Transcript: Leonard Susskind on The Black Hole Wars | Apr 23, 2005

Leonard Susskind stands on a stage by a wooden podium.
He’s in his sixties, with receding white hair and a long beard. he’s wearing a grey suit, blue shirt, and checked black tie.

He says TONIGHT
WE'RE GOING TO TALK ABOUT THE
BLACK HOLE WAR, OR BLACK HOLE
WARS.

A caption appears on screen. It reads "Leonard Susskind. Stanford University. The Black Hole Wars. Perimeter Institute, Public Lecture Series. February 2, 2005."

Leonard continues THE BLACK
HOLE WARS WERE A 25 YEAR
INTELLECTUAL BATTLE, A SERIOUS
ONE, THAT INVOLVED NOT ONLY
MYSELF AND MY COMRADE IN ARMS
GERARD T'HOOFT, INCIDENTALLY
GERARD T'HOOFT IS ONE OF THE
GREAT PHYSICISTS OF THE CENTURY.
AND ALSO STEPHEN HAWKING.
GERARD AND MYSELF WERE ON ONE
SIDE, GERARD,
GERARD,
GERARD.
T'HOOFT.
T'HOOFT IS ONE OF THE FEW NAMES
YOU'LL EVER HEAR THAT BEGINS
WITH AN APOSTROPHE.

(Audience Laughing)

Leonard continues IT DOES,
I'LL WRITE IT OUT FOR YOU.
AND HE AND I WERE DEFENDING
CONSERVATIVE PHYSICS, THE
CONSERVATIVE PRINCIPLES OF
PHYSICS AGAINST THIS WILD MAN
STEPHEN HAWKING.
AND IT TOOK 25 YEARS TO SORT IT
OUT.
THE BLACK HOLE WARS ACTUALLY
STARTED IN A RATHER ODD PLACE.
THEY STARTED IN THE SAN
FRANCISCO MANSION OF VERNER
ERHARD.
DOES ANYBODY, IF YOU KNOW THE
NAME VERNER ERHARD APPLAUD.

(Applause)

Leonard says OH GOOD.
OKAY.
THIS MAN WAS A GURU OF THE SELF
SOMETHING OF THE SELF PROMOTION
CULT.

(Audience Laughing)

Leonard continues BUT HE
LOVED PHYSICISTS.
IN ANY CASE I HAVE A PHOTOGRAPH
HERE OF MYSELF, GERARD T'HOOFT
AND STEPHEN HAWKING AT A
BLACKBOARD WHERE IF YOU WERE TO
SEE THE FACES FROM BEHIND, IF
YOU COULD SEE THE FACES YOU
WOULD SEE THE MOST INCREDIBLY
STRANGE LOOKING, NOT ANGRY BUT
JUST INTENSE FACES.
HERE'S THE PHOTOGRAPH, IT WAS
TAKEN FROM BEHIND ME.

He places a paper on a screen projector and the image appears on a giant screen on the stage. It shows a simple drawing of a man’s head seen from behind as another man and a third man in a wheelchair look at a screen with an image of a black hole on it.

(Audience Laughing)

Leonard continues I DON'T
LIKE HIGH TECH CAMERAS.
I TELL YOU SIMPLY I HAD SUCH A
PHOTO A REAL ONE AND I LOST IT
SO I DECIDED TO JUST MAKE ONE.
THE PHYSICISTS IN THE AUDIENCE
RECOGNIZE THE BLACK HOLE THERE.
ANYBODY ELSE OF COURSE
RECOGNIZES STEPHEN HAWKING.
THAT'S STEPHEN, THIS IS GERARD
T'HOOFT AND THAT'S ME AND THE
PERSON BEHIND TAKING THE PICTURE
WAS ACTUALLY VERNER ERHARD.

(Audience Laughing)

Leonard continues NOW THIS
TOOK PLACE IN SAN FRANCISCO.
THIS WAS THE FIRST VOLLEY OF THE
BLACK HOLE WARS.
STEPHEN HAD ANNOUNCED SOMETHING
AND TOLD US SOMETHING THAT BOTH
GERARD AND MYSELF REACTED TO
ALMOST VIOLENTLY INTELLECTUALLY
VIOLENTLY, WE WEREN'T GOING TO
THROW STEPHEN OUT OF HIS WHEEL
CHAIR.

(Audience Laughing)

Leonard continues UM... LET
ME TELL YOU A LITTLE BIT ABOUT
THE PERSONALITY OF THESE TWO
PEOPLE.
GERARD IS TRULY ONE OF THE
GREAT PHYSICISTS OF THE 20th
CENTURY, THERE'S NO QUESTION OF
THAT, IN MY MIND, HE MORE THAN
ANYBODY ELSE CARRIES THE MANTLE
OF EINSTEIN AND BOHR, HE'S AN
EXTREMELY DEEP THINKER, HE'S
ALSO A CONSERVATIVE LIKE MYSELF.
I THINK HE'S A CONSERVATIVE
PHYSICIST THAT IN A CERTAIN
SENSE DOESN'T REALLY LIKE NEW
RADICAL IDEAS.
NO NEW RADICAL IDEAS UNTIL
YOU'RE ABSOLUTELY BEEN FORCED TO
THEM.
NOW IF STEPHEN AND I ARE
SOMEWHAT, NOT STEPHEN, IF GERARD
AND I ARE SOMEWHAT CONSERVATIVE,
STEPHEN HAWKING IS THE EVIL
KNIEVEL OF PHYSICS.
HE'S THE EVIL KNIEVEL OF PHYSICS
IN MANY WAYS.
I'LL TELL YOU A LITTLE BIT MORE
ABOUT WHAT HAPPENED IN SAN
FRANCISCO, WE ALL DECIDED TO
TAKE A LITTLE WALK OUT IN SAN
FRANCISCO ON TELEGRAPH HILL.
NOW IF YOU KNOW SAN FRANCISCO
YOU KNOW THAT TELEGRAPH HILL'S A
VERY STEEP HILL.
IT'S ONE OF THESE FANCY HILLS
WITH BRAKE BUSTING CRAZY HILLS
IN SAN FRANCISCO AND STEPHEN
DECIDED TO COME WITH US IN HIS
POWERED WHEEL CHAIR.
AT THAT TIME HE COULD STILL TALK.
YOU COULDN'T UNDERSTAND HIM, IT
WAS HARD TO UNDERSTAND HIM, BUT
HE COULD STILL MAKE SOUNDS.
AND WE GET TO THE TOP OF
TELEGRAPH HILL AND ALL OF A
SUDDEN, STEPHEN IS GOING DOWN
TELEGRAPH HILL AT 30 MILES AN
HOUR SCREAMING AHHH!
AND WE ALL PANICKED, WE RAN
AFTER HIM, WE COULDN'T KEEP UP
WITH HIM, WE GET DOWN TO THE
BOTTOM OF THE HILL AND THERE'S
STEPHEN SITTING THERE SMILING
AND SAYING CAN WE FIND ANOTHER
STEEPER ONE THAT HE CAN TRY.

(Audience Laughing)

Leonard continues THIS IS
TRUE, THIS IS A TRUE STORY.
UM...
STEPHEN IN HIS PHYSICS IS VERY
BOLD, VERY AUDACIOUS AND VERY,
VERY MUCH THE SAME WAY.
HE LIVES HIS LIFE VERY FULLY AND
HE IS THE EVIL KNIEVEL OF
PHYSICS.
LIKE EVIL KNIEVEL HE SOMETIMES
HAS HIS CRASHES.
AND WE'RE GONNA TALK ABOUT NOT
THE CRASH, SOMETHING THAT HE
EVEN CONCEDES IS WRONG NOW ABOUT
THE 25 YEAR DISCUSSION THAT TOOK
PLACE BETWEEN US THAT ULTIMATELY
I THINK TAUGHT US A GREAT DEAL
ABOUT THE LAWS OF NATURE AND NEW
THINGS ABOUT SPACE AND TIME.
LET'S BEGIN WITH WHAT A BLACK
HOLE IS.
THE OLDEST IDEA OF WHAT A BLACK
HOLE IS BELIEVE IT OR NOT GOES
BACK TO ABOUT 1780, WHEN
LAPLACE, UH, DOES ANYBODY KNOW
LAPLACE'S FIRST NAME, I'VE
FORGOTTEN IT, BUT LAPLACE IS --

(A member of the audience speaks French)

Leonard says ALL RIGHT,
HE SAID IT, HE SPEAKS FRENCH.

(Audience Laughing)

Leonard continues UM...
SIMONE SOMETHING ISN'T IT --
PIERRE, YEAH.

He shows a new slide with a black circle, two equations, and the caption “The dark star of Laplace.”

