RAS: Accelerating Expansion of Universe Explained without Dark Energy

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RAS: Accelerating Expansion of Universe Explained without Dark Energy

Post by bystander » Fri Mar 31, 2017 2:16 pm

Explaining the Accelerating Expansion of the Universe without Dark Energy
Royal Astronomical Society | 2017 Mar 30
[c][youtube]https://www.youtube.com/watch?v=VF0Lg7CfCYA[/youtube]
A short animation that shows the expansion of the universe in the standard 'Lambda
Cold Dark Matter' cosmology, which includes dark energy (top left panel red), the new
Avera model, that considers the structure of the universe and eliminates the need for
dark energy (top middle panel, blue), and the Einstein-de Sitter cosmology, the original
model without dark energy (top right, green). The panel at the bottom shows the
increase of the 'scale factor' (an indication of the size) as a function of time. The
growth of structure can also be seen in the top panels. One dot roughly represents an
entire galaxy cluster. Units of scale are Megaparsecs (Mpc). Credit: István Csabai et al
[/c][hr][/hr]
Enigmatic 'dark energy', thought to make up 68% of the universe, may not exist at all, according to a Hungarian-American team. The researchers believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears. ...

normal and dark matter appear to fill the universe with a foam-like structure, where galaxies are located on the thin walls between bubbles, and are grouped into superclusters. The insides of the bubbles are in contrast almost empty of both kinds of matter.

Using a computer simulation to model the effect of gravity on the distribution of millions of particles of dark matter, the scientists reconstructed the evolution of the universe, including the early clumping of matter, and the formation of large scale structure.

Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions of the cosmos expand at different rate. The average expansion rate though is consistent with present observations, which suggest an overall acceleration. ...

Concordance Cosmology without Dark Energy - Gábor Rácz et al
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Re: RAS: Accelerating Expansion of Universe Explained without Dark Energy

Post by BDanielMayfield » Tue Apr 04, 2017 3:54 am

A much more efficient (runs on 68% less energy), less mysterious universe results if this holds up. Is cosmology beginning to emerge from dependence upon unknowns (dark energy, dark matter) to explain everything? Hope so.

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Re: RAS: Accelerating Expansion of Universe Explained without Dark Energy

Post by Chris Peterson » Tue Apr 04, 2017 2:33 pm

BDanielMayfield wrote:A much more efficient (runs on 68% less energy), less mysterious universe results if this holds up. Is cosmology beginning to emerge from dependence upon unknowns (dark energy, dark matter) to explain everything? Hope so.
Well, dark energy has always been a much more hypothetical thing. Dark matter, however, doesn't show any signs of going anywhere (and is, of course, much easier to explain). Too many independent pieces of our cosmology depend on dark matter, and the few efforts to eliminate it all have major problems when looking at the entire picture.
Chris

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Re: RAS: Accelerating Expansion of Universe Explained without Dark Energy

Post by BDanielMayfield » Tue Apr 04, 2017 4:09 pm

Chris Peterson wrote:
BDanielMayfield wrote:A much more efficient (runs on 68% less energy), less mysterious universe results if this holds up. Is cosmology beginning to emerge from dependence upon unknowns (dark energy, dark matter) to explain everything? Hope so.
Well, dark energy has always been a much more hypothetical thing. Dark matter, however, doesn't show any signs of going anywhere (and is, of course, much easier to explain). Too many independent pieces of our cosmology depend on dark matter, and the few efforts to eliminate it all have major problems when looking at the entire picture.
Dark matter (if it is real) is doing a fine job of defying attempts to explain it so far. Null result searches for it abound, don't they? But I get it that there are good reasons to think that dark matter is real, and so it may be, and quite likely it is in fact a real thing. But until something tangible is discovered to be that thing that we now call dark matter we still have reason to wonder.

Dark matter may be showing signs of weakness due to the finding that it is not needed to explain galactic rotation curves, so there is at least one reason to doubt the reality of DM.

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Re: RAS: Accelerating Expansion of Universe Explained without Dark Energy

Post by Chris Peterson » Tue Apr 04, 2017 4:28 pm

BDanielMayfield wrote:
Chris Peterson wrote:
BDanielMayfield wrote:A much more efficient (runs on 68% less energy), less mysterious universe results if this holds up. Is cosmology beginning to emerge from dependence upon unknowns (dark energy, dark matter) to explain everything? Hope so.
Well, dark energy has always been a much more hypothetical thing. Dark matter, however, doesn't show any signs of going anywhere (and is, of course, much easier to explain). Too many independent pieces of our cosmology depend on dark matter, and the few efforts to eliminate it all have major problems when looking at the entire picture.
Dark matter (if it is real) is doing a fine job of defying attempts to explain it so far. Null result searches for it abound, don't they? But I get it that there are good reasons to think that dark matter is real, and so it may be, and quite likely it is in fact a real thing. But until something tangible is discovered to be that thing that we now call dark matter we still have reason to wonder.

Dark matter may be showing signs of weakness due to the finding that it is not needed to explain galactic rotation curves, so there is at least one reason to doubt the reality of DM.
The inability to find dark matter particles is not very strong evidence against it. By its nature we would expect it to be difficult, perhaps impossible to detect directly. But the existence of such particles poses no conceptual difficulty, as we already have known particles (such as neutrinos) that have the same kind of properties.

Galaxy rotation curves are now among the least important elements in arguing for dark matter, despite being the first evidence found. Most convincing is the fact that physical models which produce exceptionally accurate representations of the Universe only do so when dark matter is included.
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Science: Is dark energy an illusion?

Post by bystander » Tue Apr 04, 2017 5:13 pm

Is dark energy an illusion?
Science Magazine | 2017 Apr 03
Adrian Cho wrote:
For the past 20 years, physicists have known that the expansion of the universe is accelerating, as if some bizarre “dark energy” is blowing up space like a balloon. In fact, cosmologists’ well-tested standard model assumes that 69% of the content of the universe is dark energy. However, there may be no need for the mysterious stuff, a team of theorists claims. Instead, the researchers argue, the universe’s acceleration could be driven by variations, or inhomogeneities, in its density. If so, then one of the biggest mysteries in physics could be explained away with nothing other than Albert Einstein’s familiar general theory of relativity. Other researchers are skeptical, however. ...

At issue is the way cosmologists calculate how the universe evolved over the past 13.8 billion years. Roughly speaking, they rely on two equations. One describes how matter coalesces into galaxies and clusters of galaxies. The other, known as the Friedmann–Lemaître–Robertson–Walker (FLRW) metric, comes out of Einstein’s theory of gravity, or general relativity, and scientists use it to calculate how much the universe has expanded at any time. At each step in time in a simulation, the cosmologists’ program uses the FLRW metric to calculate the “scale factor,” which specifies how much the universe has grown. The program then uses the scale factor as an input to calculate how the formation of galaxies and clusters advances in that step.

Strictly speaking, however, the FLRW equation applies to a smooth and homogeneous universe. So to calculate the scale factor at each step, cosmologists typically assume the universe is smooth and use its average density—determined from the simulation—as the FLRW metric’s input. That’s a bit dicey, because general relativity says that mass and energy warp spacetime. As a result, space should expand faster in emptier regions and slower in crowded ones, where the galaxies’ gravity pulls against the expansion. Thus, in principle, inhomogeneities in the universe can feed back through the dynamics and affect the universe’s expansion. ...
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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