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This map will become very useful when Time Travel tourism takes place!

Tepix 7y ago
When calculating your target coordinates for your time travels don't forget to account for the motion of the Sun around the center of the Milky Way. This will have killed many time travellers in the future's past.
- brixon 7y ago
  I would assume the Milky Way is moving too.
- pdonis 7y ago
  Motion is relative. Without the blueprints for the time travel device we have no way of knowing what state of motion will count as "rest" for the device.
  - ars 7y ago
    > Motion is relative. Circular motion is not, it is absolute. (Although the center of the circle may also be moving at the same time, and that motion would be relative.)
    - pdonis 7y ago
      > Circular motion is not, it is absolute. What is absolute is not circular motion, but proper acceleration and vorticity of a particular congruence of worldlines. But you can describe those phenomena perfectly well in a reference frame in which, for example, a person riding along on a rotating platform is at rest. The reference frame will not be inertial, but that does not mean it is any less valid. For that matter, we routinely describe phenomena on Earth using a reference frame in which the entire Earth is at rest, not just its center; that is perfectly valid as well.
      - ars 7y ago
        > but proper acceleration and vorticity of a particular congruence of worldlines. This is a side note, but you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them. > But you can describe .... will not be inertial, but that does not mean it is any less valid. ... that is perfectly valid Sure it's valid, but that was never the question in the first place. It still has an absolute component. And in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion.
        pdonis 7y ago
        > you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them. No, I just used standard terminology in physics. > It still has an absolute component. Yes, but "motion" is not part of what is absolute. > in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion. No, it doesn't, because there is no such thing as "motion" apart from relative motion. So the time travel device can't be using "motion" to determine what it does. It could use the other things I described, but not "motion".
- _cerv 7y ago
  This was one of those things that always ruined time travel movies for me. If I went back in time a few hours, would I be floating in the upper atmosphere? Go back few years, am I just floating in space? Does this mean that I can only really travel back to the previous galactic rotation and hope to Sagan that the galaxy both doesn't drift and the both the Sun and our arm of the galaxy are both in the same place?
  - Tepix 7y ago
    Of course the Milky Way is also moving. In quite interesting ways: https://sci.esa.int/web/gaia/-/61117-future-motions-of-the-milky-way-andromeda-and-triangulum-galaxies https://sci.esa.int/web/gaia/-/61117-future-motions-of-the-m...

When calculating your target coordinates for your time travels don't forget to account for the motion of the Sun around the center of the Milky Way. This will have killed many time travellers in the future's past.

brixon 7y ago
I would assume the Milky Way is moving too.
pdonis 7y ago
Motion is relative. Without the blueprints for the time travel device we have no way of knowing what state of motion will count as "rest" for the device.
- ars 7y ago
  > Motion is relative. Circular motion is not, it is absolute. (Although the center of the circle may also be moving at the same time, and that motion would be relative.)
  - pdonis 7y ago
    > Circular motion is not, it is absolute. What is absolute is not circular motion, but proper acceleration and vorticity of a particular congruence of worldlines. But you can describe those phenomena perfectly well in a reference frame in which, for example, a person riding along on a rotating platform is at rest. The reference frame will not be inertial, but that does not mean it is any less valid. For that matter, we routinely describe phenomena on Earth using a reference frame in which the entire Earth is at rest, not just its center; that is perfectly valid as well.
    - ars 7y ago
      > but proper acceleration and vorticity of a particular congruence of worldlines. This is a side note, but you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them. > But you can describe .... will not be inertial, but that does not mean it is any less valid. ... that is perfectly valid Sure it's valid, but that was never the question in the first place. It still has an absolute component. And in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion.
      - pdonis 7y ago
        > you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them. No, I just used standard terminology in physics. > It still has an absolute component. Yes, but "motion" is not part of what is absolute. > in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion. No, it doesn't, because there is no such thing as "motion" apart from relative motion. So the time travel device can't be using "motion" to determine what it does. It could use the other things I described, but not "motion".
_cerv 7y ago
This was one of those things that always ruined time travel movies for me. If I went back in time a few hours, would I be floating in the upper atmosphere? Go back few years, am I just floating in space? Does this mean that I can only really travel back to the previous galactic rotation and hope to Sagan that the galaxy both doesn't drift and the both the Sun and our arm of the galaxy are both in the same place?
- Tepix 7y ago
  Of course the Milky Way is also moving. In quite interesting ways: https://sci.esa.int/web/gaia/-/61117-future-motions-of-the-milky-way-andromeda-and-triangulum-galaxies https://sci.esa.int/web/gaia/-/61117-future-motions-of-the-m...