Farewell to Reality (22 page)

^*
Although ‘grand' and ‘unified', GUTs do not seek to include the force of gravity. Theories that do so are often referred to as Theories of Everything, or TOEs.

^**
Liquid water can be supercooled to temperatures up to 40 degrees below freezing.

^*
It was originally planned to be launched in 1988 on a space shuttle mission, but the shuttles were grounded following the
Challenger
disaster on 28 January 1986.

^*
The discrepancy was reduced by subsequent analysis, but it remains significant.

^*
Of course, these acronyms are not coincidental. WIMP was coined first, apparently inspiring the subsequent development of MACHO.

^*
Actually, the densities of dark matter and of baryonic matter are
derived
from the model parameters.

6

What's Wrong with this Picture?

Why the Authorized Version of Reality Can't be Right

The
truth
of a theory can never be proven, for one never knows if future experience will contradict its conclusions.

Albert Einstein
¹

The last four chapters have provided something of a whirlwind tour of our current understanding of light, matter and force, space, time and the universe. Inevitably, I've had to be a bit selective. It's not been possible to explore all the subtleties of contemporary physics, and the version of its historical development that I've provided here has been necessarily ‘potted'.

I would hope that as you read through the last four chapters, you remembered to refer back to the six principles that I outlined in Chapter 1. I'd like to think that the developments in physical theory in the last century amply demonstrate the essential correctness of these principles, if not in word then at least in spirit.

Quantum theory really brings home the importance of the Reality Principle. The experimental tests of Bell's and Leggett's inequalities tell us fairly unequivocally that we can discover nothing about a reality consisting of things-in-themselves. We have to settle instead for an empirical reality of things-as-they-are-measured. This is no longer a matter for philosophical nit-picking. These experimental tests of quantum theory are respectfully suggesting that we learn to be more careful about how we think about physical reality.

I haven't been able to provide you with all the observational and experimental evidence that supports quantum theory, the standard model of particle physics, the special and general theories of relativity
and the ΛCDM model of big bang cosmology. But there should be enough in here to verify the Fact Principle. It is simply not possible to make observations or perform experiments without reference to a supporting theory of some kind. Think of the search for the Higgs boson at CERN, the bending of starlight by large gravitating objects, or the analysis of the subtle temperature variations in the CMB radiation.

We have also seen enough examples of theory development to conclude that the Theory Principle is essentially correct. Abstracting from facts to theories is highly complex, intuitive and not subject to simple, universal rules. In some cases, theories have been developed in response to glaring inconsistencies between observation, experiment and the prevailing methods of explanation. Such developments have been ‘idea-led', with observation or experiment causing widespread bafflement before a theoretical resolution could be found.

Sometimes the theoretical resolution has been more baffling than the data, as Heisenberg himself could attest, wandering late at night in a nearby park after another long, arduous debate with Bohr in 1927. Could nature possibly be as absurd as it seemed?

In other cases, theories have been sprung almost entirely from intuition: they have been ‘idea-led'. Such intuition has often been applied where a problem has been barely recognized, born from a stubborn refusal to accept inadequate explanations. Recall Einstein's light-quantum hypothesis. Remember Einstein sitting in his chair at the Patent Office, struck by the thought that if a man falls freely he will not feel his own weight.

Ideas and theories that follow from intuition can clearly precede observation and experiment. The notion that there should exist a meson formed from a charm and anti—charm quark preceded the discovery of the J/Ψ in the November revolution of 1974. The Higgs mechanism of electro-weak symmetry-breaking preceded the discovery of weak neutral currents, the W and Z particles and (as seems likely) the Higgs boson.

I've tried to ensure that my descriptions of the theoretical structures that make up the authorized version of reality have been liberally sprinkled with references to the observations and experiments that have provided critically important tests. Although there are inevitable grey areas, in general the theories that constitute the authorized version
are regarded as testable, and have been rigorously tested to a large degree. Perhaps you are therefore ready to accept the Testability Principle.

Then we come to the Veracity Principle. It might come as a bit of a shock to discover that scientific truth is transient. What is accepted as true today might not be true tomorrow. But look back at how the ‘truth' of our universe has changed from Newton's time, or even over the last thirty years. Or even within the short period in which the Higgs boson took a big step towards becoming a ‘real' entity.

Finally, there is the Copernican Principle. Nowhere in the authorized version will you find any reference to ‘us' as special or privileged observers of the universe. As we currently understand it, the physics of this version of reality operates without intention and without passion. We are just passively carried along for the ride.

Now, you might have got the impression from the last four chapters that the authorized version of reality is a triumph of the human intellect and, as such, pretty rock—solid, possibly destined to last for all time. The four theoretical structures that make up the authorized version undoubtedly represent the pinnacle of scientific achievement. We should be — and are — immensely proud of them.

But these theories are riddled with problems, paradoxes, conundrums, contradictions and incompatibilities. In one sense, they don't make sense at all.

They are not the end. The purpose of this chapter is to explain why, despite appearances, the authorized version of reality can't possibly be right.

Some of these problems were hinted at in previous chapters, but here we will explore them in detail. It is important to understand where they come from and what they imply. The attempt to solve them without guidance from observation or experiment is what has led to the creation of fairy-tale physics.

The paradox of Schrödinger's cat

Actually, the problem of quantum measurement is a perfect problem for these economically depressed times. This is because it is, in fact,
three
problems for the price of one: the problem of quantum probability,
the collapse of the wavefunction and the ‘spooky' action-at-a-distance that this implies. Bargain!

