|"You still seem to lean heavily on the idea that an alien civilization would be at least 10 million years older than us, but I don't see where your blog remarks adequately support that notion. Perhaps you could elaborate."|
10 million years might be too low, I'm actually being conservative. It follows as a direct result of the fact that sentience combined with the ability to technologically manipulate our environment is an evolutionary adaptation that has been pursued exactly once on this planet in its 4.5 billion history, that is, us. And even with us, sentient hominids existed for millions of years before agriculture, and hence 'civilization', began. And even once civilization began, it was another 9,500 years before the scientific method, with its concomitant sustained, relatively rapid, robust rate of advance of scientific and engineering actualization knowledge became possible.
It bears remarking that each of these transitions occurred as a result of a complex set of favorable opportunities, topographical configurations, and other factors that may or may not be common elsewhere.
Given this line of thought, and the many accidents of climate, geological, and faunal change that gave rise to our brand of advanced sentience (Walking with Cavemen is an excellent series in how it explores this, not just for homo sapiens, for many of our precursor hominids as well), civilizational structures (the Fertile Crescent), and scientific institutionalization (competitive European states), to assume that it is common throughout the cosmos, aka the Star Trek model, is empirically unreasonable. We're not unique I don't believe, not saying that, but almost certainly quite rare.
Let me restate the essence of the analysis from my blog:
"Earth is 4.5 billion years old. If we are very generous and say that we started out being reasonably sentient some 3 million years ago, that means that Earth has had sentient lifeforms for only 0.0667% of its history. But of course, primitive hominids do not really constitute civilization. That is only 10,000 years old (the dawn of agriculture), or 0.0002% of Earth's entire history.
However, we need to be more discriminating still if we are going to start comparing technological civilization over the incremental version that characterized most of that 10,000 years (short and often individual-based explorations by brilliant Greeks, Romans, Muslims, Chinese, and others aside), and the accelerated version that we are currently familiar with. There are different ways to define it, but my favored definition of the start of true technological civilization begins with the institutionalization of the scientific method on a national scale, as evinced by competitive European nations a mere 500 years ago, or 5% of the 10,000 years of civilization since the dawn of agriculture. Using this definition, Earth has had technological civilization for 0.0000143% of its history."
In addition to these small percentages, based solely on the time that we've been here vis-a-vis the age of the Earth and/or the time since the rise of complex life, there's another distinct but related statistic to consider, that I haven't mentioned in my blog. That is, out of the millions and millions of species that have lived on the Earth, one has utilized sentience and manipulative technology to achieve its survive and thrive goals - that is, again, us. I'm not going to try to weave that number, yet another very tiny fraction, into the other tiny fractions based on temporal duration of our species stated above, but suffice it to say that it makes the probability of advanced alien civilizations elsewhere even less likely, even more remote, and even more widely spaced in time (that is, even more ancient).
So, 10 million years is very conservative indeed; in fact, it's probably giddily optimistic that they would be even that close to us in time.
The upshot of these tiny percentages of sentient and/or technological civilization on Earth, extrapolated to the rest of the cosmos is that this tiny blip of the rise of sentience elsewhere, the odds of this occurring more or less simultaneously with the rise of sentience on this planet are exceedingly remote. It's not impossible, not saying that, but deeply improbable that they are either close by, or close in time. Hence, the empirically-based and statistically sound proposition that they are far away physically, with a large temporal displacement - ie, much, much older than us. That falls right out from the analysis, there's really little other conclusion that can be reasonably deduced from these numbers.
Now, to make a caveat to my own line of reasoning here, I should perhaps have run a second set of percentages against not just the total age of this planet, but the rise of complex life, say, 300 million years ago. Using 300 million instead of 4.5 billion in the denominator of the fractions used to derive the percentages above, the prospects for sentient life elsewhere on other planets capable of supporting complex life look somewhat better. For example, the last 500 years becomes 0.0001667% of the history of complex life, rather than 0.0000143% of the history of the entire planet. The odds improve somewhat, an order of magnitude greater, but still quite small.
To extend this reckoning from the rise of complex life leads to certain ideas that may be optimistic, but are not without merit. There seems to be a trend throughout evolutionary history of "faster legs". At the dawn of the age of mammals (another good series is "Walking with Prehistoric Beasts", they do a great job of revealing the Eocence and subsequent epochs), running speed was relatively slow. Over time, the "speed of chase", the maximum running speed of various predators and prey have steadily increased.
