  My contribution to this collection of articles in honor of David Lee and John
Reppy on their 90th birthdays is a reflection on the remarkable phenomenology
of the excitation spectra of superfluid $^3$He, in particular the B-phase which
was identified by NMR and acoustic spectroscopy as Balian-Werthamer state shown
in 1963 to be the ground state of a spin-triplet, p-wave superconductor within
weak-coupling BCS theory. The superfluid phases of $^3$He provide paradigms for
electronic superconductors with broken space-time symmetries and non-trivial
ground-state topology. Indeed broken spin- and orbital rotation symmetries lead
to a rich spectrum of collective modes of the order parameter that can be
detected using NMR, acoustic and microwave spectroscopies. The topology of the
BW state implies its low-temperature, low-energy transport properties are
dominated by gapless Majorana modes confined on boundaries or interfaces. Given
the central role the BW state played I discuss the acoustic and electromagnetic
signatures of the BW state, the latter being relevant if an electronic analog
of superfluid $^3$He-B is realized.
