Abstract: From astronomical observations, we know that the state of the early universe
(just after the Big Bang) was extremely simple. This is surely an important clue about how
the universe began, but what exactly is it trying to tell us? I will explain our new answer to
this question: we think it is telling us that the universe before the bang is a kind of mirror
image of the universe after the bang (they are related by "CPT symmetry"). (Based on
recent work with Kieran Finn and Neil Turok: https://arxiv.org/pdf/1803.08928.pdf)