KIP S. THORNE. The Collapsing Universe: The Story of Black Holes, by Isaac Asimov BLACK HOLES TIME WARPS - Page maison de Simon Plouffe. Black Holes and Time Warps, Einstein's Outrageous Legacy - Thorne - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. Cosmology. Outrageous Legacy. KIP S. THORNE THE FEYNMAN PR. OFESSOR. Black Holes and Time Warps: Einstein's Outrageous Legacy by Kip Thorne. Reviewed by John Preskill. It is dangerous to ask a scientist to review a book on.
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Kip S. Thorne, California Institute of Technology Black Holes and Time Warps ( Norton, ).] explanations are related by Einstein's Law of Time Warps. Black Holes & Time Warps: Einstein's Outrageous Legacy and millions of other .. Kip Thorne, a Nobel Prize-winning physicist and the Feynman Professor of. Black Holes and Time Warps: Einstein's Outrageous Legacy mind−boggling rate; and over the last forty, Kip Thorne, along with Stephen Hawking, who wrote .
Copyright Reed Business Information, Inc. In other words, it is essentially correct. One of the investigators attempting to fathom the depths of the theory, Thorne here describes the people who have done the work and the trails, both false and fruitful, they have followed.
He brings us up-to-date on the state of the art in black hole research and the attempts to find definitive proof of their existence. Even with the mathematics removed, his explanations can be pretty heavy going.
Nevertheless, the payoff is worth the work. For academic and larger public library science collections. Harold D. Shane, Baruch Coll.
Wheeler, C. This rich combination plus an obvious talent as a communicator and an apparently fun loving personnality makes him both a knowlegeable and understandable writer. Some are really simple.
They make for a good introduction but are somewhat too basic for my taste. They also photograph Gargantua's black disk below you; it is about the size of the sun as seen from Earth.
At first sight it appears to blot out the light from all the stars and galaxies behind the hole. But looking more closely, your crew discover that the hole's gravitational field has acted like a lenr0 to deflect some of the starlight and galaxy light around the edge of the horizon and focus it into a thin, bright ring at the edge of the black disk.
There, in that ring, you see several images of each obscured star: The result is a highly complex ring structure, which your crew photograph in great detail for future study. The photographic session complete, you order Kares to initiate the starship's descent.
But you must be patient. The hole is so huge that, accelerating and then decelerating at 1 g, it will require 13 years of starship time to reach your goal of 1. Chapter 9. Most remarkable is the change itt the hole's black disk below the ship: Gradu;ally it grows larger.
But no; the black disk keeps right on grow-ing, swinging up around the sides of yO"Jur star. It is as though you had e11tered a cave and were plunging deeper and deeper, watching the cave's brjght mouth grow smaller and smaller in the distance. In growing panic, you appeal to DAWN for help: Have we plunged through the horizon? Are we doomed?! The bole's gravity deflects the light rays downward "gravitational Jens effect".
Darkness has covered most of the sky only because of the powerful lensing effect of the hole's gravity. Look there, where my pointer is, almost precisely overhead; that is the galaxy 3C Before you began your plunge it was in a horizontal position, 90 degrees from the zenith. But here near Gargantua's horizon the hole's gravity pulls so hard on the light rays from 3C that it bends them around from horizontal to nearly vertical.
The console displays your ship's progress in terms of both the radial downward distance traveled and the circumference of a circle around d1e hoJe that passes through your location. In the early stages of your descent, for each kilometer of radial distance traveled, your circumference decreased by 6.
The ratio of circumference decrease to radius decrease was 6. But now, as your ship nears the horizon, the ratio of circumference decrease to radius decrease is becoming much smaller than 27t: It is 5.
Such deviations from the standard Euclidean geometry that teenagers learn in school are possible only in a cunred space; you are seeing the curvature which Einstein's general relativity predicts must accompanJ' the hole's tidal force.
In its last l. Struggling to lift their hands against the painful g force, your crew direct their telescopic cameras into a long and detailed photographic session. Except for wisps of weak radiation all around you from collisionally heated, in falling gas, the only electromaguetic waves to be photographed are those in the bright spot overhead. The spot is small, just 3 degrees of arc in diameter, six times the size of the Sun as seen from Earth.
But squeezed into that spot are images of all the stars that Chapters 2 and 3. At the precise center are the galaxies that a1e truly overhead. In the outermost 00 percent of the spot is a second image of each galaxy; and 1n the outermost 2 percent, a third image! Equally peculiar, the colors of all the stars and galaxies are WTong.
A galaxy that you know is really green appears to be shining with soft X-rays: Gargantua's grc1. And similarly, the outer disk of the- quasar 3C, which you know emits infrared radiation of wavelength 5 X s meter, appears to be shining with green 5 x to- 7 meter light.
After thoroughly recording the details of the overhead spot, you turn your attention to the interior of yaur starship. You half E'Xpect that here, so near the hole's horizon, the laws of physics will be changed in some way, and those changes will affect your own physiology. But no. You look at your first mate, Kares; she appears normal. You look at your second mate, Bret; he appears normal.
You touch each other; you feel normal.
