The Last Question

Isaac Asimov

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 to 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 its 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 build, 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 many 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 technician 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—