"The point sticks in your head: physics rules. Virtue does not
triumph unless the physics allows it." - Larry Niven ||An
antigravity substance with sufficient power to propel a space
ship from the Earth to Mars. How might it be possible to travel
from the Earth to another planet? I had satisfied myself that
only one thing needful was as yet wholly beyond the reach and
even the proximate hopes of science. Human invention could
furnish as yet no motive power that could fulfil the main
requirement of the problem--uniform or constantly increasing
motion _in vacuo_--motion through a region affording no
resisting medium. This must be a _repulsive_ energy capable of
acting through an utter void. Man, animals, birds, fishes move
by repulsion applied at every moment. In air or water, paddles,
oars, sails, fins, wings act by repulsion exerted on the fluid
element in which they work. But in space there is no such
resisting element on which repulsion can operate. I needed a
repulsion which would act like gravitation thro