You drink. Kares turns on an argon ion laser; it produces the same brilliant green. Bret pulses a mby laser on and then off, and measures the time it takes for the pulse of light to travel from the laser to a miJTor and back; from his measurement he computes the speed of the light's travel. The result is absolutely d1. If you did. The hole curves spaC'.
But whereas. PROLOGUE the curvature is enormously important on the scale of the horizon's trillion-kilometer circumference, its effects are minuscule on the scale of your 1-kilometer starship; the curvature-produced tidal force between one end of the starship and the other is just one-hundredth of a trillionth of an Earth gravity 14 g , and between your own head and feet it is a thousand times smaller than that! To pursue this remarkable normality further, Bret drops from the starship a capsule containing a pulsed-laser-and-mirror instrument for measuring the speed of light.
As the capsule plunges toward the horizon, the instrument measures the speed with which light pulses travel from the laser in the capsule's nose to the mirror in its tail and back.
A computer in the capsule transmits the result on a laser beam up to the ship: The capsule has pierced the horizon, and never once as it fell was there any change in the speed of light inside it, nor was there any change in the laws of physics that governed the workings of the capsule's electronic systems.
These experimental results please you greatly. In the early twentieth century Albert Einstein proclaimed, largely on philosophical grounds, that the local laws of physics the laws in regions small enough that one can ignore the curvature of spacetime should be the same everywhere in the Universe. This proclamation has been enshrined as a fundamental principle of physics, the equivalence principle. You and your crew are now tiring of the struggle with 10 Earth gravities, so you prepare for the next and final leg of your voyage, a return to our Milky Way galaxy.
Your crew will transmit an account of your Gargantua explorations during the early stages of the voyage; and since your starship itself will soon be traveling at nearly the speed of light, the transmissions will reach the Milky Way less than a year before the ship, as measured from Earth. As your starship pulls up and away from Gargantua, your crew make a careful, telescopic study of the quasar oC27o overhead55 Figure P.
A stream of gas flows from the doughm1t to the hori'lOil, pulled by the hole's gravity. As it nears the horizon the stream, unlike any you have seen before. This hole must be spinning last.! The axis of spin is easy to identify; it is the a: The two jets, you notice, shoot out along the spin axis. They are born just above the ho-rizon's north and south poles, where they suck up energy from the hole's spin and from the doughnut 34 much like a tornado sucks up dust from the earth.
The contrast between Gargantua and 3C. Why does Gargantua, with its times greater mass and size, not possess an encircling doughnut of gas and gigantic quasar jets?
Once every few momhs a star in orbit around 3C's smaller hole strays close to the horizon and gets ripped apart by the hole's tidal force. The st. Gradually internal friction drives the strewn-out gas down into the doughnut. This fresh gas compensates for the gas that t. The doughnut and jets thereby are kept ric-. Stars also stray close to Gargantua, Bret explains. But because Gar gautua is far larger than 3C, the tidal fon. Gargantua swallows stars whole without spewing their guts into a surrounding donghnut.
And with no doughnut, Gargantua has way of producing ets or other quasar violence. As your starship continues to rise out of Gargantua's gravitational grip, you make plans for the journey home.
The changes in hwnan society will be so enormous that you don't want to return there. Instead, you and your crew decidt- to You know that just as the spin t? You do not want to arrive at some chosen hole and discover tltat other beings have already built a civilization around it; so instead of aimi11g youx starship at a rapidly spinning hole that already exists, you aim at a star system which w.
DAWN has calculated that each of those stars should have implod. Those two solar-mass holE: Several days after you arrive, you will see the holes' nonspinnin. Because the t. Home Arter a year voyage your starship finally decelerates into the Orion nebula, where DAWN predicted the two holes should be. There they are, right on the mar. Each horizon has a circumfereilC'.
Inserting these nwnbers into the general relativity formulas for gravitational-wave recoil, you conclude that the two holes should coalesce seven days from now. There is just time enough for your crew to prepare their telescopic cameras and record the details. By photographing the bright ring of focused starlight that encircles each hole's black disk, they can easily monitor the holes' motions.
You Wa. A good location, you decide, is a starship orbit ten times larger than the orbit in which the holes circle each other--an orbital diameter of , kilometers and orbital circumference of , kilometers. Kares maneuvers the starship into that orbit, and your crew begin their telescopic, photographic observations.
Over the next six days the two hoJes gradually move closer to each other and speed up their orbital motion. One day before coalescence, the distance between thf'.
One minute before coalescence: Ten seconds before coalescence: Then 1 in the last ten seconds, you and your starship begin to shake, gently at first, then more and rnore violently. And then, more suddenly than it started, the shaking stops. All is quiet. You are accustomed to gravitational waves so weak that only very delicate instruments can detect their tidal force.
However, here, close to the coalescing holes, they were enormously strong--strong enough that, had we parked our starship in an orbit 30 times smaller, it would have been torn apart by the waves. But now we are safe. The coalescence is complete and the waves are gone; they are on their way out into the Universe, carrying to distant astronomers a symphonic description of the coalescence. Training one of your crew's telescopes on the source of gravity below, you see that DAWN is right, the coalescence is contplete.
