"Annenberg Media" "¶" "LAST TIME, I TOLD YOU" "THE CONVENTIONAL HISTORY OF RELATIVITY." "THERE WAS THE THEORY OF THE ETHER," "THEN THE MICHELSON-MORLEY EXPERIMENT SHOWED IT WAS WRONG," "AND THEN ALBERT EINSTEIN" "PRODUCED THE THEORY OF RELATIVITY." "AS I TOLD YOU THEN, THAT STORY IS LOGICALLY CORRECT," "BUT NOT HISTORICALLY CORRECT." "WHAT IS THE REAL STORY?" "I'LL GET BACK TO THAT IN A LITTLE WHILE." "FIRST OF ALL, I'D LIKE TO TELL YOU ABOUT" "A PART OF THE THEORY" "WHICH IS STILL CALLED THE LORENTZ TRANSFORMATION." "IN THE LORENTZ TRANSFORMATION," "THERE IS, ABOVE ALL, THE SPEED OF LIGHT," "THE SPEED THAT SPRANG FROM MAXWELL'S EQUATIONS," "THE 300,000 KILOMETERS PER SECOND" "THAT MICHELSON MEASURED WITH LANDMARK ACCURACY," "THE SPEED WHICH IS ESSENTIAL IN MODERN PHYSICS" "AND VITAL TO UNDERSTANDING THE UNIVERSE AS IT REALLY IS." "[TRAIN WHISTLE BLOWS]" "AND AT THE END OF THE 19th CENTURY," "WHEN LORENTZ DERIVED HIS TRANSFORMATION EQUATIONS," "WHEN IT CAME TO SPEED," "THE MOST MOVING HUMAN EXPERIENCE WAS PROVIDED BY TRAINS." "THE AUTOMOBILE, WHICH WOULD EVENTUALLY OUTPACE THE TRAIN," "WASN'T QUITE IN GEAR," "AND AIR TRAVEL WAS BARELY OFF THE GROUND." "BIG OR SMALL, SOPHISTICATED OR CHILD'S PLAY..." "[CHOO CHOO!" "]" "TRAINS WERE THE VERY IMAGE OF SPEED," "AND IN FACT," "THE ONLY THING ON EARTH THAT MOVED PEOPLE FASTER" "WAS THE EARTH ITSELF." "ORBITING THE SUN AT 108,000 KILOMETERS PER HOUR," "THE INHABITANTS OF THE PLANET MAY NOT BE AWARE OF THIS SPEED," "BUT SPEED IT IS," "AND TO PHYSICISTS AT THE TURN OF THE CENTURY," "IT WAS SPEED RELATIVE TO THE ETHER." "SINCE THE TIME OF ARISTOTLE," "THE ETHER WAS BELIEVED TO BE THE VERY STUFF" "OF WHICH THE HEAVENS THEMSELVES WERE MADE." "THAT CONCEPT REMAINED MERE SPECULATION" "UNTIL TWO AMERICANS SET OUT TO PROVE ONCE AND FOR ALL" "THAT WHAT WAS THEN CALLED THE LUMINIFEROUS ETHER" "DID, IN FACT, EXIST." "THEY WERE ALBERT A. MICHELSON" "AND EDWARD MORLEY," "AND THEIR GOAL WAS TO DETECT MOTION THROUGH THE ETHER" "BY MEASURING ITS EFFECTS ON THE SPEED OF LIGHT." "IN ONE ATTEMPT AFTER ANOTHER," "WITH THE MOST SENSITIVE EXPERIMENTAL DEVICE EVER CONSTRUCTED," "THEY FOUND EXACTLY WHAT THEY WEREN'T LOOKING FOR" "THE INTERFEROMETER SHOWED THAT" "REGARDLESS OF THE MOTION OF THE OBSERVER," "THE SPEED OF LIGHT IS THE SAME." "FOR MICHELSON AND MORLEY, THIS WAS BAD NEWS," "AND IT TRAVELED FAST," "AS FAST AS A BOAT COULD CARRY IT, TO IRELAND." "THERE, PHYSICIST G.F. FITZGERALD," "AN EARLY CHAMPION" "OF MAXWELL'S