Relaxing on an idyllic beach on Grand Cayman Island in the Caribbean, Anthony Aguirre vividly describes the worst natural disaster he can imagine. It is, in fact, probably the worst natural disaster that anyone could imagine. An asteroid impact would be small potatoes compared with this kind of event: a catastrophic encounter with an entire other universe.
As an alien cosmos came crashing into ours, its outer boundary would look like a wall racing forward at nearly the speed of light; behind that wall would lie a set of physical laws totally different from ours that would wreck everything they touched in our universe. “If we could see things in ultraslow motion, we’d see a big mirror in the sky rushing toward us because light would be reflected by the wall,” says Aguirre, a youthful physicist at the University of California at Santa Cruz. “After that we wouldn’t see anything—because we’d all be dead.”
There is a sober purpose behind this apocalyptic glee. Aguirre is one of a growing cadre of cosmologists who theorize that our universe is just one of many in a “multiverse” of universes. In their effort to grasp the implications of this idea, they have been calculating the odds that universes could interact with their neighbors or even smash into each other. While investigating what kind of gruesome end might result, they have stumbled upon a few surprises. There are tantalizing hints that our universe has already survived such a collision—and bears the scars to prove it.
Aguirre has organized a conference on Grand Cayman to address just such mind-boggling matters. The conversations here venture into multiverse mishaps and other matters of cosmological genesis and destruction. At first blush the setting seems incongruous: The tropical sun beats down dreamily, the smell of broken coconuts drifts from beneath the palm trees, and the ocean roars rhythmically in the background. But the locale is perhaps fitting. The winds are strong for this time of year, reminding the locals of hurricane Ivan, which devastated the capital city of George Town in 2004, lifting whole apartment blocks and transporting buildings across streets. In nature, peace and violence are never far from each other.
Much of today’s interest in multiple universes stems from concepts developed in the early 1980s by the pioneering cosmologists Alan Guth at MIT and Andrei Linde, then at the Lebedev Physical Institute in Moscow. Guth proposed that our universe went through an incredibly rapid growth spurt, known as inflation, in the first 10-30 second or so after the Big Bang. Such extreme expansion, driven by a powerful repulsive energy that quickly dissipated as the universe cooled, would solve many mysteries. Most notably, inflation could explain why the cosmos as we see it today is amazingly uniform in all directions. If space was stretched mightily during those first instants of existence, any extreme lumpiness or hot and cold spots would have immediately been smoothed out. This theory was modified by Linde, who had hit on a similar idea independently. Inflation made so much sense that it quickly became a part of the mainstream model of cosmology.
