"That's determined by three factors," Charles answered. "The magnitude of the pulse sent, the sensitivity of the receiving detector, and the absolute velocity of the Earth through space. You see, the tau pulse reappears as detectable energy at the same point in space as it was generated. Theoretically the profile of the reappearing energy wave forms a spherical surface that expands at light-speed about that point with increasing distances back along the timeline. After one second back in time it would occupy a volume one hundred and eighty-six thousand miles in radius, after two seconds one of twice that radius, and so on."
"It can't be," Lee protested. "The machine's not big enough to pack that much power. How could one pulse from it fill a volume that big?"
"Ah, I only said that was theoretically," Charles reminded him. "That's the mathematical limit. Inside that volume, the intensity falls off exponentially from the center-point. The signal exists everywhere inside that expanding volume. However, to receive it, the receiver can only be up to a certain distance from the center of the wave pattern, depending on how sensitive it is."
"So that's where the velocity of the Earth comes into it," Lee said. "The Earth will have moved between the time of sending and the time of receiving. You can only send as far back as corresponds to moving the receiver to its limit of sensitivity."
"Exactly," Charles confirmed. "According to the data from Doppler shifting of big-bang background radiation, the Earth moves about twenty-one million miles in a day. The detectors in the machine will operate reliably up to approximately one hundred and forty-five thousand miles from the center-point of the wave pattern produced by the level of tau pulse that this machine sends. If you work that out, it gives you a range of just about ten minutes."
Lee shook his head in wonder and stared at the characters still preserved on the screen in front of Murdoch. "So how long have you had it working now?" he asked.
"Only since two days ago," Charles told him. "I got it to work for the first time the day before I called Murdoch. Even Ted Cartland hasn't seen it yet. I called him a few minutes before I called you, Murdoch, but he's stuck in Manchester and won't be able to get away until tomorrow morning." Charles cackled wheezily. "The poor fellow was becoming frantic when I talked to him again, earlier today."
Murdoch was only half listening. He was still staring at the console, mentally replaying each step of the demonstration that Charles had given. The question going through his mind was obvious. Finally he looked up at Charles. "When you set this machine up a few minutes ago, you got the hardcopy first. Then you started up a program that would time-out after sixty seconds and send back whatever I typed in. Is that right?"
"Yes," Charles said simply.
Murdoch thought for a moment longer. "Okay. Let's ask the hundred-thousand-dollar question: What would have happened if I'd simply decided not to key in anything at all after the sixty seconds? What would have happened to the characters that were already on this sheet? How could they have gotten there?"
Charles nodded as If he had been waiting for Murdoch or Lee to ask that, and moved forward to reinitiate the system. Then he stepped back. "Try it and see," he invited.
Murdoch looked at the hardcopy slot expectantly and waited. Behind him, Lee moved closer and watched intently.
Nothing happened.
Murdoch's face knitted into a puzzled frown. After a while he looked up at Charles, but there was no surprise in Charles's expression. They waited.
"I don't believe this," Lee murmured at last. "It's no different than last time. Surely an intention inside somebody's head can't make any difference to what the machine does. That's for ESP freaks."
"Wait," Charles told them.
They waited.
Suddenly the slot ejected a sheet of paper. Lee leaped forward and snatched it up.
"It says MURDOC," he announced.
"When was it sent?" Murdoch demanded.
Lee checked the time printed on the sheet and glanced at the time-of-day readout on the console. "It's still set up for sixty seconds," he said. The countdown display had appeared at the top of the screen to confirm his words.
"Right," Murdoch declared. "We'll just see." He sat back in the chair and folded his arms in determination. Clearly he had no intention of doing anything when the zero arrived. Charles watched, but said nothing. The final seconds ticked by; Murdoch and Lee became visibly tense. Then the zero appeared.
And that was that. The paper with its printed record remained in Lee's hand, and time marched on past the deadline regardless. Two faces jerked round toward Charles, demanding an explanation.
"I don't know," Charles said quietly. "I don't know who sent that, or where from, either." The other two gaped at him incredulously. They were too confused for a moment to say anything. Charles stepped forward again and used the touchboard to bring up a color display on the screen. It showed a horizontal line across the bottom, annotated with numbers like the X-axis of a graph with zero at the center; above the line, the main area of the screen was divided vertically into three broad bands: a central white one separating two of gray.
"This is a graphical representation of the machine's window of range," Charles explained. "The horizontal axis is time, with the present instant corresponding to the zero in the middle. The white zone is twenty minutes wide; that's the window of the machine's current range, extending ten minutes forward and back. The gray areas on either side are the edges of the future and the past lying outside the ten-minute range."
To the left of center inside the white area, they could see a short red bar standing up from the scale at the point denoted by -6 —six minutes into the past, and a similar, but dotted, red bar at -5 minutes. There was a second pair of bars, this time blue; the solid one was at -11/2 minutes, the dotted one at -1/2 minute.
