About the einstein quote:
Is this saying if you pick a rotating reference frame (the earth moon system say) ,then you consider it to be stationary and have everything else in the universe rotating then you have the appearance of the centrifugal force? If you pick a frame where the earth-moon system is rotating this force vanishes and is replaced by another force(the centripetal force). Essentially the change in how the force appears with respect to the frame is just due to the change in coordinate systems isn`t it? Both views are acceptable then within their own frame of reference. Or am i just confusing myself again...