The Physics of Extra-Terrestrial Civilizations By
Michio Kaku
The Physics of Extra-Terrestrial Civilizations
How advanced could they possibly be?
By Michio Kaku
The late Carl Sagan once asked this question, ^ÓWhat does 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 a macaque.^Ô
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 system.
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:
1) 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.
2) 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 consumption.
3) The laws of planetary evolution. Any advanced 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 Journal of 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 billions. But how long will it take to reach
Type II and III status?
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.
Goldsmith says, ^ÓLook 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.^Ô
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. Mark Twain once said,
^ÔEveryone complains about the weather, but no one does
anything about it.^Ó 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 their oceans.
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 films).
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 conflicts.
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
civilization.
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 terraforming 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 ^Óspecific impulse^Ô (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. A 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 galaxy?
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 ^ÓVon Neumann probes^Ô throughout the galaxy
(named after John Von Neumann, who established the
mathematical laws of self-replicating systems).
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 systems.
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)
New Developments
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.
For example, nanotechnology may facilitate the development of
Von Neumann probes. As physicist Richard Feynman observed in
his seminal essay, ^ÓThere's Plenty of Room at the Bottom,^Ô
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. Davies says, ^ÓThe
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.^Ô
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. And if 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 civilization.
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 galaxies. 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: ^Ó...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...^Ô
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 itself?
Astronomer John Barrows of the University of Sussex writes,
^ÓSuppose 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.^Ô
Civilizations 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 hypothetical civilizations).
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 galaxy. Then we will wonder, as Sagan did,
what a civilization a millions years ahead of ours will look
like...
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