Quote (Talisman)
How would you do that under water?
Different zones of temperature and pressure can act as refractory lenses. Look up "thermocline" in wikipedia.
I have doubts about underwater based technological civilizations, however. The main part is: our great achievements have all been combustion related. Fire, then internal engines, have set the pace for the rest of technological process by placing hard limits on our ability to mobilize and use energy.
Underwater conditions make the advent of combustion engines very unlikely, as a result disabling the possibility of expanding our available energy beyond daily solar influx (in other words, the food we eat to make our muscles work). When we started dipping into "solar reserves" of complex hydrocarbons (re: solar energy stored as chemical energy by preceding generations of life) our ability to bring energy to bear on various problems exponentiated. This coincides within 50 years of the population explosion from 1 billion -> 1.5, 2, 3, 4, billion and etcetera.
Another issue with underwater life is this: would the conditions of underwater life require the development of more advanced cognitive systems? food is abundant and the medium is isotropic, homogeneous, and nutrient dense. Automata with simple search-and-feed neural protocol would likely outcompete or pre-empt the development of higher cognitive faculties. Recall, that on Earth whales and dolphins re-entered the seas after a period spent as mammals on land, where they navigated more difficult environments.
Something interesting to think about is, if intelligent life developed underwater, would they use a natural number/ integer mathematical system? They develop in a world composed of gradients and gradual quantities, perhaps this would make calculus something like their "base" system and need to develop higher abstractions for dealing with "integer" units.
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