The Fermi paradox first states that it is highly likely that intelligent lives have existed on planets long ago. As in, not just on one planet, but on billions of planets.

Then the paradox goes on and states that some of these planets may have conquered their galaxy and achieved interstellar travel, and so the paradox is, where are the signs of all this interstellar travel?

What I don't understand is, why is the last conclusion so strong? It seems to make it much more easy to disregard the paradox, because all one has to say is "the planets never lived long enough to conquer space", and one can't really refute that since we know space is vast and planet's lives are finite, and we ourselves probably won't live long enough to do it.

But, the Fermi paradox doesn't even need those planets to "conquer" space, does it? All it needs is for those planets to invent radio (a fairly basic technology), and then blast that into space. Those signals will eventually reach across the stars and the galaxies, even if the originating planet is dead and gone. And if billions of planets with intelligent lives did that for billions of years, surely space should be abundant with such radio signals. Even if we just look at the milky way galaxy, it would only take a few thousand years to "explore" the entire galaxy purely with radio signals.

So my question is, why is the Fermi paradox relying on such a strong assumption (the conquering of space) rather than the much easier one of radio signals?

Second question: Are there any refutations of this "modified" Fermi paradox?

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    $\begingroup$ Could you please cite or quote your source for the Fermi Paradox? Because your version of it as stated seems to be.... not mainstream. $\endgroup$ Jul 17, 2021 at 11:48
  • $\begingroup$ My version comes straight from wiki? en.wikipedia.org/wiki/Fermi_paradox: "Some of these civilizations may have developed interstellar travel, a step humans are investigating now. Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.[8] And since many of the stars similar to the Sun are billions of years older, Earth should have already been visited by extraterrestrial civilizations, or at least their probe" $\endgroup$
    – Art
    Jul 17, 2021 at 12:54
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    $\begingroup$ You are misunderstanding the Fermi paradox. For one thing, it was a casual lunchtime conversation: "Why aren't they here?" Or as Stephen Hawking put it, "I am discounting the reports of UFOs. Why would they appear only to cranks and weirdos?" $\endgroup$ Jul 17, 2021 at 15:21
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    $\begingroup$ Most of what you are referring to are listed under the heading "4 Hypothetical explanations for the paradox". Notice the word hypothetical, these are just other peoples commentaries discussing a lot of "maybes"; maybe this, maybe that. $\endgroup$
    – Fred
    Jul 17, 2021 at 16:19

1 Answer 1


Every analysis of the Fermi Paradox is an opinion. I think it always bears mentioning that. We posit the existence of civilizations up to billions of years old based on a set of assumptions that seem very sound. Then we predict their behavior, even though we only discovered farming 12,000 years ago. It's a mistake to draw conclusions about species that, if they currently exist, have very probably been civilized for millions of years longer than we have - possibly billions of years longer. How can we hope to say what technology might be used by beings who have been making it for millions of years, or what values they hold?

There are a bunch of answers to other questions that indicate the issues with radio signals at interstellar distances.

Something not mentioned in those answers is also that as our technology advances, we use less and less power to transmit radio signals, and we've been switching a lot of our transmissions to fiber-optic cables. A more advanced civilization might leak a much smaller radio signal into space than we do, or none at all.

If I understand you correctly, you are supposing that advanced civilizations send probes out that return data about the galaxy, instead of going themselves. Such things have been considered from a variety of viewpoints. Lacking the technology ourselves to make such things, we can at least presume that they would at minimum send back data in a very narrow beam, in a highly compressed format. (Though the answers listed above indicate that's so difficult, perhaps beings on this kind of level switch to far more effective techniques that remains well beyond our abilities.) In that case, we could only detect that if we were in the path, when the transmission occurs, and were listening, in the right way, with adequate equipment. The chances of that happening even once are minuscule, even if such probes are abundant.

Or, you know, maybe we are living in a simulation of a universe. If thinking about questions on this scale doesn't bend your mind, you aren't doing it right.

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    $\begingroup$ Or maybe Cixin Liu is correct... $\endgroup$
    – Rory Alsop
    Jul 17, 2021 at 17:07

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