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Much of the evidence for dark matter comes from the study of the motions of galaxies. Many of these appear to be fairly uniform, so by the virial theorem the total kinetic energy should be half the total gravitational binding energy of the galaxies. Experimentally, however, it is found to be much greater: in particular, stars far from the center of galaxies have much higher velocities than predicted by the virial theorem. Galactic rotation curves, which illustrate the velocity of rotation versus the distance from the galactic center, cannot be explained by only the visible matter.
This is because even for weak fields and slow speeds, well-known nonlinearities change the character of the solution dramatically. The success of Newtonian mechanics in situations like our solar system can be traced to the fact that in this case the planets are basically "test particles", which do not contribute significantly to the overall field. However, in a galaxy this approximation is not a good one - all the rotating matter is also the source of the gravitational field in which everything rotates.
Originally posted by Viendin
It's empty space. That fabric of spacetime is just empty space - and despite the fact that emptiness having a deformable shape is a difficult concept to get around, it does. Outside of the deformable emptiness is irrelevant, because it simply doesn't exist.
Originally posted by ZPE StarPilot
Seems to me I read about large quantities of Mass being found in an area where there is no visible objects to be found. The asumption was that it might be a large quantity of Dark Matter, based on it's gravitation effects on ordinary Matter.
I've also seen Dark Matter maps made, that show possible Dark Matter not far from our local group of stars. How they figure this, I don't know.
Originally posted by ZPE StarPilot
Vacuum energy is definitely not the same as Dark Energy.
I don't think they have much of an idea what Dark Energy might be yet.
But vacuum energy, as best as I can say, is the "quantum jiggle" of the basic hydrogen the makes up the universe. It's everywhere. Zero vacuum empty space isn't empty, it's full of energy. That's their story.
Originally posted by ZPE StarPilot
And yes, modern improvements to Newtonian physics do quite well, compared to Einsteinian. Don't forget, orbital dynamics failed with Einstein's rules, but worked fine with Newton's stuff. We would never have made it into orbit or to the Moon. It's all about Gravity. I think one works better on sub-atomic particles (quantum), and the other on molecular. (large scale mass)
Originally posted by ShadowXIX
What about Dark energy or "Vacuum" energy which is thought to make up a much largersection of the universe then Dark matter? Empty space seems to not be empty and has some type of force that wants to push space apart. I thought that repulsive energy is the reason why the expansions of the universe is speeding up.
Originally posted by Nygdan
Dark matter has to exist, since I'm composed entirely of it. Dark matter, evil energy, ya know.
However this claim is not without its detractors. Korzynksi's response claims that the Cooperstock and Tieu model is unphysical. Namely, that it includes a "fudge factor" in a shell of matter which isn't observed and seems to be little more than a mathematical artifact... one which skews the results of Cooperstock and Tieu.
Indeed, merely resolving galactic rotation alone is insufficient to dispense with the need for dark matter. Motions of galaxies themselves within clusters, as well as diffuse hot intergalactic gas, also require far more mass than is observed. The most direct observations we have made of dark matter, using gravitational lensing of more distant galaxies, also confirm that there is far more mass than we can see there.
Most clusters have their component galaxies at such high velocities that their observed masses would have the cluster flying apart in just a few hundred million years and hence there would be no clusters remaining today. Intergalactic gas is so hot that it, too, would rapidly escape the cluster if not for the presence of much more mass than we can see. The Cooperstock/Tieu model addresses neither of these problems.
So it looks like dark matter is here to stay for the time being.
...it is not a physical model – it contains a physical singularity (which Cooperstock and Tieu write off as a mathmatical singularity, but not physical)....