Stemming from known properties of one-dimensional (1-D) and 2-D quantu
m billiards, it is conjectured that the nodal surface of the first-exc
ited state of the convex 3-D quantum billiard intersects the billiard
surface in a single simple closed curve. Examples of the validity of t
his conjecture are given for a number of elementary 3-D billiard confi
gurations. From these examples a second conjecture is introduced that
addresses convex quantum billiards which are figures of rotation and c
ontain one and only one plane of mirror symmetry normal to the axis of
rotation. Two characteristic displacement parameters are defined whic
h are labeled an axis length, L, and diameter, a. It is conjectured th
at a parameter kappa almost-equal-to 1, exists, whose exact value depe
nds on the properties of the billiard, such that for L > kappaa (''pro
latelike'') the nodal surface of the first-excited state of a quantum
billiard is a plane surface of mirror symmetry which divides the lengt
h of the billiard in half. For L < kappaa (''oblatelike'') the nodal s
urface of the first-excited state is a plane surface of mirror symmetr
y which contains the rotation axis and divides the diameter of the bil
liard in half. Arguments are given in support of a third conjecture wh
ich addresses the regular polyhedra quantum billiards, termed ''spheri
cal-like.'' It is hypothesized that the nodal surface of the first-exc
ited state for any of these billiards is any plane of reflection symme
try of the given polyhedron.