{0}{64}Now, on NOVA,
{65}{112}take a thrill ride into
{113}{173}a world stranger than science fiction,
{174}{233}where you play the game,|by breaking some rules,
{234}{293}where a new view of the universe,
{295}{330}pushes you beyond the limits
{331}{365}of your wildest imagination.
{389}{467}This is the world of string theory,
{467}{554}a way of describing|every force and all matter
{555}{640}from an atom to earth, to|the end of the galaxies --
{641}{736}from the birth of time|to its final tick --
{760}{855}in a single theory, a|theory of everything.
{856}{940}Our guide to this brave new world
{940}{1036}is Brian Greene, bestselling|author and physicist.
{1037}{1073}BRIAN GREENE
{1073}{1108}And no matter how|many times I come here,
{1109}{1155}I never seem to get used to it.
{1156}{1204}NARRATOR: Can he help us solve
{1205}{1252}the greatest puzzle|of modern physics --
{1312}{1374}that our understanding of the universe
{1384}{1444}is based on two sets of|laws, that don't agree?
{1492}{1588}Resolving that contradiction|eluded even Einstein,
{1588}{1648}who made it his final quest.
{1660}{1695}After decades,
{1696}{1768}we may finally be on the|verge of a breakthrough.
{1864}{1924}The solution is strings,
{1936}{1983}tiny bits of energy vibrating
{1984}{2031}like the strings on a cello,
{2043}{2091}a cosmic symphony
{2091}{2139}at the heart of all reality.
{2187}{2234}But it comes at a price:
{2235}{2319}parallel universes and 11 dimensions,
{2331}{2355}most of which
{2355}{2378}you've never seen.
{2379}{2427}BRIAN GREENE: We really|may live in a universe
{2428}{2498}with more dimensions than meet the eye.
{2499}{2547}AMANDA PEET People who have said|that there were extra dimensions
{2548}{2582}of space have been
{2583}{2637}labeled crackpots, or|people who are bananas.
{2638}{2691}NARRATOR: A mirage of|science and mathematics
{2692}{2762}or the ultimate theory of everything?
{2763}{2799}S. JAMES GATES, JR.
{2799}{2841}If string theory fails to provide
{2842}{2883}a testable prediction,
{2885}{2918}then nobody should believe it.
{2919}{2955}SHELDON LEE GLASHOW
{2956}{2991}Is that a theory of physics,
{2992}{3026}or a philosophy?
{3027}{3087}BRIAN GREENE: One thing that is certain
{3088}{3135}is that string theory is already|showing us that the universe
{3147}{3194}may be a lot stranger
{3195}{3243}than any of us ever imagined.
{3243}{3291}NARRATOR: Coming up tonight...
{3327}{3374}it all started with an apple.
{3375}{3411}S. JAMES GATES, JR.
{3412}{3447}The triumph of Newton's equations
{3448}{3482}come from the quest
{3483}{3531}to understand the planets and the stars.
{3543}{3591}NARRATOR: And we've|come a long way since.
{3591}{3627}BRIAN GREENE: Einstein gave the world
{3627}{3662}a new picture for what
{3663}{3710}the force of gravity actually is.
{3771}{3830}NARRATOR: Where he left off,|string theorists now dare to go.
{3831}{3903}But how close are they to|fulfilling Einstein's dream?
{3903}{3998}Watch The Elegant Universe right now.
{6504}{6606}THE ELEGANT UNIVERSE
{6607}{6708}Hosted By Brian Green
{6768}{6864}Einstein's Dream
{6888}{6983}A Theory of Everything?
{7211}{7295}BRIAN GREENE: Fifty years ago,|this house was the scene of one of
{7296}{7373}the greatest mysteries|of modern science,
{7374}{7443}a mystery so profound that today
{7443}{7511}thousands of scientists on|the cutting edge of physics
{7511}{7558}are still trying to solve it.
{7559}{7643}Albert Einstein spent|his last two decades
{7644}{7727}in this modest home in|Princeton, New Jersey.
{7763}{7834}And in his second floor study
{7835}{7955}Einstein relentlessly sought|a single theory so powerful
{7956}{8039}it would describe all the|workings of the universe.
{8087}{8159}Even as he neared the end of his life
{8159}{8230}Einstein kept a notepad close at hand,
{8230}{8320}furiously trying to come|up with the equations
{8321}{8410}for what would come to be known|as the "Theory of Everything."
{8434}{8506}Convinced he was on the verge of
{8507}{8591}the most important discovery|in the history of science,
{8592}{8674}Einstein ran out of time,|his dream unfulfilled.
{8758}{8829}Now, almost a half century later,
{8830}{8890}Einstein's goal|of unification --
{8891}{8944}combining all the laws of the universe
{8945}{8997}in one, all-encompassing|theory --
{8998}{9094}has become the Holy|Grail of modern physics.
{9106}{9202}And we think we may at last|achieve Einstein's dream
{9203}{9274}with a new and radical set of ideas
{9274}{9345}called "string theory."
{9346}{9406}But if this revolutionary|theory is right,
{9407}{9454}we're in for quite a shock.
{9490}{9537}String theory says
{9538}{9585}we may be living in a universe
{9586}{9657}where reality meets|science fiction --
{9681}{9777}a universe of eleven dimensions
{9778}{9826}with parallel universes
{9827}{9873}right next|door --
{9921}{10005}an elegant universe composed entirely
{10005}{10065}of the music of strings.
{10147}{10194}But for all its ambition,
{10195}{10267}the basic idea of string theory
{10268}{10327}is surprisingly simple.
{10339}{10398}It says that everything in the universe,
{10399}{10471}from the tiniest particle|to the most distant star
{10471}{10530}is made from one|kind of ingredient --
{10542}{10650}unimaginably small|vibrating strands of energy
{10651}{10722}called strings.
{10806}{10866}Just as the strings of a cello
{10866}{10926}can give rise to a rich
{10927}{10986}variety of musical notes,
{11022}{11118}the tiny strings in string theory|vibrate in a multitude of different ways
{11119}{11214}making up all the|constituents of nature.
{11286}{11358}In other words, the universe is like
{11359}{11405}a grand cosmic symphony
{11406}{11466}resonating with all the various notes
{11467}{11526}these tiny vibrating strands of energy
{11527}{11586}can play.
{11670}{11706}String theory is still
{11706}{11754}in its infancy,
{11755}{11801}but it's already revealing
{11802}{11862}a radically new picture of the universe,
{11862}{11922}one that is both strange and beautiful.
{11981}{12047}But what makes us|think we can understand
{12048}{12113}all the complexity of the universe,
{12113}{12197}let alone reduce it to a|single "Theory of Everything?"
