Cosmology: what the CMB reveals (Introduction)

by David Turell , Tuesday, January 28, 2020, 18:46 (1760 days ago) @ David Turell

It includes estimates of dark matter and dark energy:

https://www.quantamagazine.org/how-the-cosmic-microwave-background-reveals-the-universe...

"The team announced their first results in February 2003. Their map of the “cosmic microwave background” (CMB), which they refined in subsequent years, indicated that the familiar matter of planets, gas and stars makes up just 4.6% of the cosmos, while unseen dark matter comprises 24%. The remaining 71.4% of the cosmic pie chart had to be dark energy, which is thought to infuse the fabric of space itself. The numbers changed only a little when WMAP’s successor, the Planck satellite, took an even sharper image of the CMB 10 years later.

***

"No one has identified dark matter particles, yet the CMB reveals the large-scale behavior of the elusive substance. Ali-Haïmoud likens the situation to premodern scientists understanding buoyancy and pressure even without knowing that the chemical formula for water was H2O. Any attempt to explain away the apparent influence of dark matter, such as by tweaking the laws of gravity, will have to match the particular pulsations of the primordial fluid. No model has yet risen to the challenge.

"Dark energy, meanwhile, played a negligible role in the universe’s youth. Its presence can be inferred from the CMB’s indication that the universe is flat today. The measured quantities of dark and visible matter just don’t have the muscle to flatten space. But add 71.4% dark energy to the modern universe, and everything balances.

"This picture isn’t perfect, as recent astronomical observations have suggested that today’s universe is expanding at a faster clip than the CMB recipe implies it should be. But WMAP and Planck data have set a high bar for theorists seeking alternative, non-dark explanations for the motions of stars and galaxies. “Now that we have these detailed maps,” Dodelson said, “the CMB by itself is pretty damn good at getting almost everything.'”

Comment: The value of the CMB continues to help current theories.