Couldn't Colўn's irrational plans turn out the same way? Only instead of a years-long voyage, his route to the Orient would bring wealth much faster. And his plan, instead of enriching a tiny useless country like Portugal, would lead eventually to the Church of Christ filling the entire world!

So now, instead of thinking how to drag out the examination of Colўn, waiting for the desires of the monarchs to resolve themselves, Talavera sat in his austere chamber trying to think how to force the issue. One thing he certainly could not do was suddenly, after all these years and with no significant new arguments, announce that the committee was deciding in favor of Colўn. Maldonado and his supporters would protest directly to the King's men, and a power struggle would ensue. The Queen would almost certainly lose such an open struggle, since her support from the lords of her realm depended in large part on the fact that she was known to "think like a man." Disagreeing openly with the King would give the lie to that idea. Thus open support for Colўn would lead to division and probably would not lead to a voyage.

No, Talavera thought, the one thing I cannot do is support Colўn. So what can I do?

I can set him free. I can end the process and let him go on to another king, to another court. Talavera well knew that Colўn's friends had made discreet inquiries in the courts of France and England. Now that the Portuguese had achieved their quest for an African route to the East, they might be able to afford a small exploratory expedition toward the west. Certainly the Portuguese advantage in trading with the Orient will be envied by other kings. Colўn might well succeed somewhere. So whatever else happens, I must end his examination immediately.

But could there not also be a way to end the examination and yet turn things to the advantage of Colўn's supporters?

With a half-formed plan in mind, Talavera sent to the Queen a note bearing his request for a secret audience with her on the matter of Colўn.

Tagiri did not understand her own reaction to the news of success from the scientists working on time travel. She should be happy. She should be rejoicing to know that her great work could, physically, be accomplished. Yet ever since the meeting with the team of physicists, mathematicians, and engineers working on the time travel project, she had been upset, angry, frightened. The opposite of how she had expected she would feel.

Yes, they said, we can send a living person into the past. But if we do so there is no chance, no chance whatsoever, that our present world will survive in any form. To send someone into the past to change it is the end of ourselves.

They were so patient, trying to explain temporal physics to historians. "If our time is destroyed," Hassan asked, "then won't that also destroy the very people that we send back? If none of us are ever born, then the people we send won't have been born either, and therefore they could never have been sent. "

No, explained the physicists, you're confusing causality with time. Time itself, as a phenomenon, is utterly linear and unidirectional. Each moment happens only once, and passes into the next moment. Our memories grasp this one-way flow of time, and in our minds we link it with causality. We know that if A causes B, then A must come before B. But there is nothing in the physics of time that requires this. Think of what your predecessors did. The machine they sent back in time was the product of a long causal network. Those causes were all real, and the machine actually existed. Sending it back in time did not undo any of the events that led to the creation of that machine. But in the moment that the machine caused Columbus to see his vision on that beach in Portugal, it began to transform the causal network so that it no longer led to the same place. All of those causes and effects really happened -- the ones leading to the creation of the machine, and the ones following from the machine's introduction into the fifteenth century.

"But then you're saying that their future still exists," Hunahpu protested.

That depends on how you define existence, they explained. As a part of the causal network leading to the present moment, yes, they continue to exist in the sense that any part of their causal network that led to the existence of their machine in our time is still having effects in the present world. But anything peripheral or irrelevant to that is now utterly without effect in our timestream. And anything in their history that the introduction of that machine in our history caused not to happen is utterly and irrevocably lost. We can't go back into our past and view it because it didn't happen.

"But it did happen, because their machine exists."

No, they said again. Causality can be recursive, but time cannot. Anything that the introduction of their machine caused not to happen, did not in fact happen in time. There is no moment of time in which those events exist. Therefore they cannot be seen or visited because the temporal loci which they occupied are now occupied by different moments. Two contradictory sets of events cannot occupy the same moment: You are only confused because you cannot separate causality from time. And that's perfectly natural, because time is rational. Causality is irrational. We've been playing speculative games with the mathematics of time for centuries, but we would never have seen this distinction between time and causality ourselves if we hadn't had to account for the machine from the future.

"So what you're saying," Diko offered, "is that the other history still exists, but we just can't see it with our machines."

That's not what we're saying, they replied with infinite patience. Anything that was not causally connected to the creation of that machine cannot be said to have ever existed at all. And anything that did lead to the creation of that machine and its introduction into our time exists only in the sense that unreal numbers exist.

"But they did exist," Tagiri said, more passionately than she had expected. "They did."

"They did not," said old Manjam, who had let his younger colleagues speak for him till now. "We mathematicians are quite comfortable with this -- we have never dwelt in the realm of reality. But of course your mind rebels against it because your mind exists in time. What you must understand is that causality is not real. It does not exist in time. Moment A does not really cause Moment B in reality. Moment A exists, and then Moment B exists, and between them are Moments A.a through A.z, and between A.a and A.b there are A.aa through A.az. None of these moments actually touches any other moment. That is what reality is -- an infinite array of discreet moments unconnected with any other moment because each moment in time has no linear dimension. When the machine was introduced into our history, from that point forward a new infinite set of moments completely replaced the old infinite set of moments. There were no spare leftover moment-locations for the old moments to hang around in. And because there was no time for them, they didn't happen. But causality is unaffected by this. It isn't geometric. It has a completely different mathematics, one which does not fit well with concepts like space and time and certainly doesn't fit within anything that you could call 'real.' There is no space or time in which those events happened."

"What does that mean?" said Hassan. "That if we send somebody back in time, they will suddenly cease to remember anything about the time they came from, because that time no longer exists?"

"The person that you send back," said Manjam, "is a discrete event. He will have a brain, and that brain will contain memories that, when he accesses them, will give him certain information. This information will cause him to think he remembers a whole reality, a world and a history. But all that exists in reality is him and his brain. The causal network will only include those causal connections which led to the creation of his physical body, including his brain state, but any part of that causal network which is not part of the new reality cannot be said to exist in any way."