According to our current understanding of physics, matter can have various speeds depending on the conditions and forces acting upon it. The concept of velocity, which combines both speed and direction, applies to matter in motion.
In classical physics, the velocity of matter is not limited to a specific value and can vary based on external influences such as applied forces or interactions with other objects. For example, when you throw a ball, its velocity depends on the initial force and subsequent influences like gravity and air resistance.
On the other hand, the speed of light in a vacuum is considered to be constant, as described by Einstein's theory of special relativity. According to this theory, the speed of light in a vacuum, denoted by the symbol "c," is a fundamental constant of nature and remains the same regardless of the relative motion between the source of light and the observer. This constancy of the speed of light is supported by a wide range of experimental evidence, including the Michelson-Morley experiment and subsequent experiments that have consistently shown that light travels at the same speed in all inertial reference frames.
The evidence for the constancy of the speed of light in a vacuum apart from Einstein's theory of relativity includes:
Experimental Confirmations: Numerous experiments conducted over the years have consistently measured the speed of light in a vacuum to be approximately 299,792,458 meters per second (or about 186,282 miles per second). These experimental results have been replicated and verified by different scientists and laboratories.
Electromagnetic Theory: The constancy of the speed of light is a consequence of Maxwell's equations, which describe the behavior of electromagnetic waves. These equations predict that electromagnetic waves, including light, travel at a fixed speed determined by the electric and magnetic properties of free space.
Cosmic Observations: The observation of distant astronomical phenomena provides additional evidence for the constancy of the speed of light. The fact that we can observe distant stars and galaxies is based on the assumption that light from those objects has traveled vast distances and reached us within a reasonable time frame.
It's important to note that the constancy of the speed of light in a vacuum is a fundamental postulate of modern physics, and it is central to our understanding of space, time, and the theory of relativity. Other aspects of physics, such as the behavior of matter and its velocities, are addressed by different theories and principles that are not directly related to the constancy of the speed of light.