ROBERT A. HEINLEIN.

By His Bootstraps.

Time travel is one of the most popular of science fiction's basic themes becauseitallows the author the freedom to speculate on both the past and the future from the perspective of the present It can also provide the author and reader with the opportunity to have some intellectual funplaying with the many time-paradoxes involved-for example, if you went back in time and killed your mother before you were born, would you continue to exist?

No one in science fiction has ever engaged these issues with as muchthroughness as Robert A.

Heinlein did in this (paradoxically) rarely re-printed story that is widely considered a cla.s.sic in the field.

Bob Wilson did not see the circle grow.

Nor, for that matter, did he see the stranger who stepped out of the circle and stood staring at the back of Wilson's neck-stared, and breathed heavily, as if laboring under strong and unusual emotion.

Wilson had no reason to suspect that anyone else was in his room; he had every reason to expect the contrary. He had locked himself in his room for the purpose of completing his thesis in one sustained drive. Hehad to-tomorrow was the last day for submission, yesterday the thesis had been no more than a t.i.tle: "An InvestigationInto Certain Mathemat-ical Aspects of a Rigor of Metaphysics."

Fifty-two cigarettes, four pots of coffee and thirteen hours of continu-ous work had added seven thousand words to the t.i.tle. As to the validity of his thesis he was far too groggy to give a d.a.m.n. Get it done, was his only thought, get it done, turn it in, take three stiff drinks and sleep for a week.

He glanced up and let his eyes rest on his wardrobe door, behind which he had cached a gin bottle, nearly full. No, he admonished himself, one more drink and you'll never finish it, Bob, old son.

The stranger behind him said nothing.

Wilson resumed typing. "-nor is it valid to a.s.sume that a conceivable proposition is necessarily a possible proposition, evenwhen it is possible to formulate mathematics which describes the proposition with exactness.

A case in point is the concept 'time travel.' Time travel may be imagined and its necessities may be formulated under any and all theories of time, formulae which resolve the paradoxes of each theory.

Nevertheless, we know certain things about the empirical nature of time which preclude the possibility of the conceivable proposition. Durationis an attribute of consciousness and not of the plenum. It has no DinganSich . There-fore-"

A key of the typewriter stuck, three more jammed up on top of it. Wilson swore dully and reached forward to straighten out the cantanker-ous machinery. "Don't bother with it," he heard a voice say. "It's a lot of utter hogwash anyhow."

Wilson sat up with a jerk, then turned his head slowly around. He fervently hoped that there was someone behind him. Otherwise- He perceived the stranger with relief. "Thank G.o.d," he said to himself.

"For a moment I thought I had come unstuck." His relief turned to extreme annoyance. "Vhatthe devil are you doing in my room?" he demanded. He shoved back his chair, got up and strode over to the one door. It was still locked, and bolted on the inside.

The windows were no help; they were adjacent to his desk and three stories above a busy street. "How did you get in?" he added.

"Through that," answered the stranger, hooking a thumb toward the circle. Wilson noticed it for the first time, blinked his eyes and looked again. There it hung between them and the wall, a great disk of nothing, of the color one sees when the eyes are shut tight.

Wilson shook his head vigorously. The circle remained. "Gosh," he thought, "I was right the first time. I wonder when I slipped mytrolley? " He advanced toward the disk, put out a hand to touch it.

"Don't!"snapped the stranger.

"Why not?" said Wilsonedgily. Nevertheless he paused.

"I'll explain. But let's have a drink first." He walked directly to the wardrobe, opened it, reached in and took out the bottle ofgin without looking.

"Hey!" yelled Wilson. "What are you doing there? That'smy liquor."

"Yourliquor-" The stranger paused for a moment. "Sorry. You don't mind if I have a drink, do you?"

"I suppose not," Bob Wilson conceded in a surly tone. "Pour me one while you're about it."

"Okay," agreed the stranger, "then I'll explain."

"It had better be good," Wilson said ominously. Nevertheless he drank his drink and looked the stranger over.

He saw a chap about the same size as himself and much the same age -perhaps a little older, though a three-clay growth of beard may have accounted for that impression.

The stranger had a black eye and a freshly cut and badly swollen upper lip. Wilson decided he did not like the chaps' face. Still, there was something familiar about the face; he felt that he should have recognized it, that he had seen itmany.times before under different circ.u.mstances.

"Who are you?" he asked suddenly.

"Me?" said his guest. "Don't you recognize me?"

"I'm not sure," admitted Wilson. "Have I ever seen you before?"

"Well-not exactly," the other temporized. "Skip it-you wouldn't know about it."

"What's your name?"

"My name?Uh. . . just call me Joe."

Wilson set down his gla.s.s. "Okay, Joe Whatever-your-name-is,trot out that explanation and make it snappy."

"I'll do that," agreed Joe. "That dingus I came through"-he pointed to the circle-"that's a Time Gate."

"A what?"

"A Time Gate.Time flows along side by side on each side of the Gate, but some thousands of years apart-just how many thousands I don't know. But for the next couple of hours that Gate is open. You can walk into the future just by stepping through that circle." The stranger paused.

Bob drummed on the desk. "Go ahead. I'm listening. It's a nice story."

"You don't believe me, do you? I'll show you." Joe got up, went again to the wardrobe and obtained Bob's hat, his prized and only hat, which he had mistreated into its present battered grandeur through six years of undergraduate and graduate life. Joe chucked it toward the impalpable disk.

It struck the surface, went on through with no apparent resistance, disappeared from sight.

