Trouble in the Multiverse

BY PETER KASSAN

I think I can safely say that nobody understands quantum mechanics.

—Richard Feynman

The boundary between science and mere scientific speculation can be elusive. Albert Einstein famously performed only thought experiments, but those mere ideas yielded counterintuitive predictions leading to experiments conclusively confirming his revolutionary theory. Other thought experiments imagined by Einstein and his colleagues meant to demonstrate the impossibility of quantum theory actually turned out to be conductible. When performed, those experiments refuted Einstein’s arguments and help confirm the quantum.

Recently, however, some much more troublesome (and troubling) ideas have been advanced by some astrophysicists and cosmologists: string theory and the multiverse. The motivation and justification of string theory is to bring order to the menagerie of subatomic particles. String theory posits that we live not in a four-dimensional universe of space-time (once a highly counterintuitive notion, but now firmly established) but in a universe of many more dimensions (10 or 11, at last count), most of which we ordinary humans fail to notice simply because we’re unable to move in or through them (and because they’re very, very small relative to the more familiar ones). The usual analogy is that of two-dimensional creatures living in a flatland—on a surface (either a plane extending infinitely in two dimensions or a bounded one such as the surface of a sphere)—who would be unable to perceive a third dimension (and perhaps even to conceive of it). With 10 or more spatial dimensions, we’re told, we can conceive of subatomic particles not as point-like entities but as string-like ones vibrating in modes that can account for the variety of particles actually observed. However, no testable predictions have yet been advanced to confirm or disprove the idea.