Why Does the World Exist: An Existentia - By Jim Holt Page 0,78
physicist Hugh Everett III in the form of his many-worlds interpretation, it says that the different possible outcomes of a quantum measurement correspond to parallel universes, all coexisting in some sort of larger reality. The inflationary multiverse, by contrast, was suggested by cosmological considerations. It encompasses an infinity of bubble universes, each arising with its own Big Bang out of a primordial chaos.
The worlds making up the inflationary multiverse are separated from one another by regions of space that, since they are expanding faster than the speed of light, cannot be traversed. By contrast, the worlds making up the quantum multiverse are separated from one another by … well, no one can quite say. The image of quantum worlds “branching off” from one another suggests that they are in some sense close together; so does the notion of such parallel worlds jostling one another ever so slightly (as in the double-slit experiment).
Given such differences, one might think that we are talking about two distinct species of multiverse here. Surprisingly, though, there are distinguished physicists who happily conflate the two. One such is Leonard Susskind, a coinventor of string theory. “The many-worlds [multiverse] of Everett seems, at first sight, to be quite a different conception than the eternally-inflating universe,” Susskind has observed. “However, I think the two may really be the same thing.”
Susskind’s belief in the identity of these two seemingly distinct versions of the multiverse puzzled me, so I made sure to mention it to Steven Weinberg. “I found it puzzling too,” he said. “I’ve spoken to other people about it, and they don’t understand it either.” Although Weinberg is himself sympathetic to the many-worlds interpretation of quantum mechanics, he finds it “completely perpendicular” to the issue of the inflationary multiverse. In other words, Weinberg could see no reason to equate the two multiverses, as Susskind did. “I don’t agree with Susskind on that,” Weinberg told me, “and I don’t know why he said it.”
Whether the multiverses posited by physicists are one or many, they are certainly contingent, not necessary. There is nothing within them that explains why they exist. And the individual worlds a multiverse comprises, while randomly varying in their features, nevertheless obey the same laws of nature—laws that inexplicably take one particular form rather than another. So even the most extravagant multiverse, conceived in merely physical terms, leaves unresolved a pair of fundamental questions: Why these laws? And why should there be a multiverse that embodies them, rather than nothing at all?
“It is probable that there is some secret here which remains to be discovered,” observed the great nineteenth-century American pragmatist philosopher C. S. Peirce—the same thinker, as it happens, who mockingly regretted that universes are not “as plentiful as blackberries.” Physics alone seems impotent to discover this secret. And that has driven some physicists to flirt with—and even embrace—a mystical way of thinking about reality which harkens back to Plato, if not to Pythagoras.
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PLATONIC REFLECTIONS
See Mystery to Mathematics fly!
In vain! they gaze, turn giddy, rave, and die.
—ALEXANDER POPE, The Dunciad
Mysticism and mathematics go way back together. It was the mystical cult of Pythagoras that, in ancient times, invented mathematics as a deductive science. “All is number,” proclaimed Pythagoras—by which he seemed to mean that the world was quite literally constituted by mathematics. It is little wonder that the Pythagoreans worshipped numbers as a divine gift. (They also believed in the transmigration of souls and held the eating of beans to be wicked.)
Today, two and a half millennia later, mathematics still has a whiff of the mystical about it. A majority of contemporary mathematicians (a typical, though disputed, estimate is about two-thirds) believe in a kind of heaven—not a heaven of angels and saints, but one inhabited by the perfect and timeless objects they study: n-dimensional spheres, infinite numbers, the square root of –1, and the like. Moreover, they believe that they commune with this realm of timeless entities through a sort of extrasensory perception. Mathematicians who buy into this fantasy are called “Platonists,” since their mathematical heaven resembles the transcendent realm described by Plato in his Republic. Geometers, Plato observed, talk about circles that are perfectly round and infinite lines that are perfectly straight. Yet such perfect entities are nowhere to be found in the world we perceive with our senses. The same is true, Plato held, of numbers. The number 2, for instance, must be composed of a pair of perfectly equal units; but no two things in the sensible world are perfectly equal.