It looks like quantum physics eliminates that paradox beloved of some sci-fi writers; where someone erases themselves or someone they love by changing their past in some way. "Quantum behaviour is governed by probabilities. Before something has actually been observed, there are a number of possibilities regarding its state. But once its state has been measured those possibilities shrink to one - uncertainty is eliminated. So, if you know the present, you cannot change it. If, for example, you know your father is alive today, the laws of the quantum universe state that there is no possibility of him being killed in the past. It is as if, in some strange way, the present takes account of all the possible routes back into the past and, because your father is certainly alive, none of the routes back can possibly lead to his death."
So far so good. The article says, "In other words, you can pop back in time and have a look around, but you cannot do anything that will alter the present you left behind." But is that really likely? Surely just by breathing and leaving behind microbes we would be changing things? So, does the observer's paradox rule time travel out?
BBC NEWS | Science/Nature | New model 'permits time travel':
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