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

whether this name was plucked out of a hat or not. However, since virtual
     particlesthe quantum fluctuations in otherwise empty space are currently the best
     candidate for Kip Thorne's “exotic matter,” I think the Star Trek writers deserve credit
     for their intuition, if that's what it was.)
    More generally, if quantum fluctuations in the vacuum can be exotic, is it possible that
     some other nonclassical configuration of matter and radiationlike, say, a warp core
     breach, or perhaps Scotty's “intermix” imbalance in the warp drivemight also fill the
     bill? Questions such as this remain unanswered. While by no means circumventing the
     incredible implausibility of stable wormholes in the real universe, they do leave open the
     larger question of whether wormhole travel is impossible or merely almost impossible. The
     wormhole issue is not just one of science fact versus science fiction: it is a key that
     can open doors which many would prefer to leave closed.
    TIME MACHINES REVISITED: Wormholes, as glorious as they would be for tunneling through
     vast distances in space, have an even more remarkable potential, glimpsed most recently in
     the
    
    
     Voyager
    
    
     episode “Eye of the Needle.” In this episode, the
    
    
     Voyager
    
    
     crew discovered a small wormhole leading back to their own “alpha quadrant” of the galaxy.
     After communicating through it, they found to their horror that it led not to the alpha
     quadrant they knew and loved but to the alpha quadrant of a generation earlier. The two
     ends of the wormhole connected space at two different times!
    Well, this is another one of those instances in which the
    
    
     Voyager
    
    
     writers got it right. If wormholes exist, they can
    and will be time machines! This startling realization has grown over the last decade, as
     various theorists, for lack of anything more interesting to do, began to investigate the
     physics of wormholes a little more seriously. Worm- hole time machines are easy to design:
     perhaps the simplest example (due again to Kip Thorne) is to imagine a wormhole with one
     end fixed and the other end moving at a fast but sublight speed through a remote region of
     the galaxy. In principle, this is possible
    
    
     even if
    
    
     the length of the wormhole remains unchanged. In my earlier two- dimensional wormhole
     drawing, just drag the bottom half of the sheet to the left, letting space “slide” past
     the bottom mouth of the wormhole while this mouth stays fixed relative to the wormhole's
     other mouth:
    Because the bottom mouth of the wormhole will be moving with respect to the space in which
     it is situated, while the top mouth will not, special relativity tells us that clocks will
     tick at different rates at each mouth. On the other hand, if the length of the wormhole
     remains fixed, then as long as one is inside the wormhole the two ends appear to be at
     rest relative to each other. In this frame, clocks at either end should be ticking at the
     same rate. Now slide the bottom sheet back to where it used to be, so that the bottom
     mouth of the wormhole ends up back where it started relative to the background space.
     Let's say that this process takes a day, as observed by someone near the bottom mouth. But
     for an observer near the top mouth, this same process could appear to have taken ten days.
     If this second observer were to peer through the top mouth to look at the observer located
     near the bottom mouth, he would see on the wall calendar next to the observer a date nine
     days earlier! If he now decides to go through the worm-hole for a visit, he will travel
     backward in time.
    If stable wormholes exist, we must therefore concede that time machines are possible. We
     now return finally to Einstein's remarks early in the last chapter. Can time travel, and
     thus stable wormholes, and thus exotic matter with negative energy, be “excluded on
     physical