10mo ago

we live in an explosion

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Since relativity tells us there is no universal reference frame, then it having its reference tied to earth is perfectly valid.
Also sidenote: my favourite idea about time travel is that time travel is entirely possible, but will never be invented, because the timeline where its not invented is the only stable timeline. Because any timeline where it IS invented gets changed as soon as you use it, meaning the timeline changes over and over again every time time travel is invented repeatedly either infinitely or until someone accidentally creates a timeline where its never invented, only then does the timeline stop changing and we can actually experience it. So because we exist and can experience time, we can deduce that we will never invent time travel.
- There can be stable timelines with time travel - there's actually 3 states:
  Perpetual instability, where the timeline changes each time the time machine is used but never reaches the same state twice
  Perpetual cyclic stability, where people's actions in modifying the timeline lead to it eventually reaching the same state, eg. you go back in time to kill someone who becomes evil and oppresses you but the near death experience leads them capture you, so you can't time travel any more, and to blame your people and start oppressing them, leading to the same actions
  Stability without time travel, which is the default state but incredibly hard to get once time travel is invented as with nobody to stop time travel being invented it would probably get invented again, however parts of a cyclically stable timeline could have nobody having access to time travel, but any actions by time travellers to stop time travel would likely lead to the second rather than third option
- Yeah I think we don't have to worry about it for the same reason why you don't have to worry about getting thrown backwards when jumping in a moving train.
  
  Sure, but it's a lot of fun to think about :D
- Rotational reference frames are out though! (Unless you want to deal with magic forces acting on your masses)
  And since the earth rotates around itself and the sun, and the sun rotates around the center of the galaxy, you will always have to deal with a moving target.
  
  Since I stay on earth now when I'm moving forward in time why wouldn't I stay on earth when I move backward through time?
  
  Sure you can, but you need to adjust your position due to centrifugal forces all the time. A time machine would have to do that as well.
  If a ball is flying in a straight line through space with a speed of 1m/s I can predict without much math where it will be at any point in time. In fact, if the reference frame is chosen such that the ball is stationary you don't need any math at all, because the ball doesn't move!
  However, if you have a set of two balls orbiting each other you will always have to do math to calculate their position. I mean technically you could choose the reference frame that is rotating in sync with the balls. But still you need to do math to check that the centrifugal force, which is a real force coming from nowhere in this reference frame, exactly cancels out the gravitational pull between the two balls. Because rotating reference frames are not equivalent to each other!
  
  I really don't get why the time machine would have to do any calculations at all. The time machine is in this reference frame. You seem to assume that by going back through time you'd be teleporting through time, which leaves the open question of where you'd appear. However, I'd much rather assume that you'd actually be "going" through time. You wouldn't cease to exist until you reappeared somewhere. Instead you'd be in the machine for some time until you'd get out of the machine again. That'd mean neither you nor the machine ever leave the reference frame.
  
  Fair enough :)
- You might have better luck and accuracy using our galaxy' s black hole for reference marker depending on how much time you intend to traverse
- How much do you know about the "double slit" experiment and its subsequent variations? Because I think that's a rabbithole you'll enjoy. That first video is really just context; this next link is another video in that series, and this is the one that really pertains to the consequences of time travel: https://piped.video/watch?v=8ORLN_KwAgs

169 comments