HELLO AND WELCOME TO THE FRONTIERS OF PHYSICS
LECTURE SERIES.
TONIGHT WE HAVE SEAN CARROLL, THEORETICAL
PHYSICIST FROM THE CALIFORNIA INSTITUTE OF
TECHNOLOGY, TALKING ABOUT THE MANY WORLDS
OF QUANTUM MECHANICS.
TONIGHT IS A SPECIAL OCCASION.
IT IS THE FIRST LECTURE SINCE THE TRAGIC DEATH
THIS SUMMER, OF OUR COLLEAGUE PROFESSOR ANN
NELSON.
SO WE WILL START WITH A TRIBUTE TO HER BY
PROFESSOR STEPHEN SHARP.
GOOD EVENING.
MY NAME IS STEVE SHARP I AM A PROFESSOR IN
THE PHYSICS DEPARTMENT HERE.
BEFORE WE START WITH THE LECTURE TONIGHT,
I HAVE BEEN ASKED TO SAY A FEW WORDS ABOUT
THE TRAGIC LOSS OF OUR COLLEAGUE, WHO DIED
TWO MONTHS AGO IN A HIKING ACCIDENT.
AND WAS ONE OF THE MOST HIGHLY ESTEEMED MEMBERS
OF THIS UNIVERSITY AND THE PHYSICS DEPARTMENT,
AS INDICATED BY HER NUMEROUS AWARDS SOME OF
WHICH I HAVE LISTED HERE.
SHE WAS AWARDED THE AMERICAN PHYSICAL SOCIETY�S
SAKURAI PRIZE FOR THEORETICAL PHYSICS LAST
YEAR.
THIS IS THE HIGHEST AWARD GIVEN BY THE AMERICAN
PHYSICAL SOCIETY FOR THEORETICAL PHYSICIST.
ANN WAS A BRILLIANT PARTICLE PHYSICIST WHO
WOULD ADDRESS THE MOST FUNDAMENTAL QUESTIONS
IN THEORETICAL PHYSICS AND COSMOLOGY.
I DO NOT HAVE THE TIME TO GO INTO IT, I HAVE
LISTED SOME OF THEM HERE.
DARK MATTER, DARK ENERGY.
I DO WANT TO SAY SHE LIKED COMING UP WITH
NICE NAMES FOR THINGS.
DARK ENERGY FOR MASS FEARING NEUTRINOS, MAVENS.
SHE WAS A MAVEN HERSELF.
SOMEONE WHO HAD DEEP KNOWLEDGE OF PARTICLE
PHYSICS.
THESE ARE THE QUESTIONS THAT MOTIVATE PARTICLE
PHYSICS, ALL OF US AND COSMOLOGISTS.
SHE WAS GOOD AT TRYING TO ANSWER THEM.
BETTER THAN MOST OF US.
SHE WAS A MASTER AT COMING UP WITH THEORETICAL
MODELS WHICH COULD ADDRESS THESE PROBLEMS
IN A WAY THAT LED TO EXPERIMENT CONSEQUENCES.
SO AS WE SAY SHE WAS A THEORETICAL MODEL BUILDER.
AND I WOULD SAY WITHOUT PEER, WORLDWIDE.
ANN WAS PASSIONATE NOT ONLY ABOUT PHYSICS
BUT ALSO AS A TRUE NORTHWESTERN OR ABOUT MOUNTAINS
AND FLOWERS, THE OUTDOORS.
HERE I HAVE A BLURRY PICTURE FROM 1992 OF
ANN, MYSELF, DAVID KAPLAN, WHO IS IN THE AUDIENCE,
ON TOP OF MOUNT RAINIER.
WE DID MANY HIKES TOGETHER.
SHE WAS ALSO PASSIONATE ABOUT TEACHING.
SHE WAS AN AWARD-WINNING TEACHER.
ABOUT MENTORING SHE MEN TOWARD MANY STUDENTS.
GRADUATE STUDENTS AND POST DOCS TO BECOME
SUCCESSFUL FACULTY MEMBERS.
AND IN GENERAL, SHE LOVED BRINGING THE JOY
OF PHYSICS, SCIENCE AND HIKING TO EVERYONE.
HE OR SHE IS TEACHING PALESTINIAN STUDENTS.
IN THE WEST BANK.
IN PARTICULAR, ESPECIALLY OVER THE LAST FEW
YEARS, SHE TOOK MANY CONCRETE AND SUCCESSFUL
STEPS TO INCREASE THE DIVERSITY AND INCLUSIVITY
OF OUR DEPARTMENT.
FACULTY, STUDENT BODY AND MORE GENERALLY OUR
FIELD.
EXHORTING US ALL TO FOLLOW AND LEADING US
BY EXAMPLE.
I CANNOT DO JUSTICE IN THE SHORT TIME TO ALL
OF HER CONTRIBUTIONS TO PHYSICS, TO THE FIELD,
BUT I WANT TO SAY ONE OF THE THINGS THAT WAS
SPECIAL ABOUT ANN, DESPITE THE FACT IN ANY
DISCUSSION SHE WAS AND SHE WAS PROBABLY THE
SMARTEST PERSON.
SHE NEVER BETRAYED A HINT OF ARROGANCE.
SHE JUST WANTED TO LEARN, WANTED OTHER PEOPLE
TO LEARN AND WANTED TO HELP THEM DO THAT.
SHE WAS WARM, CARING PERSON, A FRIEND TO ME
35 YEARS, COLLEAGUE MORE THAN 25 YEARS AND
SHE WAS JUST AN AMAZING PERSON.
OVERALL SHE WAS AN INSPIRATION TO ALL OF US
AND WILL BE TERRIBLY MISSED.
IF YOU WANT TO LEARN MORE ABOUT ANN, HER OBITUARIES
IN THE SEATTLE TIMES, NEW YORK TIMES, PHYSICS
TODAY AND ALSO THE MOUNTAINEERS TO SHOW THE
TWO SIDES OF HER LIFE.
AN AMAZING PERSON.
TO CELEBRATE ANN 'S LEGACY AND HONOR HER ACHIEVEMENTS,
THE UNIVERSITY HAS SET UP A FUND FOR ENDOWING
A PROFESSORSHIP OF PHYSICS.
THE DOCTOR ANN NELSON PROFESSORS OF PHYSICS.
INDIVIDUALS COMMITTED TO DIVERSITY RELATED
WORK AND HIS RECORD OF RESEARCH, TEACHING
AND SERVICE REFLECTS THE COMMITMENT TO DIVERSITY
AND EQUAL OPPORTUNITY AND ALSO TO EXCELLENCE
IN PHYSICS.
I ENCOURAGE YOU TO CONSIDER DONATING TO THIS
FUND.
I AM SURE THE SLIDES WILL BE MADE LIFE AND
YOU CAN CLICK ON THE LINKS.
THANK YOU FOR YOUR ATTENTION.
[ APPLAUSE ]
THE GOAL OF THE FRONTIERS OF PHYSICS LECTURE
SERIES IS TO BRING RENOWNED SCIENTISTS, LIKE
SEAN CARROLL, TO GIVE FREE LECTURES TO THE
GENERAL PUBLIC ON THE MOST INTERESTING TOPICS
IN PHYSICS.
WE AIM TO SHARE WITH YOU HERE, IN SEATTLE,
THE EXCITEMENT OF PHYSICS, HOW IT ALLOWS US
TO DESCRIBE NATURE ON THE MORE FUNDAMENTAL
LEVEL HOW IT SHAPES OUR UNDERSTANDING OF REALITY.
IT IS ONLY POSSIBLE BY THE LECTURE SERIES
COMMITTEE AND OUR BENEFACTORS.
IF YOU WOULD LIKE TO LEARN MORE ABOUT HOW
TO SUPPORT THE FRONTIERS OF PHYSICS LECTURE
SERIES, AND THE ENDOWED PROFESSORSHIP OF DETERMINE
NELSON OR BECOME MORE INVOLVED IN GENERAL
PLEASE REACH OUT TO ME FOLLOWING THE LECTURE
OR CONTACT THE DEPARTMENT BY E-MAIL.
WE HOUSE THE FRONTIERS OF PHYSICS LECTURE
SERIES ABOUT TWICE YEAR AND ALL ARE FILMED
BY UWTV POSTED ONLINE AFTER THE LECTURE FOR
YOU TO WATCH AND SHARE.
OUR SPEAKER TONIGHT IS SEAN CARROLL, THEORETICAL
PHYSICIST OF THE CALIFORNIA INSTITUTE OF TECHNOLOGY.
HE OBTAINED HIS PhD AT HARVARD UNIVERSITY
UNDER GEORGE FILLED AND HELD POSITIONS AT
THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY,
UNIVERSITY OF CALIFORNIA SANTA BARBARA, UNIVERSITY
OF CHICAGO BEFORE MOVING TO CALTECH IN 2006.
HE IS AN EXPERT IN EMERGENT PHENOMENON CONVEXITY,
THE FUNDAMENTAL NATURE OF THE THAT SPACE AND
TIME AND QUANTUM MECHANICS USABILITY AMERICAN
PHYSICS SOCIETY AND HAS RECEIVED MANY NUMEROUS
AWARDS INCLUDING RECENTLY FROM THE AMERICAN
INSTITUTE OF PHYSICS IN THE GUGGENHEIM FOUNDATION
FELLOWSHIP.
HE HAS AUTHORED 100 PUBLICATIONS, MOST OF
PHYSICS BUT ALSO PHILOSOPHY, AND HAS PUBLISHED
SIX BOOKS INCLUDING A NEW YORK TIMES BESTSELLER,
THE BIG PICTURE AND HIS LATEST BOOK IS "SOMETHING
DEEPLY HIDDEN: QUANTUM WORLDS AND THE EMERGENCE
OF SPACETIME".
's CONTRIBUTIONS TO CULTURE INCLUDE CONSULTING
FOR MANY FILMS, MOST RECENTLY ADVENTURES FINISH
MAKING AND POST THE POTS CAP, WEDNESDAY.
IT IS MY PRIVILEGE TO INTRODUCE TO YOU DR.
SEAN CARROLL.
[ APPLAUSE ]
THANK YOU.
LET'S SEE IF THIS WORKS.
I'M A THEORETICAL PHYSICIST.
IT WORKS.
GREAT TO BE BACK HERE IN SEATTLE AT UW, ONE
OF MY FAVORITES, ONE OF MY FAVORITE PLACES
TO VISIT.
I WOULD LIKE TO TALK ABOUT QUANTUM MECHANICS.
I'VE WRITTEN A BOOK ABOUT QUANTUM MECHANICS.
MY PUBLISHER SAYS I'M SUPPOSED TO TELL YOU
THAT.
YOU ARE ALLOWED TO ASK WHY THE WORLD WOULD
ANYONE WRITE A BOOK ABOUT QUANTUM MECHANICS?
THERE ARE ENOUGH BOOKS ABOUT QUANTUM MECHANICS.
AS PART OF THE RESEARCH I DID FOR MY BOOK
I WENT TO AMAZON.COM AND TYPED IN QUANTUM
INTO THE SEARCH BAR AND YOU CAN GUESS WHAT
HAPPENED.
THERE'S QUANTUM PHYSICS HER BABY, A WONDERFUL
BOOK FOR YOUNGSTERS OUT THERE BUT ALSO QUANTUM
LEADERSHIP, QUANTUM YOGA, QUANTUM TOUCH, QUANTUM
HEALING, QUANTUM SUCCESS.
NONE OF THESE BOOKS ARE REALLY ABOUT QUANTUM
MECHANICS IN ANY PROFOUND WAY.
WHY IS THAT?
PART OF IT IS BECAUSE QUANTUM MECHANICS IS
HARD TO UNDERSTAND AND IT HAS BEEN MISUSED.
FILTERED INTO POPULAR IMAGINATION WAYS PROFESSIONAL
PHYSICIST WOULD NOT RECOGNIZE.
BUT ALSO BECAUSE PROFESSIONAL PHYSICIST OF
THE WORLD DOWN.
BOTH IN TERMS OF EXPLAINING QUANTUM MECHANICS
AND UNDERSTANDING IT OURSELVES.
WE GIVE PEOPLE THE IMPRESSION, ALL THESE PEOPLE
UP THERE.
WE GIVE THE PEOPLE, I WILL TRY TO REMEMBER
TO LOOK AT YOU OCCASIONALLY.
WE GIVE PEOPLE THE IMPRESSION THAT NOT ONLY
IS QUANTUM MECHANICS ARE TO UNDERSTAND IT'S
IMPOSSIBLE TO UNDERSTAND.
FUNDAMENTALLY MYSTERIOUS SO I DON'T USUALLY
LIKE TO LEAN ON AUTHORITY FOR THINGS LIKE
THIS AND SINCE I'M TALKING ABOUT A FACT ABOUT
PHYSICS BUT A FACT ABOUT OUR UNDERSTANDING
OF PHYSICS, LET ME LEAN ON THIS GUY, WHO FAMOUSLY
SAID I THINK I CAN SAFELY SAY NOBODY UNDERSTANDS
QUANTUM MECHANICS AND I WROTE A RECENT PIECE
NEW YORK TIMES POINT OF PHYSICS DON'T UNDERSTAND
QUANTUM MECHANICS AND REMARKABLY ONLY TWO
PEOPLE SAID WHAT DO YOU MEAN I UNDERSTAND
QUANTUM MECHANICS PERFECTLY WELL.
SORRY ONLY TWO PROFESSIONAL PHYSICIST WROTE
ME.
LOTS OF OTHERS WROTE IN.
OF COURSE IT MAYBE TRUE THAT THERE ARE INDIVIDUAL
PHYSICIST WHO DO UNDERSTAND QUANTUM MECHANICS
BUT THE REST OF THE FIELD DOES NOT INC. THEY
UNDERSTAND QUANTUM MECHANICS.
AS A FIELD WE DO NOT UNDERSTAND QUANTIC MECHANICS
AND PHYSICS.
AND THAT'S FINE.
IT'S FINE NOT TO UNDERSTAND THINGS.
SCIENCE IS DRIVEN BY NOT UNDERSTANDING THINGS
AND SAYING WELL LET'S WORK ON TRYING TO UNDERSTAND
THIS.
WHAT IS NOT FINE IS IN THE CASE OF QUANTUM
MECHANICS, WE HAVEN'T DONE THAT.
WE USE QUANTUM MECHANICS ALL THE TIME.
USE THE PREDICTIONS OF QUANTUM McADAMS TO
MAKE EXTRAORDINARILY PRECISE AND AMAZING TECHNOLOGIES
, DISCOVER PARTICLES, BUILD THEORIES OF THE
UNIVERSE, BUILD LASERS AND TRANSISTORS AND
OTHER APPLICATIONS OF QUANTUM MECHANICS.
BUT WE ARE USING QUANTUM MECHANICS IN THE
WAY THE TYPICAL PERSON USES THEIR SMART PHONE.
YOU CAN TEXT AND TAKE PICTURES, READ E-MAIL
BUT IF SOMEONE SAYS WHAT IS GOING ON INSIDE
WHEN THAT HAPPENS, I DON'T KNOW.
THAT IS WHAT HE MEANS WHEN WE DON'T TRULY
UNDERSTAND QUANTUM MECHANICS THE WEIRD THING
IS, NOT ONLY DO WE NOT TRY TO UNDERSTAND QUANTUM
MECHANICS, WE ACTIVELY DISCOURAGE IT.
THERE WAS A TIME IN THE 1920s AND 30s WHEN
IT WAS THOUGHT TO BE A VERY HIGH PRIORITY
THING TO UNDERSTAND QUANTUM MECHANICS.
GIVEN HOW CENTRAL QUANTUM MECHANICS IS TO
MODERN PHYSICS, YOU WOULD THINK THE ATTEMPTS
TO UNDERSTAND QUANTUM MECHANICS WOULD CONSTITUTE
THE HIGHEST STATUS SUBDISCIPLINE WITHIN PHYSICS,
RIGHT?
THE PEOPLE BEST TRYING TO UNDERSTAND QUANTUM
MECHANICS WOULD BE THE SUPERSTARS OF PHYSICS.
STOLEN AWAY BY MAJOR UNIVERSITIES, LURED WITH
HUGE SALARIES.
