Human beings have long been occupied with the question of whether or not they are alone in the universe. Recent years have seen the development of a branch of research astronomy that deals with this question that of late has been gaining momentum intensively. More scientists around the world are prepared to devote their time to this question, and the universities, research institutes and foundations that finance them are displaying a growing tendency to invest resources in building expensive instrumentation for measurement and observation, which many think will draw us closer to an answer.
In the professional astronomical framework, the accepted term for this pursuit is the Search for Extraterrestrial Intelligence – SETI, for short. Here, the popular question “Are we alone?” generally takes a slightly different form.
About 140 years ago, an exceptional event occurred in the solar system. Inhabitants of planet Earth invented the wireless radio, and began to transmit radio waves possessing a structure organized by intelligence. Because almost all radiation on the planet, whether man-made or naturally occurring, trickles partially into space, in the intervening years – and certainly with the present flood of intra-terrestrial and satellite communications by means of radiation, Earth acquired an attribute it had never previously possessed. It became a body that emits into space radiation managed by intelligence. For short, we’ll call it “intelligent radiation.”
Engaging in SETI by means of astronomical observations can, accordingly, be described as an attempt to answer the question: Is there in the Milky Way galaxy, or in the entire universe, another source of intelligent radiation apart from Earth? Practical attempts to find such a source are being made today at different sites around the world, in part with the aid of satellites, through lengthy observation of different regions of the sky, or in particular of astronomical objects, mainly with the aid of radio telescopes.
How much to invest
Is it really worth investing lengthy periods of time and other significant resources in trying to answer the SETI question by means of direct observation? Two considerations come into play here: quality and quantity. The consideration of quality has to do with how much interest there is in finding an answer to the question, both for the person who’s doing the considering and for others. The second consideration involves weighing the resources that need to be invested in the research against the chances that it will produce an answer – or at least bring the person doing it closer to the desired answer.
As for the first consideration, it appears that there is no shortage of interest in finding an answer to the question. The second consideration, however, pertaining to the quantity of resources worth investing in the task, calls for somewhat deeper thought.
- This scientist isn't warning of impending disaster. She's proving it's already here
- In pursuit of dark matter, an elusive cosmic celebrity
As with every scientific problem, in the quantitative category, a comparison needs to be made between two appraisals. On one side is the amount of resources that will need to be invested to obtain an answer to the question. On the other side is an appraisal of the likelihood that the effort and the resources invested will in fact produce an answer, or at least advance the research significantly toward that goal.
To the question posed by SETI poses, the non-detection of extraterrestrial intelligent radiation, even after lengthy searching, cannot be an answer, because non-discovery is not proof of nonexistence. Accordingly, an appraisal that will justify a large investment needs to address the likelihood of obtaining an affirmative answer – that is, the likelihood of discovering intelligent radiation from a source other than Earth.
The astronomical literature of recent years is rich in attempts, based on theoretical thought, to appraise the possibility that SETI will in fact produce an affirmative answer. Such appraisals also abound in non-professional literature and art. They are overwhelmingly based on gut feelings, powerful desire, rich science fiction, spectacular cinema, a highly developed imagination and wild guesses. An appraisal that can be termed “scientific” is also sometimes provided in different forms, but it is essentially one and the same. SETI advocates maintain that there’s a more than negligible chance that a major effort would bring about the coveted result of the reception of intelligent radiation originating outside Earth – basing this claim on what’s known as the “mediocrity principle.”
Copernican and Darwinian revolutions
In the early 16th century, Nicolaus Copernicus fomented a far-reaching revolution in Western civilization’s perception of the world. The Polish mathematician and astronomer upended one of the basic beliefs espoused for thousands of years: namely, that Homo sapiens is the jewel in the crown of creation, that Earth is the center of the universe and that the entire universe revolves around mankind. Copernicus showed that planet Earth, the birthplace of humanity, is not the center of anything, and that in terms of its place and movement, there is no attribute that differentiates it from the other five planets – those that were known in the 16th century – revolving around the sun. Bloated with arrogance, human beings found it very difficult to accept the idea that they were not the center of the universe. Western civilization needed decades if not centuries to digest and absorb that new picture of the universe. Still, Copernicus notwithstanding, most people continued to cling to the belief that the human race constitutes a different and unique essence in the universe compared to all its other constituent parts, though the details of this human singularity were always a bit blurred.
