Nature. He drew inspiration from Einstein’s theory of relativity (now corroborated by a new mapping of dark matter) and the research conducted by Karl Schwarzschild, the astronomer who first resolved Einstein’s equations of general relativity. Schwarzschild’s findings indicated that there exists a maximum limit to the amount of mass that can inhabit a specific space, and that any physical object, when confined to that volume, will inevitably collapse into a black hole. This limit is referred to as the Schwarzschild radius. For instance, the Schwarzschild radius of the sun is approximately two miles. If one were to compress the sun into a sphere having a mere two-mile radius, it would transform into a black hole.
What Pathria comprehended is that the radius of the observable universe corresponds to the Schwarzschild radius of the universe’s total mass. This is an expectation one would usually reserve for a black hole.

