Paul Hinman wrote:

REDACTED

As long as gravity exists will it ever be possible to get a perfectly
horizontal dipole?

NOPE!, At least not in wire. Theoretically, not in beams either.

In spite of a strong tensile component there will
always be a vertical component due to gravity (with a centre feed there
will also be the weight of any cable and perhaps a balun as well). The
net effect is a sag called a catenary. Granted an infinite tension on
the antenna wire would probably overcome the vertical component but the
wire might not survive. The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Most likely less effect than nearby objects like houses, trees, earth, moon,
sun, and rain. :-)

"How many pins can be placed on the head of an angel?" makes more sense than
hypothesizing about the effect of catenary on wire antennas.