This is another in a series of semi-regular pieces I do in which I try and set out what science and engineering can achieve and what it can’t do. In short, try and sort out science fact from science fantasy.

Last month, Elon Musk made a somewhat surprising announcement of a plan to build a 570 km Vactrain system from Los Angeles to San Francisco, for the bargain price of $ 6 billion. The media quickly reported it with great enthusiasm, however this has turned to gradual and increasing scepticism as they’ve inevitably asked engineers their opinion and they’ve generally taken the view that it borders on science fiction, if not science fantasy.

Certainly it has to be said, Elon Musk has a habit of proposing wacky ideas and proving his critics wrong. When he first launched an electric car business he was told that he was…

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