Somewhere out there is a happy ending to everything

Originally published 3 June 1991

One of the wack­i­er ideas to have emerged from mod­ern physics is par­al­lel uni­vers­es. That’s right, folks. This uni­verse that we live in may not be the only uni­verse. There may exist an uncount­able num­ber of uni­vers­es, some near­ly iden­ti­cal to this one, oth­ers wild­ly dif­fer­ent. Even as you read, zil­lions of new uni­vers­es may be blos­som­ing into existence.

If these oth­er uni­vers­es exist, then some of them con­tain oth­er yous and oth­er mes.

How strange those words look on the page: You and me in the plur­al. There are no such words in the dic­tio­nary. Until recent­ly there have been no such con­cepts in West­ern phi­los­o­phy. But, then again, that oth­er me in that oth­er uni­verse may not be me, by virtue of being there. On the oth­er hand, that par­al­lel me may be more like this me than the me that I will be a moment hence.

Oh dear, this is get­ting out of con­trol. I’d bet­ter back up a bit.

It all start­ed with Schrödinger’s cat.

Erwin Schrödinger was one of the founders of quan­tum physics, a math­e­mat­i­cal way of describ­ing the world that has proven fab­u­lous­ly suc­cess­ful. In fact, quan­tum physics is per­haps the most suc­cess­ful phys­i­cal the­o­ry there ever was, in the ways it sat­is­fac­to­ri­ly describes the world we expe­ri­ence. The trou­ble is, no one knows quite why quan­tum physics works.

A kind of fuzziness

When quan­tum physics is used to describe phys­i­cal events, the descrip­tions have a kind of fuzzi­ness. For exam­ple, if one tries to pin down the posi­tion of an elec­tron, then the elec­tron’s veloc­i­ty nec­es­sar­i­ly becomes less pre­cise­ly known — the so-called Uncer­tain­ty Prin­ci­ple. This fuzzi­ness is not just a prod­uct of our igno­rance, but seems to be built right into the fab­ric of reality.

This same fuzzi­ness applies to ener­gy and time, and to oth­er phys­i­cal con­cepts we use to describe the world. In the quan­tum world, pre­cise descrip­tion and pre­dic­tion is impos­si­ble. The best we can do is describe the prob­a­bil­i­ty that when we make an obser­va­tion a cer­tain thing will be observed.

The cat, for example.

Schrödinger imag­ined a cat inside a box. Also in the box is a lit­tle bit of radioac­tive mate­r­i­al, and a radi­a­tion detec­tor that will trig­ger a trip on a ham­mer poised above a glass vial con­tain­ing cyanide. If even a sin­gle par­ti­cle is emit­ted by the radioac­tive sub­stance, the ham­mer will fall, the vial will break, and the cat will die.

With the box closed, let us turn on the detec­tor for just long enough that the prob­a­bil­i­ty of a par­ti­cle being emit­ted is 50 – 50. Accord­ing to quan­tum physics, the emis­sion of par­ti­cles by radioac­tive sub­stances has an intrin­sic ran­dom­ness to it. We can know noth­ing about the exact time a par­ti­cle will be emit­ted, only the prob­a­bil­i­ty that a par­ti­cle will be emit­ted dur­ing an inter­val. At the atom­ic lev­el, nature is fuzzy.

So what is in the box after the exper­i­ment is run? A dead cat? A live cat? Appar­ent­ly, there is no way to know with­out open­ing the box and look­ing in. But Schrödinger still held to the clas­si­cal idea that nature is strict­ly deter­min­is­tic, and the uncer­tain­ty about the cat’s fate struck him as unsat­is­fac­to­ry. If there is noth­ing in the laws of nature to unam­bigu­ous­ly spec­i­fy the out­come of the obser­va­tion, he asked, then why should nature chose one out­come rather than another?

Parallel universes

But maybe, just maybe, nature does­n’t choose between two equal­ly prob­a­ble out­comes. Some physi­cists believe that both out­comes actu­al­ly hap­pen. The par­ti­cle is emit­ted and it isn’t emit­ted. The detec­tor trips the ham­mer and the detec­tor does not trip the ham­mer. Instead of set­tling for one or the oth­er out­come, the uni­verse splits into two simul­ta­ne­ous, non-inter­act­ing uni­vers­es. In one uni­verse the cat dies; in the oth­er uni­verse the cat lives.

And that’s why quan­tum physics (and nature) appears fuzzy, say these physi­cists. It’s because the uni­verse is con­stant­ly split­ting into a stu­pen­dous num­ber of branch­es. The world is con­stant­ly branch­ing into myr­i­ad near copies of itself. All of these par­al­lel uni­vers­es ful­ly exist in some hyper­space and hyper­time, but we are only aware of the uni­verse we live in. The ensem­ble of all uni­vers­es is pre­cise­ly deter­mined by the laws of nature; our uni­verse appears fuzzy because we see only a part of the whole.

Now if all of this sounds wild­ly far­fetched and almost impos­si­ble to under­stand, well, it’s because it is wild­ly far­fetched and almost impos­si­ble to under­stand (which is not to say that some wild­ly imag­i­na­tive physi­cists don’t take it seri­ous­ly). I only men­tion it because it’s base­ball sea­son. And, well, the Sox are off to a good start, but you know what’s going to hap­pen.

In this uni­verse (the one we inhab­it) they’ll win the pen­nant and lose the Series in the bot­tom of the last inning of the sev­enth game. Two men out, a man on base, the Sox lead­ing by one run. A grounder to short. The throw to first. A bounce — to the left, or to the right — a bounce so fine­ly tuned that it all depends on a quan­tum event occur­ring some­where back along the line of end­less­ly-fis­sion­ing par­al­lel universes.

The bounce is to the left. The catch is missed. The next man up knocks the ball out of the park. The Sox, not unex­pect­ed­ly, lose.

But here, dear friends, is a source of melan­choly solace. In any num­ber of par­al­lel uni­vers­es the bounce is to the right and the catch is made. In those oth­er uni­vers­es, oth­er yous and oth­er mes cel­e­brate a Sox vic­to­ry. And in some greater heav­en that over­looks all of these par­al­lel uni­vers­es, Schrödinger’s cat smiles.