Far out cosmology: DESI investigates the universe (Introduction)

by David Turell , Thursday, April 04, 2024, 17:07 (25 days ago) @ David Turell

One year in operation:

https://www.symmetrymagazine.org/article/first-results-from-desi-make-the-most-precise-...

"With 5,000 tiny robots in a mountaintop telescope, researchers can look 11 billion years into the past. The light from far-flung objects in space is just now reaching the Dark Energy Spectroscopic Instrument, enabling us to map our cosmos as it was in its youth and trace its growth to what we see today. Understanding how our universe has evolved is tied to how it ends, and to one of the biggest mysteries in physics: dark energy, the unknown ingredient causing our universe to expand faster and faster.

"To study dark energy’s effects over the past 11 billion years, DESI has created the largest 3D map of our cosmos ever constructed, with the most precise measurements to date. This is the first time scientists have measured the expansion history of the young universe with a precision better than 1%, giving us our best view yet of how the universe evolved.

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"Our leading model of the universe is known as Lambda CDM. It includes both a weakly interacting type of matter (cold dark matter, or CDM) and dark energy (Lambda). Both matter and dark energy shape how the universe expands—but in opposing ways. Matter and dark matter slow the expansion down, while dark energy speeds it up. The amount of each influences how our universe evolves. Lambda CDM does a good job of describing results from previous experiments and how the universe looks throughout time.

"However, when DESI’s first-year results are combined with data from other studies, there are some subtle differences with what Lambda CDM would predict. As DESI gathers more information during its five-year survey, these early results will become more precise, shedding light on whether the data are pointing to different explanations for the results we observe or to the need to update our model. More data will also improve DESI’s other early results, which weigh in on the Hubble constant (a measure of how fast the universe is expanding today) and the mass of particles called neutrinos.

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"Looking at DESI’s map, it’s easy to see the underlying structure of the universe: strands of galaxies clustered together, separated by voids with fewer objects. Our very early universe, well beyond DESI’s view, was quite different: a hot, dense soup of subatomic particles moving too fast to form stable matter like the atoms we know today. Among those particles were hydrogen and helium nuclei, collectively called baryons.

"Tiny fluctuations in this early ionized plasma caused pressure waves, moving the baryons into a pattern of ripples that is similar to what you’d see if you tossed a handful of gravel into a pond. As the universe expanded and cooled, neutral atoms formed and the pressure waves stopped, freezing the ripples in three dimensions and increasing clustering of future galaxies in the dense areas. Billions of years later, we can still see this faint pattern of 3D ripples, or bubbles, in the characteristic separation of galaxies—a feature called Baryon Acoustic Oscillations.

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“'We’ve measured the expansion history over this huge range of cosmic time with a precision that surpasses all of the previous BAO surveys combined,” says Hee-Jong Seo, a professor at Ohio University and the co-leader of DESI’s BAO analysis. “We're very excited to learn how these new measurements will improve and alter our understanding of the cosmos. Humans have a timeless fascination with our universe, wanting to know both what it is made of and what will happen to it.”

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"Researchers used 450,000 quasars, the largest set ever collected for these Lyman-alpha forest measurements, to extend their BAO measurements all the way out to 11 billion years in the past. By the end of the survey, DESI plans to map 3 million quasars and 37 million galaxies.

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"DESI’s data will be used to complement future sky surveys such as the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope, and to prepare for a potential upgrade to DESI (DESI-II) that was recommended in a recent report by the US Particle Physics Project Prioritization Panel.

“'We are in the golden era of cosmology, with large-scale surveys ongoing and about to be started, and new techniques being developed to make the best use of these datasets,” says Arnaud de Mattia, a researcher with the French Alternative Energies and Atomic Energy Commission and co-leader of DESI’s group interpreting the cosmological data."

Comment: from our tiny cubbyhole in the universe human ingenuity is allowing us to explore all of it. This first year of results validates its usefulness. One instance where your taxes are reasonably used. Perhaps we will learn why God had to make it so big.