ELECTROMAGNETIC THEORY OF LIGHT," "EXAMINED MICHELSON'S OTHERWISE DISAPPOINTING RESULTS." "FITZGERALD'S EXPLANATION WAS THAT" "IN ITS MOTION THROUGH THE ETHER," "ONE ARM OF THE INTERFEROMETER" "WAS CONTRACTED BY A FRACTION OF ITS LENGTH," "WHICH WAS JUST THE RIGHT AMOUNT" "TO ALLOW THE TWO LIGHT BEAMS TO ARRIVE SIMULTANEOUSLY." "IMMEDIATELY, MOST SCIENTISTS SCOFFED AT THE IDEA." "HOWEVER, WHEN HENDRIK LORENTZ ARRIVED AT THE SAME IDEA," "NO ONE WAS LAUGHING." "NOT ONLY WAS HE THE WORLD'S EXPERT" "ON MAXWELL'S ELECTROMAGNETIC THEORY," "BUT LORENTZ GAVE A TANGIBLE EXPLANATION" "FOR THE CONTRACTION PHENOMENON." "HE THOUGHT IT HAD TO BE A PROPERTY OF THE ELECTRON," "WHOSE EXISTENCE HAD JUST BEEN CONFIRMED" "BY J.J. THOMSON AND HIS COLLEAGUES IN ENGLAND." "IT SEEMED THAT, IN ELECTRONS," "THEY'D FOUND THE INNER PARTS OF ATOMS," "THE ULTIMATE CONSTITUENTS OF MATTER," "BUT THEY HADN'T DISCOVERED ALL THE THINGS" "THAT ELECTRONS ACTUALLY DO." "ONE POSSIBILITY, LORENTZ BELIEVED," "IS THAT AN ELECTRON WILL CONTRACT" "IN THE DIRECTION OF MOTION." "IF THAT WERE TRUE," "AND SINCE EVERYTHING IS COMPOSED OF ELECTRONS," "THEN AN INTERFEROMETER WOULD CONTRACT" "IN THE DIRECTION OF MOTION." "SO WOULD A RULER," "AND SO WOULD A LOCOMOTIVE." "[CHOO CHOO!" "]" "WHILE LENGTH CONTRACTION TOOK CARE OF" "THE MICHELSON-MORLEY EXPERIMENT," "LORENTZ KNEW MORE WAS NEEDED" "TO EXPLAIN ALL THE EXPERIMENTS" "THAT HAD FAILED TO DETECT MOTION THROUGH THE ETHER." "SINCE HE STILL BELIEVED IN THE ETHER" "AND THE FACT THAT THE EARTH MOVED THROUGH IT," "HE FELT THAT SOMEHOW THE ELECTRON MUST BE RESPONSIBLE" "FOR THIS AMAZING FACT ABOUT LIGHT." "REGARDLESS OF THE SPEED" "WITH WHICH THEY THEMSELVES ARE MOVING," "ALL OBSERVERS MEASURE THE SAME SPEED OF LIGHT." "CERTAINLY OTHER SPEEDS" "SAY, THE SPEED OF A MOVING TRAIN" "AREN'T THE SAME TO ALL OBSERVERS." "[CHOO CHOO!" "]" "[TRAIN WHISTLE BLOWS]" "TO AN OBSERVER ON A PLATFORM, FOR EXAMPLE," "THIS TRAIN'S PASSING AT A GOOD CLIP," "BUT TO SOMEONE ON THE TRAIN," "THE TRAIN'S SPEED SEEMS TO BE ZERO" "AND THE GROUND OUTSIDE SEEMS TO BE MOVING INSTEAD." "THEREFORE, AS GALILEO WAS WELL AWARE IN THE RENAISSANCE" "AND AS THIS FELLOW KNOWS TODAY," "THE SPEED OF AN OBJECT DEPENDS ON THE OBSERVER'S SPEED." "BUT LORENTZ SAID THAT PERCEPTIONS OF LIGHT WAVES" "WOULD BE RADICALLY DIFFERENT." "HE SUGGESTED THAT EVEN SOMEONE TRAVELING" "AT NEARLY THE SPEED OF LIGHT" "WOULD STILL OBSERVE LIGHT MOVING" "AT 300,000 KILOMETERS PER SECOND." "HOW COULD THAT