I’ve always assumed the warp factor recalibration was a result of someone not liking the warp numbers going bigger and bigger and thus limiting the max to 10, therefore the recalibration being an out of universe event. I have never stopped to think whether this was ALSO an in universe event in which the way the Federation itself measures warp changes and therefore this is something more akin to the US moving to SI units for example.

Is the warp factor recalibration in Star Trek an in universe event or is it an entirely out of universe event?


It's in-universe. I don't think this is established on screen that a switch happened beyond a comment ships were slower in the past. A warp factor according to the TNG tech manual is a local energy minimum. TNG warp coils have 9 minimums. That is for example warp 4.9 and 5.1 both require way more energy than 5.0. So this is due to warp coil technology. In theory other civilizations should have different minimums. And TOS warp coils for some reason had different minimums too.

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