INSTEAD, THEY ARE KICKED OUT.
GRADUATE STUDENTS ARE TOLD NOT TO DO THIS
AND IN PEOPLE WHO ALREADY HAVE TENURE WHEN
THEY SAY THEY ARE TRYING TO THINK ABOUT QUANTUM
MECHANICS IN A DEEP WAY COLLEAGUES GO OWE
IT IS TOO BAD YOU LOVE SERIOUS WORK BEHIND.
IN OTHER WORDS THE WAY I LIKE TO THINK ABOUT
IT, THERE IS THIS OLD FABLE, ONE OF AESOP's
FABLES ABOUT THE FOX AND THE GRAPES , THE
FOX SEES THE GRAPES, BIG, JUICY GRAPES, THEY
LOOK REALLY GOOD THE FOX JUMPS UP TO GET THE
GRAPES BUT THEY ARE JUST TOO I. THE FOX CAN'T
QUITE REACH THE GRAPES SO HE SAYS YOU KNOW
I NEVER WANTED THOSE GRAPES IN THE FIRST PLACE.
THEY WERE PROBABLY SOUR.
JUST TO SPELL OUT THE TERMS OF THE METAPHOR,
THE FOX REPRESENTS PHYSICISTS , GRAPES REPRESENT
UNDERSTANDING QUANTUM MECHANICS.
WE TRIED FOR A WHILE, DIDN'T WORK SO WE DECIDED
WE NEVER WANTED TO DO IN THE FIRST PLACE,
THAT WASN'T OUR JOB.
I THINK THAT IS WRONG.
I THINK IT IS THE JOB OF PHYSICS TO UNDERSTAND
THE NATURE OF REALITY AND EVEN THOUGH IT SOUNDS
PHILOSOPHICAL , WE SHOULD STILL PUT EFFORT
INTO IT.
LET'S SEE HOW FAR WE CAN GET.
I NEED TO TELL YOU A LITTLE ABOUT QUANTUM
MECHANICS.
IS AT THE CENTER OF ALL WE DO IN MODERN PHYSICS.
IT IS ABSOLUTELY PART OF OUR BEST UNDERSTANDING
OF REALITY, BUT IT IS ABSOLUTELY COUNTERINTUITIVE.
I DON'T WANT TO SEE IT IS MYSTERIOUS, SPOOKY
OR IMPOSSIBLE TO UNDERSTAND , BUT DOES SEEM
WEIRD FROM OUR EVERYDAY EXPERIENCE.
LET ME TREES THROUGH A VERY RATIONALIZED,
SIMPLE VERSION OF WHY WE CAME TO BELIEVE THE
WEIRDNESS OF QUANTUM MECHANICS.
YOU HAVE ALL SEEING PICTURES LIKE THIS.
THIS IS THE RUTHERFORD ADAM, A PICTURE PUT
TOGETHER IN THE VERY BEGINNING OF THE 21st
CENTURY WERE RATHER THAN AN ATOM BEING A SMOOTH
LAW THAT SEPARATES ALMOST ALL THE MASS CONCENTRATED
IN THE CENTER AND SOMETHING CALLED THE NUCLEUS
. QUEEN ANNE OF THE NUCLEUS OF AN ATOM IS
MADE UP PROTONS AND NEUTRONS, THEY WEREN'T
SURE ABOUT THAT 1909 BUT THEY KNEW THERE WAS
A NUCLEUS AND THE ELECTRON, MUCH LIGHTER THAN
THE PROTONS AND NEUTRONS , ELECTRONS ORBIT
AROUND IN A PICTURE LIKE THIS IT KIND OF LOOKS
A LITTLE SOLAR SYSTEM WITH THE NUCLEUS PLAYING
THE ROLE OF THE SUN AND ELECTRONS LOOK LIKE
PLANETS.
THIS WAS FORCED ON US BY THE DATA RUTHERFORD
SHOT LITTLE HELIUM NUCLEI AT GOLD AND NOTICED
USUALLY THEY WENT RIGHT THROUGH BUT SOMETIMES
CAREENED OFF AT CRAZY ANGLES.
HE DEDUCED, BECAUSE IT IS VERY SMART, THAT
MEANT THERE WAS A CONCENTRATED SET OF MASS
IN THE MIDDLE CALLED THE NUCLEUS.
THE PROBLEM IS, THIS CAN'T BE RIGHT.
THE RULES OF PHYSICS AS WE UNDERSTOOD THEM
IN 1909 ARE CALLED CLASSICAL MECHANICS PUT
TOGETHER BY ISAAC NEWTON IN THE 1600S.
ACCORDING TO CLASSICAL MECHANICS THERE ARE
OBJECTS, THEY HAVE LOCATIONS, THEY HAVE VELOCITY
AND FROM KNOWING THAT YOU CAN FIGURE OUT EVERYTHING
THAT IS GOING TO HAPPEN IN A PHYSICAL SYSTEM.
YOU APPLY THE RULES OF CLASSICAL MECHANICS
TO THIS ATOM.
YOU SEE ELECTRONS ORBITING AROUND , VERY QUICKLY
AROUND THE NUCLEUS.
IF YOU TAKE AN ELECTRON, THE THING ABOUT THE
ELECTRON IS A HOUSE AN ELECTRIC FIELD STRETCHING
OUT AWAY FROM IT.
IF YOU MOVE THE ELECTRON A LITTLE BIT, THE
FIELD SHIFTS IN RESPONSE.
IF YOU TAKE THE ELECTRON AND MOVE IT UP AND
DOWN, THE ELECTRIC FIELD WAVES, RIPPLES OUT.
WE CALL THESE ELECTROMAGNETIC WAVES OR LIGHT.
LITERALLY ALL OF THE LIGHT YOU SEE IN THIS
ROOM RIGHT NOW COMES FROM ELECTRONS MOVING
UP AND DOWN.
HERE YOU HAVE ELECTRONS MOVING UP AND DOWN.
MAYBE THE MOVE IN CIRCLES BUT THEY ARE STILL
MOVING.
THEY SHOULD BE GIVING OFF LIGHT.
THEY SHOULD BE GIVING OFF ELECTROMAGNETIC
WAVES.
YOU CAN CALCULATE HOW MUCH THEY SHOULD BE
GIVING OFF.
YOU CAN ASSIGN THIS TO UNDERGRADUATES IF YOU
WANT TO DO THAT.
IT DOESN'T TAKE LONG FOR THE ELECTRONS, ACCORDING
TO THIS THEORY, TO LOSE ENERGY BY GIVING OFF
LIGHT.
ENERGY IS CONSERVED, ELECTRONS GIVE OFF LIGHT
THEY SHOULD BE SPIRALING INTO THE NUCLEUS
. THE ORBIT OF AN ELECTRON AROUND THE NUCLEUS
IS NOT STABLE ACCORDING TO THE RULES OF CLASSICAL
MECHANICS.
AND YOUR UNDERGRADUATES WILL GET THE ANSWER
IT TAKES ABOUT TEN TO THE MINUS 11 SECONDS
FOR A TYPICAL ATOM TO SPIRAL INTO THE NUCLEUS.
THAT IS A VERY SHORT PERIOD OF TIME.
WE CAN DO THE EXPERIMENT.
READY, IT DIDN'T WORK . IT DIDN'T HAPPEN.
ATOMS ARE ACTUALLY STABLE IF CLASSIC MECHANICS
IN THE RUTHERFORD WERE CORRECT THIS PODIUM
WOULD COLLAPSE TO A POINT.
THAT DOESN'T HAPPEN SO THERE IS SOMETHING
GOING WRONG.
WHAT I'M TRYING TO GET TO USE WE REALLY STRUGGLE
WITH ALL THIS STUFF BEFORE WE CAME UP WITH
QUANTUM MECHANICS.
IT DIDN'T JUST POP OUT LIKE VENUS FROM THE
BROW OF ZEUS.
WE ARE FORCED TO INVENT THESE PARTICULAR IDEAS.
AT THE SAME TIME, PEOPLE NOTICED THAT LIGHT,
WHICH I JUST TOLD YOU WAS A WAVE, SOMETIMES
HAD PARTICLE LIKE PROPERTIES.
HERE IS AN ELECTRON, A PARTICLE.
MAYBE THE ELECTRON HAS WAVE LIKE PROPERTIES.
AND THAT ACTUALLY WORKED.
IF YOU SAY THE ELECTRON IS NOT A PARTICLE,
THE ELECTRON IS ACTUALLY A WAVE WHICH PHYSICIST
DID NOT WASTE THEIR BRAIN BRAINPOWER COMING
UP WITH THIS NAME, THEY DUBBED THIS THE WAVE
FUNCTION . IF YOU THINK OF THE ELECTRON AS
A WAVE FUNCTION THAT CAN TAKE ON DIFFERENT
SHAPES, THEN THAT WAVE FUNCTION CAN SETTLE
INTO ONE OF THE SHAPES, HERE ARE SOME OF THE
SHAPES THE ELECTRON COULD HAVE ORBITING A
NUCLEUS.
IT WILL JUST STAY THERE FOREVER.
IT WILL NOT SPIRAL INTO THE CENTER.
YOU CAN EXPLAIN WHY ATOM ARE STABLE IF YOU
MAKE A BOLD LEAP AND IT TOOK YEARS TO GET
THERE BUT WE DID EVENTUALLY GET THERE IF YOU
MAKE THE BOLD LEAP THAT ELECTRONS ARE NOT
PARTICLES, THEY ARE ACTUALLY WAVES.
THAT SOUNDED PRETTY GOOD . PHYSICISTS ARE
NOT HAPPY UNTIL YOU HAVE AN EQUATION.
I KNOW WE HAVE A QUIZ AFTERWARD, OF WHICH
YOU WILL BE ABLE TO SOLVE THIS EQUATION, BUT
THIS IS THE EQUATION THE CAME ALONG THEREAFTER,
TO TELL YOU HOW WAVE FUNCTIONS EVOLVE . THE
STATE OF THE ART HERE IS WE ARE IMAGINING
SUBATOMIC PARTICLES LIKE ELECTRONS ARE REALLY
NOT PARTICLES AT ALL, THEY ARE WAVES AND THEY
OBEY AN EQUATION.
YOU DON'T NEED TO KNOW THE DETAILS OF THE
EQUATION.
HERE IS ERWIN SCHRODINGER HE SAYS THIS IS
THE EQUATION THAT TELLS US HOW WAVE FUNCTIONS
BEHAVE.
HOW THEY EVOLVE OVER TIME.
SOLUTIONS TO THAT EQUATION WOULD GIVE YOU
ALL THESE DIFFERENT PICTURES FOR DIFFERENT
SHAPES.
YOU ON WAVE FUNCTION CAN HAVE IN AN ATOM FOR
EXAMPLE.
YOU CAN USE THIS EQUATION AND MAKE PREDICTIONS
FOR HOW ELECTRONS COULD GIVE OFF LIGHT UNDER
CERTAIN CIRCUMSTANCES BUT THEY COULD SETTLE
DOWN TO THEIR MINIMUM ENERGY STATE.
THIS MAKES PHYSICISTS VERY HAPPY WHEN YOU
HAVE AN EQUATION YOU HAVE FULL EMPLOYMENT
YOU CANNOT ONLY SOLVE THE EQUATION YOURSELF
YOU HAVE AN INFINITE NUMBER OF HOMEWORK PROBLEMS
TO GIVE TO YOUR STUDENTS IN THE FUTURE AND
MANY TO THIS DAY MANY QUANTUM MECHANICS CLASSES
ARE BASICALLY SOLVING THE SCHRODINGER OCCASION
OVER AND OVER AGAIN.
IT IS QUANTITATIVE AND RIGOROUS INDEFINITE
AND IT SAYS WHAT IS GOING TO HAPPEN NEXT THIS
IS DEFINITELY PHYSICIST COMFORT ZONE.
THE DISCOMFORT COMES WHEN YOU REALIZE THIS
EQUATION, BY ITSELF, DOES NOT SEEM TO FIT
OUR EXPERIMENTAL DATA.
LET ME SHOW YOU DATA, THIS IS A LITTLE QUALITATIVE,
NOT QUANTITATIVE, A TINY CHUNK OF RADIOACTIVE
URANIUM INSIDE A CLOUD CHAMBER.
WHEN THE URANIUM EMITS A PARTICLE, THAT IS
RADIOACTIVE, THIS IS A CHAMBER WHERE A CHARGE
PARTICLE WILL MAKE IONS WHICH SHOW UP.
SO WHAT YOU ARE SEEING IS LITTLE STREAKS ON
A PARTICLE IS EMITTED FROM THE URANIUM.
THAT MAKES PERFECT SENSE, RADIOACTIVITY IS
PARTICLES COMING OUT OF RADIUM, VERY GOOD.
THE PROBLEM IS WHEN YOU ASK THE SCHRODINGER
EQUATION WHAT KIND OF WAVE FUNCTION IS EMITTED
WHEN URANIUM EMITS A PARTICLE, AN ELECTRON
THE SAKE OF THE ANSWER IS IT COMES OUT IN
MORE LESS SPHERICAL DISTRIBUTION.
MORE OR LESS IN A BIG BLOB THEY GETS MORE
AND MORE DISPERSED AS IT LEAVES THE CENTER
OF THE URANIUM.
THAT'S NOT AT ALL WHAT WE ARE SEEING HERE.
WHAT WE ARE SEEING HERE OR INDIVIDUAL TRACKS
, LITTLE TRAJECTORIES, AS IF THE ELECTRON
WAS A PARTICLE AGAIN.
SO, IT SEEMS NAIVELY, IF YOU ARE REALLY AT
THE VERY DUMBEST LEVEL, WHAT YOU WOULD SAY
IS, IT SEEMS LIKE ELECTRONS ACT LIKE WAVES
WHEN YOU ARE NOT LOOKING AT THEM . AND THEY
ACT LIKE PARTICLES WHEN YOU ARE LOOKING AT
THEM.
CLEARLY, WE SHOULD BRING THE BRIGHTEST MINDS
IN ALL OF THEORETICAL PHYSICS TO BEAR ON THIS
QUESTION AND FIGURE OUT WHAT IS REALLY GOING
ON.
DANCER THEY CAME UP WITH THIS, ELECTRONS ACT
LIKE WAVES WHEN YOU ARE NOT LOOKING AT THEM
THANK YOU THEY ACT LIKE PARTICLES WHEN YOU
ARE LOOKING AT THEM.
THIS IS CALLED THE COPENHAGEN INTERPRETATION
OF QUANTUM MECHANICS . THIS IS WHAT WE TEACH
UNDERGRADUATES IN TEXTBOOKS.
ELECTRON WAVE FUNCTION MAYBE SPREAD OUT IN
SOME PARTICULAR WAY WHEN YOU ARE NOT LOOKING
AT IT IN AN ATOM FOR EXAMPLE BUT WHEN YOU
MEASURE SOMETHING ABOUT IT, WHEN YOU LOOK
AT IT, OBSERVE IT, THE WAVE FUNCTION COLLAPSES.
YOU DON'T SEE THAT BIG, SPREAD OUT PUFFY WAVE
OF WAVE FUNCTION, YOU SEE WHAT LOOKS LIKE
A PARTICLE.
A WAVE FUNCTION LOCALIZED IN SOME PARTICULAR
PLACE.
WHERE IT IS GOING TO APPEAR, YOU CAN'T SAY
FOR SURE.
THIS IS WHERE THE PROBABILITY COMES INTO QUANTUM
MECHANICS.
THE WAVE FUNCTION IS TELLING YOU BASICALLY
HOW LIKELY IT AS YOU WILL GET CERTAIN OBSERVATIONAL
OUTCOMES WHERE THE WAVE FUNCTION IS BIG , PROBABLE
TO SEE THE ELECTRON THERE WERE YOU TO LOOK
AND THE WAVE FUNCTION IS SMALL AND IMPROBABLE
BUT STILL MIGHT BE SOME CHANCE.
SO THIS IS CODIFIED IN TEXTBOOKS.
I AM NOT MAKING THIS UP.
THIS IS WHAT WE TEACH OUR STUDENTS.
