Tag Archives: Quantum mechanics

The Grandfather Paradox

26 May

Time-travel has long been a staple of genre films, novels and television shows serving as everything from a backdrop to teen-comedy hi-jinks in Back to Future to thoughtful contemplation in Ray Bradbury’s short story A Sound of Thunder. Perhaps the craziest of the time travel paradoxes was cooked up by Robert Heinlein in his classic short story All You Zombies. But in the ‘real world’ time travel is thought to be impossible. The world-famous late physicist Professor Sir Stephen Hawking famously once threw a party at the University of Cambridge which was, he said, “a welcome reception for future time travellers,” a tongue-in-cheek reference his 1992 conjecture that travel into the past is effectively an impossibility. The ‘grandfather paradox’ outlines both philosopher’s and physicist’s main objection to time-travel: the possible violation of causality. The term for this comes from the paradox’s common description: a person travels to the past and kills their own grandfather before the conception of their father or mother, which prevents the time traveller’s existence. Whilst time-travel itself remains in the realm of pure speculation, the possible results of the violation of the principle of causality and how nature may prevent them, are hotly debated topics beyond the realms of pulp-fiction with philosophers and physicists speculating on possible solutions.

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