"...reality is conditional. It is like a wave pattern on a sea. Let the waves - the probability-waves of ultimate underlying quantum chaos - change their rhythm, and abruptly that tracery of ripples and foam-swirls will be gone, transformed into another."
-Poul Anderson, Time Patrol (New York, 2006), p. 671.
In this case, Anderson does go on to say that, although twentieth century physicists already had a glimmering of quantum chaos, it was time travel that made it impact on human lives. However:
"...all the life that pulsed in the city today and in past and future, everything that begot and nourished it...he knew their whole reality for a spectral flickering, diffraction rings across abstract, unstable space-time, a manifold brightness that at any instant could not only cease to be but cease ever having been.
"The cloud-capp'd towers..." (p. 480)
I have problems with the phrase "...cease ever having been..." but my point here is that in this passage time travel is not mentioned.
A Danellian confirms:
"'Think, if you wish, of diffraction, waves reinforcing here and canceling there to make rainbow rings. It is incessant, but normally on the human level it is imperceptible. When it chanced to converge powerfully on Lorenzo de Conti, yes, then that became like a kind of fate.'"
-Poul Anderson, The Shield Of Time (New York, 1991), p. 434.
Diffraction is mentioned again. And, this time, although the Patrol needs time travel to fix de Conti, no time travel was involved in the convergence on de Conti.
"'In a reality forever liable to chaos, the Patrol is the stabilizing element, holding time to a single course...left untended, events would inevitably move toward the worse. A cosmos of random changes must be senseless, ultimately self-destructive. In it could be no freedom.'" (p. 435)
And this is "'...the meaning...'" (ibid.) The Patrol was founded not to catch criminals but to counteract chaos.