Is there anyone out there?

It's a question that has plagued humans ever since we first looked up into the stars. What's out there? Statistically - so the argument goes - we can't be the only ones floating around in space. There are billions of galaxies out there, each containing billions of undiscovered stars. It seems almost impossible that we are alone, a single inhabited planet spinning around in all that vast emptiness.

In fact, it was a long series of happy coincidences that gave us life. One great fluke after another is the only thing that sets us apart from all those other cold, barren stars. The chances of replicating the chain of events that created intelligent life are vanishingly small. If one were to set out to do so, however, it would look something like this:

Pick a galaxy sufficiently boring, so as not to be colliding with other galaxies. Your pick will need to be a third generation star so that there's a good smattering of good star-stuff like carbon and iron to play about with. Next, find a system in the boring part of that boring galaxy. A provincial place, like the unfashionable end of a spiral arm. You don't want to get too close to black holes, pulsars, and stars going supernova.

Once you've found the right galaxy, take one planet - not too hot, not too cold. Must have one good sized moon - not too close, not too far away. Ensure the local star (known locally as the "sun") is a slower-burning yellow star, and not a binary. It is good practice to locate the planet near some other, larger planets, to prevent any of the bigger asteroids from wiping the planet out before, or even after, life is born. The planet must have a molten iron core, and its moon must be able to push and pull that core. An atmosphere helps, too. It will interact with the convection currents and create weather.

Once you have found the perfect planet, maintain an evironment conducive to life for as many billions of years as possible. Eventually, something might — might — crawl out of the mud, and flop onto the shore. Wait another few billion years, and they might have legs, and have embarked on a mission to destroy the world that has sustained them.

Life, then, is perhaps much more rare than we would like to think. If just one step in the life-forming process had not occurred, or had a different result, then life as we know it could have been vastly different, or made extinct in an instant. There are many things that could have gone wrong. The moon is a planetary twin to the Earth, and it is extremely important to life here. If the moon had not broken free and settled into orbit where it did, we wouldn't have the tidal systems, tectonic plate activity, magnetic fields, or protection from the sun's radiation. Another possibility could have been Jupiter and Saturn fusing together. If that had happened, we would have had a second sun in our solar system. This could have any number of untold side effects, most of which would eventually be lethal to life on Earth.

Statistics might argue that out of the billions upon billions of planets out there, the possibility of life being on any one of them is high. But out of those billions, how many are able to support life? And out of those small few able to support life, how many could have evolved as far as we have?

Is there anyone out there? Will we know until we go and look?


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