|image: Library of Congress|
A century ago, the prevailing opinion about the universe was that it consisted
only of our Milky Way galaxy, and was static and unchanging. This puzzled
because he understood that gravity was a force that pulled matter together.
If the universe was static, and gravity was exerting its pull, making everything
move closer and closer together, why hadnâ€™t the universe collapsed on
Einstein reasoned that there must be some force in the universe that repels
gravity, something that pushed matter apart and kept the universe static.
He named this mysterious anti-gravitational force the “cosmological
Turner, chairman of the Astronomy
& Astrophysics department at the University of Chicago, explains,
“Einstein introduced the cosmological constant as a fudge factor. He
thought he knew the answer at the back of the book. He thought the universe
was static so he put in this fudge factor.”
As shown on
PBSâ€™s "NOVA", by 1929, scientists had discovered that
the universe was not static at all—it was expanding. This led to the
idea of the Big Bang, a gigantic blast that generated so much momentum that
the universe is still expanding from it. Many astronomers believed that all
matter in the universe, and all the gravity it exerts, would eventually slow
this post-Big Bang expansion down, and maybe even stop it completely, causing
a kind of Big Crunch, or implosion, at some point in the future.
Still, because Einsteinâ€™s “fudge factor” came out of his
belief that the universe was static, these new discoveries about the non-static
nature of the cosmos caused him to call his cosmological constant the greatest
blunder of his career. But it turns out that he spoke too soon.
|image: NASA/WMAP Science Team|
In February, NASA
released images from a satellite called the Wilkinson
Microwave Anisotropy Probe (WMAP), which observed the universe for 12
months. The WMAP, the result of a partnership between the Goddard
Space Flight Center and Princeton
University, captured “cosmic microwave background” radiation,
the afterglow of the Big Bang that bathes the entire universe. By measuring
small variations in the temperature of the cosmic microwave background radiation,
the WMAP created a “baby picture” of the cosmos that reveals a
lot about its nature and content.
The light in this “cosmic
portrait” taken by the satellite is from 380,000 years after the
Big Bang. It reveals that the universe is 13.7 billion years old (with a 1
percent margin of error), and that the first stars ignited about 200 million
years after the Big Bang.
According to the WMAP, the content
of the universe is only 4 percent atoms, which includes the matter that
makes up all of the planets, stars, and us. Twenty-three percent of the universe
is a mysterious type of material known as "cold dark matter,” and
73 percent is something even more mysterious—something scientists call
“dark energy.” This dark energy acts as a sort of anti-gravity,
forcing the universe not only to keep expanding, but also to accelerate in
its expansion, which contradicts the Big Crunch theory. Although the nature
of the dark energy is still a mystery, the information gathered by the WMAP
seems to indicate that it will impel the universe to expand forever.
So there is indeed an anti-gravitational force in the universe that keeps it
from closing in on itself. Einstein was right after all.
“If Einstein heard these results today, he would say, ‘Yahoo!â€™”
Filippenko, professor of astronomy at the University of California at
Berkeley. “It would be such a thrill for him, I think, to see that his
original prediction that such a weird ‘stuffâ€™ might exist in the
universe turned out to be actually true.”