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Large Hadron Collider, Cern 

On 25 May, the North Koreans conducted an underground test of a low-yield nuclear "device", and the world trembled. I call it a "device" because I once made the mistake, when working at the Los Alamos National Lab in the US, of talking about the test explosion of a "nuclear bomb". I was quickly and firmly told that a "bomb" is something you drop out of a plane and a "weapon" is something with which you attack someone else. If you detonate it under your own territory it is a "device". 

Our experts on devices assure us that the North Koreans are only sort-of experts on devices and can still only make them large and crude and probably very difficult to transport, so we can relax a bit. But what if someone could make a whole new type of bomb the size of a milk bottle, which required no fiddly precision-timed explosives or big chunks of plutonium and which could blow up a city if you just left it alone until its batteries ran out? That is the terrifying prospect raised in Angels & Demons, the latest Dan Brown pseudo-religious schlockbuster to make it to the big screen. So should we be restocking the family air-raid shelter and practising duck-and-cover?

Given Hollywood's history of scientific precision, you probably won't be surprised to discover that the answer is no. The device depicted in A&D is a small amount (about one-eighth of a gram) of anti-matter harvested from the very first run of the Atlas experiment on the Large Hadron Collider (LHC) accelerator at Cern, near Geneva in Switzerland. The anti-matter is contained in a small vacuum flask by (presumably) magnetic and electric fields driven from a small battery. The scientists involved want to harvest the anti-matter because of its tremendous promise as an energy source, and through passionate conviction push ahead despite the danger that if the battery runs out, the anti-matter would drift away and contact the normal matter from which the bottle is made. When anti-matter meets matter they annihilate, releasing the rest of the energy of both; the annihilation of that much anti-matter would produce an explosion roughly one-third of the size of the one that destroyed Hiroshima. Of course, a gratuitously vicious Hollywood baddie shows up and steals the flask, which is then concealed in the Vatican as part of an elaborate plot against the Catholic Church. It all looks very slick and high-tech on the screen (right down to the shiny white lab coats that pretty much nobody at Cern actually wears), but could it really happen?

The short answer is: obviously not. The first reason is that unlike the makers of Hollywood blockbusters, Cern scientists understand elementary thermodynamics. Anti-matter does not occur freely in nature (which is in itself a major mystery, see my article in the March issue of Standpoint). You have to make it. By one of the most fundamental and experimentally well-tested laws of physics, the law of conservation of energy, you have to put as much energy into making it as you could possibly get back when you allow it to annihilate, so it can't be a power source. It wouldn't even work as a way to store energy, because the processes producing it are phenomenally inefficient, and only something like one part in 10 billion of the energy you start with ends up stored as anti-matter. It would even be unworkable as a weapon, if Cern scientists built weapons, which they most emphatically do not. 

It would be supernaturally expensive and difficult to produce anti-matter in any quantity and incredibly dangerous to handle (if you imagine a really good vacuum in the flask shown in A&D, the annihilation with the residual gas in the container would still produce enough radiation to kill anyone holding the flask in about five seconds). Therefore the motives of the physicists in the movie make no sense (an attribute they share with most of the rest of the characters in the movie, but that is a subject for a different review). 

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