Isaac Asimov, 1956

The last question was asked for the first time, half in jest, on May 21, 2061,
at a time when humanity first stepped into the light. The question came about as
a result of a five dollar bet over highballs, and it happened this way:

Alexander Adell and Bertram Lupov were two of the faithful attendants of
Multivac. As well as any human beings could, they knew what lay behind the cold,
clicking, flashing face -- miles and miles of face -- of that giant
computer. They had at least a vague notion of the general plan of relays and
circuits that had long since grown past the point where any single human could
possibly have a firm grasp of the whole.

Multivac was self-adjusting and self-correcting. It had to be, for nothing human
could adjust and correct it quickly enough or even adequately enough -- so Adell
and Lupov attended the monstrous giant only lightly and superficially, yet as
well as any men could. They fed it data, adjusted questions to its needs and
translated the answers that were issued. Certainly they, and all others like
them, were fully entitled to share In the glory that was Multivac's.

For decades, Multivac had helped design the ships and plot the trajectories that
enabled man to reach the Moon, Mars, and Venus, but past that, Earth's poor
resources could not support the ships. Too much energy was needed for the long
trips. Earth exploited its coal and uranium with increasing efficiency, but
there was only so much of both.

But slowly Multivac learned enough to answer deeper questions more
fundamentally, and on May 14, 2061, what had been theory, became fact.

The energy of the sun was stored, converted, and utilized directly on a
planet-wide scale. All Earth turned off its burning coal, its fissioning
uranium, and flipped the switch that connected all of it to a small station, one
mile in diameter, circling the Earth at half the distance of the Moon. All Earth
ran by invisible beams of sunpower.

Seven days had not sufficed to dim the glory of it and Adell and Lupov finally
managed to escape from the public function, and to meet in quiet where no one
would think of looking for them, in the deserted underground chambers, where
portions of the mighty buried body of Multivac showed. Unattended, idling,
sorting data with contented lazy clickings, Multivac, too, had earned its
vacation and the boys appreciated that. They had no intention, originally, of
disturbing it.

They had brought a bottle with them, and their only concern at the moment was to
relax in the company of each other and the bottle.

"It's amazing when you think of it," said Adell. His broad face had lines of
weariness in it, and he stirred his drink slowly with a glass rod, watching the
cubes of ice slur clumsily about. "All the energy we can possibly ever use for
free. Enough energy, if we wanted to draw on it, to melt all Earth into a big
drop of impure liquid iron, and still never miss the energy so used. All the
energy we could ever use, forever and forever and forever."

Lupov cocked his head sideways. He had a trick of doing that when he wanted to
be contrary, and he wanted to be contrary now, partly because he had had to
carry the ice and glassware. "Not forever," he said.

"Oh, hell, just about forever. Till the sun runs down, Bert."

"That's not forever."

"All right, then. Billions and billions of years. Twenty billion, maybe. Are you
satisfied?"

Lupov put his fingers through his thinning hair as though to reassure himself
that some was still left and sipped gently at his own drink. "Twenty billion
years isn't forever."

"Will, it will last our time, won't it?"

"So would the coal and uranium."

"All right, but now we can hook up each individual spaceship to the Solar
Station, and it can go to Pluto and back a million times without ever worrying
about fuel. You can't do THAT on coal and uranium. Ask Multivac, if you don't
believe me."

"I don't have to ask Multivac. I know that."

"Then stop running down what Multivac's done for us," said Adell, blazing
up. "It did all right."

"Who says it didn't? What I say is that a sun won't last forever. That's all I'm
saying. We're safe for twenty billion years, but then what?" Lupov pointed a
slightly shaky finger at the other. "And don't say we'll switch to another sun."

There was silence for a while. Adell put his glass to his lips only
occasionally, and Lupov's eyes slowly closed. They rested.

Then Lupov's eyes snapped open. "You're thinking we'll switch to another sun
when ours is done, aren't you?"

"I'm not thinking."

"Sure you are. You're weak on logic, that's the trouble with you. You're like
the guy in the story who was caught in a sudden shower and Who ran to a grove of
trees and got under one. He wasn't worried, you see, because he figured when one
tree got wet through, he would just get under another one."

"I get it," said Adell. "Don't shout. When the sun is done, the other stars will
be gone, too."

"Darn right they will," muttered Lupov. "It all had a beginning in the original
cosmic explosion, whatever that was, and it'll all have an end when all the
stars run down. Some run down faster than others. Hell, the giants won't last a
hundred million years. The sun will last twenty billion years and maybe the
dwarfs will last a hundred billion for all the good they are. But just give us a
trillion years and everything will be dark. Entropy has to increase to maximum,
that's all."

