To take a quick break from the CMB, I was recently posed a very good question about where elements came from. We haven’t quite gotten there yet…but I think I can give a quick overview. The first elements were formed just after protons and neutrons were formed (ya know after inflation when things cooled down enough to form real particles). There first elements where mostly hydrogen and some helium but according to what I’ve read everything up to lithium and beryllium where formed before stars where created. From there stars and galaxies were created from the hydrogen and helium and proceeded with fusion. This made a lot of the elements (including a decent amount of carbon near the cores of ‘normal’ stars…that eventually became the earth!), but normal star fusion stops after iron. Once you reach iron it’s not energetically favorable to fuse nuclei anymore (I forget why right now…but I might be able to find out if you really want to know). Then a star dies and it blows up…or does a number of other random violent things. (I’ve included a picture of some of these random things) And when heavy elements like iron fly into other smaller elements like helium they fuse and form the heaviest elements, including the radioactive ones. And this is how the elements we know and love today were formed. There are other elements and exotic particles that are formed in the atmosphere when cosmic rays hit it (I’ve done some experiments involving these they’re fun)…but that’s a topic for another day.
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