#christopher fuchs

Real STL and WC St. Louis Merge

In spite of these early hints, it was only in the twenty-first century that US physicist Christopher Fuchs and British–German physicist Rüdiger Schack4, 5, 6 put forth an understanding of quantum mechanics that restored the balance between subject and object. They call their new point of view 'QBism': Q is for quantum and B is for Bayesian — a view of probability that includes an agent who makes bets and updates odds. QBism attributes the muddle at the foundations of quantum mechanics to our unacknowledged removal of the scientist from the science. Fuchs and Schack adopt the latter view. They take a wavefunction to be associated with a physical system by an agent — me, for example, based on my past experience. I use the wavefunction, following rules laid down by quantum mechanics, to calculate the likelihood of what I might experience next, should I choose to probe further. Depending on what I then perceive, I can update the wavefunction on the basis of that experience, allowing me to better assess my subsequent expectations. People who believe wavefunctions to be as real as stones have invested much effort in searching for objective physical mechanisms responsible for such changes in the wavefunction: a novel manifestation of gravity, for example, or a new kind of fundamental all-pervasive friction. But according to QBism, the change is only in my personal expectations, which I revise to accommodate my new experience.

If you have it in your heart — and not everyone does — that the real message of quantum mechanics is that the world is loose at the joints, that there really is contingency in the world, that there really can be novelty in the world, then the world is about possibilities all the time, and quantum mechanics ties them together.

QBism would say, it’s not that the world is built up from stuff on “the outside” as the Greeks would have had it. Nor is it built up from stuff on “the inside” as the idealists, like George Berkeley and Eddington, would have it. Rather, the stuff of the world is in the character of what each of us encounters every living moment — stuff that is neither inside nor outside, but prior to the very notion of a cut between the two at all.

Usually we think of the universe as this rigid thing that can’t be changed. Instead, methodologically we should assume just the opposite: that the universe is before us so that we can shape it, that it can be changed, and that it will push back on us. We’ll understand our limits by noticing how much it pushes back on us.

Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two.

He’d say things like, “In the end, the only law is that there is no law.” There’s no ultimate law of physics. All the laws of physics are mutable and that mutability itself is a principle of physics. He’d say, there’s no law of physics that hasn’t been transcended. I saw this, and I remembered my joke about how the laws of physics must be wrong, and I was immensely attracted to this idea that maybe ultimately there actually are no laws of physics. What there is in place of laws, I didn’t know. But if the laws weren’t 100 percent trustworthy, maybe there was a back door to the stars.

Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two.