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by Ciro Santilli (@cirosantilli, 25)
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Faster-than-light (FTL)

 wiki
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In special relativity, it is impossible to travel faster than light.
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One argument of why, is that if you could travel faster than light, then you could send a message to a point in Spacetime that is spacelike-separated from the present. But then since the target is spacelike separated, there exists a inertial frame of reference in which that event happens before the present, which would be hard to make sense of.
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Even worse, it would be possible to travel back in time:
  •  Table of contents
    • Faster-than-light implies time travel link
    • Tachyon link
    • Tachyonic antitelephone link
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Faster-than-light implies time travel

 Faster-than-light toc
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Figure 1. Spacetime diagram illustrating how faster-than-light travel implies time travel. Legend an explanation are shown in this answer.
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Bibliography:
  • physics.stackexchange.com/questions/13001/does-superluminal-travel-imply-travelling-back-in-time/615079#615079
  • physics.stackexchange.com/questions/574395/why-would-ftl-imply-time-travel
  • physics.stackexchange.com/questions/516767/how-does-a-tachyonic-antitelephone-work
  • www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel shows the causality violation on a Spacetime diagram
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Tachyon

 Faster-than-light toc wiki
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Tachyonic antitelephone

 Faster-than-light toc wiki

 Ancestors

  1. Speed of light
  2. Light
  3. Photon
  4. Elementary particle
  5. Subatomic particle
  6. Standard Model
  7. Particle physics
  8. Physics
  9. Natural science
  10. Science
  11. Index

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  • Faster-than-light implies time travel

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