3 ms·

Or lets say we colonize a planet with a significant time dilation (ie near a supermassive blackhole), how do you deal with this? Who has the canonical time?

• Dylan16807 6y ago
  You'd just use some math to remove the influence of the black hole. Or for a more hands-on answer, you could have some reference beacons that are significantly further away from the black hole. In a broad sense, the answer goes like this: Almost everything in the galaxy shares an approximate reference frame when it comes to velocity and special relativity. For general relativity and gravity, that's obviously a distortion so it doesn't count. In the long term, to prevent very minor drift, we can use quasars as a reference.
• ColanR 6y ago
  We'll probably come up with something similar to time zones once we become an interplanetary species. "Local seconds since 1970", vs. "Static seconds since 1970".
• flopunctro 6y ago
  AFAIK, there is no canonical time in relativity. There is the "local time", which is what your wristwatch shows, and the "time in place X", where X can be Earth, Mars, or some spaceship. These times might not be in sync, and they might even be distorted. Because, if place X is moving relative to you at a significant percentage of lightspeed, their seconds will be longer. Also, the further X is, the blurrier the concept of simultaneity becomes. Which makes the question "what time is it _now_ in place X" moot :)
  • numpad0 6y ago
    If relativity don’t allow time travel doesn’t it make time canonical? A clock on Earth from telescope might look jumpy but only in forward direction after compensating for distance I think
    • flopunctro 6y ago
      Looking at a clock from Earth through a telescope isn't as straightforward as you'd think. The image you see of that clock is actually light (photons) emitted from Earth, which will take a while to reach you - like, 1 year, if you're 1 lightyear away. During that year, Earth has moved on, maybe blew itself apart. But you can't even tell, because information can't reach you faster than light :) So you can only see Earth's past, not Earth's "now". The further you are, the more "now" loses meaning.
      • numpad0 6y ago
        Yeah but can it ever go back, other than by backing off faster than the speed of light? If it can’t then it’s at least monotonic, even if it’s not rate constant
        • dodobirdlord 6y ago
          All observers observer all clocks to advance monotonically forward in time, regardless of their location or relative speed, unless the clock is moving at the speed of light. But the rate that each clock is observed to advance at depends on things like relative speed, acceleration, and the curvature of spacetime.
          • JdeBP 6y ago
            ... unless it's the system clock in Linux, with the hardware RTC set to be interpreted as local time, and one is watching a system boot on a machine that is set up as east of the Prime Meridian (i.e. the hardware RTC is ahead of UTC). (-: * https://unix.stackexchange.com/a/600490/5132 https://unix.stackexchange.com/a/600490/5132
            • dodobirdlord 6y ago
              Given that Unix time specifically doesn’t handle leap seconds, a system clock is not a clock by the conventional definition.
• JdeBP 6y ago
  You don't have to go to science fiction for this. Science fact will do. On Earth, with Atomic Time, we already have to account for general relativistic effects. Doco from the BIPM (the SI Brochure) already talks about accounting for them across the sizes of the measuring devices.