{12198}{12293}We have R mu nu, minus|a half g mu nu R --
{12294}{12340}you remember|how this goes --
{12341}{12425}equals eight Pi G T mu nu...
{12425}{12485}comes from varying the|Einstein-Hilbert action,
{12486}{12544}and we get the field equations
{12545}{12593}and this term. You remember|what this is called?
{12594}{12629}DOG BARKS: Vau, vau!
{12653}{12725}No that's the scalar curvature.
{12726}{12797}This is the ricci tensor.
{12833}{12905}Have you been studying this at all?
{12929}{13001}No matter how hard you try,
{13002}{13067}you can't teach physics to a dog.
{13068}{13133}Their brains just aren't wired
{13133}{13193}to grasp it.
{13217}{13264}But what about us?
{13265}{13319}How do we know that we're wired
{13319}{13370}to comprehend the deepest laws
{13371}{13421}of the universe?
{13433}{13516}Well, physicists today|are confident that we are,
{13517}{13588}and we're picking up
{13588}{13672}where Einstein left off in|his quest for unification.
{13744}{13840}Unification would be|the formulation of a law
{13841}{13900}that describes, perhaps,
{13900}{13959}everything in the known universe from
{13960}{14032}one single idea, one master equation.
{14033}{14104}And we think that there|might be this master equation,
{14105}{14164}because throughout|the course of the last
{14165}{14211}200 years or so,
{14212}{14260}our understanding of the universe
{14261}{14308}has given us a variety of explanations
{14309}{14356}that are all pointing towards one spot.
{14357}{14403}They seem to all be converging
{14404}{14452}on one nugget of an idea
{14452}{14500}that we're still trying to find.
{14512}{14548}STEVEN WEINBERG
{14549}{14608}Unification is where it's at.
{14632}{14667}Unification is what
{14668}{14715}we're trying to accomplish.
{14716}{14788}The whole aim of fundamental physics
{14788}{14860}is to see more and more|of the world's phenomena
{14860}{14932}in terms of fewer and fewer and|simpler and simpler principles.
{14967}{15021}MICHAEL B. GREEN
{15022}{15075}We feel, as physicists,|that if we can explain
{15076}{15148}a wide number of phenomena|in a very simple manner,
{15148}{15207}that that's somehow progress.
{15231}{15315}There is almost an|emotional aspect to the way
{15316}{15399}in which the great theories in physics
{15400}{15459}sort of encompass a wide variety
{15460}{15518}of apparently different|physical phenomena.
{15519}{15590}So this idea that we should be aiming
{15591}{15663}to unify our understanding|is inherent, essentially,
{15664}{15735}to the whole way in which this|kind of science progresses.
{15736}{15842}Newton's Embarrassing Secret
{15843}{15927}BRIAN GREENE: And long before|Einstein, the quest for unification
{15927}{15999}began with the most famous accident
{16000}{16046}in the history of science.
{16047}{16118}As the story goes, one day in 1665,
{16119}{16179}a young man was sitting|under a tree when,
{16180}{16250}all of a sudden, he saw|an apple fall from above.
{16251}{16311}And with the fall of|that apple, Isaac Newton
{16311}{16371}revolutionized our|picture of the universe.
{16395}{16454}In an audacious proposal for his time,
{16455}{16514}Newton proclaimed that the force
{16515}{16574}pulling apples to the ground
{16599}{16670}and the force keeping the moon in orbit
{16670}{16754}around the earth were|actually one and the same.
{16766}{16970}In one fell swoop, Newton|unified the heavens and the earth
{16971}{17066}in a single theory he called gravity.
{17067}{17113}STEVEN WEINBERG:
{17114}{17185}The unification of the|celestial with the terrestrial --
{17186}{17270}that the same laws that govern|the planets in their motions
{17271}{17354}govern the tides and the|falling of fruit here on earth --
{17355}{17425}it was a fantastic
{17426}{17486}unification of our picture of nature.
{17495}{17591}BRIAN GREENE: Gravity was the first|force to be understood scientifically,
{17592}{17651}though three more|would eventually follow.
{17651}{17747}And, although Newton discovered his|law of gravity more than 300 years ago,
{17748}{17831}his equations describing|this force make such
{17832}{17891}accurate predictions that we|still make use of them today.
{17903}{17969}In fact scientists needed nothing more
{17970}{18035}than Newton's equations to|plot the course of a rocket
{18036}{18107}that landed men on the moon.
{18155}{18215}Yet there was a problem.
{18216}{18275}While his laws described
{18275}{18371}the strength of gravity|with great accuracy,
{18372}{18466}Newton was harboring|an embarrassing secret:
{18467}{18575}he had no idea how|gravity actually works.
{18695}{18778}For nearly 250 years,
{18779}{18863}scientists were content|to look the other way
{18864}{18945}when confronted with this mystery.
{18946}{19018}But in the early 1900s,
{19019}{19091}an unknown clerk working|in the Swiss patent office
{19091}{19162}would change all that.
{19174}{19258}While reviewing patent|applications, Albert Einstein
{19258}{19342}was also pondering|the behavior of light.
{19343}{19389}And little did Einstein know
{19390}{19437}that his musings on light
{19438}{19486}would lead him to solve Newton's mystery
{19487}{19534}of what gravity is.
{19570}{19696}At the age of 26, Einstein|made a startling discovery:
{19697}{19822}that the velocity of light is a kind of
{19822}{19942}cosmic speed limit, a speed that|nothing in the universe can exceed.
{19942}{19965}But no sooner
{19966}{20037}had the young Einstein|published this idea
{20038}{20104}than he found himself squaring off
{20104}{20170}with the father of gravity.
{20253}{20325}The trouble was, the idea
{20325}{20397}that nothing can go faster|than the speed of light
{20398}{20468}flew in the face of Newton's
{20469}{20553}picture of gravity.
{20554}{20624}To understand this conflict,
{20625}{20697}we have to run a few experiments.
{20709}{20811}And to begin with, let's|create a cosmic catastrophe.
{20812}{20913}Imagine that all of a sudden,|and without any warning,
{20913}{21009}the sun vaporizes and|completely disappears.
{21033}{21104}Now, let's replay that catastrophe
{21105}{21177}and see what effect it|would have on the planets
{21178}{21201}according to Newton.
{21213}{21273}Newton's theory predicts
{21274}{21368}that with the destruction of the sun,
{21369}{21488}the planets would immediately|fly out of their orbits
{21489}{21548}careening off into space.
{21663}{21728}In other words, Newton|thought that gravity was
{21729}{21764}a force that acts instantaneously
{21764}{21812}across any distance.
{21812}{21872}And so we would immediately feel
{21873}{21919}the effect of the sun's destruction.
{21920}{22016}But Einstein saw a big|problem with Newton's theory,
{22017}{22112}a problem that arose|from his work with light.