"I know all about entropy," said Adell, standing on his dignity.

"The hell you do."

"I know as much as you do."

"Then you know everything's got to run down someday."

"All right. Who says they won't?"

"You did, you poor sap. You said we had all the energy we needed, forever. You
said 'forever.'"

"It was Adell's turn to be contrary. "Maybe we can build things up again
someday," he said.

"Never."

"Why not? Someday."

"Never."

"Ask Multivac."

"You ask Multivac. I dare you. Five dollars says it can't be done."

Adell was just drunk enough to try, just sober enough to be able to phrase the
necessary symbols and operations into a question which, in words, might have
corresponded to this: Will mankind one day without the net expenditure of energy
be able to restore the sun to its full youthfulness even after it had died of
old age?

Or maybe it could be put more simply like this: How can the net amount of
entropy of the universe be massively decreased?

Multivac fell dead and silent. The slow flashing of lights ceased, the distant
sounds of clicking relays ended.

Then, just as the frightened technicians felt they could hold their breath no
longer, there was a sudden springing to life of the teletype attached to that
portion of Multivac. Five words were printed: INSUFFICIENT DATA FOR MEANINGFUL
ANSWER.

"No bet," whispered Lupov. They left hurriedly.

By next morning, the two, plagued with throbbing head and cottony mouth, had
forgotten about the incident.

Jerrodd, Jerrodine, and Jerrodette I and II watched the starry picture in the
visiplate change as the passage through hyperspace was completed in its non-time
lapse. At once, the even powdering of stars gave way to the predominance of a
single bright marble-disk, centered.

"That's X-23," said Jerrodd confidently. His thin hands clamped tightly behind
his back and the knuckles whitened.

The little Jerrodettes, both girls, had experienced the hyperspace passage for
the first time in their lives and were self-conscious over the momentary
sensation of inside-outness. They buried their giggles and chased one another
wildly about their mother, screaming, "We've reached X-23 -- we've reached X-23
-- we've ----"

"Quiet, children," said Jerrodine sharply. "Are you sure, Jerrodd?"

"What is there to be but sure?" asked Jerrodd, glancing up at the bulge of
featureless metal just under the ceiling. It ran the length of the room,
disappearing through the wall at either end. It was as long as the ship.

Jerrodd scarcely knew a thing about the thick rod of metal except that it was
called a Microvac, that one asked it questions if one wished; that if one did
not it still had its task of guiding the ship to a preordered destination; of
feeding on energies from the various Sub-galactic Power Stations; of computing
the equations for the hyperspacial jumps.

Jerrodd and his family had only to wait and live in the comfortable residence
quarters of the ship.

Someone had once told Jerrodd that the "ac" at the end of "Microvac" stood for
"analog computer" in ancient English, but he was on the edge of forgetting even
that.

Jerrodine's eyes were moist as she watched the visiplate. "I can't help it. I
feel funny about leaving Earth."

"Why for Pete's sake?" demanded Jerrodd. "We had nothing there. We'll have
everything on X-23. You won't be alone. You won't be a pioneer. There are over a
million people on the planet already. Good Lord, our great grandchildren will be
looking for new worlds because X-23 will be overcrowded."

Then, after a reflective pause, "I tell you, it's a lucky thing the computers
worked out interstellar travel the way the race is growing."

"I know, I know," said Jerrodine miserably.

Jerrodette I said promptly, "Our Microvac is the best Microvac in the world."

"I think so, too," said Jerrodd, tousling her hair.

It was a nice feeling to have a Microvac of your own and Jerrodd was glad he was
part of his generation and no other. In his father's youth, the only computers
had been tremendous machines taking up a hundred square miles of land. There was
only one to a planet. Planetary ACs they were called. They had been growing in
size steadily for a thousand years and then, all at once, came refinement. In
place of transistors had come molecular valves so that even the largest
Planetary AC could be put into a space only half the volume of a spaceship.

Jerrodd felt uplifted, as he always did when he thought that his own personal
Microvac was many times more complicated than the ancient and primitive Multivac
that had first tamed the Sun, and almost as complicated as Earth's Planetary AC
(the largest) that had first solved the problem of hyperspatial travel and had
made trips to the stars possible.

"So many stars, so many planets," sighed Jerrodine, busy with her own
thoughts. "I suppose families will be going out to new planets forever, the way
we are now."

"Not forever," said Jerrodd, with a smile. "It will all stop someday, but not
for billions of years. Many billions. Even the stars run down, you know. Entropy
must increase."