Leonard continues LAPLACE, AND THERE WAS ANOTHER
GENTLEMAN BY THE NAME OF
MITCHELL WHO ACTUALLY DID THIS
FIRST BUT WASN'T AS FAMOUS AS
LAPLACE SO VERY FEW PEOPLE KNOW
ABOUT IT.
LAPLACE ASKED THE FOLLOWING
QUESTION.
EVERY OBJECT, EVERY PLANET,
EVERY STAR AND SO FORTH HAS
SOMETHING CALLED AN ESCAPE
VELOCITY.
IT'S HOW FAST YOU HAVE TO SHOOT
AN OBJECT OFF THE SURFACE OFF
THE STAR, OFF THE SURFACE OF THE
OBJECT, IN ORDER FOR IT TO
ESCAPE THE GRAVITATION OF THE
OBJECT ALL TOGETHER.
THE ESCAPE VELOCITY.
THE MORE MASSIVE THE OBJECT, THE
LARGER THE ESCAPE VELOCITY.
THE SMALLER THE OBJECT FOR A
GIVEN MASS, THE LARGER THE
ESCAPE VELOCITY, BECAUSE IF IT'S
ALL SQUEEZED INTO A SMALL
DISTANCE, YOU HAVE A HARDER
PROBLEM GETTING AWAY FROM IT
BECAUSE EVERYTHING HAS GOTTEN
SQUASHED AND YOU'RE CLOSE TO IT.
SO WHAT LAPLACE ASKED IS WHAT
WOULD HAPPEN IF WE HAD A STAR
WHICH WAS SO DENSE, AND SO HEAVY
AND SO SMALL THAT THE ESCAPE
VELOCITY FROM THE SURFACE OF IT
WAS THE SPEED OF LIGHT OR EVEN
GREATER THAN THE SPEED OF LIGHT?
THEN, EVEN LIGHT COULDN'T GET
OUT.
AND IF LIGHT COULDN'T GET OUT
THEN THIS OBJECT WOULD APPEAR AS
A DARK STAR AND COULDN'T BE SEEN
BECAUSE THE LIGHT COULD NEVER
GET OUT.
THIS WAS THE FIRST EXAMPLE, YOU
DON'T NEED THESE EQUATIONS
HERE, I'LL JUST VERY QUICKLY
TELL YOU WHAT THIS WINDS UP
TELLING YOU THE SIZE OF THE DARK
STAR HAS TO BE PROPORTIONAL TO
ITS MASS, DON'T WORRY ABOUT THE
EQUATIONS BUT IT TELLS YOU
SOMETHING ABOUT THE SIZE OF A
DARK STAR IN TERMS OF ITS MASS,
AND THIS WAS THE FIRST INKLING
THAT SUCH A THING AS A BLACK
HOLE COULD EXIST.
NOW I'LL GIVE YOU ANOTHER
PICTURE OF A BLACK HOLE, IT IS
EINSTEIN'S PICTURE OF GRAVITY.
ALL OF THIS HAS TO DO OF COURSE
WITH GRAVITY.
BUT EINSTEIN SAID...

He fumbles around with a few papers and then places another paper on the projector.

(Audience Laughing)

Leonard continues TOLD YOU
I'M NOT A HIGH TECH GUY.

The new image shows two flat surfaces. The first has a slightly curved line and reads “ordinary star.” The second has a line that peaks down as if it were an endless gap, and reads “black hole.”

Leonard continues UM... THE WHAT EINSTEIN SAID IS
GRAVITY IS SOME SORT OF WARPING
OF SPACE TIME WHICH GIVES IT
CURVATURE AND AN ORDINARY STAR
IS JUST A LITTLE DEEPER IN SPACE
TIME, A BLACK HOLE OR A DARK
STAR, CAN EVERYBODY SEE THIS
LITTLE RING THAT'S AROUND HERE,
THIS LITTLE SLIGHT GREY RING, I
DIDN'T MAKE IT DARK ENOUGH, IS
IT POSSIBLE TO SEE?
YEAH OKAY GOOD.
UH... A BLACK HOLE BY CONTRAST
IS A GREAT BIG DIMPLE WITH A
NASTY POINT AT THE END OF IT,
THAT IF YOU FALL INTO, YOU HIT
THAT POINT AND YOU GET SKEWERED
ON IT.
BUT IT ALSO HAS SOMETHING CALLED
A HORIZON THAT GOES AROUND IT
AND THE HORIZON IS SUCH THAT IF
YOU FALL BEHIND THE HORIZON
YOU'RE SCREWED YOU'RE GONNA
GET-- EXCUSE ME THERE'S YOUNG
PEOPLE HERE, IF YOU FALL BEHIND
THE HORIZON YOU'RE GOING TO
WIND UP GETTING SKEWERED ON
THAT.
SO THAT'S WHAT A BLACK HOLE IS
ACCORDING TO EINSTEIN GRAVITY.
THIS IS NOT WHAT I WANT YOU TO
THINK OF AS A BLACK HOLE.
BECAUSE SPACE TIME GEOMETRY IS A
COMPLICATED SUBJECT.
I'M GONNA GIVE YOU INSTEAD A
METAPHOR OR AN ANALOGY FOR IT
WHICH I ACTUALLY FIND HELPFUL
WHEN I THINK ABOUT IT.
IMAGINE AN INFINITE LAKE.

A drawing shows a side-section of a lake with an area that peaks down in a funnel shape.

Leonard continues A LAKE THAT JUST FILLS ALL OF A
FLAT PLANET OVER THE WHOLE SPACE
OF IT, THERE'S THE WATER.
IT'S RATHER SHALLOW.
UH, FISH LIVE IN IT.
THESE FISH COMMUNICATE WITH EACH
OTHER AND THEY COMMUNICATE WITH
EACH OTHER WITH SOUND.
THEY CAN'T SEE, THEY'RE BLIND,
THERE'S NO LIGHT, IN THIS WORLD
THERE IS NO LIGHT, THEY
COMMUNICATE WITH EACH OTHER WITH
SOUND, AND FURTHERMORE THERE'S A
RULE.
I DON'T KNOW IF IT'S A RULE OF
NATURE OR IF IT'S A LAW THAT THE
FISH PASSED, BUT THE RULE IS NO
FISH IS ALLOWED TO GO FASTER
THAN THE SPEED OF SOUND.
NOTHING IN THE SYSTEM CAN GO
FASTER THAN THE SPEED OF SOUND.
THAT'S THE RULE.
NOW RIGHT AT THE CENTRE OF THE
LAKE THERE'S A DRAIN HOLE.
AND THE DRAIN HOLE IS OPENING UP
AND LETTING THE WATER FLOW
THROUGH, AND GUESS WHERE IT
GOES, IT GOES TO A SHARP ROCK AT
THE BOTTOM SO THAT ANYTHING THAT
FALLS THROUGH THIS HOLE IS AGAIN
DESTROYED ON THESE HARD ROCKS
HERE, THESE NASTY HARD ROCKS.
WELL IF YOU GO FAR AWAY, YOU
WILL FIND THAT THE FLUID IS
MOVING VERY SLOWLY.
AND AS YOU MOVE CLOSER AND
CLOSER AND CLOSER, THE FLUID IS
MOVING FASTER AND FASTER.
AND EVENTUALLY YOU COME TO A PLACE
WHERE THE FLUID IS MOVING AS
FAST AS ANYTHING ELSE CAN MOVE,
IN OTHER WORDS IT'S MOVING WITH
THE SPEED OF SOUND.
THAT MEANS THAT A FISH THAT GETS
IN THERE CAN'T GET OUT.
THE FLUID IS FALLING FASTER, THE
WATER IS FLOWING FASTER THAN A
FISH CAN SWIM.
NOT ONLY THAT, SINCE IT'S FALLING FASTER
THAN SOUND CAN PROPAGATE, THAT
FISH CAN'T EVEN SIGNAL HIS
OUTSIDE FRIENDS THAT HE'S THERE.
THE SOUND WILL FALL BACK DOWN.
IT'S BEING PULLED DOWN BY THE
IN FALLING WATER.
SO THAT RING THERE, THAT PLACE
WHERE THE VELOCITY EXCEEDS THE
SPEED OF SOUND, THAT IS A POINT
OF NO RETURN.
ANYTHING THAT FALLS PAST THERE
IS DOOMED.
NOW A FISH THAT IS JUST FLOATING
FREELY WILL HAVE NO IDEA THAT
IT'S PASSING THIS POINT OF NO
RETURN.
NOTHING SPECIAL HAPPENS THERE.
JUST FLOATS PAST IT AND ONLY
FINDS OUT THAT HE'S DOOMED
LATER.
THERE'S NOTHING EXTRAORDINARY,
THERE ARE NO SIGN POSTS THERE
THAT SAY POINT OF NO RETURN,
OR DANGER OR ANYTHING LIKE THAT.
JUST FLOATS ON ITS BACK DOWN
THERE AND SUDDENLY FINDS HIMSELF
IN BAD TROUBLE, BUT THERE'S
NOTHING SPECIAL GOING ON AND
THAT PLACE IS THE HORIZON.
THIS IS THE BLACK HOLE.
THE BOTTOM, THE NASTY PLACE IS
THE SINGULARITY.
THE PLACE WHERE YOU REALLY DO
GET RIPPED TO PIECES.
AND THIS WHITE LINE HERE WHERE
THE VELOCITY OF THE FLUID
BECOMES THE VELOCITY OF SOUND,
THAT'S ANALOGOUS, VERY PRECISELY
ANALOGOUS TO THE HORIZON OF A
BLACK HOLE.
THIS ANALOGY INCIDENTALLY I
LEARNED FROM MY FRIEND, BILL
UMRING WHO WAS A PROFESSOR IN
VANCOUVER, THE UNIVERSITY OF
VANCOUVER.
OKAY THAT'S EVERYTHING YOU HAVE
TO KNOW ABOUT BLACK HOLES.
THAT IS IT, THAT'S WHAT A BLACK
HOLE IS.
OF COURSE IT'S SPACE WHICH IS
MOVING, IT'S NOT FLUID WHICH IS
MOVING, IT'S SPACE WHICH IS
FLOWING IN, BUT THAT'S THE
PICTURE.
NOW, YEARS LATER AFTER THE BLACK
HOLE HAD BEEN DISCOVERED, PEOPLE
STARTED THINKING ABOUT THE
THERMAL DYNAMICS OF BLACK HOLES,
I'LL TELL YOU WHAT THAT MEANS IN
A MINUTE.
ABOUT BLACK HOLES AND HEAT AND
ABOUT BLACK HOLES AND QUANTUM
MECHANICS.
THE FIRST IDEA THAT THERE'S
SOMETHING INTERESTING AND
PECULIAR ABOUT BLACK HOLES
HAVING TO DO WITH WHAT CAME FROM
JACOB BEKENSTEIN IN 1972.
JACOB BEKENSTEIN IS AN ISRAELI
PHYSICIST, A VERY FAMOUS ISRAELI
PHYSICIST, AND HE ASKED AN
INTERESTING QUESTION.
HE ASKED ABOUT THE SECOND LAW OF
THERMAL DYNAMICS.
THE SECOND LAW OF THERMAL
DYNAMICS SAYS ENTROPY ALWAYS
INCREASES.
WHAT IS ENTROPY?
WE'LL COME TO WHAT ENTROPY IS.
BUT WHATEVER IT IS, IT'S GOT TO
DO WITH HEAT.
IT'S GOT TO DO WITH SUBSTANCES
WHICH HAVE BEEN HEATED.
THE ENTROPY OF THE WORLD ALWAYS
INCREASES.
IT'S ROUGHLY SPEAKING A
STATEMENT THAT CONFUSION ALWAYS
GETS WORSE.
AND WHAT BEKENSTEIN SAID IS HE
SAID WAIT A MINUTE, I CAN MAKE
THE ENTROPY OF THE WORLD, OR THE
WORLD THAT I'M IN CONTACT WITH,
I CAN MAKE IT DISAPPEAR.
I CAN JUST TAKE A BOX OF HOT HAS
FULL OF MOLECULES, FULL OF
ENTROPY AND LET IT FLOAT DOWN
AND FALL INTO THIS BLACK HOLE.
ONCE IT'S BEHIND THE HORIZON, I
WILL NEVER SEE IT AGAIN, I CAN
NEVER FEEL IT AGAIN, I CAN NEVER
HAVE ANY CONTACT AND EFFECTIVELY
IT'S OUT OF MY WORLD.
AND SINCE IT'S OUT OF MY WORLD
EFFECTIVELY THE ENTROPY OF MY
WORLD HAS DECREASED.
HE SAID THAT VIOLATES THE SECOND
LAW OF THERMAL DYNAMICS, THAT
THE ENTROPY SHOULD DECREASE AND
HIS SOLUTION TO IT WAS THAT WHAT
IT MUST MEAN IS THAT THE BLACK
HOLE ITSELF HAS ENTROPY, THAT
THE PICTURE WAS THAT ANYTHING
THAT FALLS INTO THE BLACK HOLE
INCREASES THE SIZE OF THE BLACK
HOLE A LITTLE BIT, ADDS SOME
MASS TO IT, ADDS SOME SIZE TO IT
AND SOME HOW THE BLACK HOLE
ITSELF HAS ENTROPY, AND BECAUSE
IT HAS GOTTEN BIGGER THE ENTROPY
MUST BE INCREASING.
HE MADE SOME ROUGH CALCULATIONS
AND CONCLUDED THAT THE ENTROPY
OF A BLACK HOLE WAS PROPORTIONAL
TO THE AREA OF THE HORIZON.
VERY INTERESTING BUT DOESN'T
MEAN ANYTHING TO ANYBODY UNLESS
YOU KNOW WHAT ENTROPY IS.
RIGHT?
SO NOW I WILL TELL YOU WHAT
ENTROPY IS.
HERE'S AN EXAMPLE, A PERFECT
EXAMPLE OF ENTROPY.

