The Birth of Time: How Astronomers Measured the Age of the Universe by John Gribbin, Yale University Press, $24.95, 237 pages. Reviewed in the Raleigh News & Observer on May 14, 2000.
The News & Observer
May 14, 2000
Cosmic riddle: Can the child be older than
its mother?
By Phillip Manning
Suppose you were born in 1940, and one day you came across your
mother's birth certificate stating that she was born in 1942.
A perplexing dilemma? You bet. That is precisely the situation
cosmologists found themselves in a few years ago. New measurements
from the Hubble Space Telescope, or HST, indicated that the universe
was younger than the oldest stars.
The inconsistency was particularly galling because cosmology was
in a golden age. In the span of one generation, astronomers had
discovered that the universe was expanding; they had postulated
the sweeping Big Bang theory of how it was formed; and they had
discovered how stars and planets were born and died. The Hubble's
new results appeared to cast doubt on those grand accomplishments.
In "The Birth of Time," the prolific British science
writer John Gribbin, who is also an astronomer, tells how cosmologists
got the universe back in order.
The story is a complex one, and this otherwise well-crafted book
suffers from a lack of technical precision, a growing but deplorable
tendency in popular-science writing. Perhaps publishers are dumbing
down their books to attract more readers. Whatever the reason,
this book (and others of this genre) would be easier to follow
if it included a few graphs or tables or even -- gasp! -- a simple
equation or two. As our society becomes ever more dependent on
science and technology, we need to learn their logic and language
rather than shy away from them. Nevertheless, the book is a worthwhile
read for anyone who wants to better understand the universe we
inhabit.
People have long speculated about the age of the world, but the
first man to actually calculate it was Archbishop James Ussher
in 1620. He used all of the "begats" in the Bible to
arrive at a date of creation of 4004 B.C. Over the years, this
date got pushed back as scientists got into the act. What about
fossils, they asked? Surely they took more than a few thousand
years to form. Isaac Newton guessed that Earth was 50,000 years
old; the French naturalist Comte de Buffon said 75,000; and in
1897 Lord Kelvin came up with the astounding figure of 24 million
years. But these were estimates of the age of the Earth and the
solar system -- not the universe, which was widely believed to
be static and eternal.
Then, in 1929, the trail-blazing astronomer Edwin Hubble revolutionized
our concept of the universe. Scientists had long known that as
a source of light moves away from an observer, it becomes redder;
the faster it is moving, the redder it appears -- this is known
as the Doppler effect. Hubble discovered that the farther a star
was from Earth, the greater its "red shift." Thus, more
distant stars are receding faster. The only reasonable explanation
for this was that space itself was expanding -- not just at the
edges of the universe but everywhere. If gravitational effects
are neglected, this means that every star is becoming more isolated
from every other star as space is created between them, much as
every point on the surface of a balloon becomes more isolated
from every other point as it is inflated.
If the universe was expanding, scientists reasoned, the stars
must have once been closer together. From the rate of expansion,
they could determine when the Big Bang, the birth of time itself,
occurred. By the 1950s, cosmologist estimated that the universe
was 15 billion years old. This number was consistent with independent
measurements of the age of the oldest stars, which were about
the same age.
This cozy state of affairs was upset in 1994 when a team of American
astronomers, using data from the recently repaired Hubble telescope
(and making one assumption), calculated that the universe was
actually between 8 and 12 billion years old. Articles in popular
magazines dramatized the discrepancy, pointing out that the new
data indicated that the universe was younger than the oldest stars.
"Crisis in the Cosmos" blared one headline; "Don't
look for a resolution to the age crisis tomorrow,"said another
article. Both statements, it turns out, were wrong.
The HST team chose a single star of known luminosity among the
billions of stars that comprise the M100 galaxy. That galaxy is
part of the Virgo Cluster, which contains more than 1,000 galaxies
and is 25 million light years across. By measuring that one star's
brightness, they could calculate its distance from Earth. Then
they used that figure to determine the Virgo Cluster's distance
from Earth. Finally, the Virgo Cluster's brightness was used as
a yardstick for measuring the distance to more remote clusters.
However, there is no way of knowing any single star's position
within the massive Virgo Cluster. Members of the HST team made
the logical assumption that their star had a better chance of
being in the middle than anywhere else. "The Birth of Time"
provides a detailed account of how this assumption was proved
wrong.
A group of astronomers from Great Britain, including Gribbin,
collected additional data and recalibrated the distance scale.
Using the new scale, astronomers found that the universe was far
older than the HST group's original estimate. This result could
be consistent with the HST data only if M100 was on the near edge
of the Virgo cluster -- not in its center.
Meanwhile, other astronomers were trying to confirm the age of
the oldest stars. Using a European satellite, they made parallax
measurements -- determining distance not by direct measurement
but through geometric principles -- of a globular cluster in the
Milky Way (our home galaxy). Within the globular clusters' millions
of stars, astronomers believe, are the oldest stars in the universe.
The parallax measurements revealed that the oldest stars were
farther away than previously reported. This meant that the stars'
intrinsic brightness must be greater than originally supposed.
(Their apparent brightness, what we see here on Earth, was of
course unchanged.) And because brighter stars burn fuel more rapidly,
they must be younger than the earlier estimates. This finding
reduced astronomers' reckoning of the age of the oldest stars.
Today, Gribbin reports, the universe is back in order. It is approximately
13 billion years old, and the oldest stars have been around for
11 billion years. The parent is again older than the child.
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