BE?" "[CHOO CHOO!" "]" "CONSIDER TWO OBSERVERS IN RELATIVE MOTION." "IN THIS CASE..." "ALBERT..." "AND HENRY..." "JUST FOR THE SAKE OF ARGUMENT." "AT THE EXACT PLACE AND TIME THEY PASS EACH OTHER," "THEY OBSERVE A FLASH OF LIGHT." "A SPHERE OF LIGHT EXPANDS OUTWARD FROM THAT POINT." "SINCE EACH MEASURES THE SPEED OF LIGHT" "RELATIVE TO HIMSELF," "EACH BELIEVES CORRECTLY THAT HE IS ALWAYS AT THE CENTER" "OF THAT EXPANDING SPHERE," "EVEN THOUGH THEY THEMSELVES MOVE FARTHER AND FARTHER APART." "HOW CAN TWO PEOPLE IN DIFFERENT PLACES" "BOTH BE AT THE CENTER OF THE SAME SPHERE?" "TO CONFIRM HIS PERCEPTION," "EACH SETS UP LIGHT DETECTORS AN EQUAL DISTANCE APART." "[DING]" "[BUZZ]" "HOWEVER, WHILE ALBERT'S DETECTORS" "REGISTER THE LIGHT ARRIVING SIMULTANEOUSLY," "HE BELIEVES THE LIGHT STRIKES HENRY'S DETECTORS" "AT TWO DIFFERENT TIMES." "[BUZZ DING BUZZ]" "MEANWHILE, HENRY SEES THE SAME THING" "IN REVERSE." "[DING BUZZ DING]" "THEY AGREE ON THE SPEED OF LIGHT," "BUT THEY DISAGREE ON WHETHER EVENTS HAPPEN SIMULTANEOUSLY" "OR AT DIFFERENT TIMES." "[BUZZ DING BUZZ]" "[DING]" "THIS IS NOT SEMANTICS, NOR A PETTY DEBATE." "IT MEANS THAT TIME, AS WELL AS DISTANCE," "HAS TO BE AFFECTED BY MOTION." "HOWEVER, AS PROFOUND AS THIS WAS," "THE FRENCH MATHEMATICIAN HENRI POINCARE" "OBJECTED TO THE LIMITED NATURE OF LORENTZ'S EXPLANATION." "WHAT WAS NEEDED, HE SAID," "WAS A NEW FUNDAMENTAL LAW OF PHYSICS" ""THE PRINCIPLE OF RELATIVITY," ""ACCORDING TO WHICH THE LAWS OF PHYSICAL PHENOMENA" ""SHOULD BE THE SAME" ""WHETHER FOR AN OBSERVER FIXED" ""OR FOR AN OBSERVER CARRIED ALONG" "IN A UNIFORM MOVEMENT OF TRANSLATION."" "IN OTHER WORDS," "AS GALILEO HAD SUGGESTED," "ONE STATE OF UNIFORM MOTION IS AS GOOD AS ANY OTHER." "AFTER ALL, THIS IDEA WAS THE BASIS OF GALILEO'S REASONING" "AND THE LAW OF INERTIA ALMOST 300 YEARS EARLIER." "BUT POINCARE WAS SUGGESTING" "THAT THE IDEA OF GALILEAN RELATIVITY" "SHOULD BE GENERALIZED TO INCLUDE ALL PHYSICAL PHENOMENA," "INCLUDING LIGHT." "FOR EXAMPLE," "AN OBSERVER COULD NOT DETERMINE WHETHER HE WAS IN MOTION" "BY MEASURING THE SPEED OF LIGHT" "SINCE THAT SPEED IS THE SAME FOR ALL OBSERVERS." "THAT MEANT AGE-OLD NOTIONS ABOUT TIME AND SPACE HAD TO CHANGE," "AND THOUGH POINCARE HIMSELF" "SHIED AWAY FROM EXAMINING THE CONSEQUENCES," "LORENTZ DEVELOPED THE EQUATIONS" "NEEDED TO SHOW PRECISELY HOW MUCH" "RULERS WOULD HAVE TO CONTRACT" "AND CLOCKS WOULD HAVE TO SLOW DOWN" "WHEN THEY WERE IN MOTION." "THE ESSENCE OF HIS REASONING" "CAN BE