Until less than two hundred years ago, man could go on land no
faster than a racing horse, and on sea no faster than the wind
could push a ship. He couldn't travel through the air at all,
although he dreamed of it, envied and studied birds and even designed
flying machines. Leonardo Da Vinci's helicopter is a beautiful
example of that dream.
Then came the Age of Vapors O The Montgolfier brothers flew the
first hotair balloon, which made a stupefying ascent of
ten whole minutes in 1783. That same year Jacques Charles, the
distinguished physicist, filled a balloon with hydrogen, the lightest
of gases, so light that our normal atmosphere buoys 't up. Hydrogen
lifted balloons into the air, floating mountainhigh.
Steam, boiling out of water, revealed the tremendous force that
vapor under pressure could exert, and steamships and locomotives
were born. Gasoline vapor could be made to explode inside a chamber,
driving a piston, and the automobile and the airplane became realities.
Finally, flaming gaseous exhausts 7 blowing furiously downward,
thrust enormous rocket vehicles upward through all the miles of
our atmosphere and out into space itself.
In less than two centuries man reached the ultimate, the very
limit of earthly speed. An astronaut, orbiting the earth in ninety
minutes, at a distance of a hundred miles or so above the earth's
surface, is traveling at nearly five miles a second, and that
is as fast as he can go without flinging himself out into space.
pt this speed the earth's gravitational pull inward is just balanced
by the centrifugal effect of his speed which is pushing him outward,
and he remains at a fairly constant height above the earth surface.
He would not remain there forever, of course. If he did not burn
rocket fuel periodically to maintain speed, the steady friction
of the thin gases of the upper atmosphere would slow him down
and pull his capsule lower and lower, Eventually his orbit would
"decay" and he would shear into the thicker gases of
the lower atmosphere, and burn up like a meteor.
Five miles a second, or 18,000 miles an hour, is Just enough to
balance the earth's gravitational pull in the near neighborhood
of our planets surface. To break free of this grasp we must achieve
speeds on the order of 25,000 miles an hour, and this has already
been done. There have been the brilliant unmanned missions to
Venus, [cars and the moon, culminating in the magnificent achievements
of Apollo's 8 and l0. Exactly 186 years elapsed between ten minutes
in the air and ten days in space.
Now once we have attained a speed of 25,000 miles an hour or seven
miles a second, we can move on indefinitely against the pull of
the earth4is gravity which' after all, gets weaker and weaker
as we move farther away At such speeds we can coast as far as
we like without the expenditure of further fuel, and provided
we avoid being trapped in the gravitational field of any other
large astronomical object. Then we can reach any point in the
universe, given sufficient time. But that's the joker because
"sufficient time" is long indeed. Planetary distances
beyond our immediate neighborworlds of Venus and Mars are
huge, and even seven miles a second is slow. It would take over
two years to reach Jupiter's orbit at such a speed, and over sixteen
years to move into Pluto's orbit.
If we accelerate to a more rapid speed before entering the coasting
stage, the time of the Journey is cut down, but there is a limit
to what we can do in that direction. Acceleration costs fuel,
tremendous quantities of it, and if we expect to accelerate to
really high velocities with chemical rockets of the types used
today to reach the moon, the quantity of fuel required would make
a spaceship prohibitively large. me chemical rocket is not the
last word, of course. Controlled nuclear explosions would drive
exhaust gases backward at far greater velocities than is the case
with ordinary chemical combustion, and the stronger thrust of
the exhaust would allow longer accelerations and greater final
coasting velocities per mass of fuel. A nuclearpowered spaceship
could be compact and yet carry enough fuel to reach the outer
planets of the solar system.
But even with nuclear power the time of journey could not be cut
to anything that we would consider reasonable. Acceleration must
be held below a certain limit; there's just so much stress that
flesh and bone can withstand before being mashed into a jelly.
Consequently, in a journey of a certain length, only a certain
velocity can be attained. It is probable that as long as we depend
on any reaction motor, whether chemical or nuclear, exploration
of the outer solar system will involve voyages that will last
for years.
A voyage of several years is perhaps within human endurance if
the prize is large enough, but even such voyages will carry men
only throughout our own solar system. What about the regions that
lie beyond? Our sun is a member of a galaxy of stars believed
by astronomers to resemble the majestic Andromeda spiral galaxy.
Unfortunately we are so positioned that we can only see our galaxy
edgeon, but when you look at the Milky Way this summer,
remember that you '5re looking at the edge of our own galaxy and
some the approximately one hundred and thirtyfive billion
stars belonging to it. Many of these stars have planetary systems
of their own, and many of the planets have evolved some form of
life. This is not mere fantasy, Cosmologists and biologists agree
that the formation of planets and the generation ~f life are inherent
in the life history of a star.
Can we reach these other stars, perhaps with planetary systems
of their own, perhaps with some form of intelligent life inhabiting
them? Unfortunately, even the nearest star is 25 trillion miles
away, and such a distance is a most effective barrier. Coasting
along at seven miles a second, it would take a spaceship one hundred
thousand years to reach that nearest star. It would take over
two billion years for it to reach the other end of our galaxy;
and forty billion years to reach the next large neighboring galaxy,
the Andromeda nebula.
