...and just who might be listening back?

 kw: book reviews, nonfiction, SETI, extraterrestrial life, philosophy

Seth Shostak is an idiot…or to be more charitable, he is dramatically misled by his own idealism. He is a very prominent proponent of sending messages toward possible alien intelligences, and he is the senior astronomer for the SETI Institute. He minimizes the possible risks we face from becoming known to "the Universe". If someone is out there listening, how will they react to learning that we exist?

In The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence, author Keith Cooper lays it out plainly. He sums it up nicely in a paragraph on page 295:

We search the Universe for evidence of extraterrestrial life to make contact with others, for humanity to be able to share the Universe with others. Yet we find ourselves in a position of not being confident about whether we should try and make contact.

We dream of learning wonderful, life-changing things from superintelligent, hyper-advanced space aliens, or ET's (ExtraTerrestrials). All too often, the idealists in particular ignore the fact that every human being is both good and evil. Under some circumstances, we are altruistic, even heroic. Under others, every single one of us is capable of murder and larceny. There are no exceptions. Can we expect anything better of the denizens of another solar system? What are the chances of any intelligent species that arises due to evolutionary processes becoming unfailingly altruistic not only among themselves, but toward others to whom they are not remotely related?

The author makes a deeper point: by searching for "others" we search for ourselves. We project our hopes and dreams on them. It reminds me of a Chinese parable:

A man prayed daily for the Dragon to come. He dreamt about meeting the celestial being, imagining the wonderful things he might learn. One day there was a knock at the door; really, more of a crashing sound. The man opened the door and he saw him: scaly, fiery orange and red, forty feet long, with eyes the size of saucers and teeth like daggers. He screamed in fright, "Who are you?" The voice hissed and roared through him, "I am the Dragon. Am I not what you wanted?"

More succinctly: Be careful what you pray for; you just might get it.

A rather unbalanced segment of American society (few people elsewhere are as enamored of ET's as Americans) lives in combined fascination and fear of "flying saucers" and the "space aliens" that might "abduct" them to do "genetic experiments". Such sexual anxiety says a lot more about these people than it does about ET's. Is it really possible that Earthly genetics can have anything to do with ET's?

Sidebar: People with biological education (whether schooled or self-taught) usually know the Central Dogma of Genetics: DNA→RNA→Proteins. More recently, it has become clear that more than half of the DNA for which we know a function does not follow this dogma directly, but is regulatory, and modifies what happens when a "coding gene" is expressed to RNA and then to a protein. The key to how this works is the coding table, or The Code, which translates 64 codons into 20 amino acids plus a "stop" signal.

A little known fact about The Code: There is one Standard Code for the nuclear DNA of nearly all eukaryotic organisms, and it is also used for the DNA of most prokaryotic organisms (bacteria and archaea, which are bacteria-sized). But on Earth there are 25 other codes! See the details at this NCBI site. A few of these alternate codes are used by simple protozoan creatures, while many are for the mitochondria in various eukaryotes, and the rest are for various families of prokaryotes. This is just for Earth life. How many alternate codes are possible? Will any aliens out there have DNA like ours, and if so, will it be based on "our" Code?

The calculation P[64:20] yields 2.1x10³⁶ permutations. In common terms it is 2.1 trillion trillion trillion. That is one estimate of the number of possible DNA-to-Protein Codes. However, while there are as many as six codons per amino acid, the codons are grouped, so the number of efficient DNA codes may be smaller by a factor of a billion or so. Even then, we are left with a 28-digit number. It is extremely unlikely that an alien species from any other star system will have any genetic similarity to Earth life. Further, there is no guarantee that the same 20 amino acids will be used everywhere. It is actually more likely that, of the hundreds of possible amino acids, there would mostly be species with hardly any proteins that are "compatible" with any of ours. The aliens may not even be able to eat Earth foodstuffs (ourselves included!).

The book has an illuminating and comprehensive history of SETI and a detailed discussion of "things to look for" besides radio signals: flickering laser or maser light, "biosignatures" (such as the presence of both oxygen and methane together), and technosignatures other than radio (such as anomalies in a star's light caused by immense clusters of solar arrays). There is no need for me to get into detail; it's hard to beat the author's writing!

The book is a great joy to read. We have a lot to think about as we consider Who Is Out There.

Will our cosmic angst ever be relieved?

 kw: book reviews, nonfiction, science, life, extraterrestrial life, SETI

About eleven years ago I posted a review of David Brin's novel Existence. In it I mentioned two books that form the "bookends" to my thinking about exo-life: Rare Earth by Peter Ward and Donald Brownlee (2000), and Vital Dust (1995) by Christian de Duve. I read both those books before I began this blog. It may be that The Possibility of Life: Science, Imagination, and our Quest for Kinship in the Cosmos, by Jaime Green, is a fourth worthy player in this space.

