The universe is out of control. Not only is it expanding but the expansion itself is accelerating. Most likely, such expansion can end only one way: in stillness and total darkness, with temperatures near absolute zero, conditions utterly inhospitable to life. That became evident in 1998, when astronomers at the Lawrence Berkeley National Laboratory and Australian National University were analyzing extremely distant, and thus ancient, Type Ia supernova explosions to measure their rate of motion away from us. (Type Ia supernovas are roughly the same throughout the universe, so they provide an ideal “standard candle” by which to measure the rate of expansion of the universe.)
Physicists, scrambling to their blackboards, deduced that a “dark energy” of unknown origin must be acting as an antigravitational force, pushing galaxies apart. The more the universe expands, the more dark energy there is to make it expand even faster, ultimately leading to a runaway cosmos. Albert Einstein introduced the idea of dark energy mathematically in 1917 as he further developed his theory of general relativity. More evidence came last year, when data from the Wilkinson Microwave Anisotropy Probe, or WMAP, which analyzes the cosmic radiation left over from the Big Bang, found that dark energy makes up a full 73 percent of everything in the universe. Dark matter makes up 23 percent. The matter we are familiar with—the stuff of planets, stars, and gas clouds—makes up only about 4 percent of the universe.
As the increasing amount of dark energy pushes galaxies apart faster and faster, the universe will become increasingly dark, cold, and lonely. Temperatures will plunge as the remaining energy is spread across more space. The stars will exhaust their nuclear fuel, galaxies will cease to illuminate the heavens, and the universe will be littered with dead dwarf stars, decrepit neutron stars, and black holes. The most advanced civilizations will be reduced to huddling around the last flickering embers of energy—the faint Hawking radiation emitted by black holes. Insofar as intelligence involves the ability to process information, this, too, will fade. Machines, whether cells or hydroelectric dams, extract work from temperature and energy gradients. As cosmic temperatures approach the same ultralow point, those differentials will disappear, bringing all work, energy flow, and information—and the life that depends on them—to a frigid halt. So much for intelligence.
A cold, dark universe is billions, if not trillions, of years in the future. Between now and then, humans will face plenty of other calamities: wars and pestilences, ice ages, asteroid impacts, and the eventual consumption of Earth—in about 5 billion years—as our sun expands into a red giant star. To last until the very end of the universe, an advanced civilization will have to master interstellar travel, spreading far and wide throughout the galaxy and learning to cope with a slowing, cooling, darkening cosmos. Their greatest challenge will be figuring out how to not be here when the universe dies, essentially finding a way to undertake the ultimate journey of fleeing this universe for another.
Such a plan may sound absurd. But there is nothing in physics that forbids such a venture. Einstein’s theory of general relativity allows for the existence of wormholes, sometimes called Einstein-Rosen bridges, that connect parallel universes. Among theoretical and experimental physicists, parallel universes are not science fiction. The notion of the multiverse—that our universe coexists with an infinite number of other universes—has gained ground among working scientists.