The vastness of space is actually more than the human mind can
imagine Consider the stars we see at night. Many of them are so
distant that it takes their light traveling at 186,300 7niles
a second, thousands of years to reach us. In other words, we are
looking at fossil, starlight. We have no way of knowing whether
the star that produced that light still exist as of this moment.
The solar system is a tiny island in this unimaginably large ocean
of' space. To cross the gap between one tiny planetary systyem
and another is a proposition altogether different from travel
within the solar system itself.
We might, perhaps, simply accept the time element. Suppose we
used efficient nuclear power and carried enough fuel to build
up a speed of 700 miles a second. It would still take a thousand
years or so to reach the nearest star and another thousand years
to return. To handle that we might build a ship large enough to
serve as a miniature world; a ship that would recycle its water
and air, supply its own energy from fusion reactors, grow its
own food, provide comfort for its own people. On that ship generations
of men would in turn, be born, live and die.
Eventually the thirtieth generation would reach the vicinity of
the nearest star with (who knows?) earth forgotten, the original
purpose of the spaceship a dim and legendary memory. Even
if records had been maintained the thirtieth generation might
have no interest in earth any longer but would continue in the
only way of life they know and cared for, journeying on forever
in the private little universe that was their own. This was the
unique yet 1ogical thesis of Robert T. Heinlein's classic sciencefiction
story, Universe.
For that matter, would the peoples of earth be able to maintain
enthusiasm for the building and outfitting of ship universes to
be launched in various directions toward various target stars
with no return possible during the millennium? We have engaged
in long range projects the medieval cathedrals, for
example, but only when progress however slow, was at least visible.
And who would volunteer for this sort of cruel confinement and
permanent punishment? Crackpots, perhaps, but the space agency
of the future will insist on as high standards for space pilgrims
as NASA does today for its astronauts. This doesn't seem to be
an answer.
Alternatively, it might be possible to freeze the ship's crew
for indefinite periods. Arthur Clarke used a variant of this device
in his 2001 Space Odyssey. Automatic machinery would thaw
and rouse the crew when the destination was reached. Students
of this quasiscience cal1 it cryonics, from the Greek, kyro
meaning "icy cold."' No method is now known that will
serve to freeze human beings into true suspended animation with
all physiological functions entirely unimpaired, but we may suppose
that some day a method for doing this will be discovered,
Through some highly sophisticated freezing technique, the origina1
crew of a spaceship might reach the destination even though thousands
of years had passed. Presumably they would take turns at being
reanimated for short periods so that there would always
be someone on duty. When all were revived at the finish of the
voyage they would remember its purpose and; hopefully; be highly
motivated to return to earth. But on earth those thousands of
years would also have passed, and the lack of' enthusiasm for
a project in which neither end nor progress was visible in one's
own lifetime would still be a factor.
Another factor: interestingly enough, would be the language barrier.
If the astronauts left in a.d. 2000 and returned in a.d. 4000
they would, as a result of suspended animation, still be speaking
the language of a.d. 2000. The rest or the world would not. Language
is alive and evolves and changes rapidly. Visualize yourself transported
back in time two thousand years and trying to communicate with
British Queen Boadcea.
Great time lapses must be eliminated, then. Higher speeds must
be attained; much higher speeds. One way in which this can be
done is by using an ion drive. Instead of making use of gases
heated by either chemical or nuclear reactors and emerging from
the rear in huge masses at several miles a second, we can send
individual ions out the rear. Ions are electrically charged fragments
of atoms. These ions would have very 1itt;e mass but they could
be made to move at speeds of over 2 tens of thousands of miles
per second.
An ion drive would produce very small accelerations because of
the tiny masses involved; but precisely because so little mass
is used up there would be enough fuel to continue that acceleration
for years if necessary. Speeds would build up to a hundred thousand
miles per second or more. At this rate, the nearest star could
be reached in a man's unfrozen life time and, what's more, it
could be reached in the lifetime of those on earth. Dozens of
stars might be reached in fifty years or less.
But these stars are only those in our immediate neighborhood. l~hat about more distant stars? Well, if one goes faster and ''a.,er the passage of time proceeds slower and slower for the pecder~ This was the revolutionary Qremise of Einstcin's Speciai Theory of Re~ativityO For speeds over 160 7 OOG mi~ es per second this slowing of time is considerable 7 and ;or speeds over 'L30~300 miles per second it is enormous O [stronaucs movii;g through space at teeter than 180,300 mi~i es per second mi~ht re~ch the other end of our galaxy in what seems to them to be .a rere twentyfive years That would be the L~ subjective timqe, their slowed time O On earth 7 With time moving a'.; its ~s~sl velocity, the ti~ lapse would. of course; be much greater, However, there is an ultimate speed b~yond which no ~ ~ can go. and that is 186,300 miles per second, the speed of li~ht in a vacuumc pt that spped Einstein"s theory re~lu ~es tha~i~ time slow to a complete s opO This has been giving some scien~e fiction authors a very hard timeO In order to enable the'ii spaceships to hop from galaxy to galaxy in a mattG` o+~ ~e='~s or rl~ont;hs they:tve been force to invent quite a ~raliety
Lsimov 5
of "hyperspace drives" which sort of slide around Finstein's constrainsts.
