by Larry Niven
What should he write? "The world is my ash tray," he decided, and slammed his toe into a ledge. He threw both hands out to break his fall, and changed his mind too late. Horrified, he watched the sculpting pencil vanish into the floor. It left a neat cylindrical hole.
Well, Mike thought furiously, that takes care of that. I've made my mark.
***
He plugged the hole with cement from the meteor repair kit on his suit belt. There was now a machine missing from the base, one that had been there in his own time, but he couldn't do anything about that. He did manage to close the airlock doors as he left.
The breathtaking beauty of the full Earth stopped him outside the ship. He gazed at the magnificent bluish-white disk, trying to decide what made it seem different. Was there more cloud area? Whatever the reason, the sight was more impressive than ever.
Then it came to him. The Earth was bigger! It was probably twice as large as he had ever seen it. Of course, there was nothing nearby to compare it to, which was why he hadn't noticed before.
Mike was smiling as he entered the lock. The Moon has been moving outward from the Earth since creation, picking up energy from'the slowing of the Earth's rotation. He must be a long way into the past.
About three billion years...
He pushed through the inner door and stood a moment, looking down the three broken rows— one along the floor of the ship, the others down the sides— of amethyst portholes. It would have been nice to be able to see out, but the glassy material was transparent only to a wide range of ultraviolet light.
He went through the motions at the control panel. Right pyramid knob in— and it had better be the right move. Generator on. Glass block between the poles. Generator off.
He floated.
Suddenly, remembering the sight of the central pyramid "turning," Mike was glad that he could not see the ship traveling through time. Obviously the aliens could stand the sight— but they could also look at the central pyramid, for they had done nothing to protect themselves from it.
A green line crept across the board, covering and wiping out the faint purple line.. Mike let it grow until the purple line was gone, then slipped on his generator.
Wrong. Wrong! He was still in free fall!
***
In hideous indecision he watched the board, waiting for it to tell him— it didn't matter what, for the board was quiet and dark. In the end he left the knob in and the generator on and pushed himself aft. He had to get a look outside.
He braced himself in the airlock, suspiciously examining the brilliant sky for any sign that he was still traveling in time. There was nothing. Mike turned on his shoes and gingerly stepped out onto the hull.
When he looked down, the Moon wasn't there.
A misty white planet floated nearby. It was a heavy atmosphere type, as uniform and featureless as a piece of bedsheet. It was Venus, if he was still in the solar sysiem. Otherwise— heavy atmospheres are the norm in space.
It seemed obvious now that he'd guessed wrong. The knob on the left must control time travel; the one on the right, space travel. It was a chance he'd had to take.
Mike watched the white disk slowly setting toward one horizon of the ship. As the last thing he might see in life it left a lot to be desired. Still, blank as it was, he could tell quite a bit about it. It couldn't be very large, for instance. If it were a giant, its atmosphere would be banded. It must be bigger than Mars to have an opaque atmosphere, but unless an oversized moon had stripped away most of the air, it couldn't be much larger than Earth.
When he saw its star he could try guessing its surface temperature.
He sat down on the hull. There were two days' worth of oxygen in the ship, and little chance that it would get him home. He was lost in both space and time. He didn't know how to go into the future; if there was a way, he could expect to spend months looking for it. It was time to face death.
Besides, he'd been running for hours, torn by conflicting emotions, through a world whose laws were more black magic than physics. It was high time for a coffee break.
Mike licked dry lips. That last, lost cup of coffee would have tasted wonderful. A cigarette would have torn his throat out after four and a half years, but it would have felt natural and smelled good smoldering between his fingers.
He'd left precious little legacy for the others at the base, a spare spacesuit that couldn't fit anyone else, three sets of lounging overalls, and a few interesting discoveries. He'd taken the spaceship; they'd cuss him out good for that...
Or had he ever lived at all? He had died before he was born. Perhaps there would be no Mike Capoferri, ever.
But UN Flight Four would find his anonymous traces when they opened the base. Footprints in moondust. A sculpting tool missing from the rec room. A hole in the floor; his cement was sure to disintegrate in three billion years. Would they ever guess how deep it was? The damn thing must have fallen all the way to the center of the Moon.
Searing light stabbed his eyes. Mike groped blindly for his filter switch, and found it. The light became bearable.
***
A sun was rising over the hull. It looked very much like the Sun as seen from the Moon; but that only meant that it wasn't. Seen from a Venus orbit, the Sun would have been much larger. He was in another solar system.
Could the ship have come home by itself? Was that the home world of the base race? No, of course not. The aliens had had a water metabolism, and there would be no water down there. That world, in an Earthlike orbit around a type G yellow dwarf, must have a surface temperature of around five hundred degrees Fahrenheit.
Mr. Parkman in Physics 1B had told the class one day that "The Earth's atmosphere goes way past the Moon." He seemed surprised by their laughter. It was his highly successful way of holding their attention.
