by Michio Kaku
Carl Sagan once asked this question,
it mean for a civilization to be a million years old? We
have had radio telescopes and spaceships for a few
decades; our technical civilization is a few hundred
years old... an advanced civilization millions of years
old is as much beyond us as we are beyond a bush baby or
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.
This question is no longer a matter of idle speculation.
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. This
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.
Today, every few weeks brings news of a new
Jupiter-sized extra-solar planet being discovered, the
latest being about 15 light years away orbiting around
the star Gliese 876. 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
But the best is yet to come. Early in the next decade,
scientists will launch a new kind of telescope, the
interferome try space telescope, which uses the
interference of light beams to enhance the resolving
power of telescopes.
For example, the Space Interferometry Mission (SIM), to
be launched early in the next decade, consists of
multiple telescopes placed along a 30 foot structure.
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!
The SIM, in turn, will pave the way for the Terrestrial
Planet Finder, to be launched late in the next decade,
which should identify even more earth-like planets. It
will scan the brightest 1,000 stars within 50 light
years of the earth and will focus on the 50 to 100
brightest planetary systems.
All this, in turn, will stimulate an active effort to
determine if any of them harbor life, perhaps some with
civilizations more advanced than ours.
Although it is impossible to predict the precise
features of such advanced civilizations, their broad
outlines can be analyzed using the laws of physics. No
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.
Physics of Type I, II, and III Civilizations
Specifically, we can rank civilizations by their energy
consumption, using the following principles:
The laws of thermodynamics.
Even an advanced
civilization is bound by the laws of thermodynamics,
especially the Second Law, and can hence be ranked by
the energy at their disposal.
The laws of stable matter.
Baryonic matter (e.g.
based on protons and neutrons) tends to clump into three
large groupings: planets, stars and galaxies. (This is a
well-defined by product of stellar and galactic
evolution, thermonuclear fusion, etc.) Thus, their
energy will also be based on three distinct types, and
this places upper limits on their rate of energy
The laws of planetary evolution.
civilization must grow in energy consumption faster than
the frequency of life-threatening catastrophes (e.g.
meteor impacts, ice ages, supernovas, etc.). If they
grow any slower, they are doomed to extinction. This
places mathematical lower limits on the rate of growth
of these civilizations.
In a seminal paper published in 1964 in the
Soviet Astronomy, Russian astrophysicist Nicolai
Kardashev theorized that advanced civilizations must
therefore be grouped according to three types: Type I,
II, and III, which have mastered planetary, stellar and
galactic forms of energy, respectively. He calculated
that the energy consumption of these three types of
civilization would be separated by a factor of many
But how long will it take to reach Type II and
Shorter than most realize
Berkeley astronomer Don Goldsmith reminds us that the
earth receives about one billionth of the suns energy,
and that humans utilize about one millionth of that. So
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.
“Look how far we have come in energy
uses once we figured out how to manipulate energy, how
to get fossil fuels really going, and how to create
electrical power from hydropower, and so forth; we've
come up in energy uses in a remarkable amount in just a
couple of centuries compared to billions of years our
planet has been here ... and this same sort of thing may
apply to other civilizations.”
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
For example, a Type I civilization is a truly planetary
one, which has mastered most forms of planetary energy.
Their energy output may be on the order of thousands to
millions of times our current planetary output.
Twain once said,
”Everyone complains about the weather,
but no one does anything about it.“
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
Currently, our energy output qualifies us for Type 0
status. We derive our energy not from harnessing global
forces, but by burning dead plants (e.g. oil and coal).
But already, we can see the seeds of a Type I
civilization. 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
By definition, an advanced civilization must grow faster
than the frequency of life-threatening catastrophes.
Since large meteor and comet impacts take place once
every few thousand years, a Type I civilization must
master space travel to deflect space debris within that
time frame, which should not be much of a problem. Ice
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.
Artificial and internal catastrophes must also be
negotiated. But the problem of global pollution is only
a mortal threat for a Type 0 civilization; a Type I
civilization has lived for several millennia as a
planetary civilization, necessarily achieving ecological
planetary balance. Internal problems like wars do pose a
serious recurring threat, but they have thousands of
years in which to solve racial, national, and sectarian
Eventually, after several thousand years, a Type I
civilization will exhaust the power of a planet, and
will derive their energy by consuming the entire output
of their suns energy, or roughly a billion trillion
trillion ergs per second.
With their energy output comparable to that of a small
star, they should be visible from space. 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.
Perhaps the only serious threat to a Type II
civilization would be a nearby supernova explosion,
whose sudden eruption could scorch their planet in a
withering blast of X-rays, killing all life forms. Thus,
perhaps the most interesting civilization is a Type III
civilization, for it is truly immortal. They have
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
Faced with a neighboring supernova, it would have
several alternatives, such as altering the evolution of
dying red giant star which is about to explode, or
leaving this particular star system and terra-forming a
nearby planetary system.
