If you go into more precision, you can keep the original frame of reference and just compute perturbation around it.
As it is natural, you do not need to talk about it explicitly. So in the Solar system, the system itself has natural frame of reference and the statement about revolution of Earth is implicitly stated in this frame of reference. The thing is, that in this first approximation there is only the Sun in whole universe and it picks up special frame of reference - the one which is locked to it (and to distant stars which fixes rotation). So in first approximation, you have just static field in vacuum of perfectly spherical object, which leads to Schwarzschild geometry. This would mean that we indeed cannot speak about revolution of Earth around Sun without stating the reference frame.īut, in the case of Sun and Earth, the gravity is pretty weak and dominated by Sun. This means, that frame of reference is usually physically meaningful only in small neighborhood of your position and the further away you are and the stronger and wilder the gravitational field, the more the frame of reference becomes just some coordinate system without any inherent meaning.
In GR, the spacetime is curved and it happens that even revolving object might be inertial, which is more or less the case of objects in free fall, like Earths revolution around the Sun. In STR, circular motion is always accelerated and this frame of reference is distinguished from inertial one. It's true in inertial frames, so it's a valid thing to say.Īll inertial motion is relative in relativity, not just any motion. There is nothing wrong with saying that the Earth orbits around the sun, or that the sun is the center of the solar system. If two frames of reference disagree on something then one of them has to be wrong. You are reading thisĪccording to the theory of relativity there is no ultimate preferred frame of reference in our universe. Ultimately, I think the issue here starts from the beginning. Even in the non-inertial frame where we see the sun moving around us we would not say that everything is revolving around us. In any inertial frame you will see all the planets moving in orbits about the sun. But in order to explain why we see this type of motion, and to explain why we are at rest, we need to bring in pseudo-forces that only "exist" in non-inertial frames.ĭoes it mean heliocentrism is not fully correct? Of course moving to a frame of reference where the Earth is stationary we will observe the sun to be moving around us. Since the sun is so massive, this essentially constitutes of the Earth orbiting around the sun, as seen from any inertial frame of reference. Technically if you are only considering an Earth-Sun system, both bodies will orbit about their center of mass.
Why then do we say only earth revolves around the sun? It should also be correct to say that the sun is revolving around the earth according to frame of reference on earth. So, yes, the idea of the Sun at the centre is a big simplification, but it is a useful one that can help our understanding of the solar system, whereas the idea of the Earth at the centre is not very useful for that. If we try to use this model then when we look at other planets we find they have very strange paths around the Earth (looping back on themselves) whereas if we consider the Sun as the centre then we find the planets orbit around the Sun. But what we can say is that it is better than the simple model of the Sun rotating around the Earth. So, yes the simple model of the Earth rotating around the Sun is not very accurate. But then the rules get a lot more complicated and perhaps we don't need that for what we are trying to understand.
We can then add in the effect of the gravity of other planets, we can use relativity and even the effect of objects outside the solar system. We can improve it by adding Newton's law of gravity and stating that the Earth and Sun revolve around a common centre of gravity. The model that the Earth revolves around the Sun (and the Sun is fixed) is not very precise, but it is very simple. For example, we know that Newton's law of gravity is not as precise as Einstein's General Relativity, but it is still good enough for most everyday purposes and the differences weren't even noticed for centuries.
These models don't necessarily have to be perfect to be useful. Scientific theories can be thought of as models that take complex physical phenomena and seek to provide rules that explain the behaviour in simpler terms.