Does motion break existing symmetries? Observations suggest that the observable universe is spatially flat and, on the largest “cosmic”scale, highly symmetric. On this scale it is modeled as always isotropic and homogeneous. In this situation Birkhoff’s theorem tells us that “exterior” matter, i.e. matter in the universe at large, exerts no gravitational influence on local masses. (In a spherically symmetric Newtonian universe this is also true, because there is no gravitational field inside any uniform spherical shell of matter, due to that shell). Now the Cosmic Microwave Background (CMB) displays tiny deviations from spherical symmetry, the most prominent of which is its dipole character. This is interpreted as showing that in a local frame of reference at rest with respect to the CMB (a CMB frame) we happen to be moving with a velocity of about 600 km per second. Can the Relativists in this forum tell me if such motion breaks the assumed perfect symmetry of the universe we observe, so that its symmetry takes on a (very slightly) uniaxial character, with concomitant observed density enhancements (due to observed Lorentz contractions) fore and aft, as it were, along the axis of motion? And is not Birkhoff’s theorem (very slightly) perturbed in this case? In the case of uniform motion, does it still preserve its essential conclusion (since the Lorentz contraction is the same fore and aft)? If the answers to these questions are “yes”, then the kinematic nature of uniform motion (Newtons first law) in our observed universe seems natural. But what then of more complex motions, for instance accelerations or rotations, which must also break the high symmetry of our observed universe and perturb Birkhoff’s theorem in more complex (higher multipolar) ways? Finally, might such symmetry breaking have a connection with Mach’s principle and the origin of inertia from the gravitational influence of remote masses, if Birkhoff's theorem is perturbed and its conclusion modified in such cases?