However, there are roadblocks to an emerging Type III
civilization. Eventually, it bumps up against another
iron law of physics, the theory of relativity. Dyson
estimates that this may delay the transition to a Type
III civilization by perhaps millions of years.
But even with the light barrier, there are a number of
ways of expanding at near-light velocities. For example,
the ultimate measure of a rockets capability is measured
by something called “specific impulse” (defined as the
product of the thrust and the duration, measured in
units of seconds).
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.)
How to Explore the Galaxy
Because distances between stars are so vast, and the
number of unsuitable, lifeless solar systems so large, a
Type III civilization would be faced with the next
question: what is the mathematically most efficient way
of exploring the hundreds of billions of stars in the
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 Von Neumann probe is a robot designed to reach distant
star systems and create factories which will reproduce
copies themselves by the thousands. 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
Similar to a virus colonizing a body many times its
size, eventually there would be a sphere of trillions of
Von Neumann probes expanding in all directions,
increasing at a fraction of the speed of light. In this
fashion, even a galaxy 100,000 light years across may be
completely analyzed within, say, a half million years.
If a Von Neumann probe only finds evidence of primitive
life (such as an unstable, savage Type 0 civilization)
they might simply lie dormant on the moon, silently
waiting for the Type 0 civilization to evolve into a
stable Type I civilization. After waiting quietly for
several millennia, they may be activated when the
emerging Type I civilization is advanced enough to set
up a lunar colony. 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.
(If this sounds a bit familiar, that's because it was
the basis of the film, 2001. Originally, Stanley Kubrick
began the film with a series of scientists explaining
how probes like these would be the most efficient method
of exploring outer space. Unfortunately, at the last
minute, Kubrick cut the opening segment from his film,
and these monoliths became almost mystical entities)
Since Kardashev gave the original ranking of
civilizations, there have been many scientific
developments which refine and extend his original
analysis, such as recent developments in nanotechnology,
biotechnology, quantum physics, etc.
nanotechnology may facilitate the
development of Von Neumann probes. As physicist
Feynman observed in his seminal essay, “There's Plenty
of Room at the Bottom,” there is nothing in the laws of
physics which prevents building armies of
molecular-sized machines. 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.
Paul Davies speculates that a space-faring civilization
could use nanotechnology to build miniature probes to
explore the galaxy, perhaps no bigger than your palm.
“The tiny probes I'm talking about will be
so inconspicuous that it's no surprise that we haven't
come across one. It's not the sort of thing that you're
going to trip over in your back yard. So if that is the
way technology develops, namely, smaller, faster,
cheaper and if other civilizations have gone this route,
then we could be surrounded by surveillance devices.”
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.
Also, information theory modifies the original Kardashev
analysis. 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.
Lastly, there is also the possibility that a Type II or
Type III civilization might be able to reach the fabled
Planck energy with their machines (10^19 billion
electron volts). This is energy is a quadrillion times
larger than our most powerful atom smasher. This energy,
as fantastic as it may seem, is (by definition) within
the range of a Type II or III civilization.
The Planck energy only occurs at the center of black
holes and the instant of the Big Bang. 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
Second, the ability to tear holes in space and time may
come in handy one day. Astronomers, analyzing light from
distant supernovas, have concluded recently that the
universe may be accelerating, rather than slowing down.
If this is true, there may be an anti-gravity force
(perhaps Einstein's cosmological constant) which is
counteracting the gravitational attraction of distant
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. All
intelligent life must die when the universe dies.
Contemplating the death of the sun, the philosopher
Bertrand Russel once wrote perhaps the most depressing
paragraph in the English language:
“...All the labors of
the ages, all the devotion, all the inspiration, all the
noonday brightness of human genius, are destined to
extinction in the vast death of the solar system, and
the whole temple of Mans achievement must inevitably be
buried beneath the debris of a universe in ruins...”
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
Astronomer John Barrows of the University of Sussex
“Suppose that we extend the classification
upwards. Members of these hypothetical civilizations of
Type IV, V, VI, ... and so on, would be able to
manipulate the structures in the universe on larger and
larger scales, encompassing groups of galaxies,
clusters, and superclusters of galaxies.”
beyond Type III may have enough energy to escape our
dying universe via holes in space.
Lastly, physicist Alan Guth of MIT, one of the
originators of the
inflationary universe theory, has
even computed the energy necessary to create a baby
universe in the laboratory (the temperature is 1,000
trillion degrees, which is within the range of these
Of course, until someone actually makes contact with an
advanced civilization, all of this amounts to
speculation tempered with the laws of physics, no more
than a useful guide in our search for extra-terrestrial
intelligence. 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
Then we will wonder, as Sagan did, what a
civilization a millions years ahead of ours will look