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Here Is a Way We Can Be Sure If We Are Living in a Multiverse

An experiment can test the idea that there is an infinite number of universes

Many scientists believe we live in a multiverse. This idea was first introduced by quantum physicist Erwin Schrödinger (1887–1961) as a way to make sense of quantum superposition, the idea that a particle exists in two different states at once before it is measured. Schrodinger claimed it was possible because the particle exists in two different states—in two different universes.

More recently, another quantum physicist, David Deutsch (pictured), has made a similar argument based on quantum wave collapse. When a quantum particle is superposed between one state and another and turns into one specific state when measured, why does it pick the one state and not the other? Physically, that is totally arbitrary and makes no sense. Deutsch claims that this, again, is evidence of a multiverse. The particle does not arbitrarily pick one state. It picks both states, one in each of two universes. The logic behind the multiverse, as Deutsch understands it, is that it would eliminate arbitrariness and ambiguity in quantum physics.

Other physicists have championed the idea of the multiverse to deal with the problem of complex specified information—the kind of information that is not only complex but also intricately patterned. There is far too much independently specified complexity in the universe to have arisen by chance.

One way to address this problem and still appeal to chance is to grant many, many opportunities for everything to somehow come together somewhere in the multiverse. But this amounts to just pulling a multiverse out of thin air to deal with a problem. The only reason the multiverse has any standing as a concept in science—one that might challenge specified complexity—is the prior justification based on quantum physics.

Now, many scientists complain that the multiverse is “unscientific,” without going into specifics. Listen to them: “Oh, we need to be able to empirically test something to be scientific.” “Oh, the multiverse is beyond anything we could ever test.” “Oh dear, it is so unscientific!” Are they perhaps just whining about something they don’t like?

Fortunately, there is a simple way we can test the multiverse hypothesis. Recall that the science-based justification for the multiverse is quantum physics: A particle must indeed exist in two different states—precisely because it exists in two different universes. Then the observers of the particle must also exist in both universes because they existed in the universe before the particle became superpositioned.

Now, let us hook up our “experiment device.” Our device performs a fair quantum coin flip, where it takes the superpositioned particle and examines its state. Let’s call the two states the heads and tails states. If our coin flipper observers that the state is heads, that’s equivalent to flipping a heads with a coin. The same goes for observing a tails. So now we have a device that performs the equivalent of a fair coin flip, except with quantum reality.

Using our quantum coin flipper, we flip our quantum coin one thousand times. Every single possible sequence must exist in some universe according to quantum multiverse theory. In that case, in one of the universes, our quantum coin flipper has flipped a thousand heads in a row. The odds of flipping a thousands heads in a row are so small as to be impossible. Therefore, the only way we can ever observe our quantum coin flipper flip a thousand heads in a row is if the multiverse is true.

Remember, we, as observers, are guaranteed to be in all the universes with all the possible sequences, and thus we are also in the universe with a thousand heads. And thus we achieve our test of the multiverse: if we ever observe our quantum coin flipper flip a thousand heads in a row, we can be almost certain the multiverse theory is true.

Now here’s the problem: We observers are not only in the thousand heads universe but also in all the other universes with arbitrary mixtures of heads and tails. To get a definitive result, we need to eliminate ourselves in all universes except the universe with a thousand heads. And so we give our quantum coin flipper a disintegration ray gun.

To guarantee that we observers are only in the universe with a thousand heads, our quantum coin flipper delivers a ray blast to the observers any time it flips tails. Because we will have ceased to exist in all universes with any tails, we must only exist in the universe with a thousand heads. Additionally, this universe with a thousand heads is guaranteed to exist, so we are guaranteed to survive this gruesome experiment.

So, for all the critics of intelligent design who claim that the multiverse disproves the existence of complex specified information, there is now a simple way to test their claim. Any takers?

Hat tip: Scott Aaronson, for the basic idea.

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Eric Holloway

Fellow, Walter Bradley Center for Natural & Artificial Intelligence
Eric Holloway has a Ph.D. in Electrical & Computer Engineering from Baylor University. He is a current Captain in the United States Air Force where he served in the US and Afghanistan He is the co-editor of the book Naturalism and Its Alternatives in Scientific Methodologies. Dr. Holloway is an Associate Fellow of the Walter Bradley Center for Natural and Artificial Intelligence.

Here Is a Way We Can Be Sure If We Are Living in a Multiverse