Where before there were two l1oles there now is just one, and it is spinning rapidly, as you see from the swirl of infalling atoms. This hole will make an ideal power generator for your crew and thousands of generations of their descendants. By measuring the starship's orbit, Kares deduces that the hole weighs 45 solar: Since the parent holes totaled 48 solar masses, 3 solar masses must have bec?. No wonder the waves shook you so hard! As you tum your telEPScopes toward the hole, a small object unexpectedly hurtles past your starship, splaying brilliant sparks profusely in all directions, and then explodes, blasting a gaping hole in your ship's side.
Your well-trained crew and robots rush to their battle stations, you search vainly for the attacking warship--and then, responding to at1 appeal for her help, DAW J announces soothingly over the ship's speaker system, "Tikhii, tikhii; we are not being attacked. That was just a freak primordial black hole, evaporating and then exploding. N repeats. What do you mean by evaporating and exploding?
You're not making sense. Things can fall into a black hole, but nothing can ever cotne out; nothing can 'evaporate. There is uo way a black hole can 'explode' and destroy itself. That's absurd. By contnlst, tiny objects-- for example, atoms, molecules, and black holes smaller than a..
They demand that any atom-sized black bole gradually evaporate and shrink until it reaches a critically small circumference, The hole, which despite its tiny size weighs about a billion tons, must then destroy itself in an enormous explosion. The explosion converts all of the hole's billion-ton mass into outpouring energy; it is a trillion times more energetic than the most powerful nuclear explosions that humans ever detonated on Earth in the twentieth century.
Just such an explosion has now damaged our ship,u DAWN explains. The only place that tiny holes were ever created was in our Universe's big bang birth, twenty billion years ago; that is why they are called primordial holes. The big bang created only a few such primordial holes, and those few have been slowly evaporating and shrinking ever since their birth.
Once in a great while one of them reaches its critical, smaJiest size and explodes. The hole's spin is obvious not only from the swirl of infalling atoms, but also from the shape of the bright-ringed black spot it makes on the sky below you: The black spot is squashed, like a pumpkin; it bulges at its equator and is flattened at its poles.
The centrifugal force of the hole's spin, pushing outward, creates the bulge and flattening. DAWN explains that this is because the horizon can capture rays of starlight more easily if they move toward you along its right edge, against the direction of its spin, than along its left edge, with its spin. By measuring the shape of the spot and comparing it with general relativity's black-hole formulas, Bret infers that the hole's spin angular momentum is 96 percent of the maximum allowed for a hole of its mass.
And from this angular momentum and the hole's mass of 45 Suns you compute other properties of the hole, including the spin rate of its The spin of the hole intrigues you. Never before could you observe a spinning hole up close. So with pangs of conscience you ask for and get a volunteer robot, to explore the neighborhood of the horizon and transmit back his experiences. You giYe the robot, whose name is Kolob, careful instructions: Use your rockets to resist both the inward pull of gravity and the tornado-like swirl of space.
At first Kolob has no problems. But when he reaches a circumference of kilometers, 56 percent larger than the horizon, his laser light brings the message, "I can't resist the swirl; I can't; I can't!
AB he descends, he is dragged into more and more rapid circulating motion. Finally, when he stops his descent and hovers ten meters above the horizon, he is encircling the hole in near perfect lockstep with the horizon itself, circuits per second. No matter how hard he blasts to oppose this motion, he cannot. The swirl of space won't let him stop. He blasts. Although he feels the usual acceleration from his blast, you see his motion change hardly at all. He still circles the hole times per second.
And then, before you can transmit further instructions, his fuel gives out; he begins to plummet downward; his laser light zooms through the electromagnetic spectrum from green to red to infrared to radio waves, and then turns blaclt with no change in his circulating motion.
He is gone, dawn the hole, plunging toward the violent singularity that you will never see. Bringing in materials from distant planets, they construct a girder-work ring around the hole. The ring has a circumference of 5 million kilometers, a thickness of 3. It rotates at just the right rate, two rotations per hour, for centrifugal forces to counterbalance the hole's gravitational pull at the ring's central layer, 1. Its dimensions are carefully chosen so that those people who prefer to live in 1 Earth gravity can set up their homes near the inner or outer face of the ring, while those who prefer weaker gravity can live nearer its center.
These differences in gravity are due in part to the rotating ring's centrifugal force and in part to the hole's tidal force--or, in Einstein's language, to the curvature of spacetime. The electric power that heats and lights this ring world is extracted from the black hole: Twenty percent of the hole's mass is in the form of energy that is stored in the tornado-like swirl of space outside but near the horizon.
Never mind that the ring world's energy extractor is only 50 percent efficient; it still has a times greater energy supply than the Sun. The energy extractor works on the same principle as do some quasars Your crew have threaded a magnetic field through the hole's horizon and they hold it on the hole, despite its tendency to pop off, by means of giant superconducting coils Figure P.
The magnetic field lines act as transmission lines for the power. There the current deposits its power. The-n it flows out of the ring world on another set of magnetic field lines and down into the hole's north and south poles in the form of positrons flowing inward. By adjusting the strength of the magnetic field, the world's inhabitants can adjust the power output: Gradually as the power is extracted, the hole will slow its spin, but it Chapters 7 and Chapters 9 and Your crew and countless generations of their desrendants can call this artificial world "home" and use it as a base for iuture explorations of the Universe.
