Two Views on Gravity Part 2: Geometry

Sometimes analogies just feel right. For instance, “as hard to find as a needle in a hay stack” is often a good way to describe trying to find a needed quote in a half-remembered book. The mental image and the actual task just fit. In physics, I sometimes feel like the hardest part is finding [...]

Gravity Probe B orbits earth, captured in its gravity well
Sometimes analogies just feel right. For instance, “as hard to find as a needle in a hay stack” is often a good way to describe trying to find a needed quote in a half-remembered book. The mental image and the actual task just fit. In physics, I sometimes feel like the hardest part is finding the perfect analogy that will make it possible for everyone in the class to visualize the concept I’m trying to explain. In the case of gravity, Einstein kindly provided the needed analogy. He said the way we need to think of gravity is as a divot in the 4-dimensional space-time reality, where orbiting objects simply roll around the inside of the well, like bicylcists racing around the sides of a velodrome. Ok, so maybe that analogy is a bit ...