Time measurement

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Clock accuracy Measurement standards Precision timing

Carbon-14 runs out at about 50000 years and deeper time needs other isotopes Geological periods are defined by rock layers and their absolute dates are a separate layer of work LIGO measured a stretch of space 1/1000 the width of a proton Hafele and Keating flew caesium clocks around the world in 1971 and the two directions were wrong in opposite ways Why one-way light signals cannot synchronise two clocks without a convention Hubble tension: two ways to measure the expansion rate differ by about 9 percent Where 13.8 billion years comes from: the CMB and the cosmic distance ladder together Uranium-lead dating in zircon: how a crystal the width of a hair dates the Earth at 4.54 billion years Distant Type Ia supernovae run slow by exactly their redshift factor Strontium optical clocks would not lose a second in 15 billion years The personal equation: 19th century astronomers' reaction times started experimental psychology NIST raised an optical clock by 33 centimetres and it measurably ticked faster GPS satellites gain about 38 microseconds a day: uncorrected that is 10 kilometres of drift Half-life is the same idea in radiocarbon dating and in pharmacology Sampling rate and aliasing: when a time series lies to you

Time Management Future Timeline Calendars Time in life Historical eras Time travel Seasons Endings Units of time