Earlier quoted context omitted.
Everything you have written is terrestrial speculation based on the same mistaken assumption - that human intelligence is as smart as it gets. If aliens exist they will be alien. They will not be a bit weird with our naive ideas of sort-of-better alien tech. They will be something entirely different, and very likely able to do entirely unexpected things. Imagine a species which has roughly the same intelligence advan…
To add to this: it is way less than 100 years since we learned to use fission and fusion. Until the two first bombs were dropped it was either unknown or, to those who realized the potential: considered impossible with the technology available at the time. I wonder what is just out of reach for us today, or what scientists are secretly working on today. Also, one step ahead, like you I also think what we are capable…
The rationale for the Dyson Swarm future it can be built incrementally, requires tech we basically have and can scale massively. The consequence is that it's not remotely subtle. These things have a distinct signature because the only way to get rid of heat in space is to radiate it away and that has a distinct IR signature.
Given all this we can reasonably conclude that there isn't a massive set of Dyson swarms within a pretty huge light cone.
So the problem of "you don't know what's possible" is that for each new known unknown (eg whether FTL is possible, whether fusion will ever work as a viable power source) and unknown unknown it gets _more_ likely we'll see these things not less.
Let's say there are 5 spacefaring civilizations in the MIlky Way other than us. The odds that 0 of them go this route and choose to remain "hidden" is much more possible than if, say, there were 1000 spacefaring civilizations in the Milk Way. In a universe with FTL those numbers (5 and 1000) now use a much bigger volume as their basis. Perhaps the Local Group. Perhaps the entire Universe.
Here's the other big problem with "You don't know what's possible": if we can't conceive of some super-advanced technology or higher existence, what are the odds that other civilizations can't either? If we're 1 of 5, we may be the sole dumb kid on the block. But out of 1000? I'd be willing to bet there are others sufficiently like us operating under similar constraints with outcomes we can reason about in aggregate.
Let me put this in perspective. Human peak energy usage is estimated at about 10^11 W (Watts). Years ago a Russian physicist postulated the Kardashev scale for energy, which is pretty simple:
- K1 (Kardashev-1) civilizations use the power output of a planet)
- K2 civilizations use the power output of a star
- K3 civilizations use the power output of a galaxy.
Obviously these aren't absolute units (eg stars have different power outputs) but it's a useful framework. Carl Sagan came along later and simplified the scale somewhat to:
- K1 = 10^16W
- K2 = 10^26W
- K3 = 10^36W (which implies ~10B stars in the "galaxy")
So if we were to advance to being a K2 civilization around our own Sun we would have access to a truly mind-boggling amount of energy. To give just one example, we could essentially sterilize the Milky Way in about 100,000 years trivially without any object going further than the orbit of Mars.
So you don't even need to decide if civilizations would on average do this or not. You just have to decide how likely is that _none_ would. 0 out of 5 doesn't defy belief here. 0 out of 1000 gets more incredulous.
So back to our alien UFOs, the odds that no one does this, a civilization advances beyond this point, they discover FTL, they use it to come here and they hide their presence from most of us. they remain basically undetected in an era where everyone basically has a high-definition camera in their pocket (as opposed to the 50s and 60s) and somehow reveal themselves when they have technology we couldn't even imagine... simply defies belief.