Scientific American January 1999 [antikvár]

FROM THE EDITORS Getting Complicated he fate of the universe used to be so simple. It was either fire or ice. Either the combined gravity of the universe would bring its expansion to a halt, compelling the cosmos to replay the big bang in reverse, or else gravity would steadily weaken and the universe would expand forever, slowly and inexorably pulling planets, stars and galaxies apart until it became a barren, frigid void. Now cosmologists realize that things aren't so straightforward. The universe may not be governed by the gravity of ordinary matter after all. If the latest observations of the distant universe (as discussed in our special report, beginning on page 27) are borne out, matter has little say in its own fate. Instead the universe may be controlled by the so-called cosmological constant, a surreal form of energy that imparts a gravitational repulsion rather than the usual attraction. The idea of the constant has been embraced and renounced more than once since Albert Einstein initially proposed it 80 years ago. This time it may be here to stay. At first glance its shadowy reinforcement of cosmic expansion suggests that, as the ultimate fate, ice will have to suffice. But that judgment is premature. Because physicists know so little—"nothing" would be a fair approximation—about the constant, the fate of the universe is back where it started: in the realm of uncertainty. One implication is that science writers who have been using Robert Frostian fire-and-ice allusions will have to find a new metaphor. Another is that the cosmos might be undergoing a second round of "inflation," a resurgence of the process that, 12 billion or so years ago, caused space to go bang. Just as that earlier period of explosive growth ended—giving form and light to what had been void—so, too, might the rekindled inflation. If so, the universe will expand to unimaginable proportions, the constant will fade away and physical possibilities will unfold that are only dimly perceived in today's theories. If there is a story to be seen in cosmic history, it is the march from the utter simplicity of the big bang to ever increasing complexity and diversity. The near-perfect uniformity of the primordial fireball, and of the laws that governed it, has steadily given way to a messy but fertile heterogeneity: photons, subatomic particles, simple atoms, stars, complex atoms and molecules, galaxies, living things, artificial things. Understanding how this intricacy is immanent in the fundamental laws of physics is one of the most perplexing philosophical puzzles in science. The basic rules of nature are simple, but their consummation may never lose its ability to surprise. A perpetual trend toward richness, the outcome of which cannot be foreseen, may be the true fate of the universe. Geometry of space-time?