Recall from last week that we discussed the principle of quantum uncertainty, which is at the heart of the attempt to reconcile quantum physics and classical physics.
On the level of the very small, i.e., the interaction of subatomic particles where quantum physics rule, the act of observation affects the result and makes accurate measurement impossible. If we cannot study the behavior of subatomic particles on the level of the very small, then all their different behaviors remain possible. That principle is known as quantum uncertainty.
What makes sense on the mathematical level in quantum physics seems patently absurd on the level of the gross physical world where classical physics rules.
In 1952 Edwin Schrodinger attempted to explain the uncertainty problem by torturing an imaginary cat.
Schrodinger described a thought experiment in which Tabby was put in a steel box with a vial of hydrocyanic acid and a tiny amount of a radioactive substance. If just one atom of the radioactive substance decayed during the test period, that atom would trigger a sequence in which a hammer would break the vial of acid and kill the cat.
As long as the box stayed closed, you wouldn’t know what had happened, so according to quantum principles, the cat is both alive and dead at the same time. It’s only when you take a measurement (look in the box) that the uncertainty ends and the cat is either alive or dead.
In fact, Schrodinger was trying to show the absurdity of trying to project quantum uncertainty into the level of the gross material world. For all his obsession with thought experiments, he was a pragmatist who believed that the cat was either dead or it wasn’t.
But that didn’t stop highly qualified physicists from claiming that the cat is indeed both dead and alive.
Since every subatomic interaction suggests a different set of possibilities and many, many subatomic particles are interacting, every interaction generates an infinite set of possibilities.
Trace that set of possibilities back to the Big Bang that created our universe and the number of possibilities becomes, well, even more infinite, if you will excuse the expression. Project all of those possibilities onto the immeasurable enormity of the universe in which we reside, and the mind boggles (if it hasn’t boggled already).
On the level of the large, did you hit the snooze button on your alarm this morning? If you did, the act generates at least two possible realities, and those two suggest at least two more. Did you have orange juice for breakfast? Did you gulp it or sip it? Well, you get the idea. And all of those alternative sequences of events happen only in universes where you existed in the first place. Because of the large number of interactions that happened before you arrived on the scene, the number of universes where you exist is a much smaller infinity than the infinity as a whole.
Now add to the picture all of the universes that might have come into being from big bangs other than our own. Proponents of such multiverses, as they are called, insist that the mathematics support their conclusions, and we’ll have to take their word for it because those multiple universes are probably separated from each other by an impenetrable firewall. They probably all operate under quite different physical laws.
All those possibilities might be all around us in separate but unequal equal spacetimes irrevocably separated from each other by the different laws that rule them.
Of course, other multiverse scenarios exist. In the quilted universe, every one of the infinite possibilities happened in our own universe as a separate “patch.” However, such great distances separate them from each other that information about them in the form of light will never reach us.
Alternatively, our universe might be part of a larger collection of universes that exist like so many bubbles floating in a glass of root beer.
One variation of the bubble universe hypothesis is the brane multiverse. It imagines that our universe exists on a membrane, or ‘brane. Our brane floats in a higher dimension or “bulk.” The bulk contains many universes that can bump into each other.
Their collision must be incredibly violent and energetic. After all, we’re talking about whole universes banging together. Every few trillion years, some mysterious force akin to gravity attracts universes to each other. As they slam together, the enormous release of energy is certainly enough to generate a big bang, and a new universe is formed.
From the perspective of the multiverse, the Big Bang that created our universe is only one of many, each with its own set of infinite possibilities.
One advantage of the brane hypothesis is that the interaction of other universes with our own ought to be detectable if we look at the microwave background radiation, the energy generated soon after our own Big Bang. Attempts have been made to do so, but they are inconclusive.
Or the parallel universes might be like membranes that exist in parallel like the many thin layers of an onion. In that case, perhaps the detection of them and travel between them is possible in ways that we cannot yet imagine except in the most imaginative sphere of all — science fiction.
Who know? I certainly don’t, and therein lives the joy of science fiction. The writers don’t understand it either, but they have the courage to speculate about some of those infinite possibilities.
Tom Burns is director of the Perkins Observatory in Delaware.