What is Photon in Physics?

In physics, photon is one of the most fundamental particles in universe. It is the elementary particle of light and all other forms of electromagnetic radiation.

To understand a photon, we have to look at it through the lens of Quantum Mechanics, where it serves as the bridge between waves and particles.

1. Dual Nature of Light

For centuries, scientists debated whether light was a wave or a particle. In the 19th century, experiments showed light behaving like a wave (rippling through space). However, in early 20th century, Albert Einstein and Max Planck discovered that light also behaves like discrete packets of energy.

• Wave Nature: Light has frequency and wavelength.

• Particle Nature: Light consists of individual units called quanta (singular: quantum).

A photon is that single quantum of light.

2. Properties 

Photons are unique compared to matter that make our bodies (like atoms or electrons). Here are their defining characteristics:

• Massless: A photon has zero rest mass. This is why it can travel at the maximum speed possible in the universe.

• Speed of Light: In a vacuum, photons always travel at exactly c = 299,792,458 meters per second.

• Energy and Frequency: energy of a photon is not random; it is directly proportional to its electromagnetic frequency. It is expressed by the Planck-Einstein relation:

  E = hf

  Where E is energy, h is Planck’s constant, and f is frequency.

• No Charge: Photons do not carry an electric charge.

• Spin: Photons are bosons, meaning they have an integer spin (specifically 1). They act as force carriers.

3. Force Carrier

In Model of particle physics, photons are classified as gauge bosons. They exchange particles for the electromagnetic force.

When two charged particles (like two electrons) interact and repel each other, they do so by exchanging photons. You can think of photons as messengers that tell charged particles how to move.

4. How are Photons Created?

Photons are generally produced when an atom’s electron moves from a higher energy state to a lower energy state.

1. An electron absorbs energy and jumps to an excited outer shell.

2. Electron eventually becomes unstable and drops back down to its original shell.

3. Excess energy is released as a photon.

The color of light (its frequency) depends on how much energy the electron lost during that jump.

Without photons, the universe would be dark and static. They are responsible for:

• Vision: Our eyes detect photons bouncing off objects.

• Communication: Wi-Fi, radio, and cell phone signals are all streams of low-energy photons.

• Heat: Infrared photons transfer heat from the sun to the Earth.

• Medical Technology: X-rays are high-energy photons used to see inside the body.

Summary Table

Property	Value
Mass	0
Charge	0
Speed	299,792,458 m/s
Classification	Gauge Boson
Force Carried	Electromagnetism