Letting N = 4 + ε (with | ε | ≪ 1 ) be the dimensionality of space–time, we work out the mathematics of the fluctuation underlining natural linewidths, using electromagnetic transitions as the template. The calculation is done in its entirety for the Lyman alpha ( Ly α ) transition of hydrogen, including the probability distribution governing ε. A new scale (i.e., a new physical constant), ℘ M , which interfaces the four-dimensional world with extra dimensions, enters into the problem. This new scale can be measured in a table-top two-electron, two-photon correlated transition, discussed in the Letter.