One of our young listeners was inspired by “Cosmos: It’s Big, It’s Weird.” Matthew, 13, wrote to ask Seth a question about parallel universes:

*Dear Seth,*

*I was thinking, does that mean there are other universes out there not like ours at all, and that there are infinite copies of them too? If there are an infinite amount of universes in general, then that would mean that there would have to be enough to represent every kind of world you or I, or anyone else can imagine.*

*If you think of a random kind of a random universe in which you are a world-wide known superhero who fights Martian aliens (just as an example). It would have to exist at least somewhere out there in the multiverse because there are an infinite number of universes, right?*

*Also, Brian Greene used the piece of “Swiss cheese” example with the “holes” representing the universes. Well, what is the “cheese” then? What is the rest of the multiverse made of?*

*From,*

* One of your many “Big Picture Science” podcast listeners and a really big fan, Matthew*

Dear Matthew,

Indeed, you’re right: if there are an infinite number of universes out there, then indeed, there is an infinite number of bad ones, and an infinite number in which anything that CAN happen in a finite amount of time has happened. It’s a dizzying thought.

As for the “cheese” — well, that’s some sort of undefined “meta space” which is not really anything like either the matter or space we’re familiar with. It’s just something to separate the various multiverses. Hard to imagine, but the usual assumption is that parallel universes are like bubbles in a bathtub. If you’re in one of them, you can’t get to the next, as they’re somehow separated. Mind you, there are ideas about the possibility of using wormholes to get from one to the next, but no one knows if any of this is true.

Thanks for writing.

Seth Shostak

For more mind-blowing thoughts about the multiverse, read Seth’s “Humble Pie” on Huffington Post.