How fast does your clock run?

In Einstein’s theory of General Relativity, one of the surprising predictions was that a clock close to a strong gravitational source will tick faster than one observed farther away. Similarly, one clock moving relative to another will also appear to tick at a different rate. These effects have been measured using pairs of atomic clocks, one on the ground the other on aircraft and spacecraft before, but advances in technology have enabled the difference in altitude to be made a little smaller. So now the difference in clock speeds when one is 35cm above the other, or travelling at 20mph have been measured. The difference is measurable, but tiny – one part in 1,000,000,000,000,000,000 – so no need to keep altering bedroom alarm clocks to keep up with the clock in the living room. Further details were broadcast on a radio show, which can be read about and heard here.


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