Helgoland by Rovelli, Erica (ebook reader below 3000 .txt) 📗

alternatives. They have come to be called “interpretations of quantum mechanics.” In one way or another, they all require the acceptance of extreme possibilities: multiple universes, invisible variables, phenomena that have never been observed, and other such strange beasts. This is nobody’s fault: it is the fundamental strangeness of the theory itself that forces us to resort to extreme solutions. The rest of this chapter is full of speculations. You may jump to the next chapter, where I get to what in my opinion is the heart of the matter; but if you want a panoramic view of the current discussion and strange ideas in play, here they are, and they are fun.

Many Worlds

The “Many Worlds” interpretation is currently fashionable in certain philosophical circles, as well as with some theoretical physicists and cosmologists. The idea is to take Schrödinger’s theory seriously. In other words, not to interpret the ψ wave as a probability—but to see it instead as a real entity, effectively describing the world as it is.

In a certain sense, the idea is to discount the Nobel Prize awarded to Max Born, given to him for having understood that the ψ wave is only an evaluation of probability.

Schrödinger’s cat, if this is how things stand, is actually described by its completely real ψ wave. Hence it is actually in a superposition of cat-awake and cat-asleep: both exist concretely. Why is it, then, that if I open the box, I see the cat either asleep or awake, and not both things at once?

Hold on tight. The reason for this, according to the Many Worlds interpretation, is that I, too, Carlo, am described by my ψ wave. When I observe the cat, my very real ψ wave interacts with the cat’s, and my very real ψ wave also separates into two parts: one representing a version of myself that sees the cat awake, and one representing a version of myself that sees the cat asleep. Both, according to this perspective, are real.

Hence the total ψ now has two components: two “worlds.” The world has branched into two: one world in which the cat is awake, and I see the cat awake, and another world in which the cat sleeps, and I see him sleeping. There are now two versions of myself: one for each world.

So why is it that I see, for example, only the cat awake? The answer is that “I” am now just one of two versions of myself. In a parallel world that is equally real, equally concrete, there is a parallel me seeing the cat asleep. This is why the cat can be awake and at the same time asleep, but if I look at it, I see one thing only. Because if I look, I also become double.

Given that the ψ of Carlo interacts continuously with innumerable systems other than the cat, it follows that there is an infinity of other parallel worlds, equally existent, equally real, where an infinite number of copies of myself exist and experience every sort of alternative reality. This is the Many Worlds theory.

Does this sound crazy? It sounds crazy because it is.

Yet there are eminent physicists and eminent philosophers who maintain that this is the best possible reading of quantum theory.42 They are not the crazy ones: the craziness lies with this incredible theory that has worked so well for a hundred years.

But in order to emerge from the fog around quantum theory, is it really worth giving credence to the real and concrete existence of infinite copies of ourselves, unknown and unobservable to us, hidden behind a gigantic universal ψ?

I have another problem with this interpretation of quantum theory. The gigantic, universal ψ wave that contains all the possible worlds is like Hegel’s dark night in which all cows are black: it does not account, per se, for the phenomenological reality that we actually observe.43 In order to describe the phenomena that we observe, other mathematical elements are needed besides ψ: the individual variables, like X and P, that we use to describe the world. The Many Worlds interpretation does not explain them clearly.

Hidden Variables

There is a way of avoiding an infinite multiplication of worlds and of copies of ourselves. It is provided by a group of theories called “Hidden Variables.” The best of these was conceived of by de Broglie, the originator of the idea of waves of matter, and refined by David Bohm.

David Bohm is a scientist who had a difficult life because he was a communist on the wrong side of the Iron Curtain. Investigated during the era of McCarthyism in the United States, he was arrested in 1949 and briefly imprisoned. He was released—but sacked by Princeton anyway, which, hypocritically, feared for its reputation. He emigrated to South America. Fearing that he would end up defecting to the Soviet Union, the American embassy canceled his passport . . .

The idea behind Bohm’s theory is simple: the ψ wave of an electron is a real entity, as in the Many Worlds interpretation; but in addition there is also the actual electron: a real material particle that has a definite position. There is only a single position, as in classical mechanics: no quantum superposition. The ψ wave evolves always following Schrödinger’s equation, while the real electron moves in physical space, guided by the ψ wave. Bohm devised an equation that showed how the ψ wave could effectively guide the electron.44

The idea is brilliant: the phenomena of interference are determined by the ψ wave that guides objects; but those objects themselves are not in a quantum superposition. They are always in a single position. The cat is awake, or it is asleep. But its ψ has both components: one corresponds to the “real” cat, the other is an “empty” wave without a real cat—but the empty wave can bring about an interference. Interfering, that is, with the wave of the real cat.

This is why we see a cat awake or asleep, and yet