> Would this be the reference frame of the center of gravity of the universe? This is a little confused, I'm afraid. The centre of gravity of any system doesn'

> Would this be the reference frame of the center of gravity of the universe? This is a little confused, I'm afraid. The centre of gravity of any system doesn't define a reference frame, it defines a location. For the universe, it doesn't even do that, since 'the observable universe' is a function of the observer: anyone anywhere can look around and observe some universe for 50 odd light years in each direction. Assuming homogeneity, the 'centre of gravity of the observable universe' is just a clumsy way of saying 'my current position'. The universe does sortof define a reference frame, and it's the frame in which the CMB (cosmic microwave background) is isotropic. In other words: if the CMB looks warmer to your left than your right, that means you're travelling left relative to the CMB frame. But it would be very surprising if the laws of physics depended on that. (Indeed, special relativity assumes the laws of physics are the same in every frame, and so far we have no evidence to contradict that).