Oh boy, that is a great question and it is actually a much bigger question than you might realize. It turns out that the speed of light is one of the fundamental constants in the Universe. The fact that it does not change was discovered in the Michelson-Morley Experiment in the 1880s. Einstein read their results (years later) and eventually that became the basis of his Theory of Special Relativity (SR). What SR explores is the idea that not only is the speed of light constant - it is constant for all observers everywhere regardless of their frame of reference. A guy standing on a train traveling at high speed in the same direction as a ray of light would measure the speed of light and get the exact same result as someone standing motionless on the ground measuring the same ray of light. There have been lots of experiments testing this idea and the the data supports it. The three big implications: time does not pass at the same rate for everyone, the length of objects changes when they move at speeds approaching the speed of light, and mass does the same. I teach an entire course on Space, Time, and Motion and it is deep! However, it all comes from the speed of light not changing - that's just an inherent property of light.
@@padlnjones Good question. No. Light will always take the shortest path through space-time. Gravitational lenses only alter the path light takes, but light is always traveling the same speed along that curved path.
Excellent presentation!
why is the speed of light constant? why doesn't it slow down?
Oh boy, that is a great question and it is actually a much bigger question than you might realize. It turns out that the speed of light is one of the fundamental constants in the Universe. The fact that it does not change was discovered in the Michelson-Morley Experiment in the 1880s. Einstein read their results (years later) and eventually that became the basis of his Theory of Special Relativity (SR). What SR explores is the idea that not only is the speed of light constant - it is constant for all observers everywhere regardless of their frame of reference. A guy standing on a train traveling at high speed in the same direction as a ray of light would measure the speed of light and get the exact same result as someone standing motionless on the ground measuring the same ray of light. There have been lots of experiments testing this idea and the the data supports it. The three big implications: time does not pass at the same rate for everyone, the length of objects changes when they move at speeds approaching the speed of light, and mass does the same. I teach an entire course on Space, Time, and Motion and it is deep! However, it all comes from the speed of light not changing - that's just an inherent property of light.
@@astro151tccc thanks for the reply! Would a gravitational lens affect the speed of light?
@@padlnjones Good question. No. Light will always take the shortest path through space-time. Gravitational lenses only alter the path light takes, but light is always traveling the same speed along that curved path.