There is an interesting thought experiment that used to be popular around the turn of the century that goes something like this. If overnight, instantaneously, everything in the universe doubled in size or halved in size, take your pick, could we tell? It used to be thought that no we couldn't because all of our measurment devices as well as ourselves would have undergone this change as well. But we know now that we would recognize this change. The formulas for gravity as well as electromagnetism rely on distance. If these distances suddenly changed without the corresponding constants changing then we would notice something awry. If the distance of all the planets from the sun suddenly doubled or halved then they would no longer be traveling through space at the correct speed to maintain their orbits. Even taking into account that their speed would have doubled or halved would still end up with the wrong speed. The orbits would drastically change or decay alltogether. On an atomic level, the energy levels of electrons would change and the distance of subatomic particle from each other would change. The constants governing those would not allow the atoms to continue to exist. The forces simply work on too small of a distance to be effective if the distance suddenly changed.

Now I realize that we are not talking about a sudden change here but the same principle still apply. Also we can see millions and billions of years into the past with telescopes and things still look like we expect them to.

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"Eternal vigilance is the price of supremacy"
------------Mark Twain

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