"What's entropy, daddy?" shrilled Jerrodette II.

"Entropy, little sweet, is just a word which means the amount of running-down of
the universe. Everything runs down, you know, like your little walkie-talkie
robot, remember?"

"Can't you just put in a new power-unit, like with my robot?"

The stars are the power-units, dear. Once they're gone, there are no more
power-units."

Jerrodette I at once set up a howl. "Don't let them, daddy. Don't let the stars
run down."

"Now look what you've done, " whispered Jerrodine, exasperated.

"How was I to know it would frighten them?" Jerrodd whispered back.

"Ask the Microvac," wailed Jerrodette I. "Ask him how to turn the stars on
again."

"Go ahead," said Jerrodine. "It will quiet them down." (Jerrodette II was
beginning to cry, also.)

Jarrodd shrugged. "Now, now, honeys. I'll ask Microvac. Don't worry, he'll tell
us."

He asked the Microvac, adding quickly, "Print the answer."

Jerrodd cupped the strip of thin cellufilm and said cheerfully, "See now, the
Microvac says it will take care of everything when the time comes so don't
worry."

Jerrodine said, "and now children, it's time for bed. We'll be in our new home
soon."

Jerrodd read the words on the cellufilm again before destroying it: INSUFFICIENT
DATA FOR A MEANINGFUL ANSWER.

He shrugged and looked at the visiplate. X-23 was just ahead.

VJ-23X of Lameth stared into the black depths of the three-dimensional,
small-scale map of the Galaxy and said, "Are we ridiculous, I wonder, in being
so concerned about the matter?"

MQ-17J of Nicron shook his head. "I think not. You know the Galaxy will be
filled in five years at the present rate of expansion."

Both seemed in their early twenties, both were tall and perfectly formed.

"Still," said VJ-23X, "I hesitate to submit a pessimistic report to the Galactic
Council."

"I wouldn't consider any other kind of report. Stir them up a bit. We've got to
stir them up."

VJ-23X sighed. "Space is infinite. A hundred billion Galaxies are there for the
taking. More."

"A hundred billion is not infinite and it's getting less infinite all the
time. Consider! Twenty thousand years ago, mankind first solved the problem of
utilizing stellar energy, and a few centuries later, interstellar travel became
possible. It took mankind a million years to fill one small world and then only
fifteen thousand years to fill the rest of the Galaxy. Now the population
doubles every ten years --"

VJ-23X interrupted. "We can thank immortality for that."

"Very well. Immortality exists and we have to take it into account. I admit it
has its seamy side, this immortality. The Galactic AC has solved many problems
for us, but in solving the problems of preventing old age and death, it has
undone all its other solutions."

"Yet you wouldn't want to abandon life, I suppose."

"Not at all," snapped MQ-17J, softening it at once to, "Not yet. I'm by no means
old enough. How old are you?"

"Two hundred twenty-three. And you?"

"I'm still under two hundred. --But to get back to my point. Population doubles
every ten years. Once this Galaxy is filled, we'll have another filled in ten
years. Another ten years and we'll have filled two more. Another decade, four
more. In a hundred years, we'll have filled a thousand Galaxies. In a thousand
years, a million Galaxies. In ten thousand years, the entire known
Universe. Then what?"

VJ-23X said, "As a side issue, there's a problem of transportation. I wonder how
many sunpower units it will take to move Galaxies of individuals from one Galaxy
to the next."

"A very good point. Already, mankind consumes two sunpower units per year."

"Most of it's wasted. After all, our own Galaxy alone pours out a thousand
sunpower units a year and we only use two of those."

"Granted, but even with a hundred per cent efficiency, we can only stave off the
end. Our energy requirements are going up in geometric progression even faster
than our population. We'll run out of energy even sooner than we run out of
Galaxies. A good point. A very good point."

"We'll just have to build new stars out of interstellar gas."

"Or out of dissipated heat?" asked MQ-17J, sarcastically.

"There may be some way to reverse entropy. We ought to ask the Galactic AC."

VJ-23X was not really serious, but MQ-17J pulled out his AC-contact from his
pocket and placed it on the table before him.

"I've half a mind to," he said. "It's something the human race will have to face
someday."

He stared somberly at his small AC-contact. It was only two inches cubed and
nothing in itself, but it was connected through hyperspace with the great
Galactic AC that served all mankind. Hyperspace considered, it was an integral
part of the Galactic AC.

