How It All Started
To understand the latest discovery about how the universe began, it helps to go back to the saga of the pigeon poop. In 1964, two radio astronomers at Bell Labs were working on an antenna for the new Telstar communications-satellite system. But no matter where Arno Penzias and Robert Wilson pointed the horn-shaped antenna, it picked up a hiss. Some kibitzers suspected that bird droppings in the antenna might be responsible, so the astronomers shoveled out the guano and shooed away the birds. Still the hiss. Scientists at Princeton University eventually traced the sound to a somewhat more distant source: the hiss was radiation left over from the cosmic fireball in which the universe was created. This "cosmic microwave background radiation" has cooled off in the 13 billion to 16 billion years since the big bang, but it still fills the heavens like a faint whisper of creation. It provides such a good clue to the conditions that created the universe that in 1992, when cosmologists first measured it in detail, they declared that they were seeing "the handwriting of God."
Last week scientists announced that they had performed what amounts to a detailed handwriting analysis. Using a telescope carried by a balloon above Antarctica, the "Boomerang" experiment produced the first-ever high-resolution map of the cosmic radiation, 40 times finer than anything done before. The measurements confirm theories of how the world began by offering "the first clear images of the embryonic universe," said astrophysicist Andrew Lange of the California Institute of Technology, co-leader of the Boomerang team with Paolo de Bernardis of the University of Rome. They also offer the strongest clue yet as to how it will end.
Lange's team had headed for Antarctica in late 1998 because of the breeze. Every year, around Christmas, a strange circular wind blows around the southern continent. When the launch window opened, the team inflated a monstrous sack of helium that eventually reached the size of a football stadium, lifted a two-ton telescope 23 miles high and then circled for 10 days before returning to its starting point. (Thus "Boomerang.") Aimed at the stretch of sky between the Earth below and the balloon above, the device was able to measure temperature differences in the cosmic microwave background of less than one hundred-millionth of a degree Celsius, using devices called bolometers. (These gadgets are cool enough to have inspired a limerick: "O Langley invented the bolometer/A very good kind of thermometer./You can measure the heat/ from a penguin bird's seat,/From a distance of half a kilometer.")
The cosmic radiation was born when the universe was about 300,000 years old, long before the formation of stars. At this tender age, the cosmos was 1,000 times hotter and 1,000 times smaller than it is today. Until then, it was so hot and dense that radiation was "tightly glued to matter," as physicist Wayne Hu of the Institute for Advanced Study writes in the journal Nature, and could not escape until the universe cooled down a bit. Once the radiation escaped, it raced along with the expanding universe. The wavelength of the radiation stretched out, like a wavy rubber band embedded in a rising loaf of dough. By now the radiation has stretched so much that it has become a sea of microwaves--the cosmic microwave background.
Boomerang discovered hotter spots and cooler spots in the radiation. Spots of different temperatures are the holy grail of cosmology, because they mark places where the baby universe had different densities--that is, more matter here, less matter there. "Gravity acts like a piston, compressing everything," says astrophysicist Michael Turner of the University of Chicago. Just as compressing air makes it warmer, gravity made dense spots hotter. The temperature differences seen today, then, actually reflect "tiny density fluctuations in the primordial soup of particles," says Hu.
These density fluctuations are important because they served as seeds for the galaxies and clusters of galaxies that are now spangled across the sky. The dense spots acted like city buses that bunch up. If one bus gets too close to the one in front of it (equivalent to the density of matter increasing in a spot), then buses behind it catch up. Pretty soon the whole blasted line is clumping together. So it was with the universe. A little bit of extra matter exerted a gravitational pull on other matter until slight excesses grew huge, giving birth to the galaxies and clusters of galaxies, surrounded by voids, that bedeck the sky.
The sizes of the hot spots offer a clue to the fate of the universe. Hot spots, recall, are the footprints of dense areas in the newborn universe. Einstein showed that matter can warp space, like balls on a rubber sheet. A bowling ball would warp the sheet a lot; a Ping-Pong ball would warp it a little. The hot (dense) spots measured by Boomerang turn out to be just the right size to warp the universe enough to keep it from expanding so wildly that its galaxies, its stars and its very atoms will drift apart until they are lonely specks in a near-empty cosmos. But the universe is not so dense that its gravity will pull the cosmos back in a reverse of the big bang--known fondly as the big crunch. At the very least, says Hu, the universe "won't collapse in the next 10 to 20 billion years." A world ending in fire--or in ice--doesn't seem to be in the cards any time soon.
Boomerang did present scientists with one puzzle. The amount of matter it measures in the universe exceeds what astronomers have calculated by adding up the weights of all the galaxies and other objects in the cosmos. What, then, is the missing matter? Normal atoms make up only about 5 percent of the universe. The rest must be exotic stuff that scientists have dubbed WIMPs and axions. "It's a very odd recipe for a universe," says Turner, "but it looks like that's what we've got." Now that scientists have seen the universe's destiny, perhaps they can figure out its ingredients.