristic of certain cosmological models. These models describe a multiverse consisting of bubbles of inflating spacetime triggered by quantum fluctuations in a vast inflaton field. We assume our universe
is a relatively unexceptional bubble in this multiverse. We further assume that each of these universes can be characterized by one of the 10
⁵⁰⁰
different possible ways of compactifying the six extra spatial dimensions demanded by superstring theory. In an alternative scenario, the hot big bang origin of our own universe could be the result of a collision between two braneworlds. There is no experimental or observational evidence for any of these assumptions.

Let's just check to see if we've understood this correctly. We live in a multiverse, ‘surrounded' by parallel universes that by definition we cannot experience directly. We can never verify the existence of these universes, and must look instead for evidence that betrays their existence indirectly in the physics of our own universe.

Of course, there is no evidence in the physics of the authorized version of reality, so we must look to the physics of superstrings or M-theory. And look! The fact that there is no preferred choice of Calabi—Yau shape from the 10
⁵⁰⁰
different possibilities is taken to imply that our universe is far from unique. There must be many, many other kinds of universe. Quod erat demonstrandum.

Justifying a multiverse theory because it is implied by superstring theory might just be acceptable if superstring theory was an already accepted description of the universe we experience. But it's not. In fact, one of the things standing in the way of superstring theory's acceptance is its inability to predict anything about our own universe. And this is partly because, with 10
⁵⁰⁰
different Calabi—Yau spaces to choose from, virtually anything and everything is possible. There's nothing in the theory that allows us to pick out the space that describes our universe uniquely.

The multiverse theory is justified by superstring theory but superstring theory cannot be proved because we live in a multiverse.

We've not just crossed a line here. We're so far over it that, to quote Matt LeBlanc as Joey in an episode
of Friends,
the line is a dot to us. To be fair, some of the most recent popular presentations of multiverse theories have included sections titled ‘Is this science?' or something similar. Some authors argue that the multiverse theory might be testable through the observation of legacy effects in the CMB from a big bang triggered by colliding branes. Others argue that the multiverse must be science because the cosmic landscape is derived from superstring theory
and superstring theory is science. Frankly, these look very much like attempts to clutch at straws, and none are convincing.

Reference to the six Principles described in Chapter 1 would lead us to conclude that theories constructed on many worlds and the multiverse are not testable
in principle.
To those who would argue that there are genuine instances in which parallel universes could impress themselves on the physics we observe in our universe, I would respectfully suggest that physicists will struggle to demonstrate that any such evidence is free from ambiguity. I honestly can't believe that it will be beyond the wit of theorists to find alternative physical explanations for such instances based on theories requiring one — and only one — universe.

Of course, this is just an opinion.

Dealing with the fallout

As you may have gathered by now, I'm rather exasperated by the relentless pursuit of SUSY, superstring theory and M-theory, and the widening gap between increasingly implausible theoretical speculations and the practicalities of experiment and observation. But I also believe that the willingness to embrace multiverse theories — what Peter Woit refers to as ‘multiverse mania' — is doing serious damage to the cause of science itself.
*

Firstly, there is mis-selling of the kind I highlighted for the superstring programme. Multiverse theories have divided the physics community and the debate is growing in vocal intensity. Although there are many notable advocates, such as Susskind, Tegmark, Greene (a relatively recent convert) and Martin Rees (Britain's Astronomer Royal), there are also notable dissidents. These include David Gross, Steinhardt and Lee Smolin. Despite this disagreement, the multiverse is still paraded in the popular science media as an accepted body of scientific theory.

Thus, in an ‘ultimate guide' to the multiverse published in the respected UK popular science weekly
New Scientist
in November 2011, science writer Robert Adler opens with:

Whether we are searching the cosmos or probing the subatomic realm, our most successful theories lead to the inescapable conclusion that our universe is just a speck in a vast ocean of universes.

He does not explain how ‘success' is defined. Nowhere in this article can I find any reference to the fact that this is not a universally accepted theory, or that multiverse theories are not actually ‘inescapable'. Or that a debate is raging about whether this is even science. On the contrary, he continues:

Three decades after the concept was born, many researchers now agree that at least some kinds of multiverse stand on firm theoretical foundations, yield predictions that astronomers and particle physicists can test, and help explain why our universe is the way it is.
²⁰

But how many is ‘many'? And, should you be in any doubt, please be reassured that
no
multiverse theory of any kind can explain why our universe is the way it is.

The second area of concern relates to the really rather obvious fact that multiverse theories represent an enormous cop-out. By arguing that all the different measurement outcomes and all the different possible universes are realized in the multiverse, theorists duck the challenge to understand why we experience these outcomes in our universe and why our universe has the physical constants, laws and spectrum of particles that it has. Greene himself acknowledges this problem in
The Hidden Reality:

By invoking a multiverse, science could weaken the impetus to clarify particular mysteries, even though some of those mysteries might be ripe for standard, nonmultiverse explanations. When all that was really called for was harder work and deeper thinking, we might instead fail to resist the lure of multiverse temptation and prematurely abandon conventional approaches.
²¹

The multiverse answer is that all possible universes exist in parallel and we just happen to find ourselves in one that supports our form of life.
*
Of course, this is no answer at all. Greene goes on to defend the multiverse approach, arguing that to abandon it because it could be a blind alley is equally dangerous.

