
#37
Jun1210, 10:26 AM

P: 716

is dark energy composed of elementary particles? 



#38
Jun1210, 10:34 AM

P: 2,078

Dark energy is much less well understood than dark matter. It appears to be a uniform "tesnion" everywhere in space. Today's data is completely explained by what is called the cosmological constant, which is constant throughout space and time. However, there are many experiments underway to determine if it is really constant or has some structure. In my judgement, no, it is not composed of elementary particles, but is more a property of spacetime.




#39
Jun1210, 12:02 PM

P: 2,281

I'm sure that this has been said, but to the OP: we look harder, with finer instruments unless a better and more predictive theory emerges. Dark matter seems like a terribly safe bet, but dark energy could be what phyzguy said, or vacuum expectation energy, or something else entirely. I don't think DE will be discovered, or the effect explained in our lifetimes, but I suspect we'll find DM soon (soon being 5 to 10 years).




#40
Jun1210, 12:27 PM

P: 716





#41
Jun1210, 12:28 PM

P: 716





#42
Jun1210, 05:41 PM

P: 2,281





#43
Jun1210, 06:10 PM

P: 2,281





#44
Jun1210, 07:53 PM

P: 716

Dark Fluid: Towards a unification of empirical theories of galaxy rotation, Inflation and Dark Energy Authors: HongSheng Zhao (SUPA, St Andrews) Baojiu Li (DAMTP, Cambridge) (Submitted on 10 Apr 2008) Abstract: Empirical theories of Dark Matter like MOND gravity and of Dark Energy like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general hence natural framework? Here we propose the natural Lagrangian of such a framework based on simple dimensional analysis and covariant symmetry requirements, and explore various outcomes in a topdown fashion. Our framework preserves the covariant formulation of GR, but allows the expanding physical metric be bent by a single new species of Dark Fluid flowing in spacetime. Its nonuniform stress tensor and current vector are simply functions of a vector field of variable norm, resembling the 4vector electromagnetic potential description for the photon fluid, but is dark (e.g., by very early decoupling from the baryonradiation fluid). The Dark Fluid framework naturally branches into a continuous spectrum of theories with Dark Energy and Dark Matter effects, including the $f(R)$ gravity, TeVeSlike theories, EinsteinAether and $\nu\Lambda$ theories as limiting cases. When the vector field degenerates into a pure Higgslike scalar field, we obtain the physics for inflaton and quintessence. In this broad setting we emphasize the nonconstant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions. Choices of parameters can be made to pass BBN, PPN, and causality constraints. The Dark Fluid is inspired to unify/simplify the astronomically successful ingredients of previous constructions: the desired effects of inflaton plus quintessence plus Cold DM particle fields or MONDlike scalar field(s) are shown largely achievable by one vector field only. 



#45
Jun1310, 08:38 AM

P: 2,281





#46
Jun2410, 06:10 AM

P: 2,900

"If I could have my pick, I would like to learn that Newton's laws must be modified in order to correctly describe gravitational interactions at large distances.That's more appealing than a universe filled with a new kind of subnuclear particle." This statement is by Vera Rubin. But what does she know about this anyway. It might even not be necesary to look for any modification. "General Relativity Resolves Galactic Rotation Without Exotic Dark Matter" http://arxiv.org/PS_cache/astroph/p.../0507619v1.pdf Regards 



#47
Jun2510, 03:57 AM

Sci Advisor
P: 1,883

Thanks, I referred to that paper in a different thread but couldn't find it anymore. It's errorneous.




#48
Jun2510, 04:43 AM

P: 2,900

Regards 



#49
Jun2510, 05:11 AM

P: 2,900

Regards 


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