Stubbornly, Rigg decided he would not yet believe in a human being transparent to photons. There must be some other explanation, and he closed his eyes and studied the slowly moving path for some kind of clue.
There was the fact that it was moving more slowly than any human being could possibly move. More important, though, was the fact that the path faded far too abruptly. The beginning of the stranger’s path into the garden was actually earlier than Rigg’s own path as he came in.
And at the head of the path, right where the person should be visible, but wasn’t, the path flickered.
Not blinking on and off, but the color of it—or flavor, or whatever sense you might want to use as a metaphor—seemed to be changing slightly in abrupt shifts.
Rigg opened his eyes again. If this was another assassin, Rigg would certainly have no problem getting away from him, his progress was so slow. Then again, he might move slowly when invisible, then turn visible and leap upon Rigg like a stooping hawk.
Still, Rigg had to learn more. So he stood up, walked directly to the head of the slow path and blocked it.
It took a few moments but the path stopped moving, and then began moving backward. But in that moment of hesitation, when the invisible one did not move forward or back, his shape became faintly visible to Rigg’s eyes. Not enough that Rigg could see him clearly, but he knew where the eyes were, could see the height. He could see the outline of the clothing and the hair, telling him that this was a woman. And in the eyes, he caught a glimpse of—what, fear? Startlement?
Rigg knew that he had revealed to the invisible person that her invisibility was not complete. But he had also learned that when the invisible person ceased moving, she became somewhat visible again.
“Who are you?” Rigg asked softly. He was so close she could not help but hear him, though no one inside the house could have. Yet there was no hint of a response. The Invisible just kept moving away, moving perhaps a little faster but not much.
Frustrated, Rigg walked up her path and did not pause, but kept moving right through the place where she had to be.
He passed right through.
Did Rigg feel anything odd during that passage? Perhaps a slight shakiness, or perhaps a little warmth. Or maybe he was just imagining the sensation because he knew he had to be passing through a living person.
When he looked back at the path, it was unchanged, except that it continued moving forward—perhaps a little more swiftly than before, if “swiftly” could be used to describe a speed that would make a snail ashamed.
Rigg had a good idea now who the Invisible might be. If he could not speak to her or force her to become more visible to him, he at least could find out where she had been and who might know who she was. Rigg stood out of the Invisible’s way and closed his eyes so he could focus on her path backward in time. Not terribly far away, the path changed—it lost its trait of rapid fading, and instead seemed quite normal as it moved through the house. Back to a bedroom where Mother lay asleep.
The Invisible had come straight from Mother’s room, and at a normal pace. But she had done so in the middle of the night, when no one was about. Rigg made the reasonable assumption: When the Invisible moved at an ordinary speed, she was completely visible, and remain unnoticed because the house was dark and everyone was asleep. As soon as the Invisible realized there was someone in the garden—Rigg—she slowed down and became invisible.
She is not “slowing down,” Rigg realized. Whatever she’s doing affects her path, and paths have to do with time. The Invisible is actually jumping forward in time, in tiny increments.
Silently in his mind, Rigg explained it all as if he were expounding his theory to Father. Suppose the Invisible moved an inch a second. Suppose that at the end of every second, she then jumped forward one second in time. To the Invisible, she is making a continuous forward movement, one second per inch. But because she is jumping forward a second at the end of every second, to an outside observer she would seem to move one inch every two seconds—but for one of those seconds she would seem to flash out of existence.
Now suppose that instead of a second per inch, it was a millionth of a second per millionth of an inch. The pace would be the same, but now she would not exist in any moment long enough for a significant number of photons to hit her.
He could almost hear Father’s voice raise an objection. If she exists in any moment for exactly as long as she does not exist between moments, then she should be half visible, for half the photons would pass through her, and half would strike her and reflect or be absorbed.
All right, Rigg answered himself. Suppose the Invisible exists for one millionth of a second, but then jumps forward a thousandth of a second. Now she exists far less time than she does not exist. She’s only reflecting light for one millionth of a second every thousandth of a second. Our eyes simply can’t notice that tiny amount of light, can’t focus on it.
She has to keep moving, though. And very quickly, so that each thousandth of a second, when she reappears so briefly, she’s in a different place. When I made her stop and back up because I stood directly in front of her, for that fleeting second she did not move quickly enough and she became much more visible—I could see her height, her shape, her eyes, a trace of her mouth. Then she sped up, moving backward, and disappeared again.
She never disappeared, really. She was always there. When I walked through her, she was there.
Father had taught Rigg that all solid objects were actually mostly empty space, the atoms very far apart, and within each atom the nucleus and electrons were separated by spaces many times their size.
So when he passed through the Invisible, the Invisible must have flashed into existence many times, maybe a thousand times. Most of the actual particles of their bodies would not have collided, and the Invisible jumped ahead in time before they could distort or destroy each other.
But some particles must have collided, and those that did . . .
No wonder the Invisible backed up rather than collide with Rigg. Even though such a collision would do no visible harm, there must be significant radiation from the relatively few crashes between atoms that did take place during the passage. If the Invisible did not avoid collisions as much as possible, eventually the radiation would become significant. Enough, perhaps, to make her sick or even kill her.
For the first time, Rigg understood that it was useful that Father had taught him so much about physics. He wanted me to be able to make sense of things like this.
Except that it didn’t really make sense yet. How could a human being divide time into such tiny bits? How could the Invisible possibly even comprehend such intervals?
Again, Rigg answered his own objection. The Invisible no more understands what she’s doing than Umbo understood what he was doing when he “slowed down time,” no more than I understood the nature of the paths that only I could see. It was instinctive. A reflex.
Like sweating. You know what causes sweat, but you don’t have to consciously activate every pore for sweating to take place.
No, sweating was involuntary. More like walking. You don’t think about each tiny muscle movement involved in walking, you just walk, and your body does what it does. Or like seeing—you decide what to look at, how wide to open your eyes, how long to stare—but you don’t have to understand the photons striking the rods and cones of your retina.
The Invisible may not even know that she’s moving forward in time. She only knows that when she becomes invisible, her forward movement slows down. With years of practice, she would learn just how much time-movement was needed to stay invisible, because if she became too invisible, her movement through space would become so slow she would be unable to get from one place to another. But if she did not move forward far enough with each tiny time-jump, she would become visible and people would see her—as a ghost, a dream, an apparition, a memory, but they would see her.