"If you can't send your machines back to historic or pre-historic times, what good are they?" Smith asked.

"Despite our limitations," Irina replied, "we do important work. By observing the universe in previous epochs, we measure things the astronomers cannot. For instance, it was the Time Laboratory which first derived the correct value for the Hubble Constant."

Smith had no idea what the Hubble Constant was, but decided not to pursue the matter.

Irina continued. "Three years ago, Pedro and I had an insight into how we might reach a particular point in s.p.a.ce and time. On the strength of that insight, we were able to obtain a substantial increase in our funding."

"Wait a minute," Smith replied. "I thought you said that it was theoretically impossible to steer a time machine!"

"Our solution hinges on a rather special case. There is one point we can be confident of hitting."

"Where?"

"Why, The Beginning, of course. If we put enough energy into the time field, we can send ourmachines back the full fourteen billion years to The Big Bang!"

Smith looked at the two scientists and wondered if he had fallen into an asylum for the criminally shortsighted. He blinked. "You lost me there. I don't see the point."

"Think of the universe as a giant funnel, Smith," Vasquez said. "The spout is The Big Bang and the mouth is the far future. As you go backwards in time, the universe shrinks. Therefore, the volume in which a time machine can materialize also shrinks. At the very beginning, the volume is so small that it may be considered a single point."

"Itwas a single point, wasn't it?" Smith asked. Science had bored him in school, but at least he had learned that much. "Besides, the density at the beginning of time was a h.e.l.l of a lot higher than 10 atoms per cubic centimeter!"

Vasquez looked at his superior. "We do seem to be getting ahead of ourselves, don't we, Irina?"

"Let me tell it," the laboratory director said. She turned to Smith. "Are you familiar with the concept of black holes?"

"Vaguely."

"A black hole occurs when a ma.s.sive star runs out of fuel and gravity causes it to collapse in upon itself. The force of the collapse is strong enough to squeeze the star's substance right out of existence, transforming it into a dimensionless point of infinite density.

"Such a hole is dimensionless. It does not appear so to us, however. The reason for that is that a black hole is surrounded by an 'event horizon,' which encompa.s.ses the region of s.p.a.ce where escape velocity exceeds the speed of light. Since nothing can go faster than the speed of light, the volume defined by the event horizon appears to us to be a sphere of absolute darkness. The size of that sphere depends on the amount of ma.s.s that has fallen down the hole, and can be quite large. For instance, the hole at the center of our galaxy is approximately the size of the Earth - or rather, the volume inside its event horizon is."

"What has this to do with the Big Bang?"

"It is directly applicable. In one sense, the universe itself is a black hole. It possesses an overall density large enough that one must exceed the speed of light to escape it. Therefore, the universe possesses an event horizon that defines the farthest point our telescopes can ever hope to see. The current event horizon is several billion light-years from here, of course. However, at the beginning of The Big Bang, when the universe was a dimensionless point of energy, its event horizon measured some 12 light-minutes in diameter."

"It was, in effect, a giant black hole?" Smith asked.

"Precisely," Irina replied. "That was the insight which Pedro and I had. We realized that if we sent our machines back to The Beginning, they would arrive in an empty bubble of s.p.a.ce some twelve light-minutes in diameter. There they would remain until the expanding shockwave from The Big Bang collapsed their time fields and kicked them back to us."

"What did you expect to get back? A cloud of superheated vapor?"

"Not at all. We calculate that it takes several nanoseconds for the explosion to build in strength untilit becomes dangerous. In that time, we can a.n.a.lyze the energy spectrum, detect elemental particles, and perform all manner of useful observations. The machine returns to us long before the explosion can damage it."

"So what went wrong?"

Vasquez stared at Smith for a second. "What makes you think something went wrong?"

"Why else am I here?"

Irina sighed. "You are quite right, John. So far, we have succeeded in reaching The Beginning with two machines. The results have been ... disappointing."

"How so?"

"How long a machine will stay in the past depends on where in the bubble of s.p.a.ce it materializes.

