Fact: In a sufficienty large universe, there must exist an exact copy of you, with your thoughts, fears, memories and talents.

Explanation: Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. The current observable universe is approximately 860 billion billion billion (or 8.3 * 10^26) metres across. But it’s easy to imagine some place bigger. What if we had an universe a googleplex metres across?

A googolplex, as you may know, is a 1 followed by a googol zeroes. A googol itself is a 1 followed by a hundred zeroes. To give you an idea of how big numbers we’re talking about, a googol is a thousand billion billion times larger than the estimated number of molecules in the universe which means if you wrote down a single digit on every molecule, you couldn’t even write out the googolplex.

In an universe of googolplex metres across, If you went far enough, you would find exact copies of yourself. This comes down to simple mathematics. Every bit of space that you are made of can be described by something called a quantum state, which is basically a way of describing what it is, how it behaves, where it is located in space and time, etc. Your body can be described by a finite, although extremely large, number of quantum states.

However, when compared to a googolplex universe, that number pales in comparison. Eventually, you would run out of different combinations and you would have to repeat, just like if you were to use the numbers 1 and 2 to fill ten spaces, some numbers would have to repeat. In a big universe, there is a combination of quantum states that is you. They think they are you, they have your memories, your skills. They like pizza, they think Harry Potter was cool. And there may be more than one of them.

And that is quite a scary idea.