INTRODUCTION
When exploring phenomena smaller than atoms, Quantum Mechanics becomes relevant, while the physics of massive objects is described by General Relativity theory. Special relativity theory comes into play when examining the behavior of the universe at extreme speeds. Speed forms the fundamental core of special relativity theory. However, what exactly is speed? In everyday life, speed is simply the ratio of distance to time. For instance, if a car covers a distance of 100 km in one hour, we can say that the car’s speed is 100 km/h. While this may seem straightforward, speed exhibits peculiar characteristics at very high values, particularly its unconventional impact on space and time. Speed is relative and can vary from one frame of reference to another. This implies that different frames of reference will measure different speeds of the same moving object. However, the speed of light does not conform to this pattern. It travels at a constant speed, meaning that the speed of light is the same for all observers, regardless of their motion. But why is the speed of light constant? Why is it always 300,000 km/s? How did scientists determine the speed of light? What groundbreaking discovery did Einstein make with the aid of understanding light’s exceptional feature? Why is it impossible for anything to surpass the speed of light? Let’s delve deeper into these questions!
HISTORY
The study of light has been a topic of discussion for approximately 2300 years, extending back to Ancient Greece when the philosopher Aristotle proposed that light had no speed and was instantaneous. This assertion endured for over 1500 years due to the difficulty of measuring the speed of light. Unlike measuring the distance a person walks, determining the speed of light is not a simple task. During the 1600s, the renowned scientist Galileo conducted experiments to measure the speed of light and believed that light had a definite speed. In an attempt to measure its speed, he and his assistant positioned themselves one mile apart on hilltops, each holding a shuttered lantern. Galileo flashed his lantern, and his assistant was instructed to open his lantern’s shutter as soon as he saw the light. However, they were unable to calculate the time it took for the light to travel the mile, as it was too short a distance to accurately measure the speed of light. In reality, it takes only 0.000005 seconds for light to reach a mile, a speed far too fast for human reflexes.
CALCULATING SPEED OF LIGHT BY JUPITER’S MOON IO
In 1670, the Danish astronomer Ole Roemer observed Jupiter‘s moon Io and noticed an anomaly in its orbital path. After two years of study, he discovered that Io consistently took 1.77 days to complete each orbit around Jupiter. However, he observed that the moon’s position did not always align with its expected location, sometimes appearing ahead of schedule and at other times behind. Roemer attributed these variations to the changing distance between Earth and Jupiter, concluding that the speed of light was finite. Through his calculations based on the locations of Earth and Jupiter, he estimated the speed of light to be approximately 200000 km/s. Subsequently, in 1728, the English astronomer James Bradley attempted to measure the speed of light using a different method. Instead of relying on Jupiter’s distance, he observed a distant star and noted its apparent position changes throughout the year. His investigations led him to calculate the speed of light to be approximately 301000 km/s, providing a close approximation to its actual value. Following these early efforts, a notable experiment in 1887 gained widespread attention. Michelson and Morley sought to demonstrate that light required a medium to propagate, akin to sound waves in air or ocean water. However, their experiment failed to support the existence of such a medium, revealing that light could travel through both a medium and a vacuum. Despite their unsuccessful attempt, the value they calculated for the speed of light, 299910 km/s, was accepted and used in scientific calculations for a considerable period.
MAXWELL’S CALCULATION
Then at a turning point in the history of science, the speed of light was precisely calculated with mathematical equations by Scottish mathematician and scientist Maxwell. He was just thinking differently. Electromagnetic waves always travel at the same speed, no matter if they are longer or shorter waves. They always travel at a constant speed. With his equations he found the speed of electromagnetic waves and velocity of light are exactly the same numbers, 300000 km/s. So, he finally concluded that if the speed of electromagnetic disturbances is equal to the speed of light, then light itself must be an electromagnetic wave. Now it’s clear that light is an electromagnetic wave which travels at a constant velocity. But what is constant? Imagine a car X traveling at the speed of 20 km/h. A stationary person near the roadside now measures that car’s speed, and he measures the value at exactly 20 km/h. Now a car called Y comes from the opposite direction at the speed of 20 km/h.
A person from car Y measures the speed of car X, and it shows 40 km/h. Velocity of car X + velocity of car Y is equal to 40 km/h. Now take another car called car Z which is moving away from car X at the speed of 10 km/h. If you measure the speed of car X from car Z, you will get the speed of car X as 10 km/h. Because 20 km/h minus 10 km/h is equal to 10 km/h. How can the speed of the same moving object give different rates of speeds for different observers? There is no need to wonder because speed is relative. But if you measure the speed of light, no matter how fast you move away from the light or no matter how fast you move towards the light it always shows the same speed 300,000 km/s. Let’s put an example of you traveling on a bike at the speed of 10 percent of our speed of light, which is 30000 km/s. So, the speed of light from your bike doesn’t equal 330,000 km/s. It always remains 300,000 km/s. Speed of light is constant and doesn’t depend on the speed of the light source. But there is no explanation for why this value is constant, it’s the fundamental law of nature. So, to maintain this constant velocity feature, space and time experience unusual features such as time dilation and length contraction. So, in this universe, everything is relative except the speed of light. With the core idea of constant velocity of light Einstein developed his special relativity theory which gave us a new way of understanding the nature of time.
SPECIAL RELATIVITY THEORY
We already know only light itself can travel at maximum speed in our universe. Can any object travel faster than the speed of light? To get the answer for this Let’s take a look at a relativistic mass equation.
Relativistic mass is nothing but how much mass increases when the object is in motion. Here rest mass means original mass of an object. V means velocity of the motion object. c means velocity of light. If an object moves 10 percent of the speed of light for example, its mass will only be 0.5 percent more than normal. But if it moves 90 percent of the speed of light, its mass will double. As an object reaches the speed of light, its mass rises precipitously. And once it tries to reach the speed of light its mass becomes infinite. If we look at Einstein’s mass energy equivalence equation with this infinite mass, the energy required to move this object also becomes infinite. Even our universe itself has finite energy; how can we get infinite energy to move the object? So, this is the reason that any massed thing in this universe can’t travel the speed of light. As we saw earlier, to maintain the constant nature of speed of light, time acts weirdly and the end of the result causes time dilation. Einstein is the only man who discovered this feature of the universe and he described this in his special relativity theory. Does this mean his theory tells us that time really slows down at an extreme speed? If it’s true, light itself actually doesn’t feel any time?