Download Lecture 25 - Black Hole Firewall

Outline
•  Hawking radiation and the LHC
•  Black Hole Firewall
•  Singularities
•  Wormholes
What happens at the end of
evaporation?
•  Eventually, energy of photon emitted would
be larger than mass-energy of black hole.
–  About a Planck mass
•  No more radiation can be emitted?
•  One last burst of particle and no remnant?
What is the smallest possible BH
mass?
•  Using general relativity, should be about a
Planck mass, 2×10-5 g = 2.4×1018 GeV
•  But, depending of what theory of quantum
mechanics and gravity we use, the mass
could be much smaller
•  Down to ~1000 GeV
LHC
•  Large Hadron Collider
LHC
•  Will collide particles at very high energy,
trying to make new particles
LHC
•  Looking for Higgs Boson
•  Predicted to exist in 1964, possibly found in
2012
LHC
•  But, LHC could also make micro black
holes
LHC
•  What happens if you make a black hole?
LHC
•  Probably the black hole will evaporate
almost immediately
•  Black holes evaporate over time
•  Very slow for big ones, almost instantly for
small ones
•  This would
be great!
LHC
•  Possible, but unlikely, that black hole won’t
evaporate, or at least not for a while
•  But it will be very small and going almost
the speed of light
•  Will shoot through the Earth without hitting
anything and keep going off into space
–  Collision like this happen all the time in the
atmosphere and we’re still here
Falling into a black hole
•  In general relativity
–  Nothing special about event horizon
–  To a falling observer, horizon always appears
to be below you
–  Eventually get pulled apart by tidal forces
–  Could be out side BH if it’s small, inside if it’s
large
Falling into a black hole
•  In general relativity
–  If you try to orbit or hover, light coming in is
blueshifted
–  Fries you if you’re too close to the horizon
–  In free-fall, this doesn’t happen
–  Hawking radiation is blue shifted, but not
enough to kill you
•  Nothing special about the Event Horizon
Quantum Information
•  In quantum theory, information can never
be destroyed
Quantum Information
•  In quantum theory, information can never
be destroyed
•  Classical example: If you know everything
about a system, you can predict its state at
any point in the future, or any point in the
past
Quantum Information
•  In quantum theory, information can never
be destroyed
•  In quantum theory, information is stored in
waveforms of particles
–  Particle can be partially in many states a once,
and only picks one when it’s measured
Quantum Information
•  In quantum theory, information is stored in
waveforms of particles
–  Particle can be partially in many states a once,
and only picks one when it’s measured
•  However, a pair of particles can be
entangles such that when you measure 1
quantity in one, you also know the state of
the other particle
Quantum Information
•  Quantum information is a problem at an
event horizon
•  If particles fall into a black hole,
information about their states is lost?
•  Information is saved?
Quantum Information
•  Quantum information is a problem at an
event horizon
•  If particles fall into a black hole,
information about their states is lost?
•  Information is saved?
•  Information could be encoded Hawking
radiation
Quantum Information
•  Quantum information is a problem at an
event horizon
•  Information could be encoded Hawking
radiation
•  A surface (the event horizon) can store
information about the quantum states inside
it
–  Similar to surface area storing entropy
Quantum Information
•  Information could be encoded Hawking
radiation
•  This creates another
problem
•  Pairs of particles near
horizon are entangled
•  Radiation is also
entangled with black
hole
Black Hole Firewall
•  Particle can only be strongly entangled with
one other particle
•  Shouldn’t also be able to be entangled with
black hole
Black Hole Firewall
•  Possible solution:
–  Particles break entanglment with infalling pair
–  Energetic particles created just inside horizon
–  Polchinski 2012
•  These particle will fry and tear apart
anything that crosses the horizon
•  Gives up principle of equivalence
Back Hole Firewall
•  Either:
–  Give up principle of equivalence
–  Allow information to be destroyed
–  Allow black hole to preserve entanglement
information until it almost evaporates
Cosmic Censorship Hypohesis
•  Singularity – point at which physics breaks
down (infinite density?)
•  Every “trapped surface” contains a
singularity
•  Every singularity is inside a horizon – no
naked singularities
Singularity – Non-Rotating BH
•  Once something makes it into a black hole,
if continues to fall towards the middle
•  In a finite (and fairly short) time, it will
reach the center
•  At the Planck scale, our understanding of
gravity breaks down
Singularity – Non-Rotating BH
•  Once something makes it into a black hole,
if continues to fall towards the middle
•  In a finite (and fairly short) time, it will
reach the center
•  At the Planck scale, our understanding of
gravity breaks down
•  In a non-rotating BH, always hit the
singularity
Falling into a Singularity
Singularity – Rotating BH
•  Singularity has angular momentum
•  Will form a ring singularity
•  Possible to fall in and miss the singularity
•  Only hit the ring if you come in in the plane
of the ring, otherwise it is repulsive
Singularity – Rotating BH
•  Ring singularity
•  Also an inner horizon where flow of space
slows down to speed of light
Rotating BH
•  Falling through inner horizon you see
infinitely blueshifted light
•  You can miss the singularity and are push
back out through another horizon
•  Black hole connects to a white hole
somewhere else
–  Another universe?
–  Pocket universe?
–  Another part of the same universe?
Falling into a Rotating BH
Wormhole
•  Rotating (or charged) black hole can act as a
wormhole
•  Unstable. Will collapse if anything tries to
go through it
•  Needs to be stabalized
Rotating BH as Wormhole
•  You can miss the singularity and fall back
out through another horizon
•  You can see another universe and escape
through the white hole
•  In reality, the connection will be unstable
and collapse once anything ties to go
through it.
See description and movies at:
•  http://jila.colorado.edu/~ajsh/insidebh/
rn.html