But not you. You long for the Narth and the friends whom you left behind, friends who must have been dead now for more t. Time travel into the future is rather easy, as your voyage among the holes has shown. Not so travel into the past.
In fact, such travel might be completely forbidden by the fundamental laws of physics. However, DAWN tells you of specuJations1 dating badt to the twentieth century, that backward time travel might be achieved with the aid of a hypothetical space warp called a wormhole.
Ou1pter Anything that enters one mouth finds itself in a very short tube the wormhole's throat that leads to and out of the other mouth. The tube cannot be seen from our Universe because it extends through hyperspace rather than through normal space. It might be possible for time to hook up through the wormhole.
By traversing t. Such a wormhole would be a time warp, as well as a space warp. These quantum wormholes must be so tiny, just 1o-. They Chapters 13 and DAWN proposes to try to catch such a wormhole as it flickers, enlarge it like a child blowing up a balloon, and keep it open long erough for you to travel through it to the home of your youth.
But DAWN warns you of great danger. Physicists have conjectured, t. By waiting nearby as she enlarges the wormhole and then plunging through it, within a fraction of a second of your own time you will arrive home on Earth, in the era of your youth 4 billion years ago. But if the time machine self-destructs, you will be destroyed with it. You decide to take the chance Indeed, part of it is: I cannot by any means guarantee that there exists a solar-mas.
Nor can I guarantee that humans will ever succeed in developing the technology for intergalactic travel, or even for interstellar tl'avel, or for constructing ring worlds on girder-work structures around black holes. These are also speculative fiction. Chapter t I guarantee that, if you send a robot probe down near the horizon of a spinning hole, blast as it may it will never be able to move forward or backward at any speed other than the hole's own spin speed circuits per second in my example.
I guarantee that a rapidly spinning hole can store as mucb as 29 percent of its mass as spin energy, and that if one is clever enmtgh, one can extract that energy and use it. How can I guarantee all these things with considerable confidence?
After all, I have never seen a black hole. Nobody has. Astronomers have found only indh-ect evidence for the existence of black holes47 and no observational evidence whatsoever for their claimed detailed properties.
How can I be so audacious as to guarantee so much about them? For one simple reason. Just as the laws of physics predict the pattern of ocean tides on Earth, the time and height of each high tide and each low tide, so also the laws of physics, if we understand them correctly, predict these black-hole properties, and predict them with no equivocation.
From Newton's description of the laws of physics one can deduce, by mathematical calculations, the sequence of Earth tides for the year or the year ; similarly, from Einstein's general relativity description of the laws, one can deduce, by mathematical calculations, everything there is to know about the properties of black holes, from the horiz.
And why do I believe that Einstein's general relativity description of the fundamental laws of physics is a highly accurate one? Successful descriptions of the fundame11tal laws contain within themselves a strong indication of where they will faiL 48 Newton's description tells us itself that it will probably fail near a black hole though we only learned in the twentieth century how to read this out of Newton's description.
Similarly, Einstein's general: This is one thing that gives me confidence in general relativity's predictions. Chapters 8 and 9. Last section of Chapter 1. General relativity has come through each teSt with flying colors.
Over the pa. My own co11tributions have been modest, but with my physicist and astronomer colleagut. This book is my attempt to convey some sense of that excitement and marvel to people who are not experts in either astronomy or physics.
Please forgive a father who is so bold as to turn to you, esteemed Herr Professor, in the interest of his son. Since then, he has been trying unsuccessf: All those in position to give a judgment in the matter, praise his talents; in any case, I can assure you that he is extraordinarily studious and diligent and clings with gl"E'.
My son therefore feels profoundly unhappy with his present lack of. If, in addition, you could secure him an A. I beg you once again to forgive me for roy impudenC'e in writing to. He had been jobless for eight months, since graduating from the Zurich Po itechnikum at age twenty-one, and he felt himself a failure. At the Polite-chnikum usually called the..
ETH" after its Germanlanguage initials , Einstein had studied under several of the wol'ld's most renowned physicisu and mathematicians, but had not got on well with them. In the tun1-of-the-century academic world where most Professors wit. Since childhood he had bristled against authol'ity, always questioning, never accepting anything without testing it. Heinrich Weber, the most famous of his two ETH physics professors, complained in exasperation: But you have one great fault: His mathe-.
He was just selective. Some parts of the coursework. Thinking was fun, joyful, and satisfying; on his own he could learn about the "new" physics, the physics that Heinrich Weber omitted from all his lectures. Newton's Absolute Space and Time, and the Aether The "old" physics, the physics that Einstein could learn from Weber, was a great body of knowledge that I shall call Newtonian, not because Isaac Newton was responsible for all of it he wasn't , but because its foundations were laid by Newton in the seventeenth century.
By the late nineteenth century, all the disparate phenomena of the physical Universe could be explained beautifully by a handful of simple Newtonian physical laws. For example, all phenomena involving gravity could be explained by Newton's law. Every object moves uniformly in a straight line unless acted on by a force.
