Parallel universes

There's a fascinating article in Scientific American this month about parallel universes. Based on the idea that space is infinite and using elementary probability, it is likely that you have a doppelgänger about 10 to the power 10²⁸ metres from here, since "even the most unlikely events must take place somewhere".

There are infinitely many other inhabited planets, including not just one but infinitely many that have people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.

I love this idea. There's someone out there who is exactly like me in every way - even down to the clothes I have on - and who's typing this, but didn't correct the typing error that I just did. And another one who did correct it, but who has the Beatles album Help! instead of Sgt Pepper. And another one who is still set on doing a Maths with Computer Science degree at uni instead of having changed her mind to Physics with Computer Science instead, or who failed her driving test, or who accepted the job offer she received in February, and another one who's done all of the above.

This type of physics is why I chose to apply for a Physics degree - it's so interesting, and I want to find out more about it! And thanks to Schrödinger's Cat (or at least, the physics behind the experiment) I know that it is literally true that when I receive my A-level results in August until I open the envelope and see them I have both passed and failed; got 4 'A' grades and 4 'U' grades and everything in between. Until I see the result, all possible results are true.

I'm still in awe that this stuff is science fact, not fiction. (And I hope I'm not misrepresenting it here.) It was a big enough shock when I found out that light doesn't travel in straight lines.

So should you believe in parallel universes? The principal arguments against them are that they are wasteful and that they are weird. The first argument is that multiverse theories are vulnerable to Occam's razor because they postulate the existence of other worlds that we can never observe. Why should nature be so wasteful and indulge in such opulence as an infinity of different worlds?

Yet this argument can be turned around to argue for a multiverse. What precisely would nature be wasting? Certainly not space, mass or atoms--the uncontroversial Level I multiverse already contains an infinite amount of all three, so who cares if nature wastes some more? The real issue here is the apparent reduction in simplicity. A skeptic worries about all the information necessary to specify all those unseen worlds.