For the pleasure of Michael and others, here again is the Universe on a T-shirt. From this perspective it is not very complicated. Everything can be described with 1-2 equations that a child could understand. Amazingly, our big Universe is really very simple.
The circle represents our entire Universe, with dimensions x, y, and z compressed into the screen. Like an ant on the surface of a globe, any direction that you travel in Space keeps you in that surface. There is no centre in Space, for every bit resembles every other bit. There is a centre in Time, commonly called a "Big Bang." We are separated from that origin by t, age of the Universe.
Relativity tells us that Space and Time are one phenomenon related by speed of light c. Scale R of the Universe is age t multiplied by c:
R = ct.
This predicts an expanding Universe, for as t increases R expands.
The Universe can't expand at the same rate continuously, for gravity slows it down. By doing some maths we can turn Einstein's thought into an equation:
Where G is Newton's Gravitational constant, M is Mass of the Universe. When t was tiny c was enormous and the Universe expanded like a Bang. Now that t is billions of years, c decreases at a rate too small to detect until recently.
Physicists are fond of using Planck units, made from combinations of h, c and G. In Planck units these equations are combined into an even simpler form:
M = R = t
Where M is Mass, R and t are expressed in Planck units.
These simple equations tell everything you wanted to know about the Universe but were afraid to ask: the size, mass, rate of expansion, and the speed of light. Mathematics predicts that the proportion of baryonic matter is 4.507034%, the amount of "dark" mass is 23.87%, and many other things. Until recently Humans have not understood something so simple, but that too is changing.