I know this is slightly tangential to the topic but I hope it's close enough, as it's something I've wondered about for ages.
Like Larni, I understand that the recession of galaxies which we observe is not the result of them flying away "through" space, but the expansion of space between them. What I've never been able to figure out is why then the space within galaxies, indeed the very space within matter itself, is not expanding also. Matter occupies space, and even solid matter itself is mostly empty space so why does this not happen?
Or
does the space within matter also expand? At the very least, given that we observe universal expansion, I don't see how it could be happening at the same rate. If all of space - both within and without matter - were expanding at the same rate then we wouldn't notice any expansion at all, would we? That is, empty space would be expanding, but so too would matter, including us and any yardstick we might use, effectively cancelling out the expansion from our reference frame.
So maybe expansion within matter does occur but at a slower rate? Perhaps the warping of space caused by the presence of mass also retards its expansion?
Ferret brain activity increased just 20 percent when looking at Keanu Reeves compared to looking at darkness, the study found.
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