Here on Earth, we are used to laws that shift according to the unique customs and demands of various regions. You can turn right on a red light while driving in most places, for instance, but not in New York City, where traffic rules are stricter to accommodate busy roads.
The physical laws of the universe, in contrast, do not tolerate any localized deviations of this sort—or so our best theory goes. Scientists operate under the assumption that there are universal laws of physics that affect matter the same way everywhere, from our own solar neighborhood to galaxies billions of light years away. In other words, while there are obviously variations in the density and distributions of matter across space, scientists assume that the universe is statistically homogenous at large scales of hundreds of millions of light years, because the actual hard wiring of the universe is equally applied everywhere.
This notion of universal laws, known as the cosmological principle, has produced centuries of theory and has so far been borne out by astronomical observations. The model of an isotropic universe helps explain crucial phenomena such as the homogeneity of the cosmic microwave background, the oldest light in the universe, as well as the apparent expansion of the universe at a uniform rate.
“The cosmological principle is, in more tangible terms: Is the universe playing fair with us?” explained Robert Caldwell, a professor of physics and astronomy at Dartmouth College, in a call. “Are the laws of physics the same everywhere? Or is there a preferred location in the universe?”
While most evidence suggests the universe is playing fair, there are also many cosmic wildcards that seem to clash with the cosmological principle. Just within the past few months, for instance, two teams of physicists published completely different observations of anomalies in the universe that hint at potential variations in fundamental laws and forces.
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