Final answer:
Light has a finite speed due to the principles of Einstein's theory of special relativity, which establishes that nothing with mass can reach the speed of light due to requiring infinite energy. Consequently, the speed of light is the universal speed limit, and measurements of time and distance become relative at velocities approaching the speed of light.
Step-by-step explanation:
Even though all motion is relative, light has a finite speed because of the principles established in Albert Einstein's theory of special relativity. This important theory refines our understanding of motion, particularly at speeds close to the speed of light (denoted as c). According to Einstein, no object with mass can attain the speed of light because doing so would require an infinite amount of energy. As a result, the speed of light is the ultimate speed limit in the universe, a fundamental principle that has been confirmed through numerous experiments. Einstein's theory resolved the contradiction between the classical Newtonian mechanics and Maxwell's equations of electromagnetism, which predict that the speed of light in a vacuum is constant and does not vary based on the relative motion of the observer or the source.
Special relativity introduced revolutionary changes to our understanding of space and time. It showed that the measurements of time and length are relative and dependent on the velocity of the observer, which is consistent with the observation that the speed of light is the same for all observers, no matter their motion relative to the light source. Einstein's postulates lead to fascinating and non-intuitive conclusions about the nature of our universe, such as time dilation, length contraction, and the equivalence of mass and energy as expressed in his famous equation E=mc^2.
An interesting implication of Einstein's theory is that, should you travel at nearly the speed of light and attempt to throw a ball at c, an observer at rest would still not see the ball exceeding the speed of light in any circumstance, ensuring that the speed of light remains the fixed maximum in any frame of reference. This finding aligns perfectly with the two fundamental postulates of special relativity.