The other you you hope to find

Are you fantastically successful in another universe? 

Somehow this seems to be an increasingly popular idea, especially among New Age types and people who misconstrue quantum mechanics. 

Let's pose some questions to Brian Greene, author of popular books on physics and cosmology, and professor at Columbia University. He's one of the latest to explicate the multiple-you idea. Greene's reasoning is logical, well thought out, and he's probably no slouch on quantum mechanics, either. 

Greene posits an infinite universe, filled with an infinite number of sub-universes. Our universe is just one of many.

How often would you expect to run into a universe similar to ours, with an Earth similar to this planet? If you take every proton, neutron and electron in our universe and combine them in every combination and permutation, the number is 1 followed by 10 to the 122nd power of zeroes. There isn't enough space in the universe to write this number.

For simplicity we will call this unimaginably large number "1 zillion."

Moving out into the multi-verse, you could expect a universe like this one about once every 1 zillion miles, or meters, (doesn't really matter). 

Because the multi-verse of universes is infinite, at some point you would find an Earth-like planet  with a person just like you, Greene asserts.  Really?

Instead of universes, we'll consider sets of numbers, because it seems much simpler.  A set of even integers is definitely infinite, but you would never find a single odd integer.  Likewise, a set of all positive numbers is infinite, but it excludes the equally infinite set of negative numbers. 

So in an infinite universe, would you necessarily find a duplicate of Earth? Maybe our and other  universes have a property corresponding to positive, negative, rational or irrational. If what extends to infinity is "negative" universes, do not expect to ever encounter our "positive" one. 

But wouldn't there also be a "positive" infinity of universes? Maybe. But isn't it possible that the positive infinity of universes follows the negative one? In that case, no matter how far you travel, you'd never find one.

 Or perhaps the cosmos somehow limits the number of ways that elementary particles can combine. Could there be an as yet unknown law of nature that constricts universes so that no two are exactly alike?  Maybe only 1 percent of universes can be identical. Who knows? 

Moreover, odds are that if a universe identical to ours is out there somewhere, it's probably exceedingly far away.  Since superluminal (faster than the speed of light)  travel is impossible, it could take longer than the age of universe to get there, billions, trillions or quadrillions of light years away.

The bottom line here is that if there is another "you" in the universe of universes, you will find her or him, unless your lifespan could somehow be increased to 1,000 billion trillion quadrillion years.