Thrice upon a Time by James P. Hogan

expectantly.
    "We must conclude that past and present versions of the universe in which we live exist and are equally real," Charles told them. "We thus have a continuum of some kind. I think we're all agreed that it can't be of the popular infinitely branching, parallel variety; that would introduce too many impossible complications. In any case, it isn't supported by the data we've seen." He looked around to invite comment, but the others just nodded silently. "Neither can it be of the simple serial variety that we considered initially; in such a model it would be impossible to affect the present by manipulating a past, and again our results seem to indicate that this is not the case. The only model I can think of that could be consistent with what we've seen is a more complex serial one in which altering the events in a past universe does affect not only the future of that particular universe as it evolves in time, but also the presents of all the other universes that lie ahead of it. In other words there is some mechanism of causal connection through the continuum that the simple serial model doesn't take account of."
    "You mean like with the jar," Lee said. "That one message changed what happened in all the universes involved, not just in the one universe where the message was received."
    "Precisely that," Charles confirmed. "To be anywhere near the reality at all, the model will have to possess a mechanism that explains such evident facts." Those at the table became quiet.
    After a while Cartland asked, "Any ideas?"
    "I think maybe I have," Charles replied. The others looked at him with suddenly renewed interest. "Everything we have discovered so far," he continued, "seems to add up to two things: First, the universe that we see around us and form part of is simply one of many, equally real universes that appear to be strung sequentially along a single timeline; second, events that happen in this universe affect not only its future, but the situations in all the other universes that lie ahead of it. That, of course, suggests a continuity throughout the system; the future universes ahead of us form a progression of states that are evolving from the present state. We need to ask ourselves what the mechanism is that provides that continuity. That same mechanism will turn out to be, unless I'm very much mistaken, the same mechanism that enables events in one universe to alter what happens in another. Obviously we're talking about a causal influence that must be propagated by some means."
    "Agreed, but I don't think you'll find you have to look very far," Cartland said with a shrug. "The continuity follows from the fact that objects don't suddenly just appear and vanish; they endure in time. So a universe an hour, say, ahead of this one will contain the same objects. They provide the continuity."
    "Objects?" Charles repeated in a mildly challenging tone. "A candle, such as the one on the table there? A mayfly? A cigarette? They'll endure in time?"
    "Oh, all right," Cartland conceded. "I used the wrong word. Molecules then. Atoms, if you like."
    "The candle, the mayfly, and the cigarette are breaking down molecules all the time," Charles pointed out. "And they all contain carbon fourteen; atoms come apart too."
    "Oh, you know what I mean, Charles," Cartland said, sounding a little surprised. "Protons, neutrons, and electrons if you like. Or quarks and photons—whatever you'll accept as the basic mass-energy quanta. They don't change."
    "They don't," Charles agreed at last. "But they do
rearrange.
Bundles of them may come together and remain attached for a while to form a tree, and then fall apart again and disperse when the tree dies and decays. But as you say, Ted, the basic entities endure. They rearrange into different patterns to produce the changes that we call time, and they provide the continuity that enables one universe to evolve from another."
    "But you said all the universes were equally real," Elizabeth said,