4 ms·

Everything you say makes sense if you already presume that FTL implies breaking causality, but I'm missing the explanation for why FTL implies breaking causalit

Everything you say makes sense if you already presume that FTL implies breaking causality, but I'm missing the explanation for why FTL implies breaking causality in the first place. I mean, it's completely logical that if you get to Mars faster then light, you can watch yourself start the trip, but why does this also mean that you are actually going back in time? Intuitively it would seem that even if you teleport to Mars with no travel time, observe yourself on Earth, then teleport back to Earth, you should arrive the next instant after you left, not before. So time travel does not follow immediately from the fact that you were able to observe yourself in the past.

maxerickson 3y ago
I guess I don't understand your intuition. My intuition: Teleport to Mars. Wait 3 minutes to watch myself go poof on Earth. Teleport to Earth. If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes.
- sunaurus 3y ago
  If you wait 3 minutes on Mars, why would an instant teleport back to Earth result in you arriving just after you went poof rather than 3 minutes after you went poof?
  - maxerickson 3y ago
    Well, the point is more that you have to wait 3 minutes on Mars if you want to watch yourself leave. But say instead of waiting you just keep going poof.
    - SAI_Peregrinus 3y ago
      They never said they wait to watch themselves leave, just watch themselves on Earth (3 minutes before they left).
      - maxerickson 3y ago
        I mean, it's completely logical that if you get to Mars faster then light, you can watch yourself start the trip, but why does this also mean that you are actually going back in time? I'm the one that introduced the 'start the trip' condition, and they used it in their comment.
- senectus1 3y ago
  >If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes. How? Teleport in this context is an instant transportation process. but the image of you going poof is not ists a speed of light. Like If I throw a ball at a target first THEN Fire a gun at the same target, the bullet will get there first but it didn't time travel to do that. Lets assume that the teleport process is a wormhole or a folding of space process that reduces the distance between the two locations rather than making you go faster. You could step through onto mars and back again and not see yourself when you arrive back but then go back to mars again and see yourself disappear and re-appear twice. still no time travel. You're just watching a delayed image.
  - maxerickson 3y ago
    You should probably start drawing diagrams or whatever.
chasd00 3y ago
Causality propagates at the speed of light. “Speed of light” is just a more intuitive way to say the speed of causality. FTL travel is the same as faster than causality travel. So going faster than light exceeds the speed of causality. To me, that means the order of events is no longer predictable so everything about cause and effect breaks down hence breaking causality.

maxerickson 3y ago

I guess I don't understand your intuition. My intuition: Teleport to Mars. Wait 3 minutes to watch myself go poof on Earth. Teleport to Earth. If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes.

sunaurus 3y ago
If you wait 3 minutes on Mars, why would an instant teleport back to Earth result in you arriving just after you went poof rather than 3 minutes after you went poof?
- maxerickson 3y ago
  Well, the point is more that you have to wait 3 minutes on Mars if you want to watch yourself leave. But say instead of waiting you just keep going poof.
  - SAI_Peregrinus 3y ago
    They never said they wait to watch themselves leave, just watch themselves on Earth (3 minutes before they left).
    - maxerickson 3y ago
      I mean, it's completely logical that if you get to Mars faster then light, you can watch yourself start the trip, but why does this also mean that you are actually going back in time? I'm the one that introduced the 'start the trip' condition, and they used it in their comment.
senectus1 3y ago
>If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes. How? Teleport in this context is an instant transportation process. but the image of you going poof is not ists a speed of light. Like If I throw a ball at a target first THEN Fire a gun at the same target, the bullet will get there first but it didn't time travel to do that. Lets assume that the teleport process is a wormhole or a folding of space process that reduces the distance between the two locations rather than making you go faster. You could step through onto mars and back again and not see yourself when you arrive back but then go back to mars again and see yourself disappear and re-appear twice. still no time travel. You're just watching a delayed image.
- maxerickson 3y ago
  You should probably start drawing diagrams or whatever.

chasd00 3y ago

Causality propagates at the speed of light. “Speed of light” is just a more intuitive way to say the speed of causality. FTL travel is the same as faster than causality travel. So going faster than light exceeds the speed of causality. To me, that means the order of events is no longer predictable so everything about cause and effect breaks down hence breaking causality.