And the converse is true- a creature that lived out its existence in a few microseconds might appear to us as a mere glitch in, say, an electric field, even though to itself, its life feels as long (or short) as ours. Entire civilisations could be passing unnoticed except as static on the radio. Cohen & Stewart's book, What Does a Martian Look Like? The Science of Extraterrestrial Life, postulates several such possibilities.