I just finished reading Jim Baggott’s new book Quantum Reality: The Quest for the Real Meaning of Quantum Mechanics – a Game of Theories. I was attracted to it due to this part of the description:
Although the theory quite obviously works, it leaves us chasing ghosts and phantoms; particles that are waves and waves that are particles; cats that are at once both alive and dead; and lots of seemingly spooky goings-on. But if we’re prepared to be a little more specific about what we mean when we talk about ‘reality’ and a little more circumspect in the way we think a scientific theory might represent such a reality, then all the mystery goes away.
Baggott begins by giving a basic primer on quantum mechanics, notably focusing on the measurement problem, the fact that quantum objects appear to behave like waves, until a measurement is made, then they behave like particles. (I gave a lightning primer on this a few weeks ago.) He then has a discussion about the philosophy of science, the demarcation problem, and scientific realism (as opposed to instrumentalism or anti-realism). He provides a number of “realist propositions”:
- There is such a thing as objective reality.
- Invisible entities such as photons and electrons really do exist.
- In quantum mechanics, the ‘base concept’ is the wavefunction.
- When deciding whether a theory or interpretation is realist or anti-realist, we ask ourselves what it encourages us to do.
The rest of the book is a discussion of various interpretations of quantum mechanics. He begins with the anti-real ones, but points out that, generally, these are anti-real only in the sense of rejecting proposition 3 above, not in terms of 1 or 2. In other words, these interpretations are not necessarily cases of idealism, or rejections of atomism, although they are sometimes assumed to be.
The main interpretation in this camp is the classic Copenhagen one with its wave function collapse. Others include Relational Quantum Mechanics, Information Theories, Consistent Histories, and QBism. It’d be a long post to describe all of these, but what they all have in common is in not claiming to provide a full understanding of the underlying physics, only our interaction with those physics. They all seem to say, “Move along, there’s nothing to see here,” or “Shut up and calculate!”
Personally, as an instrumentalist, I think the real vs anti-real distinction here is a red herring. In my view, Einstein was right, while pragmatically useful, what these theories are is incomplete. They fail to provide what we want from a scientific theory, a full framework to deduce, or at least explain, observations. The whole real vs anti-real designation just obfuscates this. My only beef with these interpretations is that the proponents often pretend that they’ve provided a final answer. In any case, once we’re willing to accept an incomplete account, I’ve never seen much benefit in moving beyond Copenhagen.
Baggott then moves on to the realist interpretations, such as deBroglie-Bohm pilot wave and various physical collapse theories. These interpretations at least make an attempt at explaining physical reality, although they all come with metaphysical costs, such as explicit non-locality in the case of pilot-wave. Baggott points out those costs, but notes that the approaches have the benefit of generating empirical investigation, something the anti-real ones aren’t good at doing.
There are a couple of discussions on decoherence. Decoherence is sometimes taken as an explanation of the wave function collapse, but it isn’t. While it describes how waves spread and become entangled into the environment, it never explains how the relation between the branches of the wave go from an and to an or, as in the particle going from being in a spin up and spin down state, to being in spin up or spin down, that is, the reduction to one reality.
In the penultimate chapter, Baggott gets to the idea of consciousness causing the collapse. John von Neumann in 1932, analyzing the dynamics, couldn’t find any mathematical reason for the wave function collapse, either at the measurement, in the measurement device, or in human sense organs. His explanation: something about the way the mind works causes it.
After expressing skepticism about the productiveness of this approach, Baggott then goes on a lightning tour of the consciousness debate, including citations of David Chalmers, Daniel Dennett, and others. It culminates in a discussion of Roger Penrose and Stuart Hammeroff’s theories about quantum consciousness. Baggott notes how aggressively speculative these concepts are, and discusses the issues that cause many in cognitive science and philosophy of mind not to take this approach seriously. Although I found his criticism here relatively gentle.
But the knives come out in the final chapter on the many worlds interpretation and its spin offs. I think it’s fair to say that Baggott detests this interpretation. He barely finishes a marginally fair description before attacking it. He goes on to discuss a number of increasingly speculative concepts, before finishing with a diatribe about multiverse theories. He groups them all together, seems to judge the lot by the most outrageous examples, then consigns all of them to hopeless metaphysics.
When I discussed Adam Becker’s book, I noted that Becker was often impatient with concerns about testability. I find the opposite vice in Baggott. He is often impatient with speculation. However, as I’ve noted before, science needs rigorous speculation to work. Baggott himself readily admits this, but doesn’t seem to apply it with theories he personally dislikes.
Anyway, it’s in the epilogue where we get something of a pay off on the promise of the book description. Here Baggott admits his sympathies with anti-real theories are growing. Many of the conundrums do seem to vanish with these approaches, but as I noted above, only because we’ve decided to make a virtue out of necessity and accept an incomplete account.
Baggott characterizes the many worlds approach as giving up, but I find this far more true with the explicitly anti-real interpretations. Maybe eventually we’ll have no choice but to live with an incomplete understanding. But I hope people never give up trying to move beyond it.
If you’re not familiar with quantum mechanics, or the interpretations in circulation, and would like a primer, this is a good book. One nice approach the book takes is to replace variables with pictures, making the quantum notation easier to deal with. Unfortunately, I think the book is marred by an unfair treatment of many worlds, but that’s not really unusual in this arena.