NUMBER 2
The Accelerating
Universe
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Cosmologists ponder whether our expanding universe is closed, open or flat. IMAGE:
LBNL
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Since
the 1920s, scientists have known that the universe is expanding. Most believe
that this expansion has been going on since the Big
Bang, estimated
to be 12 billion to 15 billion years ago.
But one of the most pressing questions in cosmology (the study of the
structure and history of the universe) is whether this expansion will continue
forever, or whether gravity will take over, reverse the course, and pull all of
the galaxies back together into a Big Crunch, which would signify the end of
time as we know it.
Suddenly, in the past two years, something weird has made the question
loom even larger: The expansion of the universe, according to two independent
studies, seems actually to be accelerating.
"This is completely unexpected," says Morris Aizenman, senior
science associate in the National Science Foundation's Mathematical and
Physical Science Directorate. "What force is causing that acceleration? We
have no answer."
Researchers speculate that the acceleration might be caused by some
strange and unknown matter or energy whose force of gravity repels,
rather than attracts, over long distances.
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Weird Fact
Albert Einstein was first to conclude that the
universe
must be expanding or contracting. But he tossed the "flawed"
idea out and rewrote his general theory of relativity.
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More About The Accelerating Universe
Anything that has mass also has gravity, and this force of gravity is
exerted across infinite space, decreasing with distance. You, for example,
exert a tiny gravitational pull on distant planets and galaxies, and they pull
on you.
And so you, your family, this Earth, and our Milky Way galaxy all tug on
other galaxies. Eventually, even though the universe is expanding in all
directions, the gravity of all the galaxies should slow the expansion, bring it
to a halt, and then pull all matter back together.
Unless, somehow, some force can overcome this "normal"
gravity.
Over the past decade, scientists have become increasingly convinced that
some form of "dark
matter"
permeates the universe, accounting for phenomena seen in space that could not
occur based on the amount of observable matter. But even this dark matter can't
account for an accelerating universe.
Instead, some have proposed, there must be small forces at work in even
the smallest "empty" spaces, inside your body, in the air and around the
universe -- a kind of antigravity which, over long distances, pushes other
stuff away.
Meanwhile, while the case for an accelerating
universe is
very strong, more evidence is needed. But even if it turns out wrong,
cosmologists say that the expansion isn't slowing down as fast as it should be,
based on what they know about mass and gravity. Something weird is going
on.
"More observations need to be made," Aizenman says, adding
that whole new theories and explanations will likely result.
NASA's MAP
mission,
set for launch this spring, will measure small fluctuations in the temperature
of a ubiquitous background of cosmic microwave radiation, which is thought to
have formed just 500,000 years after the Big
Bang. A
proposed satellite called SNAP
(SuperNova / Acceleration Probe) would map the expansion rate of the universe
at epochs varying from the present to 10 billion years ago.
Gathering such information with missions like these is expected to
reveal the size, shape, content, age and fate of the universe.
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