Monday, June 20, 2011

The Clockwork Rocket 1 - Greg Egan

"“But how does that change things?” Yalda wondered. “If I see red light and violet light at the same time . . . then the slower, red light must have left the sun earlier.”

“Right. So how does that affect what you see?”

Yalda struggled to picture it. “Where the sun is in the sky depends on which way the world is facing when the light arrives, not when it left. The red light left earlier, but that makes no difference – we just see whatever reaches us at the time we're looking. So we see all the sun's colours in the same place, not spread out in a trail.”

Vito's rear eyes widened with approval. “That wasn't too difficult, was it?”

Yalda was encouraged, but she was still far from confident that everything made sense. “And the stars? Why are they so different?”

“The stars are really moving,” Vito reminded her. “Not just rising and setting with the turning of the world. Between the time when the red light we're seeing now left a star, and the time when the violet light we're seeing now followed it, the star will have moved far enough for us to see the different colours coming from different directions. When we look at the sun, the violet light and the red light follow the same road, even though the red light begins the journey earlier. When we look at a star, the violet light's coming to us from a different place, along a different path than the red.”

Yalda turned this over in her mind. “If the stars are really moving,” she said, “then why don't we see them move?” The coloured worms were all pinned to the rigid black sky, sharing, but never exceeding, the illusory motion that came from the world's shifting gaze. Why didn't they advance along their own trails, wriggling out of their constellations into fresh new patterns every night?"

4 out of 5

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