The Physics of Star Trek Read Online Free

when Picard traveled back in time to perform them. Thus
     they have already happened, even if Picard has not yet left! In this way, a cause in the
     nineteenth century (Picard tapping) can produce an effect in the twenty-fourth century
     (Data's circuitry change) before the cause in the twenty-fourth century (Picard leaving
     the ship) produces the effect in the nineteenth century (Picard's arrival in the cave
     where Data's head is located) which allowed the original cause (Picard tapping) to take
     place at all.
    Actually, if the above plot line is confusing, it is nothing compared to the Mother of all
     time paradoxes, which arises in the final episode of
    
    
     Star Trek: The Next Generation,
    
    
     when Picard sets off a chain of events that will travel back in time and destroy not just
     his own ancestry but all life on Earth. Specifically, a “subspace temporal distortion”
     involving “antitime” threatens to grow backward in time, eventually engulfing the amino
     acid protoplasm on the nascent Earth before the first proteins, which will be the building
     blocks of life, can form. This is the ultimate case of an effect producing a cause. The
     temporal distortion is apparently created in the future. If, in the distant past, the
     subspace temporal distortion was able to destroy the first life on Earth, then life on
     Earth could never have evolved to establish a civilization capable of creating the
     distortion in the future!
    The standard resolution of these paradoxes, at least among many physicists, is to argue a
     priori that such possibilities must not be allowed in a sensible universe, such as the one
     we presumably live in. However, the problem is that Einstein's equations of general
     relativity not only do not directly forbid such possibilities, they encourage them.
    Within thirty years of the development of the equations of general relativity, an explicit
     solution in which time travel could occur was developed by the famous mathematician Kurt
     Gšdel, who worked at the Institute for Advanced Study in Princeton along with Einstein. In
     Star Trek language, this solution allowed the creation of a “temporal causality loop,”
     such as the one the
    
    
     Enterprise
    
    
     got caught in after being hit by the
    
    
     Bozeman.
    
    
     The dryer terminology of modern physics labels this a “closed timelike curve.” In either
     case, what it implies is that you can travel on a round-trip and return to your starting
     point in both space
    
    
     and
    
    
     time! Gšdel's solution involved a universe that, unlike the one we happen to live in, is
     not expanding but instead is spinning uniformly. In such a universe, it turns out that one
     could in principle go back in time merely by traveling in a large circle in space. While
     such a hypothetical universe is dramatically different than the one in which we live, the
     mere fact that this solution exists at all indicates clearly that time travel is possible
     within the context of general relativity.
    There is a maxim about the universe which I always tell my students: That which is not
     explicitly forbidden is guaranteed to occur. Or, as Data said in the episode “Parallels,”
     referring to the laws of quantum mechanics, “All things which can occur, do occur.” This
     is the spirit with which I think one should approach the physics of Star Trek. We must
     consider the distinction not between what is practical and what is not, but between what
     is possible and what is not.
    This fact was not, of course, lost on Einstein himself, who wrote, “Kurt Gšdel's [time
     machine solution raises] the problem [that] disturbed me already at the time of the
     building up of the general theory of relativity, without my having succeeded in clarifying
     it.... It will be interesting to weigh whether these [solutions] are not to be excluded on
     physical grounds.”
    
    
     1
    The challenge to physicists ever