The physics of the Universal Undo Button
Quantum cosmology represents one of those math-heavy niches of obscure research where science and science fiction tend to bump into each other a bit. To understand Tegmark’s work on multiple universes, we must take a quick detour back through the science of what is actually happening on the scale of the microscopic.
Hard evidence for an infinite, interconnected series multiple universes began with the simple experiment of the double slit, first performed by polymath Thomas Young in 1801. Young had sought to settle the argument over whether light is made of particles or waves, which had been raging for centuries.
Young allowed sunlight to shine through two tiny slits in paper cards to project patterns of light and shadow on the walls. That pattern is a classical wave form, indicating that light passed through both slits and interferes with itself. He concluded light was made of waves.
Later experiments by Albert Einstein proved that light reflects off objects in tiny packets called quanta. This was the birth of quantum physics, which Einstein helped to create but could never bring himself to accept. He concluded light was made of particles.
So, which is it? Is light made of particles or waves? Who is right and who must apologize? The answer, of course, is both and neither.
Like most debates in science and arguments over business strategy, the true path lies in a third way, a synthesis of the two. Any time your business is faced with two equally valid but mutually exclusive options, you are not thinking deeply enough about the problem.
Light is made of photons, which are neither waves nor particles but something we can’t imagine that has some of the qualities of both. Maybe call them wavicles or maybe we’ll leave the naming to someone else.
Now comes the really weird part, that opens the door to the effects of multiple universes in the real world. When you shoot individual photons toward the two slits, the pattern on the wall changes. Photons arrive one at a time like particles. But, when you turn off the particle detectors, so no one and nothing is watching, the familiar wave form pattern reappears. It seems as if each individual photon goes through both slits at the same time and interferes with itself.
That doesn’t make sense. An object like a particle can’t split into two and interfere with itself. But of course, common sense doesn’t work in the uncommon space of the quantum world. You have to just accept the evidence and try to explain it. This is the same problem that data scientists face every day when the data presents answers that business leaders don’t want to hear. The professional must follow the data, no matter what the boss says.
So, what is really happening here with the photons interfering with itself? There are three possibilities.
- Nothing is really there, until its measured. Danish physicist Niels Bohr wrote this generally accepted explanation of what’s happening in the quantum realm, known as the Copenhagen Interpretation. Bohr wrote that in the quantum world, things only exist as probabilities until they are measured. Yes, this is really the bedrock of the modern science. The math works and quantum science has produced functional miracles like lasers, X-rays, MRI machines, GPS, satellites, atomic clocks, and the computer you are using right now. They all depend on the laws of quantum physics, predicted by the Copenhagen model.
- We don’t and we can’t understand it. The Hidden Variables theory arose because Einstein couldn’t stand the Copenhagen Interpretation. He politely warred with Bohr in a series of letters filled with thought experiments. Einstein said one set of physics should apply across the universe, at every scale from microscopic to cosmic. We don’t understand the results because we haven’t figured out all the variables yet. It’s hard to argue with that but it’s not very useful either. We can’t discuss what we don’t know. Meanwhile, the Copenhagen Interpretation kept on racking up actual results in engineering, chemistry, medicine and more.
- Multiple universes. The third possibility is what we need to talk about, because that is where the Universal Undo Button comes in. Hugh Everett, a student of superstar astrophysicist John Wheeler, proposed the Everett-Wheeler model. At the moment when the photon arrives at the double slit, when things could go either way, the interference does not come from a single photon, but from another, identical copy of that photon in a nearby mirror universe. You will only ever detect one photon in our world when you turn on the particle detector because it is only measuring physical manifestations in this universe, not possibilities within the greater multiverse.
The math works for this interpretation just as well as it does for the Copenhagen model, but it answers many other problems in theoretical physics. More and more physicists are coming to the conclusion that the Everett-Wheeler, also known as the Many Worlds Interpretation, is the best answer to what’s really going on at the quantum scale. One fifth of working physicists today use the multiverse as their basic assumption in experiments, according to a survey from the University of Portland.
These ghost particles from other universes are not theoretical constructs. They are actually physically real. They are real enough to cast a shadow on the wall. What those other universes might look like is beyond the reach of modern science, just as the chemical composition of the sun was outside the reach of the science in Ancient Greece.