Ask Ethan: Could a “copy” of me exist in the Multiverse? | by Ethan Siegel | Starts With A Bang! | Sep, 2024

Within our observable Universe, there’s only one Earth and one “you.” But in a vast multiverse, so much more becomes possible.

Here in our Universe as we know it, once an outcome has occurred, there’s no going back. Once you open a bag of potato chips, you can never return that bag to its unopened state; the air molecules from inside and outside have already mixed with one another, even if you reseal it. Once you cut down a tree, you can never return the tree to the state it was in prior to you cutting it down. Even on a quantum level, once you measure a particle’s spin, you can never return it to its pre-measurement state. We have only the one Universe that we inhabit, and while future events do not yet have determinate outcomes, past events all do.

But what if there were copies of our Universe out there, far beyond the limits of what’s observable or measurable, that were identical to our own? Would it be possible for different outcomes to have occurred in those Universes, and what would that mean for a variety of systems: quantum particles, trees and potato chip bags, or even entire human beings? That’s what Danny Porter wants to know, writing in to ask:

“If the universe is infinite, and string theory suggests…