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For a specific example of something like this being important, remember the (very impressive) Watch for Rolling Rocks in 0.5 A presses video from a couple years ago? https://www.youtube.com/watch?v=kpk2tdsPh0A (For the uninitiated, this video presents a TAS of Super Mario 64 which beats the level Watch for Rolling Rocks without pressing the A button outside of keeping it held from entering the level.) It turns out that the route presented in the video actually fails console verification, since the crazy things he does trigger some annoying FPU crashes on console, but not on emulator. There is a happy end, though: a fixed route was published after this was discovered, and it passes console verification just fine (assuming the inputs dont desync over the 13 hour run)

Comment · 9 years ago

We had plenty of evidence that a deterministic primality testing algorithm exists, though. The Miller-Rabin test was known to be randomized polynomial time since the 70s, and assuming the generalized Riemann hypothesis it can be made deterministic polynomial.

And while there was some nuemerical evidence that the Polya conjecture was false, there really wasnt all that much evidence that the conjecture was false. The first counterexample is around 9 billion-- you could find it yourself if you wanted.

Comment · 9 years ago

Magnesium will only burn when heated to near its melting point of ~400 C, and thermite can only be set off at temperatures that would melt aluminum. Shipping them together is not an issue, unless the aluminum and iron oxide are freely dispersed in air.

Comment · 9 years ago

From a practical point of view, the only semi-common thermites that can actually explode are copper and silver. However, these thermites do not "detonate" as in the definition. They merely deflagrate extremely quickly, quickly enough to fool an observer but not in the true physical sense.

Comment · 9 years ago

Alternatively, the three components for gunpowder can be bought very cheaply and nigh-untraceably from hardware stores: potassium nitrate is stump remover, sulfur is used to reduce the pH of soils for gardening, and charcoal can be made from pyrolyzing wood in your backyard.

Comment · 9 years ago

Guns aren't a major industrial commodity chemical with hundreds if not thousands of valid non-violent civil uses, however...

Comment · 9 years ago

Potentially, but the neutralization of sulfuric acid releases a ton of heat (sometimes enough to crack glassware). By neutralizing the sulfuric acid without giving the heat anywhere to dissipate, you might just end up making things worse.

Also, as a small unrelated note, I doubt calcium carbonate would work well for neutralizing sulfuric acid-- the calcium sulfate formed is for the most part insoluble and stops the reaction.

Comment · 9 years ago

Yep, that server is indeed still at Stanford. It is now in the basement of the Huang building in the engineering quad.

Comment · 9 years ago

Well, pH refers to the concentration of protons in water solvent. Since pure sulfuric acid has no water (excluding that which is in equilibrium with sulfur trioxide), pH isn't really well defined for it. A better definition of acidity which does not have this problem is the Hammett acidity function. Sulfuric acid on this scale has an acidity of -12. (Note that this acidity score is not fully comparable to pH. However, with a difference so massive (a factor of one trillion times more acidic), this subtle difference ceases to be relevant.)

If you're asking about corrosivity, sulfuric acid gets its reputation because its also strongly dehydrating. Thus, it does wonderful things like rip the water out of your skin or char paper. I would hazard a guess that the water they've found in the paper does neither of those things.