The History of Dark Energy

Cosmology used to be a field where there wasn't much data. Now it's a data-rich field where we can do cross checks. We have evidence that the universe underwent this accelerated expansion when it was very, very young. The best explanation for that is called early dark energy. And it inserts another period of accelerated expansion when the universe is about 100,000 years old. This comes to another interesting puzzle that the web, I hope, will shed light on.