Now that we have completed our rather abstract journey at high altitude, let us take another look at the table with the universal constants of nature, given on the inside of the front cover and mentioned at the beginning of the book. It is just a bunch of numbers. We advocated the system of units based on the meter, the kilogram, the second and the Coulomb as units for length, mass, time and charge, respectively. These units are very much tied to the typical human scale, which – as we have been discussing in this book – is rather arbitrary in the grand total of things.

One may wonder whether nature itself doesn't have a favored set of units. Does it? In fact, around 1900 Max Planck already pointed out that a particular combination of the fundamental constants of nature could be used to define a ‘natural’ system of units of space, time and mass instead of the standard one. The Planck units involve the fundamental constants of gravity (Gn), of relativity (c) and of quantum theory (h). These are called the Planck length, time and mass, and their definitions are given in the side bar. These are the fundamental scales that are intrinsically encoded in the data we retrieved from our physical world.

There is another evocative way to characterize today's grand picture of physics, using an imaginary magical cube positioned in the ‘space of theories’ (see figure on page 94). Looking at this magical cube, one sees the network of equations we have been discussing in yet another perspective. It is a different – three-dimensional – representation of the ‘map of contents’ presented at the beginning of the book. The great turning points in physics are positioned at the corners of this cube. At the lower back edge, labeled by Newton's constant, we find the Newtonian physics (mechanical and gravitational theory) we have been harassed with in high school. The Theory of Special Relativity connected to the universality of the velocity of light opened up a new dimension, as symbolized by the bottom plane coming out of the page. But as explained before, the Special Theory was still in conflict with the Newtonian theory of gravity, a conflict that was eventually resolved by the General Theory of Relativity, where gravity was identified with the curvature of space-time.