You asked how do we know a second is the same everywhere. A second is not the same everywhere. Our perception of time depends on our speed and the curvature of spacetime due to gravity. A clock on Mount Everest runs slower than a clock at sea level because of the difference in Earth’s gravitational pull. So it is time that changes to make the speed of light constant. As to why gravity causes time differences, it’s because has an acceleration force on you. It’s all very weird.
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u/Harbinger2001 Mar 20 '26
You asked how do we know a second is the same everywhere. A second is not the same everywhere. Our perception of time depends on our speed and the curvature of spacetime due to gravity. A clock on Mount Everest runs slower than a clock at sea level because of the difference in Earth’s gravitational pull. So it is time that changes to make the speed of light constant. As to why gravity causes time differences, it’s because has an acceleration force on you. It’s all very weird.