Encyclopedia of Evolution.pdf - Online Reading Center

ago. This was the birth of the Sun. The atoms away from the
center formed clusters (planetesimals), some of gases, others
of heavier elements. The gaseous clusters never produced sufficient
pressure to ignite; they became the gas giant planets
Jupiter, Saturn, Uranus, and Neptune. The clusters of heavier
elements became the remaining planets, including Earth. This
explains why the solar system is only four and a half billion
years old, in a 14-billion-year-old universe: The Sun is a second-generation
star. New stars continue to form in nebulae:
Stars in the Orion Nebula are less than 100,000 years old.
More than 150 planets have been detected revolving around
other stars. In most cases, the presence of the planet is
detected by the movement of the star caused by the gravity
of a large planet, or by changes in light intensity caused by a
large planet moving between the star and human observers.
In 2005 the first photograph of a planet around a star other
than the Sun was published.
The “life span” of the sun will be about 10 billion years.
About half of this time has passed. Martin Rees uses the analogy
of walking across the United States from coast to coast:
Each step would represent two thousand years in the Sun’s
lifetime. All of human history would fit into three or four
steps in the middle of Kansas.
Eventually the Sun will cool to a red color and expand,
becoming a red giant. Life on Earth will have ended before
this. About the time, five billion years from now, that the
Sun explodes, the Milky Way galaxy will collide with the
Andromeda galaxy. Although galaxies are mostly empty
space, gravitation will draw stars together in many colorful
explosions—none of which humans will see.
But what will happen to the universe? Will it expand
forever, reaching a uniform deadness of absolute zero? If
the average density of the universe exceeds three atoms per
universe, origin of 0
cubic meter, the gravitational force will be sufficient to draw
the atoms back together, creating yet another big bang. The
visible matter of the universe is 50 times less than what is
required for this to happen. However, the vast majority
of matter in the universe may be “dark matter,” dispersed
between the galaxies and stars, and not reflecting any light.
Furthermore, particles called neutrinos have almost no mass
(they weigh one billionth as much as a hydrogen atom), but
there may be so many of them that they constitute a considerable
part of the mass of the universe. The density of the universe
may be great enough, after all, to cause it to coalesce
and renew.
Further Reading
Davies, Paul. The Last Three Minutes: Conjectures about the Ultimate
Fate of the Universe. New York: Basic Books, 1997.
Ferris, Timothy. The Whole Shebang: A State of the Universe Report.
New York: Simon and Schuster, 1998.
Guth, Alan H., and David I. Kaiser. “Inflationary cosmology: Exploring
the universe from the smallest to the largest scales.” Science
307 (2005): 884–890.
Lineweaver, Charles H., and Tamara M. Davis. “Misconceptions
about the Big Bang.” Scientific American, March 2005, 36–45.
Rees, Martin. Our Cosmic Habitat. Princeton, N.J.: Princeton University
Press, 2003.
Schilling, Govert. “Picture-perfect planet on course for the history
books.” Science 308 (2005): 771.
Smolin, Lee. The Life of the Cosmos. New York: Oxford University
Press, 1997.
Tyson, Neil deGrasse, and Donald Goldsmith. Origins: Fourteen Billion
Years of Cosmic Evolution. New York: Norton, 2004.
Weinberg, Steven. The First Three Minutes. New York: Basic Books,
1977.