{22136}{22232}Einstein knew light doesn't|travel instantaneously.
{22244}{22322}In fact, it takes eight minutes
{22323}{22400}for the sun's rays to|travel the 93 million miles
{22401}{22459}to the earth.
{22460}{22544}And since he had shown that|nothing, not even gravity,
{22544}{22604}can travel faster than light,
{22652}{22736}how could the earth|be released from orbit
{22737}{22807}before the darkness resulting|from the sun's disappearance
{22808}{22880}reached our eyes?
{23047}{23131}To the young upstart from|the Swiss patent office
{23132}{23215}anything outrunning|light was impossible,
{23227}{23299}and that meant the|250-year old Newtonian
{23300}{23359}picture of gravity was wrong.
{23360}{23406}S. JAMES GATES, JR.:
{23407}{23467}If Newton is wrong,
{23467}{23526}then why do the planets stay up?
{23527}{23599}Because remember, the|triumph of Newton's equations
{23600}{23670}come from the quest to understand
{23671}{23755}the planets and the stars,
{23756}{23827}and particularly the problem of why the|planets have the orbits that they do.
{23851}{23911}And with Newton's equations|you could calculate the way
{23912}{23971}that the planets would move.
{23983}{24043}Einstein's got to resolve this dilemma.
{24079}{24163}BRIAN GREENE: In his late twenties,|Einstein had to come up with
{24163}{24246}a new picture of the universe
{24247}{24306}in which gravity does not|exceed the cosmic speed limit.
{24307}{24402}Still working his day job in|the patent office, Einstein
{24403}{24498}embarked on a solitary|quest to solve this mystery.
{24558}{24641}After nearly ten years|of wracking his brain
{24642}{24714}he found the answer in a|new kind of unification.
{24765}{24810}A New Picture of Gravity
{24811}{24845}PETER GALISON
{24846}{24918}Einstein came to think of|the three dimensions of space
{24919}{24978}and the single dimension of time
{24990}{25074}as bound together in a|single fabric of "space-time."
{25218}{25265}It was his hope
{25266}{25338}that by understanding|the geometry of this
{25339}{25398}four-dimensional|fabric of space-time,
{25399}{25445}that he could simply talk about
{25446}{25518}things moving along surfaces
{25518}{25590}in this space-time fabric.
{25614}{25673}BRIAN GREENE: Like the|surface of a trampoline,
{25674}{25734}this unified fabric|is warped and stretched
{25735}{25801}by heavy objects like planets and stars.
{25865}{25949}And it's this warping|or curving of space-time
{25949}{26033}that creates what we feel as gravity.
{26057}{26128}A planet like the|earth is kept in orbit,
{26129}{26201}not because the sun reaches|out and instantaneously
{26202}{26248}grabs hold of it, as in Newton's theory,
{26249}{26320}but simply because it follows curves
{26321}{26393}in the spatial fabric|caused by the sun's presence.
{26394}{26453}So, with this new|understanding of gravity,
{26454}{26510}let's rerun the cosmic catastrophe.
{26510}{26570}Let's see what happens|now if the sun disappears.
{26630}{26702}The gravitational|disturbance that results
{26703}{26810}will form a wave that travels|across the spatial fabric
{26811}{26871}in much the same way that a pebble
{26872}{26931}dropped into a pond makes ripples
{26932}{26991}that travel across the|surface of the water.
{26992}{27050}So we wouldn't feel a change
{27051}{27105}in our orbit around the sun
{27105}{27158}until this wave reached the earth.
{27211}{27314}What's more, Einstein calculated|that these ripples of gravity
{27315}{27410}travel at exactly the speed of light.
{27458}{27513}And so, with this new approach,
{27513}{27573}Einstein resolved the|conflict with Newton
{27574}{27637}over how fast gravity travels.
{27638}{27722}And more than that, Einstein|gave the world a new picture
{27723}{27786}for what the force of|gravity actually is:
{27786}{27902}it's warps and curves in|the fabric of space and time.
{27942}{28045}Einstein called this new picture|of gravity "General Relativity,"
{28057}{28117}and within a few short|years Albert Einstein
{28118}{28172}became a household name.
{28173}{28223}S. JAMES GATES, JR.: Einstein was like
{28224}{28273}a rock star in his day.
{28273}{28325}He was one of the most widely known
{28326}{28376}and recognizable figures alive.
{28377}{28439}He and perhaps Charlie Chaplin were
{28440}{28501}the reigning kings of the popular media.
{28506}{28560}MARCIA BARTUSIAK People|followed his work.
{28561}{28657}And they were anticipating...because|of this wonderful thing
{28658}{28704}he had done with general relativity,
{28705}{28830}this recasting the laws of|gravity out of his head...
{28831}{28890}there was a thought|he could do it again,
{28890}{28957}and they, you know, people|want to be in on that.
{28967}{29046}BRIAN GREENE: Despite|all that he had achieved
{29047}{29088}Einstein wasn't satisfied.
{29089}{29167}He immediately set his sights|on an even grander goal,
{29168}{29236}the unification of his|new picture of gravity
{29237}{29305}with the only other|force known at the time,
{29305}{29347}electromagnetism.
{29348}{29410}Now electromagnetism is a force
{29411}{29472}that had itself been unified
{29473}{29521}only a few decades earlier.
{29522}{29568}In the mid-1800s,
{29569}{29653}electricity and magnetism
{29653}{29736}were sparking scientists' interest.
{29748}{29832}These two forces seemed to|share a curious relationship
{29833}{29917}that inventors like|Samuel Morse were taking
{29918}{30000}advantage of in newfangled|devices, such as the telegraph.
{30072}{30144}An electrical pulse sent|through a telegraph wire
{30145}{30204}to a magnet thousands of miles away
{30216}{30300}produced the familiar dots|and dashes of Morse code
{30301}{30384}that allowed messages to be|transmitted across the continent
{30385}{30444}in a fraction of a second.
{30468}{30534}Although the telegraph was a sensation,
{30535}{30600}the fundamental science driving it
{30601}{30648}remained something of a mystery.
{30756}{30888}But to a Scottish scientist|named James Clark Maxwell,
{30888}{30983}the relationship between|electricity and magnetism
{30995}{31139}was so obvious in nature|that it demanded unification.
{31187}{31247}If you've ever been on top of a mountain
{31248}{31318}during a thunderstorm you'll get
{31319}{31427}the idea of how electricity and|magnetism are closely related.
{31439}{31535}When a stream of electrically|charged particles flows,
{31535}{31613}like in a bolt of lightning,|it creates a magnetic field.
{31614}{31691}And you can see evidence|of this on a compass.
