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.The awards werelike the sugar frosting on the cake.I wouldn t say that is what makes all theblackness worth while.I don t think I am ever going to reconcile in my mind theswings of the pendulum that we have experienced in this house really from thedepth of a black hole to all the glittering prizes.8She explained to another journalist that her role was no longer tolook after a sick man but simply to tell him that he s not God. 9Perhaps in such statements as this the murmurings of deep-rootedresentments and disquiet can be detected.Yet in the concludingscene of the BBC s Master of the Universe program we see Stephenand Jane looking down on a sleeping Timothy in their house onWest Road while Hawking s computer voice declares, I have abeautiful family, I am successful in my work, and I have written abest-seller.One really can t ask for more. 10Hawking s children have always known that their father can be adifficult man to live with at times.In the late eighties, Lucy, in theMaster of the Universe documentary, said:I m not as stubborn as him.I don t think I would want to be that stubborn.I don tthink I have quite his strength of mind, which means he will do what he wants todo at any cost to anybody else.11 291Hollywood, Fame, and FortuneSuch stubbornness was to hold him in good stead as his personallife began to crumble and the pressures of global fame started toimpinge seriously upon him.While Hawking was reaching the pin-nacle of his success outside science, new complications began toaffect him as he made the transition from celebrity to icon. 17A Brief History of Time Travelven though Stephen Hawking turned fifty in 1992 (coin-cidentally, the year in which the first edition of this bookEwas published) and had forecast the death of physicstwelve years earlier, he has continued to be involved in scientificresearch since then.But like many grand old men of science (adescription which, against all the odds, is now an entirely apt onefor Hawking), in his later years he has turned his attention to ideasat the wilder fringes of scientific respectability.During the middlepart of the 1990s, Hawking s research contributions largelyinvolved the paradoxes and possibilities of time travel a field heentered not as a pioneer, but following in the footsteps of his oldfriend and scientific sparring partner, Kip Thorne.You may be surprised to learn that the subject of time travel is arespectable area of research at all, even at the wilder fringes ofrespectability.If so, you are not alone.When one of us wrote a bookabout time travel1 and it was reviewed in the pages of the astro-nomical magazine Observatory, the magazine received an irate letterfrom two engineers at the University of Hull, castigating the editors292 293A Brief History of Time Travelfor lending credence to such ridiculous notions by even acknowledg-ing the existence of the book.But everything in that book, and every-thing we have to tell you in this chapter, is based on solid, respectablescience, jumping off from the work of Thorne and the equally emi-nent Igor Novikov (formerly of the Soviet Union, now working inDenmark) and, of course, of Hawking himself.Building a timemachine may not yet be a practicable engineering prospect, but thepossibility that natural time machines may exist is one that anincreasing number of scientists are now taking very seriously indeed.The physical description of a working time machine that hasintrigued Hawking and other researchers recently is closely relatedto the physics of baby universes, described in Chapter 13.On thatscenario, matter that collapses into a black hole and toward a sin-gularity in our Universe can somehow be shunted sideways inspace-time, emerging to form a new expanding universe, in its ownset of space-time dimensions.But what we did not spell out in ourearlier discussion is that in principle the original black hole and thenew baby universe are still connected by the cosmological equiva-lent of an umbilical cord, a tunnel through space-time that the cos-mologists prosaically refer to as a wormhole. In the context ofbaby universes, such a wormhole would have a diameter compara-ble to the smallest quantum of length (the Planck length, about10 35 m) and since no information could get out of the black holemarking the end of the wormhole in our Universe, the connectionseems to be only of academic interest.But there is another way of looking at wormholes, one that haslong been a favorite of science fiction writers.The equations of thegeneral theory of relativity also allow for the existence of a moremodest kind of wormhole, which links two places in our ownUniverse.Einstein himself, working with Nathan Rosen atPrinceton in the 1930s, worked out the appropriate mathematical 294 STEPHEN HAWKINGdescription of such a wormhole, which is known as an Einstein-Rosen bridge.The usual problems with wormholes apply to an Einstein-Rosenbridge, which is, in effect, a wormhole linking two black holes inour Universe a shortcut through space-time.Such a wormholecould form naturally, the equations say; but the gravity of the blackholes at either end of the tunnel would snap the wormhole shutfaster than light could travel along it, closing it before there wastime for anything to get from one end to the other.This result was so well known that for fifty years no relativistsbothered to study the equations describing such wormholes indetail.But that didn t stop the SF writers leaping on the idea andusing it as a basis for moving their characters (and spaceships)around the Universe more or less instantaneously
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