When a force does act, the object's velocity changes at a rate pro portional to the force and inversely proportional to its mass. Between any two objects in the Universe there acts a gravitational force that is proportional to the product of their masses and inversely proportional to the square of their separation. By mathematically manipulating1 thE'.. Similarly, by manipulating a simple set of electric and magnetic laws, the physicists could explain lightning, magnets, radio waves, and the propagation, diffraction, and reflection of light.
Readers who wish! Fame and fortune awaited those who could harness the Newtonian laws for technology. Everything in the heavens and on Earth seemed to obey the Newtonian laws of physir.. An the old, well-established Newtonian laws and their technological applications Einstein could learn in Hei11rich Weber's lectures, and learn well. To the sole woman in his F.
TH class, Mileva Marie of whom he was e-namored , he wrote in February , "Weber lectured masterfully. J eagerly anticipate his every class. Weber lectured only on the old physics. He completely ignored some of the most important developments of recent decades, including James Clerk Maxwell's discovery of a new set of elegant electromagnetic Jaws from which one could deduce all electromagnetic phenomena: Einstein had to teach himself Maxwell's unifying laws of electromagnetism by reading up-to-date books written by physicists at other universities, and he presumably did not hesitate to inform Weber of his dissatisfaction.
His relations with W eober deteriorated. Ne-wton's absolute space was the spat. It was obvious from. We all move through this space in our own ways and at our own speeds, and regardless of our motion, we experience the space in the same way.
Newton's absolute time was the time of everyday experience, the time that flows inexorably forward as we age, the time measured by high-quality clocks and by the rotation of the Earth and motion of the planets.
It is a time whose flow is experienced in common by all humanity, by the Sun, by all the planets and the stars. According to Newton we all, regardless of our motion, will agree on the period of some planetary orbit or the duration of some politician's speech, so long as we all use sufficiently accurate clocks to time the orbit or speech.
If Newton's concepts of space and time as absolute were to crumble, the whole edifice of Newtonian physical laws would come tumbling down. Fortunately, year after year, decade after decade, century after century, Newton's foundational concepts had stood firm, producing one scientific triumph after another, from the domain of the planets to the domain of electricity to the domain of heat.
There was no sign of any crack in the foundation-until , when Albert Michelson started timing the propagation of light. If one is at rest in absolute space, then one should see the same light speed in all directions. By contrast, if one is moving through absolute space, say eastward, then one should see eastward-propagating light slowed and westward-propagating light speeded up, just as a person on an eastbound train sees eastward-flying birds slowed and westward-flying birds speeded up.
For the birds, it is the air that regulates their flight speed. Beating their wings against the air, the birds of each species move at the same maximum speed through the air regardless of their flight direction. Similarly, for light it was a substance called the aether that regulated the propagation speed, according to Newtonian physical laws.
Beating its electric and magnetic fields against the aether, Jight propagates always at the same universal speed through the aether, regardless of its propagation direction. And since the aether according to Newtonian concepts is at rest in absolute space, anyone at rest will measure the same light speed in all directions, while anyone in motion will measure different light speeds. Now, the Earth moves through absolute space, if for no other reason than its motion around the Sun; it moves in one direction in Januw: To verify this prediction was a fascinating challenge for experimental physicists.
Albert Michelson, a tweilty--eight-year--old American, took up the challenge in , using an exquisitely areurate ex. But try as he might, Michelson could find no evidence whatsoever for any variation of light speed with direction. The speed turnt. Michelson reacted with a mixture of elatiolt at his discovery and dismay at its consequem. Heinrich Weber and most other physicists of the s reacted with skepticism. It was easy to be skeptical Interesting experimentS are often terribly difficult- -so difficult, in fact, that regardless of how carefully they are carried out, they can give wrong results.
Just one little abnormality in the apparatt1s, or one tiny uncontrolled fluctuation in its temperature, or one unexpected vibration of the floor beneath it, might alter the e"periment's final result. Thus, it is not surprising that physicists of today, like physicists of the ts, are occasional! Recent examples are experiments that purported to discover a "fifth force" one not present in the standard, highly successful physical laws and other experiments denyi: Almost always the experiments that threaten our deeply cherished beliefs are wrong; their radical results are artifacts of experimental error.
However, occasionally they are right and point the way toward a revolution in our understanding of nature. One mark of an outstanding physicist is an ability to "smell" which 2. J' As technology improves and the experiments are repeated over and over again, the truth ultimately becomes clear; but if one is trying to contribute to the progress of science, and if one wants to place one's own imprimatur on major discoveries, then one needs to divine early, not later, wl1ich experiments to trust.
Several outstanding physicists of the s examined the Michelson-Morley experiment and concluded that the intimate details of the apparatus and the exquisite care with which it was executed made a strongly convincing case. This experiment "smells good," they decided; something might well be wrong with the foundations of Newtonian physics.
By contrast, Heinrich Weber and most others were confident that, given time and further experimental effort, all would come out fine; Newtonian physics would triumph in the end, as it had so many times before. It would be inappropriate to even mention this experiment in one's university lectures; one should not mislead young minds. The Irish physicist George F. Fitzgerald was the first to accept the Michelson-Morley experiment at face value and speculate about its implications.
