From the earliest stages of the hot Big Bang up through and including the present day, one cosmic picture is sufficient to describe practically everything we observe: the Lambda-Cold Dark Matter (ΛCDM) cosmological model. With a mix of dark matter, dark energy, normal matter, photons, and neutrinos, we can not only model, but can simulate the Universe from the earliest times and the smallest scales up through to the present and the full scale of the observable Universe.

In most cases, theory and observation match, and spectacularly so. But there are a few current points of tension: cosmological mysteries, that range from the expansion rate of the Universe to small-scale structure formation to the link between the pre-Big Bang Universe and our current dark-energy-caused accelerated expansion.

Where are we, how far have we come, and how far do we still have to go? I'm so pleased to welcome Dr. Santiago Casas, who specializes in many of the same sub-areas of cosmological physics I specialized in about a decade earlier, to our podcast. In this nearly 90-minute long episode, we cover a slew of fascinating topics in more depth and detail than normal, and I hope you enjoy the extra-deep dive into some of the weediest areas of modern cosmology!

This image shows a 15 million light-year long structure that arises from a detailed simulation of the cosmic web and how galaxies, galaxy clusters, and cosmic filaments form on the largest scales of all. Although this theoretical simulation, like many aspects of our standard cosmological models, largely agrees with our observations, there are points of tension that must not, despite the successes, be ignored. (Credit: Jeremy Blaizot, SPHINX project, https://sphinx.univ-lyon1.fr/)