The Speed of Light

In 1905, Albert Einstein took the first crack at the Newtonian foundational physics. In his paper on special relativity, Albert Einstein postulated that the speed of light, c, is constant in all inertial reference frames. Assume that a person on a bicycle is holding a flashlight and moving at a constant speed relative to someone who is standing still on the sidewalk. Then, both people measure the speed of light, c, to be approximately 300,000 km/s. Relative to the person standing still on the sidewalk, the light coming out the flashlight still moves at 300,000 km/s, not 300,000 km/s plus the velocity of the person holding a flashlight while cycling. This turns out to be extremely important consequences. By keeping the speed of light the same, the only two variables that can change are the distance and time that is traveled. The longer the distance, the longer the time it takes for the light to traverse the distance. The shorter the distance, the shorter the time it takes for light to travel. If there is any distance between you, the observer, and the object, then it will take some time for the immediately emitted light to travel from the object and in to your eyes. Essentially, there is a time lag between the observer and what you observe. Therefore, the light that reaches you is in fact light that was emitted some time ago. Therefore, you’re actually peering into the past! By observing different types of light that is radiated in the universe, we can learn about the origins of the universe. The oldest light that is observed is Cosmic Microwave Background (CMB).

Credits: Wikipedia

The CMB, as it turns out, is a relic of the early universe. The CMB tells us how much baryonic matter and dark matter there was in the early universe. The CMB also helps us model how stars and galaxies formed, a crucial step in understanding our cosmic address.

The constancy of the speed of light has enabled us to peer back into the past to observe, analyze, and theorize about our ever elusive origins. Perhaps in another blog I might discuss the philosophical implications of light. But as it stands, a universal constant speed and its ability to shed light on the birth of our galaxy is mind-blowing enough for one blog post.