Idiom for someone "not from this world"?
Are there idioms (or single words) in English for people who behave like they have come from another world where everything is perfect and know nothing about the reality? They usually come up with ideas that can never work, but look attractive if you don't analyze them properly. They know nothing about science, and it seems they don't know that people lie, cheat and get violent.
PS in Russian we usually use the word "эльфы" (elves) for such people, and they are supposedly visiting our world from the "world of elves". It's usually considered pejorative.
space cadet: someone with little grasp of reality. Also spacey or spaced-out.
E.T. or Extraterrestrial -- commonly used to refer to those from outer space. Commonly used to refer to actual residents of other worlds, but also applied to those that act like they are from another planet.
Eggheads: intellectuals that have little in the way of social skills or awareness. Also absent minded though this is a weaker term.
Airhead: Perhaps not stupid (though that may be implied), but lacking in reasoning skills and common sense.
Living in a dream world. Generally clueless re: reality.
Likely any similar term will be pejorative.
naive [nah-eev]
adjective
- having or showing unaffected simplicity of nature or absence of artificiality; unsophisticated; ingenuous.
- having or showing a lack of experience, judgment, or information; credulous: "She's so naive she believes everything she reads. He has a very naive attitude toward politics."
http://dictionary.reference.com/browse/naive
Such a person could be described as 'having their head in the clouds'.
A question regarding the meaning of this idiom has been posed and answered on this very website: "his or her head in the clouds" meaning
In specific relation to your example, saying that one of your elves had his head in the clouds would convey a frustration with his naive, overly simplistic, facile or optimistic view of the world, his misaligned priorities, and his general lack of self-awareness and of focus on the issues surrounding him that actually matter.
Adding to the good answers so far: Living in la-la land, and perhaps more BrE than AmE, in cloud-cuckoo land
You and your pie in the sky ideas. Not everything is rainbows and unicorns. Get down to earth. Stop dreaming.