Albert Einstein's theory of special relativity, developed in 1905, revolutionized our understanding of space, time, and the behavior of light. One of the fundamental principles of this theory is the constancy of the speed of light in a vacuum, often denoted by the symbol 'c'.
Einstein's statement regarding the constancy of the speed of light can be summarized by his postulate:
"The laws of physics are invariant under Lorentz transformations, and in particular, the speed of light in a vacuum is always measured to have the same value, regardless of the motion of the source or the observer."
This means that the speed of light in a vacuum, approximately 299,792,458 meters per second (or about 186,282 miles per second), is considered a universal constant. According to Einstein's theory, this speed is the maximum attainable speed in the universe, and nothing can travel faster than light.
Einstein's insight into the constancy of light speed led to a profound reshaping of our understanding of space and time, introducing concepts like time dilation and length contraction, where the passage of time and the length of objects change relative to an observer's motion. These ideas have been extensively tested and confirmed by numerous experiments and observations and have become foundational principles of modern physics.