SEEN WITH THE AID OF THE SIMPLEST POSSIBLE CLOCK" "TWO MIRRORS A FIXED DISTANCE APART..." "WITH A LIGHT BEAM BOUNCING BACK AND FORTH BETWEEN THEM." "EH BOUNCE OF THE BEAM" "IS A TICK OR A TOCK OF THE TIMEPIECE." "TO HENRY, HIS CLOCK IS STATIONARY" "AND ALTOGETHER ORDINARY," "BUT FOR ALBERT, THAT CLOCK IS MOVING," "AND BETWEEN TICK AND TOCK," "HE SEES THE LIGHT BEAM TRACE A DIAGONAL PATH," "WHICH MEANS IT'S TRAVELING A LONGER DISTANCE." "BUT THE SPEED OF LIGHT IS THE SAME FOR ALL OBSERVERS," "SO THE LIGHT MUST TAKE A LONGER TIME" "TO TRAVEL THE LONGER DISTANCE." "THEREFORE, ALBERT BELIEVES THE MOVING CLOCK RUNS SLOW." "BUT HOW SLOW?" "THERELATIVITYOF TIME" "ISDERIVEDFROM THERIGHTTRIANGLE" "FORMEDBY THEDISTANCESTRAVELED." "THEPYTHAGOREANTHEOREM" "SHOWSTHATTHEPATH OFTHEMOVINGLIGHT" "ISLONGERTHANTHE DISTANCE BETWEENMIRRORS..." "BYTHEFACTOR1" "OVERTHESQUAREROOT" "OF1 - v-SQUARED/c-SQUARED." "THISFACTOROCCURS SOOFTENIN RELATIVITY" "THATITIS GIVEN ITSOWNSYMBOL," "THEGREEKLETTERGAMMA." "SO TO AN OBSERVER AT REST," "A MOVING-LIGHT CLOCK SEEMS TO BE RUNNING TOO SLOWLY" "BY THE FACTOR GAMMA." "A RULER, OR ANYTHING ELSE IN MOTION," "ALSO SEEMS CONTRACTED BY THAT SAME FACTOR," "AND IT'S CALLED THE FITZGERALD CONTRACTI." "FOR SPEEDS MUCH LESS THAN THE SPEED OF LIGHT," "GAMMA ISN'T VERY LARGE." "FOR EXAMPLE, THE EARTH" "IN ITS HEADLONG DASH AROUND THE SUN" "IS SHORTENED BY NO MORE THAN THE LENGTH" "OF ONE BLADE OF GRASS." "AS FOR SPEED ON THE EARTH," "WHILE LORENTZ WAS BUSY DEVELOPING HIS THEORY," "THE STEAM LOCOMOTIVE BARRIER" "OF 100 MILES PER HOUR WAS BROKEN." "AT THAT SPEED," "THE ENTIRE TRAIN IS SHORTENED BY LESS THAN THE WIDTH" "OF ONE ATOM OF THE PAINT ON ITS ENGINE." "AND LORENTZ HIMSELF DIDN'T MOVE SLOWLY." "HE WAS THE INTERNATIONAL PHYSICIST." "YOUNG PHYSICISTS FROM AROUND THE WORLD" "ATTENDED HIS LECTURES AT THE UNIVERSITY OF LEIDEN" "IN THE NETHERLANDS" "WHERE HE'D BEEN A PROFESSOR FOR A QUARTER OF A CENTURY." "AMONG THOSE WHO CAME TO LEIDEN WAS ALBERT EINSTEIN." "OVER THE YEARS, LORENTZ WOULD HAVE" "AN ENORMOUS PROFESSIONAL AND PERSONAL INFLUENCE ON EINSTEIN." "JUST BEFORE HIS DEATH, EINSTEIN SAID," ""I HAVE ADMIRED AND LOVED LORENTZ" "PERHAPS MORE THAN ANYONE ELSE I HAVE EVER KNOWN."" "BUT IT WAS LORENTZ'S WORK AS A THEORETICAL PHYSICIST" "THAT WENT BEYOND HIS PRIVILEGED CIRCLE OF FRIENDS" "AND TRAVELED FREELY THROUGH TIME AND SPACE." "KNOWING HE WAS ON THE RIGHT TRACK," "LORENTZ PURSUED THE CONSEQUENCES AS FAR AS HE COULD." "IF MOVING THINGS