WHEN YOU'RE NOT LOOKING AT A QUANTUM SYSTEM
IT IS KIND OF LIKE CLASSICAL MECHANICS.
THERE ARE STATES OF THE PHYSICAL SYSTEM AND
THEY EVOLVE ACCORDING TO SOME EQUATION . EXCEPT
INSTEAD OF THE STATES BEING POSITIONS AND
VELOCITIES THEY ARE WAVE FUNCTIONS IN THE
STATE OF THE EQUATION EQUATION BE NEWTON's
LAW OF PHYSICS THEY ARE THE SCHRODINGER's
EQUATION.
THAT WOULD BE FINE BUT THERE IS THIS WHOLE
NEW SET OF RULES FOR WHAT HAPPENS WHEN QUANTUM
SYSTEMS ARE MEASURED WHEN YOU LOOK AT THEM.
THEN THE WAVE FUNCTION COLLAPSES AND THERE
IS A PROBABILITY OF GETTING DIFFERENT OUTCOMES.
THIS IS WHAT IS CALLED THE COPENHAGEN WORK
TEXTBOOK INTERPRETATION.
TO DRIVE THE SUM LET'S TURN TO THE THOUGHT
EXPERIMENT STYLINGS OF HERMAN SCHRODINGER
WHO DID A FAMOUS SCENARIO , ACTUALLY HE CAME
UP WITH THIS IN CORRESPONDENCE WITH EINSTEIN
. SCHRODINGER ACTUALLY DID THIS EXPERIMENT
WERE THERE IS A CAT IN A BOX AND THE POINT
OF THE EXPERIMENT IS TO AMPLIFY THE QUANTUM
WAVE FUNCTION TO MACROSCOPIC SCALES.
SO THE IDEA IS IF YOU HAVE A QUANTUM MECHANICAL
SOURCE LIKE THE URANIUM I SHOWED YOU, THERE
IS A DETECTOR LIKE A GEIGER COUNTER AND THE
WAVE FUNCTION SAYS THE FOLLOWING THING THERE
IS SOME PROBABILITY THAT THE GEIGER COUNTER
WILL CLICK AND IF THAT HAPPENS IT OPENS A
BOX OF GAS WHICH IS RELEASED INTO THE BIGGER
BOX WITH THE CAT IN A AND IF IT DOESN'T THEN
IT IS CLOSED . AND SCHRODINGER'S ORIGINAL
EQUATION , THOUGHT EXPERIMENT INSIDE THE BOX,
IT WAS CYANIDE GAS AND WILL SCHRODINGER 'S
DAUGHTER PUT IT BEST I THINK MY FATHER DIDN'T
LIKE CATS.
[ LAUGHTER ] THE CAT 'S QUANTUM WAVE FUNCTION
EVOLVES INTO A SUPERPOSITION OF BEING ALIVE
OR DEAD . THERE IS NO REASON TO KILL THE CAT
IN TERMS OF UNDERSTANDING THE PHYSICS BEHIND
WHAT IS GOING ON.
YOU MY VERSION I PUT SLEEPING GAS INSIDE THE
BOX AND THE CAT IS IN A SUPERPOSITION OF BEING
AWAKE AND ASLEEP ALL THE PHYSICS CONSEQUENCES
ARE JUST AS GOOD.
SCHRODINGER'S CAP WAS NOT INVENTED BY SCHRODINGER
SO PEOPLE COULD SAY WOW, THAT IS REALLY BIZARRE
AND WEIRD AND AMAZING USING QUANTUM MECHANICS
. IT WAS INVENTED BECAUSE SCHRODINGER WANTED
YOU TO SAY , SURELY YOU DON'T BELIEVE THAT
. SCHRODINGER AND VINTAGE SCHRODINGER'S EQUATION
BUT HE DID NOT INVENT THE INTERPRETATION OF
THE EQUATION WHICH SAYS WHAT THE EQUATION
IS TELLING US AS THE PROBABILITY OF GETTING
SOMETHING BECAUSE THE POINT OF SCHRODINGER'S
CAT IS WHEN YOU DON'T HAVE THE BOX OPEN, YOU'RE
SUPPOSED TO BELIEVE THE CAT IS LITERALLY IN
A SUPERPOSITION.
IT IS NOT TRUE IT IS EITHER ALIVE OR DEAD
BUT WE DON'T KNOW WHICH.
IT IS NEITHER AWAKE OR ASLEEP.
IT IS IN SUPERPOSITION OF BOTH AT THE SAME
TIME UNTIL YOU OPEN THE BOX AND LOOK AND CRINGE
AT THE TRADITIONAL INTERPRETATION.
THE WHOLE POINT OF WHAT DOES IT MEAN TO MAKE
AN OBSERVATION WAS LEFT A LITTLE VAGUE IN
THIS ORIGINAL INTERPRETATION.
IN OTHER WORDS, WE HAVE A CLASSICAL POSSIBILITY.
IT CAN ALWAYS BE TRUE BUT THERE IS SOMETHING
WE DON'T KNOW.
WE CAN HAVE A BOX WITH THE CAT IN IT THAT
IS EITHER AWAKE OR ASLEEP AND WE ARE JUST
NOT SURE . THAT IS CERTAINLY A PERFECTLY RESPECTABLE
INTRODUCTION OF PROBABILITY TO PHYSICS.
THAT IS BASED ON OUR SUBJECTIVE IGNORANCE
OF THE SITUATION.
THE QUANTUM MECHANICAL SITUATION IS DIFFERENT.
THE PREDICTION OF SCHRODINGER's EQUATION IS
CRYSTAL CLEAR.
IN THAT BOX THERE IS A SUPERPOSITION OF BOTH
AN AWAKE AND ASLEEP CAT.
LET ME TELL YOU WHAT HAPPENS WHEN YOU OPEN
THE BOX ACCORDING TO THE COPENHAGEN INTERPRETATION.
THE POINT OF COPENHAGEN IS, WE TREAT SMALL
SYSTEMS BY THE RULES OF QUANTUM MECHANICS
AND BIG SYSTEMS BY THE RULES OF CLASSICAL
MECHANICS.
THERE IS A DIVIDING LINE BETWEEN THE QUANTUM
REALM AND THE CLASSICAL REALM CALLED THE HEISENBERG
CUT.
BECAUSE NOT ONLY NIELS BOHR, ONE OF THE FOUNDERS
OF THE INTERPRETATION BUT HIS ACOLYTES LIKE
HEISENBERG HELP DEVELOP THESE IDEAS.
THE HEISENBERG CUT SEPARATES THE QUANTUM WORLD
FROM THE CLASSICAL WORLD.
LEVEL QUANTUM MECHANICAL CAT IN THIS CASE,
IN A SUPERPOSITION OF AWAKE AND ASLEEP ON
AND A CLASSICAL OBSERVER, IN THIS CASE THE
ROLE OF THE OBSERVER PLAYED BY NIELS BOHR.
AND WHAT THE INTERPRETATION TELLS YOU IS WHEN
THE OBSERVER OPENS THE BOX, YOU EITHER GET
A CAT THAT WAS AWAKE IN THE OBSERVER SAW IT
AWAKE OR THE CAT IS ASLEEP IN THE OBSERVER
SAW IT ASLEEP AND YOU DON'T KNOW WHICH.
ALL YOU CAN DO IS PREDICT THE PROBABILITY.
THE WAVE FUNCTION COLLAPSED ONTO ONE POSSIBILITY
OR THE OTHER.
SO THE PROBLEM WITH THIS IS IT IS CLEARLY
RUBBISH.
THIS IS ABSOLUTELY UNACCEPTABLE AS THE FUNDAMENTAL
THEORY OF NATURE . LET ME JUST MENTION TWO
PROBLEMS WITH IT.
OBVIOUSLY IT IS A STEP ALONG THE WAY I'M NOT
TELLING YOU QUANTUM MECHANICS IS FALSE OR
WRONG, IT JUST DOESN'T SEEM DONE YET.
THE TWO PROBLEMS I HAVE IN MIND WANTED WHICH
YOU CAN CALL THE REALITY PROBLEM.
THE ELECTRON SHOULD BE THOUGHT OF AS A WAVE
FUNCTION.
IF YOU LOOK AT THE ELECTRON IT DOESN'T LOOK
LIKE A WAVE FUNCTION SO THE REALITY PROBLEM
IS, WHAT IS THE WAVE FUNCTION OR FOR THAT
MATTER WHAT IS REALITY.
IS THE WAVE FUNCTION ITSELF ON TO ONE ISOMORPHIC
REPRESENTATION OF WHAT IS REALLY GOING ON?
OR SOMEHOW JUST ENCODING OUR INABILITY TO
PREDICT WHAT THE OBSERVATIONAL OUTCOME IS
GOING TO BE.
ARE THE OTHER VARIABLES OVER AND ABOVE THE
WAVE FUNCTION?
PEOPLE LIKE EINSTEIN AND OTHERS THOUGHT THEY
WERE HIDDEN VARIABLES . THAT CAN HELP US MAKE
PREDICTIONS IF ONLY WE KNEW WHAT THEY WERE.
OR DOES THE WAVE FUNCTION HAVE NOTHING TO
DO WITH REALITY AT ALL?
IS IT JUST A TOOL FOR MAKING PREDICTIONS?
OF THESE IS ANSWERED BY THE TRADITIONAL INTERPRETATION.
AND EVEN MORE FAMOUSLY WE HAVE THE MEASUREMENT
PROBLEM.
OF COURSE TO MAKE IT VIVID I SAID ELECTRONS
ACTED FROM WHEN YOU LOOK AT THEM YOU SHOULD
BE THINKING WHAT DO YOU MEAN LOOK AT THEM?
DOES IT HAVE TO BE A PERSON LOOKING?
DOES THE PERSON HAVE TO BE AWAY?
COULD IT BE THE CAT LOOKING AT ITSELF?
WHAT ABOUT A VIDEO CAMERA?
WHAT ABOUT A ROCK?
WHAT IF I GLANCED AT IT?
DOES THAT COUNT?
DOES THE WAVE FUNCTION COLLAPSE IF I GLANCED
AT IT?
DOES HUMAN CONSCIOUSNESS SOMEHOW GET INVOLVED
IN THIS GAME?
AGENCY THE ABILITY TO MAKE OBSERVATIONS AND
PRESUMPTIONS SOMEHOW RULE NATURE?
SOMEHOW WE DON'T AGREE THIS IS WHY THERE IS
A REALITY AND TRUTH TO FINDING THE STATEMENT
PHYSICIST DON'T UNDERSTAND QUANTUM MECHANICS
BECAUSE EVEN THOUGH SOME PEOPLE HAVE SOME
OPINIONS ON THESE QUESTIONS WE DO NOT HAVE
A CONSENSUS IN THE FIELD ABOUT HOW TO ANSWER
THEM.
SO, MY MAIN MESSAGE, IF I HAVE ONE, THESE
ARE ANSWERABLE QUESTIONS.
THESE ARE NOT IMPOSSIBLE, NOT JUST PHILOSOPHY,
NOT JUST SOMETHING YOU DO AFTER YOU ARE TOO
TIRED TO DO REAL WORK ANYMORE, THIS SHOULD
BE THE JOB OF PHYSICS TO ANSWER THESE QUESTIONS.
I SECONDARY MESSAGES, I THINK I KNOW WHAT
THE ANSWER IS. AND IT WASN'T INVENTED BY ME,
IT WAS INVENTED BY THIS GUY, HUGH EVERETT,
A GRADUATE STUDENT IN THE 1950s, WORKING UNDER
JOHN WHEELER.
BASICALLY, EVERY'S SUGGESTION IS WE SHOULD
ALL JUST CHILL OUT.
[ LAUGHTER ] HE SAID , HE SUGGESTED THE SIMPLEST
MOST AUSTERE, MOST PURE VERSION OF QUANTUM
MECHANICS.
HE SAID, YOU WANT TO KNOW WHAT IS REAL?
IT IS THE WAVE FUNCTION.
OBVIOUSLY THE WAVE FUNCTION WHAT ELSE WOULD
IT BE?
YOU WANT TO KNOW HOW WAVE FUNCTION DEVOLVE?
THEY OBEY THE SCHRODINGER EQUATION.
YOU KNOW THAT IS WHAT THEY DO, THEY DON'T
DO ANYTHING ELSE.
IT IS KIND OF A QUANTUM THERAPY HE IS OFFERING
PEOPLE.
IN OTHER WORDS, HERE IS THE EVERETT INTERPRETATION
OF QUANTUM MECHANICS.
THERE IS ONLY ONE SET OF RULES.
THEY ALWAYS APPLY ALL THE TIME . SYSTEMS ARE
DESCRIBED BY WAVE FUNCTION THE WAVE FUNCTION's
WILL BE THE SCHRODINGER EQUATION.
THE PROBLEM IS, ALREADY TOLD YOU WHAT THE
PROBLEM IS.
WHEN YOU LOOK AT QUANTUM MECHANICAL SYSTEM
LIKE PARTICLES BEING EMITTED FROM RADIOACTIVE
SUBSTANCES, THEY DON'T LOOK LIKE WAVE FUNCTION.
THEY DON'T LOOK LIKE THEY ARE OBEYING THE
SCHRODINGER EQUATION.
EVERETT SAYS THAT IS BECAUSE YOU NEED TO IN
CARTER ABOUT WHAT DO YOU MEAN BY LOOKING AT
SOMETHING.
AND WHEN YOU ARE DOING THAT YOU HAVE TO TAKE
QUANTUM MECHANICS SERIOUSLY.
TAKING QUANTUM MECHANICS SERIOUSLY TO EVERETT
MEANS TWO THINGS.
NUMBER1, YOU CAN'T PRETEND YOU ARE CLASSICAL.
YOU CAN'T PRETEND EVEN THOUGH YOUR OBSERVER
YOU ARE FREE FROM OBEYING THE RULES OF QUANTUM
MECHANICS.
YOU ARE JUST AS QUANTUM AS EVERYTHING ELSE.
YOU ARE MADE OF ATOMS SO YOU SHOULD OBEY THE
SCHRODINGER EQUATION ALSO.
YOU SHOULD HAVE A WAVE ACTION.
OF ELECTRONS CAN BE IN SUPERPOSITION THE POSSIBILITY
YOU CAN BE IN SUPERPOSITION THE POSSIBILITIES.
THAT IS ONE FACT.
THE IDEA THAT EINSTEIN AND OTHERS DEVELOPED
IN THE 1930s CALLED ENTANGLEMENT . THIS IS
REALLY , REALLY WHAT MAKES QUANTUM MECHANICS
SPECIAL AND INTERESTING IS THIS PHENOMENON
OF ENTANGLEMENT I WILL INTRODUCE IT BY A MODERN
EXAMPLE.
BUT THERE WERE EXAMPLES WAY BACK IN THE DAY.
WE RECENTLY, IN 2012 DISCOVERED A NEW, FUNDAMENTAL
PARTICLE OF NATURE, THE LAST PIECE WE NEEDED
IN THIS TATTERED PARTICLE PHYSICS WE DISCOVERED
THE COLLIDER IN GENEVA AND BECAUSE OF ALL
THE KNOWN ELEMENTARY PARTICLES AND HAS 0 SPIN
ELEMENTARIES PARTICLES CAN SPIN LIKE THE EARTH
SPINS AROUND ITS AXIS BUT AT THE PARTICLE
LEVEL INDIVIDUAL PARTICLES HAVE SPECIFIED
AMOUNTS OF SPIN BETTER VERY DEFINITE NUMBERS.
SOMETHING LIKE AN ELECTRON OR QUARK CAN EITHER
SPIN CLOCKWISE OR COUNTERCLOCKWISE . AS PHYSICISTS
A SPIN UP OR BEEN DOWN BUT IT HAS EXACTLY
0 SPIN.
THE IMPORTANT THING IS IT IS CONSERVED NOT
CREATED THE TOTAL AMOUNT IS PRESERVED.
SO WHEN IT DECAYS INTO TWO PARTICLES LET'S
SAY AN ELECTRON AND POSITRON ANTI-ELECTRON
OR QUARK AND ANTIQUARK, A SPIN WAS PARTICLE
IS DECAYING INTO SPINNING PARTICLES BUT THE
TOTAL SPIN HAS TO BE CONSERVED SO WHAT YOU
KNOW IS THAT THE TWO PARTICLES THAT IT DECAYS
INTO BETTER BE SPINNING THE OPPOSITE DIRECTIONS.
