US-based entrepreneur Elon Musk is not a man who's lacking ambition in life. His company Space-X has already built rockets which compete with those used by NASA and the European Space Agency, and last year one of them became the first commercial spacecraft to visit the International Space Station. This week, however, it's another of his projects which has been in the news - a new kind of train which he thinks could transport people over the 350-miles between Los Angeles and San Francisco in only 35 minutes. Like this podcast? Please help us by supporting the Naked Scientists