This tutorial covers the discussion of Nyquist capacity equation. This equation is often used to develop a capacity number for digital signals. Nyquist capacity is often considered an achievable starting point.
Then came Shannon, who gave us the expression for the bound on capacity beyond which communication transfer is not possible with any certainty. For uncoded signals, we can come within 7-10 dB of this limit and, with coding, we can come pretty darn close.
So communications engineers have done a lot better than physicists, who can come no where near the speed of light, another limit on electromagnetic signals! And all this happened in out own life time.
Here is the full tutorial in pdf format.