By comparing it with other experiments, he came to the radical conclusion that the fault lies in physicists' understanding of the concept of "length," and correspondingly there might be something wrong with Newton's concept of absolute space. In a short article in the American journal Science, he wrote in part: I have read with much interest Messrs.
Michelson and Morley's wonderfully delicate experiment Their result seems opposed to other experiments I would suggest that almost the only hypothesis that can reconcile this opposition is that the length of material bodies changes, according as they are moving through the aether [through absolute space] or ac A tiny five parts in a billion contraction of length along the direction of the Earth's motion could, indeed, account for the null result of the Michelson-Morley experiment.
But this required a repudiation of physicists' understanding of the behavior of matter: No known force could make moving objects contract along their direction of motion, not even by so minute an amount. If physicists understood correcdy the nature of space and the nature of the molecular forces inside solid bodies, then uniformly moving solid bodies would always have to re-.
Fitzgerald, upon learning of this, wrote to Lorentz expressing delight, since ''I have been rather laughed at for my ,,.
However, if one expressed Maxwell's laws in terms of the slightly different fields measured by a moving person, then the laws looked far more complicated and ugly. In particular, the "no ends'' law became, "As seen by someone in motion, most magnetic field lines are endless, but a few get cut by the motion, thereby acquiring ends. The new rnathematical discovery by T.. If the ritzgerald contraction had been the only "new physics" that one needed to make the electromagnetic laws universally simple and beautiful, Lorentz, Poincare, and Larmor, with their intuitive faith that the laws of physii:!
S ought to be beautiful, might have cast aside Newtonian precepts and believed firmly in the contraction. However, the contraction by itself was not enough. Each field line leaves the magnet's north pole, s''Yings around the magnet and reenters it at the south pole, and then travels through the magnet to the north polt'. The field line is therefore a closed cun-t'. The statement that "magnetic field lines never have ends,.
S, this version of Maxwell's law is coiTect no matter what one does with the magnet for example, even if one shakes it wildly so long as one is at rest in absolute space. No ID8fl! Now, the Newtonian laws of physics were unequivocal: Time is absolute. It flows uniformly and inexorably at the sante universal rate,. If the Newtonian laws were correct, then motion cannot cause time to dilate any more than it c-. Unfortunately, the clocks of the s were far too inaccurate to reveal the truth; and, fa--ed with the scientific and technological triwnphs of Newtonian physics, triumphs grounded firmly on the foundation of absolute time, nobody was willing to assert with conviction that time really does dilate.
Lorentz, Poincare, and Larmor waffled. To his frien. Weber, by contrast, showed no interest in such speculative issues. He kept right on lecturing about Newtonian physics as though all were in perfect order, as though there were no hints of cracks in the foundation of physics. As an Assistent he could start doing research of llis own, leading in a few years to a Ph. But such was not to be. Of the four students who passed their final exams in the combined physics-mathematics program in August , three got assistantships at the ETH working under mathematicians; the fourth, Einstein, got nothing.
Weber hired as Assistents two engineering students rather than Einstein. Einstein kept trying.
In September, one month after graduation, he applied for a vacant Assistent position in mathematics at the ETH.
He was rejected. From them he seems never to have received even the courtesy. To the saucy and strong-willed Mileva Marie, with whom his romance had turned intense, Einstein wrote on 27 March , "I'm absolutely convinced that Weber is to blame All the same, I leave no stone unturned and do not give up my sense of humor God created the donkey and gave him a thick hide.
Of Mileva his mother wrote, "This Miss Maril: I wouldn't have thought it possible that there could exist such heartless and outright wicked people! Perhaps this could be achieved by some means other than an Assistent position in a university. He managed in mid-May to get a temporary job at a technical high school in Winterthur, Switzerland, substituting for a mathematics teacher who had to serve a term in the anny. To his former history professor at the ETH, Alfred Stern, he wrote, "I am beside myself with joy about [this teaching job], because today I received the news that everything has been definitely arranged.
I have not the slightest idea as to who might be the humanitarian who recommended lne there, because from what I have been told, I am not in the good books of any of my former teachers. Despite continued turbulence in his personal life long sepa1ations fn'lm Mileva; an illegitimate child with Mileva in , whom they seem. Fro1n l through he seasoned his powers as a physicist by theorE'tical research on the nature of the forces between molecules in liquids, such as water, and in metals, and research on the.
On the job he was challenged to flgure out whP. And the job left free half his waking hours and all weeke11d. Most of these he spent studying and thinking about physics, often in the midst of family dtaos. His abili. With the words, 'Wait a minute, I've nearly finished,' he gave me the children to look after for a.
For most physicists, such isolatioll would be disastrous. Most require continual contact with colleagues working on similar problems to keep their researclt from straying off in unproductive directions. But Einstein's intellect was different; he worked mo: Sometimes it. Einstein seated at his desk in the patent oft'ioe in Bern, Switzerland, ca.
Einstein with his wife, Mileva, and their son Hans Albert, ca. Of Besso, Einstein said, "I could not have found a better sounding board in the whole of Europe. Einstein's Relative Space and Time, and Absolute Speed of Light Michele Angelo Besso was especially helpful in May , when Einstein, after focusing for several years on other physics issues, returned to Maxwell's electrodynamic laws and their tantalizing hints of length contraction and time dilation.
