Time Travel

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It is possible to affect the past, but not to change it.

The Novikov Principle does not allow a time traveller to change the past in any way, but it does allow them to affect past events in a way that produces no inconsistencies — for example, a time traveller could rescue people from a disaster, and replace them with realistic corpses seconds before it occurs.

— Wikipedia

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2009.07.17 Friday ACHK