You hear about parallel universes all the time in science fiction (see Fringe, probably a billion episodes of Star Trek, Stephen King’s Dark Tower series, etc.). But did you know that scientists take parallel universes seriously and consider them possible. There are several types of possible parallel universes. This is the fifth and final post in a series of five posts. The first can be found here, the second here, the third here, and the fourth here.

# Different Math

Everything we’ve discussed before (different observable universes, inflationary bubbles, m-theory and the many-worlds interpretation of quantum mechanics) has been pretty theoretical. Theoretical, but somewhat plausible. It’s just beyond our ability to test whether these type of parallel universes exist or not right now. With this final type of parallel universe, we’re going beyond testability, almost into philosophy more than anything else. This is the idea of parallel universes that are governed by different math. Max Tegmark calls these types of parallel universes Level IV parallel universes in his taxonomy.

We use math to describe the world around us all the time. From calculating the trajectory of a missile to measuring data from the Large Hadron Collider. Mathematics is our most useful tool in describing the universe. We’ve already had some pretty deep insights into the works of the universe with quantum mechanics and relativity. These were both possible because of math. The question is, is there an equation or system of equations that is the universe? Can the universe, everything in it, all that ever was or will be, be reduced to a handful of equations? Or, put another way, is our universe just a math equation given physical form?

We honestly have no idea. Certainly, math is invaluable in science and our understanding of the world. To illustrate this, Tegmark cites Eugene Wigner, who won the Nobel Prize for physics for his work on atomic theory: “the enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious and . . . there is no rational explanation for it.” But that does not mean that math is capable of describing everything in our universe. Yet, on the other hand, we have not yet seen any indication that there is something in our universe that math cannot describe. There are currently challenges in unifying theories, but that does not mean that we cannot do it. It just means we haven’t done it *yet*.

Assuming that the universe is a set of equations, why just these equations? There is no reason to think that only these equations govern the whole of existence. Perhaps there are other types of universes out there that are governed by different equations. Like I said, we’ve pretty much left the realm of science and are entering into a realm of philosophical speculation. As to what those other universes are like, your guess is as good as mine. We haven’t even yet found the equations that govern our universe, if they exist, so we can’t even begin to speculate what other universes may be like. And this is why science is fun; we get to wonder and strive to explore the nature of life, the universe and everything. It’s always so much more interesting than we expect.