Has anyone found the source for that 20%? Here's a paper I found:
> Between 1848 and 1854, railroad investment, in these and in preceding years, contributed to 4.31% of GDP. Overall, the 1850s are the period in which railroad investment had the most substantial contribution to economic conditions, 2.93% of GDP, relative to 2.51% during the 1840s and 2.49% during the 1830s, driven by the much larger investment volumes during the period.
https://economics.wm.edu/wp/cwm_wp153.pdf
The first sentence isn't clear to me. Is 4.31 > 2.93 because the average was higher from 1848-1854 than from 1850-1859, or because the "preceding years" part means they lumped earlier investment into the former range so it's not actually an average? Regardless, we're nowhere near 20%.
I'm wondering if the claim was actually something like "total investment over x years was 20% of GDP for one year". For example, a paper about the UK says:
> At that time, £170 million was close to 20% of GDP, and most of it was spent in about four years.
https://www-users.cse.umn.edu/~odlyzko/doc/mania18.pdf
That would be more believable, but the comparison with AI spending in a single year would not be meaningful.