{31859}{31918}Obsessed with this relationship,
{31919}{31991}the Scot was determined to explain
{31992}{32063}the connection between|electricity and magnetism
{32063}{32123}in the language of mathematics.
{32147}{32200}Casting new light on the subject,
{32201}{32254}Maxwell devised a set
{32254}{32314}of four elegant mathematical equations
{32434}{32518}that unified electricity and magnetism
{32530}{32638}in a single force called|"electromagnetism."
{32674}{32745}And like Isaac Newton's before him,
{32746}{32830}Maxwell's unification|took science a step closer
{32831}{32901}to cracking the code of the universe.
{32902}{32950}JOSEPH POLCHINSKI
{32951}{32998}That was really the remarkable thing,
{32999}{33045}that these different phenomena
{33046}{33100}were really connected in this way.
{33101}{33153}And it's another example|of diverse phenomena
{33154}{33250}coming from a single underlying building|block or a single underlying principle.
{33250}{33298}WALTER H.G. LEWIN
{33299}{33381}Imagine that everything|that you can think of
{33382}{33466}which has to do with|electricity and magnetism
{33467}{33586}can all be written in|four very simple equations.
{33617}{33701}Isn't that incredible?|Isn't that amazing?
{33701}{33748}I call that elegant.
{33749}{33815}PETER GALISON: Einstein|thought that this was
{33815}{33884}one of the triumphant|moments of all of physics
{33885}{33952}and admired Maxwell hugely|for what he had done.
{33993}{34053}BRIAN GREENE: About 50|years after Maxwell unified
{34053}{34100}electricity and magnetism,
{34101}{34172}Einstein was confident
{34173}{34257}that if he could unify his new theory of|gravity with Maxwell's electromagnetism,
{34258}{34328}he'd be able to formulate|a master equation
{34329}{34425}that could describe|everything, the entire universe.
{34426}{34472}S. JAMES GATES, JR.:
{34473}{34563}Einstein clearly|believes that the universe
{34564}{34677}has an overall grand and beautiful|pattern to the way that it works.
{34686}{34734}So to answer your question,
{34735}{34782}why was he looking for the unification?
{34782}{34842}I think the answer is simply
{34843}{34913}that Einstein is one of those physicists
{34914}{35034}who really wants to know the mind of|God, which means the entire picture.
{35070}{35118}A Strange New World
{35142}{35250}BRIAN GREENE: Today, this|is the goal of string theory:
{35251}{35334}to unify our understanding of everything
{35346}{35406}from the birth of the universe
{35407}{35466}to the majestic swirl of galaxies
{35478}{35538}in just one set of principles,
{35574}{35646}one master equation.
{35670}{35742}Newton had unified the|heavens and the earth
{35766}{35825}in a theory of gravity.
{35826}{35934}Maxwell had unified|electricity and magnetism.
{35970}{36029}Einstein reasoned all that
{36041}{36101}remained to build a|"Theory of Everything"--
{36101}{36185}a single theory that could encompass|all the laws of the universe --
{36186}{36257}was to merge his new picture of gravity
{36258}{36316}with electromagnetism.
{36317}{36371}AMANDA PEET: He|certainly had motivation.
{36372}{36425}Probably one of them|might have been aesthetics,
{36425}{36472}or this quest to simplify.
{36473}{36533}Another one might have|been just the physical fact
{36534}{36582}that it seems like the speed of gravity
{36582}{36629}is equal to the speed of light.
{36646}{36700}So if they both go at the same speed,
{36701}{36773}then maybe that's an indication|of some underlying symmetry.
{36797}{36869}BRIAN GREENE: But as|Einstein began trying to unite
{36870}{36929}gravity and electromagnetism
{36941}{37013}he would find that the difference|in strength between these two forces
{37014}{37073}would outweigh their similarities.
{37097}{37157}Let me show you what I mean.
{37181}{37253}We tend to think that|gravity is a powerful force.
{37277}{37337}After all, it's the|force that, right now,
{37337}{37397}is anchoring me to this ledge.
{37468}{37522}But compared to electromagnetism,
{37523}{37576}it's actually terribly feeble.
{37576}{37636}In fact, there's a simple|little test to show this.
{37641}{37720}Imagine that I was to leap|from this rather tall building.
{37732}{37792}Actually, let's not just imagine it.
{37799}{37833}Let's do it.
{37833}{37876}You'll see what I mean.
{38305}{38389}Now, of course, I really|should have been flattened.
{38390}{38427}But the important question is:
{38428}{38487}what kept me from crashing|through the sidewalk
{38488}{38548}and hurtling right down|to the center of the earth?
{38608}{38667}Well, strange as it sounds,
{38668}{38727}the answer is electromagnetism.
{38751}{38823}Everything we can see, from you and me
{38823}{38907}to the sidewalk, is made|of tiny bits of matter
{38908}{38955}called atoms.
{38955}{39015}And the outer shell of every atom
{39016}{39075}contains a negative electrical charge.
{39099}{39159}So when my atoms collide
{39160}{39206}with the atoms in the cement
{39207}{39267}these electrical|charges repel each other
{39279}{39350}with such strength that just|a little piece of sidewalk
{39351}{39447}can resist the entire Earth's|gravity and stop me from falling.
{39459}{39531}In fact the electromagnetic force
{39538}{39615}is billions and billions|of times stronger
{39616}{39651}than gravity.
{39651}{39686}NIMA ARKANI-HAMED
{39687}{39728}That seems a little strange, because|gravity keeps our feet to the ground,
{39729}{39765}it keeps the earth going around the sun.
{39766}{39807}But, in actual fact,
{39808}{39866}it manages to do that only because
{39867}{39939}it acts on huge enormous|conglomerates of matter,
{39940}{39998}you know -- you, me,|the earth, the sun --
{39999}{40071}but really at the level|of individual atoms,
{40071}{40143}gravity is a really|incredibly feeble tiny force.
{40250}{40327}BRIAN GREENE: It would be an|uphill battle for Einstein to unify
{40327}{40404}these two forces of|wildly different strengths.
{40442}{40512}And to make matters|worse, barely had he begun
{40513}{40562}before sweeping changes
{40562}{40634}in the world of physics|would leave him behind.
{40658}{40730}STEVEN WEINBERG: Einstein|had achieved so much
{40742}{40802}in the years up to about 1920,
{40809}{40886}that he naturally expected|that he could go on
{40910}{40970}by playing the same theoretical games
{40971}{41030}and go on achieving great things.
{41037}{41078}And he couldn't.
{41121}{41203}Nature revealed itself in other ways
{41204}{41269}in the 1920s and 1930s,
{41270}{41390}and the particular tricks and tools|that Einstein had at his disposal
{41391}{41462}had been so fabulously successful,
{41474}{41546}just weren't applicable anymore.
