An Open Thread: a place for things foolishly April, and other assorted discussions.
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
Update: Tom McCabe has created a sub-Reddit to use for assorted discussions instead of relying on open threads. Go there for the sub-Reddit and discussion about it, and go here to vote on the idea.
Relavtivity says that there are no observable consequences from imposing a uniform gravitational field on the entire universe. So, imagine that we turn on a uniform gravitational field that exactly cancels the gravitational field of the planet at your feet. Then you can use an inertial (non accelerating) frame centered at your feet. The planet, due to the uniform field, accelerates towards you. Your head experiences the gravitational pull of the planet, plus the uniform field. At the location of your head the uniform field is slightly stronger than is needed to cancel the planet's gravity, so your head feels a slight pull in the opposite direction, away from your feet.
An important principle here is that you have to apply the same transformation that lets you say your feet are at rest to the rest of the universe.