🚀 go-pugleaf

(Addition to previous note.)  I did not mean to suggest that Gary
Allen's argument is incorrect, but only to wonder whether the
classical derivation considers every possibility.  Presumably, it uses
a variational method that finds the extremum for variations in the
mass distribution of deviations from a spherical form and (correctly)
finds the shell to be optimal.  Very likely, this is correct, but I
wonder if the variational method extends to distributed variations in
density/porosity.

Eric Drexler showed me a draft calculation that showed that it is
feasible to make a lighter-than-air object with perfect carbon fibres.
However, this is entirely in accord with Gary's argument since (1)
those ideal fibres are indeed a couple of orders of magnitude better
than steel and (2) Drexler's calculation did not suggest any large
margin beyond that.  Drexler's construction involved a dense
tetrahedral lattice that supports a spherical, airtight shell.  As I
recall, Drexler was not maintaining that the hollow lattice was
superior to the uniform shell in regard to preventing buckling.  What
he did argue was that the lattice could be constructed with so fine a
grain that the fibres would be smaller than wavelengths of light.  The
resulting floating object, then, might also be invisible!  Very cute,
if true, but I don't know enough wave theory to know whether it would
end up with a substantial refractive index, in any case.