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BusyBeaver(6) Is Quite Large

(scottaaronson.blog)
271 points bdr | 1 comments | 28 Jun 25 16:53 UTC | HN request time: 0s | source
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Scarblac ◴[28 Jun 25 17:29 UTC] No.44406478[source]▶
It boggles my mind that a number (an uncomputable number, granted) like BB(748) can be "independent of ZFC". It feels like a category error or something.
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Straw ◴[28 Jun 25 17:39 UTC] No.44406590[source]▶
The category error is in thinking that BB(748) is in fact, a number. It's merely a mathematical concept.
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1. Scarblac ◴[28 Jun 25 18:47 UTC] No.44407096[source]▶
There is a finite number of Turing machines of size 748. The number of them that eventually halt is thus also finite, and BB(748) is the highest number of steps in the finite list of how many steps each took to halt. It has to be a number.

We just can't prove which number it is, we don't know which of the machines halt.