I once thought anything traveling faster than light would leave behind a motion blur that on one end recedes at the speed of light and at the other increases at the velocity of the object. If an object travels at 10x c, after one year it would leave behind it a 9 light-year motion blur of itself. This is because the light is transmitted from multiple places at any one instance. Not only does the object appear to be in two places at once, it appears to be in all the places in-between.

However I learned of two counter-examples:

1) FTL galaxies (because the expansion of the universe is not subject to FTL prohibitions) are only red-shifted but not motion blurred

2) Wikipedia's explanation of tachyons describes the situation as more complex than I thought: a flattened version appears in the direction of travel but an elongated version appears in the opposite direction.

Why does motion blur not appear with FTL when the objects emit light in all places they traverse?

  • 1
    $\begingroup$ I'd suggest reopening. The OP is asking for clarification of a real conceptual issue they have trouble with, not proposing a personal theory. The issue is why we don't see or notice motion blur in the context mentioned. $\endgroup$ – StephenG Aug 12 '19 at 9:43
  • $\begingroup$ @StephenG Yes. I know motion blur is incorrect I'm just trying to figure out why it's incorrect. This is entirely within the mainstream, similar to asking why we don't see crockoducks in evolution or purple stars in astronomy. $\endgroup$ – KevinRethwisch Aug 13 '19 at 0:24
  • $\begingroup$ Last time I stubbed my toes I certainly saw purple stars, albeit briefly. :-) At this point you just need one more reopen vote and I hope you get it. $\endgroup$ – StephenG Aug 13 '19 at 0:28