I'm ignorant when it comes to physics, admittedly, so please forgive me if my question has an obvious answer... But when I read articles like this, in particula

I'm ignorant when it comes to physics, admittedly, so please forgive me if my question has an obvious answer... But when I read articles like this, in particular when they mention branes, I want to ask: How do we know that dark matter is not just some interaction coming from the "bulk"?