relativity.pptx

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RELATIVITY



RELATIVRelativity, theory, developed in the early 20th century, which originallyattempted to account or certain anomalie! in the concept o relativemotion, "ut which in it! rami#cation! ha! developed into one o the mo!timportant "a!ic concept! in phy!ical !cience$ The theory o relativity,

developed primarily "y %erman American phy!ici!t Al"ert Ein!tein, i! the"a!i! or later demon!tration "y phy!ici!t! o the e!!ential unity o matterand energy, o !pace and time, and o the orce! o gravity andacceleration



&LA''I&AL ()Y'I&(hy!ical law! generally accepted "y !cienti!t! "e ore the development othe theory o relativity, now called cla!!ical law!, were "a!ed on theprinciple! o mechanic! enunciated late in the *+th century "y the Engli!hmathematician and phy!ici!t I!aac ewton$ ewtonian mechanic! andrelativi!tic mechanic! di-er in undamental a!!umption! andmathematical development, "ut in mo!t ca!e! do not di-er apprecia"ly in

net re!ult!. the "ehavior o a "illiard "all when !truc/ "y another "illiard"all, or e ample, may "e predicted "y mathematical calculation! "a!edon either type o mechanic! and produce appro imately identical re!ult!$Ina!much a! the cla!!ical mathematic! i! enormou!ly !impler than therelativi!tic, the ormer i! the pre erred "a!i! or !uch a calculation$ Inca!e! o high !peed!, however, a!!uming that one o the "illiard "all! wa!

moving at a !peed approaching that o light, the two theorie! would



&LA''I&AL ()Y'I&ntil *33+ no 4aw had appeared in the rapidly developing "ody ocla!!ical phy!ic!$ In that year, the 5ichel!on65orley e periment, named

a ter the American phy!ici!t Al"ert 5ichel!on and the American chemi!tEdward 7illiam! 5orley, wa! per ormed$ It wa! an attempt to determinethe rate o the motion o the earth through the ether, a hypothetical!u"!tance that wa! thought to tran!mit electromagnetic radiation,

including light, and wa! a!!umed to permeate all !pace$ I the !un i! ata"!olute re!t in !pace, then the earth mu!t have a con!tant velocity o 28/m9!ec :*3 mi9!ec;, cau!ed "y it! revolution a"out the !un. i the !un andthe entire !olar !y!tem are moving through !pace, however, thecon!tantly changing direction o the earth<! or"ital velocity will cau!e thi!value o the earth<! motion to "e added to the velocity o the !un at

certain time! o the year and !u"tracted rom it at other!$ The re!ult o



&LA''I&AL ()Y'I&7hat the 5ichel!on65orley e periment actually mea!ured wa! thevelocity o light through !pace in two di-erent direction!$ I a ray o light i!moving through !pace at >00,000 /m9!ec :*3?,000 mi9!ec;, and ano"!erver i! moving in the !ame direction at 28 /m9!ec :*3 mi9!ec;, thenthe light !hould move pa!t the o"!erver at the rate o 288,8+* /m9!ec:*3@,832 mi9!ec;. i the o"!erver i! moving in the oppo!ite direction, the

light !hould move pa!t the o"!erver at >00,028 /m9!ec :*3?,0*3 mi9!ec;$It wa! thi! di-erence that the 5ichel!on65orley e periment ailed todetect$ Thi! ailure could not "e e plained on the hypothe!i! that thepa!!age o light i! not a-ected "y the motion o the earth, "ecau!e !uchan e-ect had "een o"!erved in the phenomenon o the a"erration o light.see Inter erence. Inter erometer. 7ave 5otion$



'(E&IAL T)ECRY C RELATIAll motion i! relative, according to Ein!tein$ one o Ein!tein<! "a!ic a!!umption!wa! revolutionary. ewton had previou!ly !tated Da"!olute re!t cannot "edetermined rom the po!ition o "odie! in our region!$ Ein!tein !tated therelative rate o motion "etween any o"!erver and any ray o light i! alway! the!ame, >00,000 /m9!ec :*3?,000 mi9!ec;, and thu! two o"!erver!, moving relativeto one another even at a !peed o *?0,000 /m9!ec :*00,000 mi9!ec;, eachmea!uring the velocity o the !ame ray o light, would "oth #nd it to "e movingat >00,000 /m9!ec :*3?,000 mi9!ec;, and thi! apparently anomalou! re!ult wa!proved "y the 5ichel!on65orley e periment$ According to cla!!ical phy!ic!, oneo the two o"!erver! wa! at re!t, and the other made an error in mea!urement"ecau!e o the Lorent=6 it=%erald contraction o hi! apparatu!. according toEin!tein, "oth o"!erver! had an e1ual right to con!ider them!elve! at re!t, andneither had made any error in mea!urement$ Each o"!erver u!ed a !y!tem o

coordinate! a! the rame o re erence or mea!urement!, and the!e coordinate!could "e tran! ormed one into the other "y a mathematical manipulation$ The