APPEAR SHORTER" "AND MOVING CLOCKS RUN SLOWER," "THEN HOW CAN TWO PEOPLE" "MOVING IN RELATION TO EACH OTHER" "AGREE ON A CONSISTENT DESCRIPTION" "OF WHERE AND WHEN SOME EVENT HAPPENED?" "TO ANSWER THAT," "WHAT'S NEEDED IS A SET OF EQUATIONS" "TO REPLACE THE OLD GALILEAN TRANSFORMATIONS." "THESE EQUATIONS WEREN'T HARD TO FIND," "BUT SOME OF THEIR IMPLICATIONS" "WERE HARD TO BELIEVE." "INGALILEANRELATIVITY," "THE POSITION OF A POINT x PRIME INA MOVINGFRAME" "IS RELATED TO ITS COORDINATE INA FIXEDFRAME" "BYx - vt." "LORENTZFOUNDTHAT FORTHENEWRELATIVITY," "THISMUSTBE MULTIPLIED BYTHEFACTORGAMMA." "THAT'STHEEQUATION ALONGTHEDIRECTIONOFMOTION." "INDIRECTIONS PERPENDICULAR TO THE MOTION," "DISTANCESARETHESAME INBOTHFRAMES." "AND AS FOR TIME," "ALTHOUGH CLOCKS CAN BE SYNCHRONIZED IN ANY ONE FRAME," "THEIR READINGS IN ANOTHER FRAME" "MAY DEPEND ON WHERE THEY ARE." "THE TIME IN THE MOVING FRAME" "ISGAMMATIMESTHE QUANTITY t- vx/c-SQUARED." "[TRAIN WHISTLE BLOWS]" "TOGETHER, THESE EQUATIONS ARE THE LORENTZ TRANSFORMATION." "THEY EXPRESS THE MATHEMATICAL ESSENCE" "OF THE SPECIAL THEORY OF RELATIVITY." "THE LORENTZ TRANSFORMATION SLOWS TIME" "AND CONTRACTS DISTANCES IN A MOVING FRAME," "NO MATTER WHICH FRAME IS TAKEN TO BE MOVING." "THE OBSERVER IN THE MOVING FRAME THINKS HE'S AT REST" "AND THAT THE OTHER FRAME IS REALLY MOVING," "BUT THESE EQUATIONS DO MORE THAN THAT." "THEY ACTUALLY JOIN TIME AND SPACE TOGETHER." "WHENANEVENTOCCURRED" "HAS NO MEANING WITHOUT SAYING WHEREITOCCURRED." "1904, THE NETHERLANDS." "LORENTZ PUBLISHES THE DEFINITIVE VERSION" "OF HIS ELECTRON THEORY." "IT CONTAINS THE ESSENTIAL EQUATIONS" "OF THE THEORY OF RELATIVITY." "BUT ALBERT EINSTEIN HAS NOT YET BEEN HEARD FROM," "WHICH HAS CAUSED SOME TO SAY" "THAT HISTORY HAS GIVEN HIM MORE CREDIT THAN HE DESERVED." "1905." "BERN, SWITZERLAND." "EINSTEIN, A YOUNG PHYSICS STUDENT" "SUPPORTING HIMSELF AS A PATENT CLERK," "FINDS HIMSELF DISTURBED BY SEEMING INCONSISTENCIES" "AT THE VERY CORE OF PHYSICS." "CAN INERTIA AND THE LAWS OF MECHANICS" "BE MADE CONSISTENT..." "[RING RING]" "WITH MAXWELL'S THEORY OF OPTICS AND ELECTROMAGNETISM?" "EINSTEIN DECIDES THAT THEY MUST," "EVEN IF THAT MEANS GIVING UP NOT ONLY THE ETHER," "BUT THE TRADITIONAL MEANINGS OF TIME AND SPACE." "HE SETS FORTH TWO FUNDAMENTAL POSTULATES." "THE FIRST IS POINCARE'S RELATIVITY PRINCIPLE" "THE LAWS OF PHYSICS ARE THE SAME FOR ALL INERTIAL FRAMES." "HIS SECOND POSTULATE STATES" "THAT THE SPEED OF LIGHT IS THE SAME FOR