Hi all, I was watching some online video lectures from the Quantum to Cosmos festival, where they discussed the expansion of the universe and the problems this brings in physics. Problems like the need of dark matter and what the mysterious force is that accelerates this expansion. I've been pondering about this some more, I'm not a scientist but just like to think about such things. As I was watching this lecture today I suddenly had a crazy idea. Actually it's so simple I can not imagine I would be the first one to come up with this and since I could not find any other references to this idea it may be just too silly to even consider. I think on this forum a lot of people know much more about this so I will just throw in my idea and will see how silly this would actually be :) So, here's my thought: What if the universe is not really expanding, but in stead the galaxies are decreasing in size. Well, not just their size but their space-time. This would make it appear from our point of view that the universe is expanding, while we are actually shrinking. This is simple relativity. It this would be true we would not have to wonder about the mysterious force that expands the universe and maybe dark matter could be questioned (more). Actually this question comes down to "do we really know for sure if the universe is expanding?" (and why). If we don't know this for sure my idea may not be so crazy after all. I'd love to hear your thoughts about this.