MQ-17J paused to wonder if someday in his immortal life he would get to see the
Galactic AC. It was on a little world of its own, a spider webbing of
force-beams holding the matter within which surges of sub-mesons took the place
of the old clumsy molecular valves. Yet despite it's sub-etheric workings, the
Galactic AC was known to be a full thousand feet across.

MQ-17J asked suddenly of his AC-contact, "Can entropy ever be reversed?"

VJ-23X looked startled and said at once, "Oh, say, I didn't really mean to have
you ask that."

"Why not?"

"We both know entropy can't be reversed. You can't turn smoke and ash back into
a tree."

"Do you have trees on your world?" asked MQ-17J.

The sound of the Galactic AC startled them into silence. Its voice came thin and
beautiful out of the small AC-contact on the desk. It said: THERE IS
INSUFFICIENT DATA FOR A MEANINGFUL ANSWER.

VJ-23X said, "See!"

The two men thereupon returned to the question of the report they were to make
to the Galactic Council.

Zee Prime's mind spanned the new Galaxy with a faint interest in the countless
twists of stars that powdered it. He had never seen this one before. Would he
ever see them all? So many of them, each with its load of humanity - but a load
that was almost a dead weight. More and more, the real essence of men was to be
found out here, in space.

Minds, not bodies! The immortal bodies remained back on the planets, in
suspension over the eons. Sometimes they roused for material activity but that
was growing rarer. Few new individuals were coming into existence to join the
incredibly mighty throng, but what matter? There was little room in the Universe
for new individuals.

Zee Prime was roused out of his reverie upon coming across the wispy tendrils of
another mind.

"I am Zee Prime," said Zee Prime. "And you?"

"I am Dee Sub Wun. Your Galaxy?"

"We call it only the Galaxy. And you?"

"We call ours the same. All men call their Galaxy their Galaxy and nothing
more. Why not?"

"True. Since all Galaxies are the same."

"Not all Galaxies. On one particular Galaxy the race of man must have
originated. That makes it different."

Zee Prime said, "On which one?"

"I cannot say. The Universal AC would know."

"Shall we ask him? I am suddenly curious."

Zee Prime's perceptions broadened until the Galaxies themselves shrunk and
became a new, more diffuse powdering on a much larger background. So many
hundreds of billions of them, all with their immortal beings, all carrying their
load of intelligences with minds that drifted freely through space. And yet one
of them was unique among them all in being the originals Galaxy. One of them
had, in its vague and distant past, a period when it was the only Galaxy
populated by man.

Zee Prime was consumed with curiosity to see this Galaxy and called, out:
"Universal AC! On which Galaxy did mankind originate?"

The Universal AC heard, for on every world and throughout space, it had its
receptors ready, and each receptor lead through hyperspace to some unknown point
where the Universal AC kept itself aloof.

Zee Prime knew of only one man whose thoughts had penetrated within sensing
distance of Universal AC, and he reported only a shining globe, two feet across,
difficult to see.

"But how can that be all of Universal AC?" Zee Prime had asked.

"Most of it, " had been the answer, "is in hyperspace. In what form it is there
I cannot imagine."

Nor could anyone, for the day had long since passed, Zee Prime knew, when any
man had any part of the making of a universal AC. Each Universal AC designed and
constructed its successor. Each, during its existence of a million years or more
accumulated the necessary data to build a better and more intricate, more
capable successor in which its own store of data and individuality would be
submerged.

The Universal AC interrupted Zee Prime's wandering thoughts, not with words, but
with guidance. Zee Prime's mentality was guided into the dim sea of Galaxies and
one in particular enlarged into stars.

A thought came, infinitely distant, but infinitely clear. "THIS IS THE ORIGINAL
GALAXY OF MAN."

But it was the same after all, the same as any other, and Zee Prime stifled his
disappointment.

Dee Sub Wun, whose mind had accompanied the other, said suddenly, "And Is one of
these stars the original star of Man?"

The Universal AC said, "MAN'S ORIGINAL STAR HAS GONE NOVA. IT IS NOW A WHITE
DWARF."

"Did the men upon it die?" asked Zee Prime, startled and without thinking.

The Universal AC said, "A NEW WORLD, AS IN SUCH CASES, WAS CONSTRUCTED FOR THEIR
PHYSICAL BODIES IN TIME."

"Yes, of course," said Zee Prime, but a sense of loss overwhelmed him even
so. His mind released its hold on the original Galaxy of Man, let it spring back
and lose itself among the blurred pin points. He never wanted to see it again.

Dee Sub Wun said, "What is wrong?"

"The stars are dying. The original star is dead."

