So I was reading some stuff on Charlie Stross's blog, and it got me to thinking about sufficiently advanced technologies.
Our civilization is young, small and hot. I suspect that old, large and cold civilizations might be nearly undetectable by us.
We are young, hence we think on scales of seconds, years and centuries. We have no sense of time scale as a species of an individual.
We are small, so we are used to the idea that there is plenty of room to grow into, and getting there sooner is a significant advantage.
We are hot, in that we are amazingly inefficient. We waste lots of energy. We also expect other civilizations to do the same. We have cooled off rapidly over even the last few years of this technological revolution, with the amount of radiation we leak to space per member of the highest technology civilization on the planet falling rapidly.
An old civilization wouldn't have to think on the scale of seconds, years or centuries. It could easily think on the scale of the universe. Ie, how many cycles of computation do you get before the universe ends?
An old civilization could be a large one. Expanding, and especially expanding rapidly, doesn't matter all that much -- you are limited to c anyhow, and the amount of volume of the universe you can expand into is small relative to the size of your existing civilization, possibly even on end-of-universe time scales.
An old civilization could be a cool one. One idea is that high end civilizations would turn matter into computronium, and we'd be able to detect it by looking for hot spots of high entropy in the sky. But hot spots are wasteful. If you make your computronium sphere larger, you get more computation out of the energy, and the temperature of the waste black body radiation (high entropy radiation) drops. At maximal efficiency, the computronium sphere waste products approaches the background temperature of the universe -- the cosmic microwave background, if you hang around in intergalactic space at least. A civilization that shows up as a thermal, radar, radio or other "hot spot" is a hot civilization who is failing to use its energy at optimal thermodynamic efficiency.
We look around, and we don't see such hot spots. We do the math, and it isn't hard for a slightly more advanced civilization to colonize an entire Galaxy over a period of a gigayear or so (exploring via self replicating probes is "easy" for a slightly more advanced civilization -- and if a civilization becomes a machine one, exploring with self replicating probes is colonization). However, if such an event happened in concert with the civilization getting old, cold and large, it might fade out from view.
We could have computronium solar systems that are light years in diameter that look like background radiation. They might even "cool" the star in order to make it last longer. They might pilot the star out of the galactic disk entirely in order to reduce the background heat level, and allow them to swell the size of their sphere and cool off the surface even further.
The only thing that would leak out, and be detectable to us, would be gravity.
The expected symptom we'd see is a large amount of extra mass that we couldn't account for.
(And that is my punchline).
One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision - BRLast edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.