Thursday, October 26, 2017

The Bubble of Life

Let’s continue exploring the case where life is hard to originate, meaning it starts itself almost nowhere, but is easy to evolve, meaning once you start it, it just doesn’t stop.  If an alien civilization realizes this is the case, and decides they want to do something about it, they can undertake seeding on all nearby planets which can support the life they begin there.  So, after they have had enough time to seed all the planets within the range capability, what would there be?
If you looked at a three-dimensional map of the galaxy, with red dots for planets with life and blue dots for planets without it, you would see a large disk with a central bulge, all blue, and somewhere in the disk there would be a little red bubble, the bubble of life.  Somewhere near the center of the bubble would be the home planet of the alien civilization.  Seeded planets take billions of years to evolve from simple seed cells to new civilizations of intelligent aliens, so for some billions of years, the seeded planets wouldn’t be capable of sparking new bubbles.  During those billions of years, the galaxy would be rotating and shearing, so the bubble would not stay round, and proper motions of the stars involved would make it enlarge itself and become less distinct.  The alien civilization would likely be long gone, and their home planet would have reverted to just one more planet with life.

Suppose Earth was nearby the bubble, and was a bit younger that the seeder’s planet, so that Earth blossomed into an advanced civilization after the seeders had done  their work and proceeded to become extinct.  This, of course, is some time in our future, if we are lucky and don’t make too many emistakes.  What would we see as we examined our surroundings?  If we were a half-billion of so years later than the seeders, we would see planets with oxygen atmospheres, or other signatures of life, in something like a bubble around some central point.  This pattern is almost necessarily solid evidence of a civilization that decided to seed life wherever it could. Furthermore, it is not just evidence of life in the galaxy, but of a long-past alien civilization with space travel capability.

There doesn’t seem to be other causes for a bubble of life.  If life could originate easily, instead of a bubble of life, the whole galactic disk would have specimens.  It is the localized nature that gives rise to the idea of a difficulty in origination of life, and the possibility of a civilization seeding multiple other planets.   It’s also hard to imagine something an asteroid striking a planet with life, somehow bouncing off after adsorbing some living cells, which stay alive until the asteroid is somehow propelled out of its home solar system and travels to another, and then has another impact on a planet that can support life, and the impact doesn’t kill the cells, but leaves them in some place where they are viable.   Nor could a nearby supernova blast living cells from one planet to one in another solar system. 
One way to look at this example of seeding is a gift to civilizations that come into existence later.  A later civilization near the bubble of life would have a myriad of planets to colonize, if this were possible and they were motivated to do so.  Colonization in a galaxy barren of life can only lead to a harsh life, probably under the surface of some mineral-rich moon or planet, with no hope of surviving long enough to transform the moon or planet into something like their home world, with the right atmosphere, vegetation and animal life.
What about someone inheriting the mantle of the original seeders?  The oldest stars in the galaxy are a bit better than 13 billion years old, but that doesn’t mean the whole galaxy came into existence that quickly.  The time to form depends on what preceded it, but let’s just say 2 billion years were necessary.  Then the disk of stars might have formed, along with the bulge and the other details.  If a star formed then, and had a planet or a few, one of which originated life, we might be up to 4 billion years.  If it took 4 billion more years to evolve to a space-faring alien civilization, that might be 8 billion.  Then the alien civilization seeded planets, and it is another 4 billion for the second generation of life to reach civilization level.  There could have been a hundred or so seeded planets, and if one of them started seeding a second round, we, at 13 billion, might see a second bubble of life, seemingly growing out the side of the first one.  Since we don’t know the variability in the timing of the evolution of life, or even what it depends on, it could be 13 billion years from the oldest star’s birth is not enough, or if the timing could be shorter, the second round of seeding might be more or less complete, right up to the generation of an observable oxygen atmosphere.  The oxygen atmosphere on Earth came into existence in a geologically short time, so that signal is a good early indicator of a planet with life.  Seeing a double bubble would dramatically confirm our observations of other life in the galaxy, and give us something toward a date of the first generation.

Suppose we can find no bubble of life, no matter how far out we get our giant telescopes to search for oxygen or some other signature of life.  Then we are faced with a decision.  Perhaps we are the only life form that is going to originate in the galaxy.  Should we let it all disappear?  Or should we make it the planetary goal to figure out how to seed other planets, capable of growing life, with some seed cells.  That would be a purpose that might unite mankind, and even carry over into any AI entities that come into existence.  Or we could just figure out how to have a good time until the sun burns out.

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