Our discomfort begins with the interpretation of quantum probability. Quantum particles possess the property of phase which in our empirical world of experience scales up to give us wave-like behaviour. We identify the amplitude of the quantum wavefunction (or, more correctly, the modulus-square of the amplitude) as a measure of probability, and this allows us to make the connection with particles.
²
Thus, an electron orbiting a proton in a hydrogen atom might have a spherically symmetric wavefunction, and the modulus square of the amplitude at any point within the orbit relates the probability that the electron will be ‘found' there.

The trouble is that phases (waves) can be added or subtracted in ways that self-contained particles cannot. We can create superpositions of waves. Waves can interfere. Waves are extended, with amplitudes in many different places. The probabilities that connect us with particles are therefore subject to ‘spooky' wave effects. We conclude that one particle can have probabilities for being in many different places (although thankfully it can't have a unit or 100 per cent probability for being in more than one place at a time).

Consider a quantum system on which we perform a measurement with two possible outcomes, say ‘up' or ‘down' for simplicity. The accepted approach is to form a wavefunction which is a superposition of both possible outcomes, including any interference terms. This represents the state of the system prior to measurement. The measurement then collapses the wavefunction and we get a result — ‘up' or ‘down' with a probability related to the modulus-squares of the amplitudes of the components in the superposition.

Just
how
is this meant to work?

The collapse of the wavefunction is essential to our understanding of the relationship between the quantum world and our classical world of experience, yet it must be added to the theory as an ad hoc assumption. It also leaves us pondering. Precisely
where
in the causally connected chain of events from quantum system to human perception is the collapse supposed to occur?

Inspired by some lively correspondence with Einstein through the summer of 1935, Austrian physicist Erwin Schrödinger was led to formulate one of the most famous paradoxes of quantum theory,
designed to highlight the simple fact that the theory contains no prescription for precisely how the collapse of the wavefunction is meant to be applied or where it is meant to occur. This is, of course, the famous paradox of Schrödinger's cat.

He described the paradox in a letter to Einstein as follows:

Contained in a steel chamber is a Geiger counter prepared with a tiny amount of uranium, so small that in the next hour it is just as probable to expect one atomic decay as none. An amplified relay provides that the first atomic decay shatters a small bottle of prussic acid. This and — cruelly — a cat is also trapped in the steel chamber. According to the [wave] function for the total system, after an hour,
sit venia verbo,
the living and dead cat are smeared out in equal measure.
³

Prior to actually measuring the disintegration in the Geiger counter, the wavefunction of the uranium atom is expressed as a superposition of the possible measurement outcomes, in this case a superposition of the wavefunctions of the intact atom and of the disintegrated atom. Our instinct might be to conclude that the wavefunction collapses when the Geiger counter triggers. But why? After all, there is nothing in the structure of quantum theory itself to indicate this.

Why not simply assume that the wavefunction evolves into that of a superposition of the wavefunctions of the triggered and untriggered Geiger counter? And why not further assume that this evolves too, eventually to form a superposition of the wavefunctions of the live and dead cat? This is what Schrödinger meant when he wrote about the living and dead cat being ‘smeared out' in equal measure.

We appear to be trapped in an infinite regress. We can perform a measurement on the cat by lifting the lid of the steel chamber and ascertaining its physical state. Do we suppose that, at that point, the wavefunction collapses and we record the observation that the cat is alive or dead as appropriate?

On the surface, it really seems as though we ought to be able to resolve this paradox with ease. But we can't. There is obviously no evidence for peculiar superposition states of live-and-dead things or of
‘classical' macroscopic objects of any description.
^*
We can avoid the infinite regress if we treat the measuring instrument (in this case, the Geiger counter) as a classical object and argue that classical objects cannot form superpositions in the way that quantum objects can.

But the questions remain: why should this be and how does it work? Perhaps more worryingly, if some kind of external ‘classical' macroscopic measuring device is required, then precisely what was it that, in the early moments of the big bang when the universe was the size of a quantum object, collapsed the wavefunction of the universe? Is it necessary for us to invoke an ultimate ‘measurer-of-all-things'?

Irish theorist John Bell called this seemingly arbitrary split between measured quantum object and classical perceiving subject ‘shifty':

What exactly qualifies some physical systems to play the role of ‘measurer'? Was the wavefunction of the world waiting to jump for thousands of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system … with a PhD?
⁴

When the wavefunction collapses, it does so
instantaneously.
That doesn't seem like much of a problem if you say it quickly and move on to something else. But, of course, this is a
big
problem. In our universe nothing, but nothing, happens instantaneously across large distances. If I happen to make a measurement on one of a pair of entangled photons that has travelled halfway across the universe before reaching my detector, how does the photon on the other side of the universe discover what result I got? Surely this is completely at odds with Einstein's special theory of relativity, which assumes that the speed of light cannot be exceeded?

This isn't a hypothetical scenario. Experiments have been performed on entangled photons which have allowed a lower limit to be placed on the speed with which the wavefunction had to collapse to give the
results observed. This speed was estimated to be at least twenty thousand times faster than the speed of light.

Many physicists have reconciled themselves to this kind of result by noting that, despite the apparent speed of the collapse process (if it really happens at all), it cannot be used to communicate information. No matter how hard we try, we cannot take advantage of this seeming example of an instantaneous physical effect to send messages of any kind. And this, they claim, allows quantum measurement peacefully (if rather uneasily) to co-exist with special relativity.