How is the blue of the autumn sky and the red of the sunset explained by quantum mechanics, and how do its principles affect our lives?

This article explains why autumn skies are blue and sunsets are red with the principles of quantum mechanics, covering light scattering and energy. It also gives many examples of real-life applications of quantum mechanics, such as nuclear power and quantum computers, to emphasise its relevance to our lives.

 

Autumn is upon us, the season of the sky, and when we look up, the sky is so high and blue. Looking at the blue sky, we sometimes think about the mysteries of nature. However, not many people know that even these natural phenomena can be deeply explored scientifically. Physics provides the keys to unlocking these mysteries, and quantum mechanics in particular gives us a new perspective. So why is the sky blue?
This phenomenon can be explained by quantum mechanics. For most people, quantum mechanics is a difficult and unfamiliar subject. However, we’ve all heard the equation E=mc² before. This short expression means that energy (E) and mass (m) are essentially equal. Since light has energy, it behaves like a particle with mass according to this equation. This is called the particle nature of light.
Although we usually think of sunlight as white, it is actually made up of many different colours. To see this, we can pass sunlight through a prism, which divides it into the colours of the rainbow, which are conveniently classified as red, orange, yellow, green, blue, indigo, and violet. The reason for this division of light is that each colour has a different frequency. The frequency is the number of times the light vibrates in one second, and the higher the frequency, the greater the energy of that light. In this case, red light has the lowest frequency, and the frequency increases as you move towards blue light. Therefore, blue light has more energy than red light.
So why is the sky blue? The answer is explained by Rayleigh scattering. Rayleigh scattering is when light hits particles in the air and scatters them. Just as smaller particles bounce off lighter objects more than larger ones, higher-energy blue light scatters more than lower-energy red light. As a result, the sky appears blue.
The same principle explains the evening sunset. In the evening, the sun is lower near the horizon, so the distance the sunlight has to travel through the atmosphere is longer than during the day. This causes most of the blue light to be scattered, and the remaining red light reaches our eyes, making the sky appear reddish. If the atmosphere were thicker than it is now, the sky would always appear red, and if it were thinner, we wouldn’t be able to see the blues of autumn skies and the spectacular colours of evening sunsets. This makes us realise how important it is to have an atmospheric layer of just the right thickness.
So, is quantum mechanics just about explaining nature? No, it’s not. Quantum mechanics has important implications for real life, and nuclear power plants are a prime example. Although there have been recent controversies about the safety of nuclear power plants, their high efficiency makes it difficult to completely replace them.
The high efficiency of nuclear power comes from E=mc², which we explained earlier. While conventional power generation involves burning something or using sunlight, nuclear power converts matter itself into energy. In this process, the law of conservation of mass does not apply, and a small amount of matter can produce a large amount of energy. This is possible thanks to the principles of quantum mechanics. Without quantum mechanics, today’s nuclear power plants would be unthinkable.
Another real-life example is quantum computers. While classical computers process information in terms of zeros and ones, quantum computers can perform multiple calculations simultaneously using quantum states. This dramatically increases the speed of information processing and is expected to contribute greatly to future technological advances. For example, cryptography, complex physical calculations, and drug discovery using quantum computers would not be possible without quantum mechanics.
As you can see, quantum mechanics is not just a theoretical discipline, but is deeply rooted in real life based on fundamental principles of nature. From the blue colour of autumn skies to nuclear power and quantum computers, quantum mechanics explains many phenomena that are hidden in our everyday lives. So why not look at nature through the lens of quantum mechanics and apply its principles to make the world a better place? Quantum mechanics is no longer just an academic curiosity, but an important tool that plays a huge role in the real world.