The speed of light, denoted by the symbol c, is a fundamental constant in physics that represents the maximum speed at which all matter and information in the universe can travel.
The speed of light is typically measured using experiments involving lasers and mirrors, or through astronomical observations. In 1983, the speed of light was officially defined as exactly 299,792,458 meters per second in a vacuum by the International System of Units (SI).
According to Einstein's theory of special relativity, the speed of light in a vacuum is constant and is not affected by the relative motion of the source or observer. This means that the speed of light is the same for all observers, regardless of their relative motion.
While the speed of light is constant in a vacuum, it can be affected by the medium through which it travels. For example, light travels slower in water than in air. Additionally, the speed of light can also be affected by the curvature of space-time in the presence of massive objects.
According to our current understanding of physics, nothing can travel faster than the speed of light. This is because as an object approaches the speed of light, its mass increases and it requires an infinite amount of energy to accelerate it to the speed of light. This is known as the cosmic speed limit and is a fundamental principle in our understanding of the universe.