A new drawing shows a side-section of a full bathtub.

Leonard continues HERE'S A BATHTUB, IT'S FULL OF
HOT WATER.
A BATH TUB FULL OF HOT WATER,
HOW DO YOU DESCRIBE IT?
YOU DESCRIBE IT BY IT'S
TEMPERATURE, BY THE AMOUNT OF
WATER IN IT, MAYBE THE PRESSURE
OF THE WATER, A FEW THINGS,
THAT'S ABOUT ALL.
BUT THERE'S AN ENORMOUS AMOUNT
GOING ON IN THAT WATER THAT YOU
CAN'T SEE.
IT'S THE MOLECULAR STRUCTURE OF
THE WATER.
THERE'S AN ENORMOUS AMOUNT OF
INFORMATION IN THAT WATER ABOUT
EACH INDIVIDUAL MOLECULE.
THE POSITION OF EVERY INDIVIDUAL
MOLECULE IS A PIECE OF
INFORMATION.
BUT IT'S HIDDEN INFORMATION.
IT'S HIDDEN BECAUSE YOU'RE TOO
COURSE GRAIN, YOU'RE TOO BIG,
YOU'RE TOO GROSS, YOU'RE TOO
YOU'RE TOO BIG TO BE ABLE TO SEE
IT.
IT'S HIDDEN INFORMATION.
WHAT ENTROPY IS IS HIDDEN
INFORMATION THAT YOU CAN'T SEE
BECAUSE IT'S IN MICROSCOPIC
THINGS THAT YOU CAN'T SEE.
HERE'S A TECHNICAL STATEMENT
THAT DOESN'T MATTER.
WHAT IT MEANS ENTROPY IS HIDDEN
INFORMATION STORED IN THINGS
BECAUSE YOU CAN'T SEE THEM.
WELL THAT HAS AN INTERESTING, THERE'S
SOMETHING INTERESTING GOING ON
IF BLACK HOLE HAVE ENTROPY,
WHICH IS WHAT BEKENSTEIN HAD TO
SAY IN ORDER TO RESCUE THE
SECOND LAW OF THERMAL DYNAMICS.
THAT MEANS SEVERAL THINGS.
FIRST OF
ALL IT MEANS THEY HAVE A HEAT
CONTENT.
ENTROPY IS ALWAYS ASSOCIATED
WITH HEAT.

A new slide shows a black dot and the caption “Black holes have a heat content.”

Leonard continues SO IT MUST MEAN THAT BLACK HOLE
HAVE SOME HEAT ASSOCIATED WITH
THEM.
THEY HAVE SOME ENERGY ASSOCIATED
WITH THEM, JUST GOOD OLD
EINSTEIN'S E=MC SQUARED, SAYS
THAT A BLACK HOLE HAS SOME
ENERGY.
ANYTHING THAT HAS BOTH ENERGY
AND ENTROPY AUTOMATICALLY HAS A
TEMPERATURE.
THE TEMPERATURE IS THE ENERGY
DIVIDED BY THE ENTROPY
BASICALLY.
AND SO WHAT HAWKING REALIZED IS
THAT JACOB BEKENSTEIN'S ENTROPY
IDEA IMPLIED THAT A BLACK HOLE
HAS A TEMPERATURE, THAT IT'S NOT
A FROZEN COLD OBJECT.
AND WHAT DO THINGS WITH
TEMPERATURE DO?
THEY RADIATE.
THEY RADIATE ENERGY, THE SAME
WAY A HOT POKER THAT WAS LEFT IN
THE FIRE RADIATES SOME LIGHT, NO
MATTER HOW COOL A THING IS AS
LONG AS IT HAS ANY TEMPERATURE
AT ALL, WILL RADIATE AWAY SOME
ENERGY.
BUT IF IT RADIATES AWAY ENERGY
THAT MEANS IT'S RADIATING AWAY
ITS MASS, AND IF IT RADIATES
AWAY ITS MASS IT MEANS IT
SHRINKS.
AND SO WHAT HAWKING REALIZED WAS
THAT BLACK HOLES EVENTUALLY
EVAPORATE, THEY DISAPPEAR.
THIS IS ALL PRELIMINARY TO THE
BLACK HOLE WAR.
THIS IS THE PRELIMINARY THAT
WENT INTO UM... INTO...
THE STORY.
OH, YES, I THINK I MAY HAVE
MENTIONED ON THE OTHER SLIDE,
THE ENTROPY OF THE BLACK HOLE IS
PROPORTIONAL TO ITS SURFACE
AREA.
THAT'S VERY STRANGE.
IF YOU THINK ABOUT THE
TEMPERATURE, IF YOU THINK ABOUT
THE BATH FULL OF HOT WATER AND
YOU ASK HOW MUCH INFORMATION YOU
CAN HIDE, BASICALLY IT'S THE
NUMBER OF MOLECULES, AND THE
NUMBER OF MOLECULES IS ALWAYS
PROPORTIONAL TO THE VOLUME.
IN ALL SYSTEMS THAT ANYBODY EVER
KNEW ABOUT THE UH, THE ABILITY
TO HIDE INFORMATION WAS ALWAYS
PROPORTIONAL TO THE VOLUME.
HOW MANY MOLECULES ARE THERE IN
THIS ROOM?
WELL IT'S PROPORTIONAL TO THE
VOLUME.
WELL BEKENSTEIN FOUND WAS THAT
THE ENTROPY OF THE BLACK HOLE
WAS PROPORTIONAL TO ITS AREA.
VERY STRANGE, AS IF THERE WAS
NOTHING INSIDE THE BLACK HOLE.
PEOPLE STUDIED BLACK HOLES
EXTENSIVELY AFTER THAT AND THEY
LEARNED SOME THINGS ABOUT BLACK
HOLES WHICH WERE SURPRISING.
FROM THE POINT OF VIEW OF THE
FISH FALLING PAST THE POINT OF
NO RETURN, THERE'S NOTHING
SPECIAL ABOUT THE HORIZON.
BUT FOR THE POINT OF VIEW OF
SOMEONE OUTSIDE THE BLACK HOLE
DOING EXPERIMENTS ON THE BLACK
HOLE, IT SEEMS AS IF AT THE
SURFACE OF THE BLACK HOLE AT THE
HORIZON OF THE BLACK HOLE THERE
ARE ALL SORTS OF THINGS GOING
ON.
THE FISH OR A HUMAN BEING
FALLING THROUGH WOULD SEE
NOTHING, AND YET, THE
DESCRIPTION FROM OUTSIDE THE
BLACK HOLE, HERE'S THE KIND OF
THINGS YOU COULD DO.
YOU COULD TAKE THE TEMPERATURE
OF THE BLACK HOLE BY DROPPING A
THERMOMETER DOWN NEAR THE
SURFACE OF IT.
WHAT YOU WOULD DISCOVER IS THE
TEMPERATURE GETS HOTTER AND
HOTTER AND HOTTER AS YOU GET
DOWN NEAR THE SURFACE OF A BLACK
HOLE.
THIS IS WEIRD BECAUSE REMEMBER
THE FISH FLOATING THROUGH FEELS
NOTHING SPECIAL HAPPENING AND
YET A THERMOMETER WHICH IS
SUPPORTED AND WITH CAN BE PULLED
BACK UP REGISTERS A TEMPERATURE
THAT GROWS AND GROWS AND GROWS
AS YOU GET CLOSE TO THE
HORIZON.
YOU COULD DO AN ELECTRICAL
EXPERIMENT WHERE YOU MAKE A
CIRCUIT AND YOU PUT THE READS
DOWN NEAR THE HORIZON, YOU
WOULD DISCOVER THE HORIZON
BEHAVES LIKE AN ELECTRICAL
CONDUCTOR.
THAT SEEMS VERY STRANGE, NOTHING
GOING ON AT THE HORIZON AND YET
IT'S BEHAVING LIKE AN ELECTRICAL
CONDUCTOR.
THE HORIZON HAS TEMPERATURE IT
HAS ENTROPY, IT HAS ALL OF THESE
PHENOMENA AND YET, FROM THE
POINT OF VIEW OF SOMEBODY
FALLING THROUGH, NOTHING IS
THERE.
THIS WAS A PUZZLE, AND THE
QUESTION THAT PEOPLE WOULD ASK
IS IS THERE REALLY SOMETHING
THERE AT THE HORIZON OR IS
THERE REALLY NOT SOMETHING
THERE?
AND THE CONCLUSION OF MOST
PHYSICISTS IS THAT THIS WAS
ILLUSORY, THERE'S NOTHING REALLY
AT THE HORIZON, AND TO TEST IT,
YOU COULD FALL THROUGH THE
HORIZON AND SEE THAT THERE'S
NOTHING THERE.
BUT ON THE OTHER HAND YOU COULD
TEST IT FROM THE OUTSIDE AND
DISCOVER THERE WAS SOMETHING
THERE.
THIS WAS A GREAT PUZZLE.
IT WAS PART OF THE PUZZLE THAT
LEAD TO THE BLACK HOLE WARS.
AND IT LEAD TO A VERY, VERY
SERIOUS CONFLICT OF PRINCIPLE
BETWEEN TWO FUNDAMENTAL
PRINCIPLES OF PHYSICS.
ONE IS CALLED THE EQUIVALENCE
PRINCIPLE.
FOR OUR PURPOSES THE EQUIVALENCE
PRINCIPLE MEANS NO MORE THAN
FISH FALLING THROUGH THE POINT
OF NO RETURN FEEL NOTHING, AND
DO FALL INTO THE CENTRE.

