  Loosely inspired by the somewhat fanciful notion of detecting an arbitrarily
advanced alien civilization, we consider a general-relativistic thin-shell
Dyson mega-sphere completely enclosing a central star-like object, and perform
a full general-relativistic analysis using the Israel--Lanczos--Sen junction
conditions. We focus attention on the surface mass density, the surface stress,
the classical energy conditions, and the forces between hemispheres. We find
that in the physically acceptable region the NEC, WEC, and SEC are always
satisfied, while the DEC can be violated if the Dyson mega-sphere is
sufficiently close to forming a black hole. We also demonstrate that the
original quasi-local version of the maximum force conjecture, F <= {1/4}
F_{Stoney} = {1/4} F_{Planck}, can easily be violated if the Dyson mega-sphere
is sufficiently compact, that is, sufficiently close to forming a black hole.
Interestingly there is a finite region of parameter space where one can violate
the original quasi-local version of the maximum force conjecture without
violating the DEC. Finally, we very briefly discuss the possibility of nested
thin-shell mega-spheres (Matrioshka configurations) and thick-shell Dyson
mega-spheres.
