Quantum Reality

by Jim Baggott

  What is the justification for these assumptions? At great risk of repetition, here’s that Einstein quote once again: ‘I have no better expression than the term “religious” for this trust in the rational character of reality and in its being accessible, to some extent, to human reason.’12

  Scientists generally don’t think too long and hard or look too closely at these assumptions. Many regard them as intuitively obvious. But accepting these assumptions means buying into a specific philosophical position. This has a name—it’s called ‘scientific realism’. Curiously, those who don’t think about it at all can’t avoid making the same kind of commitment, knowingly or not, typically to an alternative but related position called ‘naïve realism’, a term which I’ve always thought to be rather pejorative. Like Monsieur Jordain in Molière’s The Bourgeois Gentleman, who discovers that he has actually been speaking prose all his life, so might some scientists discover that, at least in part, throughout their career in science they’ve also adopted a specific philosophical position, and so they’ve been doing philosophy.

  Knowingly or not, most scientists are realists, although many don’t trouble themselves with grand questions about the nature of reality, which they’ll happily leave to philosophers. Although Einstein’s philosophy evolved through his early life, as far as quantum mechanics is concerned he was a realist,* as was Schrödinger (and Popper). Many years ago I trained as an experimental scientist and I can tell you it’s really difficult to work in a laboratory and maintain your sanity without some belief in the reality of the things you’re experimenting with.

  So, let’s put our realist stake in the ground with a proposition (philosophers like propositions):†

  Realist Proposition #1: The Moon is still there when nobody looks at it (or thinks about it).

  This will actually save us quite a lot of time. In essence, it says that reality (whatever this might be) really does exist and, what’s more, it exists independently of our ability to make empirical observations and measurements on it. It continues to exist whether or not anybody is thinking about it. It is objective, not subjective. It doesn’t depend on me (or you) for its existence.

  It’s important to acknowledge that, no matter how reasonable Proposition #1 might seem to you, it is nevertheless an assumption. What’s more, it’s an assumption that you will never be able to prove. Accepting this means admitting metaphysics into the very foundations of science.

  Now we have to do something about the fact that quite a lot of science (and pretty much all of quantum mechanics) deals with things we can’t observe directly, but for which we gain empirical evidence that is indirect. These are things like photons, electrons, and quarks. These produce effects in our empirical reality of experience—such as interference patterns, lines in a cloud chamber, and ‘jets’ of hadrons observed at the Large Hadron Collider at CERN, which can be traced back to the behaviour of quarks and gluons, the force particles that hold quarks together inside protons and neutrons. We choose to interpret these effects in terms of ‘invisible’ quantum entities, and we ascribe to them physical properties such as mass, electrical charge, spin, flavour, and colour. We then explain the observable, empirical behaviour in terms of the properties we have ascribed to these invisible entities.

  Let’s agree that, based on the above discussion, these properties tell us only about the things-as-they-appear or the things-as-they-are-measured, and we have no way of acquiring knowledge of photons-in-themselves or electrons-in-themselves, and so on. But this doesn’t prevent us from assuming that the things-in-themselves really do exist, independently of any instrument required to make measurements on them. For example, we see patterns of behaviour that we explain in terms of electrical charge. But electrical charge is merely the empirical manifestation of whatever property ‘in reality’ gives rise to such effects. This could very well be electrical charge as we understand it, but the truth is we have no way of knowing.

  I propose to focus here on the reality or otherwise of the entities themselves, and set aside consideration of their properties for the next chapter. One of my favourite arguments for ‘entity realism’ comes from the philosopher Ian Hacking. In an early passage of his 1983 book Representing and Intervening, Hacking describes the details of a series of experiments designed to discover if it is technically possible to reveal the fractional electric charges characteristic of ‘free’ quarks (the answer, alas, is no). The experiments involved studying the flow of electric charge across the surfaces of balls of superconducting niobium:13

  Now how does one alter the charge on the niobium ball? ‘Well, at that stage,’ said my friend, ‘we spray it with positrons to increase the charge or with electrons to decrease the charge.’ From that day forth I’ve been a scientific realist. So far as I’m concerned, if you can spray them then they are real.

  Whilst Hacking is a realist about invisible entities, this doesn’t mean that he accepts that scientific theories about such entities are necessarily ‘true’. We’ll go on to consider the scientific representation of properties and behaviours in the next chapter, but as far as entity realism is concerned I discover that I can find no better words:

  Realist Proposition #2: If you can spray them then they are real.

  This should save us quite a bit of time, too.

