Today (December 21) is the winter solstice in the Northern Hemisphere and the summer solstice in the Southern Hemisphere. The winter solstice is the day with the shortest period of daylight and the longest night of the year, because on this day one of the Earth's poles has its maximum tilt away from the Sun. After this day, the Earth's pole will begin tilting back towards the Sun, lengthening the period of daylight, until the maximum tilt towards the Sun on the summer solstice, the longest day of the year.
In a post that I wrote four years ago, I suggested that the moral meaning of the winter solstice depends on whether one gives it a religious meaning or a secular meaning. The religious meaning is expressed in religious rituals that sacralize the importance of the Sun as the source of life, which is connected in Christian traditions to Christmas and the birth of the Savior.
The secular meaning comes from the modern cosmological and biological sciences that recognize how all complex forms of life, including intelligent life, depend on the energy of the Sun as captured through photosynthesis on Earth. Beginning with the formation of the Earth about 4.5 billion years ago, there was no life. Then the simplest forms of life probably emerged among anaerobic microbes that could extract hydrogen and carbon dioxide gases from the atmosphere to get the energy and nutrients they needed to grow and divide, while emitting methane as waste. Next, around 3.7 billion years ago, the cyanobacteria arose as the first photosynthesizing forms of life--water-using and sunlight-powered bacteria that produced oxygen as a waste product. Later, with the increase of oxygen in the atmosphere, from 2.5 billion years ago to 700 million years ago, larger and more complex forms of multicellular forms of life arose that used oxygen as a powerful source of energy.
The rise of animals and ultimately intelligence depended on the rise of oxygen as a source of energy for complex life. Human beings require on average 100 watts of power per day to run their bodies (25 watts for the brain and 75 watts for the rest of the body), and oxygen is probably the only good source of such energy. All of this depends on photosynthesis as the process by which the flow of energy from the Sun is captured in the biosphere of the Earth.
This teaches us that for billions of years in the past, there was no life. And for billions of years in the future, once photosynthesis has shut down, and the Sun has faded, there will be no life in the cosmos.
The secular moral teaching here is that the human good has no eternal cosmic support, because the human good arises from the momentary conditions of human life on Earth, which cannot exist forever. The cosmos does not care for or about us. This is what Leo Strauss identified as "the most terrible truth" of evolutionary science in Lucretius.
Whether one adopts the sacred meaning or the secular meaning of the winter solstice depends on the search for extraterrestrial intelligent life. The sacred meaning assumes that there is an extraterrestrial intelligent design behind the cosmos that cares for and about human beings, and that this philanthropic intelligent designer will secure the cosmic support for the perpetuation of human life, perhaps even for human immortality in an afterlife. The secular meaning assumes either that there is no extraterrestrial intelligent life, or that if there is, it does not care for human life on Earth, or secure human immortality beyond the Earth.
Hey, this is the debate we should have with our family and friends around our Christmas dinner table! To prepare for that Christmas dinner debate, you might want to read some of the books by astrobiologist Charles Cockell--Astrobiology: Understanding Life in the Universe (Wiley, 2nd edition, 2020), Taxi from Another Planet: Conversations with Drivers about Life in the Universe (Harvard University Press, 2022), and Interplanetary Liberty: Building Free Societies in the Cosmos (Oxford University Press, 2022). Cockell is one of those scientists who defends the secular meaning of the winter solstice and rejects the religious meaning. If you want to read a scientist who defends the religious meaning, try the astrophysicist Owen Gingerich. I have written previously about Gingerich's God's Universe (2006) and God's Planet (2014).
Studying these books suggests the four paths that the search for extraterrestrial life can take. First, in considering the cosmic location of life, we might look for life within the Solar System (the Moon, other planets, and their moons); or we might look beyond the Solar System (within and beyond our Milky Way galaxy of stars). Second, in considering the kinds of life in the cosmos, we might look for natural life (ranging from the simplest forms of microbial life to more complex plants and animals and finally to intelligent life); or we might look for supernatural life (God or gods, angels, and even human beings living immortally after death in Heaven or Hell). Third, in considering the cosmic meaning of life, we might look for evidence that the cosmos has been purposefully designed to support life and particularly intelligent life, and thus displays a cosmic teleology that constitutes a moral cosmology. Fourth, in considering the astrobiology of politics, we might wonder about how the extraterrestrial conditions of life will shape the political order of human communities in space (such as for human colonies on the Moon or on Mars); and in particular, we might think about whether extraterrestrial colonies will be inclined to liberty or tyranny.
I have written previously (here, here, and here) about how the ancient, medieval, and modern models of the universe have conceived of the distribution of these various kinds of life across the cosmos and how this might, or might not, manifest a moral cosmology.
And while many of us might assume that the search for extraterrestrial life is a recent phenomenon, it's remarkable that the prevalence of extraterrestrial life throughout the universe has been assumed by many people from ancient times to the present. The documents showing this have been collected by Michael Crowe in his edited source book--The Extraterrestrial Life Debate, Antiquity to 1915 (University of Notre Dame Press, 2008). The leading proponents of cosmic pluralism--the idea that beyond the Earth there are many, even an infinite number, of worlds with living intelligent beings--have been the Epicurean philosophers and scientists (like Lucretius and Giordano Bruno).