ALL OBSERVERS." "HE SIMPLY ASSUMES THE PHENOMENON" "THAT LORENTZ HAS BEEN STRUGGLING TO EXPLAIN." "FROM THESE TWO POSTULATES ALONE," "EINSTEIN DEDUCES EXACTLY THE SAME EQUATIONS" "LORENTZ DISCOVERERED EARLIER," "BUT NOW THEY HAVE A VERY DIFFERENT MEANING." "THE FUNDAMENTAL CONCEPTS OF SPACE AND TIME" "HAVE BECOME INTERTWINED." "THE ESSENCE OF THE IDEA CAN BE UNDERSTOOD" "BY VISUALIZING TIME AS IF IT WERE ANOTHER DIMENSION." "ALBERT, STANDING STILL IN SPACE, FLOWS THROUGH TIME..." "SO THAT A VERTICAL LINE" "REPRESENTS A FIXED POINT, x = 0," "IN HIS REFERENCE FRAME" "AT DIFFERENT TIMES..." "WHILE A HORIZONTAL CROSS SECTION" "REPRESENTS SIMULTANEOUS TIMES IN DIFFERENT PLACES." "ON THE OTHER HAND," "SOMEONE IN MOTION, GALILEO FOR EXAMPLE..." "TRACES AN OBLIQUE PATH." "SO WHILE WHAT ALBERT THINKS OF" "AS A FIXED POINT" "MAKES A VERTICAL LINE," "GALILEO'S IDEA" "OF NOTHING HAPPENING" "APPEARS AS A TILTED LINE" "AT x PRIME EQUALS 0" "OR ANYWHERE ELSE IN HIS FRAME." "BUT, OF COURSE, IF GALILEO" "HAD DRAWN THE PICTURE," "HIS LINE FOR STANDING STILL" "WOULD BE VERTICAL," "AND ALBERT'S" "WOULD BE TILTED BACKWARD." "THE SAME IDEA CAN BE USED TO SHOW THE RELATIVITY OF TIME." "WHEN HENRY AND ALBERT OBSERVE THE SAME EXPANDING LIGHT SPHERE," "IT REACHES THEIR DETECTORS" "AT DEFINITE POINTS IN TIME AND SPACE." "[BUZZ]" "[DING]" "[BUZZ]" "THESE ARE CALLED EVENTS." "MEANWHILE, THE LIGHT ITSELF TRACES OUT A CONE." "TO ALBERT, EVENTS ON THE HORIZONTAL CROSS SECTION" "ARE SIMULTANEOUS." "FOR HIM, ONE OF HENRY'S DETECTORS FLASHES FIRST," "THEN BOTH OF HIS OWN FLASH SIMULTANEOUSLY," "AND FINALLY, HENRY'S OTHER DETECTOR FLASHES." "[DING]" "SO HE THINKS THESE TWO EVENTS ARE SIMULTANEOUS," "BUT HENRY THINKS THESE TWO EVENTS ARE SIMULTANEOUS." "SO NOT ONLY ARE HENRY'S LINES OF CONSTANT POSITION TILTED," "BUT SO ARE HIS LINES OF SIMULTANEOUS TIME." "FOR HENRY, SIMULTANEOUS EVENTS TAKE PLACE EVERYWHERE" "ON A TILTED CROSS SECTION," "SO HE THINKS ONE OF ALBERT'S SIGNALS GOES FIRST," "THEN BOTH OF HIS, THEN ALBERT'S OTHER SIGNAL." "[DING]" "OF COURSE, IF HENRY WERE DRAWING THE PICTURE," "HE WOULD DRAW HIS LINES OF CONSTANT PLACE AND CONSTANT TIME" "PERPENDICULAR TO EACH OTHER." "AMAZINGLY, THAT WOULDN'T CHANGE THE LIGHT CONE AT ALL." "THIS WAY OF LOOKING AT THINGS IS CALLED A SPACE-TIME DIAGRAM," "AND MANY OF THE STRANGE EFFECTS OF RELATIVITY" "CAN BE VISUALIZED THIS WAY." "FOR EXAMPLE, ALBERT THINKS THAT HENRY'S RULER" "ISN'T QUITE A METER LONG..." "WHILE HENRY," "SEEING