today’s scientist is an astrophysicist and cosmologist named katherine (katie) mack. mack works at the north carolina state university, and is best known for her research on dark matter and vacuum decay. the project of hers that i read about today was on how vacuum decay can give quantitative limits on the size of extra dimensions, which is a whole lot of words that i don’t understand, so buckle up for an explanation that is probably riddled with factual inaccuracies. essentially vacuum decay is the idea that the physical state that governs our universe right now, which we call the vacuum state, is not actually the natural vacuum state of the universe, and is thus pretty unstable. if something were to trigger the true vacuum state of the universe, it would very quickly engulf the whole universe (at the speed of light), and all the physical laws of the universe would dissolve. its the end of the world as we know it, and all that jazz. luckily, it would take a HUGE amount of energy for this to happen. slightly less luckily, it turns out that black holes are theorized to be able to generate the amount of energy it takes to trigger vacuum decay. that’s not very nice of black holes :( so why hasn’t it happened yet? why is the world still turning? that’s where mack’s research comes in. she and another scientist named robert mcnees published a paper in 2018 that used what we know about black holes and the energy they produce, combined with the knowledge that the world has in fact, not ended, to provide bounds on the size of extra dimensions on the universe. do i know how they did that? absolutely not. but it’s pretty cool! you can find the paper here (https://arxiv.org/abs/1809.05089), and a blog post that explains the premise of the paper and their research process here (https://astrokatie.blogspot.com/2018/09/extra-dimensions-black-holes-and-vacuum.html).
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you can learn more about katie mack on her website, astrokatie.com. last year, she published a book called “the end of everything (astrophysically speaking)” that discusses the heat death of the universe (fun!). bonus fun facts about mack: she was featured on an episode of the numberphile podcast (the high jumping cosmologist), and she also inspired a hozier song (no plan):
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"There's no plan, there's no hand on the rein//As Mack explained, there will be darkness again"
-Hozier
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(written 3/8/21)
