The term black hole is of very recent origin. It was coinedin 1969 by the American scientist John Wheeler as a graphicdescription of an idea that goes back at least two hundredyears, to a time when there were two theories about light: one,which Newton favored, was that it was composed of particles;the other was that it was made of waves. We now know thatreally both theories are correct. By the wave/particle duality ofquantum mechanics, light can be regarded as both a wave anda particle. Under the theory that light is made up of waves, itwas not clear how it would respond to gravity. But if light iscomposed of particles, one might expect them to be affected¹ bygravity in the same way that cannonballs, rockets, and planetsare. At first people thought that particles of light traveledinfinitely fast, so gravity would not have been able to slow themdown, but the discovery by Roemer that light travels at a finitespeed meant that gravity might have an important effect.
On this assumption, a Cambridge don, John Michell, wrote apaper in 1783 in the Philosophical² Transactions of the RoyalSociety of London in which he pointed³ out that a star that wassufficiently massive and compact would have such a stronggravitational field that light could not escape: any light emittedfrom the surface of the star would be dragged back by thestar’s gravitational attraction before it could get very far. Michellsuggested that there might be a large number of stars like this.
Although we would not be able to see them because the lightfrom them would not reach us, we would still feel theirgravitational attraction. Such objects are what we now call blackholes, because that is what they are: black voids in space. Asimilar suggestion was made a few years later by the Frenchscientist the Marquis de Laplace, apparently⁵ independently ofMichell. Interestingly enough, Laplace included it in only the firstand second editions of his book The System of the World, andleft it out of later editions; perhaps he decided⁶ that it was acrazy idea. (Also, the particle theory of light went out of favorduring the nineteenth century; it seemed that everything couldbe explained by the wave theory, and according to the wavetheory, it was not clear that light would be affected by gravityat all.)In fact, it is not really consistent to treat light likecannonballs in Newton’s theory of gravity because the speed oflight is

分享到：