{41582}{41630}The Quantum Cafe
{41653}{41749}BRIAN GREENE: You see, in the|1920s a group of young scientists
{41750}{41809}stole the spotlight from Einstein
{41810}{41878}when they came up with an outlandish
{41879}{41939}new way of thinking about physics.
{41968}{42047}Their vision of the|universe was so strange,
{42064}{42131}it makes science fiction look tame,
{42132}{42178}and it turned Einstein's quest
{42179}{42239}for unification on its head.
{42240}{42287}Unification! Unification!
{42347}{42431}Led by Danish physicist Niels Bohr,
{42431}{42514}these scientists were|uncovering an entirely
{42515}{42569}new realm of the universe.
{42570}{42622}Atoms,
{42623}{42684}long thought to be the|smallest constituents
{42685}{42730}of nature, were found to
{42731}{42795}consist of even smaller particles:
{42796}{42846}the now-familiar nucleus
{42865}{42937}of protons and neutrons|orbited by electrons.
{42946}{43017}And the theories of Einstein and Maxwell
{43018}{43078}were useless at explaining
{43079}{43139}the bizarre way these|tiny bits of matter
{43139}{43198}interact with each|other inside the atom.
{43222}{43288}PETER GALISON: There|was a tremendous mystery
{43289}{43354}about how to account for all this,
{43355}{43425}how to account for what|was happening to the nucleus
{43426}{43486}as the atom began to be pried
{43487}{43534}apart in different ways.
{43546}{43647}And the old theories were totally|inadequate to the task of explaining them.
{43647}{43725}Gravity was irrelevant.|It was far too weak.
{43726}{43798}And electricity and|magnetism was not sufficient.
{43898}{43977}BRIAN GREENE: Without a theory|to explain this strange new world,
{43978}{44061}these scientists were lost
{44062}{44134}in an unfamiliar atomic territory
{44158}{44241}looking for any recognizable landmarks.
{44654}{44745}Then, in the late|1920s, all that changed.
{44746}{44811}During those years, physicists developed
{44812}{44876}a new theory called "quantum mechanics,"
{44877}{44949}and it was able to|describe the microscopic
{44950}{44997}realm with great success.
{45002}{45049}But here's the thing:
{45049}{45109}quantum mechanics was|so radical a theory
{45110}{45181}that it completely|shattered all previous ways
{45182}{45242}of looking at the universe.
{45242}{45301}Einstein's theories demand
{45301}{45369}that the universe is|orderly and predictable,
{45421}{45481}but Niels Bohr disagreed.
{45482}{45540}He and his colleagues proclaimed
{45541}{45601}that at the scale of|atoms and particles,
{45602}{45661}the world is a game of chance.
{45685}{45781}At the atomic or quantum|level, uncertainty rules.
{45824}{45872}The best you can do,
{45873}{45920}according to quantum mechanics,
{45920}{45967}is predict the chance or probability
{45968}{46028}of one outcome or another.
{46088}{46183}And this strange idea
{46184}{46280}opened the door to an unsettling|new picture of reality.
{46424}{46507}It was so unsettling
{46508}{46580}that if the bizarre|features of quantum mechanics
{46580}{46634}were noticeable in our everyday world,
{46635}{46691}like they are here in the Quantum Café,
{46692}{46747}you might think you'd lost your mind.
{46747}{46807}WALTER H.G. LEWIN: The|laws in the quantum world
{46808}{46862}are very different from the laws
{46862}{46915}that we are used to.
{46916}{46975}Our daily experiences|are totally different
{46976}{47035}from anything that you would|see in the quantum world.
{47036}{47075}The quantum world is crazy.
{47076}{47124}It's probably the best way to put it:
{47125}{47155}it's a crazy world.
{47167}{47202}BRIAN GREENE: For nearly 80 years,
{47203}{47263}quantum mechanics has|successfully claimed
{47264}{47311}that the strange and bizarre are typical
{47311}{47383}of how our universe actually behaves
{47384}{47443}on extremely small scales.
{47455}{47503}At the scale of everyday life,
{47504}{47550}we don't directly experiencethe
{47551}{47611}weirdness of quantum mechanics.
{47623}{47682}But here in the Quantum Café,
{47683}{47743}big, everyday things sometimes
{47744}{47803}behave as if they were|microscopically tiny.
{47804}{47863}And no matter how|many times I come here,
{47864}{47923}I never seem to get used to it.
{47947}{47983}I'll have an orange juice, please.
{47984}{48037}BARTENDER: I'll try.
{48038}{48091}BRIAN GREENE: "I'll try," she says.
{48163}{48223}You see, they're not|used to people placing
{48224}{48283}definite orders here|in the Quantum Café,
{48283}{48342}because here everything|is ruled by chance.
{48343}{48403}While I'd like an orange juice,
{48403}{48426}there is only a particular probability
{48427}{48486}that I'll actually get one.
{48582}{48654}And there's no reason to be disappointed
{48654}{48714}with one particular outcome or another,
{48714}{48762}because quantum mechanics suggests
{48763}{48810}that each of the possibilities
{48810}{48870}like getting a yellow|juice or a red juice
{48871}{48905}may actually happen.
{48906}{48953}They just happen to happen
{48954}{49013}in universes that are parallel to ours,
{49014}{49074}universes that seemas|real to their inhabitants
{49075}{49134}as our universe seems to us.
{49158}{49218}WALTER H.G. LEWIN: If there|are a thousand possibilities,
{49218}{49265}and quantum mechanics|cannot, with certainty,
{49266}{49314}say which of the thousand it will be,
{49315}{49372}then all thousand will happen.
{49384}{49438}Yeah, you can laugh at it and say,
{49439}{49487}"Well, that has to be wrong."
{49492}{49551}But there are so many|other things in physics
{49552}{49599}which -- at the time that|people came up with --
{49599}{49659}had to be wrong, but it wasn't.
{49671}{49718}Have to be a little careful, I think,
{49719}{49779}before you say this is clearly wrong.
{49847}{49894}BRIAN GREENE: And even|in our own universe,
{49895}{49954}quantum mechanics says there's a chance
{49971}{50055}that things we'd ordinarily|think of as impossible
{50056}{50115}can actually happen.
{50139}{50198}For example there's a chance
{50199}{50283}that particles can pass right|through walls or barriers
{50307}{50367}that seem impenetrable to you or me.
{50386}{50426}There's even a chance
{50427}{50487}that I could pass through|something solid, like a wall.
{50488}{50547}Now, quantum calculations do show
{50547}{50619}that the probability for this|to happen in the everyday world
{50620}{50679}is so small that I'd need
{50680}{50739}to continue walking into the wall
{50740}{50799}for nearly an eternity before having|a reasonable chance of succeeding.
{50871}{50955}But here, these kinds of|things happen all the time.
