The 2025 Nobel prize in physics was awarded to John Clarke, Michel H. Devoret, and John M. Martinis for their joint experimental work done in 1984-85, "the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit". Later work of Devoret and Martinis on this experimental platform, building on "energy quantisation" led to the development of the transmon qubit, and to the rise of superconducting quantum computers championed by Google that we read so much about. But what is "macroscopic quantum tunneling"? How is it different from regular tunneling, or from the "tunneling phenomena in superconductors" that Josephson received the Nobel prize for in 1973? And how is it related to "the most fundamental problem of modern physics, over which philosophers as well as physicists have puzzled for decades" (quote from the 1983, Caldeira and Leggett paper)?