The blink of an eye

A while back I wrote about the rather terrifying idea of the "Great Filter" -- that life, especially sentient life, might be rare in the universe because there are hurdles of varying difficulties (those are the "filters") that have to be overcome in order to get there.  These include:

• abiotic synthesis of organic molecules
• assembly of those molecules into cells
• development of cells of sufficient complexity to segregate competing biochemical reactions (eukaryotic cells)
• multicellularity
• the evolution of intelligence
• the development of technology

The first two of these seem -- at least insofar as our models currently predict -- to be fairly straightforward, so most biologists expect that Earth-like planets in the habitable zone probably have lots of single-celled organisms.  The rest?  Uncertain.  After all, we have a sample size of one to analyze, so it's a little hard to make any inferences based on that.

All of this, of course, is by way of explaining the Fermi paradox -- that despite years of searching, we've found no good evidence of extraterrestrial civilizations.  But an even more alarming possibility is that the Great Filter lies ahead of us.  Perhaps all of those steps are surmountable, so stable rocky planets with atmospheres in their star's habitable zone ultimately do evolve intelligent life, but then it inevitably self-destructs.

I'm thinking about this today because yesterday I watched a short talk by the brilliant physicist Brian Cox about the topic, and while most of what he covered was information (and theorizing) I'd heard before, there was one piece of it that I honestly hadn't considered.  Suppose the Great Filter really does lie in the future, and technological civilizations always eventually come to naught.  Perhaps it's through nuclear annihilation, or biological warfare, or the catastrophic backfire of AI -- certainly at the moment, I don't think any well-informed person would argue that these are far-fetched possibilities -- but whatever the cause, intelligent species aren't intelligent enough to save themselves indefinitely, and their brief, fitful candle flames just as quickly wink out.

What that means is that at any given time, there might only be one or two civilizations in the entire galaxy, because their lifetimes are so short.  Cox describes visiting Frank Drake, the brilliant astronomer who gave his name to the Drake Equation.  Drake's hobby was raising orchids, and Cox said that on the day of his visit, he got to see one of the rare plants in Drake's greenhouse flowering.  Drake told him that this particular species only flowers once a year, and the flower is only open for a day or two; after that, the plant goes back into its previous quiescence.  Cox had simply lucked out and visited on the right day.

Could civilizations, Cox wonders, be like this orchid -- rising and falling so fast that you only have a moment's chance of seeing them before they collapse?

If this is true, then the galaxy's planets could be littered with the debris of dead civilizations.  Imagine it... planet after planet with archaeological sites as the only evidence that an intelligent species had once lived there.

It reminds me of the brilliant Star Trek: The Next Generation episode "The Chase," in which Captain Picard (himself an erstwhile archaeology student) is given a priceless, twelve-thousand-year-old ceramic piece made by the Kurlan sculptor called "the Master of Tarquin Hill" -- the product of an extinct culture now known only from the artifacts they left behind.

Of course, even artifacts don't last forever.  A few years ago, a couple of researchers considered the "Silurian Hypothesis" -- the idea that there may have been earlier, non-human civilizations right here on Earth.  (Named, I feel obliged to point out, after the reptilian Silurian race from Doctor Who.)  The question they asked was, if there had been such a civilization -- say, a hundred million years ago -- would there be any traces left?

And the answer they came up with was "No."  Likewise, the chances of any human-made artifacts from today lasting a hundred million years into the future is vanishingly small.  Consider that there's damn little left from humans who lived ten thousand years ago.  Nothing we make is likely to last a hundred million -- however rock-solid and permanent our creations may feel to us.

Understand that they're not saying there was such a civilization; only that if there had been, we'd probably have no way to know about it.  So even if there have been many intelligent species rising and falling throughout the galaxy, the marks they left on their planets would be nearly as ephemeral.

It's kind of a bleak prospect, isn't it?  All of our strutting and fretting is, for better or worse, over in the blink of an eye.  It reminds me of Percy Shelley's haunting poem "Ozymandias," which feels like a good way to conclude:

I met a traveller from an antique land,
Who said—"Two vast and trunkless legs of stone
Stand in the desert.  Near them, on the sand,
Half sunk a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them, and the heart that fed;
And on the pedestal, these words appear:
'My name is Ozymandias, King of Kings;
Look on my Works, ye Mighty, and despair!'"
Nothing beside remains.  Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.

