Major spoilers for Outer Wilds, but I'll be developing a Dark Bramble theory/headcanon under the cut. I'm open to discussion if anyone wants to give counter arguments, but I'm currently satisfied with my headcanon.
I believe I've heard about the developers officially stating that the Dark Bramble stuff functions via the fourth dimension. Unfortunately for me, I never really found that answer satisfying, especially when recently thinking about it. Every other mechanic is given an in-world explanation that we can use to figure out how something works on our own, so having the Dark Bramble use fourth dimensional stuff instead of something known to work within the game world's rules feels a little disappointing. My solution is that Dark Bramble uses quantum properties, and I can offer some proof towards that.
First point of evidence, quantum properties only apply when you can't see the object. Any time you travel in Dark Bramble, you're in a wall of fog that prevents you from seeing. The Quantum Moon has the same thing, only moving around while you're on it and have light if you're in fog. When you want to leave the sixth location, the fastest method is to jump up and have the fog take you to another location, and anywhere else gives the fog a chance to make the moon leave without you. I wanted to cover this point first because the next point hinges on this one.
Second point of evidence, the rule of quantum entanglement. We have a confirmed in-game explanation for being able to move with a quantum object, that being that if you're vision is perfectly obscured/blocked while you're in contact with a quantum object, you are in superposition with the object and will go wherever it goes until you can see again. My current thought at the time of writing this is that the quantum object being entangled with would be the fog particles themselves. If you had to have only yourself entangled, you might lose your suit the moment you came out the other side and suffocate, so I assume that as long as you're touching the ship, the ship and everything inside of it is also affected by the quantum entanglement and gets transported with you.
Third point of evidence, the Eye of the Universe. At the Eye, we can get a quantum signal from the final part of it, proving that signals can travel through quantum locations. Additionally, the Quantum Moon changes for each location, and the Nomai mistakenly warped into Dark Bramble instead of the Eye of the Universe when following its signal. This would explain how we can hear Feldspar's harmonica from the outside, and how each space is different despite technically being within the bramble. This leaves a plot hole with the fact that the Nomai's mistaken teleportation was caused by the Owlks cutting the Eye's signal early, but I have one last point of evidence to explain that.
Fourth and final point of evidence, duplicate signals. With the black hole experiment at the high energy lab, we can confirm that duplicate signals are caused by an object genuinely existing in two places at once. Feldspar's harmonica can be heard from both the Bramble itself and the Timber Hearth seed, the and the Nomai of Escape Pod 3 got duplicate signals for The Vessel. As for how this is related to quantum properties, we can go back to superposition. According to Gabbro, and confirmed by the Quantum Moon, a quantum object exists in all states at once until observed, which would be affecting the bramble. So, if there exists a path between quantum objects of the Bramble that leads to a signal traveling across them to an outside observer, then that signal's source technically exists just inside every related section of the Bramble until a part of the Bramble is entered.
