Once robots can do physical jobs, how quickly could they become a significant part of the work force?
Here's a couple of fermi estimates, showing (among other things) that converting car factories might be able to produce 1 billion robots per year in under 5 years.
Nothing too new here if you've been following Carl Shulman for years, but I thought it could be useful to have a reference article. Please let me know about corrections or other ways to improve the estimates.
My impression is that software has been the bottleneck here. Building a hand as dextrous as the human hand is difficult but doable (and has probably already been done, though only in very expensive prototypes); having the software to actually use that hand intelligently and deftly as a human would has not yet been done. But I'm not an expert. Power supply is different -- humans can work all day on a few Big Macs, whereas robots will need to be charged, possibly charged frequently or even plugged in constantly. But that doesn't seem like a significant obstacle.
Re: WW2 vs. modern: yeah idk. I don't think the modern gap between cars and humanoid robots is that big. Tesla is making Optimus after all. Batteries, electronics, chips, electric motors, sensors... seems like the basic components are the same. And seems like the necessary tolerances are pretty similar; it's not like you need a clean room to make one but not the other, and it's not like you need hyperstrong-hyperlight exotic materials for one but not the other. In fact I can think of one very important, very expensive piece of equipment (the gigapress) that you need for cars but not for humanoid robots.
All of the above is for 'minimum viable humanoid robots' e.g. robots that can replace factory and construction workers. They might need to be plugged in to the wall often, they might wear out after a year, they might need to do some kinds of manipulations 2x slower due to having fatter fingers or something. But they don't need to e.g. be capable of hiking for 48 hours in the wilderness and fording rivers all on the energy provided by a Big Mac. Nor do they need to be as strong-yet-lightweight as a human.