John Hislop gave a fascinating talk about how Einstein's relativity has relevance to hams. We talk about the ether but does it exist? Do radio waves need a medium to travel through? The Michelson and Morley experiment proved the non-existence of the ether but Einstein realised that the result led to the fact that radio waves travel at a constant speed, whatever the speed of the measurer. On the International Space Station the astronauts are younger by milliseconds due to their huge speed. Is there gravity in the ISS? Of course there is, it just seems to disappear. This can be shown by the distortion of space time by planet Earth. This is relevant to satellites such as the GPS system which have to be corrected to take into account Einstein's general relativity.