Echoing Robert Frost, cosmologists seem torn between theories that the universe will end in fire and those that favor ice. In recent years, ice seemed the victor: The evidence appeared to imply a fate in which every galaxy would end up alone, surrounded by vast, cold emptiness. Andrei Linde of Stanford University, one of the lead architects of cosmology, is turning that idea on its head. He predicts a terminal Big Crunch, in which everything collapses to a fantastically hot, dense dot. He also says it could happen in as little as 10 billion years, in which case the universe is already past middle age.
Linde and his colleague Renata Kallosh came up with this scenario by re-examining some of the assumptions in recent cosmic models. The models build on the discovery that expansion of the universe appears to be speeding up, driven by a mysterious component called dark energy. Cosmologists generally regard dark energy as a kind of repulsive force that acts counter to gravity. Linde and Kallosh say that might not always be the case. Their calculations suggest that dark energy could gradually reverse, dragging the universe back toward a crushing doomsday.
The only way to know for sure, Linde says, is through observation. New generations of telescopes that can examine the light from distant supernova explosions will reveal whether all parts of the visible universe are still expanding. "If it continues accelerating, we don't worry. But if it has already slowed down, there is danger ahead," Linde says.