Around 300 years after Copernicus, another great revolution occurred in Europe regarding humanity’s understanding of the world. In his book “On the Origin of Species,” Charles Darwin suggested, and also proved to a certain degree, that all creatures in the biological world known on Earth can be understood as natural products of a chain of uncontrolled processes, known as evolution, that occur without any sort of guidance and without deliberate intention. According to Darwin, the chain of events that led to the appearance on Earth of the species Homo sapiens is no different from any other aspect of evolution that brought about the emergence on the planet of any other species of the phenomenon called life.
One implication of Darwin’s explanation for the development of life on Earth was that the human species lost all preference over any other form of life, contrary to what most people had continued to believe even after Copernicus. This was another powerful blow to human arrogance, perhaps even more powerful than the one it had endured 300 years earlier. It’s also the reason that even today, more than 160 years after the publication of Darwin’s book, many millions of people in the world do not want to accept, or are unable to internalize his insight.
The mediocrity principle
Over the past 30 years, astronomical observations have discovered thousands of planets revolving around thousands of stars in the Milky Way galaxy. Based on simple considerations, it can be inferred from these discoveries that there are billions of planets, in our galaxy alone, of which hundreds of millions or billions resemble Earth from every observable or measurable viewpoint. The fact that by now we know of this vast number of Earth-like planets populating the galaxy is an additional, dramatic confirmation by observation of the Copernican picture of the world. According to this picture, Earth possesses no attribute or distinctive feature to differentiate it from any other of the similar planets. Earth is a “mediocre” planet: It lacks anything singular compared to those planets, which number in the billions. The Copernican principle – that Earth is not the center – or in its formulation as the mediocrity principle, that Earth is one mediocre planet among billions, is the basis for the prediction that there is a high likelihood of obtaining an affirmative answer from SETI.
Conditions exist on Earth that made possible the emergence and development of life, specifically also the development of a form of life that possesses intelligence. Indeed, proof of this is that such a form of life did indeed develop on Earth. Over the course of millions of years of evolution, Earth acquired the property of a planet that transmits intelligent radiation into space. Knowing the mediocrity of Earth in the galaxy, we can deduce that on many millions of similar planets there conditions exist that make possible the development of intelligence on them. From the mediocrity of Earth, in the absence of any sign of its distinctiveness, we can also deduce that the processes that occurred and are occurring on it are taking place in equal measure on many other Earth-like planets and are rendering them, too, potential sources of intelligent radiation. SETI is an attempt to detect radiation from such planets. It follows from the mediocrity principle, with high likelihood, that such radiation is indeed spreading in the galaxy, and an intense effort by SETI is likely to detect it.
Earth’s mediocrity within the community of planets is universally accepted – no astronomer would dispute it. At the same time, and notwithstanding, there is also no one who would dispute that Earth is a singular object and that there is nothing exactly like it anywhere else the galaxy. The intensity of Earth’s magnetic field, the angle of inclination of its axis of rotation, the atmospheric composition, the amount of water, the structure of the continents and oceans, the length of the year, the duration of the lunar month, the number of grains of sand and also the almost infinite number of Earth’s other features and attributes – all are the result of the planet’s evolution, and there is nothing precisely like them elsewhere. One of these numberless properties that Earth acquired over its billions of years of existence is its emission of intelligent radiation. Most, if not all, the scientists in the world would agree that there is no point in searching the galaxy for a planet that is a clone of Earth, not even one that is completely identical in just one attribute or in one measured value among the array of indices that belong to Earth. Advocates of SETI, in contrast, choose one attribute of Earth – its being a body that discharges intelligent radiation into space – and exclude it, without any apparent grounds, from the sweeping agreement about the pointlessness of searching for clones in the galaxy.
It is possible that Earth is the only planet that transmits intelligent radiation, just as every phenomenon or occurrence on Earth, and in the universe as a whole, is always singular and unique, with the possible exception of events in the submolecular world.