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Parsing the Drake Equation

The Drake Equation is one of those curiosities that is looked upon as valid science by some and as pointless speculation by others.  Here's what it looks like:

Math-phobes, fear not; it's not as hard as it looks.  The idea, which was dreamed up by cosmologist Frank Drake back in 1961, is that you can estimate the number of civilizations in the universe with whom communication might be possible (Nb) by multiplying the probabilities of seven other independent variables, to wit:

R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the fraction of those stars with planets whose planets are in the habitable zone
fl = the fraction of planets in the habitable zone that develop life
fi = the fraction of those planets which eventually develop intelligent life
fc = the fraction of those planets with intelligent life whose inhabitants develop the capability of communicating over interstellar distances
L = the average lifetime of those civilizations

Some of those (such as R*) are considered to be understood well enough that we can make a fairly sure estimate of its magnitude.  Others -- such as fp and ne -- were complete guesses in Drake's time.  How many stars had planets?  Could be nearly 100%, or it could be the Solar System was some incredibly fortunate fluke, and we're one of the only planetary systems in existence.  But now, with improvements in the techniques for surveying stars, we're finding planets everywhere we look -- most stars seem to have planets, and some research published just last month by a team of astronomers at the University of Witwatersrand (South Africa) has shown that planets could form stable orbits in multiple-star systems, something previously thought extremely unlikely.

That they can do so is fortunate not only for alien intelligence enthusiasts like myself -- as much as half of all stars are thought to be part of multiple-star systems -- but for this guy:

So the estimates keep being revised upward.  The one we still have no real idea about is L -- how long civilizations tend to last.  Carl Sagan, when he described the Drake Equation in his amazing series Cosmos, was pessimistic -- many civilizations, he suggested, lasted long enough to develop weapons of mass destruction, then proceed to blow themselves to smithereens.

But the fact is, we just don't know about L.  But one that was complete speculation -- fl, the fraction of planets in the habitable zone that develop life -- just got a bit of a boost from a study done at the University of Bristol (England).  The researchers, Holly C. Betts, Mark N. Puttick, James W. Clark, Tom A. Williams, Philip C. J. Donoghue, and Davide Pisani, published their results in Nature: Ecology and Evolution last week in a paper titled "Integrated Genomic and Fossil Evidence Illuminates Life's Early Evolution and Eukaryote Origin."  And one of the points the team makes is that once the Earth's surface had cooled sufficiently that water was able to exist in liquid form, life appeared in a relative flash -- while it was still being clobbered every other day by meteorites.

The authors write:

Establishing a unified timescale for the early evolution of Earth and life is challenging and mired in controversy because of the paucity of fossil evidence, the difficulty of interpreting it and dispute over the deepest branching relationships in the tree of life.  Surprisingly, it remains perhaps the only episode in the history of life where literal interpretations of the fossil record hold sway, revised with every new discovery and reinterpretation.  We derive a timescale of life, combining a reappraisal of the fossil material with new molecular clock analyses.  We find the last universal common ancestor of cellular life to have predated the end of late heavy bombardment (>3.9 billion years ago (Ga)).

Besides being of obvious interest to evolutionary geneticists, this should get astronomers' blood pumping; it implies that life originated on Earth when the conditions were still nothing short of hostile, with the corollary that once a planet has conditions that allow liquid water, life probably follows soon thereafter.

The implication being that it's likely that every planet with water that sits in its star's habitable zone has some form of life.

So understandably enough, I think this is way cool.  It doesn't give us any information about the remaining variables we have little information about, especially fi, fc, and L.  There's no particular reason to believe that intelligence is a necessary outcome of evolution; it's tempting to think that the process always drives organisms to be bigger, better, stronger, and smarter, but that's not supported by the evidence.  After all, it bears remembering that by far the dominant life-forms on Earth right now, both in terms of biodiversity and overall numbers, are... insects.

It might be that intelligence sufficient to communicate over interstellar distances is a very uncommon occurrence, which leads to the most likely scenario (in my opinion) being plentiful planets with huge diversity of life, but few that have anything like us.

Still, the galaxy is a big place, with billions of stars, so even if it's unlikely, intelligent life probably exists somewhere.  Which segues into tomorrow's post, which is about the Fermi Paradox.  When told about the Drake Equation, physicist Enrico Fermi famously shrugged his shoulders and said, "Then where is everybody?"

Tomorrow we'll look at a few possible answers -- some of which are considerably more cheerful than others.

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This week's Skeptophilia book recommendation is from one of my favorite thinkers -- Irish science historian James Burke.  Burke has made several documentaries, including Connections, The Day the Universe Changed, and After the Warming -- the last-mentioned an absolutely prescient investigation into climate change that came out in 1991 and predicted damn near everything that would happen, climate-wise, in the twenty-seven years since then.

I'm going to go back to Burke's first really popular book, the one that was the genesis of the TV series of the same name -- Connections.  In this book, he looks at how one invention, one happenstance occurrence, one accidental discovery, leads to another, and finally results in something earthshattering.  (One of my favorites is how the technology of hand-weaving led to the invention of the computer.)  It's simply great fun to watch how Burke's mind works -- each of his little filigrees is only a few pages long, but you'll learn some fascinating ins and outs of history as he takes you on these journeys.  It's an absolutely delightful read.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]