Geoff the Medio wrote:Bigjoe5, you're not reading what eleazar is writing correctly. He's saying that there's nothing keeping the sphere in place, with the star at the centre. It (or a Niven ring) are dynamically unstable, and can drift away from being centred on the star unless actively stabilized.
He's not saying that there would be no apparent centrifugal force that seems like gravity to an observer in a reference frame fixed to the inner surface of a rotating ring or sphere.
My understanding of what he was saying is that the artificial gravity would have no relation to the actual gravity acting on the sphere. I am saying that it would, because the speed of the spheres rotation changes as the latitude changes. Both the effect* of actual gravity on any part of the sphere and the artificial gravity on that part of the sphere are affected by the speed of spheres rotation.
*by effect, I mean the path through space that any given part of the sphere would take due to the sun's gravity, if not for it's attachment to the rest of the sphere. But that's too wordy for me to make it make sense in that sentence.
Edit: Also, regarding the poles of the Dysonsphere, the force of gravity from the sun at a distance equal to Earth's oribtal radius is much much weaker than the force of gravity on the surface of the Earth due to the Earth itself. A Dysonsphere spinning fast enough to produce about one Earth gravity centrifugal force outward at its equator would perhaps tear itself apart much more readily than the "domes" over the poles would collapse under their own weight without spin to hold them up.
That's true. I had originally envisioned the equator rotating at a rate equal to that of an inertial orbit until I realized that if it were, the artificial gravity would simply cancel out the effect of the gravity of the star, in other words, someone "standing" on the sphere would also be in inertial orbit. Still, as you have stated, the poles would have to exert a considerable force on the equator to counteract the centrifugal force. This, in addition to the same tension in the equator that the Niven Ring experiences, would cause greater overall tension in the sphere than in the ring. I don't know whether or not these two perpendicular tensions would actually make it more likely for the thing to fly apart than if only the greater tension was in place. If it isn't, than I guess my entire argument is moot.
eleazar wrote:Your italicized quote is accurate, i believe, because the interior is filled with an atmosphere, and thus everything is carried along with the rotation. In the case of a ringworld, is a spacecraft approached the ring "above" (relative to an observer on the inside of the ring) the ring would be moving with extreme speed beneath it, but the craft would not be compelled "down" or in any direction by the ring, until it entered the atmosphere, and started getting pushed around by the air.
IIRC "Ringworld" dealt with this issue.
My apologies. I may have confused Geoff here because I thought you said inaccurate, and responded as such.
Edited to be (I think) comprehensible for Geoff's sake.