It seems plain and self-evident, yet it needs to be said: the isolated knowledge obtained by a group of specialists in a narrow field has in itself no value whatsoever, but only in its synthesis with all the rest of knowledge and only inasmuch as it really contributes in this synthesis toward answering the demand, “Who are we?”
Erwin Schrödinger, Science and Humanism, Physics In Our Time
A couple of days ago, I saw a 16 minute video titled “How Quantum Mechanics produces REALITY & perhaps ARROW of TIME.”1 With my interests in ways in which quantum theory can be utilized by historical inquiry I had to watch, and I am glad I did.
The beginning of the video shows Ash explaining that using classical laws of motion we can work out exactly where a basketball would be as it is thrown towards a hoop. We can calculate the trajectory by examining the forces on the ball. He then states that quantum mechanics doesn’t allow us to do the same for a particle. All we can know is where the particle could be at a later time. It is a question of probability due to the indeterminate world of quantum dynamics. Ash then moves on to suggest that the rectification of the classical and quantum is a “story of time.” He explains it as the boundary between becoming and being, the possible and the actual. As a historian, this has to be pertinent to my field of study. After all, isn’t history a study of time and the transition from the possibilities of the past to the actualities of the more recent?
Ash describes a quantum particle in a state of superposition. In this state, the particle’s spin is both up and down and thus indeterminate. Mathematically, this is presented as a wave function wherein you can deduce the probability of the spin, not’s its absolute. Ash describes the double slit experiment that provides evidence of the indeterminate state of particles. That is, until the particle is observed; then “the very act of measuring forces the universe to make that choice.” Once the particle is measured, the quantum properties vanish and it becomes like a classical object with definite position and properties. Measurement, or observation leads to wave collapse and the determination of the state of the particle. The question of how this switch happens is one of the biggest challenges in quantum theory.
Generally unsatisfied with the Copenhagen Interpretation of wave collapse, Ash posits that “We need to understand what goes on in a measurement.” These measurements are the result of a particle’s interaction with its environment. The particle becomes entangled with other particles and the more particles it is connected with, the greater its decoherence. The imprint of the particle on its environment then is what we are defining as measuring the particle. Therefore, measurement isn’t collapse, “but rather a gradual leaking and filtering of information about the quantum object into the measuring apparatus.” Because the interaction of the particle with its entangled environment is boundless, its decoherence seems to grow beyond the ability to pinpoint the entanglement. However, if large numbers of these particles are examined we can see the patterns of indeterminate quantum particles. Ash discusses how in several experiments researchers have actually been able to reverse this process into recoherence wherein the original properties of the particle are regained. He defines quantum as a process that is reversible, and classical as one that is not. It is only when something is irreversible that we can truly say what happened. The problem is that there is debate on when the process could or does cease to be reversible.
Lee Smolin’s recent paper2 is the next piece of the puzzle that Ash introduces us to. It posits that these quantum theories are what separates the past and the present. Smolin posits that the past is classical and the present is quantum. “The past consists of things that definitely happened, and can never unhappen. The present though is quantum. It’s still unfolding.” What then separates past and present is not only the question of irreversibility, but the knowability of the events. The past is therefore “something we can say, ‘it was like this’” while the present is an indefinite set of probabilities. The arrow of time then becomes the change of these quantum possibilities to the classical known past. “Once something is definite, its job is done and it is gone. But, the future is a quantum future. It’s a place only of possibilities, not certainties. Not everything is possible in the future though, but only things that can emerge from the present through the laws of quantum mechanics. Like the past it doesn’t truly exist, but for different reasons. The past is not real because its job is done and it can have no further influence on the world. The future is not real because nothing in it can be made concrete until the present, forever moving forward in time, reaches it.” We are living in the present, the point of condensing and changing. We live in the wave collapse which is the borderland between the classical past and quantum future.
A question of the many futures not selected by the decohering present remains unanswered. Are they part of a multiverse? Are they strings vibrating to an unheard frequency? Are they alternate realities, or is there but one reality? Ash leaves these questions unanswered, but as a historian my interest is piqued.
Now, let us begin by looking at Ash’s discussion through a slightly different lens. Let’s compare an event to the particle Ash describes. This event is unknown until it is observed and measured. It’s time and location can be seen as an indeterminate possibilities. Of course, just as with the double slit experiment, by looking at the interference of many events, we can see general probability patterns, but the specifics of a singular event cannot be determined without the collapse of the wave function.
Consider the well-known event of the 7 December 1941 bombing of Pearl Harbor as an example. President Roosevelt made it very clear that the location and time of this event were known. It was a day that would live in infamy3. However, wasn’t this just collapsing the wave function, or as Smolin would describe it, the gradual leaking and filtering of information into the measuring device until it becomes irreversible? Is the 1939 termination of the treaty governing trade with Japan one of those leaks, or is the attack on Pearl Harbor a piece of the environment entangled by the termination a year and a half previously?4 Maybe they’re both artifacts of the London Naval Conference. Does Pearl Harbor become the known event because it is irreversible? Roosevelt’s definition of the event on 8 December seems to move it from the probability amplitudes of the present to the known realities of the past.
Everyone agrees that the attack definitely happened, and can never unhappen; it is something we can say, ‘it was like this.’ and then, according to Smolin, its job is done and it is gone. However, 80 years on, and not only is the event not gone, its influence continues to resonate across the historical landscape. The past then continues to shape conceptions of the present which in turn influence the potential outcomes of the future. This is one of the places the historian and physicist collide. For in the world of the historian, the events of the past continue to exert influence on the world. They continue to shape the world, and the world continues to shape the events of the past in a complex adaptive system. It’s the trip down the rabbit hole of the Neumann-Wigner Interpretation wherein our consciousness becomes the final barrier of the collapse of the wave function.5 It’s where the system containing all the successes, failures, aspirations, and identities of the past present and future collapses onto what historians call post structuralism, and we are left to wonder what the artifacts of the event 80 years ago mean for our decisions of today. Crazy to consider isn’t it?