From Dr. Becky.

Our predictions of Big Bang Nucleosynthesis come from modelling how the strong and weak force behave in a rapidly expanding and cooling universe. So we know that when it’s still very hot get a lot of weak force interactions with neutrons merging with neutrinos to make protons and electrons, and also protons and neutrinos to make neutrons and positrons. After a certain temperature though these reactions stop and that freezes the ratio of protons to neutrons with 6 protons for every neutron. As the Universe cools some more its then possible for the strong force to bind neutrons and protons together to make atomic nuclei and you start to get a series of reactions occurring. WE know which reactions because we’ve recreated them in labs to study them in great detail and we know exactly how much energy is required for each one. But these reactions are a cycle of binding and decay, so the amount of each element you end up with ends up depending on the ratio of the amount of normal matter to particles of light, photons, since photons add more energy into the whole system. It was only recently in the 2000s that we were able to measure that ratio using our measurements of the cosmic microwave background, the leftover echo from the Big Bang. With that we can then get accurate predictions for how much of each of hydrogen, deuterium, helium and lithium are made in first few minutes of the universe’s lifetime, what’s known as the primordial universe. Matter that eventually goes on to make the first stars in the universe a few 100 million years later….

Watch the full video here: https://www.youtube.com/watch?v=5fZas1BFu1I

👩🏽‍💻 I’m Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about black holes, cosmology, dark matter, the early universe, the James Webb Space Telescope, and the biggest unsolved mysteries in astrophysics. I like to focus on how we know things, not just what we know. And especially, the things we still don’t know. If you’ve ever wondered about something in space and couldn’t find an answer online – you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.

http://drbecky.uk.com