Still, no matter how quickly the initial shockwave reaches it, up until that time, the universe should be totally black. There is absolutely nothing to sense. No light, no energy, and especially no cosmic background radiation!"

"And that wasn't what you found?"

Irina shook her head. "The first machine detected an average CBR temperature of 20 degrees Centigrade and a random fluctuation 15C around that. There shouldn't be any CBR at all, and the fluctuation is totally incomprehensible."

"How long was the machine in the past?"

"Three minutes 12 seconds."

"And the second machine?"

"Four minutes, 25 seconds. The CBR readings were more or less the same both times."

"Tell him the rest," Vasquez said.

Irina chewed on her lower lip for a moment. "Energizing a time field for such a long trip is terribly expensive, John. Our appropriation allowed us to budget for up to 100 trips. By materializing throughout the 12 light-minute bubble of s.p.a.ce, we hoped to emerge within a few light-seconds of the point where The Big Bang began. Out of 75 attempts, however, we failed to reach The Beginning a total of 73 times. We have no idea why."

"What has all of this to do with me?"

"Our previous machines have been instrumented to observe the cataclysmic birth of the universe.

They were not optimized for general observations. It is our intent to use our remaining energy budget to send a different type of machine into the past. This one will be equipped with the widest possible range of sensors. It has occurred to us that there is one very general observation tool that we have not tried yet."

"What is that?" Smith asked.

"We would like to send an observer. There should not be anything to see at The Beginning, but we cannot afford to take chances. We'd like to send you!"# The time machine was a sphere some two meters in diameter. It was an instrument probe that had been modified to carry a man. It was smooth save for the various instrumentation ports and the hundred-centimeter square window set directly in front of the pilot's cramped seat. It reminded Smith of some of the first s.p.a.ce capsules.

"What sort of instruments are those?" he asked, pointing toward the square boxes that dotted the sphere's interior bulkhead.

"Film cameras," Irina said.

"Kind of old fashioned, aren't they?"

She shrugged. "All of our modern equipment uses the principle of photonics. Pedro believes that there is something about conditions at The Beginning that cause photonic devices to malfunction. For that reason, we have provided this machine with the widest possible range of technologies. Film photography may be archaic, but it was used for centuries with good results."

"I take it you don't believe your failure was due to a malfunction," he said.

She hesitated. "I can't help wondering if we are up against some sort of exclusion principle."

"What's that?"

"Consider the black hole that we were discussing earlier. Once inside the event horizon, nothing can get out. Not light, or ma.s.s, or information. What goes on inside the hole can never be known by those outside. The astrophysicists say that information exchange through an event horizon is excluded and that anexclusion principle is at work."

"And you think the same is true for visiting the moment of the Big Bang?"

"How else can our failures be explained?"

He shrugged. "It's too deep for me. I'm just the bus driver here."

She turned to him. "Then you accept our offer?"

"I'm tempted," he admitted. "Still, I need more information. As I told you at my apartment, I do not jump into these things foolishly. Why don't either you or Vasquez go?"

Irina smiled. "As you said, some of us aren't adventurous."

"Why not? Is it dangerous to travel in time?"

"Oh no! People do not ride the machines anymore, but when the laboratory was first built, several successfully traveled backward in time. They all returned safely and showed no ill effects afterwards."

"Any chance I might collide with one of your previous probes?"

"None. Time fields cannot overlap. No machine can approach another closer than about 50 meters."

"So what is there to worry about?"Again, she bit her lip in a way that Smith found very fetching. Her evening gown looked out of place in the cavernous laboratory from which the machines were launched. Still, he was glad that she had not changed into something more appropriate.

"Thereis a theoretical danger. It involves the exclusion principle."

"Oh?"

"If such a principle exists - and remember, it is only an hypothesis - it means that human beings can never know what happened during that first moment in time. We may well have suffered instrument malfunctions in the two machines that made it to The Beginning. That may have been the reason they were successful. The others did not complete their jumps because their instruments werenot malfunctioning. If there is an exclusion principle at work, any probe capable of returning meaningful data will automatically be prevented from reaching The Beginning."

