Starfarers and Time Travelers

Is it time travel if only information is transmitted to the past? Once, in conversation with James Blish, I referred to what I called "the limited time travel" of his story, "Beep," to which he replied that there was no time travel in "Beep." What happens is that Dirac transmissions are instantaneous. It follows that, in a four dimensional continuum, each Dirac device simultaneously receives all transmissions from past, present and future in a single beep from which individual messages can be filtered and slowed down so that information can be received from the future.

It might be said that information at least has traveled through time but, in any case, this situation does generate the causality paradoxes that are familiar from speculations about time travel.

In Poul Anderson's Starfarers, intelligent quantum states near a black hole can form giant spinning nuclei causing space-time warps through which they send information. Again, a causality paradox results. The quantum states can immediately communicate with newly arrived human explorers because they have been told how to do so by their later selves who know how to communicate with human beings because they have already done so.

Earlier in Starfarers, another situation, while not time travel, was also relevant to time travel paradoxes. The quantum jump that formed the universe was not to the lowest but to a higher energy level. The starfarers' "zero-zero drive" spaceships instantly boost to near light speeds by borrowing energy from the lowest level. It is feared that this exchange of energy between levels destabilizes the universe so that it might collapse to the lowest level. It is stated later in the novel that this fear is unfounded and that instead the energy exchanges strengthen cosmic stability.

However, while the fear was entertained, it was thought that a sphere of nothingness expanding at light speed could engulf the universe. This is comprehensible. However, a character then adds:

"- the past itself annulled, and we not only cease to be, we never were." (1)

And, in the Time Patrol series:

"...brightness that at any instance might not only cease to be but cease ever having been." (2)

This is incoherent. We can exist until time t, can cease to exist at t and can no longer exist after t but we cannot exist until t, than at t cease having existed until t.

The speaker's companion replies that it has not happened yet to which she responds:

"It may already have happened somewhere. It may be on its way to us. We'll never know." (1)

If a sphere of nothingness is on its way to us now, then we exist now so that we have not been prevented from existing until now. We can fear for the future but not in the same way for the past. These few lines could be deleted without affecting the rest of the novel.

(1) Anderson, Poul, Starfarers, New York, 1999, p. 290.
(2) Anderson, Poul, The Time Patrol, New York, 1991, p. 301.