YOU DON'T KNOW WHETHER THIS IS UP AND THIS
ONE IS DOWN OR VICE VERSA BUT YOU KNOW THEY
ARE OPPOSITES OF THE TOTAL SPIN ADDS TO 0
BECAUSE THAT IS WHAT IT STARTED FROM.
ON THE MECHANICS IS YOU DON'T KNOW WHAT THE
SPIN OF THE FIRST PARTICLE IS GOING TO BE
IT COULD BE SPIN UP OR SPIN DOWN BUT THERE
IS A RELATIONSHIP BETWEEN THE SPIN OF THAT
ONE IN THE SPIN OF THE OTHER.
THE WAVE FUNCTION OF THE HIGGS IS INTO THE
SUPERPOSITION THE SUPERPOSITION OF PARTICLE
SPIN UP AND PARTICLE 2 SPIN DOWN PARTICLE
2 SPIN DOWN AND PARTICLE 2 SPIN UP IF YOU
WERE TO OBSERVE THE SPIN OF PARTICLE ON YOU
DON'T KNOW WHAT ANSWER YOU GET IT COULD BE
UP OR DOWN.
IF YOU OBSERVE THE SPIN OF PARTICLE 2 YOU
DON'T KNOW WHAT ANSWER YOU WILL GET COULD
BE DOWN OR UP BUT IF YOU OBSERVE THE SPIN
OF ONE OF THEM, LET'S SAY YOU OBSERVE SPIN
ON PARTICLE OF PARTICLE ONE HAS SPIN UP THEN
YOU KNOW WHAT PARTICLE 2 IS GOING TO BE IT
HAS TO BE THE OPPOSITE TO BALANCE OUT.
THAT IS QUANTUM ENTANGLEMENT.
YOU DON'T KNOW, THERE IS NO DEFINITE FACT
OF THE MATTER ABOUT THE SPIN OF EITHER PARTICLE
BUT THERE IS A RELATIONSHIP BETWEEN THEM.
THIS IS A FEATURE OF THE FACT THAT THERE IS
A DEEP DEEP FEATURE OF QUANTUM MECHANICS,
WHICH REALLY MAKES IT DIFFERENT THAN CLASSICAL
MECHANICS.
CLASSICAL MECHANICS YOU GIVE TWO PARTICLES.
PARTICLE ONE IS DOING SOMETHING, PARTICLE
TWO IS DOING SOMETHING ELSE.
THERE IS A STATE OF PARTICLE ON , POSITION,
VELOCITY AND SPIN AND THERE IS A STATE TO
PARTICLE 2 POSITION, VELOCITY AND SPIN.
YOU MIGHT THINK IN QUANTUM MECHANICS EVERY
PARTICLE HAS A WAVE FUNCTION AND SOMETIMES
WE TALK THAT WAY.
PARTICLE ONE COULD HAVE A WAVE FUNCTION THAT
IS SUPERPOSITION OF SPIN UP AND SPIN DOWN
LIKEWISE PARTICLE 2 BUT NO THAT IS NOT HOW
QUANTUM MECHANICS WORKS.
THERE IS ONLY ONE WAVE FUNCTION FOR ALL THE
PARTICLES AT ONCE.
THERE IS ONLY THE WAVE FUNCTION OF THE UNIVERSE.
AND IN THIS CASE THE WAVE FUNCTION OF THE
UNIVERSE IS THIS PARTICULAR ENTANGLED SUPERPOSITION.
THIS IS PROBABLY, FOR THE FIRST TWO THIRDS
OF THE TALK THIS IS THE DEEPEST CONCEPT I'M
GOING TO LAY ON YOU.
YOU'VE GOT TO UNDERSTAND THIS.
ENTANGLEMENT YOU DON'T KNOW WHAT PARTICLE
1 OR PARTICLE 2 BUT IF YOU WERE TO MEASURE
1 THEN YOU KNOW WHAT YOU GET IF YOU WERE TO
MEASURE 2.
SO LET'S APPLY THIS IDEA OF ENTANGLEMENT AND
THE IDEA THAT YOU YOURSELF ARE A QUANTUM SYSTEM
TO THE SCHRODINGER'S CAT EXPERIMENT.
THAT IS WHAT HUGH EVERETT SUGGESTS THAT WE
DO. AND THERE IS NO SPECIAL ROLE PLAYED BY
OBSERVATION OR MEASUREMENT OR CONSCIOUSNESS.
YOU ARE JUST A PHYSICAL SYSTEM OBEYING THE
LAWS OF NATURE.
YOU HAVE THE CAT , IT IS IN A SUPERPOSITION
OF AWAKE AND ASLEEP AND YOU HAVE THE OBSERVER
NOW PLAYED IN THE ROLE BY HUGH EVERETT, AND
THE IDEA OF MEASUREMENT IS, YOU OPENED THE
BOX AND YOU SOLVE THE SCHRODINGER EQUATION.
IN THE SCHRODINGER EQUATION DESCRIBES THE
CAP IT ALSO DESCRIBES YOU.
SO AGAIN ABSOLUTELY NO AMBIGUITY ABOUT WHAT
THE SCHRODINGER EQUATION PREDICTS.
BEFORE THE COPENHAGEN INTERPRETATION, WE MADE
UP A RULE THAT SAYS, WHEN YOU OPEN THE BOX
AND OBSERVE IT COLLAPSES AND YOU SEE ON OUTCOME
WITH OTHER . EVERETT SAYS JUST DO WITH THE
SCHRODINGER EQUATION SAYS.
AND THE ANSWER IS THAT YOU AND THE CAT EVOLVED
TO AN ENTANGLED SUPERPOSITION OF THE CAT WAS
AWAKE AND YOU SAW IT AWAY, PLUS THE CAP WAS
ASLEEP AND YOU SAW IT ASLEEP.
AGAIN, NO ON DOUBTS THAT IS WHAT THE SCHRODINGER
EQUATION PREDICTS.
THE PUZZLE IS, IT SEEMS LIKE YOU ARE NOW IN
A SUPERPOSITION OF HAVING SEEN THE CAT AWAKE
AND HAVING SEEN THE CAP ASLEEP NO ONE EVER
FEELS LIKE THEY ARE IN A SUPERPOSITION.
NO ONE EVER OPENS THE BOX , WELL PART OF ME
THINKS THE CAT IS AWAKE AND PART OF ME THINKS
THE CAT IS ASLEEP.
THAT IS NOT WHAT YOU THINK.
IT IS NOT CRAZY TO THINK THAT EVERETT WAS
CRAZY, IT SOUNDS LIKE WHAT HE IS SAYING IS
OBVIOUSLY WRONG.
IN FACT, IN SOME SENSE HE WAS AHEAD OF HIS
TIME BECAUSE THE SOLUTION TO THIS PUZZLE REALLY
WASN'T UNDERSTOOD UNTIL THE 70s OR 80s WITH
THE IDEA THAT WE NOW CALL DECOHERENCE . REMEMBER
I ALREADY TOLD YOU THAT THERE IS ONLY ONE
WAVE FUNCTION FOR THE ENTIRE UNIVERSE ALL
AT ONCE . AND I SHOWED YOU A PICTURE ON THE
LAST SLIDE WITH THE WAVE FUNCTION OF THE CAT
AND THE OBSERVER.
WHAT ABOUT THE REST OF THE ENTIRE UNIVERSE?
IT REALLY SHOULD INCLUDE THE REST OF THE ENTIRE
UNIVERSE IF I'M NOT CHEATING YOU.
SO WE BUNDLE UP THE ENTIRE REST OF THE UNIVERSE.
WE DON'T KEEP TRACK OF EVERYTHING, WE CALL
IT THE ENVIRONMENT, REPRESENTED HERE BY LEAVES
OF GRASS.
BUT THE ENVIRONMENT COULD BE THE PHOTONS OR
THE AIR MOLECULES BOUNCING AROUND IN THE ROOM.
ALL OF THE THINGS, ALL THE PARTICLES, DEGREES
OF FREEDOM THAT WE DON'T KEEP TRACK OF INDIVIDUALLY
IN OUR EXPERIMENT.
BUT YOU CAN TELL OF THE ENVIRONMENT IS THE
AIR MOLECULES OR THE PHOTONS IN THE BOX , THEY
INTERACT WITH THE CAT LONG BEFORE WE OPEN
IT.
SO THAT PROCESS IS CALLED DECOHERENCE, BECAUSE
THE CAT BECOMES ENTANGLED WITH THE ENVIRONMENT.
IF THE CAT IS AWAKE AND OVERHEAR A CERTAIN
PHOTON MIGHT HIT THE CAT AND BE OBSERVED WHEREAS
IF THE CAP IS ASLEEP PHOTON GOES RIGHT ON
BY.
THE WAY THE ENVIRONMENT INTERACTS WITH THE
CAT DEPENDS ON WHETHER IT IS AWAKE OR ASLEEP.
SO THE CAT VERY, VERY QUICKLY BECOMES ENTANGLED
WITH THE ENVIRONMENT.
AND THE PROCESS IS CALLED DECOHERENCE.
THE OBSERVER JUST GOES ALONG FOR THE RIDE
UNTIL THEN THEY OPENED THE BOX AND THEN THEY
BECOME ENTANGLED WITH BOTH THE CAT AND THE
ENVIRONMENT.
THIS STORY I JUST TOLD YOU IS A SLIGHTLY MORE
ACCURATE VERSION OF THE STORY I TOLD YOU ON
THE LAST SLIDE.
SO WHY AM I BOTHERING TO TELL YOU THIS SLIGHTLY
MORE ACCURATE STORY?
BECAUSE YOU CAN SHOW, USING MATH AND STUFF
LIKE THAT, THAT THIS STATE OF THE ENVIRONMENT
ENTANGLED WITH THE CAT IS PERPENDICULAR TO
THIS ENVIRONMENT ENTANGLED WITH THE SLEEPING
CAT. AND WHAT THAT MEANS IS WHAT HAPPENS IN
THE FUTURE, IN THIS PART OF THE WAVE FUNCTION,
IS NEVER AFFECTED IN ANY WAY BY WHAT IS GOING
ON IN THIS PART.
THEY HAVE BECOME UNCOMMUNICATIVE.
THEY DO NOT TALK TO EACH OTHER, THEY DO NOT
INTERACT ANYMORE.
THAT IS WHAT DECOHERENCE REALLY IS ABOUT.
THAT IS WHAT MEASUREMENT IS ACCORDING TO THE
EVERETT VERSION OF QUANTUM MECHANICS.
MEASUREMENT IS SIMPLY ON A SMALL QUANTUM SYSTEM
BECOMES ENTANGLED WITH ITS ENVIRONMENT.
AND WHAT HAPPENS IS THE WAVE FUNCTION IS A
SUPER POSITION BUT THE DIFFERENT PARTS OF
THE SUPER POSITION GO THEIR OWN WAY.
HAPPENS IN ONE IS INDEPENDENT OF WHAT HAPPENS
TO THE OTHER.
THEY BRANCH AS EVERETT PUT IT.
THEY SPLIT INTO TWO POSSIBILITIES.
IT IS AS IF THOSE TWO PARTS OF WAVE FUNCTION
DESCRIBE SEPARATE , INDEPENDENT WORLDS.
AND THAT IS WHY THE EVERETT INTERPRETATION
HAS BEEN DUBBED THE MANY-WORLDS INTERPRETATION
OF QUANTUM MECHANICS, BECAUSE THESE TWO PARTS
OF THE WAVE FUNCTION, HERE AND HERE DON'T
TALK TO EACH OTHER ANYMORE.
WE SHOULD TREAT THEM AS IF THEY HAVE NOTHING
TO DO WITH EACH OTHER.
AS IF THEY ARE INDEPENDENT.
WHAT I WANT TO EMPHASIZE IS, I DID NOT PUT
IN A BUNCH OF WORLDS.
ALL I DID WAS TAKE THE SCHRODINGER EQUATION
SERIOUSLY.
SCHRODINGER EQUATION PREDICTS THE EXISTENCE
OF MANY-WORLDS.
EVERY OTHER VERSION OF QUANTUM MECHANICS IS
A GET RID OF THE OTHER WORLDS INTERPRETATION.
AND MAYBE THAT IS WORTH DOING . BUT EVERETT
SAYS WHY BOTHER ? WHAT HAPPENS WHEN I OBEY
THE SCHRODINGER EQUATION IS WHAT WAS ONE COPY
OF ME IS NOW TO GET COPIES OF MEAN FUTURE
BUT THEY ARE SEPARATE PEOPLE.
THEY DON'T HAVE ANY WAY TO TALK TO EACH OTHER
OR ANYTHING LIKE THAT.
JUST TAKE THEM AT FACE VALUE, THERE IS TO
GET DIFFERENT WORLDS, THAT'S IT LIVE WITH
IT, CHILL OUT DON'T MESS WITH THE RULES OF
QUANTUM MECHANICS.
PEOPLE DON'T LIKE THIS.
[ LAUGHTER ] IT DID NOT GO OVER WELL.
FAVORITE'S THESIS ADVISOR, JOHN WHEELER, WAS
AN ACOLYTE OF NIELS BOHR, THE GRAHAM PUMBAA
AND MANY HARSH LETTERS WERE SENT BACK AND
FORTH OVER THE ATLANTIC OCEAN.
EVERETT NEVER TRIED TO GET AN ACT BIG ACADEMIC
JOB HE LEFT TO DO DEFENSE CONSULTING AND THE
INTERPRETATION WAS MORE OR LESS FORGOTTEN
BUT HAS BEEN REDISCOVERED.
SO, THERE ARE GOOD REASONS TO BE SKEPTICAL,
OR AT LEAST PUZZLES YET TO BE ANSWERED IN
THE EVERETT INTERPRETATION BUT ALSO A BUNCH
HAVE NOT SO GOOD REASONS TO NOT LIKE IT.
I DON'T MIND IF YOU COME AWAY FROM THE LECTURE
AT THE END OF THE DAY NOT BELIEVING EVERETT
INTERPRETATION BUT I WANT TO NOT LEAVE IT
FOR THE RIGHT REASONS IF THAT'S POSSIBLE.
LET ME TRY TO ASK AND ANSWER SOME OF THE SIMPLEST
QUESTIONS ABOUT THIS.
THE SIMPLEST QUESTION TO WHICH I ONLY HAVE
A VERY UNSATISFACTORY ANSWER IS, HOW MANY-WORLDS
ARE THERE ANYWAY?
I JUST SHOWED YOU A PICTURE WHEREWITH THE
CAT ON WORLD BRANCHED INTO TWO.
WITH AN ELECTRON, IF YOU MEASURE THE LOCATION
OF THE ELECTRON , HOW MANY DIFFERENT POSSIBLE
ANSWERS COULD YOU GET?
THE ANSWER IS INFINITY ANSWERS.
THERE IS AN INFINITE NUMBER OF POINTS IN SPACE
FOR THE ELECTRON COULD BE LOCATED.
NAIVELY, MAYBE IN REALITY, THERE ARE INFINITELY
MANY- WORLDS.
THE REALITY IS WE DON'T KNOW HOW MANY-WORLDS
THERE ARE IN THE MANY-WORLDS INTERPRETATION
OF QUANTUM MECHANICS.
THERE COULD BE INFINITELY MANY IN WHICH CASE
YOU SHOULDN'T TALK ABOUT HOW MANY THERE ARE,
YOU SHOULD TALK ABOUT THE RELATIVE WEIGHT
OF WORLDS ACTING ON WAY VERSUS WORLDS ACTING
ANOTHER WAY.
WHAT I WANT TO GET ACROSS IS, PEOPLE WORRY
SOMETIMES ABOUT CONSERVATION OF ENERGY . BY
MEASURE A SPIN AND SUDDENLY THERE IS T UNIVERSES
WORD ALL THE ENERGY COME FROM FOR STARS AND
GALAXIES IN THAT UNIVERSE?
WHAT IS REALLY HAPPENING IS AS TIME GOES UP,
YOU START WITH ONE, BIG UNIVERSE.
