What is length? One can give what is called an operational definition. One way might to be compare the length of a thing to a meter stick. And so for time: One explains how to construct a particular kind of clock and start it. Or one could use the pulses of his heart when he is well-rested. You can think of some other operational definition of time.
How is the age of the universe determined? Look for the oldest-looking galaxy and estimate its age. Currently the redshift of a distant galaxy is used to calculate its age according to a numerical procedure worked out by astronomers over many years or maybe now they just use a chart of the relationship between the redshift of a distant galaxy and its theoretical age.
How is the age of the universe determined? Look for the oldest-looking galaxy and estimate its age. Currently the redshift of a distant galaxy is used to calculate its age according to a numerical procedure worked out by astronomers over many years or maybe now they just use a chart of the relationship between the redshift of a distant galaxy and its theoretical age.
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