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Comets are in elliptical orbits around the sun so literally half the time they're traveling away from the sun.

kgwgk 1y ago
Sometimes they don’t make it: https://en.wikipedia.org/wiki/Sungrazing_comet https://en.wikipedia.org/wiki/Sungrazing_comet https://www.space.com/8478-comet-collision-sun-captured-3.html https://www.space.com/8478-comet-collision-sun-captured-3.ht...
- Gravityloss 1y ago
  Yea and those happen when other forces than gravity come into play. When matter starts colliding.
  - kgwgk 1y ago
    Every object has been subject to forces other gravity at some point. And the point is that sometimes comets do indeed fall into the Sun. If you object to people calling that a comet that’s fine - we can use whatever name you want.
    - Gravityloss 1y ago
      The point is that the gravity interactions are time reversible. Not so with friction etc.
      - kgwgk 1y ago
        Sure, nothing in the laws of physics prevents a celestial body from distancing itself from the Sun or from the Moon. But it would like suspicious! Wouldn't you suspect that you were watching a reversed video?
        Gravityloss 1y ago
        You don't understand my point. If we watch purely gravity interactions, the video can be reversed and you wouldn't be able to detect it. If a meteor crashes into the moon, there's other effects than gravity that makes the video not reversible. Ie it's not only gravity. That's the point. In other words, if a comet approached the moon at high speed, missed and slingshotted in another direction, it would be traveling away from the moon, but the video would be time reversible and you couldn't be able to detect it. Gravity only interaction.
        kgwgk 1y ago
        I think you don’t understand my point. Someone wrote “If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video?” I replied “If you saw a comet coming from the sun, or a meteorite coming from the moon, etc. you would also find that suspicious.” I don’t know what part do you object to (if any). > If a meteor crashes into the moon, there's other effects than gravity that makes the video not reversible. If a meteor (or an apple) is still in a crashing trajectory when you stop recording there are no effects other than gravity. The video is reversible - it just looks weird when you play it in reverse (because the meteor seems to be coming from the Moon and the apple seems to be coming from the black hole if you try to imagine where they were before).
        Gravityloss 1y ago
        Well yes for example if there was a cannon firing an apple from the moon, then it would travel the same trajectory, just in reverse. But we know there are no apple firing cannons on the moon. Ie if an object was coming from the moon and its past trajectory intersected with the moon's surface, you could say "this is reverse video".
        kgwgk 1y ago
        That was exactly my point, that an apple coming from a black hole may seem problematic but so does an apple coming from the Sun. I don't see an essential difference regarding the "reversibility" of the physical process (but I could be wrong).

Sometimes they don’t make it: https://en.wikipedia.org/wiki/Sungrazing_comet https://en.wikipedia.org/wiki/Sungrazing_comet https://www.space.com/8478-comet-collision-sun-captured-3.html https://www.space.com/8478-comet-collision-sun-captured-3.ht...

Gravityloss 1y ago
Yea and those happen when other forces than gravity come into play. When matter starts colliding.
- kgwgk 1y ago
  Every object has been subject to forces other gravity at some point. And the point is that sometimes comets do indeed fall into the Sun. If you object to people calling that a comet that’s fine - we can use whatever name you want.
  - Gravityloss 1y ago
    The point is that the gravity interactions are time reversible. Not so with friction etc.
    - kgwgk 1y ago
      Sure, nothing in the laws of physics prevents a celestial body from distancing itself from the Sun or from the Moon. But it would like suspicious! Wouldn't you suspect that you were watching a reversed video?
      - Gravityloss 1y ago
        You don't understand my point. If we watch purely gravity interactions, the video can be reversed and you wouldn't be able to detect it. If a meteor crashes into the moon, there's other effects than gravity that makes the video not reversible. Ie it's not only gravity. That's the point. In other words, if a comet approached the moon at high speed, missed and slingshotted in another direction, it would be traveling away from the moon, but the video would be time reversible and you couldn't be able to detect it. Gravity only interaction.
        kgwgk 1y ago
        I think you don’t understand my point. Someone wrote “If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video?” I replied “If you saw a comet coming from the sun, or a meteorite coming from the moon, etc. you would also find that suspicious.” I don’t know what part do you object to (if any). > If a meteor crashes into the moon, there's other effects than gravity that makes the video not reversible. If a meteor (or an apple) is still in a crashing trajectory when you stop recording there are no effects other than gravity. The video is reversible - it just looks weird when you play it in reverse (because the meteor seems to be coming from the Moon and the apple seems to be coming from the black hole if you try to imagine where they were before).
        Gravityloss 1y ago
        Well yes for example if there was a cannon firing an apple from the moon, then it would travel the same trajectory, just in reverse. But we know there are no apple firing cannons on the moon. Ie if an object was coming from the moon and its past trajectory intersected with the moon's surface, you could say "this is reverse video".
        kgwgk 1y ago
        That was exactly my point, that an apple coming from a black hole may seem problematic but so does an apple coming from the Sun. I don't see an essential difference regarding the "reversibility" of the physical process (but I could be wrong).