THERE IS A LOT OF WEIGHT A LOT OF WAVE FUNCTION
ATTACHED TO THE SINGLE BRANCH OF THE UNIVERSE.
THROUGH A SERIES OF PHYSICAL INTERACTIONS
GOVERNED BY THE SCHRODINGER EQUATION, THAT
UNIVERSE IS DIVIDED UP INTO MULTIPLE COPIES.
IT IS NOT THAT YOU ARE CREATING NEW STUFF,
THE UNIVERSES MATHEMATICALLY WELL-DEFINED
SENSE, DINNER THAN THEY USED TO BE BECAUSE
THEY ARE DIFFERENTIATING FROM EACH OTHER.
YOU ARE NOT CREATING MORE STUFF YOU ARE JUST
DIFFERENTIATING THE STUFF THAT WAS ALREADY
THERE INTO MANY, MANY COPIES.
THE PEOPLE IN THE COPIES DON'T KNOW THIS,
BUT THAT IS WHAT THE MATH SAYS.
DON'T WORRY ABOUT CONSERVATION OF ENERGY OR
ANYTHING LIKE THAT.
ANOTHER QUESTION IS, I JUST DON'T LIKE IT
BECAUSE THERE IS TOO MANY UNIVERSES.
I DON'T WANT TO, YOU KNOW, I DON'T WANT TO
DISPARAGE THIS KIND OF QUESTION TOO MUCH,
BUT I AM TRYING TO ACCURATELY CAPTURE THE
FACT THAT REALLY THE REASON WHY PEOPLE DON'T
LIKE THE MANY-WORLDS INTERPRETATION BECAUSE
IT SEEMS TOO EXTRAVAGANT.
YOU ARE TRYING TO ANSWER A SIMPLE QUESTION
ABOUT ELECTRONS AND YOU END UP INVENTING AN
INFINITE NUMBER OF UNIVERSES.
DOESN'T THAT SEEM LIKE BRINGING AN AWFUL LOT
OF AMMUNITION TO BEAR ON A FAIRLY SMALL PUZZLE?
I THINK THAT IS EXACTLY BACKWARDS.
I THINK EVERETT REALLY IS THE SIMPLEST , MOST
STRAIGHTFORWARD READING OF QUANTUM MECHANICS.
REMEMBER, ALL THE MANY-WORLDS INTERPRETATION
IS , IS THE STATEMENT THAT THERE ARE WAVE
FUNCTION's AND THEY OBEY THE SCHRODINGER EQUATION.
THE WORLD's ARE A CONSEQUENCE OF THAT.
YOU DID NOT PUT THEM IN.
IF YOU BELIEVE AN ELECTRON CAN BE IN A SUPERPOSITION
OF SPINNING CLOCKWISE AND SPINNING COUNTERCLOCKWISE
, YOU BELIEVE THE WORLD OBEYS THE RULES OF
QUANTUM MECHANICS, THEN YOU CAN BE IN THE
SUPERPOSITION OF HAVING SEEN THE ELECTRON
DO ONE THING AND DO OTHER THINGS.
IN THE UNIVERSE CAN BE IN A SUPERPOSITION.
YOU CAN'T STOP LIKING IT WHEN THE SUPERPOSITION's
BECOME BIG UNLESS YOU WANT TO CHANGE THE RULES
OF QUANTUM MECHANICS IN SOME WAY. AND YOU
ARE VERY WELCOME TO DO THAT, THAT MAKES THE
THEORY MORE COMPLICATED.
IT DOESN'T MAKE IT SIMPLER.
EVERETT IS SIMPLY THE SIMPLEST WAY TO GO.
THE OTHER EASILY OF TENSION IS THIS CAN BE
TESTED . YOU HAVE MADE A LOT OF WORLDS AND
YOU HAVE ALREADY SAID I CANNOT INFLUENCE THEM
IN ANY WAY OR BE INFLUENCED BY THEM IN ANY
WAY.
THAT DOESN'T SOUND LIKE SCIENCE TO ME IF I
CAN'T GET THERE.
BUT THAT IS NOT RIGHT.
EVERY THEORY MAKES PREDICTIONS THAT CAN'T
BE TESTED.
WE DON'T COUNT IT AGAINST THE THEORY WHEN
IT MAKES SOME PREDICTIONS THAT CAN'T BE TESTED.
WE ASK, WHAT ARE THE PREDICTIONS THAT CAN
BE TESTED AND RETESTED THEM, RIGHT?
THE TYPICAL CRITERIA WOULD LIKE TO USE, NOT
PERFECT OR PRETTY GOOD, IS FALSIFIABILITY.
AND WE IMAGINE AN EXPERIMENT THAT WOULD TELL
US THIS THEORY, IF YOU GOT THE RIGHT ANSWER
IT WOULD TELL US THE THEORY IS NOT CORRECT.
IT IS FALSIFIED.
AND THE CASE OF EVERETT IN QUANTUM MECHANICS
ARE WAVE FUNCTIONS OF THE SCHRODINGER EQUATION.
CAN YOU IMAGINE EXPERIENCE THAT FALSIFY THOSE
ASSUMPTIONS?
YES.
THEY ARE BEING DONE AND IT IS GOING ON RIGHT
NOW.
ALL YOU HAVE TO DO IS OBSERVE AN ISOLATED
QUANTUM SYSTEM VIOLATE THE SCHROEDER GROUP
EQUATION.
THERE ARE THEORIES IN WHICH THAT HAPPENS AND
THEY ARE BEING EXPERIMENTALLY TESTED RIGHT
NOW.
EVERETT IS THE MOST FALSIFIABLE THEORY EVER
INVENTED . IT JUST HASN'T BEEN FALSIFIED YET.
ALL RIGHT.
THE OTHER THING I WANT TO SAY, I MENTIONED
BEFORE, IT IS NOT JUST PHILOSOPHY.
I DON'T WANT TO DENIGRATE PHILOSOPHY.
I AM A BIG FAN OF PHILOSOPHY.
I THINK POSSIBLY IS IMPORTANT.
EMPIRICALLY PHILOSOPHERS OF PHYSICS HAVE DONE
A MUCH BETTER JOB TAKING QUANTUM MECHANICS
SERIOUSLY THAN PHYSICISTS HAVE.
I DO THINK THAT MAYBE WE SHOULDN'T BE SURPRISED
THAT WE ARE STRUGGLING WITH CERTAIN PUZZLES
WITHIN PHYSICS IF WE HAVE ABANDONED THE QUEST
TO UNDERSTAND QUANTUM MECHANICS FOR ITS OWN
SAKE.
IF YOU CLAIM , IF SOMEONE CAN GET UP IN FRONT
OF THE ROOM AND SAY I DON'T THINK ANYONE UNDERSTANDS
QUANTUM MECHANICS AND SOMEONE ELSE COMES UP
AND SAYS WE DON'T UNDERSTAND THE QUANTUM THEORY
OF GRAVITY FOR EXAMPLE, WILL WHY SHOULD WE
IF WE DON'T UNDERSTAND QUANTUM MECHANICS?
THIS IS NOT USUALLY THE WAY PEOPLE THINK BECAUSE
WE TEND TO START WITH THE CLASSICAL THEORY
AND QUANTIZE IT SO THE SEARCH FOR SOMETHING
LIKE QUANTUM CAVITY IS STARTING WITH THE RIGHT
CLASSICAL THEORY OF GRAVITY TURNING INTO A
QUANTUM THEORY.
PRESUMABLY NATURE DOESN'T DO THAT . MAJOR
DOESN'T START WITH THE CLASSICAL THEORY AND
QUANTIZE IT NATURE IS JUST QUANTUM FROM THE
START.
MAYBE THE REASON WE DON'T UNDERSTAND QUANTUM
GRAVITY IS BECAUSE WE DON'T UNDERSTAND QUANTUM
MECHANICS.
I SUGGEST THIS NOT ONLY IS A LOGICAL POSSIBILITY
BUT IT MIGHT ACTUALLY BE TRUE.
JUST TO REMIND YOU OF HOW GRAVITY WORKS, THOSE
OF YOU WHO HAVE NOT READ MY TEXTBOOK ON GENERAL
RELATIVITY, OUR BEST CURRENT THEORY OF GRAVITY
IS EINSTEIN'S THEORY OF GENERAL RELATIVITY.
GRAVITY IS THE CURVATURE OF SPACETIME . YOU
HAVE TO BELIEVE THERE IS SOMETHING CALLED
SPACE-TIME, THE THREE DIMENSIONAL SPACE ALL
AROUND US PLUS TIME EVOLVING THIS FORWARD,
EINSTEIN SAYS YOU SHOULD THINK OF SPACETIME
NOT NEARLY AS THE BACKGROUND AS THE STAGE
ON WHICH PHYSICS HAPPENS, THE PLAYER IN THE
GAME IN ITS OWN RIGHT.
SPACE-TIME IS DYNAMICAL.
IT WORKS, IT ENDS, AND CHANGES IN RESPONSE
TO STUFF IN THE UNIVERSE.
TO MATTER, TO MOMENTUM, TO ENERGY IS THE SIMPLEST
WAY OF THINKING ABOUT IT.
WHEN AN APPLE FALLS FROM THE TREE BECAUSE
THE ENERGY OF THE EARTH IS WARPED THE SPACE
AND TIME AROUND IT SO FALLING IS THE SIMPLEST
THING THAT APPLE CAN DO.
IF YOU WANT A MOTTO FOR GENERAL RELATIVITY,
THE GEOMETRY OF SPACETIME IS SOMEHOW RELATED
TO ENERGY.
THIS IS THE THING WE WOULD LIKE TO GET OUT
OF A QUANTUM MECHANICAL DESCRIPTION OF NATURE.
AS I ALREADY SAID, WE DON'T UNDERSTAND QUANTUM
MECHANICS, WE DON'T UNDERSTAND QUANTUM GRAVITY.
MAYBE THESE LACKS OF UNDERSTANDING ARE SOMEHOW
RELATED.
THE PROGRAM IS RATHER THIN QUANTIZE IN GRAVITY,
WE SHOULD FIND THE GRAVITY WITHIN QUANTUM
MECHANICS.
WE SHOULD START WITH THE PURELY QUANTUM IDEA
WHICH BY THE WAY THIS IS A POINT OF DOING
EVERETT QUANTUM MECHANICS THERE ARE ALTERNATIVES
TO EVERETT.
THEIR VERSIONS WERE THERE ARE HIDDEN VARIABLES,
THE SCHRODINGER EQUATION IS VIOLATED, AND
ALL OF THESE , SOME LINGERING ELEMENT OF CLASSICAL
REALITY IS PUT IN BY HAND AT THE START.
THERE IS SOME CLASSICAL PRESUPPOSITIONS THAT
COME INTO HOW WE GET TO ALL OF THOSE OTHER
WORLDS . EVERETT IS THE MOST PURELY QUANTUM
OF ALL THE APPROACHES TO QUANTUM MECHANICS
THERE ARE.
IF YOU WANT TO PLAY THE GAME WITH THE PURELY
QUANTUM DESCRIPTION OF NATURE AND SEE HOW
THE CLASSICAL DESCRIPTION ARISES, PUTTING
IN THE FRAMEWORK OF EVERETTI MECHANICS IS
WHAT WE'RE GOING TO TRY TO DO . NOT TO TRAUMA
GRAVITY.
WE ARE ALLOWED TO TAKE HINTS FROM THE REAL
WORLD.
THE BEST THEORY WE HAVE OF THE REAL WORLD
THAT DOESN'T INCLUDE GRAVITY IS SOMETHING
CALLED QUANTUM FIELD THEORY.
I TALKED ABOUT PARTICLES LIKE ELECTRONS AND
QUARKSS, THAT IS A BIT OF A FAKE.
IN MODERN PHYSICS THE FUNDAMENTAL INGREDIENTS
OF NATURE ARE NOT PARTICLES AT ALL, THEY ARE
FIELDS.
A VERY SUBTLE THING TO TALK ABOUT BECAUSE
I ALREADY TOLD YOU ELECTRONS ARE REALLY PARTICLES
THEY ARE WAVES.
BUT NOW I'M TELLING YOU THAT THE THINK THAT
IS QUANTUM IS AN EVEN THE PARTICLE.
YOU GO FROM PARTICLE TO WAVE FUNCTION YOU
GO FROM WAVE FROM A FIELD TO A WAVE FUNCTION
OF THE FIELD.
THIS IS VERY COMPLICATED.
I WROTE MANY WORDS ABOUT THEM I PUT THEM IN
MY BOOK, AND MY EDITOR TOLD ME TOO LEAVE THEM
BECAUSE NO ONE WOULD KNOW WHAT I'M TALKING
ABOUT.
IT'S THE FINAL ANSWER AT THE END OF THE DAY
THIS IS HOW THINGS WORK.
FOR THE PURPOSES OF THE LECTURE YOU HAVE TO
TRUST ME ON THIS.
THE POINT OF FIELDS VERSUS PARTICLES IS, A
PARTICLE HAS A LOCATION IN SPACE.
IT IS THERE, IT IS NOT ANYWHERE ELSE.
A FIELD IS THE OPPOSITE.
THE FIELD IS EVERYWHERE.
THE MAGNETIC FIELD YOU MIGHT SEE BECAUSE YOU
HAVE FILINGS SPREAD AROUND A MAGNET THERE
IS A VALUE OF THE MAGNETIC FIELD OF THE UNIVERSITY
EVERY POINT IN SPACE.
YOU MIGHT BE ZERO IN SOME PLACES, LARGE OTHER
PLACES THAT FIELDS EXIST EVERYWHERE.
QUANTUM FIELD THEORY THE BASIS OF THE STANDARD
MODEL OF PARTICLE PHYSICS, THE QUANTUM VIBRATIONS
OF THOSE FIELDS ARE WHAT YOU AND I PERCEIVE
OF AS PARTICLES.
WHAT THAT MEANS IS THAT EVEN EMPTY SPACE HAS
STUFF GOING ON . THIS IS A FOUNDATIONAL, FUNDAMENTAL,
REALLY IMPORTANT FEATURE OF QUANTUM FIELD
THEORY , GLOSSED OVER MOST OF THE TIME PEOPLE
TALK ABOUT IT BECAUSE YOU JUMP RIGHT TO THE
PARTICLES.
AND QUANTUM FIELD THEORY THERE ARE THESE WAVES
THAT EXIST ALL OVER THE PLACE.
THEY ARE ALL QUANTIZED AND LOW ENERGY STATE
AS IF SOMETHING IS NOTHING IS GOING ON.
PARTICLE WHEN YOU TAKE THAT QUANTUM FIELD
AND YOU VIBRATED STRONGLY.
MORE STRONGLY THAN IT WOULD IN ITS LOWEST
ENERGY STATE WE PRESUME THAT IS A PARTICLE.
OF THE WORD REALLY MADE OF PARTICLES WE WOULD
SAY THERE IS PARTICLES IN SOME PLACES AND
EMPTY SPACE ELSEWHERE.
AT THE WORLD WAS MADE OF QUANTUM YIELDS WE
HAVE SOME VIBRATING MODES WHICH WE CALL PARTICLES,
THE THERE ARE STILL MODES, VIBRATIONS OF THE
QUANTUM YIELDS EVEN IN EMPTY SPACE ITSELF.
YOU WILL NOT BE SURPRISED TO LEARN THAT THESE
LITTLE PATCHES OF VIBRATING FIELDS ARE ENTANGLED
WITH EACH OTHER.
ALL THE FIELDS OF VIBRATING AND IF THEY ARE
RIGHT NEXT TO EACH OTHER, IF THEY HAD NOTHING
TO DO WITH EACH OTHER, NO RELATIONSHIP THERE
WOULD BE A LOT OF ENERGY CONTAINED THERE.
SO THE LOWEST ENERGY THING TO DO THE EMPTY
SPACE STATE OF THE QUANTUM FIELD IS ONE WHERE
NEARBY PATCHES OF SPACE ARE HIGHLY ENTANGLED.
AND REGIONS OF SPACE THAT ARE VERY FAR AWAY
ARE NOT VERY ENTANGLED.