Einstein's search for some way to make sense of these hints was impeded by a mental block. To clear the block, he sought help from Besso. As he recalled later, "That was a very beautiful day when I visited [Besso] and began to talk with him as follows: So I came here today to bring with me a battle on the question.
The next day I visited him again and said to him without greeting: I've complet. There is no such thing as absolute space. There is no such thing as absolute time. Newwn 's foundation for all ofphysics was flawed And as for the aether: It does not exisL By rejecting absolute space, Einstein made absolutely meaningless the notion of "being at rest in absolute space.
One can measure the Earth's velocity only relative to other physical objects such as the Sun or the Moon, jt1st as one can measure a train's velocity only relative to physical objects such as the ground and the air. For neither Earth nor train nor anything else is there any standard of absolute motion; motion is purely "relative.
On the contrary, Einstein insisted, length, height, and width are "relati1-V! They depend on the relative motion of the object being measured and the person doing the measuring. By rejecting absolute time, Einstein rejected the notion that everyone, regardless of his or her motion, must experience the flow of time in the same manner.
Time is relative, Einstein asserted. Each person traveling in his or her own way must experience a different time flow than others, traveKng differently. It is hard not to feel queasy when presented with these assertions. If correct, not only do they cut the foundations out from under the entire edifice of Newtonian physical law, they also deprive us of our commonsense, everyday notions of space and time.
But Einstein was not just. He was also a creator. He offered us a new foundation to replace the old, a foundation just as firm and, it has tnmed. Einstein's new foundation consisted of two new fundamental principles: The principle of the absoluteness of the speed of light: Whatever might be their nature, space and time must be so constituted as to.
This principle is a resounding affirmation that the Michelson--Morley experiment was correct, and that regardless of how accurate lightmeasuring devices may become in the future, they must always continue to give the same result: The principle of relativity: Whatever might be their nature, the laws of physics must treat all states or" motion on an equal footing.
This principle is a resounding rejection of absolute space: If the laws of physics did not treat all states of motion for example, that of the Sun and that of the Earth on an equal footing, then using the laws of physics, physicists would be able to pick out some "preferred" state of motion for example, the Sun's and define it as the state of "absolute rest.
We shall return to this later in the chapter. From the absoluteness of the speed of light, Einstein deduced, by an elegant logical argument described in Box 1.
This "mixing of space and time" is analogous to the mixing of directions on Earth. Nature offers us two ways to reckon directions, one tied to the Earth's spin, the other tied to its magnetic field. In Pasadena, California, magnetic north the direction a compass needle points is offset eastward from true north the direction toward the Earth's spin axis, that is, toward the "North Pole" by about 20 degrees; see Figure 1. This means that in order to travel in the magnetic north direction, one must travel partly about 80 percent in the true north direction and partly about 20 percent toward true east.
You like to drive your car down Colorado Boulevard in Pasadena, California, at extremely high speed in the depths of the night, when I,. To the top of your car you attach a series of firecrackers, one over the front of the hood, one OYer the rear of the trur1k, and many in between; see 'Pigure 1.
You set the firecrackers to detonate simu. Figure 1. Drawn vertically is the flow of time, as measured by you "your time'". Drawn horizon tally is distance along your car, from back to front, as measured by yott "your space". Since the firecrackers are all at rest in your space that is, as seen by you , with the- passage of your time they all remain at the same horizontal locations in the diagram.
The dashed lines, one for each firecracker, depict this. They extend vertically upward in the diagram, indicating no rightward or leftward motion in space whatsoever as time passes--and they then terminate abruptly at the moment the firecrackers detonate. The detonation events are depicted by asterisks.
This figure is called a spacetime diagram because it plots space hori.. Correspondingly, it is convenient to think of each horizontal line in the diagram as depict. For example, the dotted horizontal line is youl" space at the moment of firecracker detonation. Correspondingly, it is convenient to think of eac-.
I, in the police station, were I not napping, would draw a rather different spacetime diagram to depict your car, your firecrackers, and the detonation Figure 1. I would plot the flow of time, as measured by me, vertically, and distance along Colorado Boulevard horizontally.
As time passes, each firecracker moves down Colorado Boulevard with your car at high speed, and corrE'. At the time of its detonation, the firecracker is farther to the right down Colorado Boulevard than at earlier times. Now, the surprising conclusion of Einstein's logical argument Box 1. From my viewpoint the rearmost firecracker on your car detonates first, and the frontmost one detonates last. Correspondingly, the dotted line that we called "your space at moment of detonation" Figure 1.
From Figure 1. In this sense, your space is a mixture of my spare and my time. This is just the same sense as the statement that magnetic north is a mixture of true north and true east compare Figure t. You might be tP. However, physicists, building on I-: It has helped them to decipher Einstein's legacy his new laws of physics , and to discover in that legacy a set of seemingly outrageous phenomena: From the absoluteness of the speed of light and the principle of relativity, Einste-in deduced other remarkable features of space and time.
