Since the time of the ancient Greeks, the pursuit of a theory of the universe has remained an unfinished task, even as humanity has entered the twenty-first century. Few know that, to lead this development, Einstein defined a scientific task called Einstein’s cosmos and offered a methodical approach called principle theory. Indeed, it is astounding in this scientific golden era that this is not more well known. We have previously promoted some of Einstein’s work in this area. Herein, as an extension of our previous literature, we apply principle theory to develop a theoretical framework of our oscillating universe and use this framework to examine research practices concerning the universe, elementary particle physics, and cosmology critically. This paper has two goals: first, to promote Einstein’s cosmos and principle theory, to restore his scientific thoughts to their deserved place in the precious pursuit of a final theory of the universe; second, to invite elementary particle physicists and cosmologists to pursue Einstein’s cosmos collectively under this theoretical framework of the oscillating universe.