Ask the average scientist about the possibility of an encounter with an extra-terrestrial lifeform, and it's likely you'll find you've prompted 'the giggle factor'. After rolling their eyes, they remind you that the distances between stars are so vast, it's virtually impossible for any aliens to visit us.
But a potential flaw is assuming an extraterrestrial civilisation would be only a few hundred years ahead of us in technology. How about civilisations that may be a million years ahead of ours?
The late scientist and author Carl Sagan once asked: "What does it mean for a civilisation to be a million years old? We have had radio telescopes and spaceships for a few decades; our technical civilisation is a few hundred years old ... an advanced civilisation millions of years old is as much beyond us as we are beyond a bushbaby or a macaque."
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