Now that we know at least the existence of more than 5,500 exoplanets, plus more than 8,000 "candidates" that are being vetted, it is clear that planets outnumber stars.  A few hundred planets are in the "earthlike" range of size and mass and surface gravity; as of late July 2023 this Wikipedia page lists 63 "potentially habitable" objects in the "Earth to Super-Earth" size range, small enough to be "probably rocky". That is well over 1% of the known exoplanets, which implies that such planets number between 10 billion and 20 billion in our galaxy (accepting the extrapolations of scientists who publish about this). It is well to note that a rocky planet with 2.5 Earth's size would have 15.6 times Earth's volume and, if of the same density, 15.6 times its mass. The greater radius would mean, by the cube-square law, that the surface gravity would be 2.5 times that of Earth. It is unlikely that the density would be the same, so that's just a very rough starting point.

As the author points out in a late chapter, somewhat channeling Peter Ward, bacterial life (or something very like it) appeared on Earth within half a billion years after it was formed, but since there was a period of "molten crust" for 300-400 million years, it could have come into existence rather rapidly, on cosmic timescales. But then, it took another billion years for photosynthesis to emerge, and another billion or 1.5 billion years for the first eukaryotic (complex, nucleus-bearing) cells to be produced. So even with our whole planet for a chemical-evolutionary playground, it was apparently rather hard for the basics of complex life to arise. Once it did arise, the next period, called the "boring billion", was required for the evolution of multicellular creatures bigger than a poppy seed. So, is de Duve right, that these developments are inevitable, or are Ward and Brownlee right, that the several big steps in this progression are so hard and rare that we cannot logically claim that a sequence like this happened more than once?

To my statistical mind, it seems we need some way to determine the variance in those numbers, applied to billions of planets. For example, let us first suppose that the production of eukaryotic cells takes, on average, five billion years after photosynthesizing bacterial cells originate, with a standard deviation of half a billion years. In such a case, for it to take only 1.5 billion years is a 7-sigma outlier; it can only happen on one planet out of 390 billion. Thus, if there are, to be generous, about 20 billion "habitable" planets per large galaxy, there would only be eukaryotes that arose this "quickly" on one planet per 20 galaxies. Our chances of having a near neighbor are slim indeed! On the other hand, if 1.5 billion is closer to the average, and the standard deviation is half a billion years, then about half the "habitable" planets on which life originates can be expected to develop complex life in 2-4 billion years from the inception of life. The Milky Way is big, with a volume of about 30 billion cubic parsecs. Divide 30 billion by 10 billion: three cubic parsecs per planet, or about 100 cubic light-years. The radius of a sphere of this size is about 3 light years; double this to get 6 light-years from planet to planet. That points to a galaxy littered with inhabited planets. This is no improvement over the Drake equation, which is easy to manipulate to find any result. We still suffer from a dramatic lack of knowledge.

The book has six (longish) chapters, and the tone is wistful and lyrical rather than coldly analytical; more like Vital Dust than Rare Earth. I enjoyed it very much. The big questions, to which Ms Green returns again and again, are how we would recognize life on another planet, from a distance, and then if/when we meet "aliens", how we might communicate. At one point she muses on the problem we are facing to communicate with our descendants, across a gap of 10,000 years—about 350 generations—regarding the danger of radioactive wastes stored at Yucca Mountain or other repositories. Consider how English has changed in just 1,000 years. Old English, also called Anglo-Saxon, cannot be read nor heard intelligibly by anyone without learning it as a foreign language. Although it was a Germanic language, modern German speakers are equally befuddled. That was just 1,000 years ago. Middle English, or Chaucerian, of 500-600 years ago, is barely intelligible; many words we can recognize in print are pronounced differently now than they were then (for example, the "e" that ends so many words such as "made" or "file" was explicitly pronounced). Even the "English" of the King James Bible takes some getting used to, even though the latest edition of the KJB was produced in 1769; the "original" text of 1611 is very difficult for most of us to read. If we have such trouble with human language (and there are hundreds of "extinct" languages that still cannot be read by anyone), how will we ever learn a truly alien language, "spoken" by a creature that is not even as well related to us as an octopus?

Most science fiction stories about contact with ET's sidestep the problem by having the aliens figure out some of our languages before arriving, or by having telepathy, or they have a "universal translator" such as those on Star Trek. I've read one story that took a serious swipe at the problem: human astronauts find an abandoned spaceship, and one of them finds a chemistry handbook and locates the Periodic Table of the Elements. Right away that yields, not just the alien words for about 100 elements, but the symbols for the alien number system. A big leg up. How to go beyond that? It still won't be easy. Maybe an alien version of the CRC Handbook would help…

Nonetheless, I think the occurrence of life is somewhere in the middle, such that at least a few planets within 100 light years (31 parsecs) will be found to have complex life. Whether any of those planets will host technological species is more iffy, but I am hopeful. Life that gets any kind of start is going to diversify. The diversity of plants and animals is astonishing, and in the Bacterial/Archaean realm there may be 100 times as many species. I think that, as the Ian Malcolm character said in Jurassic Park, "Life finds a way." (Picture from Mongabay)