Finally, and most importantly, we must be concerned about the implications of multiverse theories for the future development of science itself. The multiverse theorists know that they are on weak ground regarding the Testability Principle, and rather than admit that their theories are not science, they argue instead that the rules of science must be adapted to accommodate this kind of metaphysical speculation.

They want to change the very
definition
of science. This is a very slippery slope.

*
This does not necessarily contradict the observation of the kinds of macroscopic superpositions described in Chapter 3, in which a wavefunction is formed in which billions of electrons flow in opposite directions around a superconducting ring. It just means that we have to work very hard to stop it from decohering.

*
Strictly speaking, the term ‘universe' means ‘everything there is', but it quickly gets confusing if we refer to lots of parallel universes as ‘the universe'. The logic that prevails here is that we consider our known universe of visible stars, galaxies, dark matter and dark energy as merely one among many such universes that exist alongside ours in parallel. We call this collection of different parallel universes the ‘multiverse'.

*
Strictly speaking, the probabilities are given by |0.866|
²
and |0.500|
²
. We use the modulus-squares because the coefficients could be complex (they could include
i,
the square root of-1).

*
See
www.math.Columbia.edu/~woit/wordpress/?cat=10.

*
We will further explore this kind of reasoning in Chapter 11.

10

Source Code of the Cosmos

Quantum Information, Black Holes and the Holographic Principle

The physicist has to limit himself very severely: he must content himself with describing the most simple events that can be brought within the domain of our experience; all events of a more complex order are beyond the power of the human intellect to reconstruct with the subtle accuracy and logical perfection the theoretical physicist demands.

Albert Einstein
¹

The Reality Principle introduced in Chapter 1 argues that reality consists of things-in-themselves which are, by definition, inaccessible to us and of which we can never hope to gain knowledge. Science is the process by which we continue to refine our knowledge of the things-as-they-appear or the things-as-they-are-measured, from which we can
infer
what reality is ‘really' like if we first assume that reality has objective, independent existence.

As we have no way of knowing what such an independent reality is actually like, this leaves us with some considerable freedom to speculate.

The reductionists among us might be tempted simply to conclude that reality must be ultimately composed of irreducible bits or fields of ‘stuff', however we choose to define these. These bits or fields impress themselves on our empirical reality of observation and measurement in ways that are hopefully logical and accessible to human reason. Whatever reality is, this stuff manifests or projects itself to produce effects which we interpret as quarks and leptons and force particles, and so on.

But what if, instead, there is no ‘stuff'?
*
After all, Einstein set some remarkable precedents in the early twentieth century. In the special and general theories of relativity he showed that space and time are not absolute, they are relative. They depend on the things that exist within them and, it can be argued, they have no existence independently of these things.

The Higgs mechanism turns mass into a secondary quality, like colour. We begin to get the sense that, though tangible, mass is an effect — it is the result of things interacting with the Higgs field — rather than something primary, something that exists independently of such interactions.

And then the experimental violation of Leggett's inequality tells us that what we call ‘properties' — for example, the spin orientations of quarks and leptons — cannot be considered to be inherently pre-existing attributes of these things. They are instead products of the process of measurement — they are the ‘projections' (if that's the right word) of the things-in-themselves into our empirical reality of measurement.

The story of modern physics is really the story of the not-so-gradual undermining of our naïve ideas about reality. It tells of the erosion of our broadly common-sense, taken-for-granted notions and their replacement by uncertainty and doubt. Can we expect this erosion of confidence to continue indefinitely?

What if we stripped away all the things we call ‘properties', the things that define what it means for a quantum particle to be present in a specific quantum state, the things that determine how the particle is going to behave. What would be left?

There are at least two possible answers to this question. The first is that by stripping away all the empirical dressing — energy, mass, spin, space, time, etc. — what we are left with is abstract
mathematics
. A second answer is that we could consider the irreducible ‘stuff' of the universe (or multiverse) to be
information.

The Mathematical Universe Hypothesis

The principal exponent of the notion that the core description of everything in the universe might be essentially mathematical is MIT theorist Max Tegmark. Now, theorists have always tended to wax rather lyrical about what Eugene Wigner called the ‘unreasonable effectiveness of mathematics in the natural sciences'.
²
The creative processes involved in fashioning theories out of the often arcane and esoteric concepts, rules and language of mathematics are arguably equivalent in many ways to art. And just as great art seems to tell us vivid truths about human existence, so perhaps great maths relates deep truths of physical existence.

In this hypothesis, however, Tegmark argues that the effectiveness of mathematics is not at all unreasonable, or even surprising.

First, some groundwork. The hypothesis is premised on what Tegmark calls the External Reality Hypothesis (ERH). There exists an external physical reality that is completely independent of human beings.