Never

Silence is a lack of sound.
Darkness is the absence of light.
Cold is the absence of heat.
Nothing shows that something is missing.
Nobody: no person.
Emptiness: the absence of matter.

Physically seen silence, darkness, cold and emptiness have no meaning!
Yet the insights used to be otherwise. There was a time that besides the calory
the ancient unit of heat (and energy in general),
there was the cold unit frigorie.

To philosophize

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