Questions tagged [fermi-paradox]

"If extraterrestrial intelligence exists, why have we found no evidence?", first defined as a paradox by Enrique Fermi and colleagues, after estimating based on various facts that an advanced civilization has had time to colonize the entire galaxy many times over.

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What percentage of the universe's galaxies are within our reply-lightcone before they're Hubble-flow expanded away too far to reply? [duplicate]

Because of the Hubble constant, how far can we now send a signal and still be in range to hear an immediately-issued (the moment they receive a signal) reply? And what percentage of today's visible ...
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Copernican principle based question about ET

As mentioned, I'm following the Copernican principle for this line of questioning. Yes I've considered and read many other possibilities, but this question is for Copernican-style answers ONLY. Your ...
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265 views

Is there good estimates/measures on the variables that make up the Fermi paradox?

Here's what I've got: Universe size: Milky way is 100,000 LY wide. Nearest galaxy is 2.2m LY away. Number of stars: about 300,000,000,000 in the Milky way. 100,000,000,000 galaxies. Age of ...
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Is a combination of 'space is big' and 'humans haven't been around long' a good solution to the Fermi paradox?

The Fermi paradox is basically that: There are billions of stars, life is probably abundant throughout the universe. Even though it may take tens of thousands or millions of years for life on other ...
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2answers
678 views

Could unexpectedly high levels of interstellar space debris be the Great Filter?

I've heard (though I can't find the source) that sufficiently large interstellar space debris has the potential to destroy spacecraft, and that there is considerable uncertainty about how much of a ...
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Could Von Neumann probes be forbidden by technological limitations?

The famous Fermi paradox asks an important question: if space-faring civilizations exist and are not extremely rare, why are they not already here? Von Neumann proposed a probe, that flies to nearest ...