- #106
RUTA
Science Advisor
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marcus said:Well. That's how the real world operates It's not a big deal. Better to get your message out with a little distortion than not to reach the Nature journal audience.
Absolutely!
marcus said:Well. That's how the real world operates It's not a big deal. Better to get your message out with a little distortion than not to reach the Nature journal audience.
atyy said:I agree in general that there is a fine tuning problem with the cc coming from quantum effects. But I thought the Casimir effect isn't evidence of this since it can be calculated without using zero-energy, like in http://arxiv.org/abs/hep-th/0503158?
Physics Monkey said:I always found it interesting that Jaffe's paper does not mention what might be called the topological Casimir effect. In this case the fields are confined by the topology of compact space instead of by any "perfectly conducting sheets" and so forth. Naively, it seems that there is no coupling dependence in such a situation.
marcus said:Or you could just think of Λ as the zero-point curvature that is intrinsic to nature's geometry.
And as curvature that would be an inverse area, so that 1/Λ is an area.
And therefore 1/√Λ is a length.
Which length we believe to be 9.3 billion LY based on the large amount of supernova data which has accumulated.
...
atyy said:Bianchi and Rovelli are not saying anything new, are they? Take eg. this 2007 review
http://arxiv.org/abs/0705.2533
"The observational and theoretical features described above suggests that one should consider cosmological constant as the most natural candidate for dark energy. Though it leads to well known problems, it is also the most economical [just one number] and simplest explanation for all the observations. Once we invoke the cosmological constant, classical gravity will be described by the three constants G, c and Lambda"
atyy said:Padilla mentions the Galileon stuff in the introduction of his PRL paper, and says that it is closely related. The Galileon stuff was originally motivated by DGP - which passed First-Year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Constraints on Non-Standard Cosmological Models.
marcus said:Good point! What about his current paper? The March 2012 one.
atyy said:Hmmm, seems unrelated to the Fab Four idea.
Marcus said:What ( Kimpton and Padilla) are talking about ...is a mathematical
technique to "degravitate" the QFT vacuum energy ...
Dark energy is a hypothetical form of energy that is believed to make up about 68% of the universe. It is thought to be responsible for the observed accelerating expansion of the universe. However, some scientists argue that dark energy is a fake problem because it is based on assumptions and has not been directly observed or measured.
Scientists study dark energy through observations of the universe's expansion and the distribution of galaxies. They also use mathematical models and simulations to understand its effects on the universe. However, since dark energy has not been directly detected, these methods are still being refined and debated.
Some alternative theories to dark energy include modified theories of gravity, such as MOND (Modified Newtonian Dynamics), which suggest that our understanding of gravity may need to be revised. Other theories propose that the universe is not expanding at all, but rather that the observed effects can be explained by other factors.
The cosmological constant is a term in Einstein's theory of general relativity that represents a constant energy density in space. Some scientists argue that dark energy can be explained by the cosmological constant, while others believe that the two concepts are not equivalent and that dark energy is a separate phenomenon.
While there is no direct evidence for dark energy, there is observational evidence that suggests the expansion of the universe is accelerating. This evidence comes from studies of distant supernovae, the cosmic microwave background, and the large-scale structure of the universe. However, the interpretation of this evidence and its relationship to dark energy is still a subject of debate among scientists.