"Father Inire smiled. It was the first time she had seen him smile, and though she knew he meant only that she had amused and pleased him (perhaps more than a grown woman could have) it was not pleasant.
'No, no. Let me outline the problem to you. When something moves very, very fast - as fast as you see all the familiar things in your nursery when your governess lights your candle - it grows heavy. Not larger, you understand, but only heavier. It is attracted to Urth or any other world more strongly. If it were to move swiftly enough, it would become a world itself, pulling other things to it. Nothing ever does, but if something did, that is what would happen. Yet even the light from your candle does not move swiftly enough to travel between the suns.'
(The Fish flickered up and down, forward and back.)
'Couldn't you make a bigger candle?' I feel sure Domnina was thinking of the paschal candle she saw each spring, thicker than a man's thigh.
'Such a candle could be made, but its light would fly no more swiftly. Yet even though light is so weightless we have given its name to that condition, it presses against what it falls on, just as wind, which we cannot see, pushes the arms of a mill. See now what happens when we provide light to mirrors set face to face: The image they reflect travels from one to the other and returns. Suppose it meets itself in returning - what do you suppose happens then?' "Domnina laughed despite her fear, and said she could not guess.
'Why it cancels itself. Think of two little girls running across a lawn without looking where they're going. When they meet, there are no more little girls running. But if the mirrors are well made and the distances between them are correct, the images do not meet. Instead, one comes behind the other. That has no effect when the light comes from a candle or a common star, because both the earlier light and the later light that would otherwise tend to drive it forward are only random white light, like the random waves a little girl might make by flinging a handful of pebbles into a lily pond. But if the light is from a coherent source, and forms the image reflected from an optically exact mirror, the orientation of the wave fronts is the same because the image is the same. Since nothing can exceed the speed of light in our universe, the accelerated light leaves it and enters another. When it slows again, it reenters ours - naturally at another place.'
'Is it just a reflection?' Domnina asked. She was looking at the Fish.
'Eventually it will be a real being, if we do not darken the lamp or shift the mirrors. For a reflected image to exist without an object to originate it violates the laws of our universe, and therefore an object will be brought into existence.'
