Quantum physics proves that reality is in the eye of the beholder
Van Gogh may have understood quantum physics intuitively.
I visited one of the Van Gogh immersive experiences recently, having purchased the tickets months ago on impulse to try something different. The experience exposes you to a lot of his work at once, hundreds of paintings all created in a short period of time. Indeed, for a while his productivity was one painting every 36 hours.
Van Gogh’s work is not intended to be true to life. He was certainly capable of making exact drawings. The effect of his art is to convey through color and thick wavy brushstrokes a world overlaid with emotional intensity. The world is not as it appears but rather the world through the eyes of the artist.
At the time Van Gogh was creating his art, the world of physics had reached the end of its classical period. Physics, largely drawing from the philosophy of English rationalism of the 18th century, portrayed a world where measurement was purely objective, with the measurer or observer invisible and irrelevant. In other words, everything in the world had a definite, objective state.
Van Gogh, on the other hand, was portraying a world not as it is but as he saw it. To the thinkers of the 19th century this was wrong; a single definite reality existed, apart from any individual observer.
All that changed with the dawn of the 20th century.
First came Einstein with his relativity that forever made measurement relative to the person observing.
Then came quantum mechanics which destroyed objectivity entirely.
Heisenberg was one of the first to articulate the need to move away from classical concepts like position and momentum to quantum versions that tied the observer and the observed together.
The reason why has to do with the way that measurements occur in quantum mechanics. If you consider an apparatus designed to measure spin, for example, you find that the alignment of the apparatus affects the outcome. That is not because the apparatus is changing the spin of the particles it is measuring, but because the measured and measurer are inherently connected.
There was a lot of disagreement in the 1920s about how to interpret all this. Einstein presided at a meeting, for example, in 1924 where Heisenberg, only 22 at the time, gave a talk on his interpretation. The elder Einstein, twice his age, strongly objected to Heisenberg’s approach. They went for a walk after the talk and discussed it. When they came back, Einstein said they were largely in agreement but refused to say about what. It seems as though Heisenberg convinced the superstar that his approach was similar to Einstein’s own approach to relativity.
Heisenberg would write his famous synthesis of quantum and classical physics the following year at Helgoland, taking a page out of Einstein’s book. His approach rejected Schrodinger’s wave mechanics that gave rise to paradoxes like his cat. Instead, it reinterpreted position and momentum of particles, redefining them in the same way that Einstein had redefined “time” as something measured by clocks. Position and momentum in the quantum realm were not inherent properties of particles but something measured by measuring apparati. That does not mean that they don’t mean anything. It is just that they are inseparable from the thing doing the measuring in the same way that color, light, and shadow were inseparable from Van Gogh’s feelings about what he was looking at.
Heisenberg’s equations show how these strange new matrix quantities that replace classical position and momentum evolve in time. People still use these equations today but don’t often think about what a departure they were from ordinary thinking.
Heisenberg, a young man amid strong older personalities, however, would shift his understanding under the influence of Neils Bohr, nicknamed “the Pope”. Bohr’s approach to quantum physics was Kantian in that he believed that concepts like position and momentum from classical physics that made sense in the macroscopic world broke down in the microscopic world. Rather than reinterpreting position and momentum as quantum concepts, Heisenberg altered his work to placate Bohr so that the classical meanings were retained and the reinterpretation became an analogy or intuition about what was going on in the microworld. Neither Bohr nor Heisenberg was satisfied.
Later Heisenberg denied that he ever disagreed with Bohr, but it is clear from his papers, published work, correspondence, and interviews that his earlier interpretation had been significantly different and much more in line with relativity.
The philosopher Patrick Heelan who worked with some of the luminaries of quantum physics such as Eugene Wigner and interviewed Heisenberg as well, suggested that Heisenberg’s was the more “concrete” and objective interpretation while Bohr relied on concepts like waves and particles as analogies or pictures that did not necessarily correspond to anything real. Was Bohr, therefore, an anti-realist? It is hard to say. Some have accused both he and Heisenberg for being anti-realist, yet it may be that Bohr simply did not want to commit to a particular interpretation because there were too many equivalent ones.
The core concept for both Einstein’s relativity and Heisenberg’s early interpretation was the observable and how that is obtained. Time is obtained by clocks, in Einstein relativity, not defined by some watchmaker God. Length is given by rods. These do not have an objective existence apart from the observer. Rather they are subject to the observer’s own state of motion. Heisenberg extended these concepts to location, velocity, trajectory, and so on. Measuring apparati define them. Therefore, since these concepts change depending on how the measuring apparati are set up, they must be relativistic in the same way that time and length are.
The underlying reality is something that combines all possibilities somehow, as the four component velocities in spacetime define the objective reality of a body in motion. Yet is that essential reality or merely convenient abstraction? This question would lead to controversy between Heisenberg and another luminary of quantum theory: Erwin Schrödinger.
