This will probably get dismissed as "optimistic futurism" but I find the argument compelling that the future of any civilization is a Dyson Swarm for many reasons such as:
- Planets are inefficient uses of mass to create living area. IIRC 1% of the mass of Mercury could make enough living area from habitats to house at least a million times as many people as we have now.
- Gravity is a tyrant. Spinning a habitat achieves much the same thing without the negatives (as in the cost of launch).
- This is entirely feasible on solar power alone. The importance of this is that practical fusion power is not a prerequisite.
- This requires no new science. It's largely an engineering problem (albeit a significant one).
I deliberately use the term "Swarm" here not "Sphere", which is true to the original concept. "Sphere" suggests this is a solid shell. That was never the intent. No known or theorized material could support a solid shell around the Sun.
If you accept this premise then it's about the most un-subtle thing you could do and should be easily detectable millions of light years away in the IR spectrum. Why? Simple:
- Stars generate heat
- If the habitats hit by the energy from the star will heat up
- In space you can only radiate heat away
- If you don't remove that heat you'll ultimately fry
- The wavelength from radiating heat is determined by the temperature of that object
The standard counter to this is:
Q: What if you recycle the heat instead?
A: You can improve the efficiency but you can never perfectly consume all that heat. To do so would be to violate thermodynamics. If that's possible, well then all bets are off.
A thousand years ago we were stabbing each others with swords. In a thousand years the above scenario is far from overly optimistic (IMHO). So in a cosmic blink of an eye we go from undetectable (from a SETI perspective) to being detectable from tens or hundreds of millions of light years away.
So that's why I think SETI is pointless.
Some say "you never know what fruit science will bear". While true, taken further this means it doesn't matter what science you invest in so why is SETI special?