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The stars themselves are evidence of Nature's alluringly cyclical nature. Gases and Dust are drawn together by virtue of the force of gravity each possess, into a central point of rapid consolidation until ignition produces new elements, new sources of fuel, and new cycles of explosions until so rapid is the expanse that the explosions sustain the series of collapses. This process produces a star, which will eventually extinguish all it consumes, and either burn out or explode. In either case, material for new stars is born. Stars produce heat and light, but only so much of it, and the bone chilling universe of darkness always has the advantage. The two pairs are adversarial. The one is still, quiet, and determined. The other is passionate, intrusive, and fickle. They battle endlessly for control of the Whole, but neither has any means with which to even assault, let alone extinguish the other. Light and heat may push away darkness and cold, but only for so long. These each must inevitably recede, and darkness and cold are sure to close upon them in step. Between the Stars that give and receive, and the Void which these inhabit, there are planets.
Planets exist between these two absolute kinds of reality, or phases. Cosmologists are fond of what is called the "Goldie Locks" argument, invoking the childhood story of a girl who prefers the soup not-too-hot and not-too-cold, and chooses to rest in a bed that is not-too-long and not-too-short. This is genuinely a perfect metaphor for the aspects of our planet and solar system and star, relative to other known arrangements found in the galaxy around us and in the universe. Our star is not too hot, and not too cold. It is not too big, not too small. We are not too close to it, and not too far. Assuming we didn't hit the cosmic nail squarely on the head, there must logically be a range of conditions similar to ours, surrounded on the continuum by the too hots and too smalls, etc... Supposed, as measured between one and nine, our seemingly cyclical universe was as likely to evenly produce condition-sets one through three, four through six, and seven through nine. If we assumed that our conditions could only be found at position five, with one through four being two hot, big, or close, and six through nine being too cold, small, or far away, that still leaves us with one position in nine under each heading for which the guages must line up. this is (1/9)^3 or 1/729.
The average of modern estimates for the number of stars in the Milky Way Galaxy alone is 200 Billion. This would yield about 275 million stars around which there is at least an arguably high probability that life may be found. The Galaxy is suspected to be about 100,000 light years across, which would produce a spherical volume of (4.19X10^15ly)^3, which we then divide by those 275 million stars(assuming an even distribution, which is flawed, but viable enough for the sake of this purely rhetorical exercise in self-awareness) to get 15.2 million cubic light years. Why are we doing this? Because when you take the cube root of this last number, the answer, the answer you get (247, depending on how you did your rounding) is the average number of light years one should reasonably expect to look in any direction to find life in our galaxy.
Our model assumes everything fits into a neat little continuum, and certainly it doesn't. At best, even though there are infinite vectors on a three dimensional plane from any given point of origin (readers will forgive me for skipping a more complex discussion of mathematical protocol), It is completely reasonable to assume (under this pre-existing mountain of possibly preposterous assumptions) that there is a strong probability that Earth will encounter life along three of those vectors, within or around an average distance of 274 light years. As far as Goldie Locks goes, this is actually kind of a comfortable number. It is still incredibly far away, but certainly less intimidating than inter-galactic space travel, and equally less intimidating than scouring the galaxy for needles in a haystack. Stars are pretty big and pretty easy to spot against the black distance. Often light years apart, they are generally well isolated, and each account for large swaths of space which can be discounted on relatively (always, relatively) simple observations, such as a distinct absence of orbiting planets, the color of those planets, the temperature and size of the stars, their age, and so on.
With these thoughts in mind, the search for life in our galaxy becomes a provocative opportunity for optimism, but implies a proportionately sober, disciplined approach to exploration and research, and a selfless capacity for patience, and for quite some time to come, disappointment and frustration. Our Voyager II spacecraft is estimated to be travelling at 516,000 thousand kilometers per year. At that speed, it would take eighteen thousand years to travel a single light year. To travel that distance 274 times would take almost five million years. Our first radio signals left the earth at light speed in January of 1910. These would have to travel for another hundred and sixty five years to reach our three comfortably hypothetical planets. Even then, it is a profoundly grandiose supposition to imagine these messages being received by sentient, technologically capable lifeforms like ourselves, who would then respond in kind. Such a response wouldn't arrive until the year 2460 A.D.
Readers are not thus encouraged to start an atheist version of the Millerite movement, holding one eye on the Heavens and another eye on the wall calender. These numbers are pure fantasy, but they give us a sense of things. As humans, we struggle to find a way to relate to the enormity of the universe. Our greatest comforts precede from the urge to simplify the madness of totality into something tangible and comprehensible, without fully depriving the world of its mystery and wonder. The number, 275 million, may be purely speculative in terms of the number of potential new homes waiting for us in the Milky Way, but it is a pretty solid guess in terms of how many years of habitability the Earth will provide.
By then, the Earth will be about half way into its death spiral, and the moon will likely have already disintegrated into a swirling, fiery ring of dust around the earth. This last phenomenon will be the final extinction event before the Earth is wiped away for ever. Ages later, our star will die too, ending with it all remaining dependent life in our solar system. Perhaps too the galaxy will someday collapse, and the universe too. But until then, we must operate as though the possibility exists for this species to reach beyond the planetary confines of our Eden. This is the next stage of human evolution. Or it is the last.
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