Wilson got up, walked carefully around the circle and examined the bare floor. "A neat trick," he conceded. "Now I'll thank you to return to me my hat."

The stranger shook his head. "You can get it for yourself when you pa.s.s through"

"That's right. Listen-" Briefly the stranger repeated his explanation about the Time Gate. Wilson, he insisted, had an opportunity that comes once in a millennium-if he would only hurry up and climb through that circle. Furthermore, though Joe could not explain in detail at the mo-ment, it was very important that Wilson go through.

Bob Wilson helped himself to a second drink, and then a third. He was beginning to feel both good and argumentative. "Why?" he said flatly.

Joe looked exasperated. "Dammit, if you'd just step through once, explanations wouldn't be necessary.

However-" According to Joe, there was an old guy on the other side who needed Wilson's help. With Wilson's help the three of them would run the country. The exact nature of the help Joe could not or would not specify. Instead he bore down on the unique possibilities for high adventure. "You don't want to slave your life away teaching numskulls in some freshwater college," he insisted. "This is your chance.

Grab it!"

Bob Wilson admitted to himself that a Ph.D. and an appointment as an instructor was not his idea of existence. Still, it beat working for a living. His eye fell on the gin bottle, its level now deplorably lowered.

That explained it. He got up unsteadily.

"No, my dear fellow," he stated, "I'm not going to climb on your merry-go-round. You know why?"

"Why?"

"Because I'm drunk, that's why. You're not there at all.Thatain't there." He gestured widely at the circle. "Thereain't anybody here but me, and I'm drunk. Been working too hard," he added apologetically. "I'mgoin ' to bed."

"You're not drunk."

"Iam drunk. Peter Piper pepped a pick ofpipperedpeckles ." He moved toward his bed.

Joe grabbed his arm. "You can't do that," he said.

"Let him alone!"

They both swung around. Facing them, standing directly in front of the circle was a third man. Bob looked at the newcomer, looked back at Joe, blinked his eyes and tried to focus them. The two looked a good bit alike, he thought, enough alike to be brothers. Or maybe he was seeing double.Bad stuff, gin.

Should 'aveswitched to rum a long time ago. Good stuff, rum. You could drink it, or take a bath in it.

No, that was gin-he meant Joe.

How silly! Joe was the one with the black eye. He wondered why he had ever been confused.

Then who was this other lug? Couldn't a couple of friends have a quiet drink together without people b.u.t.ting in?

"Who are you?" he said with quiet dignity.

The newcomer turned his head,then looked at Joe."He knows me," he saidmeaningly .

Joe looked him over slowly. "Yes," he said, "yes, I suppose I do. But what the deuce are you here for?

And why are you trying to bust up the plan?"

"No time for long-winded explanations. I know more about it than you do-you'll concede that-and my judgment is bound to be better than yours. He doesn't go through the Gate."

"I don't concede anything of the sort-"

The telephone rang.

"Answer it!" snapped the newcomer.

Bob was about to protest the peremptory tone, but decided he wouldn't. He lacked the phlegmatic temperament necessary to ignore a ringing telephone. "h.e.l.lo?"

"h.e.l.lo," he was answered. "Is that Bob Wilson?"

"Yes. Who is this?"

"Never mind.I just wanted to be sure you were there. Ithought you would be. You're right in the groove, kid,right in the groove."

Wilson heard a chuckle, then the click of the disconnection. "h.e.l.lo," he said. "h.e.l.lo!" He jiggled the bar a couple of times, then hung up.

"What was it?" asked Joe.

"Nothing.Some nut with a misplaced sense of humor." The telephone bell rang again. Wilson added, "There he is again," and picked up the receiver."Listen, you b.u.t.terfly-brained ape! I'm a busy man, and this isnot a public telephone."

"Why, Bob!"came a hurt feminine voice.

"Huh? Oh, it's you, Genevieve. Look-I'm sorry. I apologize-"

"Well, I should think you would!"

"You don't understand, honey. A guy has been pestering me over the phone and I thought it was him.

You know I wouldn't talk that way to you, babe."

"Well, I should think not. Particularly after all you said to me this afternoon, and all wemeant to each other"

"Huh?This afternoon? Did you saythis afternoon?"

"Of course.But what I called up about was this: you left your hat in my apartment. I noticed it a few minutes after you had gone and just thought I'd call and tell you where it is. Anyhow," she added coyly, "it gave me an excuse to hear your voice again."

"Sure. Fine," he said mechanically. "Look, babe, I'm a little mixed up about this. Trouble I've had all day long, and more trouble now. I'll look you up tonight and straighten it out. But Iknow I didn't leave your hat in my apartment-"

"Yourhat, silly!"

"Huh? Oh, sure! Anyhow, I'll see you tonight.'By." He rang off hurriedly. Gosh, he thought, that woman is getting to be a problem.Hallucinations. He turned to his two companions.

"Very well, Joe. I'm ready to go if you are." He was not sure just when or why he had decided to go through the time gadget, but he had. Who did this other mug think he was, anyhow, trying to interfere with a man's freedom of choice?

"Fine!" said Joe, in a relieved voice."Just step through. That's all there is to it."

"No, you don't!" It was the ubiquitous stranger. He stepped between Wilson and the Gate.

Bob Wilson faced him. "Listen, you! You come b.u.t.ting in here like you think I was a b.u.m. If you don't like it, go jump in the lake-and I'm just the kind of guy who can do it!You and who else?"