Why is the Fermi paradox' assumptions so strong? Do they even need to be?

Question

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?

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.

• The answers to What exactly do they look for when searching for extraterrestrial intelligence?
• This answer to How far away would an alien civilization need to be for us to not notice them?
• This answer to What would it take to get a message to another star?

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.