  We explore how thermal fluctuations affect the mechanics of thin amorphous
spherical shells. In flat membranes with a shear modulus, thermal fluctuations
increase the bending rigidity and reduce the in-plane elastic moduli in a
scale-dependent fashion. This is still true for spherical shells. However, the
additional coupling between the shell curvature, the local in-plane stretching
modes and the local out-of-plane undulations, leads to novel phenomena. In
spherical shells thermal fluctuations produce a radius-dependent negative
effective surface tension, equivalent to applying an inward external pressure.
By adapting renormalization group calculations to allow for a spherical
background curvature, we show that while small spherical shells are stable,
sufficiently large shells are crushed by this thermally generated "pressure".
Such shells can be stabilized by an outward osmotic pressure, but the effective
shell size grows non-linearly with increasing outward pressure, with the same
universal power law exponent that characterizes the response of fluctuating
flat membranes to a uniform tension.
