Light Particles - Photons

Light particles are known as photons. They are the fundamental units of electromagnetic radiation, which includes visible light, radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays. The wave-particle duality of photons means that photons can sometimes act like particles and sometimes act like waves. This is a strange idea because we usually think of particles as small, solid objects, and waves as something that spreads out like water ripples. But photons can do both!


When photons hit a metal surface, they can act like particles and knock electrons off the metal. This is called the photoelectric effect. But photons can also spread out like waves when they pass through a small opening.

Scientists found that photons can act like both particles and waves, which is a key part of quantum mechanics. Quantum mechanics is a strange and complicated branch of physics that explains how things work at a very small level.

Photons are the smallest possible particles of electromagnetic energy and therefore also the smallest possible particles of light. Photons can travel at the speed of light because they have no mass. Photons also have no charge. Photons represent the entire spectrum of electromagnetic radiation.

A photon is the quantum of electromagnetic radiation that describes the particle properties of an electromagnetic wave. The energy of a photon is given by the equation E = hf, where E is energy, h is Planck's constant, and f is frequency. This equation tells us that as the frequency of radiation increases (wavelength decreases), the photon energy increases. The wavelength of a photon depends on the frequency of radiation of the electromagnetic wave and is given by the relationship wavelength = speed of light/frequency.

The concept originated (1905) in Albert Einstein's explanation of the photoelectric effect, in which he proposed the existence of discrete energy packets during the transmission of light.

Earlier (1900), the German physicist Max Planck had prepared the way for the concept by explaining that heat radiation is emitted and absorbed in distinct units, or quanta. The concept came into general use after the U.S. physicist Arthur H. Compton demonstrated (1923) the corpuscular nature of X-rays. The term photon (from Greek phōs, phōtos, “light”), however, was not used until 1926. The energy of a photon depends on radiation frequency; there are photons of all energies from high-energy gamma- and X-rays, through visible light, to low-energy infrared and radio waves. All photons travel at the speed of light. Considered among the subatomic particles, photons are bosons, having no electric charge or rest mass and one unit of spin; they are field particles that are thought to be the carriers of the electromagnetic field.

Wave-Particle Duality: Photons exhibit both wave-like and particle-like properties. We could discuss experiments that demonstrate this duality, such as the double-slit experiment.
Quantum Electrodynamics (QED): QED is the theory that describes the interactions between charged particles and electromagnetic fields. We could explore how photons play a crucial role in this theory.

Applications of Photons: From optics to medical imaging, photons have numerous applications. We could discuss specific examples and the underlying principles.
Photons in Astrophysics: Photons are essential for our understanding of the universe. We could explore how astronomers use photons to study distant stars, galaxies, and other celestial objects.

In current physics, particle energy and photon energy are not related through equations. This is another example of the separation of the laws of physics between the classical and quantum worlds. The equation to relate energy to mass is Einstein’s famous E=mc2 and the equation for photon energy is Planck’s E=hf. There is no method in physics to describe the energy change from particles to photons or vice versa. Although particles and photons are both measured as energy, the variables in their equations cannot be reconciled to make them equivalent. One is based on mass (m), and the other uses a variable that describes a type of wave, using frequency (f) terms.

Understanding particle and photos: A particle's mass determines how much it resists changing its speed or position when it encounters a force. Not all fundamental particles have mass. The photon, which is the particle of light and carries the electromagnetic force, has no mass at all. Protons and neutrons, for example, get most of their mass from the strong nuclear force that holds their quarks together.

In equation form, the photon energy is E = hf, where E is the energy of a photon of frequency f and h is Planck's constant.

Plank’s constant: The Planck constant, or Planck's constant, denoted by h,[1] is a fundamental physical constant[1] of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and the wavelength of a matter wave equals the Planck constant divided by the associated particle momentum.

The constant was postulated by Max Planck in 1900 as a proportionality constant needed to explain experimental black-body radiation. Planck later referred to the constant as the "quantum of action". In 1905, Albert Einstein associated the "quantum" or minimal element of the energy with the electromagnetic wave itself. Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta".








Therefore If you take Einstein's equation E = m c^2 , where m = mass and c = speed of light, and the Planck equation for the energy of a photon, E = h f , where h = Planck's constant and f = the frequency of the photon, and combine them you get: m c^2 = hf or that m = h f/c^2.


An outside observer may notice that the photon takes time to get from one place to another, but due to time dilation, the photon itself doesn't actually experience any passage of time. It doesn't accelerate or change direction or do anything at all in between the moment of its creation and the moment it is absorbed. Therefore, when we witness the sky and see a bright star 4.24 light-years with a telescope with an aperture of at least 8 cm (3.1 in).

To convert 4.24 light yr to km, we can use the following conversion:

1 light-year = 9.461 × 10^12 km

Therefore, the distance to Proxima Centauri in km is:

4.24 light-years × 9.461 × 10^12 km/light-year ≈ 4.013 × 10^13 km

So, Proxima Centauri is about 40,130,000,000,000 km away from Earth.

The photon light travels to our and yes is actually a past.
-4.24 light year ago.


How far are the galaxies? A picture of illustration: