Time and Distance: Feynman's Physics Explained
Time is what a clock reads; distance is what a ruler reads. But how do you measure the age of the Earth or the distance to a galaxy? You cannot use a stopwatch or a meter stick, so scientists invent new clocks — like the radioactive decay of uranium — and new rulers — like the parallax shift of stars. The key point is that our ideas of time and distance are tied to the actual operations we perform to measure them. Physics is not abstract philosophy; it is about what we can really measure.
The big idea
A measurement is only as meaningful as the method behind it.
Think about it
If you had no clock, what natural events could you use to measure the passage of a day, a year, or a thousand years?
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