Dear readers, today I invite you to explore the first in a series of articles related to one of the most fascinating phenomena of nature: light. To understand its essence, it is necessary to delve into the universe of fundamental particles, the photons. These particles, which have no rest mass*, travel at the speed of light in a vacuum (300,000 Km/s) carrying energy and momentum (QDM). In the complex Standard Model of particle physics, photons are classified as gauge bosons, particles that mediate fundamental forces, in this case, the electromagnetic interaction.

Deeping: Bosone e QDM

A gauge boson, explained in simple terms, is a particle that acts as an intermediary for the forces of nature, allowing particles to interact with each other. Photons, for example, are the messengers of electromagnetism, the force that governs the interactions between charged particles.

Momentum, on the other hand, represents the product of an object’s mass and its velocity, a vector quantity that indicates both the direction and intensity of motion. Although photons have no rest mass, their energy and velocity confer momentum, allowing them to influence other particles and objects.

Let us then prepare to embark on this fascinating journey into the universe of light, with the hope that it may illuminate your understanding of physics and the world around us.

Our dear quanta of radiation, upon reaching the retina, are received by photoreceptors known as cones and rods, which convert their light energy into electrical impulses that, once sent to the brain, are decoded and transformed into images, allowing us to see the world in all its splendid complexity.

Premise

To understand the nature of light, it is essential to explore the electronic configuration of atoms, specifically the famous Bohr atom. Each chemical element possesses a unique set of energy levels, meaning the arrangement of electrons around the atomic nucleus. Electrons, in fact, occupy specific energy levels determined by atomic structure, following fundamental principles such as Pauli’s exclusion principle, the Aufbau principle, and Hund’s rule.

Deepening: Fundamental Principles

The Aufbau principle states that electrons fill the lowest available energy orbitals first, while Pauli’s exclusion principle asserts that each orbital can hold a maximum of two electrons with opposite spins. Hund’s rule, finally, indicates that electrons occupy degenerate orbitals (with the same energy) singly before pairing up. This organization of electrons in the various orbitals is crucial for determining the chemical and physical properties of elements.

Electrons can be excited to higher energy levels by absorbing energy, and when they return to lower levels, they release the excess energy in the form of photons. Are you wondering why they return to the lowest level? Well, the answer is stability. The tendency to return to their ground energy level is related to their ground state, which is the lowest energy state an electron can occupy, making it the most stable state.

The difference in energy between the levels determines the wavelength of the emitted light, which corresponds to various visible colors. This emission of light is fundamental for many applications, from spectroscopy to laser technology.The difference in energy between the levels determines the wavelength of the emitted light, which corresponds to various visible colors. This emission of light is fundamental for many applications, from spectroscopy to laser technology.

Deepening Energy Levels

This behavior is in accordance with the second law of thermodynamics, which states that a system tends to move towards a state of minimum energy. When an electron returns to its ground energy level, the absorbed energy is released in the form of a photon, with a wavelength determined by the energy difference between the excited and ground levels. Forcing an electron to remain at a higher energy level requires a continuous input of energy, making such a state highly unstable and unsustainable in the long term.

Northern Lights

The fascinating and enchanting polar auroras are one of the most well-known natural phenomena on our planet, resulting from the interaction between photons and the Earth’s atmosphere. These extraordinary displays primarily occur in polar regions, due to the interaction between the solar wind and atmospheric gases.

The solar wind, a continuous stream of charged particles (protons and electrons) emitted by the Sun, reaches Earth and interacts with the Earth’s magnetic field. This field acts as a shield, deflecting most particles, but in polar regions, where the field is weaker, some of these particles manage to penetrate the Earth’s atmosphere. This is where the aurora generation process begins.

The solar wind particles, once they enter the atmosphere, collide with atoms and molecules of gases like oxygen and nitrogen. This collision causes the excitation of electrons within the atoms, causing them to move to higher energy levels. However, these electrons tend to return quickly to their ground energy state, releasing the accumulated energy in the form of photons. The photons emitted during these energy transitions are what we see as light in the auroras.

The colors of the auroras depend on the composition of atmospheric gases and the altitude at which the interaction occurs. For example:

• Green: Emitted by oxygen at about 100 km altitude.
• Red: Produced by oxygen at higher altitudes.
• Blue and Violet: Derived from nitrogen at lower altitudes.

These different emissions create the multicolored spectacle of the auroras, where each color corresponds to a particular energy transition of a specific gas at a given altitude.

Non-Terrestrial Lights

Auroras are not an exclusive phenomenon to Earth; they also occur on other planets in our solar system, such as Jupiter, Saturn, Uranus, and Neptune, and each of these celestial displays has unique characteristics. Planetary auroras form when charged particles from the solar wind interact with the magnetic fields of the planets, inducing spectacular light displays in the atmosphere.

On Jupiter, for instance, the auroras are powered not only by the solar wind but also by the interaction with the moon Io, known for its intense volcanic activity. Jovian auroras can extend for thousands of kilometers, making them much larger than those on Earth, and are visible at the poles of the planet as bright rings that light up in a variety of colors.

Spectacular auroras are also observed on Saturn, though with different characteristics. Saturn’s magnetic field is extremely powerful and envelops the entire planet, contributing to auroras that can cover entire poles. Auroras on Saturn are of impressive size, with rings of light extending for thousands of kilometers along the high latitudes. The composition of Saturn’s atmosphere, dominated by hydrogen, gives these auroras a fascinating variety of colors. Observations made by the Cassini probe have shown that these lights can last for many hours, and their intensity varies depending on the conditions of the solar wind and the planet’s inclination relative to the Sun.

Thank you for traveling with us!

Polar auroras are not just a light show in the sky; they are a living manifestation of the fundamental laws of physics. As Richard Feynman said, “If you think you understand electrons, you don’t.” These subatomic particles, so elusive and mysterious, reveal their complexity in natural displays like auroras, where the invisible becomes visible, and hidden energy transforms into light.

Through the lens of physics, every photon emitted in the auroras becomes a messenger of the interaction between cosmic forces and our atmosphere, while their trajectory, curved and deflected by gravity, reminds us that light itself is subject to the rules that govern the universe. In these plays of light and gravity, we can see a deep connection between terrestrial phenomena and cosmic principles, united by an invisible thread that links the microcosm of electrons to the macrocosm of galaxies. Thank you.