Here's my second post about Heinrich Pas' book The One: How An Ancient Idea Holds the Future of Physics, the first post being here.
I realize that probably I'm more interested in quantum mechanics than most people visiting this blog, so I'll do my best to make my posts about the book as simple as possible.
Which isn't easy, since quantum mechanics is confusing at best and totally mystifying at worst -- at least for those of us who aren't professional physicists, and even they readily admit that much about quantum mechanics is difficult to grasp.
The so-called "measurement problem," for example.
Quantum entities, like photons, are described by a wave function that evolves deterministically. However, the wave function doesn't say where a particle is located or what its momentum is. Rather, it gives probabilities for location and momentum.
Those probabilities exhaust all the possibilities, which can be surprising indeed. For example, while an oxygen atom is most likely in a box filled with oxygen, there's a slight probability that the atom is outside the box, a phenomenon called quantum tunnelling.
When a measurement is made, though, the wave function for the atom collapses to a single location and momentum. At least, that's the traditional Copenhagen view. (Copenhagen is where the early pioneers of quantum mechanics like Niels Bohr worked things out in the first part of the 20th century.)
As is well known, Albert Einstein didn't like quantum probabilities, famously saying that he couldn't believe that God played dice with the universe. God wasn't meant in the usual sense, but was shorthand for the primal laws of nature.
Einstein thought there were hidden variables that caused a measurement to reveal an atom in a certain way. But over time experiments ruled out the existence of hidden variables, so Einstein lost that argument.
The measurement problem remained, though. There was much debate among physicists about whether a conscious observer was needed for a quantum measurement or observation, or whether collapse of the wave function could happen in other ways.
Currently my understanding is that there's a fairly firm consensus that quantum decoherence, as it is called, happens as a result of an entity interacting with its environment.
Not to divert the subject of this blog post, but this is why quantum computers are so difficult to fashion: the quantum entities used for calculations have to be isolated from their environment in order to preserve their quantum nature where all things are possible in terms of probabilities.
OK, most of what I've said so far in this post comes from my own understanding of quantum mechanics, which I've been reading about as an interesting layman for thirty or so years. I may have gotten some details wrong above, but what I've said is roughly right.
Which gets me to a key theme in Pas' book, the many worlds interpretation of quantum mechanics formulated by Hugh Everett in the 1950s. His Ph.D. thesis put forward a theory that solved the measurement problem by stating that there is no collapse of the wave function.
Instead, Everett said that all of the possibilities and probabilities embodied in the wave function occur. All of them. Pas writes:
Thus, according to Everett, when a particle being in a superposition of two possible locations is observed, the particle doesn't collapse into one of the possible spots but rather the observer and its observation device split into two copies, one copy observing the particle in the first place and another copy finding the particle in the second place.
...As a consequence, every single quantum process results in a multitude of observers, witnessing every possible outcome and thus living in their private individual realities, universes, or "Everett branches": "This universe is constantly splitting into a stupendous number of branches... Moreover, every quantum transition taking place on every star, in every galaxy, in every remote corner of the universe is splitting our local world on earth into myriad copies of itself... Here is schizophrenia with a vengeance," Bryce DeWitt dramatically wrote of the unsettling consequence of Everett's interpretation.
Now, this doesn't seem like a recipe for finding the oneness that is the theme of Pas' book. Actually it is, though.
Because Everett did away with a key duality in the traditional Copenhagen view of quantum mechanics: the difference between the world of microscopic quantum phenomena and the macroscopic classical world of observers and measurement devices. Pas writes:
There is a core contradiction to be resolved as we explore what Everett's theory has to say about a monistic view of the universe. It may seem that by trying to take quantum mechanics seriously as a theory describing the reality of nature, Everett sacrificed the uniqueness of this universe and replaced it with a multiverse of many worlds.
But this conclusion results from a superficial consideration. What is typically overlooked in this picture is that Everett's multiverse is not fundamental but rather apparent or "emergent," as philosopher David Wallace of the University of Southern California insists.
From a fundamental perspective, rather than splitting the universe apart, Everett's formalism allows application of quantum mechanics to the entire universe and thereby enables entanglement to merge the universe into an all-encompassing "One."
Everett put this point straight, when asked about it in 1977 by the young French physicist Jean-Marc Levy-Leblond: "The question is one of terminology: to my opinion there is but a single (quantum) world, with its universal wave function. There are not 'many worlds,' no 'branching,' etc., except as an artifact due to insisting once more on a classical picture of the world."
...The fundamental single quantum universe not only alleviates the purported problem of Everett's interpretation featuring a "heavy load of metaphysical baggage" (as Wheeler complained) but totally invalidates this criticism as such a fundamental reality isn't only a single universe but a single unique entity comprising matter, space, and time as well as all potentially possible events and situations.
Not only is there just a single world, but this single world is all there is!
Little known as it is, this consequence of his theory may turn out to be Everett's paramount legacy. As Wojciech Zurek affirmed,"It was Everett who gave us the permission to think about the universe as wholly quantum mechanical."
Well, that's more than enough for this blog post. Difficult stuff to grasp, but I find it fascinating, even as I struggle to understand it. Fortunately, I've got about half of the book left to read. And I haven't described all of the key points in the first half, so hang in there with me if you're confused. Hopefully my posts to come will resolve some of that confusion.