Why us?

Someone was posting on a web forum about the odd coincidence that chemical rockets are barely capable of reaching orbit from the surface of the Earth; if the planet was even 10% larger that would become extremely difficult, and if it was 50% larger probably impossible.

While I’ve wondered myself whether there’s anything special about those numbers that makes life more likely to evolve (e.g. chemical rockets are largely powered by the energy bonds between atoms which also determine many of the properties of life on Earth), there’s also another argument that makes sense to me:

If you assume that you’re a random member of the population of the universe, then you’re most likely to be a member of the most populous species in space-time. So if you find yourself confined to a single planet, you’re also likely to find that it’s a planet that the laws of physics allow you to escape from so your species can colonise the galaxy. There may be other technological species out there, but if their gravity is 50% higher then they can’t get off the planet with chemical rockets and using nuclear rockets in an atmosphere is problematic, to say the least; hence they’re likely to either wipe themselves our or be wiped out by our descendants when we find their solar system.

This is kind of related to the Doomsday Argument, which assumes that we’re around 50% of the way through the population of the human race and attempts to predict how much longer the human race is likely to survive. We could have been born in an unusual situation purely by chance, but my money is on the human race being the first in this galaxy and the ones who will take it over; though by the time we reach the far side of the galaxy we probably won’t look much like the humans you see today.

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