The Speed of Light
Original post date: November 08, 2018
It is the astronomical speed limit for any object in this universe. Nothing can go faster than light. This might seem unremarkable at first, but in reality, it shapes our universe itself.
The speed of light was first calculated by Olaus Roemer, a Danish scientist who used observations of Jupiter's moons and their eclipses in 1676. His results were close, but not accurate. What is worth noting is that the speed of light is always a constant, even for objects in motion.
Consider a bullet fired from a gun. If you have a vehicle faster than the bullet, you can chase it down before it reaches its destination. Now take a torch and switch it on. No matter how fast you travel to catch that first ray of light, you will never reach it. Why? No one really knows why, in a practical sense. It is a universal truth, and everything in this universe is bound by it. But there are reasons that satisfy our curiosity.
To understand the concept of speed properly, we need to define what speed actually is. Speed is relative. You cannot define the speed of an object without a frame of reference. When I say I am at rest, I mean that with respect to a stationary object nearby, I am not moving. Simple enough. But things get complicated once you realize that Earth is spinning, Earth is revolving around the Sun, the Sun is moving through the Milky Way, and the Milky Way itself is moving through the universe. Nothing in this universe is truly at rest. Measuring the speed of an object relative to something actually stationary is impossible.
Light has a very special property here. According to Einstein, regardless of the observer's own motion, the speed of light is always the same constant: 299,792,458 m/s. Whether you measure it standing still or travelling on a jet, the result does not change. This is precisely why you can never catch or overtake light. You might reach 99.9% of the speed of light through extraordinary means, but that remaining 0.1% is permanently out of reach.
What happens at 99.9% of the speed of light? The laws of classical physics start to break down. According to special relativity, objects travelling at high speeds become heavier. As speed approaches that of light, mass increases sharply. To accelerate a heavier object further requires more energy, and since the mass growth has no upper limit, the energy required approaches infinity. That is not physically achievable.
Time also behaves differently at such speeds. In fact, time does not run the same for any object in motion. Some physicists go as far as claiming that time does not truly exist. If you have seen Nolan's Interstellar, you already have an intuition for time dilation.
Here is a thought experiment. Twin A stays on Earth with a clock synchronized to his brother's. Twin B boards a spaceship travelling at the speed of light. When they say goodbye, both are 10 years old. After 10 years on B's clock, he turns around and comes home. When he arrives, his brother is 95 and in a wheelchair. The clocks are no longer in sync. This is not science fiction. Scientists have confirmed this effect using atomic clocks on jet planes. In a future where high-speed travel is possible, staying younger for longer may not be so far-fetched.
Time dilation occurs because the speed of light is the same for every observer. As a result, the rate at which time passes changes depending on how fast the observer is moving relative to objects at or near light speed.
These are just some of the things light does. What lies beyond the speed of light remains one of the most fascinating open questions in physics. This universe, after all, has no shortage of mysteries.
Next time you switch on a torch or light a lamp, remember: you will never catch that first ray again.
Originally posted on thedopplerdude.blogspot.com.