The question of the applicability of physical theories throughout the entire universe, especially when our observations are limited to a small fraction of it, is an important and challenging one. While we cannot directly observe the entire universe, scientists rely on several principles and methods to infer the universality of physical theories:
Copernican Principle: The Copernican principle is a foundational assumption in cosmology that states that there is nothing special or privileged about our location in the universe. It suggests that the laws of physics that we observe locally should be applicable on larger scales and in different regions of the universe unless there is compelling evidence to the contrary.
Uniformity of Natural Laws: One of the fundamental assumptions of science is that the laws of nature are universal and consistent throughout the universe. This assumption is based on the observation that physical laws have been found to apply consistently across a wide range of scales and regions that we have been able to observe.
Cosmic Microwave Background (CMB): The cosmic microwave background radiation is an important piece of evidence for the uniformity of the early universe. The CMB is the residual radiation from the Big Bang and is highly isotropic, meaning it appears nearly the same in all directions. This isotropy suggests a high degree of uniformity on large scales.
Cosmological Principle: The cosmological principle is another assumption in cosmology that states that, on large scales, the universe is homogeneous (uniform) and isotropic (looks the same in all directions). This principle forms the basis for the standard cosmological models, such as the Big Bang theory and the inflationary model.
It's worth noting that our understanding of the universe is continually evolving as new observations and data become available. Scientists conduct experiments, make observations, and develop theories to explain the observed phenomena. Over time, as our observational capabilities improve and more data is gathered, our understanding of the universe becomes more refined.
As for the possibility of obtaining a provable understanding of the entire universe, it is a challenging task due to several factors, including the vastness of the cosmos, the limitations of our technology and observational capabilities, and potential fundamental limits to human knowledge. While scientists strive to develop comprehensive models and theories that explain the universe, it is important to recognize the limits of our current understanding and the potential for future discoveries to reshape our understanding of the cosmos.