To be young again
I guess it's relative

from Macklemore and Ryan Lewis (Ft. Macklemore) – Cowboy Boots Lyrics on Rap Genius

Being literally young and “young” in the heart are two different things

Einstein’s theory of relativity states that time moves more slowly for an object approaching the speed of light; Speculating upon that if you surpass the speed of light, you could potentially go backwards in time, hence “to be young again”

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