And more importantly, how not to build a galaxy. Uniform discs of pure gas turn out to be almost impossible. Exponential discs - where there's a much greater density in the centre - work, but they don't match observations. By far and away the easiest solution is to add a gazillion tonnes of dark matter. That stabilises everything to the point where the disc becomes practically indestructible.
I also look at a claim by some mathematicians that you don't need dark matter because the gravitational field of a disc is very different to sphere. It turns out the field is very different - and this is often overlooked - but this cannot possibly explain why galaxies are rotating so fast. Although they do some mathematics that's way too complicated for me, I found a way to sidestep that and get the same results. The flaw in their argument is that they use a density profile that's completely ruled out by observations, and doesn't give that good a result anyway. They also neglect the fact that the gas is a fluid but actually you can't approximate this as a simply a collection of orbiting points - even if you use the prescribed formula that accounts for the gravity correctly, the thing tears itself apart in a wide variety of interesting ways.
Whatever its faults on other scales, dark matter really is the easiest solution here.
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In the last batch of simulations, we dropped a long gas stream into the gravitational potential of a cluster to see if it would get torn... -
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Of course you can prove a negative. In one sense this can be the easiest thing in the world : your theory predicts something which doesn...
Nope they form out of a black hole
ReplyDeleteNope the blackhole itself is relative to the paradox that reverse engineered it to the reflection
ReplyDeleteJashua Fowler That's simply nonsense.
ReplyDeleteThe cross is also relative to the same equasion and the universe is looped to a singularity but the stars taught me that
ReplyDeleteMaby one day science will catch up to what I allready know
ReplyDeleteInteresting side-point about ringworld stability.
ReplyDeleteIn nature, we find stable rings around planets like Saturn, or the Main Asteroid belt. I suppose this is because the ring's own gravity is negligible enough compared to the central body's, so it can be treated as a series of independently orbiting bodies (that happen to more or less share the same orbit).
I wonder at which point a ring becomes unstable. Maybe a sufficiently light ringworld would be possible?
Another thing that may help the stability of a ringworld is solar pressure.
Statites use a solar sail to keep stationary, balancing solar pressure against gravity. Driven to its logical extreme, we have a Dyson bubble (or Dyson balloon? I'm not sure of the common name), a Dyson sphere keeping its shape and position by basically being a spherical solar sail all around the star. Cut it in half and you have a Benford-Nieven star engine.
The interesting thing is, the close you approach, the stronger solar pressure is, it scales similarly to gravity.
So maybe putting solar sails on the ringworld could help keeping it in place.
The problem with both this ringworld and the Dyson bubble are, if it is damaged and the solar pressure becomes asymetric, you'll have to fix it before the whole thing crashes into the star. Though maybe it is possible to build reasonably passive self-balancing ones?
Elie Thorne
ReplyDelete"In nature, we find stable rings around planets like Saturn, or the Main Asteroid belt. I suppose this is because the ring's own gravity is negligible enough compared to the central body's, so it can be treated as a series of independently orbiting bodies (that happen to more or less share the same orbit)."
That would be my guess. The planet should behave just like the dark matter, only instead of being maybe a thousand times more massive (at most) than the gas, it would probably be more like a million times more massive than the ring, if not more. So the gravitational field of the ring can be neglected.
"I wonder at which point a ring becomes unstable. Maybe a sufficiently light ringworld would be possible?"
I don't think the gravity of the ringworld matters. With a heavy ring, a test particle dropped at random inside it will be attracted to the nearest point. But with a light ring that's off-centre from a heavy particle, the situation is reversed - the nearest part of the ring is attracted more strongly to the particle than the other side. That won't be the case with a swarm of structures though, since there wouldn't be any tension caused by pulling one part of the ring more strongly than the others.
"The problem with both this ringworld and the Dyson bubble are, if it is damaged and the solar pressure becomes asymetric, you'll have to fix it before the whole thing crashes into the star. Though maybe it is possible to build reasonably passive self-balancing ones?"
Without doing the numbers I guess that using sail as the only support for a ringworld would require a prohibitively large area even for a civilization capable of building a ringworld. But what about using a combination of rotational and pressure support ? Just use the sail for the relatively small adjustments needed to keep the ringworld centred on the star. That way in the worst-case scenario you have many months to evacuate if the sail is irreparably damaged and the orbits of each segment start to decay - they'll be sent into orbits which maybe make them intolerably hot but not actually crash into the star, so you could even salvage them later on. Or make the world flexible rather than rigid.
To me the universe is a giant computer and a black hole is "eve"and the earth is her womb and it's all a matter of perspectives I seen the universe compute itself backwards as the stars perspectively danced around the sky and I know what I saw I don't care if you believe me either because I am the reason it became looped 666=carbon atom and Google the Crystal pyramid discovery under Bermuda triangle to know it's reflection and how it was rooted in the earth I am likewise to the computer a spinwheele or if you prefer a snake Lucifer Project the only way to manifest a galaxy out of absolutely nothing is to reverse engineer a black hole
ReplyDeleteCan you provide more details about your simulation code? What algorithm did you use?
ReplyDeleteWhy do you think the Google algorithm changed all of a sudden and without reason ?
ReplyDeleteJashua Fowler, er what on earth are you talking about?
ReplyDeleteGoogle Crystal pyramid discovery under Bermuda triangle
ReplyDeleteChris Greene It's a rather obscure SPH code called gf. Details here : http://www.aanda.org/articles/aa/pdf/2001/30/aa9391.pdf
ReplyDeleteJashua Fowler Well okay, that's your opinion, but it has nothing whatsoever to do with this thread. Write some code that makes galaxies based on your ideas and then we'll talk.
ReplyDelete666......code enough ?
ReplyDeletehttps://www.python.org/about/gettingstarted/
ReplyDelete6proton 6neutron 6electron and be in the beginnings as it was in the end
ReplyDelete=Carbon atom
ReplyDeleteJashua Fowler Please go away.
ReplyDeleteAm I wrong ?
ReplyDeleteYou're not conveying meaningful information.
ReplyDeleteRhys Taylor thanks Rhys!
ReplyDeletePerspectivly perhaps you should broaden your "horizon"
ReplyDeleteWow, Incredible e spectaculare
ReplyDelete