Since the advent of relativity theory in the early 1900s, the laws of physics have been written in [[covariance|covariant]] equations, meaning that they are equally valid in any frame. Heliocentric and geocentric theories are both used today, depending on which allows more convenient calculations. | Since the advent of relativity theory in the early 1900s, the laws of physics have been written in [[covariance|covariant]] equations, meaning that they are equally valid in any frame. Heliocentric and geocentric theories are both used today, depending on which allows more convenient calculations. |