A new slide shows a drawing of a vertical cylinder with a red shaft, and four fish swimming towards it.

Leonard continues THIS IS AN IMAGINARY BLACK HOLE,
VERTICALLY I'VE PLOTTED TIME,
HERE'S THE HORIZON OF THE BLACK
HOLE, AND HERE ARE THE FISH
FALLING INTO THE BLACK HOLE WITH
TIME, AND RIGHT AT THE CENTRE
IS THE NASTY SINGULARITY WHERE
IT'S BOUND TO GET KILLED.
OKAY SO
THIS FISH JUST SAILS RIGHT
THROUGH, AND IF THAT FISH
HAPPENS TO CARRY ANY INFORMATION
WITH IT, SUCH AS THE
ENCYCLOPAEDIA BRITANNICA OR
ANYTHING THAT IT'S CARRYING WITH
IT, THAT INFORMATION WILL GO
RIGHT BEHIND THE HORIZON.
ONCE IT GOES BEYOND THE HORIZON
HERE IT CANNOT GET OUT.
BLACK HOLES
CANNOT, OR THE HORIZON OF BLACK
HOLES ARE A ONE WAY THING, YOU
CANNOT GET BACK OUT, NOT WITHOUT
EXCEEDING THE SPEED OF LIGHT.
ON THE OTHER HAND, ALL OF THESE
RADIATION, ALL OF THIS RADIATION
IS COMING OUT OF THE BLACK HOLE.
THIS IS THE STUFF THAT HAWKING
DISCOVERED.
HAWKING DISCOVERED THAT BLACK
HOLES RADIATE AND AS THEY
RADIATE THEY GIVE OFF ENERGY.
SO IT SEEMS THAT IF HAWKING IS
CORRECT THAT INFORMATION FALLS
INTO THE BLACK HOLE AND CANNOT
GET OUT, AND IF THE ENERGY DOES
GET OUT, IN THE FORM OF THIS
HAWKING RADIATION.
WHY IS THIS A PUZZLE?
IT'S A PUZZLE BECAUSE IT MEANS
THAT INFORMATION IS LOST, TRULY
LOST, AND THIS IS SOMETHING
WHICH IN ALL OF PHYSICS, UP TO
THE PRESENT TIME, NO ONE WAS
EVER ALLOWED -- REAL INFORMATION
IS ALWAYS THERE IN THE SYSTEM NO
MATTER HOW SCRAMBLED IT GETS,
NO MATTER HOW HARD IT IS TO
RECOVER, THE INFORMATION IN THE
HOT BATH OF WATER IS THERE.
IF YOU COULD STUDY EVERY
MOLECULE, YOU WOULD DISCOVER
EVERYTHING THAT EVER HAPPENED TO
THAT BATH.
AND HERE IS HAWKING SAYING
SOMETHING REALLY NEW, HE WAS
SAYING THAT WHEN YOU HAVE A
BLACK HOLE AROUND, INFORMATION
IS TRULY LOST.
THERE'S A PROCESS THAT TAKES
PLACE IN THE BLACK HOLE THAT
COMPLETELY WIPES OUT THE PAST.
IT COMPLETELY WIPES OUT ANY
INFORMATION IN THE PAST, AND
THIS IS WHAT DISTURBED GERARD
T'HOOFT AND MYSELF.
WHY DID IT DISTURB US?
BECAUSE THIS VIOLATED EVERYTHING
WE KNEW ABOUT PHYSICS.
ORDINARILY IN PHYSICS,
INFORMATION IS NEVER LOST.
IT MAY BE SCRAMBLED BUT IT IS
NEVER DESTROYED.
GERARD AND MYSELF BELIEVED
STEPHEN WAS WRONG.
STEPHEN BELIEVED HE WAS RIGHT.
BUT IT BECAME A SORT OF MEXICAN
STAND OFF.
WE COULDN'T FIGURE OUT WHAT WAS
WRONG WITH HIS ARGUMENT, AND HE
CERTAINLY DIDN'T BELIEVE US.
25 YEARS WENT BY OF ARGUING.
LET ME PHRASE IT TO YOU ANOTHER
WAY.
LET ME GIVE YOU TWO STORIES, TWO
STORIES AND LET'S SEE IF WE CAN
DECIDE AMONG US BY TAKING A VOTE
WHICH OF THE TWO STORIES IS
CORRECT.
BOTH OF THESE STORIES INVOLVE
THROWING SOMEBODY INTO A BLACK
HOLE.

He presents another slide, in which the face of George W. Bush is tossed into two circles representing black holes. The first circle is captioned “Hawking’s view” and the second circle is captioned “T’Hooft, Susskind view.”

(Audience Laughing)
(Cheers and Applause)

Leonard says WHAT YOU LIKE THAT?
OH OKAY.
I HAVE ANOTHER ONE IF YOU DON'T
LIKE THAT.

He shows another slide which is identical, except for the fact that now it’s Condoleezza Rice’s face being chucked into the black holes.

(Audience Laughing)
(Applause)

Leonard says I HAVE A
FEW MORE BUT IT'LL TAKE US ALL
NIGHT.
I'LL TELL YOU -- WHAT I TRIED TO
DO, I WANTED TO TELL A JOKE
HERE.
SO I ASKED MY FRIENDS, WHO IS
THE DUMBEST MOST DISLIKED
POLITICIAN IN CANADA?
BECAUSE I WANTED TO HAVE ONE
MORE WITH A CANADIAN ON IT.
AND THEY SCRATCHED AND THEY
THOUGHT AND NOBODY COULD COME UP
WITH AN ANSWER.

(Audience Laughing)

Leonard continues IS THIS
TRUE, COME ON.
WHO, ROB OR...?
SO... ALL RIGHT SO HERE'S THE
QUESTION, THIS WAS SERIOUS.
THERE APPEAR TO BE TWO
DISCREPANT STORIES THAT COME
FROM TWO DIFFERENT PRINCIPLES OF
PHYSICS.
ACCORDING TO ONE PRINCIPLE OF
PHYSICS ANYBODY WHO FALLS
THROUGH A BLACK HOLE EXPERIENCES
NOTHING SPECIAL AT THE HORIZON,
NOTHING AT ALL AND SIMPLY FALLS
THROUGH AS HAPPY AS THEY EVER
WERE UNTIL THEY GET NEAR THE
SINGULARITY WHERE THEY GET
CRUSHED, WHERE THEY GET
MUTILATED, WHERE THEY GET
DESTROYED WHERE THEY GET.
(Laughing)
WHERE...
WHERE...
THAT'S ONE STORY.
I'M IMAGINING, I'M IMAGINING A
BLACK HOLE WHICH IS SO LARGE
THAT IF SOMEBODY FALLS THROUGH
IT, THEY CAN SURVIVE FOR A
NUMBER, FOR 100 MILLION YEARS
FOR EXAMPLE.
ONE MILLION YEARS, EXCUSE ME.
FOR ONE MILLION YEARS, A MILLION
LIGHT-YEAR BLACK HOLE.
CONDI HERE CAN SURVIVE FOR A
MILLION YEARS AND ENCOUNTERS
NOTHING SPECIAL AT THE HORIZON.
NOW THERE'S ANOTHER STORY, THE
OTHER STORY COMES FROM HAWKING’S
AND BEKENSTEIN'S CONCLUSION
THAT THERE'S A HEAT CONTENT ON
THE SURFACE OF THE BLACK HOLE
AND ALSO Bill Unruh’s CONTRIBUTION, AND THEIR
CONTRIBUTION SAID, BEKENSTEIN'S
AND PARTICULARLY Unruh’s,
THAT VERY NEAR THE SURFACE OF
THE BLACK HOLE, IT IS HOT,
THAT'S WHERE ALL OF THIS ENTROPY
IS, THE TEMPERATURE GETS HIGHER
AND HIGHER AS YOU GET DOWN CLOSE
TO IT, AND IN THAT PICTURE,
CONDI HERE FALLS IN AND WHEN SHE
GETS NEARER AND NEARER TO THE
SURFACE OF THE HORIZON SHE GETS
COOKED, SHE'S GETS EVAPORATED,
SHE GETS IONIZED AND EVENTUALLY
TURNED INTO JUST HOT PHOTONS
WHICH GO OUT.
THESE WERE THE TWO PICTURES
WHICH LOOKED TOTALLY
IRRECONCILABLE, CANNOT POSSIBLY
BE THE SAME.
AND YET ONE
LAW OF PHYSICS, NAMELY THE
CONSERVATION OF INFORMATION THAT
NOTHING EVER GETS LOST MOST SAY
THAT CONDI'S BITS GET SPIT OUT
BY THE BLACK HOLE BEFORE THEY
EVER FELL IN, AND THE TO HER
PICTURE WHICH IS THE EQUIVALENCE
PRINCIPLE, SAYS NOTHING SPECIAL
HAPPENS AT THE HORIZON.
SO NOW WE
TAKE A VOTE, HOW MANY PEOPLE,
LET'S DO THIS AS A VOICE VOTE,
HOW MANY PEOPLE THINK THAT CONDI
SURVIVES UNTIL SHE HITS THE
SINGULARITY?

