National Geographic : 2001 Sep
by. This process is known as redshift, and by measuring it-and thus the rate at which the galaxies are flying apart-it's possible to figure how long it has been since they were all con tained together in one point of infinite density at the moment of the creation of the cosmos. In other words, astronomers can use that rate along with other cosmological data to tell how old the universe is. Today's estimate for the expansion rate indicates that the universe is 13 billion years old. Knowing the age of the universe is as impor tant to astronomers as knowing the age of the Earth is to geologists. It lets them start putting together its history. How, for example, did the universe get from a uniform big bang to the state it's in today, with galaxies separated by vast stretches of relatively empty space? Did giant clusters of matter break down into galaxies, or did groups of stars join together? Djorgovski's quasar has a redshift that indi cates it formed less than a billion years after the universe began. "What we're after is the first galaxies," he says. Djorgovski and others have been puzzled by evidence that these youngest galaxies are already rich with elements like carbon and oxygen-elements that can only be produced in mature ST stars. "We find galax- Find resources and field notes from the author and photographer at nationalgeo graphic.com/ngm/0109. ies in a good state of assembly after only a few hundred million years. How did they form so quickly?" says Djorgovski. Well into the 21st century, astronomers will be wrestling with the puzzle of how so many galaxies evolved so fast after the dawn of the universe. By ten o'clock Djorgovski was waiting for the next observation. Sitting there with him, looking at the signs of young galaxies, I thought about what it means for something to be old. If you are 12 years old, or 50, or 90, that only means that a certain network of atoms has come together for that time. Many of the indi vidual atoms that make up that network will stay in your body only a short time before being replaced by new ones. And all of those atoms have been wandering through the air and ground and ocean for billions of years, and before then they were made in stars out of other atoms, which in turn reach back to the dawn of galaxies, to the first second of the uni verse when all matter came into being. "Hey, George, how's your little girl?" asked Teresa Chelminiak, an observatory assistant working at the computer next to Djorgovski. "Let me show you," Djorgovski said. With one kick, he propelled his chair over to another screen. "Here's the other thing these machines are good for," he said. He got on the Web and pulled up his home page. Slowly, strip by strip, the spectrum of a baby galaxy was hidden behind a photograph of Djorgovski's own baby. She was uncomplicated in her happiness. Her carbon 14 had no anomaly. Her redshift was zero. Once again, the clock was reset. ... the Shroud of Turin? 610 to 740ya old Dating technique: Carbon 14 Long revered by many Roman Catholics as Christ's burial covering, the linen Shroud of Turin was dated to A.D. 1260-1390 with carbon 14, a radioactive isotope used to date organic material. How it works: Cosmic rays turn nitrogen in the upper atmosphere into C 14, which is taken in by all living things. When an organism dies, its C 14 intake stops, and the C 14 within it decays at a measurable rate. ... this Sabertooth Skull? ,00 , d Dating technique: Carbon 14 Discovered alongside many other Pleisto cene animals in California's La Brea tar pits, this saber-toothed cat was one of the last to walk the Earth. The final ice age extinction happened roughly 11,500 years ago.