And if humanity were to last longer than we have supposed, long enough to see the laws evolve before its eyes? Or even if it came to acquire instruments delicate enough that this variation, slow as it is, becomes sensitive after a few generations? It would not then be by induction, by inference, that we would know the changes of the laws, it would be by direct observation. Would not the previous reasonings lose all value? The memoirs in which the experiences of our predecessors are reported would still be vestiges of the past, which would only give us an indirect knowledge of the past. The old documents are for the historian what the fossils are for the geologist, and the works of the old scientists would be only old documents. They would only inform us of the thought of these scholars in so far as the old men would be like us. If the laws of the world were to change, all parts of the universe would suffer the consequences and humanity could not escape; admitting that it could survive in a new environment, it would have to change to adapt to it. And then the language of the old men would become incomprehensible to us; the words they used would no longer make sense to us or would have a different sense than for them. Is it not already what happens after a few centuries, although the laws of physics have remained unchangeable?
And then we always fall back into the same dilemma: either the documents of the past will have remained perfectly clear to us, and it will be then that the world has remained the same, and they will not be able to teach us anything else; or they will become indecipherable enigmas, and they will not be able to teach us anything at all, not even that the laws have evolved; we know enough that it is not necessary for them to be for us a dead letter.
Besides, the old men, like ourselves, have never had natural laws but fragmentary knowledge. We would always find a way to connect these two fragments even if they had remained intact; even more so if we have nothing left of the older one than a weakened, uncertain and half-effaced image.