{50978}{51014}EDWARD FARHI
{51015}{51062}You have to learn to|abandon those assumptions
{51062}{51122}that you have about the world
{51123}{51170}in order to understand|quantum mechanics.
{51171}{51230}In my gut, in my belly,
{51230}{51278}do I feel like I have a deep intuitive
{51279}{51326}understanding of quantum mechanics?
{51338}{51386}No.
{51403}{51458}BRIAN GREENE: And neither did Einstein.
{51482}{51542}He never lost faith that the universe
{51543}{51590}behaves in a certain
{51591}{51638}and predictable way.
{51662}{51733}The idea that all we can|do is calculate the odds
{51734}{51794}that things will turn|out one way or another
{51818}{51890}was something Einstein deeply resisted.
{51902}{51950}MICHAEL DUFF
{51951}{51997}Quantum mechanics says that you
{51998}{52046}can't know for certain
{52047}{52094}the outcome of any experiment;
{52095}{52129}you can only assign|a certain probability
{52130}{52165}to the outcome of any experiment.
{52166}{52226}And this, Einstein disliked intensely.
{52227}{52298}He used to say "God|does not throw dice."
{52334}{52429}BRIAN GREENE: Yet,|experiment after experiment
{52430}{52501}showed Einstein was wrong
{52502}{52573}and that quantum mechanics|really does describe
{52574}{52646}how the world works|at the subatomic level.
{52658}{52693}WALTER H.G. LEWIN:
{52693}{52753}So quantum mechanics is|not a luxury, something
{52754}{52801}that you can do without.
{52801}{52849}I mean why is water the way it is?
{52849}{52909}Why does light go straight through|water? Why is it transparent?
{52910}{52957}Why are other things not transparent?
{52958}{53004}How do molecules form?
{53005}{53065}Why are they reacting|the way they react?
{53066}{53125}The moment that you want to understand
{53125}{53185}anything at an atomic level,
{53197}{53256}as non-intuitive as it is,
{53257}{53365}at that moment, you can only make|progress with quantum mechanics.
{53366}{53401}EDWARD FARHI: Quantum mechanics
{53402}{53437}is fantastically accurate.
{53438}{53484}There has never been
{53485}{53539}a prediction of quantum mechanics
{53540}{53593}that has contradicted an observation,
{53605}{53653}never.
{53665}{53713}Gravity|- The Odd Man Out
{53725}{53785}BRIAN GREENE: By the|1930s, Einstein's quest
{53786}{53845}for unification was floundering,
{53869}{53916}while quantum mechanics
{53917}{53965}was unlocking the secrets of the atom.
{54001}{54049}Scientists found that gravity
{54049}{54084}and electromagnetism
{54085}{54169}are not the only forces|ruling the universe.
{54192}{54252}Probing the structure of the atom,
{54253}{54312}they discovered two more forces.
{54360}{54444}One, dubbed the "strong nuclear force,"
{54445}{54491}acts like a super-glue,
{54492}{54552}holding the nucleus|of every atom together,
{54553}{54624}binding protons to neutrons.
{54665}{54737}And the other, called|the "weak nuclear force,"
{54737}{54809}allows neutrons to turn into protons,
{54810}{54881}giving off radiation in the process.
{54912}{54935}At the quantum level,
{54936}{54996}the force we're most familiar with,
{54997}{55067}gravity, was completely overshadowed
{55068}{55152}by electromagnetism and|these two new forces.
{55205}{55236}Now, the strong and weak forces
{55237}{55272}may seem obscure,
{55279}{55323}but in one sense at least,
{55324}{55368}we're all very much|aware of their power.
{55380}{55488}At 5:29 on the morning|of July 16th, 1945,
{55489}{55547}that power was revealed by an act
{55548}{55596}that would change the course of history.
{55620}{55667}In the middle of the|desert, in New Mexico,
{55684}{55727}at the top of a steel tower about
{55727}{55823}a hundred feet above|the top of this monument,
{55824}{55883}the first atomic bomb was detonated.
{55902}{55962}It was only about five feet across,
{55962}{56022}but that bomb packed a punch
{56030}{56118}equivalent to about twenty|thousand tons of TNT.
{56284}{56358}With that powerful explosion, scientists
{56359}{56433}unleashed the strong nuclear force,
{56445}{56516}the force that keeps|neutrons and protons
{56517}{56588}tightly glued together|inside the nucleus of an atom.
{56605}{56660}By breaking the bonds of that glue
{56661}{56720}and splitting the atom apart,
{56756}{56816}vast, truly unbelievable amounts
{56817}{56876}of destructive energy were released.
{57013}{57056}We can still detect remnants of
{57057}{57099}that explosion through
{57099}{57135}the other nuclear force,
{57136}{57175}the weak nuclear force,
{57176}{57236}because it's responsible|for radioactivity.
{57237}{57307}And today, more than 50 years later,
{57308}{57380}the radiation levels|around here are still
{57381}{57440}about 10 times higher than normal.
{57464}{57480}So,
{57481}{57564}although in comparison to|electromagnetism and gravity
{57565}{57649}the nuclear forces act|over very small scales,
{57650}{57732}their impact on everyday|life is every bit as profound.
{57824}{57883}But what about gravity?
{57884}{57950}Einstein's general relativity?
{57950}{58015}Where does that fit in|at the quantum level?
{58075}{58123}Quantum mechanics tells us
{58123}{58195}how all of nature's forces|work in the microscopic realm
{58196}{58243}except for the force of gravity.
{58255}{58303}Absolutely no one could
{58304}{58350}figure out how gravity operates
{58351}{58399}when you get down to the size of atoms
{58400}{58447}and subatomic particles.
{58447}{58506}That is, no one could figure out
{58507}{58639}how to put general relativity and quantum|mechanics together into one package.
{58735}{58782}For decades,
{58783}{58843}every attempt to describe|the force of gravity
{58844}{58903}in the same language|as the other forces --
{58904}{58951}the language of|quantum mechanics --
{58963}{59010}has met with disaster.
{59011}{59059}S. JAMES GATES, JR.: You|try to put those two pieces
{59059}{59107}of mathematics together,
{59107}{59155}they do not coexist peacefully.
{59162}{59203}STEVEN WEINBERG: You get answers
{59204}{59239}that the probabilities of the event
{59240}{59275}you're looking at are infinite.
{59276}{59323}Nonsense, it's not profound,
{59323}{59358}it's just nonsense.
{59359}{59407}NIMA ARKANI-HAMED: It's very ironic|because it was the first force
{59407}{59455}to actually be understood in some decent
{59456}{59502}quantitative way, but, but,
{59502}{59574}but it still remains split
{59575}{59634}off and very different|from, from the other ones.
