Originally published 10 June 2003
The May [2003] issue of Scientific American has been laying on my desk for weeks now. The teaser on the cover keeps jumping out at me, some days more forcefully than others: “Parallel Universes Really Exist.”
Note that the teaser says “really” exist, not “may” exist. As if doubt was unthinkable. And why some days rather than others? We’ll get to that in a moment.
The article in question is written by astrophysicist Max Tegmark of the University of Pennsylvania, who makes his living studying the universe (ours) on the largest scale. He doesn’t claim to have visited a parallel universe, but he does contend that the existence of parallel universes is affirmed by empirical evidence.
Which means that beyond this universe that we observe with our telescopes there are other universes, perhaps an infinite number. Some of them are identical to our own, down to the smallest detail, except that — uh, oh! — maybe in the next instant they will diverge, going their separate ways.
Somewhere among those myriad universes you and I have a doppelgänger — an exact duplicate — maybe a bunch of them, living on planets exactly like the earth.
Tegmark describes four ways that parallel universes might exist. For a complete explanation, you should read Tegmark’s article. But let me see if I can describe what he calls Level I parallel universes, which are regions of space too far away for their light to have reached us yet.
The farthest we can observe is about 42 billion light-years, the distance light has been able to travel since the big bang 14 billion years ago. (The distance is greater than 14 billion light-years because cosmic expansion has stretched distances.)
But current observations suggest that the universe is infinite in extent, which means that most of it is unobservable. Within our observable bubble of infinite space there are a very large but finite number of particles, which have therefore a vastly larger but still finite number of arrangements.
If the universe is infinite, then somewhere out there are other bubbles of space with the same arrangement of particles as here. Also bubbles with every other conceivable arrangement of particles that is consistent with the laws of physics.
Yeah, yeah, I know. Spooky. Really spooky. But if you think this is bizarre, wait till you get to Tegmark’s Level III parallel universes, based on the laws of quantum physics. At every instant, every one of an infinity of universes splits into multiple universes representing every conceivable outcome of every quantum event. Infinities of infinities.
Or his Level IV parallel universes, in which the laws of physics themselves are variable.
Tegmark claims that these speculations are not mere pipe dreams. Since they are based on the laws of physics as we know them (except for IV), and because they can conceivably be refuted by observation, they qualify as science, he says.
So what is this to you and me?
Well, consider this. Right now I’m looking at a “to do” list as long as my arm, and I haven’t a clue how I’m going to get it all done. It gives me a certain solace to think that at this very instant in some parallel universe my doppelgänger is trapped in an elevator with Cameron Diaz, his “to do” list forgotten.
No kidding. According to Tegmark, precisely this scenario must be somewhere unfolding. I wink. She smiles. Lucky doppelgänger.
There are also parallel universes in which my doppelgänger has a full head of hair, robust good health, and a bulging bank account. There might even be a Level IV universe where time runs backward and my doppelgänger gets younger every year.
You see what I mean? On those days when things look dreary one can imagine a parallel universe where events flow in a more cheerful direction.
But there’s a downside, too. For every parallel universe where I’m trapped in an elevator with Cameron Diaz, there’s another parallel universe where I’m trapped in an elevator with Dick Cheney.
Now that’s spooky.
