I just finished the excellent book What Is Real? by Adam Becker. It tackles an important open question in physics. Maybe the most important. It is this: What does quantum physics say about the nature of reality?
The question arises because of the measurement problem. Before measurement, quantum systems exist in a superposition of states. But when you measure, you get only one result. The classic double-slit experiment illustrates this. Fire photons at two slits and they go through both like a wave, creating a telltale wave pattern. But put a measuring device on one slit, and the photons go through only it, like particles.
The so-called Copenhagen interpretation explains this as a “collapse of the wave function.” Somehow, measurement causes a collapse of probabilities into a single outcome. This is still the most well-known explanation, especially amongst the lay public. And it has led to a proliferation of pseudoscience about the role of consciousness in quantum physics. Like the idea that only conscious beings can collapse the wave function. And hence that conscious minds are necessary for anything to exist.
Well, Becker shows that the Copenhagen interpretation not only isn’t logical. There also isn’t even just one interpretation. Rather, political and economic forces led to physicists believing the measurement problem was solved when it wasn’t. They called this solution, whatever they thought it was, the Copenhagen interpretation. And they outright ostracized anyone who wanted to investigate alternatives to Copenhagen. This includes Einstein, whom history has incorrectly cast as not grasping quantum physics despite co-inventing it. In fact, Einstein understood it well. His crime was challenging Copenhagen, earning him derision.
But he was right. Copenhagen didn’t solve the measurement problem. And now, as Becker shows, we’re seeing a resurgence of new theories that better explain it.
The one I still find most convincing is many-worlds. This theory holds that there is no wave function collapse. Every possible outcome of a quantum superposition is realized in some universe. But we only see one outcome. So to us, it looks like a collapse from probabilities to a single outcome. But in fact, we just become entangled with the probabilities. By measuring one slit in the double-slit experiment, we cause the universe to branch. In our branch, the photon has gone through the slit we measured.
I find many-worlds even more compelling because multiple universes is now a recurring theme in physics and cosmology. We see it in inflationary cosmology and string theory. As Becker notes, these separate multiple universes may in fact be different ways of describing the same thing. It’s exciting to think that we might arrive at such a peculiar but possibly true description of reality from three different angles.
Even if you don’t buy into many-worlds, What Is Real? is worth reading. Science isn’t apolitical or immune to forces of history and economics. By seeing just how much politics, economics, and world events influenced the very understanding of reality, you may be more likely to question other dismissals of challenges to the scientific status quo.