{59635}{59671}S. JAMES GATES, JR.: The laws of nature
{59671}{59707}are supposed to apply everywhere.
{59708}{59743}So if Einstein's laws
{59744}{59778}are supposed
{59778}{59814}to apply everywhere,
{59815}{59850}and the laws of quantum mechanics
{59850}{59885}are supposed to apply everywhere,
{59886}{59958}well you can't have two|separate everywheres.
{59982}{60066}Strings to the Rescue
{60090}{60186}BRIAN GREENE: In 1933,|after fleeing Nazi Germany,
{60198}{60258}Einstein settled in|Princeton, New Jersey.
{60270}{60353}Working in solitude,|he stubbornly continued
{60354}{60450}the quest he had begun|more than a decade earlier,
{60451}{60510}to unite gravity and electromagnetism.
{60558}{60593}Every few years,
{60594}{60641}headlines appeared,
{60642}{60690}proclaiming Einstein was|on the verge of success.
{60702}{60737}But most of his colleagues
{60738}{60804}believed his quest was misguided
{60804}{60867}and that his best days|were already behind him.
{60868}{60929}STEVEN WEINBERG: Einstein,|in his later years,
{60930}{61014}got rather detached|from the work of physics
{61014}{61086}in general and, and stopped|reading people's papers.
{61086}{61134}I didn't even think he knew
{61135}{61182}there was such a thing|as the weak nuclear force.
{61183}{61229}He didn't pay attention to those things.
{61229}{61283}He kept working on the same problem
{61284}{61337}that he had started|working on as a younger man.
{61373}{61445}S JAMES GATES, JR.: When the|community of theoretical physicists
{61446}{61505}begins to probe the atom,
{61505}{61582}Einstein very definitely|gets left out of the picture.
{61601}{61691}He, in some sense, chooses not
{61692}{61780}to look at the physics|coming from these experiments.
{61781}{61865}That means that the|laws of quantum mechanics
{61877}{61973}play no role in his sort|of further investigations.
{61985}{62045}He's thought to be this doddering,
{62057}{62104}sympathetic old figure
{62105}{62189}who led an earlier revolution|but somehow fell out of it.
{62227}{62261}STEVEN WEINBERG: It is as if a general
{62273}{62345}who was a master of horse cavalry,
{62357}{62416}who has achieved great things
{62417}{62477}as a commander at the beginning|of the First World War,
{62489}{62561}would try to bring mounted cavalry
{62573}{62632}into play against the barbwire
{62633}{62692}trenches and machines|guns of the other side.
{62788}{62891}BRIAN GREENE: Albert Einstein|died on April 18, 1955.
{62908}{62986}And for many years it|seemed that Einstein's dream
{62987}{63064}of unifying the forces|in a single theory
{63065}{63124}died with him.
{63125}{63172}S. JAMES GATES, JR.:
{63172}{63220}So the quest for unification
{63221}{63268}becomes a backwater of physics.
{63290}{63338}By the time of Einstein's death
{63338}{63386}in the '50s,
{63398}{63493}almost no serious physicists
{63517}{63589}are engaged in this|quest for unification.
{63738}{63773}RIGHT SIDE BRIAN GREENE:|In the years since,
{63774}{63841}physics split into two separate camps:
{63842}{63900}one that uses general relativity
{63901}{63948}to study big and heavy objects,
{63949}{64033}things like stars, galaxies|and the universe as a whole...
{64045}{64111}LEFT SIDE BRIAN GREENE: ...and|another that uses quantum mechanics
{64112}{64177}to study the tiniest of objects,
{64178}{64225}like atoms and particles.
{64237}{64297}This has been kind of|like having two families
{64298}{64337}that just cannot get along
{64338}{64376}and never talk to each other...
{64388}{64448}RIGHT SIDE BRIAN GREENE:|...living under the same roof.
{64453}{64525}LEFT SIDE BRIAN GREENE: There|just seemed to be no way to combine
{64526}{64560}quantum mechanics...
{64561}{64633}RIGHT SIDE BRIAN GREENE: ...and|general relativity in a single theory
{64633}{64705}that could describe the|universe on all scales.
{64844}{64872}BRIAN GREENE: Now, in spite of this,
{64873}{64932}we've made tremendous progress
{64933}{64957}in understanding the universe.
{64992}{65052}But there's a catch:
{65064}{65136}there are strange realms of the cosmos
{65137}{65195}that will never be fully understood
{65196}{65268}until we find a unified theory.
{65292}{65364}And nowhere is this more evident
{65365}{65400}than in the
{65400}{65472}depths of a black hole.
{65496}{65531}A German astronomer named
{65532}{65574}Karl Schwarzschild
{65575}{65615}first proposed
{65616}{65664}what we now call black holes
{65665}{65700}in 1916.
{65760}{65820}While stationed on the front lines
{65821}{65880}in WWI,
{65916}{65963}he solved the equations
{65964}{66024}of Einstein's general relativity
{66024}{66084}in a new and puzzling way.
{66108}{66180}Between calculations of|artillery trajectories,
{66216}{66263}Schwarzschild figured out
{66264}{66324}that an enormous amount of mass,
{66324}{66378}like that of a very dense star,
{66379}{66431}concentrated in a small area,
{66432}{66503}would warp the fabric of space-time
{66504}{66551}so severely
{66575}{66646}that nothing, not even light,
{66647}{66719}could escape its gravitational pull.
{66767}{66803}For decades,
{66803}{66851}physicists were skeptical
{66852}{66899}that Schwarzschild's calculations
{66900}{66947}were anything more than theory.
{66995}{67030}But today
{67031}{67085}satellite telescopes probing deep
{67086}{67136}into space
{67137}{67186}are discovering regions
{67187}{67247}with enormous gravitational pull
{67248}{67295}that most scientists believe
{67295}{67355}are black holes.
{67367}{67414}Schwarzschild's theory
{67415}{67475}now seems to be reality.
{67487}{67546}So here's the question:
{67547}{67613}if you're trying to figure out
{67614}{67676}what happens in the|depths of a black hole,
{67677}{67739}where an entire star is crushed
{67740}{67786}to a tiny speck,
{67787}{67839}do you use general relativity
{67839}{67907}because the star is incredibly heavy
{67912}{67966}or quantum mechanics
{67967}{68027}because it's incredibly tiny?
{68027}{68086}Well, that's the problem.
{68087}{68147}Since the center of a black hole
{68147}{68206}is both tiny and heavy,
{68207}{68261}you can't avoid using
{68262}{68314}both theories at the same time.
{68314}{68374}And when we try to put|the two theories together
{68375}{68429}in the realm of black holes,
{68429}{68482}they conflict. It breaks down.
{68482}{68554}They give nonsensical predictions.|And the universe is not nonsensical;
{68555}{68589}it's got to make sense.
