marklar

727C doesn't sound like much, anything under 1000C is easy with a solar Fresnel lens 1m in diameter. These are available for $200-300 and can melt a penny to liquid in a couple of seconds. just google it to see the stuff people melt with them. I forget the exact calculation but a 1m lens will focus about 1KW of heat/light. The other great thing is that there is almost no heat limit unlike coal or electrical elements, all you need to do is insulate and wait for the heat to rise. Oh yeah and it's clean and free to use too

Having a ringworld with gravity would require huge material strength and having gravity in a dyson sphere would not be possible accross it's whole surface, so let's forget about gravity. If the structure is in a zero gravity orbit it doesn't have to be strong, in fact it doesn't even have to be held together as long as it is extremely accurately placed (thrusters would probably be handy). If gravity is your thing, then you would need a long string of rings rotating with the orbital path as their axis (kinda like a candy necklace). The string of this necklace would be a guide and have no force exerted on it. Anyway, a sufficiently large ring made of thousands of planets (finding a way to empty out a couple of black holes would help) could have a crust thickness similar to the diameter of the Earth meaning it would have it's own natural gravity without having to simulate it artificially.

insane_alien: Indeed, I think the solution is to enclose the entire volume of the aircraft within an active aerofoil. Since the force on the aerofoil is proportional to the volume of air displaced, increasing the volume should increase lift. While this is fine in theory, you can never make the entire aircraft generate lift and I'm sure there is a limit to undercarriage size.

What about people that go to the gym? I wonder if treadmills (not electric ones obviously), cycles, rowing machines and even weight machines could have generators fitted to produce a meaningful amount of power. Cycles / rowing machines are probably most suited but a weight machine is the easiest to calculate: if a 20kg weight is lifted 50cm every 2 seconds (1 up, 1 down) it could generate 200N x 0.5m / 2s = 50 watts as it falls (assuming 100% efficiency). Not brilliant, let's try a cycle. A cycle simulating a 1:100 gradient for a 75kg person travelling at 10m/s could generate 750N x 1m / 10s = 75W. Hmm, better and more sustainable. If it was enough, you could make gym membership free and just sell the power. Unfortunately assuming electricity costs of $0.08/KWh (the only figure I could find) you'd make 0.6 cents an hour cycling.

The point you make that the net result of attractive / repulsive forces assumes that the first force is attractive. If the first force is repulsive, the opposite would be true (although I don't think that the net result would be anything other than 0 anyway). Bear in mind that the 'poles' are always active so there are not only 2 positions where they would interact but rather a constantly changing force that has been present since the particles were formed.