I'm having trouble resolving the contradiction between theories of the Cosmic Microwave Background, and Special Relativity. Einstein denied the existence of any absolute standard of rest. As einstein-online.info paraphrases: "In the real world, there exists no such state of absolute rest. That's the content of the so-called principle of relativity, which is one of the basic postulates of the special theory of relativity." However, there now seems to be the concept of "at rest" with regard to the CMB. This shows that there does exist an experiment that different observers can perform which will give variable results based on their inertial motion. Why doesn't this undermine relativity, which is itself the foundation of most of our cosmological models?