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by Michio Kaku
from MichioMaku Website
The late Carl Sagan once asked
this question,
“What 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.”
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:
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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.
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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.
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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?
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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,
“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.
Mark
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 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
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.
A variety of
propulsion systems would be available for sub-light speed probes (such as
ram-jet fusion engines, photonic engines, etc.)
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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
“Von Neumann probes” 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)
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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, “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.
Davies says,
“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.
.
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.
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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
itself?
Astronomer John Barrows of the University of Sussex
writes,
“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.”
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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