(Mumbling)
(Audience Laughing)

Leonard continues I CAN NEVER
GET PEOPLE TO VOTE.
RAISE YOUR HAND IF YOU THINK SHE
SURVIVES.

A few people in the audience raise their hands.

Leonard continues OKAY GOOD.
HOW MANY PEOPLE THINK SHE GETS
HER JUST DESSERTS AT THE
HORIZON?

(Audience Laughing)

A few other people raise their hands.

Leonard continues OH OKAY,
MORE AT THE HORIZON THAN AT
THE--
THAT'S INTERESTING.
THIS IS ONE OF MY FAVOURITE
UH... QUOTES OF SHERLOCK HOLMES.
I KNEW HIM WELL.

A slide reads “When you have eliminated all that is impossible, whatever remains must be the truth, no matter how improbable.”

Leonard continues THE ANSWER
IS, IN A CERTAIN SENSE THAT I
WILL TRY TO MAKE CLEAR --

Another slide reads “Both stories are true depending on who is telling them! Black hole complementarity, 1993.”

(Audience Laughing)

Leonard continues WHAT DID
BILL CLINTON SAY, IT DEPENDS ON
WHAT “IS” MEANS?

(Audience Laughing)

Leonard continues ALL RIGHT.
A CONCEPT, A NEW CONCEPT HAS
ARISEN IN PHYSICS THAT SAYS
BOTH OF THESE STORIES ARE TRUE
IN A CERTAIN SENSE.
AND THAT NEW CONCEPT IS CALLED
BLACK HOLE COMPLEMENTARITY.
THIS IS ONE OF THE THINGS WHICH
HAS COME OUT OF THIS GREAT
DEBATE.
INCIDENTALLY, STEPHEN AND I AND
GERARD ARGUED AND ARGUED AND
ARGUED AND ARGUED, AND
EVENTUALLY, I AND GERARD JUST
AGREED WITH EACH OTHER, NOBODY
ELSE THAT THIS MUST BE WHAT'S
GOING ON, SOMEHOW BOTH STORIES
ARE TRUE.
SO WE INTRODUCED AN IDEA CALLED
BLACK HOLE COMPLEMENTARITY.
WHAT IS COMPLEMENTARITY?
COMPLEMENTARITY IS A CONCEPT IN
PHYSICS THAT GOES BACK TO “NILS
BOR.”
SO LET ME TELL YOU WHAT IT SAYS
OR THE KIND OF THING IT SAYS.
IT'S VERY INTERESTING.
NILS BOHR WAS INTERESTED IN
CONFLICTING DESCRIPTIONS.
DESCRIPTIONS OF THINGS THAT
APPARENTLY CONFLICTED.
FOR EXAMPLE, LIGHT IS A WAVE.
HOW DO YOU SEE THAT LIGHT IS A
WAVE?
YOU SEE INTERFERENCE PATTERNS
WHEN YOU SENT LIGHT THROUGH
LITTLE HOLES.
MAKES PATTERNS THAT LOOK LIKE
WAVE PATTERNS.
LIGHT IS A WAVE.
ON THE OTHER HAND, IF YOU SEND
LIGHT THROUGH VERY, VERY SLOWLY
MEANING A VERY, VERY DILUTE BEAM
OF LIGHT, YOU ATTENUATE THE
LIGHT SOMEHOW, PUT A LOT OF
FILTERS IN THE WAY OR SOMETHING
LIKE THAT, THEN YOU FIND OUT
THAT THE LIGHT ARRIVES ON THE
SCREEN OVER HERE AS LITTLE
PIECES, LITTLE BITS PHOTONS.
QUANTA, PARTICLES.

A slide shows a drawing of particles of light travelling through a small hole and landing in different places on a flat screen.

Leonard continues LIGHT IS A WAVE, AND LIGHT IS A
PARTICLE.
NOW, WRONG LANGUAGE, LIGHT IS A
WAVE OR LIGHT IS A PARTICLE.
DEPENDING ON THE EXPERIMENT THAT
YOU DO.
THIS IS WHAT NILS BOHR TAUGHT US.
DEPENDING ON THE EXPERIMENT THAT
YOU DO, LIGHT MAY BEHAVE AS A
WAVE OR IT MAY BEHAVE AS A
PARTICLE.
THE QUANTITATIVE STORY THAT
GOES WITH THE PARTICLES HERE, IS
THAT THE ENERGY OF THESE LITTLE
QUANTA DEPEND ON THE FREQUENCY
OF THE LIGHT WAVE THROUGH PLUNKS
CONSTANT.
E=H NU.
THIS IS ONE EXAMPLE OF
COMPLEMENTARITY WHERE TWO
APPARENTLY IRRECONCILABLE
DESCRIPTIONS OF SOMETHING YOU
CAN SEE THEY'RE BOTH TRUE BUT I
WOULDN'T WANT TO SAY IT IS A
WAVE AND IT IS A PARTICLE, I
WOULD WANT TO SAY IT IS A WAVE
OR A PARTICLE DEPENDING ON THE
EXPERIMENT THAT YOU DO.
THAT'S THE FIRST EXAMPLE OF
COMPLEMENTARITY, I'LL GIVE YOU
TWO MORE.
THE SECOND EXAMPLE HAS TO DO
WITH HEISENBERG'S UNCERTAINTY
PRINCIPLE.
ANYBODY HERE WHO'S NEVER HEARD
OF HEISENBERG'S UNCERTAINTY
PRINCIPLE?
A FEW PEOPLE.
ALL RIGHT.
WELL... MOST PEOPLE HAVE HEARD
OF HEISENBERG'S UNCERTAINTY, IF
THEY'RE IF THEY'RE CERTAINLY IF
THEY HAVE A SCIENTIFIC
BACKGROUND, BUT I'LL TELL YOU
VERY SIMPLY WHAT IT SAYS.
IF YOU HAVE AN OBJECT, THAT
OBJECT TYPICALLY HAS A POSITION,
A LOCATION IN SPACE, MY FIST.
ALL RIGHT, IT ALSO TYPICALLY HAS
A VELOCITY.
IN ORDER TO KNOW WHAT'S GOING TO
HAPPEN TO IT NEXT YOU HAVE TO
KNOW WHERE IT IS AND HOW IT'S
MOVING.
AND SO IN CLASSICAL PHYSICS, ONE
ALWAYS ASSUMED THAT OBJECTS
HAVE BOTH POSITION AND VELOCITY
AND A AND B, AN OBJECT HAS A
POSITION AND A VELOCITY.
WHAT HEISENBERG SHOWED IS THAT
ANYTIME YOU TRY TO MEASURE THE
POSITION OF AN OBJECT YOU DO
IT WITH LIGHT, THE LIGHT
CONSISTS OF QUANTA, YOU CAN ONLY
SEE THE POSITION OF A PARTICLE
IF YOU USE A VERY SHORT WAVE
LENGTH QUANTA.
YOU CANNOT SEE THE LOCATION OF A
THING ACCURATELY BY USING LONG
WAVE LENGTH RADIO WAVES.
IF YOU WANT
TO SEE SOMETHING ACCURATELY YOU
HAVE TO USE SHORT WAVE LENGTHS
AND THE QUANTA THAT MAKE UP THE
SHORT WAVE LENGTH LIGHT WAVE
HAVE A GREAT DEAL OF ENERGY.
AND SO EVERY TIME A QUANTA HITS
THIS OBJECT IT GIVES IT A KICK
AND IT CHANGES THE VELOCITY.
SO WHAT HEISENBERG UNDERSTOOD
AND WHAT BOHR AFTER HIM
UNDERSTOOD.
WAS THAT
PARTICLES DON'T HAVE, OR OBJECTS
DON'T HAVE POSITIONS AND
VELOCITIES, DEPENDING ON WHAT
EXPERIMENT YOU DO YOU EITHER
DESCRIBE THEM AS HAVING A
POSITION OR A VELOCITY.
AND THIS WAS QUANTIFIED BY
HEISENBERG'S UNCERTAINTY
PRINCIPLE, WHICH SAID THE
UNCERTAINTY IN THE POSITION
TIMES THE UNCERTAINTY IN THE
MOMENTUM OR THE VELOCITY IS
SOMETHING LIKE PLUNK'S CONSTANT,
OR BIGGER THAN PLUNK'S CONSTANT.
THIS IS ANOTHER EXAMPLE WHERE
SYSTEM, OR TWO DESCRIPTIONS ARE
COMPLIMENTARY AND WHERE THE
RIGHT IDEA IS OR RATHER THAN AND.
LET ME GIVE YOU A THIRD ONE.
AN EVENT, MY EVENT HERE IS THE
EXPLOSION OF A BOMB, OKAY.
AN EVENT HAS A TIME, IT HAPPENS
WITH SOME TIME, AND IT HAS AN
ENERGY, THE AMOUNT OF ENERGY
RELEASED BY THE BOMB FOR
EXAMPLE.
OR IT COULD BE AN ELEMENTED
PARTICLE DECAYING, AN ELECTRON,
NOT ELECTRON, A NEUTRON COMING
AND DECAYING INTO AN ELECTRON OR
A PROTON, I DIDN'T DRAW THE
NEUTRINO BUT YOU CAN'T SEE
NEUTRINOS.
UH...

