How light behaves

The comparison of Earth to an atom is a fascinating analogy to help us understand the structure of atoms and their mostly empty nature.

Atoms are incredibly tiny, with the nucleus at the center and electrons moving around in electron clouds. The nucleus contains protons and neutrons, while the electrons exist in specific energy levels or orbitals, forming a "quantum cloud" or electron cloud.

The reason why light doesn't pass through the atoms in everyday objects like cars, houses, or food is because of the nature of light and the interactions between photons (particles of light) and electrons in the atoms.

When light interacts with matter, it can be absorbed, transmitted, or reflected. The interaction depends on the properties of both the light and the atoms in the material. In most cases, the light interacts with the electrons in the atoms. While the electron cloud may seem "mostly empty" in terms of tangible matter, it still has an electric charge and exerts forces on the photons of light.

When light encounters matter, the photons can interact with the electrons in the atoms. These interactions cause the electrons to absorb and reemit the photons or to change their energy states.

The electrons in metals are typically arranged in a way that they can easily absorb and re-emit the photons, reflecting the light back, which is why metals appear shiny and reflective. So, while atoms are mostly empty space, the interactions between the quantum cloud of electrons and photons are what give materials their various properties, including opacity, transparency, and reflectivity, preventing light from simply passing through them as if they were completely empty.

Glass is composed of silicon and oxygen atoms, similar to sand. When the sand is melted and cooled rapidly, the atoms form an organized but disordered arrangement.

At the atomic level, electrons around the nucleus exist in specific energy levels, or orbits, at different distances from the nucleus. When a photon of light encounters an atom and possesses exactly the right

amount of energy, it can be absorbed by an electron in the atom. This absorption causes the electron to move to a higher energy level.

For the particular atoms that make up glass, the energy levels are relatively far apart, and visible light photons do not have enough energy to boost the electrons to higher energy levels. As a result, visible light passes through the glass, making it transparent.

On the other hand, UV light photons carry enough energy to power up the electrons in the glass atoms, causing them to move to higher energy levels. As a result, UV light gets absorbed by the glass, making it opaque to most UV rays. This is why glass is see-through and transparent to visible light, but it blocks and absorbs harmful UV rays, protecting us from excessive UV exposure and sunburn when we are indoors. Different materials interact differently with various wavelengths of electromagnetic radiation based on their atomic structures and energy levels. This property is what gives materials their unique optical characteristics, such as transparency, opacity, and color.

In short, the transparency or opacity of a material to light depends on the energy of the photons and the electronic structure of the material's atoms. Visible light may not have enough energy to penetrate deeply into most materials, including our bodies, which is why we are not transparent to visible light. On the other hand, X-rays have higher energy levels that allow them to pass through certain materials, making them transparent to X-rays.