Meanwhile, a few experiments are taking furtive stabs at a figure for omega using still other methods. In one approach, several groups of researchers have used the Hubble Space Telescope and ground-based observatories to examine the red-shifts of far distant explosions called Type Ia supernovae. Their measurements seem to show that the Hubble expansion has not slowed appreciably over cosmological time, suggesting that the universe will expand forever and has a value of omega of approximately 0.8. Then again, by looking at X-ray-emitting clusters of galaxies at different ages of the universe and comparing the number density of those clusters, U of C graduate student Daniel Reichert, working with Robert Nichol of Carnegie Mellon University, has obtained a higher value for omega, perhaps as great as 1.

More reliable results should be obtained from steadily improving measurements of the cosmic background anisotropy. While COBE has mapped the cosmic background across the entire sky with an angular resolution of 7 degrees, and ground-based and balloon-borne instruments are mapping small swaths at 1- degree resolution, a definitive answer to omega awaits the first years of the next millennium. Then, a $70-million NASA satellite mission called MAP, for Microwave Anisotropy Probe, will sweep out the sky with a beam of 0.2 degree.

Stephan Meyer, an associate professor of astronomy and astrophysics at Chicago, is an experimentalist who was part of the COBE satellite mission and is on the MAP team as well. The detectors on MAP, Meyer explains, are not the most sensitive. But the probe will have an advantage by virtue of the place from which it will view the sky. After launch in August 2000, MAP will take three months to fly to a spot known as L2, the second Lagrange point. L2 is on the Earth-sun line, but outside Earth’s orbit. The satellite will keep perfect time with the Earth as it orbits the sun, keeping its backside toward both. On the side away from the sun, Meyer explains, the optics will cool to some 60 or 70 kelvin and not change temperature at all. That thermal stability is the key to precise measurement, Meyer says.

The antennas will sweep the sky in a searchlight pattern that “kind of looks like a spirograph between an inner and outer circle,” Meyer says. The outer circle is 180 degrees, so MAP will look at half of the sky, except for the piece right in the middle. “The whole pattern gets repeated every hour or hour and a half, during which we’ve only seen about 40 percent of the sky,” Meyer says. But because the Earth is moving around the sun, the center blind spot sweeps around, so that in a year MAP will see the whole sky.

Even the prospect of MAP’s results has Michael Turner almost dancing on air: “By measuring the tiny 10-microkelvin variations in the temperature, we’ll be able to determine omega. That’s just mind-boggling. It’s been so hard weighing the universe, and all I can tell you is that there’s more than 20 percent of critical density. All of a sudden, we’re going to get [omega] to within 1 percent.”

Yet another probe, a project of the European Space Agency called Planck, is planned for launch five years after MAP. It will boast a beam width of only 0.1 degree. Meyer, who is helping develop the detectors for Planck, says the probe will take measurements at several frequencies to remove interference from the galaxy’s dust emission. “Planck is a much more complicated satellite,” than MAP, he adds, “costing easily five times as much, to do the ultimate experiment.” MAP is very “aimed” at the cold dark matter picture, Meyer says. “If it turns out that the cold dark matter picture is right and everything fits in perfectly, then MAP will have made the important discoveries,” he says. With a scientist’s skepticism, he adds, “I’m guessing that’s just not so. And if MAP doesn’t prove the existence of cold dark matter, Meyer notes, it will not be able to specifically finger any of the other models.

“I believe MAP will fly,” Meyer continues. “It will answer the burning questions of the moment, but it will pose a whole new set. Planck is going to be poised, five years later, just perfectly—we will have digested the questions of MAP, and Planck will be stepping in to answer those.”

If definitive satellite results—from either MAP or Planck—indicate that omega does equal 1, can the cosmologists just go home? The nature of cosmic inflation virtually insures that the universe will then be even more rich with possibilities than it is now. “If you prove inflation takes place, I think you make a very strong case that there is no beginning, there is no end,” Turner says, “for the following reason: What we call the Big Bang is just the beginning of our inflationary patch or region. It’s just when it took off. And if inflation took place once, it probably is taking place constantly—not in our neck of the woods, but somewhere. And it could well be that these regions that inflate develop very differently—as differently as you can possibly imagine. It could be that they have different numbers of spatial dimensions, or that they have different realizations of the laws of physics.”

Meyer too believes that even a conclusive value for omega may not foretell an ultimate fate. “How do we know that there isn’t a larger-scale force than gravity?” he asks. “Suppose you lived in a universe hot enough to be generating nuclei. You wouldn’t know about gravity, because it’s so weak at nuclear scales. You form the light elements, and that’s it,” he says. “You would be unaware of the existence of any force that could change them. You would despair that the nuclei are stable, and you don’t know the best is yet to come: You’ll form stars, galaxies, clusters, planets, and, by God, people. You could not predict people if you did not know about gravity,” he observes. After all, it takes gravity to make stars, and stars to make carbon.

And if the little nuclear guy could not see gravity, Meyer asks, “how can we be sure we have yet seen all the scales of structure and the dominant force of the universe? How do we know there isn’t something to come, that will follow what we perceive as a cold death? We should be careful not to be smug—the answer may lie beyond.”