10. THE GREAT SETI DEBATE
Do galactic civilizations exist?
There are two categories of thinkers:
- Contact Optimists. Those who contend that simple reasoning indicates a Universe in which life and intelligence is commonplace.
- Proponents of Uniqueness Hypothesis. Those who suggest that the Earth is probably the first and only abode for technical civilization in our Galaxy.
A philosophical debate has always raged between these two categories of thinkers. Physicist Frank Tipler, a proponent of the Uniqueness Hypothesis, assumed the von Neumann probe would be commonly adopted by advanced civilizations (if they at all exist) for galactic colonization because it is the fastest and most economical means of doing so. He proposed a conservative value of 300 million years, or less than 5% of the present age of the Galaxy. Thus, there should be a significant and obvious presence of such devices within the Solar System. Yet, no such presence has been detected. Tipler therefore concludes that we are the only intelligent society among the Galaxy’s several hundred billion stars.
The validity of this conclusion has been disputed by, among others, planetary scientists Carl Sagan and William I. Newman. Their objection is based on the Cosmological principle: “our position in the Universe cannot be preferred in any sense”. It follows from the cosmological principle that what was possible on the Earth, should be possible elsewhere. This is the problem of the locality or non-locality of the existence of life. The locality of life would mean that the life is not common phenomenon.
Sagan and Newman’s objection is a largely philosophical. Their arguments were succinctly summarized by David Darling in his website:
“[Sagan and Newman] first pointed out that Tipler had underestimated the number of von Neumann probes there ought to be. With exponential growth, a single self-replicating probe could be expected to convert the entire mass of the Galaxy into copies of itself within 2 million years. Any species intelligent enough to build such a probe, Sagan and Newman argued, would also be intelligent enough to realize the danger of it and so would not embark upon the project in the first place. In the event of a von Neumann probe being released either accidentally or maliciously, it would be a prime duty of other, responsible civilizations, said Sagan and Newman, to stamp out the “infection” before it could spread.”
The two scientists also argued that intelligent aliens might refrain from constructing fleets of self-replicating von Neumann probes because such machines might “cannibalize” their creators. Advanced aliens might have “much more exciting and fulfilling objectives…than strip-mining or colonizing every planet in sight.” Only benevolent civilizations are “pre-adapted to live with other groups in mutual respect.” And our Milky Way is packed with advanced civilizations: “We think it is possible that the Milky Way is teeming with civilizations that are far beyond our level of advance as we are beyond the ants; and paying us about as much attention as we pay to the ants.”
A similar argument was put forth by Michio Kaku: “Let’s say we have an ant hill in the middle of the forest. And right next to the ant hill, they’re building a ten-lane super-highway. And the question is: Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?” In other words, higher civilizations may exist all around us but our current technology reach is too primitive to perceive them.
On the other hand, the Rare Earth hypothesis is commonly used as an argument for the apparent absence of inhabited planets. According to this hypothesis evolution of life and eventually of intelligent life on Earth is due to a large number fortuitous events, some of which are:
- The age, size, and composition of our sun.
- The location of the Earth and inclination of its axis.
- Earth’s powerful magnetic field, caused by its nickel-iron core coupled with its rapid rotation, protects it from the effects of solar wind.
- Abundance of water and a stable oxygen-rich atmosphere.
- Development of a carbon-based chemistry requires a fine adjustment of physical constants, such as the electric charge, and even the dimension of space-time. If these constants had significantly different values, either the nucleus of the carbon atom would not be stable, or the electrons would collapse into the nucleus.
- Earth’s active interior; movement of the tectonics plates was responsible for creation of the major mountain ranges such as the Alps, the Himalayas and the Andes, giving rise to different ecological conditions favorable for the propagation of a great variety of species.
- The presence of the Moon, Jupiter, and Saturn (as shields for the bombardment of comets and meteorites during the early stages of Earth).
- Long ice ages, and especially the numerous and fortuitous catastrophes, such as the extinction of many species, like the one 65 million years ago, which led to the extermination of dinosaurs, paving the way for more diversified and complex life forms.
The prokaryotic bacteria, the first primitive life forms on Earth appeared about 500 million years (a) after the cooling off of the Earth’s crust and (b) once the epoch of dense bombardment of meteorites and comets ended. These bacteria were the only lifeforms during the first two billion years of Earth’s 4.6-billion-year history. Mammals, including apes and humans, appeared much later, only after the extinction of the dinosaurs 65 million years ago. Proconsul, an extinct genus of primates with whom gibbons, great apes and humans share a common ancestral lineage, existed from 23 to 25 million years ago during the Miocene epoch. The Australopithecus, one of the longest-lived and best-known early human species, existed only 3 to 4 million years ago. In short, it took almost 4 billion years, or about 96 percent of the age of Earth, for intelligent life to evolve, which is a long time, even in a cosmic scale.
Distinguished evolutionary biologist, Ernst Mayr, highlighted the enormous complexity of the DNA and RNA and their functions for the production of proteins, the basic building blocks of life. He estimated that the likelihood that similar biological developments happening elsewhere in the universe is almost nil.
Needless to say, proponents of both schools of thought have attempted to solve the Fermi paradox in their favor using highly speculative arguments. With so little experimental evidence, it is virtually impossible to ascertain which viewpoint is correct. It depends on the personal biases and other considerations. Sagan and Newman acknowledged that as well. Their paper “The Solipsist Approach to Extraterrestrial Intelligence” ends with the following lines:
“The question touches on religious and political matters where predispositions have traditionally played important roles. But it is abundantly clear from the history of science that no convincing resolution of this issue is likely to come from protracted debates carried on with great passion and sparse data. We have an alternative denied to the medieval scholastics: we are able to experiment. We can organize a scientifically rigorous systematic search for extraterrestrial intelligence using the technology of modern radioastronomy. That is where the energies should be focused of those concerned with the great issue of the existence of other technical civilizations in the cosmos.”
Sagan and Newman’s dream of a “scientifically rigorous systematic search” has recently become a reality, but using a completely unrelated methodology for search. This search, not so much as to find extraterrestrial civilizations, but to find signs of life in our Galaxy and beyond, is the topic of our next Section.