15 Entanglement

Quantum entanglement is the notion that two detections of light, understood to be two photons created together in a single compound event, are part of the same phenomenon or event, and that the whole is properly described by a single mathematical function, or ‘wavefunction’.

This much is perfectly reasonable, so far as it goes. However, there is a further argument, dating back to von Neumann, that this means that what you do as an experimenter in measuring one part of this event (detecting one photon) has an effect, instantaneously and at a distance, on the other. There are two ways in which this whole topic is often handled poorly in the physics literature, and these are commonly obscured by the complex and often metaphysical language used.

The first is to do with the adoption by physics of ideas that come from the philosophical school of logical positivism. In philosophy, this was an attempt to introduce rigour by limiting discussion to what we can actually know through observation. In quantum physics, it is the superficially similar admonition to limit theory to what we can actually observe. Schrödinger described it as the decision to ‘forgo connecting the description, as we did hitherto, with a definite hypothesis as to the real structure of the Universe. ’[i]

Since light, at least prior to Krausz, is something we observe solely through a detection event, the absorption of a photon’s worth of energy, then the positivist position is that we forgo all consideration of the mechanics of how the energy travelled between emission and detection.

Logical positivists are not very popular with other philosophers, as they seem to condemn them as pointless. Even Professor AJ Ayer, who developed logical positivism from the work of the German positivists, said later in life that:

‘The biggest problem with logical positivism is that it is mostly wrong.’[ii]

In quantum mechanics, the question that must be asked is whether this approach has proved beneficial, and we might conclude, with Schrödinger, that it has not.

Entanglement provides the strongest example of this. Positivism advises us, entirely sensibly, not to make unwarranted assumptions about the transit of light, but a powerful opinion within physics takes this further, to conclude that this effectively rules out any mechanistic reality for light between these events.

When we do this, we are making assumptions about the nature of physics. This is, literally, meta-physics, and, if we are to be consistent in our philosophical position, then we must be sure that this conclusion itself is properly warranted. Some of the evidence for this has been addressed in earlier chapters, and found wanting. We will look at more, shortly.

A key argument in relation to entanglement is based on this assumption that a photon has no tangible reality until it is absorbed, or ‘measured’. This suggests that the photon is only given reality by the process of measurement, and gives rise to the focus in quantum mechanics on the importance of the observer. The idea appears to originate with von Neumann, and has created a conceptual problem, known as ‘the measurement problem’, for quantum physics.

Vast amounts of time and paper have been expended on this idea, much of it valueless. Does a report from another observer qualify, or from a machine? And what is the state of a detection before it is known? In the terminology of probabilism, the photon has neither arrived nor not arrived, but is in a superposition of the two states. It is this view that Schrödinger set out to parody with his famous but apocryphal cat. Quantum mechanics is known to be weird, and it is the measurement problem and entanglement that are central to most of that weirdness.

When we consider entangled photons, a particular problem is created. Theorists have concluded, from positivism but with little regard for consistency in applying that principle, that the photon with its associated polarisation has no reality until measured. For the partner photon, its polarisation, being linked to the measured one, is therefore created at that same instant. This in turn has been interpreted as instantaneous transfer of information over an arbitrary distance.

This is one of the most interesting conflicts between relativity and quantum theory. The former rules out instantaneous action at a distance, while the other embraces it. This book has found it important to maintain a common sense, mechanistic view, and therefore is comfortable with the relativity position on this, but not the quantum theoretical one.

If we are to preserve the requirement for sound reasoning, then the quantum theory argument from positivism and entanglement is invalid. We have seen that there is a central inconsistency in the quantum theoretic position on non-reality, in that it draws far stronger conclusions than are reasonable given the positivist position that it has adopted. On the basis of its own philosophical platform the conclusion that the photon lacks reality until it is measured is unwarranted. On any other basis, and as a logical or scientific conclusion, it is valueless.

The second way in which the subject of entanglement is handled poorly is in the interpretation of experimental findings. Earlier observation has shown particle-like effects for light, which we had thought was a wave, and wave-like effects for electrons and atoms, which we had thought of as particles. This has encouraged quantum physicists to treat light and matter, sometimes casually, as essentially the same thing.

We have seen this in relation to ‘quantum’ computing, where the theoretical discussion is of the benefits of using the quantum properties of the photon to encode and extract more information from a single photon than a single binary unit or ‘bit’ of information. Hence the term ‘q-bit’.

Yet the ‘demonstration’ of successful quantum computing uses neither photons nor q-bits. Instead it uses four single atoms, and properties of them that it deems quantum properties, to count up to fifteen. Impressive though the demonstration is, it is not a demonstration of q-bit computing: anyone slightly familiar with standard computer arithmetic will confirm that this is standard binary counting,[iii] with no evidence of q-bits at all.

We see this imprecision of thought in a different form in quantum cryptography. Here, despite the lip service paid to the duality model, all the theoretical discussion is based entirely on a particle view. In this argument, individual photons carrying information are known to have entirely bypassed the eavesdropper because it is known or assumed that photons are essentially particle-like entities that can be detected only once. We have not yet examined all the evidence for this, but the claim appears to run counter to ‘duality’, and we will not find in its favour.

Given the recent history of ideas in physics, it is all too easy for a passionate adherent of the particle model to overlook inconvenient facts about the wave nature of light. For these rogue physicists, entanglement of photons as discrete particles and their non-existence until one is detected is a scientific fact. This myopic commitment to poor reasoning and a failed hypothesis is the reason why we still see claims for ‘quantum teleportation’ in scientific journals and the popular scientific press. The same observations are advanced in support of quantum cryptography, for reasons that are unclear.

Reports of experiments in entanglement are impressive, but when we examine the details we see that the imprecise forms of thinking exposed above are liberally employed to puff up these experimental findings into something they are not. It is hard to fault the second-party reporters in this, as quantum entanglement appears to those outside the inner circle as a firmly established concept and the reasoning is no weaker in kind than we find elsewhere in advanced physics.

Schrödinger once admonished that ‘without an absolutely precise model thinking itself becomes imprecise, and the consequences to be derived from the model become ambiguous’[iv], an observation that is proving exceptionally prescient.

[i] Nobel Address delivered in Stockholm on December 12th, 1933

[ii] The Ayer quote is something I heard him say on a radio programme many years ago. It was curiously omitted from the book based on that series of programmes, but is still remembered by many.

[iii] 0 to 15 in binary: 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111

[iv] Science and Humanism, page 25.

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