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The paradox suggested by Piled Higher and Deeper (21 November), that travelling forward in time to peek at the results of your research would mean the research was never undertaken, is akin to the ¡°grandfather paradox¡±: what happens if you go back in time and kill your grandfather before he reproduces?

Some theories suggest the universe would ¡°protect¡± itself from this paradox by creating a black hole at the physical location of the time traveller. Like the positive feedback in a screeching microphone, backwards time travel would create a loop as the universe moves forward in time, feeding evermore energy into the time slip until the energy, equivalent to mass, builds up and pinches off the time travel locale into a black hole. Grandad is safe.

Perhaps the emergence of black holes in response to time travel paradoxes explains where all the research money has gone.

Hillary J. Shaw
Director and senior research consultant
Shaw Food Solutions
Newport, Shropshire