"Fissile material is not useful for making nuclear weapons (of any more than the dirty bomb variety). So far, we seem to have converged on uranium and plutonium, and while at least uranium is relatively common in the Earth the processing and dredging required to get a useful amount of it, and then the refining to get the useful isotopes from that, is nontrivial."
I did not express myself well; this is exactly my point -- the barrier to (U-235 based) nuclear weapons is isotopic enrichment -- very difficult engineering -- and not so much access to natural uranium -- raw materials. So that, should difficult engineering become unexpectedly easy (as with singularity-type scenarios), then would be no major barrier to weapons, as access to uranium cannot possibly be blocked.
"Thank you for attaching some interesting facts. Allow me to do the same:"
Apologies for editing and expanding my comment after you read it -- it's a bad habit. ("Release early and release often"?)
"Engineering and fast computers are great and all, and will get you arbitrarily close to the physical limits--but we're there right now, and physics says you aren't getting a centrifuge with meaningful output in your garage."
Could you elaborate on this? I know the underground Fordow complex is about 6,000 m^2 [Forden] -- only about 1-2 orders of magnitude off, and it's built for human workers to access (not robots). And there's at least a factor-of-4 miniaturization in current laser technology (refs [APS][NYT]). I can't describe a design for a garage-sized enrichment plant, but I don't know that it's strictly precluded by physics or engineering constraints.
"1.6 to 16 times more efficient than first-generation gas centrifuges"
Even taking the SILEX claims at face value, that's compared with first-gen gas centrifuges--presumably those used in the early 20th century.
That's still not going to produce output in a form factor usable in a garage. Moreover, the argument I'd posited earlier doesn't hinge on the refinement--the sheer issues of scale of processing for ingress that much raw material are what gets in the way. Then you also have to dispose of the waste tailings.
"A single centrifuge might produce about 30 grams of HEU per year, about the equivalent of five Separative Work Unit (SWU). As as a general rule of thumb, a cascade of 850 to 1,000 centrifuges, each 1.5 meters long, operating continuously at 400 m/sec, would be able to produce about 20-25 kilograms of HEU in a year, enough for one weapon."
Even going with the factor of 20 speedup (overestimation from your provided article with the SILEX quote), we would expect to need 50 centrifuges, on the order of 1.5m long each--that's quite a lot. There's also the supporting equipment, power conditioners and piping and so forth.
In fact, powering the entire apparatus is also a big concern. The article I linked suggests a power draw on the order of several hundred thousand kilowatt-hours (compare with around six thousand for a normal home per year) per year. So, again, I don't see the garage fab making sense.
Oh, and during all that time?
You bet your ass the government is datamining your browsing history, purchase orders, and hobbies. I've ignored it so far in the discussion, but if you want to play the magical singularity wand I'll play the fascist police state card.
I did not express myself well; this is exactly my point -- the barrier to (U-235 based) nuclear weapons is isotopic enrichment -- very difficult engineering -- and not so much access to natural uranium -- raw materials. So that, should difficult engineering become unexpectedly easy (as with singularity-type scenarios), then would be no major barrier to weapons, as access to uranium cannot possibly be blocked.
"Thank you for attaching some interesting facts. Allow me to do the same:"
Apologies for editing and expanding my comment after you read it -- it's a bad habit. ("Release early and release often"?)
"Engineering and fast computers are great and all, and will get you arbitrarily close to the physical limits--but we're there right now, and physics says you aren't getting a centrifuge with meaningful output in your garage."
Could you elaborate on this? I know the underground Fordow complex is about 6,000 m^2 [Forden] -- only about 1-2 orders of magnitude off, and it's built for human workers to access (not robots). And there's at least a factor-of-4 miniaturization in current laser technology (refs [APS][NYT]). I can't describe a design for a garage-sized enrichment plant, but I don't know that it's strictly precluded by physics or engineering constraints.
[Forden] http://forden.armscontrolwonk.com/archive/2481/cut-and-cover