"No, it's true. Of course, it gets pretty thin. The idea is that the Earth's atmosphere ends where its density drops to the density of surrounding space. In the same way the Sun's atmosphere goes out beyond Mars.
"Well, the air is thin enough to behave like separate particles at that distance. So the Moon is constantly whipping through this cloud of gas molecules" —he made frantic motions with his hands— "and it pulls some of them up to escape velocity every time it goes by. Naturally they're never heard from again. The air keeps replacing itself, more or less, by volcanic action.
"Now, most planets don't have giant moons, so they grow tremendous air envelopes. Like Venus.
Here's where the greenhouse effect comes in..."
Mike snapped back to the present because of something small and dark and spinning. With the light filter over his eyes he couldn't see more. He looked away. Something was worrying at the bottom of his mind.
Again his mind's eye watched the sculpting tool fall into a tunnel of its own making. He saw it lying at the center of the Moon, perhaps carving out a little pit for itself...
Wrong. There would be millions of tons of pressure to flatten any cavity into oblivion ...
Any cavity but one. Now the picture was right.
The Sun had dropped below the hull, though part of the corona still showed. Mike raised his filter and searched for the spinning blob. He knew what it was, now.
At first glance it looked like a walnut shell; but not quite, for the shape was wrong and the convolutions were too deep. What it really resembled was a deflated beach ball which somebody has crushed between his hands.
The Moon had had a long time to push itself through a sphere an inch and a half in diameter. Probably it had not taken more than a few millennia. Afterward there had been nothing but this crumpled ball of waste, too light and rigid for gravity to compress it further. For three billion years the Earth had been moonless.
"...six to eight hundred degrees!" Mr. Parkman waited a moment while the scribblers caught up. "They knew about the greenhouse effect, but they hadn't dreamed that it would apply to little Venus. You could melt lead in such a greenhouse."
"The point
is, the astronomers were using Earth as a norm. It isn't. The Earth-Moon system is an astronomical freak. A normal planet in Earth's orbit would have an opaque, very thick atmosphere, so thick that wind and light and temperature changes would never reach the surface. An eternal searing black calm."
***
Mike turned and crawled into the airlock, moving as fast as he dared in free fall. He could have gone mad waiting for the inner door to open, but he didn't dare. The knowledge of certain death had been better than this aching sense of responsibility.
The door opened and he jumped toward the control board. Already he was planning. He had to go back some time before his first arrival. Then— remove the sculpting tools from the rec room, or somehow scramble the controls of the base airlock, or leave a message for "himself" on the outer door. Anything to restore the past.
The glass block had not floated out of place. All he had to do was cut the magnetic field. He watched the purple line until he was sure that it was longer than it had been before. When he flipped the generator back on his feet thumped satisfyingly against the floor. Half the battle.
Ghosts from his childhood whispered to him while he waited for the outer door to open. Parkman was there but Mike refused to listen to him. He remembered Tony; which was unfair, because he'd only robbed Tony of eight years.
The door opened on the Moon. Mike bounded toward the base... Or had he? He really should have known better than to loan Tony his Flexy. His Flexy, because Tony's had a broken wheel. Had he told Doctor Stuart that? No.
"Time is a one-way street," said Doctor Stuart, sympathetically but firmly. He was wrong, dead wrong.
Mike stood before the base airlock wriggling his fingers like a clarinet player. How far back had he come this time? He turned left to see the size of the Earth.
It wasn't there.
But it was always there! Bewildered, Mike peered around him. The Moon must still be rotating...
To his right, the Earth was a vast, incredible crescent, and the plain was full of ships. They were of many different sizes, but they all had the same lumpy cylindrical shape. Tiny figures moved among them.
Stuart was right, he thought idiotically. You go the wrong way on a one-way street, you've got to have accidents. He turned and ran.
Behind him the lock swung open. Two ten-foot tripeds turned to each other and gestured rapidly, like nests of striking snakes. Then one of them hopped after him and picked him up.
About the Author
Larry Niven was born on April 30, 1938, in Los Angeles, California. In 1956, he entered the California Institute of Technology, only to flunk out a year and a half later after discovering'a bookstore jammed with used science-fiction magazines. He graduated with a B.A. in mathematics (minor in psychology) from Washburn University, Kansas, in 1962, and completed one year of graduate work in mathematics at UCLA before dropping out to write. His first published story, "The Coldest Place," appeared in the December 1964 issue of Worlds of If.
Larry Niven's interests include backpacking with the Boy Scouts, science-fiction conventions, supporting the conquest of space, and AAAS meetings and other gatherings of people at the cutting edge of the sciences.
He won the Hugo Award for Best Short Story in 1966 for "Neutron Star," and in 1974 for "The Hole Man." The 1975 Hugo Award for Best Novelette was given to "The Borderland of Sol." His novel Ringworld won the 1970 Hugo Award for Best Novel, the 1970 Nebula Award for Best Novel, and the 1972 Ditmars, an Australian award for Best International Science Fiction. With Jerry Pournelle, he has written Lucifer's Hammer and Footfall, both national bestsellers.