Definition & Meaning of "[live|be] on another (planet|world)"

What is the origin of the idiom "live on another planet" and when to use it?

The idiom "live on another planet" has its origins in the early days of science fiction literature and the popularization of space exploration. During the mid-20th century, as humanity's fascination with space grew, the idea of living on other planets became a prominent theme in science fiction stories. Today, this idiom is often used figuratively to describe someone who seems detached from reality, lost in their own thoughts or imagination, or having different interests or priorities than those around them. It can be used in various contexts, such as describing individuals deeply engrossed in their own fantasies, daydreamers, or those who have unconventional or eccentric viewpoints. This idiom is often used in casual conversations or informal settings to convey a sense of disconnect or otherworldliness.