The Fine-Structure Constant The two fundamental assumptions about modern cosmology (the study of the origins of the universe) and astrophysics are homogeneity and universality.  The first means that matter is evenly spread out through the universe (if you average out over large enough scales), while the second means that the laws of physics are the same throughout the universe.  The principle of homogeneity has always seemed arbitrary to me, and unjustified; at the local level we find matter is quite clumpy, from … Continue reading →

Brace yourself, because this question is a lot more complex than it sounds.  We’re asking what the Earth’s speed is, but speed is always measured in relation to something and we usually use the Earth itself as the reference point.  When we say a car is traveling at 120 km/h, we mean that it travels 120 km across the Earth in one hour and ignore the fact that the Earth itself is moving.  In ordinary everyday situations, we simply assume … Continue reading →