'(E&IAL T)ECRY C RELATIAccording to the relativi!tic tran! ormation, not only would length! in theline o a moving o"Bect "e altered "ut al!o time and ma!!$ A cloc/ inmotion relative to an o"!erver would !eem to "e !lowed down, and anymaterial o"Bect would !eem to increa!e in ma!!, "oth "y the "eta actor$

The electron, which had Bu!t "een di!covered, provided a mean! o te!tingthe la!t a!!umption$ Electron! emitted rom radioactive !u"!tance! have!peed! clo!e to the !peed o light, !o that the value o "eta, or e ample,might "e a! large a! 0$@, and the ma!! o the electron dou"led$ The ma!!o a rapidly moving electron could "e ea!ily determined "y mea!uring thecurvature produced in it! path "y a magnetic #eld. the heavier theelectron, the greater it! inertia and the le!! the curvature produced "y agiven !trength o #eld$ E perimentation dramatically con#rmed Ein!tein<!prediction. the electron increa!ed in ma!! "y e actly the amount hepredicted$ Thu!, the /inetic energy o the accelerated electron had "een



%E ERAL T)ECRY C

RELATIVITYIn *8*@ Ein!tein developed the general theory o relativity in which hecon!idered o"Bect! accelerated with re!pect to one another$ )e developedthi! theory to e plain apparent con4ict! "etween the law! o relativity andthe law o gravity$ To re!olve the!e con4ict! he developed an entirely newapproach to the concept o gravity, "a!ed on the principle o e1uivalence$



%E ERAL T)ECRY C

RELATIVITY The principle o e1uivalence hold! that orce! produced "y gravity are inevery way e1uivalent to orce! produced "y acceleration, !o that it i!theoretically impo!!i"le to di!tingui!h "etween gravitational andaccelerational orce! "y e periment$ In the theory o !pecial relativity,Ein!tein had !tated that a per!on in a clo!ed car rolling on an a"!olutely!mooth railroad trac/ could not determine "y any conceiva"le e periment

whether he wa! at re!t or in uni orm motion$ In general relativity he !tatedthat i the car were !peeded up or !lowed down or driven around a curve,the occupant could not tell whether the orce! !o produced were due togravitation or whether they were acceleration orce! "rought into play "ypre!!ure on the accelerator or on the "ra/e or "y turning the car !harplyto the right or le t$



%E ERAL T)ECRY C

RELATIVITYAcceleration i! de#ned a! the rate o change o velocity$ &on!ider an a!tronaut !tandingin a !tationary roc/et$ Gecau!e o gravity hi! or her eet are pre!!ed again!t the 4oor othe roc/et with a orce e1ual to the per!on<! weight, w. I the !ame roc/et!pace, ar rom any other o"Bect and not in4uenced "y gravity, the a!tronaut i! again"eing pre!!ed again!t the 4oor i the roc/et i! accelerating, and i the acceleration i! 8$3m9!ec 2 :>2 t9!ec 2; :the acceleration o gravity at the !ur ace o the earth;, the orce withwhich the a!tronaut i! pre!!ed again!t the 4oor i! again e1ual to w. 7ithoo the window, the a!tronaut would have no way o telling whether the roc/et wa! at re!ton the earth or accelerating in outer !pace$ The orce due to acceleration i! in no waydi!tingui!ha"le rom the orce due to gravity$ According to Ein!tein<! theory, ewton<!law o gravitation i! an unnece!!ary hypothe!i!. Ein!tein attri"ute! all orce!, "othgravitational and tho!e a!!ociated with acceleration, to the e-ect! o acceleration$ Thu!,when the roc/et i! !tanding !till on the !ur ace o the earth, it i! attracted toward thecenter o the earth$ Ein!tein !tate! that thi! phenomenon o attraction i! attri"uta"le toan acceleration o the roc/et$ In three6dimen!ional !pace, the roc/et i! !tationary andthere ore i! not accelerated. "ut in our6dimen!ional !pace6time, the roc/et i! in motion



%E ERAL T)ECRY C

RELATIVITY Thu!, ewton<! hypothe!i! that every o"Bect attract! every other o"Bect indirect proportion to it! ma!! i! replaced "y the relativi!tic hypothe!i! thatthe continuum i! curved in the neigh"orhood o ma!!ive o"Bect!$Ein!tein<! law o gravity !tate! !imply that the world line o every o"Bect i!a geode!ic in the continuum$ A geode!ic i! the !horte!t di!tance "etweentwo point!, "ut in curved !pace it i! not generally a !traight line$ In the

!ame way, geode!ic! on the !ur ace o the earth are great circle!, whichare not !traight line! on any ordinary map .



