There could be as many as 5^500 universes in the multiverse, according to string theory.1
That's five hundred zeroes, Ladies and Gentlemen. When I heard this I had to laugh out loud. Then I paused the video, stared into infinity and cackled insanely for a good quarter of an hour.
The number derives from the variations of possible ways of compacting the extra dimensions in string theory.2 The way the dimensions are compacted dictate the fundamental physical laws of that universe.
In other words, the laws of physics are determined by how 6 extra dimensions are knottet up. (yeah, I don't really, really get it either)
They can be knottet up a lot of different ways. Here's how many ways, here's five hundred zeroes:
(yeah, I get that those are not all viable - for human life - universes, but it's a big number, and I - we - like to go "ooh" over big numbers)
Regarding the low estimate, this slide mentions 10^1000 as well ![[Pasted image 20210309214538.png]] Source: https://www.d.umn.edu/~vvanchur/2013PHYS1021/vanchurin.pdf
It seems these possible universes are not all viable, if I understand it correctly, listening to [[Michio Kaku]] on [[into the impossible]] podcast 2021-05-02. Some don't even have internally consistent mathemathics, like you could prove 2+2=5 in some of them.