"Those two solid lines represent signals that the machine has received and logged," Charles explained. "The red one at minus six minutes is the random sequence of characters that Murdoch sent back a little while ago. Some of the control bits sent with every signal denote the time of transmission, so the computer can plot on the display when the signal was sent, which it does by adding a dotted line of matching color in the appropriate place. You can see that the dotted red line is a minute ahead of the solid one in time. If you watch closely, you should just be able to make out that the whole pattern is creeping slowly to the left as time advances. Thus the zero in the center always corresponds to the current instant." Charles paused and took a long breath, as if he were being forced to say something that he didn't really believe. He raised his arm and pointed at the second, blue pair of bars. "The solid blue line, now at minus two minutes, represents the reception of the signal that Lee read out two minutes ago. And the corresponding dotted line"—he pointed with his finger—"is the machine's reconstruction of where it was sent from—a point in time that is now one minute behind where we are right now." He stopped speaking and waited for the protests that he knew would come.
"That's crazy!" Murdoch exclaimed. "I didn't send anything one minute ago. You were both watching me. Nobody sent anything one minute ago. There has to be something screwy with the system. How could— What the… ?" He sat forward abruptly and stared wide-eyed at the screen. A solid green bar had appeared right on the zero-point of the scale, indicating that another signal had been received at that very instant. At the same time a dotted green bar had appeared sixty seconds ahead of it—sixty seconds in the future. The hardcopy slot disgorged another sheet.
"It says 'CRAZY,' " Lee told them in a bewildered voice. "What in hell's going on?"
A solid yellow bar appeared at zero to the right of the green one, which had already moved a few seconds leftward into the past. Its dotted yellow companion was well over to the right of the white area, denoting that something had come in from about eight minutes in the future. Charles touched a pad to deactivate the hardcopy unit.
"We can look at what the signals actually say later," he said. "I don't think it matters all that much
for now." It was almost as if he knew what was going to happen next. The display suddenly went wild. Bars of every shade and color added themselves at the zero-point as fast as the ones already there could shuffle out of the way, producing a solid, rectangular, rainbow spectrum that steadily extended itself relentlessly toward the left. At the same time the right-hand half of the white area, representing the future ten minutes of the machine's range, filled haphazardly with matching dotted bars to complete each pair.
Murdoch slumped back in the chair, shaking his head as his mind abandoned the struggle of trying to find reason in what his eyes told him was happening. The solid bars merged into a block of color that grew until it covered the full ten minutes of the past. By that time the isolated red and blue bars with which the whole thing had begun had been pushed out of the white area completely, and were now standing alone in the left-hand gray zone, beyond the ten minutes of the machine's range; almost twenty minutes had elapsed since Charles's initial demonstration.
And then Murdoch noticed something. He sat forward and peered closely at the block of colors denoting incoming signals. The block was not completely solid; there were a few thin, scattered gaps, indicating points in time during the previous ten minutes at which no transmissions had been received. That much was fact—already recorded and firmly sealed in what was now the past. A thought occurred to him. He pointed toward the screen and looked up at Charles.
"Those small gaps there," he said. "Could we set up the machine to send a signal back into one of them?"
"We could," Charles answered. "Which one?"
"How about that one?" Murdoch pointed. Charles went quickly through the routine of initiating the system to transmit and set the time-shift to select the gap that Murdoch had indicated.
"It's all yours," he announced.
Murdoch studied the display for a moment and paused with his fingers an inch from the touchboard while he thought about exactly what he wanted to do. He licked his lips and mentally composed a message. Anything would do—any nonsense word sufficiently distinct to be identifiable, such as MURDOC or CRAZY or…
And then it slowly dawned on him. He was not going to prove anything or uncover anything sensational. What else did all the bars crowded together across the screen tell him but that somebody—some where, some time—had already asked the same question as he, and was trying to do the same thing. And that somebody wasn't getting any answers. If he were, why did he keep trying the same thing over and over again? Doing so obviously wasn't getting that somebody anywhere; there was no reason to suppose it would get Murdoch anywhere either. He drew his hands back from the touchboard and sank back with a sigh to find Charles nodding slowly, as if Charles had already read his mind.
"You were thinking of trying to fool it, weren't you?" Charles said. "The screen says there were a few times in the past ten minutes at which nothing came in. Fact. You wondered what would happen if you tried sending something back to one of those times anyway. How could that be reconciled with what's staring you in the face? Am I right?"
Murdoch nodded. "You've thought the same thing, haven't you?"
"Naturally."
"And?" Lee asked.
"I never tried it," Charles answered. Then his voice took on a mysterious note. "Or at least if I did, I don't know anything about it." He looked from one to the other and took in their puzzled frowns, then waved a hand in the direction of the display. "Look there. Who sent all those signals that are plastered all over the place? A lot of them were sent in what has become the past already, but none of us here sent them. Somebody must have." The statement voiced what was already written across Murdoch's and Lee's faces.
Charles activated the hardcopy unit to obtain a single-sheet summary of all the messages that had come in. He scanned quickly down it. "There's no real rhyme or reason to any of it," he told them. "Things like TEST1 and TIME1… Here's an interesting one. It says, GAPFIL. It suggests that perhaps whoever sent it was thinking exactly what you were thinking, Murdoch." He handed the sheet to Murdoch and proceeded to shut down the system.