Remnant from the past
Underlying the use that SETI proponents make of the mediocrity principle as the grounds for encouraging the search for intelligent radiation elsewhere in the galaxy are feelings, intuitions and beliefs that are actually remnants of an image of the world that prevailed in the pre-Copernican era. The expectation of discovering in space a copy of Earth’s attribute as the transmitter of intelligent radiation conflicts with the universally agreed-upon recognition that we should not expect to discover a precise replication of any other property or attribute of our planet. Such an expectation implies a belief that the attribute of being a source of intelligent radiation is subject to a law that does not apply to any other element in the world. Not only is that viewpoint not supported by Copernican and Darwinian theory – it contradicts them.
Darwin imparted to humanity the understanding that the human species, with all its attributes, including intelligence, is a product of evolution. But the fact that human intelligence, like all species of cats in the world, is a product of evolution, does not lead to any logical inference (and did not on Darwin’s part, either) that the evolutionary process necessarily gives rise to a particular result possessing properties or attributes that can be presupposed, or that the essence or form of an evolutionary product necessarily stems from the nature of the evolutionary process. An evolutionary explanation for a phenomenon can be assigned to a phenomenon in nature only in retrospect.
Darwin closed the door on the presumption which, for example, underlies most religious faiths: that humanity is the ultimate purpose of creation. In other words, that something about human beings, notably about their intelligence, renders them separate, distinct and generally also superior to all the other manifestations of nature in the world. SETI advocates are effectively bringing in through the back door the presumption of the special pedigree and superiority in the universe of the creature that possesses intelligence: the human being. The argument that the mediocrity principle gives rise to a high degree of probability of the existence of intelligence outside Earth, either conceals, or states almost explicitly, the presumption that at some stage of evolution, intelligence similar to that of humanity appears as its necessary, or almost necessary product.
The implication of this argument, coming with no experimental evidence or systematic theory behind it, is that there exists in the world a mysterious element that leads evolution to create physical entities that possess intelligence, or planets that transmit intelligent radiation. The SETI advocates also resemble people who possess religious faith in that they, too, like religious believers, are ready to pay a price in order to maintain this cosmic arrogance – namely, they are ready to accept the possibility that there are intelligences that are superior to that of humanity.
Between mediocrity and the mediocre
When you light a fire under a kettle, there is a high likelihood that the water in it will boil after a few minutes. Expectation of this is based on the fact that one found in the past that in such a situation, boiling occurs after a few minutes. It can be said that one’s expectation is based on the mediocrity principle. The water that boiled in the kettle yesterday, like the water in the kettle today, is “mediocre” water. There is no identifiable attribute in today’s water that would render its fate different from yesterday’s. Similarly, the SETI advocates say, Earth produces intelligent radiation. From Copernicus we learned that Earth is mediocre. The Milky Way galaxy is teeming with hundreds of millions or billions of planets similar to Earth that could also constitute venues for evolution similar to that which occurred on Earth and transformed it into a planet that transmits intelligent radiation. Accordingly, like the owner of the kettle who presumes, on the basis of water’s mediocrity, that a high probability exists that the water will boil today just as it did yesterday, it is reasonable for us to suppose on the basis of the experience of Earth and the mediocrity principle that there are other planets in the galaxy emitting the intelligent radiation that SETI is intended to detect.
However, a vast difference of principle exists between the expectation of the boiling of today’s water, even though it is not yesterday’s water, and the expectation of intelligent radiation being emitted from a planet that is not Earth. The expectation that the water will boil today the same way it did yesterday is based on countless occasions on which, every time we put water over a flame, it did in fact reach the boiling point. The almost infinite recurrence of the phenomenon, without any exception, is what is called a law of nature. It led humanity to understand that the transformation of water into vapor is a necessary result of its being heated.
This is absolutely not the case with regard to Earth’s mediocrity in the family of the billions of planets that are like it. We possess no information about a planet – apart from our own, of course – that underwent a process of evolution that transformed it into one that transmits intelligent radiation. The evolution that made Earth capable of that also made it a planet on which there are bodies that have a navel close to their center of mass. On the basis of the mediocrity principle, should we assume that there are in the galaxy other bodies, extraterrestrial, that have a navel close to their center?
