By David K. Johnson, Ph.D., King’s College
In a Futurama episode, Farnsworth invented a time machine that only went forward in time. After he went too far forward, he decided to fast-forward to the end of the universe. But after it ended, another big bang happened and history unfolded just as it did before. But, it appears the universe is more uncertain than it seems.
Difference between Our Universe and Other Universes
Now, what would the universes in a multiverse be like? Would they, like in Futurama, contain all the same events—happening over and over again? Or would their histories be different? According to Alexander Vilenkin, since there is an infinite amount, “inevitably, an unlimited number of [universes] of all possible types will be formed”. So they’d be different.
But if other universes are governed by the same physical laws as ours—and granted, some might not be—but of those that are, one might suspect that they will also turn out just like ours because they started in the same way too. Same starting conditions plus the same laws yield the same results.
It is known that determinism is false. All events are not governed by the laws of physics. On the micro quantum level, some events happen randomly and without cause. So everything won’t be exactly the same, even in universes governed by the same laws.
But quantum randomness gets averaged out on the larger, macro, scale. That’s why physical laws have predictive power. So it still could be that universes with the same laws would all be the same on the macro level. It would depend on whether the outcome of random quantum events could ever determine what happens in the macro-world. And it seems they could.
This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on Wondrium.
Schrödinger’s Unlucky Cat in an Uncertain Universe
Take, for example, Schrödinger’s cat. Schrödinger imagined a cat in a box, next to a vial of poison—a poison that would be released only if a Geiger counter detected the decay of a radioactive atom.
Whether the atom decays is a micro quantum event, determined randomly. And so, whether the cat lives (a macro event) is also determined randomly.
So, if there were two universes, identical in every other way, both containing cats in these circumstances, it could very well turn out that one cat lives in one universe and one cat dies in another.
Now, that wouldn’t be a big difference, but if the outcome of quantum events have an effect on the macro scale often enough, two universes with the same starting point and the same laws could end up being considerably different.
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The Not So Identical Universes
How could this happen? Well, suppose that the outcome of the physical processes in brains that generate decisions are dictated by the outcome of quantum events. If a quantum particle in someone’s brain does one thing, they’ll do X, and if it does the other, they’ll do Y.
If so, two universes could be exactly the same up to the moment they make a decision, but then diverge, with the person doing X in one universe and Y in another. If all the different ways that everyone’s decisions could go are compiled, and all the other choices that they could present people, this would give a wide array of different universes—some only slightly different, others vastly so.
For any event, there is an infinite number of possible outcomes. Choices determine which outcomes will follow. But there is a theory in quantum physics that all possibilities [in other words, all choices] that can happen, do happen, in alternate quantum realities.
In fact, this explanation appears to invoke an actual interpretation of quantum mechanics which suggests that a multiverse exists. That for every way that a quantum event could turn out, there is a universe in which it turns out that way. To properly understand this interpretation of quantum mechanics, however, will take some explaining.
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The Superposition of Particles
What quantum mechanics tells us is that, until they are measured, subatomic particles like electrons and photons don’t determinately have certain properties, like location or momentum. They do have properties like mass and charge, but they are not in any particular location or moving with any specific momentum. They are in what is called a superposition.
They can be described with mathematical functions called wave functions, but these wave functions suggest that the particles have multiple seemingly contradictory properties at once. An electron could be, say, 20 percent here and 40 percent there. These wave functions can be used to accurately predict the particle’s behavior; when measured, 20 percent of the time such an electron will be here, and 40 percent of the time it will be there.
But it’s not in any particular location until it is measured and the wave function collapses. And to be clear, it’s not that it can’t be figured out what location or momentum such particles have until they are measured. It has been shown experimentally that such particles do not have such properties until they are measured. In short, they exist as waves until they are measured—at which point they become a particle.
Common Questions about the Uncertainties of Our Universe
The main reason is that all events are not governed by the laws of physics. On the micro quantum level, some events happen randomly and without cause. So everything won’t be exactly the same, even in universes governed by the same laws. However, quantum randomness gets averaged out on the larger, macro, scale.
Quantum mechanics teaches us that, in this uncertain universe, subatomic particles do not have particular locations or momentum until they are measured. So they are in what is called a superposition.
Schrödinger imagined a cat in a box, next to a vial of poison—a poison that would be released only if a Geiger counter detected the decay of a radioactive atom. Whether the atom decays is a micro quantum event, determined randomly. And so, whether the cat lives, which is a macro event, is also determined randomly.