316 | Niayesh Afshordi and Phil Halper

Hello everyone, welcome to the Mindscape Podcast. I'm your host, Sean Carroll. One of the downsides, there aren't that many, but one of the downsides of being a cosmologist is that sometimes when your fellow cosmologists try to explain the important ideas of your field to the rest of the world, they cut corners now and then, or they take shortcuts, use different jargon words in specific ways and not everything always becomes clear. A classic example of this is the phrase the Big Bang.

As I've said various times on Ask Me Anything and elsewhere in the podcast, the Big Bang phrase means different things to different people. To some people it means the event The moment in time when the universe was singular at the beginning, t equals zero, time equals zero, as predicted by classical general relativity. To other people, since classical general relativity is not correct and that Big Bang singularity is just a breakdown of our understanding, they use the phrase Big Bang to mean the hot, dense, rapidly expanding, super early phase that the universe was in. People who believe in inflationary cosmology will sometimes use the phrase Big Bang to mean whatever happened before inflation.

Other people who believe in inflationary cosmology will use the phrase Big Bang to mean what happened right after inflation when the universe reheats into matter and energy. Many people will use the Big Bang to be the whole model of the universe. the whole last 14 billion years plus whatever happens in the future. That's the Big Bang model. Okay?

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