- Black holes are staples of science fiction and many think
astronomers have observed them indirectly. But according to a physicist
at the Lawrence Livermore National Laboratory in California, these awesome
breaches in space-time do not and indeed cannot exist.
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- Over the past few years, observations of the motions
of galaxies have shown that some 70% the Universe seems to be composed
of a strange 'dark energy' that is driving the Universe's accelerating
expansion.
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- George Chapline thinks that the collapse of the massive
stars, which was long believed to generate black holes, actually leads
to the formation of stars that contain dark energy. "It's a near certainty
that black holes don't exist," he claims.
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- Black holes are one of the most celebrated predictions
of Einstein's general theory of relativity, which explains gravity as the
warping of space-time caused by massive objects. The theory suggests that
a sufficiently massive star, when it dies, will collapse under its own
gravity to a single point.
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- But Einstein didn't believe in black holes, Chapline
argues. "Unfortunately", he adds, "he couldn't articulate
why." At the root of the problem is the other revolutionary theory
of twentieth-century physics, which Einstein also helped to formulate:
quantum mechanics.
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- In general relativity, there is no such thing as a 'universal
time' that makes clocks tick at the same rate everywhere. Instead, gravity
makes clocks run at different rates in different places. But quantum mechanics,
which describes physical phenomena at infinitesimally small scales, is
meaningful only if time is universal; if not, its equations make no sense.
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- This problem is particularly pressing at the boundary,
or event horizon, of a black hole. To a far-off observer, time seems to
stand still here. A spacecraft falling into a black hole would seem, to
someone watching it from afar, to be stuck forever at the event horizon,
although the astronauts in the spacecraft would feel as if they were continuing
to fall. "General relativity predicts that nothing happens at the
event horizon," says Chapline.
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- Quantum Transitions
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- However, as long ago as 1975 quantum physicists argued
that strange things do happen at an event horizon: matter governed by quantum
laws becomes hypersensitive to slight disturbances. "The result was
quickly forgotten," says Chapline, "because it didn't agree with
the prediction of general relativity. But actually, it was absolutely correct."
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- This strange behaviour, he says, is the signature of
a 'quantum phase transition' of space-time. Chapline argues that a star
doesn't simply collapse to form a black hole; instead, the space-time inside
it becomes filled with dark energy and this has some intriguing gravitational
effects.
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- Outside the 'surface' of a dark-energy star, it behaves
much like a black hole, producing a strong gravitational tug. But inside,
the 'negative' gravity of dark energy may cause matter to bounce back out
again.
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- If the dark-energy star is big enough, Chapline predicts,
any electrons bounced out will have been converted to positrons, which
then annihilate other electrons in a burst of high-energy radiation. Chapline
says that this could explain the radiation observed from the centre of
our galaxy, previously interpreted as the signature of a huge black hole.
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- He also thinks that the Universe could be filled with
'primordial' dark-energy stars. These are formed not by stellar collapse
but by fluctuations of space-time itself, like blobs of liquid condensing
spontaneously out of a cooling gas. These, he suggests, could be stuff
that has the same gravitational effect as normal matter, but cannot be
seen: the elusive substance known as dark matter.
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- References
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- Chapline G. Arxiv, http://xxx.arxiv.org/abs/astro-ph/0503200
(2005).
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- Bill Hamilton AstroScience Research Network http://www.astrosciences.info/
"I don't see the logic of rejecting data just because they seem incredible."
Fred Hoyle
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- http://www.nature.com/physics/=
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