A new model that uses the laws of quantum mechanics gets rid of the famous “grandfather” paradox surrounding time travel.

According to Einstein, space-time can curve back on itself, theoretically allowing travelers to double back and meet younger versions of themselves.

And now a team of physicists from the US and Austria says this situation can only be the case if there are physical constraints acting to protect the present from changes in the past.

The researchers say these constraints exist because of the weird laws of quantum mechanics. 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.