And this raises a thought. Is it absolutely necessary to transfer a massive object itself through space? Can we, perhaps, merely transfer a description of the mass? ps a familiar analogy, we need not send a document across a continent; we merely reduce it to a succession of light and dark dots that adequately characterize the documentO These are converted into a flctuating electric current, and th,is current sends its message, at the speed of light, across the continent to be reassembled at a receiving pdut into a facsimile document, Much the same technique was used in the transmission of the photographs of iilars from t~lariner IV.
Is it possible to reduce matter to a fluctuating beam of photoss (the tiny ~partic~ es" that make up light and other forms of radiant energy) that wohld completely describe that matter? The beam could then be sent across space for reconversiOn to a duplicate of that matter at some receiving point. Could a photonbeam of this sort be made to represent a human body, or a complete spaceship with its cargo of human bodies? I would hate to predict that it could, for it would be an accomplishment of unimaginable complexity, but I would have said this in 1800 concerning a flight to the moon.
If "masstransference'' becomes possible' then an astronaut could conceivably be transported anywhere in the universe at the speed of light. To that traveler no time at all would seem to have elapsed from conversion to reconversion r However, though the astronaut might experience little or no subjective timelapse at all, time uould still proceed in its ordinary fashion on earth. The photonbeam that is an astronaut would still take 4.3 years, eartht~ me, to reach the nearest star and 100,000 years to traverse the galaxy from end to end. (Incidentally, he could traverse the distance frm ear~h to moon in less than two seconds, though such a trip would take a little longer, due to the slow speeds at takeoff and landing.) Nothing so far described would make it possible to do more than reach our neighborhood stars within the lifetime of a stayathome on earth, and it would be only these neighborhood journeys that earth might be willing to support'
I!Iell then, could a spaceship travel at speeds greater than that of light? Until last year the answer would have had to be a flat negative. tgain Finsteinits imperative. The speed of light in a vacuum is the ultimate velocity, according to the Special Theory of Relativity, and no one today doubts the validity of that theory.
But in 1968 a vision that stretched beyond the ultimate was presented. Gerald Feinberg of Coulumbia University pointed out that if the speed of light was viewed as an impenetrable limiting wall, then it might be argued that a wall has two sides. On the other side of that wall there might exist a whole universe of particles that could only move faster than the speed of light, and could never slow down below the speed of light. These superfast particles he called "tachyons," from the Greek word meaning "swift O "
A.~i mr~v ~
Such tachyons would have odd properties indeed 7 and the one than concerns us at the moment is thiso The more energy you pump into a tachyon, the slower it woud go, until at very large energies it would slow down almost to the speed of lighto The less energy present in a tachyon, the faster it would go, until at very low energies it would ~ravff~ millions of lightyears per seccnd.
Tachyons would not intelact wil,h ordin~ry p~rticles and could not be detected through collishons~ which is ho~w 6~Te detect our own Einsteinian particles by tracing tneir col:Lision paths through bubblechambers O Since theymove so rapidly they remain in our vacinity for only a t.ny frcaction or a second, hardly enough for detectionO Nevertheless' theory requires a tachyon to produ~e a minute but pcrhaps dete~table iiash of light as it passes byO Physic~sts have tried to detect those flashes, but so far have [ailedO That' T~owe~cr: ~oesn~t really matter. Even if tachyons do not ex st~ Feinberg maintains that they can exist 9 and perhaps that mcanG that thougli none are to be found at the moment, some can be created f we only knew how,
I'Je have already imagined the conversion of mat, ;er hnto a stream of photons that would carry al' th_ in~ormation of matter to be reconverted into an exact dupl:'c~;c oi the original on a fardistant plo.netO Having gone t~lt''0 hogwild, why not go one more step and suppose that ma~ter co~lld be turned into a stream of tachyons rather '~han jjhotonv?
Such a beam of tachyons' if sufficiently low in energy' would move so rapidly that it migh; rc~ach th?i~cini'.r of the nearest star in five seconds That flv3 .sec~nd ti.mc.~la~se would hold not ~ly for the travelGrs themselv.< Vu' also for the stayathome earthmen, The galaxy r~ gh'. be s~anne.l in a minute; the most distant outer galax.e.s c ched a~n a week. To such a beam of tachyons the whole enormous uri!.~ers^~ould be butan insignigicant speckO
It might also be possib:.e to use modu2.ated beams of tachyons
to carry messages f: om one distant star to another. In this ~Jay
both ~'anspoli~.~inn anl commu~!.nation might become
possible over all ;3 stan^r~, how:rcr ~ :.: n?.t~ and with
virtually no timelapse' rl1his means that 'c .,s no
longer inconceivable that the day (c. ~ k~.~; a favvdiscant
one) might come when the vast universe kecomes man~s nei~hborhood