Up to the year 2100, the numbers of mankind had increased rapidly and
continuously, but from that time on, there was a steady decrease. By
2500, their number was a scant two millions, out of a population that
once totaled many hundreds of millions, and was close to ten billions in
2100.

Some few of these remaining two millions devoted themselves to the
adventure of discovery and exploration of places unseen, of other worlds
and other planets. But fewer still devoted themselves to the highest
adventure, the unseen places of the mind. Machines--with their
irrefutable logic, their cold preciseness of figures, their tireless,
utterly exact observation, their absolute knowledge of mathematics--they
could elaborate any idea, however simple its beginning, and reach the
conclusion. From any three facts they even then could have built in mind
all the Universe. Machines had imagination of the ideal sort. They had
the ability to construct a necessary future result from a present fact.
But Man had imagination of a different kind, theirs was the illogical,
brilliant imagination that sees the future result vaguely, without
knowing the why, nor the how, and imagination that outstrips the machine
in its preciseness. Man might reach the conclusion more swiftly, but the
machine always reached the conclusion eventually, and it was always the
correct conclusion. By leaps and bounds man advanced. By steady,
irresistible steps the machine marched forward.

Together, man and the machine were striding through science
irresistibly.

Then came the Outsiders. Whence they came, neither machine nor man ever
learned, save only that they came from beyond the outermost planet, from
some other sun. Sirius--Alpha Centauri--perhaps! First a thin scoutline
of a hundred great ships, mighty torpedoes of the void a thousand
kilads[1] in length, they came.

And one machine returning from Mars to Earth was instrumental in its
first discovery. The transport-machine's brain ceased to radiate its
sensations, and the control in old Chicago knew immediately that some
unperceived body had destroyed it. An investigation machine was
instantly dispatched from Deimos, and it maintained an acceleration of
one thousand units.[2] They sighted ten huge ships, one of which was
already grappling the smaller transport-machine. The entire fore-section
had been blasted away.

The investigation machine, scarcely three inches in diameter, crept into
the shattered hull a