The braneworld model of the universe adds a fifth dimension to Einstein’s general relativity spacetime model. The extra dimension in the braneworld model is a (fourth) spatial dimension. Interestingly, the braneworld model opens the door to (and perhaps requires) a varying speed of light and parallel universes! Mathematical physicists are working out plans to test for the presence of this fourth spatial dimension based on the theory that while matter and light would be limited to the standard three spatial dimensions, gravity would not. The hope is to locate objects which defy the laws of gravity (such as Newton’s inverse square law) applied to a universe with just three spatial dimensions.
Perhaps the whole world will one day realize what Twilight Zone fans have long known – Rod Serling was a visionary!
[For those who somehow missed out altogether on either the original TV series (1959-1964) or the perpetual airing of late night reruns of the sci-fi TV classic Twilight Zone, Rod Serling (narrator, host and most frequently the writer of the show) would open each episode with the monologue:
There is a fifth dimension, beyond that which is known to man.
It is a dimension as vast as space and as timeless as infinity. It is the middle ground between light and shadow, between science and superstition. And, it lies between the pit of man's fears and the summit of his knowledge. This is the dimension of imagination. It is an area which we call the Twilight Zone.
Actually, this was only the opening to most of the episodes in the first season. The opening monologue kept getting tweaked after that first season.]
But why stop with adding just one extra spatial dimension to a cosmic model? In fact physicists refer to the braneworld model as a 4-brane model and refer to the model with p spatial dimensions as the p-brane model. (And yes, it’s pronounced pea-brain.)