In the course of perhaps billions of years in which biological evolution brought about a situation in which Earth became a planet that does emit intelligent radiation, evolution in the realm of geology also occurred, and continues to occur, on Earth, following the same laws of nature. This led to Earth’s being a planet in whose terrestrial crust there is a summit that rises 8,848.86 meters above sea level. The natives call it Mt. Everest. Does it follow from the mediocrity principle that resources should be invested in a search for another planet where the elevation of the highest mountain in its terrestrial crust is 8,848.86 meters? Is there any point in searching for a site in the universe in which countless other products of evolution on Earth also exist? Human beings started playing soccer professionally around the same time they started transmitting messages to one another by means of intelligence-controlled radio waves. What is the prospect of discovering in the galaxy’s expanses an extraterrestrial soccer game between players in yellow shirts and players in red shirts – a game which, like the production of intelligent radiation, is also a clear result of evolution?
Grasping the full meaning of the Copernican revolution means internalizing and accepting the fact that we need to approach the term “intelligence” with a deep sense of cosmic humility. Members of the human species can maintain with considerable justice that they constitute one type of object that developed in the process of cosmic evolution, which possesses a portion of intelligence that is perhaps the largest among all the portions of intelligence of all the classes of material objects known to us, of which the world is composed.
Questions such as what intelligence is, whether artificial intelligence is identical to natural intelligence, the connection between intelligence and consciousness, and so forth, are part of a broad field of interesting research with multiple implications for the essence of the cosmic phenomenon of intelligence. However, from the mediocrity principle, it follows that the study of intelligence whose existence is discerned on Earth needs to be conducted with the same theoretical and experimental tools that are used in the study of every other phenomenon or process discerned on Earth. This does not include the investment of large resources in a blind search for copies of such findings in extraterrestrial sites.
The existence of extraterrestrial intelligence, or of a planet that transmits intelligent radiation, are not phenomena that contradict the laws of nature known to us, as is proved by the existence of Earth and the reality that exists on it. Thus, the content of this essay should not be seen as support for the belief that we are alone in the universe. The argument here is that at the present stage of the development of human knowledge, the idea that we are alone in the universe does not in any way contradict the mediocrity principle. It is possible that Earth is the only planet that transmits intelligent radiation, just as every phenomenon or occurrence on Earth, and in the universe as a whole, is always singular and unique, with the possible exception of events in the submolecular world, throughout the subatomic reality of the universe.
To internalize the realization that a planet that emits intelligent radiation can be a singular phenomenon is actually to adhere to the mediocrity principle. It expresses a demurral from a human arrogance, which characterized the entire pre-Copernican world, that held that humanity or intelligence are a privileged essence in a universe whose existence derives from a law different than the one according to which other entities in the world developed and exist. True cosmic humility, which it is right to adopt in the wake of the revolutions fomented by Copernicus and Darwin, and a deep recognition of the mediocrity of humanity and of its home, the planet Earth, lead to the conclusion that the fact that Earth is a source of intelligent radiation cannot be a basis for positing a high likelihood of the existence in the universe of another astronomical object with a similar trait.
‘All is vanity’
There may be Jews who would find it easy to accept the Copernican principle in its deep sense, and the cosmic humility that follows from it, if they knew that it was given expression in the past by a well-known Jewish figure. That person, Kohelet ben David, preceded Copernicus by about 2,000 years. Even within his geocentric, pre-Copernican world, in which the sun revolves around Earth, he took note of the mundanity of the existence of humanity and its place of abode, and wrote, “The sun also ariseth, and the sun goeth down, and hasteth to his place where he ariseth... That which hath been is that which shall be, and that which hath been done is that which shall be done; and there is nothing new under the sun.” He also antedated Darwin when he wrote, “man hath no pre-eminence above a beast; for all is vanity.”
Kohelet internalized well the mediocrity principle, albeit for reasons different from those of the European intellectual giants, and expressed it in words of unsurpassable clarity: “Vanity of vanities, saith Kohelet; vanity of vanities, all is vanity.”
Elia Leibowitz is professor emeritus of astronomy at Tel Aviv University.