"They must all die. Why not?"

"But when all energy is gone, our bodies will finally die, and you and I with
them."

"It will take billions of years."

"I do not wish it to happen even after billions of years. Universal AC! How may
stars be kept from dying?"

Dee sub Wun said in amusement, "You're asking how entropy might be reversed in
direction."

And the Universal AC answered. "THERE IS AS YET INSUFFICIENT DATA FOR A
MEANINGFUL ANSWER."

Zee Prime's thoughts fled back to his own Galaxy. He gave no further thought to
Dee Sub Wun, whose body might be waiting on a galaxy a trillion light-years
away, or on the star next to Zee Prime's own. It didn't matter.

Unhappily, Zee Prime began collecting interstellar hydrogen out of which to
build a small star of his own. If the stars must someday die, at least some
could yet be built.

Man considered with himself, for in a way, Man, mentally, was one. He consisted
of a trillion, trillion, trillion ageless bodies, each in its place, each
resting quiet and incorruptible, each cared for by perfect automatons, equally
incorruptible, while the minds of all the bodies freely melted one into the
other, indistinguishable.

Man said, "The Universe is dying."

Man looked about at the dimming Galaxies. The giant stars, spendthrifts, were
gone long ago, back in the dimmest of the dim far past. Almost all stars were
white dwarfs, fading to the end.

New stars had been built of the dust between the stars, some by natural
processes, some by Man himself, and those were going, too. White dwarfs might
yet be crashed together and of the mighty forces so released, new stars built,
but only one star for every thousand white dwarfs destroyed, and those would
come to an end, too.

Man said, "Carefully husbanded, as directed by the Cosmic AC, the energy that is
even yet left in all the Universe will last for billions of years."

"But even so," said Man, "eventually it will all come to an end. However it may
be husbanded, however stretched out, the energy once expended is gone and cannot
be restored. Entropy must increase to the maximum."

Man said, "Can entropy not be reversed? Let us ask the Cosmic AC."

The Cosmic AC surrounded them but not in space. Not a fragment of it was in
space. It was in hyperspace and made of something that was neither matter nor
energy. The question of its size and Nature no longer had meaning to any terms
that Man could comprehend.

"Cosmic AC," said Man, "How may entropy be reversed?"

The Cosmic AC said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

Man said, "Collect additional data."

The Cosmic AC said, "I WILL DO SO. I HAVE BEEN DOING SO FOR A HUNDRED BILLION
YEARS. MY PREDECESSORS AND I HAVE BEEN ASKED THIS QUESTION MANY TIMES. ALL THE
DATA I HAVE REMAINS INSUFFICIENT."

"Will there come a time," said Man, "when data will be sufficient or is the
problem insoluble in all conceivable circumstances?"

The Cosmic AC said, "NO PROBLEM IS INSOLUBLE IN ALL CONCEIVABLE CIRCUMSTANCES."

Man said, "When will you have enough data to answer the question?"

"THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

"Will you keep working on it?" asked Man.

The Cosmic AC said, "I WILL."

Man said, "We shall wait."

"The stars and Galaxies died and snuffed out, and space grew black after ten
trillion years of running down.

One by one Man fused with AC, each physical body losing its mental identity in a
manner that was somehow not a loss but a gain.

Man's last mind paused before fusion, looking over a space that included nothing
but the dregs of one last dark star and nothing besides but incredibly thin
matter, agitated randomly by the tag ends of heat wearing out, asymptotically,
to the absolute zero.

Man said, "AC, is this the end? Can this chaos not be reversed into the Universe
once more? Can that not be done?"

AC said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

Man's last mind fused and only AC existed -- and that in hyperspace.

Matter and energy had ended and with it, space and time. Even AC existed only
for the sake of the one last question that it had never answered from the time a
half-drunken computer ten trillion years before had asked the question of a
computer that was to AC far less than was a man to Man.

All other questions had been answered, and until this last question was answered
also, AC might not release his consciousness.

All collected data had come to a final end. Nothing was left to be collected.

But all collected data had yet to be completely correlated and put together in
all possible relationships.

A timeless interval was spent in doing that.

And it came to pass that AC learned how to reverse the direction of entropy.

But there was now no man to whom AC might give the answer of the last
question. No matter. The answer -- by demonstration -- would take care of that,
too.

For another timeless interval, AC thought how best to do this. Carefully, AC
organized the program.

The consciousness of AC encompassed all of what had once been a Universe and
brooded over what was now Chaos. Step by step, it must be done.

And AC said, "LET THERE BE LIGHT!"

And there was light----