&C IR5ATIC A H 5CHI I&AA! in the ca!e! mentioned a"ove, cla!!ical and relativi!tic prediction! aregenerally virtually identical, "ut relativi!tic mathematic! i! more comple $

The amou! apocryphal !tatement that only ten people in the worldunder!tood Ein!tein<! theory re erred to the comple ten!or alge"ra andRiemannian geometry o general relativity. "y compari!on, !pecialrelativity can "e under!tood "y any college !tudent who ha! !tudied

elementary calculu!$



&C IR5ATIC A H 5CHI I&A%eneral relativity theory ha! "een con#rmed in a num"er o way! !ince it wa!introduced$ or e ample, it predict! that the world line o a ray o light will "e curved inthe immediate vicinity o a ma!!ive o"Bect !uch a! the !un$ To veri y thi! prediction,!cienti!t! #r!t cho!e to o"!erve a !tar appearing very clo!e to the edge o the !un$ 'ucho"!ervation! cannot normally "e made, "ecau!e the "rightne!! o the !un o"!cure! anear"y !tar$ Huring a total eclip!e, however, !tar! can "e o"!erved and their po!ition!accurately mea!ured even when they appear 1uite clo!e to the edge o the !un$E pedition! were !ent out to o"!erve the eclip!e! o *8*8 and *822 and made !ucho"!ervation!$ The apparent po!ition! o the !tar! were then compared with theirapparent po!ition! !ome month! later, when they appeared at night ar rom the !un$Ein!tein predicted an apparent !hi t in po!ition o *$+ @ !econd! o arc or a !tar at thevery edge o the !un, with progre!!ively !maller !hi t! or more di!tant !tar!$ Thee pedition! that were !ent to !tudy the eclip!e! veri#ed the!e prediction!$ In recentyear!, compara"le te!t! were made o radio6wave de4ection! rom di!tant 1ua!ar!, u!ingradio6tele!cope inter erometer!$ The te!t! yielded re!ult! that agreed, to within *percent, with the value! predicted "y general relativity$



&C IR5ATIC A H 5CHI I&AAnother con#rmation o general relativity involve! the perihelion o theplanet 5ercury$ or many year! it had "een /nown that the perihelion :thepoint at which 5ercury pa!!e! clo!e!t to the !un; revolve! a"out the !unat the rate o once in > million year!, and that part o thi! perihelionmotion i! completely ine plica"le "y cla!!ical theorie!$ The theory orelativity, however, doe! predict thi! part o the motion, and recent radar

mea!urement! o 5ercury<! or"it have con#rmed thi! agreement to withina"out 0$@ percent$



&C IR5ATIC A H 5CHI I&A Yet another phenomenon predicted "y general relativity i! the time6delaye-ect, in which !ignal! !ent pa!t the !un to a planet or !pacecra t on the

ar !ide o the !un e perience a !mall delay, when relayed "ac/,compared to the time o return a! indicated "y cla!!ical theory$ Althoughthe time interval! involved are very !mall, variou! te!t! made "y mean! oplanetary pro"e! have provided value! 1uite clo!e to tho!e predicted "y

general relativity $ umerou! other te!t! o the theory could al!o "ede!cri"ed, and thu! ar they have !erved to con#rm it$



&C IR5ATIC A H 5CHI I&A The general theory o relativity predict! that a ma!!ive rotating "ody willdrag !pace and time around with it a! it move!$ Thi! e-ect, called ramedragging, i! more noticea"le i the o"Bect i! very ma!!ive and very den!e$In *88+ a group o Italian a!tronomer! announced that they had detected

rame dragging around very den!e, rapidly !pinning a!tronomical o"Bect!called neutron !tar!$ The a!tronomer! ound evidence o rame dragging

"y e amining radiation emitted when the gravitational pull o a den!eneutron !tar !uc/! matter onto it! !ur ace$ Thi! radiation !howed !lightdi-erence! rom the radiation that wa! predicted "y cla!!ical phy!ic!$



&C IR5ATIC A H 5CHI I&AIn *883 another group o a!tronomer! rom the nited 'tate! and Europeannounced that the or"it! o !ome arti#cial !atellite! around the earth!howed the e-ect! o rame dragging$ The earth i! much lighter and le!!den!e than a neutron !tar, !o the e-ect! o the earthJ! rame dragging aremuch more !u"tle than tho!e o the neutron !tarJ! rame dragging$ Thea!tronomer! ound that the or"it! o two Italian !atellite! !eem to !hi t

a"out 2 m :a"out + t; in the direction o the earthJ! rotation every year$ The launch o the $'$ !pacecra t %ravity (ro"e G in 2000 !hould provideeven more evidence o rame dragging around the earth and other "odie!$

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