If time is relative, whose clock determines the age of the universe?
Trying to age the universe or assign it an arbitrary birthday has always seemed like a very human and somewhat meaningless task. We commonly say the universe is approximately 13.8 billion years old, counting from the Big Bang. But what precisely does that age mean when elapsed time depends on the observer?
For example, someone remaining close to a black hole could experience much less time than someone far away. Their clocks would record different durations between comparable stages of the universe’s evolution. So whose elapsed time are we referring to when we assign the universe a single age? The early universe was incredibly dense, on a level that males black holes seem like a piñata so might that imply strong time dilation. I suspect I’m incorrectly applying the analogy of a black hole within surrounding space to the universe as a whole. Would “time ran more slowly back then” even mean anything without an external clock to compare it with? Peace