Generally speaking, physics is a thing that happens in real life, not in fiction. And especially not science fiction - except for a relatively small sub-genre. There are two types of science fiction*:
- That which extrapolates technological and social trends to a potentially somewhat disturbing vision of the future, and explores the social themes associated with the changes from contemporary society. The science is generally grounded in reality, just advanced a bit along a plausible trajectory.
- That which just says "sod it" to physics and tosses it out the window if it means bigger and cooler explosions.
* N.B. This is a joke. There may in fact be more types of science fiction.
Commentary by memnarch (who has not seen the movie)
Hah, I'm not the only one thinking of the issues surrounding the Peace Moon firing. On the other hand, you know what else is terrible physics? Hyperdrives, heat convection, The Force, non-volatile power sources that fit in garbage-can-sized robots....... Heck, the very existence of hyperdrives allowing for FTL travel means that Star Wars physics already are somewhat different to the players/our universe. Even blasters can't be just laser guns as we can see the blasts as they fly through the air.
Hmmmm...... it could be this is also one of those things where not enough information is shared yet. Like what if the C-Beam isn't just a giant laser beam? What if it's something else? Epileptic tree time: the Peace Moon actually fires Force powered missiles with equipped with better versions of the prototype hyperdrive! We've already had Force time manipulation, hyperdrives that don't care about things being in the way, visible proof that it's not a laser beam, and they could be mashed together to break physics with the stupid amounts of energy from the Orb! That wouldn't completely fit the movie of course (as the Orb is a Darths construct), but perhaps the first two parts get mentioned as components of whatever the Peace Moon's real name is at some point. That'd be a neat callback to Episode IV where the Force is said to be stronger than the battlestation in the movie.
Commentary by Keybounce (who has not seen the movie)
[Keybounce's comments will appear here when received.]
Rey: This may be sweet geophysics, but it’s terrible physics.
Rey: How far away is the Peace Moon?
GM: Endor’s about 90 light years from Takodana.
Rey: And how far is Chandrila?
GM: Uh... <flip flip>... about 43 light years.
Rey: This beam should take decades to reach the target. And even if it was somehow instantaneous, it’d be 43 years before any explosion could be seen from here.
GM: What can I say...?
Rey: You could say we don't see any beam, or explosion.
Finn: He’s already said we saw it. Can we just run with that?
Yanni: Yeah, it’s kinda cool.
Rey: That’s the greatest idea since the Hindenburg designers said, “Hydrogen floats, let’s just run with that.”