Series
The Time Series
The deceptively simple question of what time it is — from sundials and shipwrecks to atomic clocks and black holes, time travel and distributed systems. Part of Under the Hood.
Under the Hood · Time
What Time Is It?
The hour on your phone is a fragile compromise between the sun and politics. Sundials, shipwrecks, railway time, DST, and the volunteer-maintained database that keeps the world's clocks roughly honest.
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What Day Is It?
The date next to the time on your phone is its own kind of fragile. Calendars argue with the moon, the sun, and each other; whole days have been deleted by decree; and the year number on your screen depends on which monk's arithmetic your ancestors trusted.
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Ticks or Tocks?
A second used to be a fraction of the day. Now it's defined by the vibrations of a caesium atom -- and even that might not be precise enough. From quartz watches to optical lattice clocks, the story of how we learned to count time.
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Time Is Broken
Time doesn't flow at the same rate everywhere. It slows near massive objects, dilates at high speeds, and might not 'flow' at all. From GPS corrections to black holes, the physics that makes time truly strange.
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Does Time Even Exist?
The arrow of time isn't in the equations. "Now" isn't a location. The most fundamental theories of physics may contain no time variable at all. A tour of the foundations, from the block universe to the holographic principle.
Read articleCan You Turn Back Time?
General relativity permits time loops. Quantum mechanics hints that the future can influence the past. Hawking threw a party for time travellers and nobody came. The physics of time travel is stranger -- and more serious -- than science fiction suggests.
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