UFO's

[Anomalocaris]

Water as reaction mass for a propulsion system may not seem nearly science fictiony enough for an future age we are told that would be populated by warp factors and Alcubierri drives,  but there seems to be no reason why such reaction propulsion systems can not form the basis of interstellar civilization.

If ET is using water as a reaction mass then they will never leave their home system.

The Tyranny of the Rocket Equation.

There is no real difference between using water as reaction mass or using some gas like helium as reaction mass.   You can build very efficient ion propulsion by vaporizing, dissociating water, and ionizing the oxygen and hydrogen and use them as reaction mass using electric propulsion.

Ion drive can be much more efficient than chemical propulsion.  

We’ve already sent probes out of our solar system using chemical propulsion.

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Science fiction writers seem to imagine the first alien to come to our system would be much more advanced than we are, and can easily squash us like bugs.   That probably is a statistically reasonable assumption.

However, I think it is more interesting to speculate the reverse, taking a cue from Ming and Qing dynasty China.    What happens if the first alien who comes to us are technologically more backwards and poorer then we are, like the Europeans were technologically more backwards than Ming and early Qing dynasty China, and far poorer and less productive than the mogul empire in India, but they are far more ruthless and enterprising than we are?

We fantasize that we are mean little buggers, and even if we are not technologically competitive, we are just good at fighting, hence all the fantasy novel of human mercenaries serving technologically superior aliens.    but what if we’ve not compare to them?  We are rich, fat, complacenct buggers compare to the real carnivores of the universe?

We think discovery of extraterrestrial intelligence will instantly unite humanity.  I think not.  We will each seek to enlist the aliens to help overmatch our fellow men.   In the end the aliens will find it effortless to divide and conquer us.   They hardly need to break out the fancy hardware and clouds of wicked looking machines. They just drip feed some offers of help in our fight against our fellow humans and we will trip over ourselves to do their biddings, just as a few tens of thousands of brits hardly had to conquer much of India by force to completely subjugate the entire subcontinent of four hundred million.