One of the most famous arguments in popular culture history is why at the end of the movie Titanic, Jack had to die when it clearly looked like there was enough space for both him and Rose to lie on the floating door.
Since the movie’s release in 1997, countless fans have lamented how the birds-eye view shows that both people could have laid side by side to fit on the door.
But alas, science is an unforgiving mistress and it has since been shown that it would have been physically impossible for the two lovers to survive together on that makeshift raft (which was a wooden panel, not a door).
The film actually shows Jack trying to get on to the panel, when it tilts and starts to submerge, nearly flicking Rose off. Jack realises that the panel would not support both of them and chooses to only keep his upper body on it, while fending off other survivors trying to latch on. Unfortunately, this is not enough to keep him alive as he quickly succumbs to hypothermia and sinks to the bottom of the ocean.
The important question is not whether the two would fit on the panel, but whether the panel is buoyant enough to support both of them.
Buoyancy is the force that makes things float in liquids. It depends on the volume of the floating object and the density of the liquid it floats in. If buoyancy is greater than the pull of gravity, the object floats.
Now, let us calculate how much buoyancy we would need to keep the panel, Rose and Jack afloat.
For the two to survive, no more than the door itself can be submerged, keeping the bodies above water level. Therefore, the volume of the submerged object is the volume of the raft. Estimating from stills from the film and Kate Winslet’s height, we can calculate the raft as being roughly 1.85m x 0.95m x 0.15m, or 0.264m³.
Ergo, the buoyancy of the panel would be Volume x Density of ice cold salt water x force of gravity = 0.264m³ x 1000kg/m³ x 9.8m/s² = 2587N (Newtons). If more than 2587N of weight is placed on top (including the panel itself), it would sink.
At the time of the production of Titanic, the estimated weight of Kate Winslet and Leonardo DiCaprio were around 549N and 686N respectively (note that in physics, weight is mass times the acceleration of gravity, measured in Newtons).
Subtracting these values from 2587 leaves us with 1352N free for the panel. Since we know the volume of the panel, as long as we know what wood it was made out of, we can find the density and calculate the final weight.
Three types of wood were commonly used on the Titanic: teak, oak and pine. The densities of these woods are 980kg/m³, 770kg/m³ and 420kg/m³ respectively, meaning that the door would be 2535N if it was made of teak, 1992N for oak and 1087N for pine.
Therefore, the maths show that for the two to have a snowball’s chance in hell of surviving together on the panel, it had to be made of pine. Teak and oak would have been too heavy.
This is where the final key becomes relevant: the wooden panel was likely made of oak.
The Maritime Museum of the Atlantic in Halifax, Nova Scotia, holds the largest piece of debris from the actual wreckage of RMS Titanic. If you look at this wooden panel (from above a doorframe), it looks remarkably similar to the wooden panel that Rose survives on. In fact, a replica of this debris was used for the filming of the film. The material of the actual wooden panel? Oak.
If the panel was made out of oak, it could only hold Rose, as 1992 + 549 = 2541N, which is just enough for Rose to stay afloat above the water level.
And there you have it. Not even the power of love can overcome the cold-hearted, brutal law of the universe that is science.