Everything is a quantum wave?

In the last post, I discussed Amanda Gefter’s critique of Vlatko Vedral’s view that observers have no special role in reality. Conveniently, Vedral published an article at IAI discussing his view: Everything in the universe is a quantum wave. (Warning: possible paywall.) Vedral puts his view forward as a radical new interpretation of quantum mechanics.

As a quick reminder, the central mystery of quantum mechanics is that quantum particles seem to act like waves, including portions of the wave interfering with itself, but when measured, behave like tiny localized balls. This is known as the measurement problem.

There are numerous interpretations of what’s happening here. But they seem to take one of three broad strategies. The first simply rejects that the waves are real, instead insisting that they are only probabilities, albeit probabilities which evolve deterministically and interfere with each other. In other words, it’s all happening in our mind. In its stronger incarnations, this has idealist or semi-idealist aspects, claiming that observation or interaction creates reality. These are the approaches in the epistemic versions of the Copenhagen Interpretation and its descendants, like QBism and RQM (relational quantum mechanics).

The second strategy is to add new structure to wave mechanics. Due to Bell’s theorem, these additions must be non-local in nature, that is, they must involve “spooky” action at a distance. The ontic version of Copenhagen takes this approach when it adds a physical collapse, as do its variations and descendants like consciousness-causing-the-collapse and other objective collapse theories. Another version of the second strategy is what are historically called “hidden variable” approaches, like Bohmian Mechanics (pilot-wave theory), where there is both a wave and a particle the entire time, with the wave guiding the particle.

The third strategy is to accept the mathematical structure of quantum theory as a full account, or one only requiring a few ancillary assumptions. This became easier with the development of decoherence theory in the 1970s, an extrapolation of quantum wave mechanics, in essence quantum entanglement en masse, that explains why quantum interference disappears at larger scales. It’s the approach Hugh Everett proposed, which eventually became known as the many-worlds interpretation.

And it’s the strategy Vedral uses for his interpretation, which he characterizes as “many-worlds on steroids.” Although he dislikes talking in terms of other worlds, noting that the classical worlds are only a small slice of the possibilities. He prefers to talk in terms of one world but with quantum mechanics being universal, applying at all scales.

Vedral makes a point I made in the last post, that under this universal quantum waves approach, an observation is just two quantum systems becoming entangled, that is, becoming correlated in certain ways. A reminder: entanglement is when two quantum systems have each of their states in superposition become correlated with each of the states in the other system. In other words, for each state in the first system, there is a correlated state in the second. The two systems are now part of the same wave function.

Vedral notes this could be characterized as the quantum particle observing the measuring device as much as the device is observing it. In this view, entanglement is what the apparent collapse looks like from the outside, and collapse is what entanglement looks like from the inside. So contra Gefter’s stance, there’s no special role for observers, at least unless by “observer” we mean everything.

As I noted in the last post, I like Vedral’s approach here of focusing on the physics rather than getting into multiverse language, which as I’ve noted before, often ends up being a distraction. But it’s hard for me to see how his view is radically different from the standard Everettian one. It’s worth noting that Everett’s original proposal was a theory of the universal wave function, essentially the “everything is a quantum wave” view Vedral is advocating. Everett didn’t talk in terms of a multiverse. It was Bryce DeWitt in the 1970s who characterized that way, although Everett saw it as just an alternate way of describing his view.

One difference from contemporary many-worlds views, which Vedral shares with Everett, is that the quantum nature of macroscopic objects is not beyond testability. Everett reportedly maintained that the quantum states of macroscopic objects were in principle detectable. I haven’t read Vedral’s book, but it sounds like a large part of it is finding ways to test his view.

This seems resonant with the progress being made in experimental research, where tiny macroscopic objects can now be held in a quantum superposition, which is putting increasing pressure on ontic collapse theories. And Vedral mentions the ongoing efforts in quantum computing, which is stress-testing quantum theory in ways scientists of earlier decades could only dream of. In the end, we need data, and these efforts are providing more of it.

As a minimalist Everettian myself, I find a lot in Vedral’s discussion compelling. But as he notes in his article, the various interpretation camps are like entrenched armies in World War I, unlikely to be moved except by the strongest experimental results. Even then, I suspect Max Planck’s observation that science moves forward “one funeral at a time” will likely be true here as it always has.

What do you think of Vedral’s views? Does the idea of everything being a quantum wave make sense? Or are there difficulties both he and I are overlooking with this approach?