(Audience Laughing)

Leonard continues RIGHT, OKAY.
A PARTICLE, DECAYING.
IT HAPPENS AT A TIME AND IT
GIVES OFF A CERTAIN AMOUNT OF
ENERGY.
SO, IT HAS A TIME AND AN ENERGY,
NO, IT DOESN'T HAVE A TIME AND
AN ENERGY, IT HAS A TIME OR AN
ENERGY, IF YOU PRECISELY KNOW
THE TIME THAT IT DECAYS IT MUST
MEAN THAT THE ENERGY IS VERY,
VERY BIG AND UNCERTAIN.
IF YOU KNOW THE ENERGY OF THE
OBJECT IT MEANS THAT THE TIME OF
DECAY IS VERY UNCERTAIN.
SO HERE'S ANOTHER EXAMPLE OF
WHERE OR HAS TO REPLACE AND.
YOU COULD EITHER DESCRIBE IT AS
HAVING ENERGY OR TIME, BUT NOT
BOTH, YOU CAN'T MEASURE BOTH.
NOW WE COME TO BLACK HOLES.
BLACK HOLES WE HAVE A SIMILAR
KIND OF PUZZLE, WE HAVE ANOTHER
SITUATION WHERE WE WOULD LIKE TO
SAY PERHAPS WE'D LIKE TO SAY
AND.
BUT AND DOESN'T MAKE SENSE.
HERE'S THE SITUATION.

He places the slide with the picture of the fish again and continues FISH ARE FALLING INTO THE BLACK
HOLE.
AND THEY'RE CARRYING THEIR
INFORMATION WITH THEM.
IT GOES BEHIND THE HORIZON SO
THE INFORMATION MUST BE
EVENTUALLY BEHIND THE HORIZON.
WHY?
BECAUSE THE HORIZON IS NOT A
SPECIAL PLACE TO THE THE FALLING
FISH.
ON THE OTHER HAND ANOTHER
PRINCIPLE OF PHYSICS TELLS US
THAT INFORMATION CAN NEVER BE
LOST, SO SOMEBODY OUT HERE MUST
BE ABLE TO DETECT THAT SAME
INFORMATION, THAT SAME FACT THAT
A FISH FELL IN, BY STUDYING VERY
VERY CAREFULLY THE EVAPORATION
PRODUCT, TALKING OF ASPIRATION
PRODUCTS THAT COME OUT.
SO, WE COULD SAY, A BIT, A BIT
OF INFORMATION IS BEHIND THE
HORIZON AND A BIT THE SAME BIT
OF INFORMATION IS IN FRONT OF
THE HORIZON.
BUT THAT'S NOT SOMETHING THAT'S
ALLOWED IN QUANTUM MECHANICS.
YOU CAN'T HAVE THE SAME BIT OF
INFORMATION TWICE.
HOWEVER YOU MIGHT SAY THERE'S A
BIT OF INFORMATION IN BEHIND THE
HORIZON OR A BIT OF INFORMATION
IN FRONT OF THE HORIZON IN THE
SENSE THAT TWO COMPLETELY
DISTINCT EXPERIMENTS,
EXPERIMENTS DONE BY THIS THEN
FALLING FISH WHICH CAN NEVER BE
COMMUNICATED TO THE OUTSIDE OR
EXPERIMENTS ON THE OUTSIDE WHICH
CAN'T BE COMMUNICATED TO THE
INSIDE, WE'LL MODIFY THAT IN A
MINUTE CAN NEVER TALK TO EACH
OTHER.
SO NO CONTRADICTION CAN BE
DERIVED.
IT'S ONE OR THE OTHER DEPENDING
ON WHICH EXPERIMENT CAN BE DONE.
THIS IS A CLASSIC EXAMPLE OF
BOHR'S COMPLEMENTARITY.
BUT THEN THERE'S AN INTERESTING
QUESTION.
SUPPOSING THIS LADY HERE WHO
COLLECTS THE BIT OF INFORMATION
THAT THE FISH FELL IN, COLLECTS
IT IN THE HAWKING RADIATION,
DECIDES TO JUMP INTO THE BLACK
HOLE WITH THAT BIT, HOLDING THAT
BIT IN HER POCKET BOOK.
NOW WE HAVE TWO BITS OF
INFORMATION, PRESUMABLY THE SAME
INFORMATION, BOTH BEHIND THE
HORIZON.
NOW THIS FISH COULD SEND A
MESSAGE TO THIS LADY HERE AND
SHE WOULD DISCOVER TWO VERSIONS
OF EXACTLY THE SAME THING, THIS
IS BAD, I'M GONNA TELL YOU WHY.
I WASN'T GONNA TELL YOU WHY THIS
IS BAD BUT LET ME TELL YOU WHY
THIS IS BAD.
THIS WOMAN OVER HERE MIGHT HAVE
MADE A MEASUREMENT WHICH WAS
EQUIVALENT TO MEASURING THE
POSITION OF THE FISH.
THE FISH, MIGHT SEND THE MESSAGE
TELLING HER WHAT ITS VELOCITY
WAS AND NOW THIS LADY WOULD KNOW
THE FORBIDDEN INFORMATION OF
BOTH THE POSITION AND THE
VELOCITY.
THIS IS THE REASON WHY YOU
CANNOT HAVE THE SAME BIT OF
INFORMATION IN TWO PLACES, IT
WOULD VIOLATE THE UNCERTAINTY
PRINCIPLE.
AND SO YOU CAN'T HAVE BOTH BITS
BUT COULD THERE BE A SENSE IN
WHICH THERE'S AN OR.
IT'S EITHER THIS OR THIS.
COULD THERE BE A REASON WHY THIS
FISH BEHIND THE HORIZON COULD
NEVER SEND A MESSAGE TO THIS
WOMAN IN FRONT OF THE HORIZON?
WELL IF YOU
THINK ABOUT IT, IF THIS FISH
TRIES TO SEND A MESSAGE AND HE'S
BEHIND THE HORIZON THIS MESSAGE
GETS SWEPT ALONG WITH THE SPACE,
AND FALLS TO THE SINGULARITY,
JUST LIKE THE HOLE IN THE LAKE.
THAT MESSAGE GETS SWEPT TO THE
SINGULARITY WHERE IT'S
DESTROYED.
SO THAT MEANS THE FISH MUST SEND
ITS MESSAGE VERY QUICKLY AFTER
PASSING THE HORIZON.
EXTREMELY QUICKLY RIGHT IMMEDIATELY AFTER
PASSING THE HORIZON IF IT WANTS
TO GET THE MESSAGE TO THIS LADY
THERE.
BUT IF IT'S GONNA SEND THE
MESSAGE THAT QUICKLY IT HAD
BETTER BE ARMED WITH A CLOCK,
AND THAT CLOCK HAD BETTER TELL
IT YOU HAD BETTER SEND THE
MESSAGE INSTANTLY AFTER PASSING
THE HORIZON HERE.
AND THAT CLOCK HAS TO BE
EXTREMELY ACCURATE.
UNFORTUNATELY IF THAT CLOCK IS
VERY ACCURATE THAT CLOCK MUST
ALSO HAVE AN ENORMOUS MASS.
THAT'S AGAIN THIS ENERGY TIME
UNCERTAINTY PRINCIPLE THAT SAYS
IF YOU KNOW THE ENERGY OF
SOMETHING THE MASS MUST BE OR
THE ENERGY IF YOU KNOW THE
ENERGY OF SOMETHING THE TIME
MUST BE COMPLETELY UNCERTAIN AND
IF YOU KNOW THE TIME THE ENERGY
MUST BE COMPLETELY UNCERTAIN.
THAT MEANS THAT FOR THIS FISH TO
SEND THAT MESSAGE IN THE FORM OF
A PHOTON IT HAD BETTER HAVE A
HUGE RESERVOIR OF ENERGY IN THE
FORM OF A CLOCK.
IN FACT, HOW BIG AN ENERGY?
IT'S ENERGY MUST BE E TO THE
SQUARE OF THE MASS OF THE BLACK
HOLE.
ENORMOUS.
AND OBJECT THAT BIG CANNOT FIT
INTO A BLACK HOLE AND SO THERE
IS NO WAY THAT YOU CAN RUN INTO
A CONTRADICTION THIS WAY.
SOME HOW HAWKING WAS MISSING
THIS.
HE DIDN'T UNDERSTAND THAT.
WE HAD A HARD TIME EXPLAINING
THAT TO HIM BUT EVENTUALLY WE
EXPLAINED IT TO HIM.
AND THE RESULT IS THAT AGAIN
THERE'S NO QUESTION OF A
CONTRADICTION.
IT'S EITHER ONE EXPERIMENT OR
THE OTHER EXPERIMENT.
EITHER YOU'RE THE FISH YOU'RE
THIS WOMAN, IN ONE CASE YOU SEE
THE BIT ON THE OUTSIDE, AND THE
OTHER CASE YOU SEE THE BIT ON
THE INSIDE.
THIS WAS REALLY SHOCKING.
THIS WAS VERY, VERY STRANGE FOR
MOST PEOPLE AND THEY HAD A HARD
TIME ACCEPTING IT THAT THE SAME
BIT OF INFORMATION COULD BE IN
TWO VERY, VERY DIFFERENT PLACES.
HOW COULD IT POSSIBLY BE THAT
THE SAME THING COULD BE SO
CONFUSED ABOUT WHERE IT IS, THE
BIT OF INFORMATION CARRIED BY
THE UH... BUT THE UM, AND WHAT
DOES IT HAVE TO DO WITH STRING
THEORY, AND WHAT DOES IT HAVE TO
DO WITH STRING THEORY?

