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TeubenRoald's profile
Roald Teuben
Roald Teuben
Roald Teuben
@TeubenRoald

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Roald Teuben

@TeubenRoald

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Baltimore, MD
Joined July 2017

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    1. Roald Teuben‏ @TeubenRoald Jan 20
      Replying to @karlbykarlsmith

      Since light speed is finite, there are regions in space-time (outside the light cone) with no causal relationship to you at the origin. (If a tree falls in the forest and nobody is around...)

      1 reply 0 retweets 0 likes
    2. Daniel Houck‏ @daniel_houck Jan 20
      Replying to @TeubenRoald @karlbykarlsmith

      Right, which is *everything not in either the past or future light-cone*. What does the flat plane drawn for the present represent?

      1 reply 0 retweets 0 likes
    3. Roald Teuben‏ @TeubenRoald Jan 20
      Replying to @daniel_houck @karlbykarlsmith

      For simplicity, the diagram assumes a 2-D space with 1 time dimension. We are familiar with 3-D space + time, but a corresponding 4-D diagram is not simple to draw. You may interpret the hypersurface as the volume that is 3-D space at an instant in time.

      1 reply 0 retweets 0 likes
      Roald Teuben‏ @TeubenRoald Jan 20
      Replying to @TeubenRoald @daniel_houck @karlbykarlsmith

      shorter answer: pretend the hypersurface plane is a volume 🤔

      10:36 AM - 20 Jan 2018
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Daniel Houck‏ @daniel_houck Jan 22
          Replying to @TeubenRoald @karlbykarlsmith

          I get the 2-d simplification. But what distinguishes that plane from one tilted 15° , or a hyperbola with 40° asymptotes, or any other surface that stays outside the past and future lightcones?

          1 reply 0 retweets 0 likes
        3. Roald Teuben‏ @TeubenRoald Jan 22
          Replying to @daniel_houck @karlbykarlsmith

          Those examples sound like spaces where the speed of light differs by orientation/region. Or maybe it's nonsense, because the y-axis is time and a non-planar space occupies multiple times. Not sure what to make of it.

          1 reply 0 retweets 0 likes
        4. Daniel Houck‏ @daniel_houck Jan 22
          Replying to @TeubenRoald @karlbykarlsmith

          The point is that “simultaneous” is observer-dependent in special relativity (if you had a different velocity the plane would be tilted), and I dom’t think it’s even globally defined in general relativity.

          1 reply 0 retweets 0 likes
        5. Roald Teuben‏ @TeubenRoald Jan 22
          Replying to @daniel_houck @karlbykarlsmith

          Thanks for the insight, indeed a tilted plane is a reference frame with a velocity whereras flat is stationary. What do you mean about general relativity?

          1 reply 0 retweets 0 likes
        6. Daniel Houck‏ @daniel_houck Jan 22
          Replying to @TeubenRoald @karlbykarlsmith

          I mean that, to the best of my (very limited) knowledge, there is no coherent way to define “simultaneous” for distant events under GR, and the best you can do is “spacelike separated” (not in each others’ lightcones).

          0 replies 0 retweets 0 likes
        7. End of conversation

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