Why the “door” could not carry two people
The scene’s argument turns on a distinction that is easy to miss: fitting on a floating object is not the same as being supported by it. A person can climb onto a plank or panel that looks large enough, yet still push it too deep into the water to stay afloat safely.
A floating object works by displacing water. The water it pushes aside exerts an upward force; as more weight is added, the object sinks farther and displaces more water. But a piece of debris has a limit. If two people’s combined weight exceeds what it can displace before water washes over the surface, it submerges or becomes unusably unstable.
The difference between space and buoyancy
That is why the question cannot be settled just by looking at the panel’s dimensions. Its material, thickness, shape, and how much of it remains above water all affect its carrying capacity. Position matters, too: shifting weight toward one edge can tilt the panel, allowing water to spill over even if the total load seems close to what it can bear.
Cameron’s test was aimed at this practical problem rather than the image of two people lying side by side. The key question was whether the debris could keep both bodies supported above the water—not merely whether both could initially get onto it. The test’s reported result was that the combined weight pushed it under.
Why the argument lasted
The scene offers a simple visual puzzle, but a real person in cold water would also have to climb onto the debris and keep balance while it shifted. A panel that barely floats under ideal conditions is not a reliable refuge once it is loaded and moving in the sea. That is the uncomfortable engineering point behind the movie debate: a few inches of visible wood above water can be the difference between a raft and a sinking surface.
