This is written after reading a book of essays in honour of David Bohn, edited by B.J. Hiley and F. David Peat, which I only partly understood. Yet I feel the urge to put down some thoughts I recorded.

Quantum phenomena for sub-atomic particles are well authenticated by experiments and the observations, though weird to our everyday thinking, have to be accepted as valid and real. However, interpretations can differ. Thus, while quantum phenomena are firmly established, there is more than one quantum THEORY. There may be more that we have not thought of yet.

The usual interpretation is the “Copenhagen interpretation”, attributed to Nils Bohr and Werner Heisenberg, though there was a lengthy dispute about it in the beginning (Albert Einstein, among others, did not like it, as well as De Broglie), and even now, some physicists doubt it, David Bohm being prominent among them.

I want to simply enumerate some of the features that people do not like, without explaining them at this point:

1. Complementarity (wave and particle aspects of both fermions and bosons).
2. Indeterminacy (one cannot measure both the position and the momentum of a particle with complete accuracy at the same time).
3. Wave-packet collapse when a certain measurement is made. This has consequences named in the next three points.
4. The observer (subject) unavoidably interacts with the object being observed.
5. Measurement paradox: why does the measuring apparatus not also obey quantum laws? (Classical laws are usually assumed.)
6. The dramatic thought experiment about the Schrodinger cat: it is neither dead nor alive until somebody looks in the box.
7. Contradictions with the theory of general relativity. (This is a separate point, not linked to (3)).

It is possible to avoid these difficulties and paradoxes in alternative interpretations, but then usually some other assumptions not quite consonant with common sense have to be made. But to some people at least, these might be more acceptable than those of the Copenhagen interpretation.

There are obviously two ways out of the complementarity dilemma: either accept the waves as real and the particles as at least partially an illusion; or accept the particles as real and the waves as merely indicating our uncertainty, i.e. waves as an illusion.

Accepting the waves as real leads to the “multiple worlds” interpretation of Wheeler and Hawking, combined with the anthropic principle, which places us as observers in only one of the zillions of existing universes. This may be so, but most people do not like that much either. The wave-packet collapse then merely indicates that we have blotted out all the other worlds except one; they have not really collapsed, but we can no longer observe them.

Accepting the particles as real can be done in 3 ways:
(a) Vigier’s “statistical” theory, which is causal (deterministic, not probabilistic), but non-classical.
(b) Bohm’s “implicit order” with its enfolding and unfolding of the explicit (observable) order from the deeper order underneath. This interpretation involves non-local effects (i.e. action at a distance) and inseparability of parts within the whole (like a hologram), i.e. non-decomposability, as well as “hidden variables”.
(c) De Broglie’s (and Betchov’s) peak of non-linearity (see my essay of that name), where the soliton or standing wave which moves around with superluminal speed is the particle.

Thus, to get away from the 7 difficulties of the Copenhagen interpretation, we have to instead accept:
either non-classical causality; or non-locality, hidden variables, and non-decomposability (radical holism); or non-linearity (i.e. turbulence and chaos).

As well, all the interpretations have to accept the non-distinguishability of particles (both fermions and bosons), so that they could obey either Fermi-Dirac or Bose-Einstein statistics, respectively. (Classical particles, which are distinguishable, obey Maxwell-Boltzmann statistics.) The usual interpretation is that particles twinkle in and out of existence rather than having continuous existence. This does not make them any less “real”, only not permanent.

These assumptions do not seem all that outrageous at second thought. Non-local effects can be explained by MPC (macroscopic phase coherence), possible for bosons which can occupy the same quantum state as other bosons (fermions can achieve this by forming Cooper pairs, which become bosons, as in superconductors). MPC is observed in plasmas, superconductors (and to some extent in ordinary conductors, i.e. metals), and helium-type liquids (superfluids). Some people postulate this also in very complex structures such as brains, giving rise to consciousness. [Do lasers also show MPC?]

Non-classical causality: I am not quite sure what Vigier means, bur the notion of causality has certainly been modified a lot lately, e.g. from a straight “causal chain” to a causal network, which can not only branch but loop around in positive and negative feedbacks. (This can be “massively parallel”, as they say of recently invented brain-like computers.) As well, necessary and sufficient causes and “contributing factors” have to be distinguished.

I have no problem admitting non-decomposability and non-linearity; they seem to be just generalizations from the former simpler decomposable (analyzable into parts) and linear models.

Actually, I rather like complementarity too; it is a useful notion. But I cannot abide the Schrodinger cat for even a fraction of a nano-second.