ALBERT SPEED BY," "THINKS ALBERT'S RULER IS SHORTER." "ON THE SPACE-TIME DIAGRAM..." "ALBERT MEASURES LENGTHS ON HIS SPACE AXIS" "WHERE HENRY'S RULER IS SHORTER." "BUT ON HENRYS' AXES, THE SITUATION IS REVERSED" "AND ALBERT'S RULER IS SHORTER." "AND WHAT ABOUT THE MYSTERY OF THE CLOCKS?" "HOW CAN EACH THINK THE OTHER'S CLOCK IS SLOW?" "ON THE SPACE-TIME DIAGRAM," "JUST FOLLOW THE BOUNCING LIGHT BEAMS." "ON ALBERT'S TIME AXIS," "HENRY'S TICKS ARE FARTHER APART THAN HIS OWN..." "BUT ON HENRY'S TIME AXIS," "ALBERT'S TICKS ARE FARTHER APART," "NO MATTER HOW HE LOOKS AT IT." "ACTUALLY, THERE'S MORE THAN ONE WAY" "TO LOOK AT THE LORENTZ TRANSFORMATION ITSELF." "WHILE IT WAS FIRST DERIVED BY LORENTZ," "EINSTEIN ARRIVED AT THE SAME EQUATIONS" "BUT FROM A COMPLETELY DIFFERENT DIRECTION." "LORENTZ USED THE EQUATIONS" "TO EXPLAIN THE MICHELSON-MORLEY EXPERIMENT," "WHILE EINSTEIN'S GOAL WAS TO ESTABLISH RELATIVITY" "AS A FUNDAMENTAL AND UNIVERSAL PRINCIPLE FOR ALL OF PHYSICS." "FOR LORENTZ, THE CONSTANT SPEED OF LIGHT" "FOR ALL OBSERVERS" "WAS A MERE APPEARANCE." "FOR EINSTEIN, THIS CONSTANT SPEED WAS A PRINCIPLE" "FROM WHICH ALL ELSE SHOULD BE DERIVED." "LORENTZ WAS, PERHAPS, THE LAST GREAT CLASSICAL PHYSICIST," "BUT THE EQUATIONS THAT BEAR HIS NAME" "ARE AT THE HEART OF RELATIVITY" "AND THE FUTURE IT CREATED." "IN ANY CASE," "THERE ARE TWO COMPLETELY INDEPENDENT HISTORIES" "OF THE THEORY OF RELATIVITY." "THERE WAS THE ETHER THEORY," "AND THEN THE MICHELSON-MORLEY EXPERIMENT," "AND OTHER EXPERIMENTS FAILED TO DETECT ITS EXISTENCE." "AND THEN POINCARE AND LORENTZ, WITH GREAT DIFFICULTY," "PRODUCED THE FORMULAS THAT WERE NECESSARY" "TO EXPLAIN THE RESULTS OF THOSE EXPERIMENTS." "AND THEN, COMPLETELY SEPARATELY AND INDEPENDENTLY," "YOUNG ALBERT EINSTEIN WAS WORRIED ABOUT A DEEP PROBLEM" "HAVING TO DO WITH THE NATURE OF LIGHT AND ELECTRICITY," "AND HE DECIDED THAT THIS WAS THE WAY THE WORLD HAD TO WORK." "AND HE CAME UP WITH EXACTLY THE SAME THEORY" "BUT WITH A FAR, FAR DEEPER UNDERSTANDING OF WHAT IT MEANT." "SO IT'S POSSIBLE TO SAY" "THAT EINSTEIN MADE ONLY MINOR CONTRIBUTIONS" "TO THE THEORY OF RELATIVITY," "JUST AS IT'S POSSIBLE TO SAY THAT COPERNICUS DID NOTHING" "BUT A TRIVIAL MATHEMATICAL TRANSFORMATION OF COORDINATES." "BUT TO SAY THAT IGNORES IN THE MOST PROFOUND POSSIBLE WAY" "THE REAL HISTORY OF BOTH OF THOSE SUBJECTS." "WE'LL GO ON WITH OUR DISCUSSION" "OF THE THEORY OF RELATIVITY NEXT TIME." 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