There is no physical law to prevent time travel - nothing in physics to say that it is not possible. So surely having a time machine is just a matter of ...time In Build Your Own Time Machine, Brian Clegg takes inspiration from his childhood heroes of Doctor Who and H. G. Wells to explain the nature of time. How do we understand it and why measure it the way we do? How did the theories of one man change the way it was perceived by the world? And why wouldn't H. G. Wells' time machine have worked? By clearly explaining the most famous of Einstein's theories, those of special and general relativity, Clegg applies them to the laws of time to show the real science of time travel and how possible it really is.