The cosmos is a repository of a great many mind-blowing notions, be it dark energy, dark matter, the notion of infinity, the billions of galaxies each with billions of stars, the Big Bang narrative, and the breathtaking spaceship journeys. But the cosmos is also a source of great gifts and surprises. The last comes from the last Kepler space mission data, indicating that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones within the Milky Way, with many of them possibly orbiting Sun-like stars.
Credits: Third Party Reference
The notion of habitable zone is already a first non-trivial point. Generally, according to NASA indications, planetary surface habitability is thought to require orbiting at the right distance from the host star for liquid surface water to be present, in addition to various other geophysical and geodynamical aspects that we cannot discuss here.
The extraordinarily high number of planets in the so-called habitable zones makes me immediately think that in some of them there is life. And then immediately, however, comes to mind the famous “Fermi paradox”. It is also based on the high number of potentially habitable planets, asking, however, this question: “yes, but where is everybody?” – pointing to the fact that we have not received any sign of alien life – ever.
There are a lot of considerations about this question and the Fermi paradox in general, and in this brief article, we will deal with some of them. Let us instead first make the acquaintance with some of the planets which are considered habitable. An arbitrary short list (eliminating the planets that are more than 50 light-years away) is given below :
• Proxima Centauri b is just a rocky planet which is “only” 4.2 light-years away, a mass 1.3 times that of the Earth, and it orbits Proxima Centauri every 11.2 days. According to our astronomers, it may allow for the presence of liquid water.
• Wolf 1061c: This exoplanet is located about 13.8 light-years from Earth in the constellation Ophiuchus, making it the second-closest known potentially habitable planet to Earth, after Proxima b.
• Gliese 832c Gliese 832c is located just 16 light-years from Earth and lies within the habitable zone of a red dwarf star called Gliese 832.
• Gliese 581 g This more controversial planet, in the constellation Libra, is a rocky world. It is about 20 light-years away from Earth, and two to three times as massive as Earth.
• Gliese 667Cc is about 22 light-years away in the constellation Scorpius. The planet is at least 4.5 times bigger than Earth. GJ 667C – the parent star – is actually part of a triple-star system.
• Trappist-1d, discovered in 2016, orbits around an ultracool dwarf star known as Trappist-1, which lies approximately 40 light-years away from Earth in the constellation of Aquarius.
• HD 40307g lies about 42 light-years away from Earth in the constellation Pictor.
• HD 85512b, discovered in 2011, is about 3.6 times more massive than Earth. It is about 35 light-years away from Earth’s sun, in the constellation Vela.
Credits: Third Party Reference
The question “where are they?” implies communication between at least two different civilizations, and this in turn implies two conditions: the condition of “quasi simultaneity”, namely that the worlds in question were born and evolved temporarily close to each other, to possibly permit similar technical evolution, and that they are close enough in space to pay a visit to each other or at least to send/receive mutual signals.
The Fermi Paradox:
Based on the data, let’s go back to the Fermi paradox. Indeed, it does not make much sense to consider the communication between worlds that are, say, one hundred million years apart, with origin and evolution. The first of these two conditions is born out from the consideration that if alien visitors were to come to our Earth only ten million years ago, they would not have found any intelligent life; and it is very doubtful that they would find intelligent life if they were to come in one million years from now. In other words, intelligent life is most probably restricted to a modest window of time (in cosmic geological terms).
I believe that the condition of the “quasi simultaneity” of two different worlds already accounts for the Fermi paradox. If then we add the other condition, namely that the two worlds should be close enough to each other to permit communicability, then we really get into a non-winning ticket. In particular, concerning the “visit”, we learn from the previous list of habitable exoplanets that there is nothing in our vicinity closer than 4 light-years.
This means that even if their spaceship were to fly at the speed of 1/100 of the speed of light (which is orders of magnitude faster than the Apollo 10, which was 31 Km/s), it would take ca. 400 years to arrive at us. This does not exclude the possibility of mutual signals at the speed of light, and to that, we can only answer that until now, we have not received any signal from an alien world. Of course, all these arguments to explain or rule out the Fermi paradox are based on our present scientific knowledge.
