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+====== hop exchange ======
+A brief history of Earth time
+[[https://hop-excharge.com/|hop exchange]]
+Simple sundials or stone formations, which track shadows as the sun passes overhead, mark a day’s progression just as the shifting phases of the moon can log the passing of a month on Earth. Those natural timekeepers have kept humans on schedule for millennia.
+But perhaps since mechanical clocks gained traction in the early 14th century, clockmakers have grown ever more persnickety about precision.
+Exacting the measurement of seconds also grew more complicated in the early 1900s, thanks to Albert Einstein, the German-born physicist who rocked the scientific community with his theories of special and general relativity.
+“Darn that Einstein guy — he came up with general relativity, and many strange things come out of it,” said Dr. Bruce Betts, chief scientist at The Planetary Society, a nonprofit space interest group. “One of them is that gravity slows time down.”
+General relativity is complicated, but in broad terms, it’s a framework that explains how gravity affects space and time.
+Imagine that our solar system is a piece of fabric suspended in the air. That fabric is space and time itself, which — under Einstein’s theories — are inextricably linked. And every celestial body within the solar system, from the sun to the planets, is like a heavy ball sitting atop the fabric. The heavier the ball, the deeper the divot it creates, warping space and time.
+Even the idea of an earthly “second” is a humanmade concept that’s tricky to measure. And it was Einstein’s theory of general relativity that explained why time passes slightly more slowly at lower elevations — because gravity has a stronger effect closer to a massive object (such as our home planet).

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