alternative timeline. We know we can improve our chances."
"What do we think happened to this Roman?" Athene asked.
"During the invasion of Britain he and some close family members were killed by Celts," Dr Chu explained, "and until then, as much as possible must remain unchanged so we don't simply replace one paradox with another. Some of Vespasian's men caught up with the Celts and killed all of them, so we're in luck: since everybody in this incident dies, our altering what happened by taking the Roman and any others off-world won't create another paradox. Since we get more than one go, we try for one big change at a time, so two guesses don't cancel out each other."
"So what do I do specifically?"
"This new time-line commences at a temple to . . . like to guess?"
"How would I know?" she frowned.
"To you!"
"What?"
"The Roman falls asleep between two large stone objects and underneath a statue in a disused temple to Pallas Athene," Chu smiled, "which I thought might appeal to you. Do what you can just before he wakes, then if the overall probability of resolving the paradox improves, the intensity of the line increases and we get more detail. Then you can have another go, a little earlier. You get about six attempts. After that, well . . ."
"What do I know about this Roman?"
"Fortunately, quite a bit, because he featured strongly in a thesis about why Roman science did not advance. Four students spent quite a lot of time viewing him, and we have their recordings. I'll download the notes into your notebook, if you wish."
"So you want me to give him a quick physics lesson?"
"No! I am afraid he must make the discovery himself. You must inspire him."
"I don't want to be unduly negative," Athene said, "but I just don't believe you can turn a Roman soldier into a leading physicist . . ."
"We know it's not easy," Chu nodded, "but it's our only chance to undo this disaster. According to the thesis, he was toying with the heliocentric theory, and had a debate with his teacher. He lost that debate when his teacher provided physical proof that the Earth could not travel around the sun and he gave up; his attitude could be summarized as Aristotle was obviously right, and in any case, who cares? So you must inspire him to greater things and also give him information that will get him through a couple of crises."
"There's another reason he must prove his heliocentric theory," Grenfell added. "We're asking a Roman to board an alien space ship and comprehend what's going on. When told, he must accept there are other planets going around other stars."
"We're asking him to do what Galileo did from roughly the same starting point," Chu added. "He nearly did it, so it's possible, if he can undo Aristotle's errors."
"But he didn't do it," Athene pointed out.
"The hardest part of making a discovery," Dr Chu smiled, "is convincing yourself that you can, that it's possible."
"Are you sure I'm the right person to . . ."
"Oddly enough, yes," Chu smiled. "If you could inspire what would have become a wine-sodden nothing to change his life and write two of the greatest pieces of literature of classical times, you can do this."
"I don't know enough about physics," she warned, although secretly she was very pleased with herself to receive such an accolade.
"You don't have to," Chu nodded supportively. "What you have to do is prod him in the right direction. I'll tell you what you should tell him, but leave you to work out how to say it. Will you do it?"
"I'll try," she replied. "I mean, it's not as if I've much choice, is it?"
"It's when you've got no choice you tend to make the right one," Chu smiled. "If we can help in any way, ask, but don't waste time. There will be no further supplies of food or spare parts, and we do not know how long this will take."
"Do we know how long we can exist in this state of paradox?"
"Until the paradox is resolved or until we run out of food," Dr Chu said. "The instant our interventions cannot