Returning guest and theoretical astrophysicist Ethan Siegel joins the podcast for an eye-opening and incredibly informative discussion that will lead you to question one of the most fundamental aspects of existence: how the universe began. Scientists and laypersons alike almost always point to the Big Bang theory, which posits that 13.8 billion years ago, all matter and energy that would give rise to the entire universe as we observe it today was condensed into a single dense point before starting to expand. In simple terms, the Big Bang theory was developed by extrapolating backward from what we observe today—an expanding universe that’s becoming less and less dense as wavelengths are elongating and objects are getting further apart.

So, what’s the problem with the Big Bang theory? If you were to ask Ethan Siegel that question, he would respond with some questions of his own: “Why is the universe the same temperature in all directions to one part in 30,000? Why is the universe perfectly spatially flat and balanced between expansion rate and all energy in the universe?

And why are there no high-energy relics left over from this early, hot, dense state if the temperatures got arbitrarily high?” According to Siegel and many other cosmologists who study the universe for a living, these are some of the puzzles that the widely accepted theory simply cannot account for.

He explains each of these questions in detail (what exactly they mean, how they’ve come to be asked, and why it’s important to answer them), and also what we need to do in order to move beyond this theory. What would a new theory capable of replacing the Big Bang theory even look like? And how would we go about determining if it gives correct predictions? Siegel discusses all of this, drawing from a seemingly endless wealth of information and making for a fascinating conversation that’ll take you out of this world.

Interested in diving deeper into this topic? Siegel is writing a whole book on it, which is set to be released during the first quarter of 2020 (and maybe even earlier). In the meantime, check out his blog, Starts With A Bang!