SO IT IS VERY NATURAL THAT IN QUANTUM FIELD
THEORY AS WE UNDERSTAND IT, THERE IS A RELATIONSHIP
BETWEEN THE GEOMETRY OF SPACE , BECAUSE THAT
IS WHAT YOU TALK ABOUT WHEN YOU TALK ABOUT
DISTANCES AND TRIANGLES AND LENGTHS AND STUFF
LIKE THAT, AND THE AMOUNT OF ENTANGLEMENT
BETWEEN THOSE DIFFERENT REGIONS OF SPACE.
THE SHORTER THE DISTANCE THE MORE THE ENTANGLEMENT.
SO LET'S TURN THIS AROUND.
THAT WAS TAKING A CLUE FROM WHAT WE ALREADY
KNOW ABOUT THE UNIVERSE.
OUR PROJECT IS NOT TO TAKE SOME FIELDS AND
QUANTIZE THEM TO TAKE SOMETHING INTRINSICALLY
QUANTUM AND FIND THE STUFF WE KNOW IN IT.
SO INSTEAD OF SAYING WHEN THINGS ARE CLOSE
TOGETHER THEY ARE PROBABLY HIGHLY ENTANGLED.
MAYBE WHAT WE CAN SAY IS, WHEN THINGS ARE
HIGHLY ENTANGLED, LET'S DEFINE THAT TO BE
CLOSE TOGETHER.
I AM USING THE WORD THINGS BECAUSE THERE IS
MORE MATH INVOLVED FIGURING OUT WHAT THE FUNDAMENTAL
INGREDIENTS OF THESE KINDS OF DESCRIPTIONS
ARE BUT ONE FUNDAMENTAL QUANTUM DEGREES OF
FREEDOM ARE NOT VERY ENTANGLED THAN THEY ARE
FAR AWAY FROM EACH OTHER.
IN OTHER WORDS, IF YOU GIVE ME A BUNCH OF
QUANTUM STUFF AND YOU TELL ME HOW IT IS ENTANGLED,
THAT KNITS THEM TOGETHER AND IF WE ARE LUCKY
IT NEEDS THEM TOGETHER TO DO MINE A SPACE
, THREE DIMENSIONAL SPACE WITH A CERTAIN GEOMETRY
THAT YOU CAN EXTRACT FROM THE ENTANGLEMENT.
THERE IS A VERY NATURAL RELATIONSHIP BETWEEN
GEOMETRY AND ENTANGLEMENT.
THERE IS ALSO A VERY NATURAL RELATIONSHIP
BETWEEN ENTANGLEMENT AND ENERGY.
REMEMBER, WE SAID THAT IN EMPTY SPACE THE
LOWEST ENERGY STATE, THINGS ARE ENTANGLED
IN A VERY SPECIFIC WAY.
WE ALSO SAID THAT PARTICLES WHICH CARRY ENERGY,
PARTICLES REQUIRE YOU DO SOMETHING EXTRA TO
THE QUANTUM FIELDS IN ONE REGION OF SPACE.
THE EXTRA THING YOU DO GENERICALLY BREAKS
THE ENTANGLEMENT BETWEEN THE LITTLE EXTRA
VIBRATION YOU PERCEIVE AS A PARTICLE IN THE
DEGREES OF FREEDOM AROUND IT.
WHEN YOU PUT PARTICLES AND THEREFORE ENERGY
INTO A REGION OF SPACE, IT BECOMES LESS ENTANGLED
WITH ALL THE STUFF AROUND IT.
SO THERE IS ANOTHER DIRECT RELATIONSHIP BETWEEN
ENTANGLEMENT AND ENERGY ADDING PARTICLES DECREASES
ENTANGLEMENT.
WHAT DO WE GET OUT OF THIS BUNCH OF HANDWAVING?
AGAIN THERE ARE SOME EQUATIONS ATTACHED TO
THIS THE LET MAY BE VERY HONEST.
THIS IS SPECULATIVE STUFF.
LETTING YOU IN ON THE CUTTING EDGE BY STUFF
I DON'T AGREE WITH EXCEPT ME AND MY STUDENTS.
BUT WE HAVE IS VERY NATURAL FOR ENTANGLEMENT
TO BE RELATED TO GEOMETRY.
BUT WE KNOW FROM QUANTUM FIELD THEORY IS THE
DEGREES OF FREEDOM IN EMPTY SPACE ARE MORE
ENTANGLED WHEN THEY ARE NEARBY.
WE CAN IN PRINCIPLE EXTRACT THE GEOMETRY OF
SPACE FROM KNOWING THE ENTANGLEMENT BETWEEN
EVERYTHING IN THE WORLD.
THERE IS ALSO A VERY NATURAL RELATIONSHIP
BETWEEN ENTANGLEMENT AND ENERGY.
WHEN YOU CHANGE THE ENTANGLEMENT , YOU BREAK
THE ENTITLEMENT BETWEEN SOME DEGREES OF FREEDOM
AND OTHER ONCE IT IS LIKE PUTTING ENERGY IN
THERE.
THUS, THERE IS A RELATIONSHIP BETWEEN GEOMETRY
AND ENERGY.
NOT STARTING FROM A DESCRIPTION OF SPACE,
TIME, FIELDS AND STUFF, JUST FROM STARTING
WITH THE QUANTUM FUNCTION WITH DIFFERENT BITS
OF ENTANGLED IN THE RIGHT WAY.
IF YOU START WITH THAT QUANTUM DESCRIPTION
AND TRY TO SAY WHAT CLASSICAL THING DOESN'T
NATURALLY CORRESPOND TO, THE ANSWER IS A SPACE
WITH A GEOMETRY, WHERE THE GEOMETRY IS RELATED
TO THE ENERGY INSIDE.
GUESS WHAT?
THAT IS GENERAL RELATIVELY.
THAT IS THE RULES OF SPACE AND TIME AND GRAVITY
THE EINSTEIN INVENTED BACK IN 1915.
WHAT EINSTEIN HAD TO DO WAS CAUSE IT, AN EQUATION
RELATING THE ENERGY AND SPACETIME TO THE AMOUNT
OF CURVATURE.
WHAT WE ARE ABLE TO DO UNDER A LONG LAUNDRY
LIST OF ASSUMPTIONS THAT ARE NOT YET PROVEN
TO PUT IT POLITELY, AND YET YOU PROVEN TO
BE CORRECT BUT UNDER SOME REASONABLE SOUNDING
ASSUMPTIONS WE CAN DERIVE EINSTEIN'S EQUATION
FROM THE ENTANGLEMENT OF QUANTUM DEGREES OF
FREEDOM.
AGAIN THIS IS VERY PRELIMINARY AND WORK BEING
DONE BY CERTAIN PEOPLE, THE RELATIONSHIP BETWEEN
ENTANGLEMENT AND SPACETIME IN GEOMETRY AND
SO FORTH.
WE CAN AT LEAST SEE THE VAGUE OUTLINE OF A
PROGRAM WHERE RATHER THAN QUANTIZE SEEING
SOME CLASSICAL THEORY CALLING THAT QUANTUM
GRAVITY, WE TAKE QUANTUM MECHANICS SERIOUSLY.
THERE IS WAVE FUNCTION's ENTANGLED ETC. AND
WE ASK AFTER THE FACT WHAT IS THAT QUANTUM
WAVE FUNCTION?
HOW WOULD WE INTERPRET IT?
WHAT IS THE CLASSICAL LIMIT?
WHAT ARE THE EMERGENT REALITIES THAT COME
OUT OF THAT?
IS VERY NATURAL IT SEEMS FOR THAT EMERGING
REALITY TO LOOK LIKE SPACETIME, OBEYING EINSTEIN'S
EQUATION OF GENERAL RELATIVITY.
LET ME CLOSE WITH A QUOTE FROM DAVID DEUTSCH,
ONE OF THE LEADERS OF QUANTUM THEORY IN GENERAL
AND THE MANY RULES OF INTERPRETATION IN PARTICULAR.
DESPITE THE UNRIVALED EMPIRICAL SUCCESS OF
QUANTUM THEORY, WHICH MEANS THE MANY-WORLDS
INTERPRETATION OF QUANTUM THEORY, THE VERY
SUGGESTION THAT IT MAYBE LITERALLY TRUE AS
A DESCRIPTION OF NATURE IS WITH CYNICISM AND
COMPREHENSION AND EVEN ANGER.
I'M HOPING THAT THE END OF TODAY'S TALK AT
THE VERY LEAST THE INCOMPREHENSION WILL BE
LESS THAN IT WAS AT THE BEGINNING.
THANK YOU VERY MUCH.
[ APPLAUSE ]
I THINK THERE IS TIME FOR QUESTIONS.
I BELIEVE I AM IN CHARGE.
WHAT HE WILL DO IS RUN PELL- MELL UP TO THESE
MICROPHONES RIGHT HERE AND GET IN LINE AND
I WILL PICK ON YOU.
I DON'T KNOW ARE THERE ANY MICROPHONES OF
THERE?
NO?
SORRY.
YOU'RE WELCOME TO COME DOWN.
YOUR FIRST.
THANKS FOR THE GREAT TALK.
THANKS.
THE COPENHAGEN INTERPRETATION OF QUANTUM MECHANICS
E-BOOK ABOUT TWO ISSUES ONE OF WHICH IS THE
OBSERVER ISSUE WHAT COUNTS AS AN OBSERVED
AND WHAT IS THAT MEASUREMENT GET MADE?
ISN'T THAT STILL AN ISSUE IN THE EVERETTIAN
INTERPRETATION OF QUANTUM MECHANICS?
WHAT CONSTITUTES AN EVENT IN WHICH BRANCHING
WHITAKER?
GOOD.
THAT'S A GREAT QUESTION BECAUSE I KNOW THE
ANSWER.
[ LAUGHTER ] . WAY.
OCCURS WHEN INTEGUMENT BECOMES ENTANGLED WITH
THE OUTSIDE WORLD AND NEEDS COHERENCE . OKAY.
TO UNDERSTAND WHEN THE MEASUREMENT HAPPENS
IN EVERY ALL YOU HAVE TO DO IS HOLD THE SCHRODINGER
EQUATION.
TO BE MORE FAIR, THERE IS A QUESTION OF EMERGENCE.
THERE IS A QUESTION OF MICROSCOPIC AND MACROSCOPIC
VOCABULARIES IN WHICH TO DESCRIBE THE WORLD.
IF YOU THOUGHT YOU KNEW THE WAVE FUNCTION
OF THE UNIVERSE, IF YOU WERE STEPHEN HAWKING
AND KNEW THE WAVE FUNCTION OF THE UNIVERSE
YOU DON'T NEED TO TALK ABOUT BRANCHES . YOU
DON'T NEED TO TALK ABOUT SUBSYSTEMS YOU HAVE
THE WAVE FUNCTION OF THE UNIVERSE WHERE THE
RICH?
THE ANSWER IS BECAUSE THE REALITY WE PERCEIVE
AS SUBSYSTEMS OF THE UNIVERSE IS THIS EMERGENT,
HIGHER-LEVEL, INCOMPLETE THING WHICH IS NOT
THE WAVE FUNCTION OF THE UNIVERSE.
THE SINGLE HARDEST THING TO DO IN THE EVERETT
VERSION OF QUANTUM MECHANICS IS NOT TO WRITE
DOWN WITH THE FORMALISM IS , IT IS TO CONNECT
THAT FORMALISM TO OUR EXPERIENCE.
OF COURSE WE HAVE AN IDEA OF WHAT CONSTITUTES
A MEASUREMENT, OPENING UP THE BOX, PUTTING
THE ELECTRON IN A CLOUD CHAMBER, WHATEVER.
THERE IS SOME WORK TO BE DONE AND ATTACHED
THE FORMALISM TO THAT.
IN PARTICULAR SHOWING THE WORLD's REALLY DO
SPLIT AND NOT TALK TO EACH OTHER AND ALSO
SHOWING WHY THERE IS A PROBABILITY RULE IN
THE WAVE FUNCTION SQUARED.
THAT IS THE ONGOING RESEARCH OF THE EVERETT
PROGRAM . IN MY VIEW, IT IS ALL VERY DOABLE
STUFF.
THANKS.
SHIRT.
YES?
SO, WHEN YOU ARE SAYING LIKE WHEN YOU OBSERVE
A PARTICLE, ARE YOU JUST SAYING IT IS AN EXCITED
PART OF THE QUANTUM FIELD AND THAT LIKE JUST
BECAUSE YOU ARE OBSERVING IT DOESN'T MEAN
THAT ENTANGLEMENT DOESN'T EXIST IT IS JUST
LESS ENTANGLED?
IS THAT WHAT YOU ARE SAYING?
I'M NOT SURE WHAT I'M SAYING THERE.
WHAT I'M SAYING IS , LET ME SAY SOMETHING
I AM SAYING AND WE WILL SEE IF IT IS SOMETHING
YOU HOPE I AM SAYING.
WHEN THERE IS A PARTICLE WHICH IS SWEEPING
THE PARTICLES AS REALLY CERTAIN EXCITATIONS
IN A QUANTUM FIELD BUT THAT IS KIND HAVE NOT
ESPECIALLY GERMAIN FOR THE QUESTION . IT COULD
HAVE BEEN A PARTICLE OR IT COULD HAVE BEEN
A FIELD TO BE QUANTIZED.
THE THING WE ARE OBSERVING HAS A WAVE FUNCTION.
WHEN WE MAKE THAT OBSERVATION OF ITS POSITION,
VELOCITY OR WHATEVER WE CANNOT PREDICT WITH
CERTAINTY WHAT ANSWER WE WILL GET AHEAD OF
TIME.
THAT IS THE EMPIRICAL FACT.
THE EVERETTIAN EXPLANATION FOR THE EMPIRICAL
FACT AS YOU BECOME ENTANGLED WITH THE THING
YOU ARE OBSERVING AND ALL THE POSSIBLE MEASUREMENT
OUTCOMES ARE ACTUALIZED BUT ACTUALIZED IN
DIFFERENT PARTS OF THE ENTANGLED POSITION
WHERE YOU HAVE DIFFERENT FEELINGS ABOUT WHAT
YOU THINK YOU JUST MEASURED .
OKAY.
THANK YOU.
CLOSE ENOUGH?
[ LAUGHTER ] BETTER THAN I USUALLY GET [ LAUGHTER
]
SO, I WAS READING YOUR BOOK, AND I WAS TRYING
TO APPLY IT TO THE DELAYED CHOICE EXPERIMENT
. IN THAT NORMAL DELAYED CHOICE APPEARS WHEN
YOU REACH EITHER THE SPOT MEASUREMENT ARE
NOT YOU ARE GOING TO HAVE THE COHERENCE FOR
THAT DIFFER NOT INTERFERE OR INTERFERE.
IT IS VERY CONFUSING TO UNDERSTAND WHAT IS
HAPPENING -- THE SIGNAL IS HEATING THE SCREEN
BEFORE ANY OF THE -- WHICH PATH IS GOING TO
HAPPEN.
YOU HAVE A PATTERN YOU CANNOT SEE AND YOU
HAVE A PATTERN , YOU CAN SEE BECAUSE YOU KNOW
WHICH ONE BUT THE PATTERN IS THERE AN BRANCHING
HAS TO HAPPEN THERE . HOW YOU CAN BRANCH THEIR
IF YOU STILL DON'T KNOW WHICH ONES ARE GOING
TO GO WHICH WAY?
GOOD.
I AM NOT GOING TO BE ABLE TO GIVE A COMPLETE
EXPLANATION HERE.
THIS IS A LONGER STORY.
THOSE OF YOU WHO ARE NOT HANGING OUT ON THE
WRONG STREET CORNERS THERE'S SOMETHING CALLED
THE DELAYED CHOICE QUANTUM ERASER EXPERIMENT
WHERE THIS IDEA HE MAKE A MEASUREMENT IT WAS
A WAY THAT LOOKS LIKE A PARTICLE SEEMINGLY
IS DELAYED . YOU MAKE THE MEASUREMENTS OF
EVERYTHING BEFORE YOU ACTUALLY PREVIOUSLY
MEASURED THE PARTICLE.
IT ACTS WAVELIKE OR PARTICLE LIKE DEPENDING
ON SOMETHING AFTER THE EXPERIMENT IS OVER
WHICH SEEMS WEIRD AND ALMOST AS IF SIGNALS
WENT BACKWARD IN TIME.
