Could you imagine if pagers made a comeback? Sure, your smartphone would still be your notepad-flashlight-camera-personal assistant-MP3 player-wallet-social media browser. But imagine if pagers made it so easy to do that one important thing – pinging your friends and associates – that we all brought them back into our lives, or adopted them for the first time.

A redemption arc like this is happening in cosmology, the study of the history of our universe. The hero – rather than old technology – is an epoch of cosmological history called Big Bang Nucleosynthesis, or BBN.

Some cosmologists have thought that BBN is too old-school to be as good a tool for cosmology as other probes of the early universe. But BBN is the darling of my research program, where I use cosmology to learn more about particle physics. I have seen firsthand how recent results from this old cosmological epoch can guide new research about our universe.

The smartphone of cosmology

Cosmology’s superstar is the Cosmic Microwave Background, or CMB, which formed some 400,000 years after the Big Bang. It’s an all-sky mosaic of hot and cold patches of light, which appeared while electrons and nuclei combined into the first neutral atoms. Viewed from Earth, each hot or cold patch is small enough for the Moon to block out.

The CMB’s intricate patterning has been the subject of several intense observational campaigns, and for good reason. The key scientific model in cosmology has six major unknown quantities that researchers must measure to understand the universe. All of these quantities can be inferred with good measurements of the CMB.

But........

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