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Top Comments: An Exhaustive Data Survey Yields Precise Conclusions about Our Universe [1]

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Date: 2022-10-27

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A series of papers recently published in the Astrophysical Journal provide the most precise constraints on amounts of matter (ordinary and dark) as well as dark energy. The analysis, called Pantheon+, collects and analyzes all supernova data in a statistically consistent way in order to reduce uncertainties and place constraints on theories used to explain the observed phenomena. The headline news is that the universe consists of 66.2 % dark energy, and 33.8 % total matter (ordinary matter and dark matter combined)—never mind that we still don’t know what either dark energy or dark matter actually are. The data consist of 1500 observed Type 1a supernovae throughout space and time, some occurring as far away as 10 billion light years (meaning that such supernovae occurred 10 billion years in the past). Thus, the analysis is capable of accounting for how the dynamics of the universe have changed over much of its lifetime. (The universe is about 13 billion years old according to current data.)

How is it possible to draw these kinds of conclusions from the data provided by supernova observation? Here’s a succinct explanation:

Pantheon+ is based on the largest dataset of its kind, comprising more than 1,500 stellar explosions called Type Ia supernovae. These bright blasts occur when white dwarf stars -- remnants of stars like our Sun -- accumulate too much mass and undergo a runaway thermonuclear reaction. Because Type Ia supernovae outshine entire galaxies, the stellar detonations can be glimpsed at distances exceeding 10 billion light years, or back through about three-quarters of the universe's total age. Given that the supernovae blaze with nearly uniform intrinsic brightnesses, scientists can use the explosions' apparent brightness, which diminishes with distance, along with redshift measurements as markers of time and space. That information, in turn, reveals how fast the universe expands during different epochs, which is then used to test theories of the fundamental components of the universe. The breakthrough discovery in 1998 of the universe's accelerating growth was thanks to a study of Type Ia supernovae in this manner. Scientists attribute the expansion to an invisible energy, therefore monikered dark energy, inherent to the fabric of the universe itself. Subsequent decades of work have continued to compile ever-larger datasets, revealing supernovae across an even wider range of space and time, and Pantheon+ has now brought them together into the most statistically robust analysis to date.

The Pantheon+ analysis has also provided additional precise measurements of the Hubble constant—the speed with which the universe is expanding—as well as a controversy called the “Hubble tension,” which refers to a conflict between astrophysicists who have measured the Hubble constant by two different methods and obtain two statistically distinct (though only slightly different) values. (The two different methods of observation are (1) observations of Type 1a supernovae, and (2) fitting the cosmic background radiation to current theories of the universe.) What the analysis revealed about the “tension” is that these two distinct values survive the analysis, and indeed, pass the 5-sigma test, the so-called gold standard for distinguishing a real phenomenon from noise that disappears when more observations are performed. So now theorists face the challenge of coming up with a theory of the cosmos that can explain why these two observations given different values for the Hubble constant, and then determining which one is right.

Nonetheless, the results of the analysis indicate that the current model for the evolution of the universe is the correct one, but so many questions remain unanswered.

Comments are below the fold.

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