  You might be tempted to think that we’re now faced with a simple choice between the metaphysical reality of the philosopher and the empirical reality of the scientist. Some scientists and philosophers have indeed argued that this is a straightforward, black-and-white choice between metaphysics and empiricism. An outright rejection of metaphysics led arch-empiricist Ernst Mach to conclude that there could be no such things as atoms. In the 1920s and 1930s, a group called the Vienna Circle, led by philosophers Moritz Schlick, Rudolph Carnap, and Otto Neurath (and others), concluded that all metaphysics should be rejected as meaningless. They attempted to establish a scientifically based philosophy in which experience is the only valid source of knowledge. This is logical positivism, a kind of ‘seeing-is-believing’ brand of philosophy, which was directly influenced by Mach.14

  But the fact is that Mach got atoms hopelessly wrong and the logical positivist programme failed.15 It is actually impossible to eliminate all metaphysics from science and, incidentally, this kind of realization is one way in which it is possible to see progress in philosophy. This is another reason why scientists inadvertently end up doing at least some philosophy, whether they are aware of it or not.

  The problems arise just as soon as we try to go beyond the empirical evidence—the numbers, the effects, the doing this and getting that. Going beyond the evidence means opening the door to metaphysics. For the simple reason that it is impossible to engage in any meaningful dialogue about ‘why?’ and ‘how?’ without first developing some notions about the reality that we assume to lie beneath the empirical data. Scientists choosing this path have no choice but to indulge their inner metaphysicians.

  This brings me rather neatly to the analogy I mentioned in the Preamble. To understand how science is done we need to recognize and respect the very distinct ways of thinking about reality adopted by scientists and philosophers, and the fundamentally important relationship that exists between them. I’ve tried to achieve this by conceiving of them as shores, separated by a sea, as illustrated in Figure 7.

  Figure 7 A metaphor for scientific theorizing: sailing the Ship of Science across the Sea of Representation, between the shores of Metaphysical and Empirical Reality.

  Giving flight to fancy, I think of the shores of Metaphysical Reality as idyllic. This is a warm, sunny, and welcoming place; of soft, sandy beaches and lush tropical vegetation. It is a place of abstract imagination and absolute perfection. Here you will find conceptions for how reality might be, could be, or should be. These are conceptions born from the personal values and prejudices of the individual scientists who visit, based on everything they have been taught and have come to understand about the nature of reality, and many thin
gs they can only guess at.

  This is the place where scientists can be human—more Kirk than Spock. Here they can express their emotions, set free their desires, vent their frustrations, and just be themselves. Here it is possible to believe without evidence, to accept something as true without proof, to have faith. Some may look to find God here (in which case this place is a kind of heaven). Those scientists who prefer to deny the existence of God may instead look here to find nothing at all, because (for them, at least) conjuring something from nothing by physical mechanism alone represents the ultimate triumph of scientific (but actually just another kind of metaphysical) reasoning over religious superstition.

  Such metaphysics might involve grand visions of reality, its cause, nature, and ultimate fate. But, on average, it is more likely to be concerned with some of reality’s rather more mundane aspects, the things-in-themselves and the ‘nuts and bolts’ required to assemble reality and hold it together.

  You might be doubtful that scientists really need this place. Why should they want to come here? Surely they have everything they need in Empirical Reality? So let me try to illustrate why scientists find themselves needing to make frequent visits.

  As we saw in Chapter 1, driven by otherwise inexplicable evidence, physicists of the early twentieth century were obliged to torture quantum mechanics from the classical mechanics that preceded it. As a result, our understanding of physical concepts such as linear momentum was profoundly and irreversibly changed. But some classical concepts were retained.

  For one thing, the classical mechanics we inherited from Newton requires an absolute space and time. This is a problem because, if it existed, an absolute space would form a curious kind of container, presumably of infinite dimensions, within which some sort of mysterious cosmic metronome marks absolute time. It implies a vantage point from which it would be possible to look down on the entire material universe, a ‘God’s-eye view’ of all creation. The arch-empiricist Mach rejected this notion too, and Einstein arguably (and finally) dispensed with it in 1915 in his general theory of relativity, in which space and time emerge as dynamic variables.

  Absolute space and time or, more correctly, absolute spacetime, is a metaphysical construction. And yet here it is still, dragged largely unchanged from classical mechanics to form the backdrop to a quantum mechanics, against which we imagine quantum events play out. Knowingly or not, anyone doing quantum mechanics is accepting the notion that reality consists of an absolute spacetime. They accept this without the benefit of any empirical evidence, its truth (or at least its acceptance) established without the need for proof.

  Scattered along these shores you will also find the abstract, metaphysical concepts needed to lubricate the mathematical machinery of science. These are things such as the perfect circle and the perfect sphere; the infinitesimally small point; the infinitesimal angle; the infinite straight line; the natural limit; and many other things besides. These concepts do not exist in Empirical Reality, and yet without them we would struggle to do mathematically based science of any kind.16

  For scientists who spend even a short amount of time here, all this gets bundled up into a set of metaphysical preconceptions. These summarize how scientists think about reality and the kinds of things they believe it should possess. They include preconceptions that might be based on abstract notions such as beauty, symmetry, elegance, or simplicity. They give rise to convictions that theoretical explanations should be ‘natural’. Or that reality must be deterministic, with effect always following inevitably from cause. Or that there are some unassailable ‘natural laws’ (for example, of conservation) that must always be respected. Or that spacetime must be absolute.17

