# Spell Propagation Speed?

(This question was inspired by this question:How Fast do Spells Travel in the Harry Potter Universe?)

The above question asked about the speeds at which projectile spells travel. This question is more about spells that target a specific thing or work(like accio, taboo spell or apparating).

Relativity tells us that there is a speed limit on the propagation of physical phenomenon in the universe (that is, the speed of light in a vaccum). Is there any indication/theories as to if spells have this finite propagation speed.

For example, let's say that I cast "accio book." If I cast it close enough so relativistic effects did not make a difference then the object immediately start moving. But if wizards start colonizing the galaxy (and assuming I can concentrate enough to have the spell work over such distances), I can cast it around alpha centrari, and what will happen to the book that I am thinking about? There seems to be two cases:

CASE 1: Spells have finite propagation speed. The "Mirions" from my wand must travel to earth, then interact with the book, at which point it will start travelling in my direction. If this is the case, can my foe on a spaceship inbetween earth and alpha centari cast "finite incantatem" to stop it? If so, at what point do they have to be(inside the sphere, at the boundary, or outside it)? Also, would it then be possible for the "Mirions" to miss earth over such great distances?(also what happens in the similar case of apparation? could my foe kill me by dispersing my particles by stopping my spell?)

CASE 2: Spells have infinite propagation speed (or effectivly infinite). Then(since the only known thing that can travel faster then light is spacetime itself) it would have to work somewhat similarly to the Alcubierre drive. This would imply that what all of these teenagers are really doing is bending the fabric of spacetime every time they cast a spell in one of their classes(which seems far-fetched to me). There seems to be a lot more that the wizarding world could do with this ability. Is there really no wizard that knew physics and saw the possibilities of this?

Is there any indication as to which case is correct?

• Is there any indication/theories as to if spells have this finite propagation speed? Magic. Anyway, there are no limits on a Ship of Imagination. Oct 24, 2015 at 1:16
• Apparition is one of the spells mentioned to have a finite range. So the speed of apparition at least will be less than the speed of light. Oct 24, 2015 at 1:26
• To my knowledge there's no evidence spacetime distortions can propagate faster than light, so even that may fail. However, there's also the Case 3, which is that a world with magic obviously involves physics beyond what we have now, and there's nothing stopping magic from traveling at whatever speed the author wants. That said, there may be an in- or out-of-universe answer detailing propagation speeds so the question isn't necessarily bad. I know in Once Upon a Time, certain curses seem to propagate at fairly slow speeds, so there's precedence for non-instant spells elsewhere. Oct 24, 2015 at 2:10
• An African or European spell? Oct 24, 2015 at 11:04
• Based on meta consensus regarding science questions, this is on-topic. Oct 24, 2015 at 12:54