The Bulk Is Not Empty
If extra dimensions exist and the bulk is real, an immediate question arises: is the bulk empty? Theoretical physics suggests it is not. Gravitons propagate through it. Dark matter may reside in it. Other branes — other universes — may float alongside ours.
The bulk could contain structures, dynamics, and even forms of organisation that we have no words for, because we have never directly experienced anything outside our brane. Our physics describes the surface. The bulk is the ocean beneath.
Could There Be Life?
If other branes exist in the bulk, the question of life becomes unavoidable. Could other branes support complex structures? Could beings exist that navigate the bulk the way we navigate three-dimensional space? This is where physics meets one of the oldest questions in philosophy.
A bulk-native being would perceive our entire brane as a surface — just as we perceive a sheet of paper. It could see "inside" closed objects. It could appear and disappear from our perspective by stepping off our brane and back on. Its capabilities, from our vantage point, would appear to violate physics. They would not violate physics. They would obey a larger physics that includes dimensions we cannot access.
The Flatland Thought Experiment Extended
Edwin Abbott's 1884 novella Flatland imagined a two-dimensional world visited by a three-dimensional sphere. The sphere could see inside the Flatlanders' houses. It could appear and disappear. It could lift a Flatlander out of its plane and show it a world it could never have imagined.
Now extend this analogy with full rigor. A being native to a higher-dimensional space interacting with our brane would exhibit precisely the characteristics that our most puzzling observations report: the ability to appear from and disappear to nowhere, to pass through solid barriers, to manoeuvre in ways that seem to defy inertia and gravity. The Flatland analogy is not just a teaching tool. It is a precise mathematical template for understanding cross-dimensional interaction.