  Across the sea we find the shores of Empirical Reality. Now, this is the reality of our everyday experience, so I should apologize up front if you find the way I paint it to be intolerably bleak. Aside from anything else, I want to contrast Empirical Reality with the sandy, sylvan, alluring loveliness of Metaphysical Reality, and I’m mindful of Humphrey Davy’s homily about science being a harsh mistress, delivered to the impressionable young Michael Faraday, who on 1 March 1813 was newly appointed to a position at London’s Royal Institution.*

  So, the shores of Empirical Reality are rocky and frangible, tormented by high winds and lashing waves. This is the inhospitable home of hard, if not rather brutal, empirical facts, of numbers and effects, of doing this and getting that. It is of course here where we discover how nature actually appears. This is where (supposedly according to Benjamin Franklin) gangs of brutal facts have been known to murder beautiful theories or, according to Thomas Huxley, we witness the ‘great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact’.18 This is where scientists must set their emotions and their prejudices aside and practise a cold and calculating rationality—definitely more Spock than Kirk.

  But don’t think for a minute that there’s no room for metaphysics, even here. We are obliged to accept that no observation or experiment is possible unless we have at least some idea of what we’re looking at, or experimenting on. Of course this doesn’t mean we can never discover new things, just that it is impossible to make an observation or a measurement without the context of a supporting theory of some kind, though that theory might change or be replaced entirely as a result.

  French physicist and philosopher Pierre Duhem once suggested that we go into a laboratory and ask a scientist performing some basic experiments on electrical conductivity to explain what he is doing:19

  Is he going to answer: ‘I am studying the oscillations of the piece of iron carrying this mirror?’ No, he will tell you that he is measuring the electrical resistance of a coil. If you are astonished, and ask him what meaning these words have, and what relation they have to the phenomena he has perceived and which you at the same time perceived, he will reply that your question would require some long explanations, and he will recommend that you take a course in electricity.

  Empirical facts are never theory-neutral; they are never free of contamination from some theory or other. As we construct layer upon layer of theoretical understanding of phenomena, the concepts of our theories become absorbed into the language we use to describe the phenomena themselves. Facts and theory become hopelessly entangled: what we observe in Empirical Reality depends to a certain extent on how we look at it.

  No wonder the logical positivists failed.

  The shores of Metaphysical and Empirical Reality are separated by a sea. As I explained earlier, if we are to make sense of the empirical facts by developing explanations which deepen our understanding, we must find ways to bring together our preconceptions and the facts. We must create some tension between them. We therefore set sail in the Ship of Science, bringing all our metaphysical preconceptions with us and using our knowledge of the empirical facts to develop a workable representation of reality, or what we call a scientific theory. Our purpose in crossing the Sea of Representation is to find a way to accommodate both our preconceptions and the facts in a single, typically (but not exclusively) mathematical structure.

  There are many different ways of making the journey across the sea, suggesting that it is indeed possible to develop many different theories, each with a different mix of preconceptions, and each of which provide perfectly adequate accounts of the empirical data. This is known to philosophers of science as the underdetermination of theory by data. It is a bit of a disappointment for anyone who thinks that science should deliver a description of reality that is unambiguously ‘true’, unquestioned, and fixed for all time.

  And there you have it. Philosophers are content to contemplate and debate the nature of Metaphysical Reality, what purpose it might serve, and whether it has any real meaning or significance. They are philosophers, and do not concern themselves with the business of sailing aboard the Ship of Science.* In contrast, this is what scientists do. The ship ploughs back and forth on the Sea of Representation, refining metaphysical preconceptions here and gathering not-ent
irely-neutral empirical facts there, travelling in hope of a successful theory.

  So let’s see how that might work.

  * I’m reluctant to write ‘those who suffer from it’ as some synesthetes regard themselves as gifted.

  * I should point out that identifying the noumenon with Kant’s ‘thing-in-itself’ (Ding an sich), is still debated today among philosophers and somewhat controversial. For a good discussion, see Sebastian Gardner, Kant and the Critique of Pure Reason (Routledge, London, 1999), pp. 200–1.

  * Kant’s Critique is tough going, and it’s clear that his take on phenomena is not as simple and straightforward as I’m suggesting here. Phenomena are not ‘derived’ from noumena in the same way that shadows are cast by the objects in Plato’s cave. Our senses don’t think, and the human mind can intuit nothing without sensory perception. To gain knowledge we need to bring the two together. Phenomena are then ‘conceptualized appearances’ determined by the way the mind works, including our intuitions of space and time. Kant argued that such appearances are nevertheless objective, as demanded for the ‘synthetic unity of thought’.

  * At least since Kant and, arguably, since Plato. Of course, this doesn’t stop some contemporary philosophers (and, as we will see later in this book, some theoretical physicists) arguing that pure metaphysics can still somehow generate objective knowledge.

  * Einstein read Kant’s Critique of Pure Reason at the age of 13, and for a time Kant was his favourite philosopher.