Sure, there are plenty of alternative theories, just no tested at the highest possible human level alternative facts. The odds that either side is exactly right is zero, that's what makes it interesting unless it's a totally crackpot idea like EMDrives.Funny how arguing about the fundamentals can become such a big deal among geeks...
I'm not used to this sort of discussion, so I'm guessing there's a "school" out there that argues against the equivalence principle...