If light and gravity were instantaneous, the universe would appear drastically different, with events observable simultaneously from various locations. The gravitational effects would also change immediately, meaning if the sun vanished, Earth would lose its orbit at once. Days would be longer, as we would see the sun earlier, eliminating delays in communication and travel at light speed. Special Relativity would lose significance, as cause and effect would occur simultaneously, and the limitations of radio communication would be alleviated. Overall, our understanding of the universe's history and structure would be fundamentally altered, with a bright night sky if the universe is infinite.
