by Michio Kaku
August 18, 2008
The late Carl Sagan once asked this question,
Although any conjecture about such advanced civilizations is a matter of sheer speculation, one can still use the laws of physics to place upper and lower limits on these civilizations.
In particular, now that
the laws of quantum field theory, general relativity,
thermodynamics, etc. are fairly well-established,
physics can impose broad physical bounds which constrain
the parameters of these civilizations.
Soon, humanity may face an existential shock as the current list of a dozen Jupiter-sized extra-solar planets swells to hundreds of earth-sized planets, almost identical twins of our celestial homeland.
may usher in a new era in our relationship with the
universe: we will never see the night sky in the same
way ever again, realizing that scientists may eventually
compile an encyclopedia identifying the precise
co-ordinates of perhaps hundreds of earth-like planets.
The most spectacular of these
findings was photographed by the Hubble Space Telescope,
which captured breathtaking photos of a planet 450 light
years away being sling-shot into space by a double-star
With an unprecedented resolution approaching the
physical limits of optics, the SIM is so sensitive that
it almost defies belief: orbiting the earth, it can
detect the motion of a lantern being waved by an
astronaut on Mars!
matter how many millions of years separate us from them,
they still must obey the iron laws of physics, which are
now advanced enough to explain everything from
sub-atomic particles to the large-scale structure of the
universe, through a staggering 43 orders of magnitude.
In a seminal paper published in 1964 in the Journal of Soviet Astronomy, Russian astrophysicist Nicolai Kardashev theorized that advanced civilizations must therefore be grouped according to three types:
He calculated that the energy consumption of these three types of civilization would be separated by a factor of many billions.
But how long will it take to reach Type II and
we consume about one million billionth of the suns total
energy. At present, our entire planetary energy
production is about 10 billion billion ergs per second.
But our energy growth is rising exponentially, and hence
we can calculate how long it will take to rise to Type
II or III status.
Physicist Freeman Dyson of the Institute for Advanced Study estimates that, within 200 years or so, we should attain Type I status.
In fact, growing at a modest rate of 1% per year, Kardashev estimated that it would take only 3,200 years to reach Type II status, and 5,800 years to reach Type III status.
Living in a Type I, II, or III civilization
Mark Twain once said,
This may change with a Type I civilization, which has enough energy to modify the weather.
They also have enough energy to alter the
course of earthquakes, volcanoes, and build cities on
We see the beginning of a planetary
language (English), a planetary communication system
(the Internet), a planetary economy (the forging of the
European Union), and even the beginnings of a planetary
culture (via mass media, TV, rock music, and Hollywood
ages may take place on a time scale of tens of thousands
of years, so a Type I civilization must learn to modify
the weather within that time frame.
Dyson has proposed that a Type II civilization may even build a gigantic sphere around their star to more efficiently utilize its total energy output. Even if they try to conceal their existence, they must, by the Second Law of Thermodynamics, emit waste heat.
From outer space, their
planet may glow like a Christmas tree ornament. Dyson
has even proposed looking specifically for infrared
emissions (rather than radio and TV) to identify these
Type II civilizations.
Thus, perhaps the most interesting civilization is a Type III civilization, for it is truly immortal.
exhausted the power of a single star, and have reached
for other star systems. No natural catastrophe known to
science is capable of destroying a Type III
Chemical rockets can attain specific impulses of several hundred to several thousand seconds. Ion engines can attain specific impulses of tens of thousands of seconds. But to attain near-light speed velocity, one has to achieve specific impulse of about 30 million seconds, which is far beyond our current capability, but not that of a Type III civilization.
variety of propulsion systems would be available for
sub-light speed probes (such as ram-jet fusion engines,
photonic engines, etc.)
In science fiction, the search for inhabitable worlds has been immortalized on TV by heroic captains boldly commanding a lone star ship, or as the murderous Borg, a Type III civilization which absorbs lower Type II civilization (such as the Federation).
However, the most
mathematically efficient method to explore space is far
less glamorous: to send fleets of "Von Neumann probes"
throughout the galaxy (named after John Von Neumann, who
established the mathematical laws of self-replicating
A dead moon rather than a planet makes the ideal destination for Von Neumann probes, since they can easily land and take off from these moons, and also because these moons have no erosion.
These probes would live off the land, using
naturally occurring deposits of iron, nickel, etc. to
create the raw ingredients to build a robot factory.
They would create thousands of copies of themselves,
which would then scatter and search for other star
Physicist Paul Davies of the
University of Adelaide has even raised the possibility
of a Von Neumann probe resting on our own moon, left
over from a previous visitation in our system aeons ago.
At present, scientists have
already built atomic-sized curiosities, such as an
atomic abacus with Buckyballs and an atomic guitar with
strings about 100 atoms across.
Furthermore, the development of biotechnology has opened entirely new possibilities.
These probes may act as
life-forms, reproducing their genetic information,
mutating and evolving at each stage of reproduction to
enhance their capabilities, and may have artificial
intelligence to accelerate their search.
The current SETI project only scans a few frequencies of radio and TV emissions sent by a Type 0 civilization, but perhaps not an advanced civilization. Because of the enormous static found in deep space, broadcasting on a single frequency presents a serious source of error.
Instead of putting all your eggs in one basket, a more efficient system is to break up the message and smear it out over all frequencies (e.g. via Fourier like transform) and then reassemble the signal only at the other end.
In this way, even if certain frequencies are disrupted by static, enough of the message will survive to accurately reassemble the message via error correction routines.
However, any Type
0 civilization listening in on the message on one
frequency band would only hear nonsense. In other words,
our galaxy could be teeming with messages from various
Type II and III civilizations, but our Type 0 radio
telescopes would only hear gibberish.
But with recent advances in quantum gravity and superstring theory, there is renewed interest among physicists about energies so vast that quantum effects rip apart the fabric of space and time.
Although it is by no means certain that quantum physics allows for stable wormholes, this raises the remote possibility that a sufficiently advanced civilizations may be able to move via holes in space, like Alice's Looking Glass.
these civilizations can successfully navigate through
stable wormholes, then attaining a specific impulse of a
million seconds is no longer a problem. They merely take
a short-cut through the galaxy. This would greatly cut
down the transition between a Type II and Type III
But this also means that the universe might expand forever in a Big Chill, until temperatures approach near-absolute zero. Several papers have recently laid out what such a dismal universe may look like. It will be a pitiful sight: any civilization which survives will be desperately huddled next to the dying embers of fading neutron stars and black holes.
intelligent life must die when the universe dies.
Today, we realize that sufficiently powerful rockets may
spare us from the death of our sun 5 billion years from
now, when the oceans will boil and the mountains will
melt. But how do we escape the death of the universe
beyond Type III may have enough energy to escape our
dying universe via holes in space.
But one day, many of us will gaze at the encyclopedia containing the coordinates of perhaps hundreds of earth-like planets in our sector of the galaxy.
Then we will wonder, as Sagan did, what a civilization a millions years ahead of ours will look like...