Smith shrugged. "That's why you are sending me, isn't it? So that I can observe in the event of an instrument malfunction."

"Don't you see, John? By providing you with a window, we have turned you into one of our instruments. If you observe and report, then you violate the exclusion principle!"

"Are you saying that there's no chance of this machine reaching The Beginning if I'm alive and awake?"

"That is one possibility. The other is that you may make it, but that you yourself could malfunction."

"How?" he asked. "Die? Go blind?"

"We don't know."

He frowned. "What about the instruments in the two probes? Did they check out after their return?"

She nodded. "They pa.s.sed every diagnostic test we could think of."

"Then what is there to worry about?"

"We don't know," she replied. "That is what has us worried."

He slowly circled the small spherical craft with Irina in tow. Vasquez was watching them from a catwalk that ran completely around the cavern. Finally, Smith stopped and gazed through the observation hatch of the machine. The window was five centimeters thick and solid when he rapped on it with his knuckles.

"Seem's st.u.r.dy enough," he said. "I'll do it!"

"You'll pilot the machine?" she asked.

"h.e.l.l, yes! It sounds like fun."

John Thurman Smith sat in a powered lounger in Irina Scorvini's private office and sipped a tall cold drink of something he did not recognize. It had fruit juice in it and not a little alcohol. It soothed him as he lay back and collected his thoughts. His jumpsuit showed large splotches under his arms and downhis back, while his hair was plastered to his head from perspiration. No one had told him the time machine would get so hot.

He had checked his chronometer just before they had pried him out of his spherical coffin. The total trip into the past had taken 90 minutes. His machine had not reached The Beginning on the first jump, or on the eighteen tries that had followed.

A time machine that does not make it to The Beginning materializes in a universe very different from the one he was used to. It halts a few million years short of The Big Bang. In that early universe, the sky is filled with a red the color of old coals where subtle shadings mark the places giant protostars are being born.

Each time he discovered himself in the protostar universe, Smith palmed the control that returned him to the Time Laboratory. There he had waited while the machines that generated the time field recharged themselves. Then he had jumped again. On the twentieth attempt, he arrived in a place that was vastly different from the protostar universe. One look out the window told him that he had made it to the bubble of s.p.a.ce that was his goal.

His first sight of The Beginning had told him something else. In one breathtaking moment, all that was mysterious became blindingly clear. He knew the reason the previous probes had brought back such confusing data. He also knew, as Irina Scorvini had suspected, that human beings were forever precluded from observing The Big Bang. The reason for this had nothing to do with universal exclusion principles. The answer was far simpler and much more surprising!

"Did you make it?" Irina asked, speaking for the first time since white-coated technicians had helped him out of the capsule and out of the s.p.a.cesuit he had worn. Pedro Vasquez sat across the office from her, nervously twirling the ends of his mustache.

"I made it," Smith confirmed between sips.

"Well, what did you see?"

"Have you checked the cameras yet?"

"They are being unloaded now. We'll have the film developed within the hour."

"Good. I will need photographic evidence to back up what I am about to tell you. It's the only way anyone will ever believe me."

"Out with it man!" Vasquez growled.

Smith set his gla.s.s down and turned to face the deputy director of the laboratory. "One thing I learned from my travels is that the universe is a very large place indeed. How many stars would you say are in an average galaxy, Vasquez?"

"Approximately 100 billion."

"And how many galaxies in all?"

"A trillion or more."

"Did it ever occur to either of you that there might be other intelligent races out among the stars?"

"Of course," Irina said. "It's a mathematical certainty.""What about time? Do you suppose there were races that developed before the Earth cooled, and others who will come into existence long after our sun has sputtered out?"

"Highly likely. What has this to do with the problem at hand, John?"

"Have you considered that every race which reaches a certain technological level will probably invent time travel? What are the chances that any of them will be able to steer their machines any better than we can?"