Nyquist - the amazing 1928 BREAKTHROUGH which showed every communication channel has a capacity

In 1928, Harry Nyquist published a paper which would change the course of history [1]. But his original contribution was not the sampling theorem.

Inspired by the work of Fourier, Nyquist discovered that there is a maximum rate at which signals could be sent through a bandlimited channel. For a bandwidth of B, 2B signals per second is the limit (the capacity). This, of course, does not set the limit on how much information you can squeeze into a single symbol/signal, but it shows something remarkable - the bandwidth of the channel limits the signaling rate of a channel. 20 years later, and inspired by Nyquist, Claude Shannon would publish his Mathematical Theory of Communication [2], which combined Nyquist's signalling rate capacity in a bandlimited channel with the impact of noise.

Sources:
[1] H. Nyquist, "Certain Topics in Telegraph Transmission Theory," in Transactions of the American Institute of Electrical Engineers, vol. 47, no. 2, pp. 617-644, April 1928, doi: 10.1109/T-AIEE.1928.5055024.
[2] C. E. Shannon, "A mathematical theory of communication," in The Bell System Technical Journal, vol. 27, no. 3, pp. 379-423, July 1948, doi: 10.1002/j.1538-7305.1948.tb01338.x.