The mystified look on Murdoch's face deepened as he read. "What are you getting at, Grandpa? Are you trying to say that I did send all this? That's ridiculous!"
"I don't know," Charles replied. "You tell me. Are those the kinds of words that would have occurred to you?"
"But it worked," Lee murmured. He was massaging his brow with his fingers, still struggling to find some shred of sanity in what had transpired in the previous half-hour. "That first test you showed us when we came in—it worked."
"Aye," Charles agreed. "When Murdoch had no idea of what I was going to ask him to do, it worked. But as soon as he knew what to expect and began forming ideas in his head about trying to fool it, we got nothing but nonsense from that point on."
"I still say the whole thing's impossible," Lee insisted. "It's what you do that affects what comes out of a machine, not what you might do or what you think of doing."
"Yes, but what you think now might be the cause of what you do later," Charles pointed out "And that's the kind of thing we're messing around with." He started for the door; Lee turned to follow, and Murdoch stood up and moved away from the console. Charles went on, "I think what it proves is that idle playing around like this isn't going to help us make sense out of it. We need to sit down and work out a systematic approach. I agree with you, Lee. I don't believe in mystical forces or any of that trash either. As I've said, I've only been working on this myself for a matter of days, so I don't pretend to have many answers as yet. This whole thing takes us into a new realm of physics that's stranger than anything you can imagine. But I believe it is part of physics, nevertheless, and there is some kind of sense at the back of it all. That's what we have to see if we can work out."
As Murdoch turned to follow them toward the door, a slight movement from the lowest of the storage shelves by the workbench caught his eye. A tangle of wire and cabling, balanced precariously on the edge of the shelf, was moving as if alive. As he watched in amazement, it rolled off and tumbled to the floor. A sleepy, bewildered, black-and-white, whiskered face poked itself out and gazed about.
"Hey, who's this?" Murdoch said, stooping to disentangle the kitten from the wreckage. "A new member of the household?"
Charles looked back from the door. "Och, the wee rascal must have followed us in. He's been here a few weeks now. Do you remember John Massey who runs the garage down in the village? His wife gave it to Morna. Their cat had a litter o' five."
"He's cute." Murdoch picked up the squirming ball of fluff and held it up in front of his face. "The black chin and white patches make him look mad, kinda like a pug. What's his name?"
Charles told him.
Murdoch's mouth opened in surprise. "What!" he exclaimed. "James Clerk Maxwell? You can't call a cat that!"
"And why not, might I ask?" Charles demanded gruffly. "It's a grand name of science, and a good Scottish one on top o' that." He closed the lab door and began walking along the passageway toward the stairs that led up to the main hall. "I'll no' have any of your 'Kitty' or your 'Tibbles' or such other damn trash for as long as I'm master o' this house," he told them.
Chapter 5
Despite having been born in Los Angeles, Murdoch Ross did not consider himself to be truly an American at heart. He was by inclination more of a thinker than a proverbial American man of action. The Americans seemed to get things done while the rest of the world found time to think about what it all meant, and therefore to criticize.
One of the things he valued in life was peace and quiet. He appreciated friends who talked when they had something to say and shut up when they hadn't. That was probably one of the reasons why he had always got along well with Lee.
Breakfast next morning in the kitchen, which was where Murdoch preferred to eat when he was late in rising, was marked by a distinct lack of conversation. The meal passed with hardly a word being said, and at the end of it Murdoch found himself gazing at his empty, egg
-smeared plate with the riddle of the previous night's events still turning over and over in his mind. On the far side of the table Lee, presumably occupied with similar thoughts, was toying idly with a fork while behind him Mrs. Paisley, Charles's middle-aged, buxom, gray-haired cook, was pouring coffee into two large mugs.
Evidently, Murdoch told himself, future selves did exist who were just as "real" as the selves that existed at a given present moment. That had to be so since somebody had sent the "phantom" signals. Whoever had sent them had clearly not existed in the universe that Murdoch had perceived and formed part of, and for that matter that he still perceived and still did form part of. Therefore whoever had sent the signals had to exist in some other universe. But what universe?
There appeared to be only two possibilities. First, the phantom selves might have existed elsewhere in a system of "serial universes" similar to that which Murdoch had described to Lee during the drive from Edinburgh. On that basis there would be a future universe, one ten minutes ahead of the present one for example, in which certain events were unfolding as shaped by the past circumstances of that universe; when the present universe had advanced ten minutes, it could find that the events that it came to experience were not the same. In the meantime the former future universe would have moved onward to lie still ten minutes ahead.
This model would be like a procession of boats drifting down a river on the current, with the river being the timeline and each boat being one of an infinity of universes following sequentially along it. Each boat would be accompanied by its own present circumstances, which would be continually evolving and providing memories of pasts; a past as remembered, however, would not necessarily be identical to, or even similar to, the events that some other boat back in the line upstream was experiencing. Thus a patch of floating weed might constitute a permanent feature in the universe of one boat, but not exist at all in the universes seen by the rest.
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