The Fermi paradox revisited: Technosignatures and the contact era

1. Planets are incredibly inefficient in creating living area per unit mass;

2. Orbitals are incredibly efficient at creating living area per unit mass. IIRC 1% of Mercury's mass could create a full Dyson Swarm around the sun and have billions of times of the living area of Earth;

3. Space orbitals as typified by an O'Neil Cylinder (being 2-4 miles wide and 20-40 miles long) don't require new physics or new materials. Stainless steel has sufficient tensile strength;

4. Orbitals easily allow energy generation from solar power collection, which in space would be much more efficient than on Earth. So this idea isn't even predicated on nuclear fusion power generation becoming commercially viable. If that does happen, this becomes even more likely. The point is it's not required;

5. Dyson Swarms (being a collection of orbitals that would capture the energy output of the Sun in the same way that water droplets in a fog would obscure something) can be built incrementally. We use the term "Dyson Swarm" instead of the original "Dyson Sphere" because of the misconception that a Dyson Sphere is a rigid sphere. There is no known of theorized material with sufficient strength for that. Same for ringworlds;

6. Such a Dyson Swarm built between the orbits of Venus and Mars would not be that crowded. The mean distance between orbitals would still be hundreds of thousands of kilometers;

7. Orbitals will generate heat. That heat needs to be vented. The only way to do that in space is by expelling mass, which isn't really sustainable, or by radiating it away. Physics tells us that the wavelength of light radiated away is basically just a function of temperature of the radiating object. At any reasonable temperature, that means largely infrared ("IR") radiation;

8. The amount of energy such a megastructure would have available is beyond comprehension. We use an estimated 10^11 Watts of power. Capturing Solar output would mean ~10^26 Watts of power. That means if the population of humans was a quadrillion people (ie 10^15), the average power each person has would be the same as the entire Earth currently uses. Think about that;

9. This is likely the most practical way to travel between star systems, as in imparting momentum from light onto a spaceship. People who have looked at this see it as quite practical to get to ~0.86c this way. Beyond this, believe it or not, the aerodynamic drag of interstellar gas slows you down too much; and

10. The timeline from going from this to coloizing the entire galaxy is pessimistically 10 million years (assuming 0.01c and 100k LY across the galaxy).

If you accept these premises, such a structure would stick out. There's no hiding something like this. The signature would be heavy on the IR spectrum and would be visible from thousands of LY away. A galaxy that had been fully colonized this way would be obvious from millions of LY away.

I find this idea attractive because it is incremental and requires no new physics or theoretical materials (unlike, say, the many attempts to come up with a mathematical basis for warp drives).

Radio band usage in this scenario is completely irrelevant.

Even at the speed of Voyager 2, (15km/s), in a billion years it would cover about 4 * 10^17 km or about 40 thousand light years. I am pretty sure people who have been developing for hundreds of millions of years can do better than that, by orders of magnitude.

Also you put a totally strange assumption that all civilisations will only restrict themselves to visiting planets. If there is a lot of civilisation it is more likely they will have different motivations.

Central limit theorem states that the "average" of "any" kind of distribution is normally distributed. It doesn't make the underlying distribution behave in any particular way.