It can look dumb, but I always had this question as a kid, what physical principles would prevent this?

  • I_Has_A_Hat@lemmy.world
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    11 days ago

    So folks have already explained the stick, but you’re actually somewhat close to one of the ways you can sort of bend the rules of FTL, at least when it comes to a group of photons.

    Instead of a stick, imagine a laser on earth pointed at one edge of the moon. Now suddenly shift the laser to the other side of the moon. What happens to the laser point on the moon’s surface?

    Well, it still takes light speed (1.3 seconds to the moon) for the movement to take effect, but once it starts, the “point” will “travel” to the other side faster than light. It’s not the same photons; and if you could trace the path of the laser, you’d find that the photons space out so much that there are gaps like a dotted line; but if you had a set of sensors on each side of the moon set up to detect the laser, they would find that the time between the first and second sensor detecting the beam would be faster than what light speed would typically allow.

    It’s not exactly practical, and it’s such an edge case that I doubt we can find a good way to use it, but yeah; FTL through arc lengths can kind of be a thing. At least if you tilt your head and squint funny at it.

    • elidoz@lemmy.ml
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      11 days ago

      this isn’t at all what this example depicts, here there is actual information transfer.

      this depiction is actually just false, the light would send information faster than the stick, because in the stick information only travels as fast as speed of sound in the stick, which is why completely rigid objects don’t exist

    • SocialMediaRefugee@lemmy.ml
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      11 days ago

      You’d still be limited by light speed to transmit the information between the two locations to compare times or indicate they received a signal.

    • OutsiderInside@lemmy.world
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      11 days ago

      I’m not sure. The beam of light would bend as it travels to the moon, delaying the projected dot on the moons surface.

      Just like it happens with a stream of water coming out of a hose. You point the hose in a new direction, but it won’t get wet before the the time it takes the water to travel from the hose to the pointed location.