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People born after 2000 have never seen the cosmic microwave background on their TV set.
(startrek.website)
A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. A showerthought should offer a unique perspective on an ordinary part of life.
It is, but those late model CRTs often had a lot of digital circuitry that displayed a solid color on channels with nothing on them. Unless there was a much older CRT around, they never would have seen it.
Most of the CRTs are going to be older