The most accurate atomic clocks in operation now lose less than one second every 30 billion years — and the reason this matters isn't precision for its own sake, it's that gravity itself slows time sl

There is a particular fact about the most precise atomic clocks currently in operation that the wider cultural register has, on the available evidence, not yet adequately absorbed. The fact is that these clocks are now sensitive enough that they can directly measure the difference in the rate at which time passes between two positions […]