Holly wrote:Guest wrote;However if such sophisticated civilisations do exist nearby we haven't seen any evidence of it - such as radio or microwave or other forms of electromagnetic radiation signals from space
Isn't it possible that 'they" have already been living amongst us for quite a very long time?
Perhaps they do have a "headquarter" under water?
We haven't even explored a fraction of our oceans.
Who knows what's going on deep down their?
Why do we always see these crafts disappear into the ocean?
Look, I can only guess, but I don't see it as impossible.
As for not seeing any evidence of radio, microwave or other forms of electromagnetic radiation signals.
Perhaps they don't want to interfere with how this planet is progressing?
If advanced civilisations existed underwater we would have detected electromagnetic radiation signals they would use to communicate among themselves. If these craft flew into the sea at incredible speeds and continued at these speeds as has been claimed then they would defy all known physics as they would otherwise create detectable shock waves, heat signatures and em radiation. The ocean floor is being mapped and as yet nothing "alien" has been detected.
https://oceanexplorer.noaa.gov/explainers/mapping.html
For an advanced civilisation to develop we know from "science" that this would have to first evolve on a habitable planet - from chemicals to unicellular organisms to multicellular organisms to organisms that produced tools to organisms capable of invention. It is possible that most organisms that had advanced to the technological stage would wipe themselves out fairly shortly after they had reached the technological stage. The Industrial Revolution of the late 18 to 19 century could be said was the period that Homo Sapiens became technological. The nuclear bomb was developed during WWII in the 1940s and during the 1950s and 1960s that technology improved. Today we have a media and politicians that seem less cautious in their descriptions of conflicts. There are also some nations that are trying to develop nuclear weapons that are run by religious fundamentalists and a concept of martyrdom and the "next world".