It is usual, on discussing these themes, to rapidly arrive at science fiction, and to invoke tele-transportation, ships or signals that go faster than light, or unknown forms of intelligent life. All this makes perhaps the dialogue more amusing, but then, it is no longer a scientific discourse. It is not science fiction to accept the idea of a possible form of intelligent life that developed independently in one or a few of those billions of planets discovered by the Kepler space mission. But there is no way to know.
The arguments above, centered around the Fermi paradox, are about intelligent life. A different question is whether some form of much simpler life, for example, bacterial life, can exist in those exoplanets. We have to consider in this regard that on our own planet, where life exists since ca. 4 billion years, there have been only microbes, unicellular bacterial life, for the first two billion years.
Bacterial Life:
Only ca. 700 million years ago, multicellular life began to develop, and mankind appeared only 7 million years ago. In fact, when we talk about the origin of life on Earth, we should think in terms of three qualitatively different origins – and there is no logical follow-up from one to the other. But let us stay with the simple question: could at least bacterial life exist on the other planets?
But even that does not warrant a clear positive answer. Those astronomical data, relating to the habitable zones, concern in fact only one aspect of the problem: the necessary conditions for life. Certainly, we need the right set of temperature, pressure, atmosphere, liquid water, and so on. Is this enough to make sure about life? Well, what about the necessary conditions?
Again, let us move within the frame of science, leaving aside science fiction. Accordingly, life on earth originated from non-life, namely from simple molecular structures which underwent a process of molecular evolution, creating more and more complex structure/functions spontaneously, till the arising of structures that could reproduce themselves, the first living cells.
Credits: Third Party Reference
This view, completely based on natural forces, eliminates any divine intervention in the creation of life – and of course, if you change this premise, and have faith in a Creator, all changes. But then it is no longer science, but faith. Based on this premise, commonly shared by the vast majority of scientists in the field, our scientists have been studying the origin of life since the 1950s, with some of the best minds in chemistry, biology, and molecular biology, and nobody has discovered how life started on Earth, or how we can create life in the laboratory.
Actually, two generations of chemists have tried hard to find the conditions for making life, even in the simplest possible forms, in the laboratory, and failed, even forcing somehow conditions, for example, starting from already formed membranes, or even from some magically formed RNA molecules. But actually, we do not even know how ordered macromolecules like proteins or nucleic acids have originated on our Earth. There are, of course, speculations and hypotheses, like the story of the prebiotic RNA world, a nice speculation without any sound chemical basis, as I have argued in my 2016 book.
Generally, this failure of our science to understand how life started on Earth, and/or how to make simple life in the laboratory, unequivocally shows that bacterial life is not a trivial outcome of the necessary conditions. Life does not arise spontaneously, and therefore, to have a set of necessary conditions on another planet, temperature and pressure, chemicals, and environmental conditions like ours, does not demonstrate anything about the possible presence of life on that planet.
Contingency, namely the fortuitous juxtaposition of per se independent parameters, has been for modern science the creative driving force for the origin of life. An event then of incommensurably small probability, certainly not a thermodynamic drive towards an energy minimum. This, again, at the stand of our present science. Tomorrow, a new bio-Einstein may discover how life started on our planet.
Actually, let me add something important in this regard: let us suppose that in the near future we discover the existence of bacterial life on many planets in the cosmos. Well, this discovery would probably force us to abandon the notion of contingency in favor of some deterministic drive to make life. But for the moment, we are still facing a mystery. In conclusion, are we perhaps alone in the universe?
Mass psychology and Jungian archetypes are such that the majority of people, emotionally, do not like to accept this view. For most uneducated people in science, feelings and emotions are more important than scientific truth, and this since primordial times, and probably for the next centuries to come.
I am skeptical, but have to acknowledge that when in the night, all alone, I look at the many stars in the sky, the question: “Is it possible that nobody is there?” comes immediately to my mind. Accepting science may be hard and, in this sense, let me close with a quotation of Jacque Monod, who interpreted – I believe this relation between science and feelings (from his 1971 book, Chance and Necessity).
Reference: https://human-wrongs-watch.net/2018/09/30/is-there-life-in-other-planets/