I THINK THE IDEA, I THINK THAT THE STANDARD
POPULAR LEVEL EXPLANATIONS OF THIS EXPERIMENT
ARE ALL NEEDLESSLY , INTENTIONALLY MAKING
THINGS DIFFICULT AND IT ALL MAKES PERFECT
SENSE IN ORDINARY QUANTUM MECHANICS WITHOUT
ANY SIGNALS GOING BACKWARD IN TIME AND THE
BASIC TRICK IS TO FUSS AROUND WITH WHAT DO
YOU MEAN BY MAKING A MEASUREMENT . IN COPENHAGEN
QUANTUM MECHANICS WHAT WE MEAN BY MAKING A
MEASUREMENT IS LEFT A LITTLE BREAK.
IN EVERETT IS 100% CLEAR YOU ARE SOLVING THE
SCHRODINGER EQUATION.
MEASUREMENT OCCURS WHEN THE QUANTUM SYSTEM
BECOMES ENTANGLED WITH THE WORLD BUT WHAT
IF RATHER THAN INTENTIONALLY WITH A BILLION
PHOTONS YOU TINGLY WITH ONE ANOTHER ELECTRON?
THEN YOU CAN KEEP THAT ELECTRON, SHIELDED
FROM THE REST OF THE WORLD AND ON ENTANGLE
IT.
YOU COULD APPARENTLY DO THE OBSERVATION BUT
UNDO IT AND CHANGE THE RESULT YOU GET THERE
BY.
BUT ALL I WILL SAY ABOUT IT , IT IS 100% COMPLETELY
COMPATIBLE WITH THE ORDINARY EVOLUTION OF
THE STRONGER EQUATION FORWARD IN TIME . WE
HAVE A LONG LINE, SORRY.
I DIDN'T -- THERE IS A BLOG POST ABOUT THIS
SO YOU CAN LOOK THAT UP.
ANOTHER SECTION MY EDITOR FORCED ME TOO CUT
FROM THE BOOK.
I WAS WONDERING IS THE SPLIT LIKE FROM ONE
RANCH TO TWO BRANCHES INSTANTANEOUSLY?
YES.
IT IS NOT INSTANTANEOUS IT TAKES ABOUT THAT
LONG.
IT IS VERY, VERY FAST.
LITERALLY SOMETHING CALLED THE DECOHERENCE
TIMESCALE.
IF A PHOTON HITS YOUR EYEBALL YOU CAN ASK
HOW LONG DOES IT TAKE FOR THAT TO DECOHERENCE
BECAUSE THE EYEBALL IS A WARM WET THING THAT
INTERACTS WITH THE ENVIRONMENT VERY ROUGHLY
LESS THAN TEN THE MINUS 22nd.
IT'S NOT INSTANTANEOUS REALLY FAST.
HAVE A QUESTION ABOUT GENERAL RELATIVITY.
IN SPACE HAS A CERTAIN RATE AT WHICH IT MOVES
. IN A GRAVITY FIELD HAS A SLOWER RATE RELATIVE
TO THAT CLOCK IN SPACE . SO ON EARTH WOULD
GO SLOWER , CORRECT?
IF --YOU COMMERCIALLY BECAUSE IT'S CLOSER
TO THE CENTER OF THAT GRAVITY.
IF IT GOES INTO A HOLE IN THE EARTH, IT IS
EVEN CLOSER.
BUT, IT IS UNDER LESS GRAVITY BECAUSE IT IS
INSIDE THE EARTH . SO, DOES IT GO SLOWER OR
FASTER THAN THE ONE ON THE SURFACE?
-SLOWER.
THANK YOU.
[ LAUGHTER ]
HI.
THANKS WITH A GREAT TALK.
ABOUT IT WAS QUITE ILLUMINATING.
MY QUESTION IS A BIT RELATED TO CAUSALITY.
I THINK A COUPLE OF PEOPLE TOUCHED IT BEFORE
ME IN THE QUESTIONS.
WHEN YOU HAVE THIS BRANCHING, THE CAUSALITY
OF IT IS BECAUSE THE OBSERVE DECIDES I'M GOING
TO OPEN THE BOX AND IN THE CASE OF SCHRODINGER'S
CAT EXPERIMENT, I'M GOING TO OPEN THE BOX
OR NOT.
SO HOW DO YOU KIND OF INCORPORATE CAUSALITY
INTO THE STRUCTURE OR THE EVERETTIAN MODEL?
AND THE SECOND THING IS, I KNOW YOU HAD DAVID
CHALMERS ON YOUR PODCAST AND HE HAS AN INTERESTING
PERSPECTIVE HOW INNER TAKES THE PROBLEM
I THINK WE GET ONE QUESTION.
SORRY.
THE QUESTIONS CONNECTED SO BECAUSE CAUSALITY
IS KIND OF CONNECTED IN MY VIEW TO CONSCIOUSNESS
TO BEGIN WITH BECAUSE WHO DECIDES AT THE BEGINNING
OF THE SINGULARITY , WHO DECIDES WHO YOU BRANCH
OUT OR WHAT ARE THE BRANCHES?
IN MY VIEW OF IT, CONSCIOUSNESS IS ENTIRELY
EPIPHENOMENAL ON THE PHYSICAL GOING ON's THAT
ARE IN THE UNIVERSE.
THE ONLY THING THAT EVER HAPPENS IN THIS VIEW
OF THE UNIVERSE IS THERE IS A WAVE FUNCTION
OBEYING THE SCHRODINGER EQUATION.
GUESS WHAT?
THE SCHRODINGER EQUATION IS COMPLETELY DETERMINED
HOLISTIC.
THERE IS A QUESTION, A GOOD PHILOSOPHY QUESTION
HOW YOU DERIVE PROBABILITIES IN EMPIRICAL
REALITY, BUT THE WAVE FUNCTION ITSELF IS COMPLETELY
DETERMINISTIC.
AT THE LEVEL OF WAVE FUNCTION AN BRANCHING,
THERE IS NO SUCH THING AS DECISIONS.
YOU ARE JUST OBEYING THE SCHRODINGER EQUATION.
AND THERE'S NO SUCH THING AS CAUSALITY.
YOU'RE JUST OBEYING THE SCHRODINGER EQUATION.
ALL OF THOSE ARE WORDS THAT ARE USEFUL AT
THE EMERGENT LEVEL OF HIGHER-LEVEL THINGS
LIKE YOU IN NEED BUT THEY ARE NOT THERE IN
THE MICRO PHYSICS.
OKAY.
REGARDING THE BRANCHING YOU SAID TWO BRANCHES
DON'T TALK TO EACH OTHER.
DOES THAT MEAN THEY CAN'T INTERFERE?
YES THAT'S EXACTLY WHAT IT MEANS.
THEY CAN'T INTERFERE AT ALL?
THAT IS CLEVER.
SORRY.
[ LAUGHTER ] OTHERWISE A LOT MORE SCIENCE
FICTION STORIES WE COULD TELL.
YES.
SO, QUANTUM MECHANICS TO ME REMINDS ME A BIT
OF STATISTICAL MECHANICS, BECAUSE THEY BOTH
DEALING PROBABILITIES.
FROM STATISTICAL MECHANICS STANDPOINT, IF
WE WERE TALKING ABOUT THE BULK PROPERTIES
OF SOME SPACE, FOR EXAMPLE THIS ROOM, THE
PRESSURE AND TEMPERATURE DOESN'T REALLY DEPEND
ON WHERE THAT PARTICULAR MOLECULE OF OXYGEN
IS.
MY QUESTION IS, IF THAT IS INDEED THE CASE,
HOW USEFUL IS THE MULTI-WORLD INTERPRETATION
OF ALL OF THOSE WORLDS, IF THE BULK PROPERTIES
OF ALL OF THOSE WORLDS ARE EXACTLY THE SAME?
ARE EXACTLY THE SAME?
YES.
I AM NOT SURE I EXACTLY GET THE THRUST OF
THE QUESTION.
THE WORLD's ARE NOT EXACTLY THE SAME.
THEY HAVE DIFFERENT OBSERVATIONAL's IN THEM.
THE CAT IS AWAKING ON GOLD AND ASLEEP IN THE
OTHER WORLD THE REST OF THE WORLD OF THE SAME
BUT THERE'S A HUGE DIFFERENCE BETWEEN QUANTUM
MECHANICS AND STATISTICAL MECHANICS BECAUSE
THE WAVE ACTION IS ONTOLOGICAL.
IT REPRESENTS WHAT REALITY IS DOING.
DISTRIBUTION FUNCTION IN CLASSICAL MECHANICS
REPRESENT OUR KNOWLEDGE OF WHAT IS GOING ON
SO YES THERE IS SOMETHING GOING ON WITH BOTH
POSITIONS AND VELOCITIES, WE JUST DON'T KNOW
BUT THE WEIGHT FUNCTION IS REALLY REALITY
IN THIS PICTURE.
THANK YOU.
SURE.
SO MY QUESTION WAS ABOUT THE MANY-WORLDS THEORY.
YOU MENTIONED ON THE BOTTOM OF THE PAGE DUPLICATING
TO TALK ABOUT THE CONSERVATION OF ENERGY THAT
WHEN YOU HAVE , BECAUSE YOU HAVE THE SPLIT
AND IT IS NOT DUPLICATION YOU DON'T END UP
WITH INFINITE ENERGY, RIGHT?
COULD YOU NOT WORK BACKWARDS WITH THAT ARGUMENT
AND SAY THAT IN ORDER TO HAVE THIS YOU WOULD
HAVE TO HAVE AN INFINITE INITIAL UNIVERSE
OR OTHERWISE WOULD END UP EVENTUALLY TO THE
POINT THE SPLITTING HAS BECOME SO INTENSE
THAT YOU CAN NO LONGER SPLIT?
OR IS THERE ALWAYS GOING TO BE THE AVAILABILITY
TO SPLIT?
KNOW EXACTLY WHAT YOU'RE SAYING.
's ARTICLE IS DISTRACTED I'M GOING TO CALL
A HALT TO MORE PEOPLE GETTING IN LINE.
EIGHT PEOPLE GET QUESTIONS OTHERWISE I WILL
BE HERE ALL DAY.
YES.
SO, YOU ARE ABSOLUTELY RIGHT.
THERE IS, IF AS I BELIEVE, IF THERE IS A LIMIT
TO HOW MANY TIMES THE WAVE FUNCTION CAN BRANCH,
ONLY A FINITE NUMBER OF POSSIBLE BRANCHES,
THEN YOU WILL REACH A POINT AT WHICH BRANCHING
IS NO LONGER POSSIBLE.
THE POINT IS BASICALLY THERMAL EQUILIBRIUM
WHERE EVERYTHING IS PUSHED OUT COSMOLOGICALLY
IT WILL LOOK LIKE EMPTY SPACE AND THERE WILL
BE NO SUCH WAY, NO SENSIBLE WAY OF DELINEATING
DIFFERENT BRANCHES OF THE WAVE FUNCTION.
WE ARE NOWHERE CLOSE TO THAT RIGHT NOW.
THAT IS A QUESTION FOR OUR ANCESTORS . DESCENDANTS.
PHYSICISTS . [ LAUGHTER ] THANK YOU.
MY QUESTION IS ABOUT --SHE SAID ENTANGLEMENT
CAN RELATE THE ENERGY AND THE GEOMETRY OF
THE SPACE . BUT, SPACETIME BOUNDARY LOCALLY
LOOKS LIKE -- JUST BASED ON WHAT IF WE CHOOSE
THE BOUNDARY OF THE BLACK HOLE AND INFINITE
ON LEFT AND ON THE RIGHT IF WE USE THE ENTANGLEMENT
RELATED TO THE ENERGY AND GEOMETRY WE HAVE
A CALCULATION ON THE QUANTUM GRAVITY WITH
THE BOUNDARY OF THE BLACK HOLE ?
RIGHT I WILL ONLY DO A PARTIAL ANSWER THAT
TO THAT QUESTION BECAUSE YOU CLEARLY HAVE
BEEN CHEATING ON ME LISTENING TO OTHER PEOPLE
OTHER THAN ME TALK ABOUT QUANTUM GRAVITY.
THERE IS A THING FOR THOSE OF YOU WHO DON'T
KNOW IN THE AUDIENCE THERE'S SOME THING CALLED
ADS EFTU RELATIONSHIP BETWEEN A COSMOLOGICAL
SPACETIME WHERE GRAVITY IS IMPORTANT, CALLED
ADS AND A PARTICULAR KIND OF QUANTUM FIELD
THEORY IN ONE LOWER DEMAND TO HIM CALLED CONFORMAL
FIELD THEORY OR CFT AND THEY ARE THE SAME
THEORY TO SOME APPROXIMATION IN VERY DIFFERENT
SIZES.
THE THEORY OF QUANTUM GRAVITY THAT IS THE
SAME AS A THEORY WITHOUT GRAVITY AT ALL.
NATURALLY, THIS IS A WONDERFUL DISCOVERY BY
A PHYSICIST, MUCH EFFORT HAS GONE INTO UNDERSTANDING
THINGS ABOUT GRAVITY FROM UNDERSTANDING FIELD
THEORY AND VICE VERSA.
IN PARTICULAR, WHAT YOU CAN SHOW , FIRST MENTIONED
, THE THING THAT GETS YOU THE CURVATURE OF
SPACETIME ON THE GRAVITY SIDE OF THE RELATIONSHIP
IS THE ENTANGLEMENT OF THE FIELDS IN THE QUANTUM
FIELD THEORY SIDE OF THE RELATIONSHIP.
THERE IS A RELATIONSHIP BETWEEN GEOMETRY AND
ENTANGLEMENT.
THAT RELATIONSHIP IS COMPLETELY DIFFERENT
FROM THIS RELATIONSHIP EVEN THOUGH THIS IS
ALSO A RELATIONSHIP BETWEEN GEOMETRY AND ENTANGLEMENT.
ADS CFT IS WHERE THEY ARE MAXIMALLY FAR AWAY
IN SOME SENSE FROM EMPTY SPACE.
THERE IS A COSMOLOGY THAT IS DEFINITELY BIG
FULL OF NEGATIVE ENERGY DENSITY IN THIS HOLOGRAPHIC
BACK THAT THINGS GOING ON , ON THE BOUNDARY,
REFLECTED IN THE CURVATURE INSIDE, IS TAKING
ADVANTAGE OF GRAVITY REALLY BEING DIFFERENT
WHEN GRAVITY IS STRONG OR WHEN SPACETIME IS
BIG.
LIKE A BLACK HOLE WHERE ADS WOULD BE LIKE
THAT.
HERE, I'M WORKING IN THE WEEK FILLED LIMIT
CLOSE TO EMPTY SPACE.
MY GOAL, THIS ENTANGLEMENT IS NOT IN A FARAWAY
BOUNDARY, THIS ENTANGLEMENT IS RIGHT HERE
IN THIS ROOM.
AS MY GOAL IS TO UNDERSTAND WHY APPLES FALL
FROM TREES , NOT TO UNDERSTAND A BLACK HOLE
IN A FIVE DIMENSIONAL SPACE-TIME.
THANK YOU.
SURE.
I FEEL LIKE THIS IS PROBABLY NOT A VERY GOOD
QUESTION, BUT WHAT DOES IT MEAN WHEN THINGS
ARE ENTANGLED?
WHAT IS IT MEAN WHEN THINGS ARE ENTANGLED?
GOOD.
IS THAT IT?
YES.
THE BURDEN YOU ARE STRUGGLING UNDER HIS HAVING
GROWN UP IN A CLASSICAL UNIVERSE.
YOU THINK THAT IF I HAVE A PARTICLE , NOT
YOU PERSONALLY, BUT PEOPLE THINK THAT IF I
HAVE A PARTICLE IT HAS A LOCATION IN SPACE.
THAT IS A VERY NATURAL, INNOCENT SOUNDING
THING . AND QUANTUM IN QUANTUM MECHANICS WHEN
YOU HAVE THIS WAVE FUNCTION, THERE IS THIS
WAY OF TALKING THE PEOPLE HAVE THAT SAYS,
THE WAVE FUNCTION TELLS ME WHERE THE PARTICLE
IS WHEN I LOOK AT IT WITH CERTAIN PROBABILITY.
