The Physics of Star Trek by Lawrence M. Krauss Read Free Book Online Page B

three-dimensional wormhole, which could, in principle,
     connect distant regions of space-time. As exciting as this possibility is, there are
     several deceptive aspects of the picture which I want to bring to your attention. In the
     first place, even though the rubber sheet is shown embedded in a three-dimensional space
     in order for us to “see” the curvature of the sheet, the curved sheet can exist without
     the three-dimensional space around it needing to exist. Thus, while a wormhole could exist
     joining A and B, there is no sense in which A and B are “close”
    
    
     without
    
    
     the wormhole being present. It is not as if one is free to leave the rubber sheet and move
     from A to B through the three-dimensional space in which the sheet is embedded. If the
     three-dimensional space is not there, the rubber sheet is all there is to the universe.
    Thus, imagine that you were part of an infinitely advanced civilization (but not as
     advanced as the omnipotent Q beings, who seem to transcend the laws of physics) that had
     the power to build wormholes in space. Your wormhole building device would effectively be
     like the pencil in the example I just gave. If you had the power to produce huge local
     curvatures in space, you would have to poke around blindly in the hope that somehow you
     could connect two regions of space that, until the instant a wormhole was established,
     would remain very distant from each other. In no way whatsoever would these two regions be
     close together until the wormhole produced a bridge. The bridge-building process
    
    
     itself
    
    
     is what changes the global nature of spacetime.
    Because of this, making a wormhole is not to be taken lightly. When Premier Bhavani of
     Barzan visited the
    
    
     Enterprise
    
    
     to auction off the rights to the Barzan wormhole, she exclaimed, “Before you is the first
     and only stable wormhole known to exist!” Alas, it wasn't stable; indeed, the only
     wormholes whose mathematical existence has been consistently established in the context of
     general relativity are transitory. Such wormholes are created as two microscopic
     “singularities” regions of spacetime where, the curvature becomes infinitely sharp find
     each other and momentarily join. However, in a time shorter than the time it would take a
     space traveler to pass through such a worm-hole, it closes up, leaving once again two
     disconnected singularities. The unfortunate explorer would be crushed to bits in one
     singularity or the other before being able to complete the voyage through the wormhole.
    The problem of how to keep the mouth of a wormhole open has been hideously difficult to
     resolve in mathematical detail, but is quite easily stated in physical terms: Gravity
     sucks! Any kind of normal matter or energy will tend to collapse under its own
     gravitational attraction unless something else stops it. Similarly, the mouth of a
     wormhole will pinch off in nothing flat under normal circumstances.
    So, the trick is to get rid of the normal circumstances. In recent years, the Caltech
     physicist Kip Thorne, among others, has argued that the only way to keep wormholes open is
     to thread them with “exotic material.” By this is meant material that will be measured, at
     least by certain observers, to have “negative” energy. As you might expect (although naive
     expectations are notoriously suspect in general relativity), such material would tend to
     “blow” not “suck,” as far as gravity is concerned.
    Not even a diehard trekker might be willing to suspend disbelief long enough to accept the
     idea of matter with “negative energy”; however, as noted, in curved space one's normal
     expectations are often suspect. When you compound this with the exotica forced upon us by
     the laws of quantum mechanics, which govern the behavior of matter on small scales, quite
     literally almost all bets are off.
    BLACK HOLES