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B Earth time dilation vs Sun time dilation

  1. Dec 19, 2016 #1
    In the MinutePhysics video "How long is a day in the Sun?"

    it is said 24 hours on Earth is 86,400.0 seconds, but on the Sun 86,400.2 seconds would pass.

    However, if time passes slower with more massed objects, then wouldn't a twin on the Sun be younger than a twin on the Earth? If so, is the video wrong in saying more time has elapsed on the Sun?
  2. jcsd
  3. Dec 19, 2016 #2
    I suppose they mean 86,400.2 earth-seconds would pass while you measure only 86,400 seconds on the sun. So time would flow slightly slower, and the Earth twin would age more (by .2 seconds per day).
  4. Dec 19, 2016 #3


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    Natural language isn't well adapted for describing things like this unambiguously. As @Gan_HOPE326 says, if you put a clock on the surface of the Sun and sat on Earth with a powerful telescope watching that clock, it would not show that 86,400s had elapsed until slightly more had passed on your own clock. The Sun-based clock would always have a lower (and getting farther behind) reading than your clock - so it would be younger than yours by an increasing margin.

    I haven't checked their numbers.
    Last edited: Dec 19, 2016
  5. Dec 19, 2016 #4
    (slight aside: it's funny I should read this remark today as I've just started reading the story from which the movie "Arrival" is adapted and

    it dwells a lot on how different the language as well as the physics of an alien race with an a-temporal perspective is. For example they find extremely natural and fundamental the concept of "action" while they need to derive quantities such as velocity. Similar considerations I assume would apply to someone who developed in a context in which relativistic effects are daily occurrences.

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