In previous posts (here and here, for example) I have discussed the strangeness of quantum mechanics, one of the 3 great revolutions in physics in the previous century. From its very beginning, quantum mechanics has stimulated debates about the nature of physical reality. Einstein didn’t care for a lot of its implications, like “spooky action at a distance.” Schrodinger very much disliked the instantaneous “jumping” favored by Bohr. And many physicists have, over the years, recommended that we “shut up and calculate” – in other words, stop worrying about the nature of physical reality as revealed by quantum mechanics.
Inevitably, some physicists have refused to take this advice, and continue to stretch the envelope of our understanding. A case in point are recent experiments concerning the nature of quantum jumps. When an electron moves from one energy level to another within an atom, emitting or absorbing a photon in the process, this “movement” occurs very rapidly. So rapidly, in fact, that for decades it seemed to be instantaneous. But is it really instantaneous? The answer is no. In an experiment published in 2019, physicists at Yale used “artificial atoms” to monitor quantum jumps. They found that jumps in fact are not instantaneous. The transition takes a few microseconds and follows a very predictable trajectory. There is even a “prejump” signature just before the actual jump. A jump can be reversed before it completes, enabling the researchers to keep a system in a particular state indefinitely, even though they can see that it is “trying” to make jumps from time to time.
The details of these “jumps” were in fact predicted in the 1990’s by something called quantum trajectory theory. This theory held that the behavior of a single particle during a so-called “jump” consisted of a transition through a series of superposed states. It’s important to realize that this trajectory is NOT like that taken by a baseball moving through the air. It is a trajectory through an ABSTRACT SPACE. And since the “prejump” signature only gives the experimenter a tiny amount of lead time, there is still no way to precisely predict when a jump will occur over the long term.
All of this is well and good, but it certainly doesn’t erase the strangeness of quantum mechanics. And whether jumps are instantaneous or not, we are still faced with the bizarre world of superposition. Take an electron in an atom for example. An ordinary object, like a baseball, has a precise position in space at all times. An electron, however has a position probability density. An electron is superposed. An electron in an atom exists in an orbital, but it isn’t in orbit. If the electron were in a precise location at a particular time, moving from one precise location to another, we would see the electrical charge constantly shifting in position as it moved. We don’t. If the electron were actually moving in a curved path around the nucleus, it would be accelerating, causing photons to be emitted constantly. This doesn’t happen. An electron has a position probability density, which is another way of saying that it’s in multiple locations at once.
This seems to get us right back to the “jumping” problem. If an electron is in many places at once, isn’t this is like saying it is making instantaneous jumps? No, because a jump implies that it is in one location at time A and a different location at time B. An electron is smeared out in space. It isn’t jumping. It is superposed. The problem is that our intuitive understanding of the world is built on large objects like baseballs. A baseball is never at multiple locations simultaneously. If it were, we would immediately question our whole approach. We wouldn’t think in terms of particles. We would think in terms of position probability densities, which are dictated by wave functions. These wave functions are in turn built from complex numbers, which have imaginary components. Which brings me to another recent study.
The mathematics of quantum mechanics uses imaginary numbers. Schrodinger disliked this as well, and came up with a way to do the math without imaginary numbers. The 2 approaches seemed to be equivalent – until just a few months ago. A group of theoretical physicists published a paper in Jan apparently showing that the 2 approaches do NOT necessarily yield the same predictions. They even suggested an experiment that would clearly distinguish between the 2 mathematical systems. Most researchers feel confident that the math built on imaginary numbers is correct. If so, then the “hack” using only real numbers is wrong, and imaginary numbers are necessary to accurately describe the universe.
Does this mean that imaginary numbers are “real,” as some observers suggest? Well, is F = ma “real”? Is the gravitational constant “real”? These are mathematical “constructs” that we use to describe our measurements. Then there are the actual measurements. The objects we examine and their behavior. We tend to separate this “objective” reality from the abstractions we use to describe it. But are they really 2 separate things? Ultimately I believe they are all made of the same “stuff,” and I am certainly not the first person to think so. Physicist John Wheeler famously suggested that what we call objective reality is composed of information. This includes matter, energy, space, time, and all of the abstract principles governing their relationships. If we let go of our insistence that there are “objects” out there made of something very different from the abstractions that govern their behavior, I think we will find that what seems very strange about quantum mechanics will turn out to be not so strange.
Quantum mechanics is all about information. It is fundamentally a description of what happens when one system incorporates information about another system. It is only when we try to interpret the math as describing something more than information systems that we run into trouble. When everything that we think of as “objective” reality – matter, energy, space, time, and all of their interactions – is conceptualized as active information, the problems of interpretation fall away. Baseballs are made of molecules, molecules are made of atoms, atoms are made of quarks and electrons. What are quarks and electrons made of? I think we have our answer. They are made of the same “stuff” that the abstractions describing their behavior are made of – active information.
In a way, those who argue that we should “shut up and calculate” are right, but not because we shouldn’t try to interpret quantum mechanics. But if we ask, “What is the information about?” I think we are asking the wrong question. A superficial observer, looking at a running flight simulator program, might be led to believe that the plane and the rules that govern its behavior are fundamentally 2 different things. But in fact they are merely different elements of the same underlying reality – active information.