(Audience Laughing)

Leonard continues THAT'S THE
QUESTION, WHAT DOES IT HAVE TO
DO WITH STRING THEORY?
ALL RIGHT, SO THE FIRST THING
THAT I WANT TO EXPLAIN HAS TO
DO WITH CLOCKS NEAR A BLACK
HOLE.
IF YOU'RE OUTSIDE A BLACK HOLE
AND YOU'RE WATCHING A CLOCK, THE
CLOCK SLOWS DOWN.
THIS IS ONE OF THE FUNNY THINGS
THAT EINSTEIN DISCOVERED.
THAT CLOCKS SLOWED DOWN IN A
GRAVITATIONAL FIELD.
THE CLOSER THE CLOCK GETS TO THE
HORIZON THE SLOWER AND SLOWER
AND SLOWER IT SEEMS TO GO.
YOU SEE THE CLOCK GOING VERY
SLOWLY.
NOW WHAT DOES THAT HAVE TO DO
WITH DOGS?

(Audience Laughing)

A new slide shows a black hole, a dog, and a whistle.

Leonard continues DOGS CAN HEAR SOUNDS THAT PEOPLE CAN'T HEAR.
THEY CAN HEAR EXTREMELY HIGH
FREQUENCY SOUNDS BECAUSE THEIR
EARS ARE ATTUNED TO HIGH
FREQUENCY SOUNDS.
AND SO THEY CAN HEAR A WHISTLE,
A HIGH FREQUENCY WHISTLE THAT
YOU CAN'T HEAR.
OKAY, BUT NOW TAKE THAT WHISTLE
AND TAKE IT IN CLOSE TO THE
BLACK HOLE HORIZON AND LISTEN TO
IT FROM THE OUTSIDE.
THE WHISTLE SEEMS TO SLOW DOWN.
THE WHISTLE NEAR THE BLACK HOLE
IS SEEN AS GOING SLOWER, IS
HEARD AS GOING SLOWER AND SO THE
PERSON ON THE OUTSIDE SUDDENLY
AS THE WHISTLE GETS CLOSER AND
CLOSER TO THE HORIZON SUDDENLY
BEGINS TO HEAR IT, SUDDENLY
BEGINS TO SENSE HE VERY VERY
HIGH FREQUENCY OSCILLATIONS OF
THE WHISTLE THAT THEY COULDN'T
SENSE WHEN THE WHISTLE WAS NOT
NEAR A BLACK HOLE HORIZON.
OKAY.
WHAT DOES THIS HAVE TO DO WITH
STRINGS?
WHAT IT HAS TO DO WITH STRINGS
IS THAT STRINGS OSCULATE AND
VIBRATE IN THE SAME WAY THAT
WHISTLES DO.
YOU CANNOT HEAR OR SEE OR DETECT
THEIR VERY, VERY HIGH FREQUENCY
OSCILLATIONS UNLESS THEY GET
CLOSE TO A BLACK HOLE.
IN WHICH CASE YOU ON THE OUTSIDE
CAN SUDDENLY START TO BE
SENSITIVE TO THE VERY, VERY
RAPID FLUCTUATIONS OF STRING
THEORY.
I'M NOT GONNA TELL YOU WHAT
STRING THEORY IS, ALL I'M GOING
TO TELL YOU IS THE IMPLICATIONS
OF THIS AND THEY'RE VERY
STRANGE.
INSTEAD OF HEARING THE STRING...
YOU SEE THE STRING AND THE WAY
THAT YOU SEE THE STRING IS WITH
THE HAWKING RADIATION BUT THAT
DOESN'T MATTER.
YOU SEE IT OSCILLATE MORE AND
MORE WITH HIGHER FREQUENCY
OSCILLATIONS, AND AS IT DOES SO,
IF YOU'RE WATCHING IT FROM THE
OUTSIDE IT SEEMS TO OSCILLATE
MORE AND MORE VIBRATE AN
VIBRATE WITH BIGGER AND BIGGER
VIBRATIONS UNTIL IT'S SPREAD
OVER THE WHOLE ENTIRE BLACK
HOLE.
ON THE OTHER HAND, IMAGINE
YOURSELF NOW FALLING THROUGH THE
HORIZON WITH THE WHISTLE.
WHISTLE, LET'S GO BACK TO
WHISTLES.
YOU'RE FALLING THROUGH, YOU DO
NOT GET TO HEAR THE WHISTLE,
BECAUSE YOU'RE FALLING THROUGH
WITH THE WHISTLE.
SO YOU DON'T GET THE BENEFIT OF
THIS FUNNY EFFECT ON CLOCKS.
AND SO THE RESULT IS SOMEBODY
WHO IS FALLING THROUGH WITH THIS
STRING DOES GET TO SEE THE
STRING SPREAD OUT OVER THE HORIZON.
WELL THIS
SOUNDS LIKE EXACTLY THE RIGHT
KIND OF THING, TWO COMPLETELY
DIFFERENT DESCRIPTIONS, ONE FROM
THE OUTSIDE AND ONE FROM
SOMEBODY FALLING THROUGH, AND
STRING THEORY HAS THIS PROPERTY
THAT THE PLACE WHERE THE
INFORMATION IS DEPENDS ON YOUR
STATE OF MOTION.
IF YOU'RE
OUTSIDE OF IF YOU'RE FALLING
THROUGH YOU SEE TWO TOTALLY
DIFFERENT WAYS THAT THE STRING
IS DISTRIBUTED.
THAT'S ALL I'M GONNA TELL YOU
ABOUT STRING THEORY, EXCEPT THAT
THE MODERN PICTURE OF BLACK
HOLES OR ONE OF THE MODERN
PICTURES OF BLACK HOLES THE
HORIZON IS REPRESENTED BY AN
INCREDIBLE TANGLE OF STRING.

A new slide shows a black hole covered by hundreds of tangled strings.

Leonard continues THAT STRING SO THERE TO ANYBODY
ON THE OUTSIDE AND LOOKS AT IT,
AND IT'S EXACTLY THIS TANGLE OF
STRING WHICH IS THE MICROSCOPIC
STRUCTURE, THE MICROSCOPIC
DEGREES OF FREEDOM WHICH ARE
CARRYING ALL THIS ENTROPY, THAT
THE ATOMS OF THE BLACK HOLE OF
THE BATHTUB FULL OF HOT WATER,
EXCEPT THEY'RE ALL DISTRIBUTED
ON THE SURFACE, THEY'RE NOT ON
THE INTERIOR.
THIS TURNED OUT TO BE AN
IMPORTANT PART OF THE RESOLUTION
OF THIS PARADOX.
BUT THE OTHER THING I WANT TO
SAY ABOUT IT, WAS NOT ONLY WAS
IT AN EXAMPLE OF BOHR'S
COMPLEMENTARITY BUT IT'S
A TOTALLY NEW AND REALLY WILD
EXAMPLE OF RELATIVITY, A NEW
KIND OF RELATIVITY, NOT ORDINARY
OLD FASHIONED EINSTEIN
RELATIVITY, OLD FASHIONED
EINSTEIN RELATIVITY SPECIAL
RELATIVITY, SAID THAT CERTAIN
THINGS ARE RELATIVE TO THE STATE
OF MOTION.
FOR EXAMPLE IF TWO FLASH BULBS
GO OFF, AND WE ASK IF THEY GO
OFF AT THE SAME INSTANT, THEN
ANYBODY WHO STUDIED THE SPECIAL
THEORY OF RELATIVITY KNOWS THAT
THAT DEPENDS ON WHETHER THE
OBSERVER IS MOVING OR NOT.
A MOVING OBSERVER WILL SEE TWO
FLASH BULBS NOT GO OFF AT THE
SAME INSTANT OF TIME EVEN THOUGH
AN OBSERVER AT REST SEES THE TWO
FLASH BULBS GO OFF AT THE SAME
TIME.
SIMULTANEITY IS RELATIVE.
BUT, EINSTEIN WOULD NEVER HAVE
GONE SO FAR AS TO SAY A FLASH
BULB INSIDE A SOUP CAN, LET'S
MAKE THIS A SOUP CAN, A FLASH
BULB INSIDE A SOUP CAN IS SEEN
AS A FLASH BULB OUTSIDE A SOUP
CAN BY AN OBSERVER WHO'S MOVING
IN SOME FUNNY WAY IF THE FLASH
BULB WAS INSIDE IT'S INSIDE IF
IT'S OUTSIDE IT'S OUTSIDE.

A new slide shows two cans, one with a bulb inside and the caption “inside is inside,” and one with a bulb next to it and the caption “outside is outside.”

