[janalsncm]

Building out a supercomputer capable of breaking cryptography is exactly the kind of thing I expect governments to be working on now. It is referenced in the article, but the analogy to the Manhattan Project is clear.

Prior to 1940 it was known that clumping enough fissile material together could produce an explosion. There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.

I say this because there’s a meme that governments are cooking up exotic technologies behind closed doors which I personally tend to doubt.

This is almost perfect analogy to the MP though. We know exactly what could happen if we clumped enough qubits together. There are hard engineering challenges of actually doing so, and governments are pretty good at clumping dollars together when they want to.

[O3marchnative]

> There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.

FWIW, constructing a weapon with highly enriched uranium is, relatively, simple. At the time, the choice was made to use a gun-type weapon that shot a projectile of highly enriched uranium into a a "target" of highly enriched uranium. The scientists were so sure it would work that the design didn't necessitate a live test. This was "little boy", which was eventually dropped on Hiroshima.

Fat Man utilized plutonium which required an implosion to compress the fissile material that would set off the chain reaction. This is a much more complex undertaking, but it's much more efficient. Namely, you need much less fissile material, and more of that fissile material is able to participate in the chain reaction. This design is what allows for nuclear tipped missiles. The same principles can be applied to a U-235 based weapon as well.

The implosion based design is super interesting to read about. One memorable aspect is that the designers realized that applying a tamper of uranium (U-238) around the fissile material allows for significant improvement in yield. The chain reaction is exponential, so the few extra nanoseconds that the uranium keeps the fissile material together leads to significant increase in yield.

https://en.wikipedia.org/wiki/Little_Boy

https://en.wikipedia.org/wiki/Fat_Man

[Cider9986]

>I say this because there’s a meme that governments are cooking up exotic technologies behind closed doors which I personally tend to doubt.

Like when the government made XKeyscore[1]?

[1] https://en.wikipedia.org/wiki/XKeyscore

[tptacek]

What's exotic about XKeyScore?

[bitexploder]

The Manhattan project employed some significant % of all of America. A project of that scale will likely never happen again.

It was also about far more than the science. It was about industrializing the entire production process and creating industrial capability that simply did not exist before.

[janalsncm]

My comment was not limited to the U.S. government.

And the Manhattan Project cost $30B in today’s money. Compared with some of the numbers Congress has allocated recently, I’d call that a bargain.

[bitexploder]

I am skeptical you could do something of that scale for 30B today. That is just the dollar cost based on inflation. If you used CPI indexing probably hundreds of billions to a trillion dollars now.

[bastawhiz]

Does quantum computing need that though? We don't suddenly need a large, unique supply chain for these computers. We don't need to dig up the qubits and refine them. Testing doesn't blow up the computer.

[rcxdude]

The Manhattan project had a huge impact but it was not that big as far as efforts in the war went (they managed to hide the budget allocated to the project from most of congress, for example).

[brohee]

Yeah and some of the figures often quoted like consuming 14% of the electricity produced in the US are wrong, it was below 1%. https://ui.adsabs.harvard.edu/abs/2011APS..APRH13004R/abstra...

[bitexploder]

It was like 0.5% GDP. It wasn’t insane, but still, you are right.

It was very focused. What do we get out of the F-35 program? By comparison, it has eaten (projected total lifetime cost) 2 trillion dollars. It is 4.5% of the GDP. I had no idea. This is just a military and government contractor subsidy. What are we doing…

[fluoridation]

That's $ 2 trillion over the course of 20 years, so by your own numbers 0.23% of GDP.

[burnerRhodov2]

>governments are cooking up exotic technologies behind closed doors which I personally tend to doubt.

You don't use zero days immediately. You stockpile them for when the time is right. A quantum computer is the ultimate zero day.

[janalsncm]

Maybe I should be more clear. Quantum computers already exist. Nuclear fission was already known about prior to the manhattan project.

When I say they’re not hiding “exotic technologies” I’m referring to things that would at a minimum win a Nobel prize. Alien technologies like antigravity or faster than light travel that people sometimes talk about. I am not even talking about things like Stuxnet which was impressive but not revolutionary.