where ''c'' is athe constant[[speed of light]] and ''t'' is the time coordinate.<ref group="Note">Originally Minkowski tried to make his formula look like Pythagoras's theorem by introducing the concept of [[imaginary number|imaginary]] time and writing −1 as i<sup>2</sup>. But Wilson, Gilbert, Borel and others proposed that this was unnecessary and introduced real time with the assumption that, when comparing coordinate systems, the change of spatial displacements with displacements in time can be negative. This assumption is expressed in differential geometry using a [[metric tensor]] that has a negative coefficient.</ref>
Multiplication by ''c'', which has the [[Dimensional analysis|dimensions]] {{nowrap|''L'' ''T'' <sup>−1</sup>}}, converts the time to units of length and this constant has the same value as the [[speed of light]]. So the spacetime interval between two distinct events is given by
