Space-time diagrams
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Change frame-velocity by double clicking on a moving particle.

Canvas 1: Time dilation.
Particle lifetime is frame dependent.
Lifetime in lab: 20s.
Lifetime in particle rest frame: 17.32s.

Canvas 2: Length contraction.
Grey particles represent ends of a rod. Separation of the ends is frame dependent.
Rod length in lab: 10m.
Rod length in rod rest frame: 22.94m.

Canvas 3: Spaceship collision.
Spaceship1 collides with an asteroid. Explosion warns spaceship2 of asteroid who instantaneously accerates to a safe speed (changing its rest frame).

Canvas 4: Twins "Paradox": a hidden asymmetry.
Earth Frame:
  • Time between departure and direction change: 5 - 0 = 5yr.
  • Time between direction change and arrival: 10 - 5 = 5yr.
    • Total time elapsed on earth: 5 + 5 = 10yr.

    Spaceship Departure Frame:
  • Time between departure and direction change: 3 - 0 = 3yr.
  • Time between direction change and arrival has no meaning in this frame.
    • Spaceship Return Frame:
  • Time between departure and direction change has no meaning in this frame.
  • Time between direction change and arrival: 16.67 - 13.67 = 3yr.
    • Total time elapsed on ship: 3 + 3 = 6yr.

    → Twin on spaceship arrives 4 years younger than twin sibling on earth.