Have you ever wished to go back in time to change a decision you made or perhaps to redo a math exam?  If we can associate time with a coordinate t like any spatial coordinates (x, y, z), then there is nothing stopping you from doing just that.  But unfortunately, we are not able to go back in time, so something must be different about a coordinate associated with time from that of a spatial one.  How should we think of time?  Does it even make sense to do geometry with both spatial and time coordinates together?  Come and find out how these questions are considered in the fascinating subject of Lorentzian geometry - a geometry that contains a time coordinate and was born out of Einstein's monumental work on relativity.