Leonard continues THERE WOULD BE NO CONFUSION IN
THE STANDARD THEORY OF
RELATIVITY.
BUT HERE WE'RE FINDING SOMETHING
NEW.
THAT THE ANSWER TO THE QUESTION
OF WHETHER A BIT OF INFORMATION
IS INSIDE A BLACK HOLE OR
OUTSIDE OF A BLACK HOLE DEPENDS
ON WHETHER IT'S BEING STUDIED BY
SOMEBODY OUTSIDE THE OUTSIDE OR
SOMEBODY FALLING THROUGH.
THIS WAS SOMETHING RADICALLY
NEW, IT'S TEACHING US SOMETHING
VERY STRANGE ABOUT SPACE AND
TIME.
SOMETHING TOTALLY UNEXPECTED, I
THINK I'M NOT GOING TO GO
THROUGH ALL OF MY TRANSPARENCIES
HERE, THERE'S TOO MANY OF THEM.
BUT THE LAST THING I'M GOING TO
TELL YOU ABOUT IS SOMETHING
CALLED THE HOLOGRAPHIC
PRINCIPLE.
THE HOLOGRAPHIC PRINCIPLE WAS AN
EVEN STRANGER DEVELOPMENT THAT
GREW OUT OF THE BLACK HOLE WARS.
AGAIN IT WAS SOMETHING THAT
T'HOOFT AND I PUT FORWARD IN
1993, 94.
HERE'S THE IDEA.
SUPPOSING WE HAD A REGION OF
SPACE, THIS ROOM AND I WANTED TO
KNOW HOW MUCH INFORMATION COULD
BE HIDDEN IN THE MOLECULAR
STRUCTURE OF THIS ROOM.
ROUGHLY SPEAKING HOW MANY
MOLECULES DO YOU HAVE TO KNOW,
HOW MANY QUESTIONS DO YOU HAVE
TO KNOW THE ANSWER TO TO KNOW
EVERYTHING ABOUT THIS ROOM?
WELL, ONE WAY THE PHYSICIST
MIGHT ATTACK THIS IS TO DIVIDE
THE ROOM UP INTO LITTLE CELLS,
TINY LITTLE CELLS AND REDUCE THE
QUESTION, ALL QUESTIONS ABOUT
THE ROOM SEQUESTERED TO EACH CELL.

A new slide shows a three-dimensional cube made of hundreds of smaller cubes, some of which have pink particles in them.

Leonard continues IS THERE A PARTICLE IN THERE,
ISN'T THERE A PARTICLE IN THERE?
LET'S MAKE THE CELLS SMALL
ENOUGH SO THAT YOU CAN'T JAM TWO
ATOMS IN.
AND THEN WE COULD COMPLETELY
KNOW EVERYTHING THAT'S GOING ON
IN THIS ROOM IF WE KNEW WHETHER
EVERY CELL WAS OCCUPIED OR NOT
OCCUPIED.
THAT'S ONE WAY THE PHYSICISTS
HAVE TO ARE GOING ABOUT STUDYING
THE PROPERTIES OF A SYSTEM LIKE
THIS ROOM IS TO DIVIDE IT INTO
LITTLE CELLS.
HOW MANY POSSIBILITIES ARE
THERE, HOW MANY BITS OF
INFORMATION, IN OTHER WORDS HOW
MANY ANSWER DO YOU NEED IN ORDER
TO KNOW EVERYTHING?
WELL THE NUMBER OF ANSWERS THAT
YOU NEED IS PROPORTIONAL TO THE
VOLUME.
THE NUMBER OF CELLS.
THE MAXIMUM NUMBER OF BITS THAT
YOU CAN HIDE IS ALMOST ALWAYS
PROPORTIONAL TO THE VOLUME,
“PLANCKIAN” JUST MEANS THE
LITTLEST SMALLEST THAT YOU CAN
IMAGINE, AND THIS IS A VERY DEEP
AND BASIC PRINCIPLE OF PHYSICS
THAT'S ALWAYS BEEN TRUE, MISSING
INFORMATION, ENTROPY,
PROPORTIONAL TO VOLUME.
BUT WHAT BEKENSTEIN HAD TAUGHT
US IS THAT THE MISSING
INFORMATION OF A BLACK HOLE IS
PROPORTIONAL TO ITS AREA.
WELL A BLACK HOLE IS THE
OBJECT WHICH IS HIDING THE
MAXIMUM AMOUNT OF INFORMATION
FOR ITS SIZE AND THAT MEANT THAT
THE MAXIMUM AMOUNT OF
INFORMATION THAT YOU COULD HIDE
IN A REGION OF SPACE IS
PROPORTIONAL TO ITS AREA NOT
PROPORTIONAL TO ITS VOLUME, THE
AREA IS MUCH SMALLER THAN THE
VOLUME FOR MOST SYSTEMS.
IF THIS ROOM IS 1000 WHAT IS IT
1000 INCHES BY 1000 INCHES BY I
DON'T KNOW ANOTHER 1000 INCHES
LET'S SAY THEN 1000 TIME 1000
TIME 1000 IS A BILLION CUBIC
UH... INCHES, RIGHT.
ON THE OTHER HAND THE AREA IS
ONLY 1000 TIMES 1000 AND THAT'S
ONLY A MILLION.
SO THE AREA IS MUCH LESS THAN
THE VOLUME.
BUT WHAT
PHYSICS WAS TELLING US AND THE
BLACK HOLES WERE TELLING US AND
WHAT BEKENSTEIN WAS TELLING US
WAS THE AMOUNT OF INFORMATION
THAT YOU NEED TO DESCRIBE A
SYSTEM IS ONLY PROPORTIONAL TO
THE AREA OF THE WALLS.
THE IMPLICATION OF THIS IS VERY
STRANGE.
DOES EVERYBODY KNOW THE WORLD
“VOXELS”?
ANYBODY KNOW THE WORD PIXELS?
PIXELS IS WHAT YOU GET IF YOU
TAKE AN IMAGE OR A PICTURE AND
DIVIDE IT UP INTO CELLS.
AND MAKE EACH CELL HAVE SOME
DISCREET PIECE OF INFORMATION IN
IT.
SO A PHOTOGRAPH OF SOMETHING OR
A PAINTING OF SOMETHING CAN BE
DIVIDED UP INTO PIXELS AND THE
NUMBER OF PIXELS IS PROPORTIONAL
TO THE AREA.
SOME PEOPLE USE THE WORLD VOXELS
TO DESCRIBE WHAT WOULD HAPPEN IF
YOU DIVIDE THE WORLD INTO TINY
LITTLE CELLS, EACH A CERTAIN
VOLUME.
RIGHT THE NUMBER OF VOXELS IS
PROPORTIONAL TO THE VOLUME, THE
NUMBER OF PIXELS IS PROPORTIONAL
TO THE AREA.
WHAT THIS NEW PRINCIPLE WAS
SAYING IS IN SOME WAY EVERYTHING
THAT TAKES PLACE IN A REGION OF
SPACE IS DESCRIBED NOT BY
DIVIDING THE WORLD INTO VOXELS,
BUT DIVIDING THE BOUNDARY OF THE
WORLD INTO PIXELS.
IN OTHER WORDS IN SOME FUNNY
WAY, SOME NEW WAY EVERYTHING
THAT GOES ON IN THE WORLD CAN BE
DESCRIBED BY ONLY THOSE THINGS
WHICH GO ON ON THE SURFACE, IT'S
A HOLOGRAM.
IT IS SOME KIND OF HOLOGRAM.
SOME KIND OF NEW HOLOGRAM THAT
DESCRIBES EVERYTHING IN THREE
DIMENSIONAL SPACE, AS IF IT WERE
ON A TWO DIMENSIONAL FILM.
ON THE BOUNDARIES OF THE WORLD.
THIS IS AN IDEA WHICH AT FIRST
WAS MET WITH A GREAT DEAL OF
SCEPTICISM BUT IN THE END, I'M
NOT EVEN GONNA TELL YOU WHAT
THIS PICTURE IS BUT IT'S SO
LOVELY THAT I HAVE TO SHOW IT.
IT'S GOT NOTHING TO DO WITH THE
LECTURE.

A new slide shows a circular pattern made of black shapes resembling bats, which repeat from the middle outwards in decreasing size.

(Audience Laughing)

Leonard continues THE EXPERTS
IN THE AUDIENCE WILL RECOGNIZE
THAT THERE'S AN ANTI DISINTER
SPACE.
AND I'M NOT EVEN GOING TO TELL
YOU WHAT IT IS.
WHAT I AM GOING TO TELL YOU IS
THAT STRING THEORISTS EVENTUALLY
PUT SOME VERY, VERY HARD
MATHEMATICS --
HARD NOT IN
THE SENSE OF DIFFICULT BUT HARD
IN THE SENSE OF PRECISE ON THESE
IDEAS SO THAT ALL OF THESE IDEAS
HAVE NOW EMERGED AS PART OF THE
BEDROCK FOUNDATION, NOT JUST OF
STRING THEORY BUT MUCH OF MODERN
PHYSICS.
BLACK HOLE COMPLIMENTARY, THE
HOLOGRAPHIC PRINCIPLE THAT THE
WORLD IS DESCRIBED BY THE THINGS
GOING ON ON IT'S BOUNDARY, THESE
HAVE BECOME OVER THE LAST FIVE
SIX SEVEN TEN YEARS.
THESE HAVE
BECOME PART OF THE BEDROCK
FOUNDATION OF UH... OF PHYSICS.
THE BLACK HOLE WAR, WELL THE
BLACK HOLE WAR HAS ENDED.
STEPHEN HAS VERY GRACIOUSLY
CONCEDED THAT HE WAS WRONG.
HE NOT ONLY GRACIOUSLY CONCEDED
HE WAS WRONG BUT HE GRACIOUSLY
TOLD US THAT HE WOULD TELL
US HOW HE FIGURED ALL OF THIS
OUT.

(Audience Laughing)

Leonard continues SO THE
BLACK HOLE WAR IS ENDED,
INFORMATION DOES GET OUT OF
BLACK HOLES, THE HOLOGRAPHIC
PRINCIPLE SEEMS TO BE A PART OF
PHYSICS THAT'S GOING TO STAY
WITH US.
WHAT ITS IMPLICATIONS WILL BE,
PARTICULARLY FOR COSMOLOGY,
PARTICULARLY FOR THE WHOLE
UNIVERSE AND SO FORTH, WE DON'T
KNOW YET.
BUT ONE OF ITS IMPLICATIONS IS
THAT BASIC QUANTUM MECHANICS,
THE RULES OF QUANTUM MECHANICS,
THE RULES OF INFORMATION
CONSERVATION WILL NOT HAVE TO BE
GIVEN UP, ONCE AGAIN THE
CONSERVATIVES HAVE WON.

(Audience Laughing)

Leonard continues THANK YOU.

(Long applause)

A caption reads “Perimeter Institute for Theoretical Physics.”

Watch: Leonard Susskind on The Black Hole Wars