Here's a breakdown of the meaning:
* Space: This part of the idiom references the vastness of space, suggesting that the person's thoughts are far away and unconnected to the present moment.
* Cadet: This part alludes to a trainee in a military academy or space program, often seen as someone inexperienced and prone to making mistakes.
The idiom is often used in a playful or humorous way, but it can also be a bit derogatory, implying that the person is not very intelligent or capable.
Examples:
* "Don't ask him to help with the dishes, he's a total space cadet."
* "She's always zoning out, like a space cadet."
* "He's so absent-minded, he's practically a space cadet."
Origin:
The exact origin of the phrase is unclear, but it likely emerged in the 1960s or 1970s during the height of the space race and the popularization of science fiction. The image of an astronaut floating weightlessly in space became a symbol of detachment and a lack of earthly grounding.