“The speed of light is constant regardless of the observer's motion”

It's a common assumption that if you're running towards a light source, the light should appear to travel faster to you, or slower if you're running away. This intuition comes from our everyday experience with speeds: if you throw a ball forward from a moving train, its speed relative to the ground is the sum of your speed and the ball's speed. For centuries, scientists similarly expected light's speed to depend on the observer's motion through a hypothetical medium called the "luminiferous aether." This expectation formed a significant part of classical physics.

However, groundbreaking experiments in the late 19th century, most famously the Michelson-Morley experiment, failed to detect any evidence of this aether or any change in the speed of light due to Earth's motion. These perplexing results suggested that light behaved differently from anything else known. The inability to find a varying speed for light challenged the very foundations of how relative motion was understood and led to a profound shift in scientific thought.

The resolution to this puzzle arrived with Albert Einstein's theory of special relativity in 1905. Einstein boldly postulated that the speed of light in a vacuum is an absolute constant, approximately 299,792,458 meters per second, for all observers, regardless of their own motion or the motion of the light source. This seemingly simple postulate had revolutionary implications, fundamentally altering our understanding of space, time, mass, and energy, and has been consistently confirmed by countless experiments since.

The reason this confirmed truth often feels like a "myth" is precisely because it so dramatically contradicts our deeply ingrained, everyday intuition about relative speeds. Our experiences are limited to objects moving at speeds far, far less than the speed of light, where classical mechanics accurately describes motion. The constant speed of light is a unique property of the universe that only becomes apparent when considering extreme velocities, making it a concept that continues to challenge and fascinate.