How Old Is the Universe?

How Old Is The Universe?

13.7 Billion Years

Astronomers are at an enormous disadvantage, compared with other scientists. A biologist can bring a collection of fruit flies into his laboratory, encourage a particular behavior among those flies, and apply all the tools of his trade to studying that behavior. A chemist can mix chemicals together, heat them up or cool them down, and study how they react in the controlled environment of her laboratory. A geologist can hike up a mountain, collect rocks from a particular outcrop, and return these samples to his laboratory for analysis. A physicist can power up a laser and test the mechanical properties of a newly-created polymer and can do this on her vibration-isolated, experimental table. Astronomers? They cannot drag the stars into their laboratories. They cannot make stars hotter or cooler to see how they behave when their temperatures change. They cannot slice open galaxies in order to peer into their cores. Astronomers can only take what the universe offers— light and a few small rocks—and make the most of it.

For centuries, astronomers have measured the brightnesses, colors, and positions of objects in the nighttime sky, as one generation after another has sought to understand the nature and behavior of the remote objects shining in the heavens. Using basic principles of geometry, and the physics describing light, heat, and gravity, astronomers deduced that some of those glimmering objects in the sky are akin to our Sun: They are stars. They also discovered that stars have a wide range of sizes, masses, and temperatures, and that stars are born, live out their lives, and then die. Proving seemingly obvious things, however, like the fact that stars are distant (which prompted the thorny question, how distant?), was extremely difficult. To answer the question of how far away stars are—not to mention how hot, how massive, and how large or small they are—astronomers had to learn how to take detailed measurements of celestial objects that lie at great distances from our telescopes. Since the stars could not be brought to Earth to be weighed and measured, astronomers had first to develop the right tools for measuring stars. Then they were able to apply their knowledge of concepts like Doppler shifts, radioactivity, and nuclear fusion to the measured properties of stars, and answers to all sorts of previously unanswerable questions, including ones that had frustrated astronomers since antiquity, began to rain down from the heavens. This deluge of evidence led eventually to an astonishing and hard-won intellectual triumph on the grandest possible scale: the answer to one of the most fundamental questions ever to puzzle humanity, How old is the universe?

Copyright © 2011 by Princeton University Press