Note: the idea of 'ashen light' is IMO a beautiful example of cognitive biases which hinder objective reasoning.
"Before the development of more powerful telescopes, early astronomer Franz von Gruithuisen [March 19, 1774 – June 21, 1852] believed that Ashen light was from the fires from celebration of a new Venusian emperor, and later believed that it was the inhabitants burning vegetation to make room for farmland."
Nice theories, don't you think? It was likely the best speculation of its time, but just consider how human culture centric those thoughts really were.
- "fires from celebration of a new Venusian emperor" = Venus has an emperor - implying a hierarchical society - celebrations are conducted on a primitive fashion through the lighting of massive planet-wide fires.
- "inhabitants burning vegetation to make room for farmland" = there is a lot of vegetation on Venus, enough so that it needs to be burnt on a massive scale in order to conduct agriculture.
Basically these thoughts mirrored the current sociological-technological-philosophical environment surrounding von Gruithuisen and were projected into an alien environment. The tacit assumption seemed to be that the sociological-technological-philosophical status quo where von Gruithuisen was living in at the time (hierarchical society, all hail the leader, dependence on agriculture, etc.) was the most natural state of things and therefore it was reasonable to think that alien places, even civilizations on other planets, would follow this model.
Let's extend these thoughts to SETI. What are we trying to do with SETI? We're trying to pick up (radio) signals of an alien civilization.
Not withstanding arguments on the necessarily narrow time window when we could pick up anything in the first place, notice that there are many assumptions we're making: radio signals are used, the "water hole" is preferred, potential willingness for the alien race to actively attempt contact, supposition that we could detect and distinguish an artificial signal from a natural one, etc.
What if we're going the way of Baron von Gruithuisen here? What if what we're trying to find is simply so alien, that we cannot comprehend it based on our sociological/technological/philosophical tradition and background? What if we're trying to find traces of a hive mind of superintelligent translucent slime who thinks since they communicate by clanging on pipes of ice under liquid methane oceans, others must surely do the same?
My questions are not meant to imply that SETI is a waste of time and that we should stop it - on the contrary!
What I am saying is we should remember Baron von Gruithuisen, and try to think outside of the box, through de-assumptionizing (does this word win the Scrabble?) and re-thinking the "model of the space alien", since we really have no good reason to assume anything specific in that area.