## Extra dimensions: What’s up?

 Edwin Abbott’s 1884 book “Flatland” describes in a very easy to understand way the idea of additional dimensions.

Extra dimensions pop up again and again in science fiction. For instance, an episode of Star Trek portrays a bearded Spock in a malevolent parallel universe. The idea of evil twins is pretty absurd, so how likely is that extra dimensions are a reality?

This scenario makes for an excellent plot device, but the idea of extra dimensions in physics has a more technical meaning. A single dimension is just a direction, like driving on a straight country road. You can go forward or backward. To identify a location in this one dimension, you need just one number. If you stop at a gas station to ask the location of the nearest restaurant, the clerk you talk to will tell you to drive half a mile up the road or a mile back the way you came. If we defined the direction you were originally driving as positive, scientists would say that the location of the restaurant was plus half a mile or minus a mile.

We live in more than one dimension. We can go forward or backward, right or left and up or down. For example, to tell someone my location in Wilson Hall, I’d need three bits of information: the east side, on the eighth floor, about 40 feet past the elevators. In order to set up a meeting, we’d also have to specify the time, say 3:30 p.m. Those three bits of spatial information and one time coordinate (east side, eighth floor, 40 feet, 3:30 p.m.) are necessary to identify my location in four dimensions.