Do We Live in a Giant Cosmic Bubble?

Do We Live in a Giant Cosmic Bubble?

Clara Moskowitz
Staff Writer
SPACE.com 1 hour, 37 minutes ago

If the notion of dark energy sounds improbable, get ready for an even
more outlandish suggestion.
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Earth may be trapped in an abnormal bubble of space-time that is
particularly void of matter. Scientists say this condition could
account for the apparent acceleration of the universe's expansion, for
which dark energy currently is the leading explanation.

Dark energy is the name given to the hypothetical force that could be
drawing all the stuff in the universe outward at an ever-increasing
rate. Current thinking is that 74 percent of the universe could be
made up of this exotic dark energy, with another 21 percent being dark
matter, and normal matter comprising the remaining 5 percent.

Until now, there has been no good way to choose between dark energy or
the void explanation, but a new study outlines a potential test of the
bubble scenario.

If we were in an unusually sparse area of the universe, then things
could look farther away than they really are and there would be no
need to rely on dark energy as an explanation for certain astronomical
observations.

"If we lived in a very large under-density, then the space-time itself
wouldn't be accelerating," said researcher Timothy Clifton of Oxford
University in England. "It would just be that the observations, if
interpreted in the usual way, would look like they were."

Scientists first detected the acceleration by noting that distant
supernovae seemed to be moving away from us faster than they should
be. One type of supernova (called Type Ia) is a useful distance
indicator, because the explosions always have the same intrinsic
brightness. Since light gets dimmer the farther it travels, that means
that when the supernovae appear faint to us, they are far away, and
when they appear bright, they are closer in.

But if we happened to be in a portion of the universe with less matter
in it than normal, then the space-time around us would be different
than it is outside, because matter warps space-time. Light travelling
from supernovae outside our bubble would appear dimmer, because the
light would diverge more than we would expect once it got inside our
void.

One problem with the void idea, though, is that it negates a principle
that has reined in astronomy for more than 450 years: namely, that our
place in the universe isn't special. When Nicholas Copernicus argued
that it made much more sense for the Earth to be revolving around the
sun than vice versa, it revolutionized science. Since then, most
theories have to pass the Copernican test. If they require our planet
to be unique, or our position to be exalted, the ideas often seem
unlikely.

"This idea that we live in a void would really be a statement that we
live in a special place," Clifton told SPACE.com. "The regular
cosmological model is based on the idea that where we live is a
typical place in the universe. This would be a contradiction to the
Copernican principle."

Clifton, along with Oxford researchers Pedro G. Ferreira and Kate
Land, say that in coming years we may be able to distinguish between
dark energy and the void. They point to the upcoming Joint Dark Energy
Mission, planned by NASA and the U.S. Department of Energy to launch
in 2014 or 2015. The satellite aims to measure the expansion of the
universe precisely by observing about 2,300 supernovae.

The scientists suggest that by looking at a large number of supernovae
in a certain region of the universe, they should be able to tell
whether the objects are really accelerating away, or if their light is
merely being distorted in a void.

The new study will be detailed in an upcoming issue of the journal
Physical Review Letters.
--
Bob.

.

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