WHAT EVERETT IS TRYING TO TELL US IS, THAT
IS NOT RIGHT.
THE WAVE FUNCTION DOESN'T TELL YOU THE PROBABILITY
OF THE PARTICLE BEING THERE.
THE WAVE FUNCTION IS ALL THAT EXISTS.
BEFORE YOU LOOKED AT IT, THERE IS NO SUCH
THING AS WHERE THE PARTICLE IS.
THERE IS ONLY THE WAVE FUNCTION.
WHAT POSITIONS ARE IN EVERETTI QUANTUM MECHANICS
OF THE FUNDAMENTAL OUTCOMES THEY ARE NOT THE
GREETINGS OF WHICH THINGS ARE MADE IF YOU
HAVE TWO PARTICLES, THEN YOU CAN ASK WHAT
ARE THE POSSIBLE OBSERVATIONAL OUTCOMES . IF
YOU WERE TO OBSERVE THE POSITIONS OF BOTH
PARTICLES.
OR NEARLY WITH INK WHERE ARE THE PARTICLES
. I'M TRYING TO TRAIN YOU THINK WHAT ARE THE
POSSIBLE OBSERVATIONAL OUTCOMES.
ENTANGLEMENT IS SIMPLY WHEN THE POSSIBLE OBSERVATIONAL
OUTCOMES ARE ON PARTICLE A RELATED IN SOME
NONTRIVIAL WAY TO THE POSSIBLE OBSERVATIONAL
OUTCOMES OF THE OTHER PARTICLE.
YOU CAN SAY I DON'T KNOW WHERE THIS PARTICLE
WILL BE OBSERVED, BUT IF I OBSERVE IT HERE,
THEN I CAN SAY SOMETHING ABOUT THE OTHER PARTICLE
. THAT IS ENTANGLEMENT.
OKAY.
THANK YOU.
A QUESTION WAS TOUCHED ON JUST BRIEFLY.
SO I'M GLAD HAVE THE OPPORTUNITY.
IF I WAS GOING TO ASK YOU IS IF THIS IS WHAT
YOU CHOOSE TO WORK ON WHICH IS ONE OF THE
BIG QUESTIONS A PHYSICIST HAS TO ANSWER INTRIGUED
GIVE A VERY INTERESTING RESPONSE BUT IT WOULD
BE WRONG BECAUSE THERE IS NO CHOICE OR FREE
WILL IN THIS ? IF YOU HAVE A BIG ENOUGH COMPUTER
AND YOU CAN PREDICT EVERYTHING.
IF I AM AN EVIL HACKER WITH RANSOMWARE LIKE
$100 MILLION TRYING TO DECIDE WHETHER TO DO
IT OR NOT, I COULD MAKE TWO OPINIONS I COULD
SAY THINK ABOUT THE FUTURE I HAVE DONE THIS
AWFUL DEED, LOOKING BACK I HAVE NO CHOICE
BECAUSE THERE IS NO CHOICE NO BIG DEAL LET'S
DO IT NUMBER 2 WHICH IS WORSE IS I COULD SAY,
ONE OF MY DOPPELGANGERS , I HAVE LOTS OF DOPPELGANGERS
SPLITTING OFF ALL THE TIME EVERY POSSIBLE
THING A LOT OF THIS ARE DOING THIS AWFUL THING
SO WHY DON'T I DO AND GET THE BENEFIT IN MY
BRANCH SO I QUESTION IS WHY SHOULD ANYBODY
WHO BELIEVES IN MANY-WORLDS THEORY STRIVE
TO LIVE AN ETHICAL LIFE?
[ LAUGHTER ]
IT.
THE SHORT ANSWER TO THAT IS READ CHAPTER NINE
OF MY BOOK.
[ LAUGHTER ]
I HAVE READ CHAPTER NINE.
HERE IS THE LONGER ANSWER.
IF YOU TRULY BELIEVE THAT YOU DON'T HAVE THE
ABILITY TO MAKE CHOICES AND AFFECT THE FUTURE,
EVERYTHING THAT IS GOING TO HAPPEN TO YOU
IS DETERMINED BY THE LAWS OF PHYSICS.
I SUGGEST YOU IMPLEMENT THIS LEAF IN YOUR
EVERYDAY LIVES , LIKE SOMEONE SAYS WHAT YOU
WANT TO HAVE FOR DINNER, WITH THE LAWS OF
PHYSICS HAVE PREDICTED I WILL HAVE FOR DINNER.
DO YOU LOVE ME?
I DON'T KNOW WHATEVER THE LAWS OF PHYSICS
SAY I WILL SAY.
I PREDICT YOU WILL NOT GET VERY FAR IN YOUR
LIFE DOING THIS.
AND I CAN EXPLAIN WHY IT IS BECAUSE THERE
ARE DIFFERENT VOCABULARIES FOR TALKING ABOUT
THE WORLD THAT IT WILL BE DIFFERENT RULES.
THERE IS A VOCABULARY FOR TALKING ABOUT THE
WORLD THAT IS FUNDAMENTAL AND MICROSCOPIC
AND REDUCTIONISTIC WHERE YOU HAVE THE WAVE
FUNCTION OF THE UNIVERSE WILL BE THE SCHRODINGER
EQUATION.
AND INDEED NOT VOCABULARY THERE IS NO SUCH
THING AS TRACES OR FREE WILL OR OPTIONS.
IT IS DETERMINISTIC IT DOES WHAT IT DOES.
BUT THERE IS ANOTHER VOCABULARY IF YOU'RE
TALKING ABOUT THE WORLD WE HAVE PEOPLE IN
PLANETS AND PUPPIES AND CHOICES AND OPINIONS
AND DESIRES AND ETHICS.
AND DID NOT VOCABULARY, THINGS ARE NOT DETERMINED
BECAUSE WE HAVE WOEFULLY INCOMPLETE INFORMATION
ABOUT THE WAVE FUNCTION OF THE UNIVERSE.
AND HAVE THE ABILITY TO MAKE CHOICES.
I SUGGEST YOU TAKE ADVANTAGE.
[ APPLAUSE ].
THANK YOU .
I WAS JUST WONDERING IF THERE WAS -- YOU SAID
THAT -- WHEN THE SCHRODINGER EQUATION IS COMPLETED
THERE IS A SPLITTING OF THE UNIVERSE I'M WONDERING
IF EACH , I GUESS, MANY SEPARATE WORLDS OF
THE MANY-WORLDS THEORY HAS LIKE PREDETERMINED
WEIGHT OR IS IT ALL THE SAME THINGS LIKE THAT?
YES, NO.
YES, NO.
THE THICKNESS OF THIS DIAGRAM IS SUPPOSED
TO SORT OF COLORFULLY SUGGEST THE DIFFERENT
WEIGHTS THAT GO INTO THIS.
VERY TYPICALLY WHEN WE ARE GIVING THIS EXAMPLE
OF SPIN THAT WE ARE GOING TO MEASURE, SPIN
UP OR SPIN DOWN WE ARE OFTEN GIVEN AN EXAMPLE
WITH THE SUPERPOSITION IS AN EQUAL WEIGHT
BETWEEN SPIN UP AND SPIN DOWN YOU SEE THERE
IS A 50/50 CHANCE THAT IT'S VERY EASY TO PREPARE
WE AUCTIONS FOR SPINS WHERE IT IS ONE THIRD
LIKELY TO BE SPIN UP IN TWO THIRDS LIKELY
TO BE SPIN DOWN.
THAT IS A PUZZLE FOR EVERETTIANS WHERE THIS
COMES FROM.
THE ONLY DIFFERENCES THE WEIGHT IS DIFFERENT.
AND I THINK THERE ARE VERY GOOD ARGUMENTS
AS TO WHY , BASICALLY IT I WILL GIVE YOU THE
22nd ANSWER.
WHEN THE SPLITTING HAPPENS, EXACTLY BECAUSE
DECOHERENCE IS VERY, VERY, VERY FAST, THE
SPLITTING ALWAYS HAPPENS BEFORE YOU KNOW IT.
SO EVEN THOUGH THIS PERSON HERE CAN PREDICT
WITH 100% CERTAINTY THAT THERE WILL BE A COPY
OF THEM THERE AND A COPY OF THEM THEY ARE,
ONCE THEY ARE THERE THEY ARE WILL ALWAYS BE
A MOMENT IN TIME WHEN THESE TWO PEOPLE DON'T
KNOW WHICH BRANCH THEY ARE ON AND IT TURNS
OUT THERE IS A UNIQUELY SENSIBLE WAY TO ASSIGN
IT CREDENCE TO BEING ON THIS PRINTER THIS
BRANCH AND IT IS A WAVE ACTION SQUARE.
OKAY.
YES I HEAR MUMBLING.
[ LAUGHTER ]
I HAVE THE TWO PARTNER.
ON HOW TO WORLD SPLIT IN TWO HOW DOES YOUR
ANSWER , DECOHERENCE PERHAPS, AVOID THE SAME
FLAWS AND COPENHAGEN INTERPRETATIONS.
HAD A WAVE FUNCTION SPLIT?
IT IS EXACTLY MY ANSWERS DECOHERENCE, GOOD
YOU PREDICTED ME CORRECTLY.
THE DIFFERENCE IS THAT I HAVE A VERY SPECIFIC
EQUATION THAT TELLS ME WHAT HAPPENS OF THE
MICROSCOPIC LEVEL, THE SCHRODINGER EQUATION.
IT IS EXACT AND ALWAYS OBEYED IN THIS PICTURE.
ALL ELSE IS COMMENTARY.
THE DIVIDING UP OF THE WAVE FUNCTION INTO
DIFFERENT BRANCHES ETC. IS ALL CONVENIENT
FOR COMING BEINGS IN EXACTLY THE SAME WAY
IT IS CONVENIENT TO DIVIDE THIS ROOM WHICH
IS FULL OF ATOMS, PROTONS , HIGHER-LEVEL APPROXIMATE
DESCRIPTION.
THERE IS NO IMMEDIATE MOMENT WHEN THE WAVE
FUNCTION BRANCHES.
IT HAPPENS GRADUALLY OVER TIME . YOU SOLVE
THE EQUATION, THE AMOUNT OF TIME IT TAKES
IS THIS REALLY PREPOSTEROUSLY TINY NUMBER
LIKE TEN TO THE MINUS 20 SECONDS.
THE WAY TO MAKE THAT QUANTITATIVE IS TO ASK
HOW QUICKLY DO THESE TWO STATES, THE ENVIRONMENT
ENTANGLED WITH THE AWAKE CAT IN THE ENVIRONMENT
ENTANGLED WITH THE ASLEEP CAT HOW LONG DOES
IT TAKE TO MAKE THEM GO PERPENDICULAR?
THAT IS A VERY QUANTITATIVE QUESTION YOU CAN
ASK AND THE ANSWER IS VERY, VERY FAST AND
THAT IS WHEN THE MEASUREMENT HAPPENS.
THE MEASUREMENT HAPPENS WHEN THE QUANTUM SYSTEM
BECOMES ENTANGLED WITH THE ENVIRONMENT AND
THE TWO ENVIRONMENT STATES ENTANGLED WITH
THE CAP BECOME PERPENDICULAR TO EACH OTHER
.
THANKS.
SURE.
SO, SUPPOSE YOU HAD TWO ENTANGLED PARTICLES
THAT WERE LIGHT YEARS APART WITH A CORRESPONDING
PROBABILITY OF THEM BEING THERE AND YOU MEASURED
ON TO BE SPIN DOWN WOULD YOU AUTOMATICALLY
KNOW THE OTHER IS SPIN UP?
AND IF SO WOULDN'T THAT VIOLATE THE FACT THAT
INFORMATION CAN'T TRAVEL FASTER THAN THE SPEED
OF LIGHT?
SO YES AND DEPENDS.
[ LAUGHTER ] WHAT YOU ARE SUGGESTING IS EXACTLY
THE EPR PUZZLE . EPR BEING EINSTEIN , ONE
OF EINSTEIN'S GREAT CONTRIBUTIONS TO QUANTUM
MECHANICS.
THERE IS A MYTH EINSTEIN WAS TOO OLD AND CURMUDGEONLY
TO REALLY UNDERSTAND QUANTUM MECHANICS.
HE UNDERSTOOD IT BETTER THAN ANYBODY ELSE,
HE JUST WASN'T HAPPY WITH IT AND THIS IS ONE
OF THE REASONS WHY BECAUSE IF YOU HAVE TWO
ENTANGLED PARTICLES YOU CAN MOVE AS FAR APART
AS YOU WANT.
YOU DON'T KNOW WHAT MEASUREMENT OUTCOME YOU
ARE GOING TO GET BUT WHEN YOU MEASURE ONE
OF THEM YOU INSTANTLY KNOW WHAT THE OTHER
ONE WILL BE.
THE PROBLEM IS, IT IS COMPLETELY USELESS FOR
SENDING SIGNALS FOR COMMUNICATING BECAUSE
YOU HAVE MEASURED THIS ONE BUT THEY DON'T
KNOW YOU HAVE MEASURED IT, THEY DON'T KNOW
WHAT THE ANSWER IS.
YOU HAVE TO SEND THEM THE INFORMATION ABOUT
WHAT YOUR ANSWER WAS IF YOU SENT THEM IN THE
SIGNAL MOVING AT THE SPEED OF LIGHT.
RIGHT?
SO THERE IS A NO SIGNALING THEREMIN QUANTUM
THEOREM IN QUANTUM MECHANICS YOU CAN'T USE
ENTANGLEMENT TO SEND SIGNALS FASTER THAN THE
SPEED OF LIGHT.
IT SEEMS LIKE SOMETHING KIND OF HAPPENS FASTER
THAN THE SPEED OF LIGHT THAT MIRACULOUSLY
CANNOT BE USED TO SEND INFORMATION . SHOULD
THAT BOTHER YOU?
IT IS UP TO YOU [ LAUGHTER ] I WILL NOT TELL
YOU TO BE BOTHERED.
LAST QUESTION.
OH MY GOODNESS THE PRESSURE IS ON YOU.
THIS IS A REALLY SIMPLE QUESTION NOW THAT
I'VE HEARD ALL OF THESE.
SO, YOU HAVE BROUGHT UP A LOT OF REALLY INTERESTING
TOPICS.
BUT IF YOU COULD JUST SUM UP AND HELP US UNDERSTAND
THE ONE TOPIC , WHAT DO YOU WANT US WALKING
AND WE WOULD TRULY UNDERSTANDING?
WHAT WOULD IT BE?
OF THAT'S A GREAT QUESTION ACTUALLY.
I THINK I WANT IT TO BE , THE THING I WANT
YOU TO TAKE AWAY AND REMEMBER TEN YEARS FROM
NOW, PEOPLE ASK YOU ABOUT THIS TALK.
AT THAT, SURE.
IT IS NOT ANY FACT ABOUT QUANTUM MECHANICS
OR AFFECT ABOUT PHYSICS.
IT IS THE ATTITUDE THAT THE JOB PHYSICS IS
TO UNDERSTAND REALITY.
IT IS NOT JUST TO MAKE PREDICTIONS.
PHYSICISTS POST ALL THE DIFFICULTIES IN QUANTUM
MECHANICS HAVE OCCASIONALLY TAUGHT THEMSELVES
INTO THE IDEA THAT PHYSICS IS NOT ABOUT REALITY.
PHYSICS IS JUST ABOUT MAKING PREDICTIONS.
I THINK IT IS A BAD ATTITUDE ANYTHING QUANTUM
MECHANICS IS NOT MAGIC . IT IS PHYSICS AND
WE SHOULD TRY TO UNDERSTAND IT LIKE WE SHOULD
TRY TO UNDERSTAND COSMOLOGY AND WHAT HAPPENED
TO BIG BANG AND THE RELATIONSHIP OF PHYSICS
TO CONSCIOUSNESS AND ALL THOSE OTHER THINGS.
THAT IS HER JOB AND WE CAN DO IT AS LONG AS
WE TRY.
THANK YOU [ APPLAUSE ]
THANK YOU .
