has identified a possible quantum origin
for the ever-growing volume of black holes...
The problem is that even though these mysterious, invisible spheres appear to stay a constant size as viewed from the outside, their interiors keep growing in volume essentially forever.
How is this possible?
First discovered a century ago as shocking solutions to the equations of Albert Einstein's general theory of relativity, they've since been detected throughout the universe. (They typically form from the inward gravitational collapse of dead stars.)
Einstein's theory equates
the force of gravity with curves in space-time, the four-dimensional
fabric of the universe, but gravity becomes so strong in black holes
that the space-time fabric bends toward its breaking point - the
infinitely dense "singularity"
at the black hole's center.
Even though, from the outside, the black hole appears to stay a constant size, expanding slightly only when new things fall into it, its interior volume grows bigger and bigger all the time as space stretches toward the center point.
For a simplified picture of this eternal growth,
In reality, a black hole is a funnel that stretches inward from all three spatial directions.
A spherical boundary
surrounds it called the "event
horizon," marking the point of no return.
What Einstein's theory describes as warped space-time in the interior is presumably really a collective state of vast numbers of gravity particles called "gravitons," described by the true quantum theory of gravity.
In that case, all the
known properties of a black hole should trace to properties of this
This is the number of
different possible microscopic arrangements of all the particles
inside the black hole, or, as modern theorists would describe it,
the black hole's storage capacity for information.
This radiation causes black holes to slowly evaporate away, giving rise to the much-discussed "black hole information paradox," which asks what happens to information that falls into black holes.
Quantum mechanics says
the universe preserves all information about the past.
But how does information about in-falling stuff, which seems to
slide forever toward the central singularity, also evaporate out?
But one might also ask:
a professor of theoretical physics
at Stanford University,
in Palo Alto, California.
This angle led Susskind and his collaborators to identify a candidate for the evolving quantum property of black holes that underlies their growing volume.
What's changing, the theorists say, is the "complexity" of the black hole - roughly a measure of the number of computations that would be needed to recover the black hole's initial quantum state, at the moment it formed.
After its formation, as particles inside the black hole interact with one another, the information about their initial state becomes ever more scrambled.
complexity continuously grows...
And, whereas Bekenstein
calculated that black holes store the maximum possible amount of
information given their surface area, Susskind's findings suggest
that they also grow in complexity at the fastest possible rate
allowed by physical laws.
Researchers are still puzzling over the implications of Susskind's thesis.
Aron Wall, a theorist at Stanford (soon moving to the University of Cambridge), said,
One challenge is defining
complexity in the context of black holes, Wall said, in order to
clarify how the complexity of quantum interactions might give rise
to spatial volume.
If complexity does underlie spatial volume in black holes, Susskind envisions consequences for our understanding of cosmology in general.