How many people could live on the surface of a Dyson sphere? - Answers

A "Dyson Sphere" is not really a sphere at all, but a dense network of solar energy collection devices orbiting around a star, effectively collecting all (or most of) the energy emitted from the star. There is no common "surface" for this network. But even if you were talking about the "surfaces" of each of the millions (billions) of satellites, none of them would have an atmosphere, and therefore, no one could live on those surfaces. I suspect you're actually talking about a "Dyson Shell", which is a shell of solid matter around a star. Note that this is not an invention of Freeman Dyson, but of Science Fiction writers. Freeman Dyson himself, when answering letters from people who misunderstood his idea as a Dyson Shell, stated flatly that a Dyson Shell was physically impossible. I won't go so far as to say that a Dyson Shell is physically impossible. However, there are serious impediments that are not likely to be overcome. First and foremost, there's not enough matter in the solar system to create a Dyson Shell, at 1AU distance from the sun, of sufficient thickness. Using all the "easily usable building material" in the solar system, a shell of only 8-20 cm thick could be constructed. That is not nearly thick enough to withstand impacts from interstellar bodies. Moreover, even if such a shell could be constructed, the inner surface of that shell would exert virtually no gravity on objects inside the sphere, and thus anything placed inside the sphere would fall into the star. That includes gases, so there wouldn't be any atmosphere around the inner surface of the shell. And speaking of gravity, it's doubtful that the 8-20-cm-thick shell could withstand that kind of gravity. Even if all of this could somehow be overcome, there is nothing to keep the shell in position with respect to the star, nor the star in position with respect to the shell. They would just drift around with respect to each other until the star hit the surface and punched through. Of course, anyone living on that inner surface would die from either extreme heat or extreme cold long before the breakthrough. Then there's the issue of feeding the population of the Dyson Shell. Remember, we used up all the solid material in the solar system just to build a rigid shell. Where are we going to get the soil to plant crops in? But, assuming all of these obstacles could somehow be overcome, the inside surface of a Dyson Shell would have an area of about 550 million times the surface area of Earth. So, however many people could live on the surface of the Earth, multiply that by 550 million.