Dr. Katie Mack and I talk about big bang stuff.    the question is from bob: "Hello again Ben. I've found and listened to the QB episodes. Thanks for the help with locating them. Since you seem to have ready access to a cosmologist, I'd like to offer for QB a trio of related cosmological questions that have bugged me for some time. 1. How do we know that all the matter in the universe came from the big bang? 2. How do we know that the big bang did not expand into an existing precursor universe? (It seems plausible to me that this may be the case but we have no way to know because the hyperinflation immediately after the big bang and accelerating expansion due to dark energy will permanently keep us outside of the light cone of any event in this hypothetical precursor universe. I'm not fond of unfalsifiable theories...)"