It might sound like the sort of thing Arthur C Clarke or HG Wells might have dreamt up, but the "Hyperloop" took another small step towards implementation with its first public test in the Nevada desert.

The proposed system would fire pods of people along a low pressure tunnel, floating on a cushion of air at an impressive speed of 1,200 km/h. The propulsion system is based on a linear accelerator, such as those used in rollercoasters.

So far, so good, but are there technological and indeed financial hurdles that still need to be overcome? For a vacuum tube over a significant length, although the thermal expansion in percentage terms is small, in absolute terms this may pose major problems (it's not like a vacuum tube can incorporate gaps or overlaps to accommodate the expansion). For example, over a length of 600km, thermal expansion of about 300 metres could be expected (i.e. the size of a station!).

Financially, the initial proposal stated that the necessary viaducts could be built at a fraction of the cost of a conventional railway. Even to the uninformed this would seem to be rather ambitious.

However, sometimes (like a lot of ground breaking science and technology) it's good just to pursue the impossible and see where it takes us!