I’ve heard talk about “suitcase” nuclear weapons, which someone could carry around and detonate anywhere. Is this possible? I’m not talking about whether someone could get hold of the proper components or be mad enough to pull it off. Rather, I always thought uranium and plutonium were really heavy and the amount needed for a bomb would be too much for one person to tote around. Gold, for example, is much heavier than most people think, certainly heavier than movies typically suggest, and plutonium has a much greater atomic weight and thus should be even heavier. In the end a suitcase-sized nuclear device in the back of a truck is just as awful as a totable one, but the image put forth in the media seems highly inaccurate to me. –Jonathan, via e-mail

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As so often, we need to define our terms. If you’re asking whether it’s possible to make a practical nuclear bomb small and light enough to carry around one-handed in a Teletubbies lunch box, the answer is probably not. However, if we expand the menu of mininuke delivery systems to include, say, a bowling-ball bag or, better yet, a garden-variety wheeled suitcase, I wouldn’t rule anything out. And if we conjure up what in my opinion is an entirely plausible scenario with a guy in a parking meter service uniform pulling an ash-can-sized two-wheeled coin vault through busy downtown streets at rush hour–well, I’ll make the usual disclaimer about the proper components not being easy to come by, etc. Strictly from the standpoint of design feasibility, though, piece of cake.

Not to worry, the experts say: The suitcase nuke threat is exaggerated–if any were actually out there, given the global surplus of fanatics, by now they’d surely have been used. Producing weapons-grade uranium and plutonium is a huge industrial operation requiring skills and equipment not easily concealed; even the craziest terrorist knows there are easier ways to make things go boom. Despite what alarmists would have you believe, you can’t just buy ten kilos of P-239 on the Tashkent black market and get a recipe from alt.nukes.made.simple. To which the pessimist, knowing that we’re inevitably headed toward a more nuke-dependent world as other energy sources dry up, can only reply: Not yet.