The story of the most radical idea to have been proposed in physics since Einstein's relativity - the suggestion that the speed of light may not be constant - by the scientist who first proposed it.

The idea that the speed of light is a constant - at 186,000 miles per second - is one of the few scientific facts that almost everyone knows. That constant - c- also appears in the most famous of all scientific equations- e=mc2- Yet over the last few years, a small group of highly reputable young physicists have suggested that the central dogma of modern physics may not be an absolute truth - light may have moved faster in the earlier life of the universe, it may still be moving at different speeds elsewhere today.

In telling the story of this heresy, and its gradual journey towards acceptance, Joao Magueijo writes as one of the three central figures in the story, introducing the reader to modern cosmology, to the implications of VSL (variable speed of light) and to the world of physicists. The initial rejection of Magueijo's ideas is beginning to give way to a reluctant acceptance that the young men may have a point - only the next few years will tell the final fate of this 'dangerous' idea.