After the discovery of dark energy, Perlmutter concluded that the next generation of dark-energy telescopes would have to include a space-based observatory. But the search for financing for such an ambitious project can require as much forbearance as the search for dark energy itself. “I don’t think I’ve ever seen as much of Washington as I have in the last few years,” he says, sighing. Even if his Supernova Acceleration Probe didn’t now face competition from several other proposals for federal financing (including, perhaps inevitably, one involving his old rival Riess), delays have prevented it from being ready to launch until at least the middle of the next decade. “Ten years from now,” says Josh Frieman of the University of Chicago, “when we’re talking about spending on the order of a billion dollars to put something up in space — which I think we should do — you’re getting into that class where you’re spending real money.”

Even some cosmologists have begun to express reservations. At a conference at Durham University in England last summer, a “whither cosmology?” panel featuring some of the field’s most prominent names questioned the wisdom of concentrating so much money and manpower on one problem. They pointed to what happened when the government-sponsored Dark Energy Task Force solicited proposals for experiments a couple of years ago. The task force was expecting a dozen, according to one member. They got three dozen. Cosmology was choosing a “risky and not very cost-effective way of moving forward,” one Durham panelist told me later, summarizing the sentiment he heard there.

But even if somebody were to figure out whether or not dark energy changes across time and space, astronomers still wouldn’t know what dark energy itself is. “The term doesn’t mean anything,” said David Schlegel of Lawrence Berkeley National Laboratory this past fall. “It might not be dark. It might not be energy. The whole name is a placeholder. It’s a placeholder for the description that there’s something funny that was discovered eight years ago now that we don’t understand.” Not that theorists haven’t been trying. “It’s just nonstop,” Perlmutter told me. “There’s article after article after article.” He likes to begin public talks with a PowerPoint illustration: papers on dark energy piling up, one on top of the next, until the on-screen stack ascends into the dozens. All the more reason not to put all of cosmology’s eggs into one research basket, argued the Durham panelists. As one summarized the situation, “We don’t even have a hypothesis to test.”

Michael Turner won’t hear of it. “This is one of these godsend problems!” he says. “If you’re a scientist, you’d like to be around when there’s a great problem to work on and solve. The solution is not obvious, and you could imagine it being solved tomorrow, you could imagine it taking another 10 years or you could imagine it taking another 200 years.”

But you could also imagine it taking forever.

“Time to get serious.” The PowerPoint slide, teal letters popping off a black background, stared back at a hotel ballroom full of cosmologists. They gathered in Chicago last winter for a “New Views of the Universe” conference, and Sean Carroll, then at the University of Chicago, had taken it upon himself to give his theorist colleagues their marching orders.

“There was a heyday for talking out all sorts of crazy ideas,” Carroll, now at Caltech, recently explained. That heyday would have been the heady, post-1998 period when Michael Turner might stand up at a conference and turn to anyone voicing caution and say, “Can’t we be exuberant for a while?” But now has come the metaphorical morning after, and with it a sobering realization: Maybe the universe isn’t simple enough for dummies like us humans. Maybe it’s not just our powers of perception that aren’t up to the task but also our powers of conception. Extraordinary claims like the dawn of a new universe might require extraordinary evidence, but what if that evidence has to be literally beyond the ordinary? Astronomers now realize that dark matter probably involves matter that is nonbaryonic. And whatever it is that dark energy involves, we know it’s not “normal,” either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.

That possibility always gnaws at scientists — what Perlmutter calls “that sense of tentativeness, that we have gotten so far based on so little.” Cosmologists in particular have had to confront that possibility throughout the birth of their science. “At various times in the past 20 years it could have gotten to the point where there was no opportunity for advance,” Frieman says. What if, for instance, researchers couldn’t repeat the 1963 Bell Labs detection of the supposed echo from the big bang? Smoot and John C. Mather of NASA (who shared the Nobel in Physics with Smoot) designed the Cosmic Background Explorer satellite telescope to do just that. COBE looked for extremely subtle differences in temperature throughout all of space that carry the imprint of the universe when it was less than a second old. And in 1992, COBE found them: in effect, the quantum fluctuations that 13.7 billion years later would coalesce into a universe that is 22 percent dark matter, 74 percent dark energy and 4 percent the stuff of us.