{68590}{68614}EDWARD WITTEN
{68615}{68649}Quantum mechanics works really well
{68650}{68698}for small things, and general relativity
{68699}{68746}works really well for|stars and galaxies,
{68747}{68793}but the atoms, the small things,
{68794}{68842}and the galaxies, they're part of the
{68843}{68884}same universe.
{68885}{68926}So there has to be some description
{68926}{68974}that applies to everything.
{68975}{69016}So we can't have one|description for atoms
{69017}{69062}and one for stars.
{69063}{69106}BRIAN GREENE: Now, with string theory,
{69107}{69153}we think we may have found
{69154}{69214}a way to unite our theory of the large
{69215}{69274}and our theory of the small
{69275}{69321}and make sense of the universe
{69322}{69382}at all scales and all places.
{69418}{69490}Instead of a multitude|of tiny particles,
{69511}{69559}string theory proclaims
{69560}{69607}that everything in the universe,
{69607}{69666}all forces and all matter
{69667}{69727}is made of one single ingredient,
{69739}{69811}tiny vibrating strands of energy
{69812}{69858}known as strings.
{69859}{69894}MICHAEL B. GREEN: A string
{69895}{69943}can wiggle in many different ways,
{69944}{69991}whereas, of course, a point can't.
{69992}{70039}And the different ways in|which the string wiggles
{70039}{70087}represent the different kinds
{70088}{70123}of elementary particles.
{70128}{70183}MICHAEL DUFF: It's like a violin string,
{70184}{70231}and it can vibrate just like violin
{70232}{70279}strings can vibrate.
{70280}{70326}Each note if, you like,
{70327}{70370}describes a different particle.
{70371}{70403}MICHAEL B. GREEN: So it has incredible
{70404}{70437}unification power,
{70438}{70471}it unifies our understanding
{70471}{70506}of all these different kinds
{70507}{70543}of particles.
{70544}{70578}EDWARD WITTEN: So unity
{70579}{70615}of the different forces and particles
{70616}{70651}is achieved because they all
{70652}{70687}come from different kinds of vibrations
{70688}{70735}of the same basic string.
{70736}{70782}BRIAN GREENE: It's a simple idea
{70783}{70825}with far-reaching consequences.
{70825}{70867}JOSEPH LYKKEN
{70867}{70915}What string theory does is it
{70916}{70951}holds out the promise that,
{70952}{70987}"Look, we can really
{70988}{71034}understand questions that
{71035}{71095}you might not even have thought|were scientific questions:
{71119}{71167}questions about how the universe began,
{71167}{71226}why the universe is the way it is
{71227}{71274}at the most fundamental level."
{71286}{71334}The idea that a scientific theory
{71335}{71382}that we already have in our hands
{71383}{71443}could answer the most basic questions
{71443}{71479}is extremely seductive.
{71480}{71521}Science of Philosophy?
{71522}{71562}BRIAN GREENE: But this|seductive new theory
{71586}{71634}is also controversial.
{71658}{71705}Strings, if they exist,
{71706}{71772}are so small,
{71773}{71837}there's little hope of ever seeing one.
{71838}{71886}JOSEPH LYKKEN: String theory
{71887}{71934}and string theorists|do have a real problem.
{71934}{71981}How do you actually test string theory?
{71982}{72029}If you can't test it in the way
{72030}{72078}that we test normal theories,
{72079}{72114}it's not science, it's philosophy,
{72115}{72149}and that's a real problem.
{72150}{72186}S. JAMES GATES, JR.:|If string theory fails
{72187}{72228}to provide
{72229}{72274}a testable prediction,
{72274}{72318}then nobody should believe it.
{72354}{72389}On the other hand,
{72390}{72462}there is a kind of|elegance to these things,
{72474}{72528}and given the history of how theoretical
{72529}{72582}physics has evolved thus far,
{72606}{72666}it is totally conceivable
{72666}{72725}that some if not all
{72725}{72785}of these ideas will|turn out to be correct.
{72786}{72821}STEVEN WEINBERG:
{72821}{72857}I think, a hundred years from now,
{72858}{72893}this particular period,
{72894}{72953}when most of the brightest|young theoretical physicists
{72954}{73001}worked on string theory,
{73013}{73073}will be remembered as a heroic age
{73085}{73157}when theorists tried and succeeded
{73158}{73204}to develop a unified
{73205}{73264}theory of all the phenomena of nature.
{73265}{73349}On the other hand, it may be|remembered as a tragic failure.
{73350}{73396}My guess is
{73397}{73445}that it will be something like|the former rather than the latter.
{73469}{73517}But ask me a hundred years from now,
{73517}{73553}then I can tell you.
{73738}{73792}BRIAN GREENE: Our|understanding of the universe
{73793}{73841}has come an enormously long way
{73841}{73889}during the last three centuries.
{73954}{73997}Just consider this.
{74025}{74061}Isaac Newton,
{74061}{74109}who was perhaps the greatest scientist
{74110}{74156}of all time, once said,
{74157}{74229}"I have been like a boy playing on the
{74230}{74301}sea shore, diverting myself in now
{74301}{74381}and then finding a smoother pebble|or a prettier shell than usual,
{74385}{74452}while the great ocean of truth
{74452}{74524}lay before me, all undiscovered."
{74584}{74607}And yet,
{74608}{74656}two hundred and fifty years later,
{74657}{74679}Albert Einstein,
{74680}{74728}who was Newton's true successor,
{74729}{74788}was able to seriously suggest
{74789}{74835}that this vast ocean,
{74836}{74883}all the laws of nature,
{74884}{74944}might be reduced to a|few fundamental ideas
{74951}{75004}expressed by a handful
{75005}{75052}of mathematical symbols.
{75129}{75159}And today,
{75160}{75225}a half century after Einstein's death,
{75232}{75291}we may at last be on
{75292}{75352}the verge of fulfilling|his dream of unification
{75364}{75412}with string theory.
{75656}{75747}But where did this daring and|strange new theory come from?
{75843}{75902}How does string theory achieve
{75903}{75963}the ultimate unification|of the laws of the large
{75963}{76011}and the laws of the small?
{76033}{76105}And how will we know|if it's right or wrong?
{76106}{76141}SHELDON LEE GLASHOW: No experiment
{76142}{76188}can ever check up what's going on
{76189}{76249}at the distances that are being studied.
{76250}{76309}The theory is permanently safe.
{76310}{76361}Is that a theory of physics
{76362}{76397}or a philosophy?
{76397}{76433}STEVEN WEINBERG: It|isn't written in the stars
{76433}{76481}that we're going to succeed,
{76482}{76535}but in the end
{76536}{76589}we hope we will have a single|theory that governs everything.
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