1. After the old Joe travels, there will be problems with memory, because the little Joe has established a relationship with it - the present and the future of the same time and space. That is to say, what little Joe does now will affect the old Joe's inherent memory.
2. The memory of old Joe is quantized. That is to say, old Joe encountered the uncertainty of memory. The reason why his memory is blurred is that what exists in his mind is a superposition of all possibilities (see Copenhagen explanation and Schrödinger's cat).
3. Before the young Joe makes a definite decision, the old Joe can only judge by "probability". The greater the possibility, the deeper the impression in his mind, and vice versa. This is in line with the theory of quantum mechanics. Although we cannot accurately predict the state of a single quantum, we can predict the state of multiple quantums through probability.
4. When little Joe makes a decision, it is equivalent to our observation of the quantum, then all the possible superposition states disappear, and Schrödinger's cat is dead or alive and there is a result. A certain possibility in old Joe's mind finally settled into a clear and clear memory.
5. The above is still what Ying Shuyan said, but it can be regarded as a kind of thinking. Although the film did not achieve the effect I expected, I think it is better to have a little fun of this kind of thinking.
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