Wormholes help resolve black hole information paradox
A RIKEN physicist and two colleagues have found that a wormhole-a
bridge connecting distant regions of the Universe-helps to shed light
on the mystery of what happens to information about matter consumed
by black holes (
https://bit.ly/3tSbARE).
Einstein's theory of general relativity predicts that nothing that
falls into a black hole can escape its clutches. But in the 1970s,
Stephen Hawking calculated that black holes should emit radiation
when quantum mechanics, the theory governing the microscopic realm,
is considered. "This is called black hole evaporation because the
black hole shrinks, just like an evaporating water droplet,"
explains Kanato Goto of the RIKEN Interdisciplinary Theoretical and
Mathematical Sciences.
This, however, led to a paradox. Eventually, the black hole will
evaporate entirely-and so too will any information about its
swallowed contents. But this contradicts a fundamental dictum
of quantum physics: that information cannot vanish from the
Universe. "This suggests that general relativity and quantum
mechanics as they currently stand are inconsistent with each
other," says Goto. "We have to find a unified framework for
quantum gravity."
Many physicists suspect that the information escapes, encoded
somehow in the radiation. To investigate, they compute the entropy
of the radiation, which measures how much information is lost from
the perspective of someone outside the black hole. In 1993, physicist
Don Page calculated that if no information is lost, the entropy will
initially grow, but will drop to zero as the black hole disappears.
When physicists simply combine quantum mechanics with the
standard description of a black hole in general relativity, Page
appears to be wrong-the entropy continually grows as the black hole
shrinks, indicating information is lost.
But recently, physicists have explored how black holes mimic
wormholes-providing an escape route for information. This is not
a wormhole in the real world, but a way of mathematically computing
the entropy of the radiation, notes Goto. "A wormhole connects the
interior of the black hole and the radiation outside, like a bridge."
When Goto and his two colleagues performed a detailed analysis
combining both the standard description and a wormhole picture, their
result matched Page's prediction, suggesting that physicists are right
to suspect that information is preserved even after the black hole's
demise.
"We discovered a new spacetime geometry with a wormhole-like
structure that had been overlooked in conventional computations,"
says Goto. "Entropy computed using this new geometry gives a
completely different result."
But this raises new questions. "We still don't know the basic
mechanism of how information is carried away by the radiation,"
Goto says. "We need a theory of quantum gravity."
