A number of
imaginative solutions have been proposed to the gravity crisis. Professors Sheringham and Beckham of the
Bognor Regis Polytechnic have suggested converting electrical
potential energy into
gravitational potential energy by building powerful
electric motors at the tops of high
mountains, and
not turning them on.
To be most effective, these gravity accumulators should start out light and gain mass, so that the longer they sit idle the more weight their unused electrical capacity has to leak into. A light machine also saves the gravity wasted hauling components up the mountainside, which outweighs the positive benefit of each workman's effort using up less gravity in the lighter mountain air. One possibility is to build them of light but tough titanium-aluminium alloys, and cause avalanches just above them. Too far above and too much gravity is wasted in the falling, and there is an increased risk that displaced matter would fall on either side of the accumulators instead of resting on them.
A bolder idea is to use an aerosol foam of carbon nanotubes to build the electrical equipment. This would be either an excellent conductor of electricity if the machinery were switched on, or possibly a terrible disappointment, but in either case it wouldn't matter, as it would never be intended for use for its intended purpose. The great advantage of the foam is there is so much room in it to trap Higgs bosons that would otherwise float out into space.
It has been observed that conversion of the Earth's core and possibly inner mantle to a black hole would not affect the Earth's overall gravity because the mass would all still be there. This would be true considering the whole Earth's effect as concentrated at its centre of mass, as we can reasonably do in calculating the orbit of the Moon, the effect on which would be very slight.
But by the general gravitational law, people on the surface of the earth are further away from the mass, so would indeed weigh less. In fact there would be a slight tidal effect as portions of neighbouring crust began to overcome the effects formerly exerted by nearby mantle. Not only would we be taller and spindlier, our legs would stick out at the sides more. This would be unlikely to present any major health risk, since few us walk consistently in one direction. Hitch-hikers across the continental USA, however, would be advised to stop and do pirouettes from time to time in the intervals between watching for cars.