In 1926 Schrödinger introduced wave mechanics and the concept of the wavefunction. It was a beautiful theory that used many concepts from classical physics of waves. This got a lot of physicists excited because it appeared to be an objective definition of quantum particles, merging them with Newtonian style evolution equations. Heisenberg’s matrix mathematics, on the other hand, was abstract and confusing. It rejected the closely held idea of the “invisible observer” which was still popular despite Einstein. Schrödinger provided the “pictures” that Bohr wanted of what was going on at the microscopic level. People could be rationalist and believe in the wavefunction and its collapsing or they could be Kantian and believe it was just a picture of what was going on. Either way, they could keep their classical notions sacrosanct.
Bohr had Heisenberg and Schrödinger meet that year to discuss their respective differences. Each rejected the others’ approach. Heisenberg complained that Schrödinger’s theory threw quantum theory out in favor of a simplistic wave theory that said nothing about measurement. Schrödinger complained that Heisenberg’s theory was overly abstract and unrealistic, partly because of Heisenberg’s belief that the world was discontinuous with particles making random jumps all the time. Bohr believed that they both must be right somehow because their equations were mathematically equivalent. He called this idea complementarity.
Heisenberg continued to hold fast to the illogic of wave mechanics. There was no wavefunction. Rather, you could only talk about a quantity like location if you also talked about how it was measured — in some lab reference frame for example. There is no mysterious wavefunction expanding towards the apparatus and collapsing. Rather, position is simply dots on a graph that show where and when you measured a particle. Thus, you can’t talk about the particle having a position in between those dots because it isn’t with respect to a measuring apparatus. Of course, you could talk about what it might be if you did measure it with that apparatus, hypothetically, but you can’t talk about its having an objective reality apart from the measurer.
It is interesting to see how different this controversy is compared to the similar extension Minkowski made to Einstein’s relativity twenty years earlier. Einstein spoke of rods and clocks in his relativity while Minkowski spoke of four dimensional spacetime. Einstein embraced Minkowski to extend those ideas to curved spacetime in a new theory of gravity, the first since Newton. Yet Minkowski’s spacetime was much like the wavefunction — an abstraction away from measurement and observation that was central to Einstein’s understanding of reality — to some underlying reality. The real problem, however, isn’t that Heisenberg thought there was no underlying reality or like Bohr that it was inaccessible. Rather he believed that his theory somehow provided it and Schrödinger’s was a mathematical farce.
So what did Heisenberg think the wavefunction was? To him it was simply a measure of the scientist’s own ignorance of where the particle is and had nothing to do with reality.
This is, unfortunately, a very classical, probabilistic way of thinking about it — hardly worthy of quantum physics. A better way to think about the wavefunction, following from Heisenberg’s own ideas, is that it is a measure of how much the particle is deviating from classical mechanics. In other words, how much away from Newtonian deterministic evolution is it wandering. It is not a measure of ignorance so much as a measure of the inherent lack of classical determinism.
Heisenberg never quite made the Copernican leap that his youthful insight could have made had older minds not dampened it. His original insight opened the door to a new, relational view of knowledge which can be applied to anything knowable. Classical physics was concerned with obtaining knowledge by enlarging or expanding what we observe so as to see it better. An analogy would be like using a telescope to observe a far away star or planet. We are passively collecting information about a thing’s intrinsic properties. Quantum physics, according to Heisenberg’s early insight, is about obtaining knowledge by comparing one thing to another and understanding the inter-relationship. This is more like a scale or balance where the thing of interest is placed on the scale and measured against some unit. The essential knowledge we can obtain about the world is relational rather than intrinsic. Observable knowledge fundamentally is about both subject and object. Schrödinger’s wave view is simply a Minkowskian-style extension of Heisenberg’s Einsteinian viewpoint to an abstraction (the wavefunction) that we ultimately cannot observe but only think about.
What Van Gogh understood intuitively, Heisenberg appeared to very nearly grasp logically, but could not divest himself of the baggage of classical physics. It is this: that all knowledge is fundamentally relational and that what we can know about the world depends directly on who is doing the observing. Even when we view a Van Gogh, we are looking at how Van Gogh saw something but also cannot avoid overlaying our own feelings on top of the Van Gogh so that it is like seeing the world through multiple lenses. Whatever objective reality is, we can only view it through abstractions like spacetime or the wavefunction. Yet, direct experience of the world can only be in relationship, and it fundamentally relative.
Heelan, Patrick A. “The Discovery of Quantum Mechanics.” Quantum Mechanics and Objectivity. Springer, Dordrecht, 1965. 23–43.
Heelan, Patrick A. “Heisenberg and radical theoretic change.” Zeitschrift für allgemeine Wissenschaftstheorie 6.1 (1975): 113–136.
Crease, Robert P. “Experimental life: heelan on quantum mechanics.” Hermeneutic Philosophy of Science, Van Gogh’s Eyes, and God. Springer, Dordrecht, 2002. 31–41.