ArmonSore wrote:I take the same stance here. It's not wrong to say that a feather is accelerating, but it's not right either. It's unprovable(which sounds to me to be a very godelian statement). So we needn't say that the feather is accelerating at all. For example, if we're in a spaceship that is accelerating upwards at 9.8 m/s^2, and we drop a feather, we can't tell the difference between doing the same experiment on earth. Which is to say, the feather does the same exact thing as it does in a vacuum near the earth's surface. So you can talk about either as being true, if you want to.
But this bothers me a little bit. My above argument seems to break down since we "know" that we're in a gravitational field, not free space. If it is impossible to tell the difference then how do we know this to be true? Does someone have an answer to this? Is there a completely consistent way to view our experience on earth as not being due to a gravitational field?
I believe the key here is that earth's gravitational field is non-uniform - it weakens with distance, and points toward the center of the earth. These variations in strength and vector differentiate it from what would be observed if Earth were accelerating (at least if we are able to correlate experiments conducted in different portions of the field), and indicate that it is in fact gravitational in nature.