In the language of the above story: Einstein deduced that, as you speed eastward down Colorado Boulevard, I must see y9ur space and everything at rt-. This was the contraction inferred by Fitzgerald, but now put on a firm foundation: The contraction is caused by the peculiar nature of space and time, and not by any physical forces that act on moving matter.
Similarly, Einstein deduced that, as you speed eastward, you must see my space and everything at rest in it my police station, my desk, and me contracted along the east-west direction, but not north-south or up-down. That you see me contracted and I see you contracted may seem puzzling, but in fact it could not be otherwise: It leaves your state of motion and mine on an equal footing, in accord with the principle of relativity.
Einstein also deduced that, as you speed past, I see your flow of time slowed, that is, dilated. The clock on your car's dashboard appears to tick more slowly than my clock on the police station. Einstein's Proof of the Mixing of Space and Time Einstein's principle of the absoluteness of the speed of light enforces the mixing of space and time; in other words, it enforces the relativity of simultaneity: Events that are simultaneous as seen by you that lie in your space at a specific moment of your time , as your sports car speeds down Coloudo Boulevard, are not simultaneous as seen by me, at rest in the police station.
I shall prove this using descriptive words that go along with the spacetime diagrams shown below. This proof is essentially the same as the one devised by Einstein in Place a flash bulb at the middle of your car. Trigger the bulb. It sends a hurst of light forward toward the front of your car, and a burst backward toward the hack of your car.
Since the two bursts are emitted simultaneously, and since they travel the same distance as measured by you in your car, and since they travel at the same speed the speed of light is absolute , they must arrive at the front and back of your car simultaneously from your viewpoint; see the left diagram, below. The two evt-. Next, examine the light bursts and their arrival events A and B from my viewpoint as your car speeds past me; see the right diagram, below.
From my viewpoint, the back of your car is moving forward, toward the backward-directed burst of light, and they thus meet each other event B sooner as seen by me than as seen by you. Similarly, the front of your car is moving forward, away from the frontward-directed burst, and they thus meet each other event A later as seen by me than as seen by you. These conclusions rely crucially on the fact that the speeds of the two light bursts are the same as seen by me; that is, they rely on the absoluteness of the speed of light.
Therefore, I regard event Bas occurring before event A; and similarly, T see the firecrackers near the back of your car detonate before those near the front. Note that the locations of the detonations your space at a specific moment of your time are the same in the above spacetime diagrams as in Figure 1. This justif1es the asserted mixing of space and time discussed ]n the text.
Sjmilarly, in accord with the principle of relativity, as you speed past rne, you see my fiow of time slowed.
You see the clock on my station wall tick more slowly than the e on your dashboard. To you I seem to speak more slowly, rny hair gro""-s more slowly, and I age more slowly than you. How can it possibly be that I see your time flow slowed, while you see mine slowed? How is that. The answer lies in the relativity of simultaneity. You and. I disagree about whether events at difftorent locations in our respective spaces are simultaneous.
To de1nonstrate this consistency, howevt-. How is it that we as humans have never noticed this weird behavior of space and time ii1 our everyday lives?
Tl1e answer lies in our slowness. We always move relative to each other with speeds far Sinaller than that of light. If your C'ctr Indeed, a wide variety of ex-periments in the late twentieth century have verified that spaee and titne do behave in just this way.
Not by examining the results of experiments. Clocks of his era were too inaccurate to exhibit, at the low speeds available, any time dilation or disagreements about simultaneity, and measuring rods weie- too inaccurate to exhibit length contraction. The only relevant e per.
These were very skimpy data indeed on which to base such a radical revision of one's notions of space and time! Moreover, Einstein paid little attention to these experiments. Instead, Einstein relied on his own innate intuition as to how things ought to behave.
After much reflection, it became intuitively obvious to him that the speed of light must be a universal constant, independent of direction and independent of one's motion. Only then, he reasoned, could Maxwell's electromagnetic laws be made uniformly simple and beautiful for example, "magnetic field lines never ever have any ends" , and he was firmly convinced that the Universe in some deep sense insists on having simple and beautiful laws.
He therefore introduced, as a new principle on which to base all of physics, his principle of the absoluteness of the speed of light.
This principle by itself, without anything else, already guaranteed that the edifice of physical laws built on Einstein's foundation would differ profoundly from that of Newton. Having deduced that space and time are relative, Einstein was then led onward by his questfor simplicity and beauty to his principle ofrelativity: Not only was experiment unimportant in Einstein's construction of a new foundation for physics, the ideas of other physicists were also unimportant.
He paid little attention to others' work. He seems not even to have read any of the important technical articles on space, time, and the aether that Hendrik Lorentz, Henri Poincare, Joseph Larmor, and others wrote between and In their articles, Lorentz, Poincare, and Larmor were groping toward the same revision of our notions of space and time as Einstein, but they were groping through a fog of misconceptions foisted on them by Newtonian physics.
Einstein, by contrast, was able to cast off the Newtonian misconceptions. His conviction that the Universe loves simplicity and beauty, and his willingness to be guided by this conviction, even if it meant destroying the foundations of Newtonian physics, led him, with a clarity of thought that others could not match, to his new description of space and time. The principle of relativity will play an important role later in this book.
F01 this reason 1 shall devot. A deeper explanation requires the concept of a reference.