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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Dark energy | 6/7 | https://en.wikipedia.org/wiki/Dark_energy | reference | science, encyclopedia | 2026-05-05T11:00:50.324824+00:00 | kb-cron |
=== Observational skepticism === Some alternatives to dark energy, such as inhomogeneous cosmology, aim to explain the observational data by a more refined use of established theories. In this scenario, dark energy does not actually exist, and is merely a measurement artifact. For example, if we are located in an emptier-than-average region of space, the observed cosmic expansion rate could be mistaken for a variation in time, or acceleration. A different approach uses a cosmological extension of the equivalence principle to show how space might appear to be expanding more rapidly in the voids surrounding our local cluster. While weak, such effects considered cumulatively over billions of years could become significant, creating the illusion of cosmic acceleration, and making it appear as if we live in a Hubble bubble. Yet other possibilities are that the accelerated expansion of the universe is an illusion caused by the relative motion of us to the rest of the universe, or that the statistical methods employed were flawed. A laboratory direct detection attempt failed to detect any force associated with dark energy. Observational skepticism explanations of dark energy have generally not gained much traction among cosmologists. For example, a paper that suggested the anisotropy of the local Universe has been misrepresented as dark energy was quickly countered by another paper claiming errors in the original paper. Another study questioning the essential assumption that the luminosity of Type Ia supernovae does not vary with stellar population age was also swiftly rebutted by other cosmologists.
=== As a general relativistic effect due to black holes === Another theory called "cosmological coupling" has been proposed as an explanation of dark energy effects. The idea is to require the local description of black holes, the Kerr metric, to match the description of the overall universe assumed in modern cosmology, Friedmann-Robertson-Walker metric, rather than spatially flat spacetime at infinity. Then one finds that black holes gain mass as the universe expands. The rate is measured to increase proportionally to a3 , where a is some scale factor for matter in the universe. This particular rate means that the energy density of black holes remains constant over time, mimicking dark energy (see the technical definition of Dark Energy). Other astrophysicists are skeptical, with a variety of papers claiming that the theory fails to explain other observations. Still other work suggests observations cannot rule out this model.
=== Shockwave Cosmology === Shockwave cosmology, proposed by Joel Smoller and Blake Temple in 2003, has the "big bang" as an explosion inside a black hole, producing the expanding volume of space and matter that includes the observable universe. A related theory by Smoller, Temple, and Vogler proposes that this shockwave may have resulted in our part of the universe having a lower density than that surrounding it, causing the accelerated expansion normally attributed to dark energy. They also propose that this related theory could be tested: a universe with dark energy should give a figure for the cubic correction to redshift versus luminosity C = −0.180 at a = a whereas for Smoller, Temple, and Vogler's alternative C should be positive rather than negative. They give a more precise calculation for their shockwave model alternative as: the cubic correction to redshift versus luminosity at a = a is C = 0.359. Although shockwave cosmology produces a universe that "looks essentially identical to the aftermath of the big bang", cosmologists consider that it needs further development before it could be considered as a more advantageous model than the big bang theory (or standard model) in explaining the universe. In particular, and especially for the proposed alternative to dark energy, it would need to explain big bang nucleosynthesis, the quantitative details of the microwave background anisotropies, the Lyman-alpha forest, and galaxy surveys.