One of the most common criticisms of the many-worlds interpretation (MWI) of quantum mechanics is that it is absurdly complicated, and therefore violates Occam’s razor. Most people’s first reaction, on hearing of MWI, think that the theory is (to quote Martin Gardner) “bizarre”, “monstrous”, “fantastic”, “radical”, “appalling”, “nonsense”, “frivolous”, and “low”. And many people seem to think that theorists who ascribe to MWI have their heads in the clouds to believe such nonsense. MWI seems to be taken, in fact, as evidence that physics has lost its way—as if (supposedly) blind belief in such frivolity is indicative of a philosophical rot that pervades theorists like me.
There are so many refutations of such criticisms that I don’t know where to start. First of all, although MWI is popular, it is by no means canon, and I daresay that a majority of physicists reject it still. So there! We’re not all sheep. Still, MWI has become almost mainstream (especially with cosmologists) so maybe it’s the cosmologists and the ivory-tower theorists who should be singled out for criticism?
People who think this have probably never met a theoretical physicist before in their life. Getting such people to agree is like herding cats; every theory one puts forth (in a journal article or in a conference talk) is debated, criticized—dare I say, attacked. And that is as it should be. There is not, contrary to popular belief, some holy scripture that every theorist quotes verbatim. We are all different, and have basically come to interpret quantum mechanics in our own personal way…not at the behest of some lord on high.
How do I know this? Because I was never taught about interpretations of quantum mechanics. Ever. Everything I know about such things, I learned on my own since graduation. Thinking of taking a quantum mechanics class at your local university? Guess what: they will probably not talk about MWI, or the Copenhagen interpretation, or Schrodinger’s f***ing cat. Why not? Because those are philosophy topics, not physics. You can do quantum mechanics without ever interpreting a single thing. There’s no crying in baseball, and there’s no philosophy in quantum mechanics. It is a purely mathematical theory, that undeniably works, and most people just leave it at that. The idea that thousands of physicists subscribe to one particular world-view just because they constitute a single monolithic conformist society is ludicrous. Invite a physicist to lunch if you don’t believe me.
But I still haven’t addressed the idea that MWI is obviously absurd. It is absurd, right? I mean, come on!
But wait. Let’s think back to the Copernican revolution. It’s obvious that the Earth is stationary, no? I bet people thought that Copernicus and Galileo and their ilk were bizarre, monstrous, fantastic, radical, appalling, nonsensical, frivolous, and low.
And what about the idea that there are billions and billions of galaxies, each with billions and billions of stars? We forget now, but this idea was radical when first presented and wasn’t settled until the 1920’s. Why are we OK with a multiplicity of stars, but not a multiplicity of universes? Why aren’t people complaining about the absurd notion (fact) that there are more stars in the observable universe than there are grains of sand on Earth’s beaches?
So, Occam’s razor. MWI just seems to have too much baggage, right? For a lot of people MWI is too high a cost to bear to have a mathematically simple interpretation of quantum mechanics. And let’s be clear: MWI is a simpler theory than (say) the Copenhagen interpretation (CI). For you can start with three postulates, and add a fourth about wave-function collapse, and you get CI. Or you can start with just three, and say nothing of wave-function collapse, and you get MWI. Which interpretation seems simpler now? MWI is a consequence of accepting the three basic postulates of quantum mechanics. If you don’t like that, then you must introduce a fourth postulate ex nihilo to make yourself feel better.
But wait! you say. 10100 universes doesn’t seem simpler. It’s a huge number! It’s ridiculous!
OK. You wanna go there? I’ll turn the argument around. By that rationale, you probably believe that there are only a finite number of integers, because any finite number is simpler than infinity. There. That makes sense, right?
The truth is that an infinite set is often simpler than a single member of that set. Take the natural numbers. I can write a computer program in BASIC that writes every natural number. Here it is:
20 PRINT x
40 GOTO 20
On the other hand, if I want to print out the number
then my computer program is longer:
10 PRINT “5679200359662711389685023885761799”
Count the keystrokes. The second program requires more typing. And note that the first (simpler) program will eventually print this number—the long arbitrary program is “contained” within the first.
In information theory, the information “content” of something is related to its algorithmic complexity—roughly speaking, how easy it is to write a computer program that “specifies” the object. By that measure, “all the natural numbers” is a simpler concept than the number
Similarly, “all possible universes” is a much simpler concept than one specific arbitrary universe. You want to recreate this universe? Good luck…you’ll have to specify the position and momentum of every particle in the universe. That’s a long computer program. However, if you just say “create all possible universes” then eventually this one will pop up…
Do I believe in the MWI? Yes. Why? It’s not because I was indoctrinated into such belief; I don’t think a single professor in graduate school ever mentioned MWI. It’s because I’ve looked at the evidence over a number of years, and (tentatively) decided that it fits the data best. That is the only reason to ever believe something, ever. It fits the data best. But I stress that my conclusion is tentative because, hey, it’s science. There is no dogma. There is just stuff that we are 99.44% sure of.
Like evolution by natural selection, or heliocentrism, or the existence of ghosts. I mean, seeing’s believing, right?
[Note: more Americans believe in ghosts than evolution. Sigh.]
If you enjoyed this post, you may also enjoy my book Why Is There Anything? which is available for the Kindle on Amazon.com.
I am also currently collaborating on a multi-volume novel of speculative hard science fiction and futuristic deep-space horror called Sargasso Nova. Publication of the first installment will be January 2015; further details will be released on Facebook, Twitter, or via email: SargassoNova (at) gmail.com.