Michio Kaku, professor of theoretical physics at City University of New York, in the current issue of Cosmos writes that Sagan’s question is no longer just a matter of idle speculation.

Soon, humanity may face an existential shock as we discover Earth-sized twins of our planet orbiting nearby solar systems. This may usher in a new era in our relationship with the universe, so that we will never see the night sky in the same way. Realizing that scientists may eventually compile an encyclopedia identifying the precise coordinates of perhaps hundreds of Earth-like planets, gazing at the night sky, we will forever after wonder if someone is gazing back at us.

Kaku takes up where some/one of the world’s pioneer astronomers left off with a definition of civilizations in the universe that mimics the work of Russian astrophysicist Kardashev. Inspired at the age of five by a Moscow Planetariumshow about Giordano Bruno,  Kardashev definined three levels of advanced civilizations based on how they harness energy to fuel their societies. All three categories of civilizations, even the most advanced Type 111, would still be bound by the laws of physics thatallow us to predict the behavior of the universe from the subatomic world to the large-scale structure of the universe, through a staggering 43 orders of magnitude (a factor of 10 million billion billion billion billion).

Type 1 civilizations would have a technological level similar to ours at present, as measured by total energy consumption. Carl Sagan estimated that Earth qualifies as a Type 0.7 civilisation.Type 11 civilizations would be capable of harnessing the energy of their own star -constructing, for example, a Dyson Sphere. And Type 111 civilizations would be able to utilize energy on the scale of their own galaxies. Kardeschev and Kaku believe there is an extremely low probability of detecting Type 1 civilizations and suggests that type 11 or 111 civilizations would make better targets.Kardeschev calculated that the energy consumption of these three types of civilizations would be separated by a factor of about 10 billion.

In 1963 Kardeschev searched for traces of the more advanced type 11 and 111 at the 920 MHz wavelength creating an uproar of excitement thinking he had discover signals from a Type 11 civilization that later proved to be an ordinary quasar with a large redshift. A similar uproar occurred in 1967 when regular signals were detected by radio telescopes at Cambridge, England, which turned out to be the first discovery of neutron stars.

Over the next few years, according to Kaku, “New spaceborne telescopes will finally become powerful enough to identify twins of Earth. The Kepler telescope, to be launched in 2008, will probably be able to identify terrestrial planets – rocky worlds rather than gas giants like Jupiter and Saturn. Until 2012 it will scan as many as 100,000 Sun-like stars up to 2,000 light years away, and perhaps identify hundreds of Earth-like worlds by detecting the slight loss of light they cause as they pass in front of their mother star. Kepler will hopefully identify 185 such planets with less than 1.3 times the radius of Earth, and as many as 640 terrestrial planets less than 2.2 times.”

The Terrestrial Planet Finder, expected to be launched in about 2014, will scan the brightest 1,000 stars within 50 light years of Earth, and focus on the 50 to 100 brightest planetary systems, analyzing the faint light reflected from these planets to determine if they can support the organic chemistry that make life possible.

All this, Kaku predicts “will stimulate an active effort to discover if any of them harbor life, perhaps some with civilizations more advanced than ours. According to the laws of planetary evolution, any advanced civilization must grow in energy consumption faster than the frequency of life-threatening catastrophes, such as meteor impacts, ice ages, or supernova explosions. If their growth rate stays any slower, they are doomed to extinction. Thus, this places mathematical lower limits on the growth rates of these civilizations.

Kaku believes along Princeton physicist Freeman Dyson, that although human civilization has only recently begun to master planetary energies -fossil fuels, passive solar, wind, geothermal and nuclear fission, and may one day soon crack nuclear fusion-hat, within a century or two, we should attain Type I status. In fact, growing at a modest rate of 1 per cent 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.

By definition, Kaku proposes that 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 to million years, a Type I civilization must master space travel to deflect space debris within that time, which should not be much of a problem. Ice ages may take place on a time scale of tens of thousands of years, and so a Type I civilization must learn to modify the weather within that period.

Artificial and internal catastrophes must also be negotiated. Global pollution is a mortal threat for a Type 0 civilization, but not a Type I civilization, which has lived for several millennia as a global force and necessarily achieved ecological balance with its home planet. Internal problems such as wars do present a serious recurring threat, but emerging civilizations have thousands of years in which to solve their racial, national, and sectarian conflicts. Since it would take centuries or even millennia for a Type I civilization to terraform nearby planets, its peoples will have plenty of time to work out their internal differences on the same planet before they finally leave the mother planet in any significant numbers.

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 life-destroying gamma-rays. The most potentially interesting civilization is a Type III civilization, “for it is truly immortal. It has exhausted the power of a single star, and has reached out to other star systems. No natural catastrophe known to science has the capacity to destroy a Type III civilization.”

Faced with an exploding supernova, a Type 111 would have several alternatives, for example altering the evolution of a dying red giant star which is about to explode, or leaving this particular star system and terraforming a nearby planetary system. Kaka continues:

However, there are roadblocks to an emerging Type III civilization. Eventually, it bumps into Einstein’s theory of relativity. Nothing can travel faster than light, which is about 300,000km a second (for a possible loophole, see the end of this article). Since the universe is so vast and space is so empty, this absolute speed limit tends to hold back a civilization’s successful expansion. Dyson estimates that this roadblock may delay the transition from a Type II to a Type III civilization by perhaps a million years or more.

So what is the most efficient way of exploring the hundreds of billions of stars in the galaxy?

Kaku writes that the solution is to to send fleets of ‘von Neumann probes’ throughout the galaxy (named after John von Neumann, the Hungarian-born mathematician who defined the mathematical laws of self-replicating systems).

A von Neumann probe is a robot designed to reach distant star systems and create factories that will reproduce copies of themselves by the thousands. For von Neumann probes, a planet is a less ideal destination than a dead moon; these have no atmosphere and no erosion, which means the probes can easily land and take off and can ‘live off the land’, using naturally occurring deposits of iron, nickel and other minerals to build replicants for dispersal in search for other star systems.

Arizona State University physicist Paul Davies, has even raised the possibility that a von Neumann probe could be resting on our own Moon, left over from a previous visitation in our system aeons ago -the plot foundation of the film, 2001: A Space Odyssey. Originally, apparently, Stanley Kubrick began the film with a series of scientists explaining how von Neumann-like probes would be the most efficient method of exploring space. Unfortunately, at the last minute, Kubrick cut the opening segment from his film, and the famous monoliths – von Neumann probes – became mystical entities that triggered human evolution.

The irony of a search for a Type III civilization is that they probably wouldn’t resemble anything we’d be able to recognise immediately.

Kaku concludes that that “one day, many of us could gaze at the encyclopadia that contains the coordinates of perhaps hundreds of Earth-like planets in our sector of the galaxy. Then we will ponder with wonder, as Sagan did, what an intelligent civilization a millions years ahead of ours will look like.”

Read Kaku’s brilliant essay in its entirety at Cosmos Magazine.

Posted by Casey Kazan.