Dark Energy Spectroscopic Instrument
DESI is scheduled to see 'first light' in September. [its] survey of the northern sky — using the Mayall 4-meter Telescope at Kitt Peak National Observatory near Tucson — could start as early as January 2020.
Following are excerpts and a few comments relevant to EUT.
The survey will track cosmic expansion by measuring features of the early Universe, known as baryon acoustic oscillations (BAOs). These oscillations are ripples in the density of matter that left a spherical imprint in space around which galaxies clustered.
Tracking BAOs requires a 3D map of galaxies made by measuring their redshifts. Redshifts measure how fast a galaxy is receding from the Milky Way, which indicates how far away that galaxy is.
Red shifts known to be associated with distance (how far away) are also incorrectly associated with velocity (how fast) using the same Z value. As long as that conundrum persists, this analysis is wrong.
The assumption is this collection of million+ galaxy spectra will provide red shifts which show the ripples in the density of matter. I suspect red shift fluctuations (compared to what?) are thought to be caused by a varying density of matter. When the cosmology has only gravity that leaves only this unlikely explanation.
The more redshifts that are measured, the more precise the BAO tracking. Eisenstein and others have found the unmistakable BAO signature in previous galaxy surveys, in particular the Baryon Oscillation Spectroscopic Survey (BOSS), which ended in 2014, and the Australia-based Two-degree-Field Galaxy Redshift Survey, which finished in 2002. Together, those surveys mapped nearly 2.4 million galaxies.
This is ironic to suggest more measurements will improve resolution. I expect each analysis will use the same assumptions.
Many cosmologists recently convened in July and agreed the many measurements of Hubble's constant have failed to converge on a single value. This uncertain value is the foundation of modern cosmology. After that failure now they hope future datasets will generate a value which can be agreed upon. That mystery persists, as a 'crisis' for cosmology.
Adding more surveys will undoubtedly fail to provide a reliable 3-D map of millions of galaxies when the analysis is based on a wrong assumption.
In addition to probing dark energy, DESI will study the role of dark matter in the growth of galaxies and clusters of galaxies by measuring motion in clusters. This will provide "exquisite tests" of the current favourite models of how dark matter drives large-structure growth, she says, versus alternatives that explain the formation of these structures by tweaking Albert Einstein's general theory of relativity.
These surveys are an opportunity to test the 'favourite' models or to 'tweak' relativity as the explanation. Another 'alternative' like EUT is irelevant. This effort is only to confirm not to learn.
The primary cosmology mission of DESI is to study the nature of dark energy: How does its energy density evolve in time, and how does it affect the clustering of matter? To do this, DESI will use its maps to measure two cosmological effects: BAOs and redshift-space distortions. The same maps will also provide other opportunities to study cosmology and the physics of galaxies, quasars, and intergalactic gas.
When DESI measures the redshift of galaxies, this measurement is actually composed of two contributions: the large shift coming from the cosmological expansion of the universe, and a smaller shift that results from the motion of the galaxy due to the gravitational pull from the universe's surrounding large-scale structure. The latter is known as the peculiar velocity. By measuring the size of the peculiar velocity, scientists can measure the amount of mass in the large-scale structure.
Or if that is known from other methods, we can test whether gravitational attractions on scales of hundreds of millions of light-years follows the predictions of Albert Einstein's theory of general relativity, which relates to gravity. The testing of general relativity on these enormous scales is important as it might reveal alternative explanations, known as modified gravity theories, for the universe's accelerating expansion rate. On the very largest scales we find that the expansion rate is evolving very differently from what would be predicted from the attractions of known matter and the physics that are so well-tested on solar system scales. Perhaps this breakdown has other signatures in the universe's large-scale structure.
Everything above implies: all this red shift data will be manipulated to conform to the assumed expectations of expansion. I have the unfortunate expectation 'testing relativity' means new gyrations with spacetime.
'[The] expansion rate is evolving very differently from physics so well-tested on solar system scales.'
I always find this admission stunning, especially when it is common.
When data sets include millions of items in special formats it is difficult to analyze the raw data.
I had posted on June 21 published red shifts and distances do not conform to Hubble's Law now, so I expect that lack of conformance to continue.
The outcome of these surveys will probably be misleading data for someone else to analyze.
Nonetheless there are always revealing surprises to help understand the 'real' universe.
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