A very similar idea might pertain to the realm of intelligence. That is, the average intelligence of creatures over time (us being of course the spectacular example) may also be increasing in a similar way, as a response to evolutionary pressures.
If this is true, then even if we pass from the scene from some unhappy event, it may not be another 4 billion years before we see another sentient lifeform like us on this planet. It would be a long time to us, but in the big picture of Earth, maybe not so long - perhaps 50-100 million years, guesstimating here. Much depends on the nature of the unhappy event - a large asteroid strike could reset the clock, as it were, and it might be hundreds of millions of years before another sentient species became a possibility.
If this is true, and this trend is prevalent on all planets with sentient lifeforms, then my very low statistical percentages go up considerably, perhaps an order of magnitude, maybe two orders of magnitude - but they remain quite tiny. Therefore, we're still talking millions of years of likely separation between us and the nearest sentient civilization, either behind or ahead of us, and physically far away, unless we win the cosmic lottery in some way, against all odds.
Yet another dimension to considering the question of the abundance (or lack thereof) of advanced alien civilizations involves exploring the character of the preponderance of life-friendly planets that are out there. An excellent show regarding this is "Extraterrestrial" (http://en.wikipedia.org/wiki/Aurelia_and_Blue_Moon), specifically Aurelia. The great majority of stars in the sky are ones we can't see, small red dwarfs. Because these are the preponderance of suns, the preponderance of life-bearing worlds will probably be found orbiting stars like these. However, in order to be life-friendly, because of a red dwarf's dimness, the planet around such a sun would have to orbit so closely that it would be tidally locked. That is, one side always pointing at the sun, the other in eternal darkness.
This is not as bad as it seems for life per se; in fact, one of the revelations of this show was that it incorporated state-of-the-art simulations of the climate of such a planet, and instead of the sun-facing side being baked and inhospitable (the prevalent notion up to that time), instead a perpetual hurricane forms at the center of the sun-facing side of this world, and between this perpetual hurricane and the eternally-frozen dark side of the planet is an aureole-shaped zone quite suitable for life.
This is great news for life, but perhaps not sentient life. This planet would be about as strange a world as we can imagine, if we were stand on it. There would be no seasons; wherever you stood on the planet's surface, the sun would never move in the sky. Much of the seasonal and other forms of dynamism that we take for granted and that were absolutely crucial to the rise of our sentience would be wholly absent on such a world.
Not saying that the rise of sentience on such a world would be impossible, but it would seem far less likely in such a scenario. And these planets represent in all likelihood the vast preponderance of theaters for life-bearing worlds throughout this galaxy and beyond. This consideration is not incorporated into the Drake Equation, it's too new for that, but it perhaps should be - that is, the cosmic, seasonal, and geological dynamism of the world in question, whether or not it can inherently support life.
Another consideration to the Aurelia-type planet dynamic question is tidal dynamism. If Earth didn't have a moon, it would have no tides, and the character of life on this planet would in all likelihood be far different - probably, far less dynamic, because simple ocean tides are a huge evolutionary influence on the critical land-to-ocean boundary. It wasn't covered in the show, but could an Aurelia, a planet tidally-locked to its sun, have a moon, and if so, would its orbit be favorable to the elicitation of evolutionary interesting tides?
Having built a case from many different directions to support the idea of the extreme rarity of sentient, advanced alien civilizations, let me restate unequivocally that I do not believe that we are entirely unique in the cosmos. That would be as deeply improbable as suggesting that they inhabit every star system. But, I would not be surprised if there were only one or two, or even none, in this galaxy, they might be that rare. And if there are one or two others in this galaxy, I might guess that one perhaps is in the vicinity of the galactic center (far enough away from the core to be safe, of course), and perhaps the other on the other side of the galaxy.
If this is the case, then we have some time to think about this. Assuming that they gather information about the cosmos primarily through the light and other electromagnetic radiation emitted and/or reflected by various cosmic bodies, if they are there they almost certainly know about Earth and its life-bearing properties already, but it will be another 40,000 years from now before the galactic center knows about our earliest rise of agricultural civilization, even though that light's been traveling for 10,000 years already. It will be 90,000 years before the far reaches of the other side of the galaxy is aware of this event.
This seems like a long time, and it is; but to an advanced alien civilization millions of years old, possibly populated by what would seem to us citizens of essentially immortal age (I will get into that in a future blog entry), this is just another aspect of gathering the knowledge of the cosmos to gain insights that we are only beginning to get the tiniest glimmer of understanding around.