Up to the beginning of the 20th century, it was common for many people to believe that the Solar System was full of life--particularly, on the Moon and Mars, the planetary bodies nearest the Earth. But as telescopes became ever more powerful instruments for exploring the planets and moons of the Solar System, it has become clear that there is no clear evidence for extraterrestrial intelligent life beyond the Earth. Moreover, there has not yet been any evidence for even the simplest forms of life in the Solar System, although many astrobiologists see tantalizing evidence that there might have been at least some microbial life somewhere in the past. The landing of men on the Moon and of robotic vehicles on the Moon and Mars has extended this exploratory search for the signs of extraterrestrial life in the Solar System.
In 1584, Giordano Bruno (in his book On the Infinite Universe and Worlds) asserted:
"In space there are countless constellations, suns and planets; we see only the suns because they give light; the planets remain invisible, for they are small and dark. There are also numberless earths circling around their suns, no worse and no less than this globe of ours. For no reasonable mind can assume that heavenly bodies that may be far more magnificent than ours would not bear upon them creatures similar or even superior to those upon our human earth."
Until recently, however, no planets outside the Solar System had been discovered. The first discovery of a planet outside our solar system was in 1995. Now, as of today, NASA lists 5,284 confirmed "exoplanets" in 3,899 planetary systems, most discovered by the Kepler space telescope. Surely, out of so many planets, there must be some with life, even intelligent life. Only some of these planets are in the "habitable zone": at a distance from their stars that would allow for the existence of liquid water (that is, not too hot and not too cold); and they also need to be rocky planets, as opposed to gaseous. According to some current estimates, there are over 80 billion Earth-sized planets in the habitable zone of their stars in the Milky Way galaxy, and probably many more in the trillions of other galaxies.
So far, there has been no evidence of life on any of these planets. But the problem here is that exoplanets are so far away from us that we cannot even send a satellite to explore them. The exoplanet nearest to us--Proxima Centauri b--revolves around Proxima Centauri, the star nearest to the Sun. This exoplanet is in a habitable zone. But it is about 4.2 light years away (25 trillion miles). NASA's New Horizons spacecraft flying at 52,000 miles per hour would take 54,000 years to reach this planet!
If Proxima Centauri b had intelligent life and a technologically advanced civilization, then we might expect that they could communicate with us through radio transmissions. Since radio waves travel at the speed of light--186,000 miles per second--a signal could reach the Earth in 4.2 light years. But even though scientists have been scanning the cosmos for many years trying to detect such radio transmissions from extraterrestrial intelligence, there is still no evidence for this.
This lack of evidence has provoked what is called the "Fermi Paradox," named after physicist Enrico Fermi, who once asked: "Where is everybody?" If extraterrestrial intelligent life is common in the cosmos, then why haven't we heard anything from them? Well, maybe ET intelligence is extremely rare and so far away that we're just not likely to hear from them. Or perhaps ET civilizations with the technology for interplanetary communication go extinct after a few million years. Or perhaps they're out there, but for various reasons they choose not to communicate with us.
But at some point we have to consider the possibility that the conditions for the evolution of intelligent life are so exceptional that this has happened only once in the cosmos--on the Earth and nowhere else. That's the "Rare Earth Hypothesis" of Peter Ward and Donald Brownlee (Rare Earth: Why Complex Life Is Uncommon in the Universe, Copernicus, 2000). The conditions for complex life and particularly intelligent life might be so rare as to be unique to the Earth, and even then only during the last 250,000 years of Earth's history.
The conditions for simple forms of life, such as microbial life, might be so much more common that microbial life might be found throughout the cosmos. Ward and Brownlee suggest that. And other astrobiologists (such as Cockell agree).
If the Earth is uniquely adapted for the emergence of human intelligent life, does that mean that the laws of nature have been fine-tuned to support human life on Earth? If that is so, is that fine-tuning just an accident? Or does it show purposeful design--by the Divine Intelligent Designer? Owen Gingerich says yes, and that's why he calls the Earth "God's Planet."
But as I suggested in my posts on Gingerich, there are some weaknesses in his arguments. The fine-tuning of the unique conditions for human life on Earth looks mysterious. But to explain the mystery by saying "God did it" is fallacious because this explains a mystery by positing an even deeper mystery--the mystery of God as Creator.
Moreover, it's not clear that the evolution of life in the cosmos with a special place for intelligent life on the Earth shows a divinely ordained purpose that supports the unique dignity of human life. After all, for most of the history of the cosmos since the Big Bang, there has been no life; and if the distant future of the cosmos brings the extinction of all life, as many astrophysicists expect, then life, and particularly human life, would seem to be only a momentary blip in the history of a mostly dead cosmos. That would seem to deny any conception of a cosmic teleology supporting a moral cosmology to guide human life.
But even without such a cosmic teleology, there can be a human teleology rooted in the human purposes of evolved human nature. And as long as that evolved human nature endures, even without being permanent, it sets the natural ends or purposes of human life. Isn't that enough?
That could hold true even for extraterrestrial human life--that is to say, when human beings travel in space or colonize a moon or a planet beyond the Earth, they will be moved by the same natural desires that move them on the Earth.
Or will the extraterrestrial conditions for life distort or frustrate those natural human desires? For example, when human beings colonize Mars, will the extreme conditions on Mars force the human beings there to submit to a tyrannical government that controls the constraining equipment and regimented institutions that secure the life-support systems necessary for human survival on Mars? Or will human beings organize their social and political order on Mars to secure their individual liberty even in the extreme conditions of Mars?
I will take up those questions in a future post.