The Fundamental Forces - Introduction

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 Table of contents 

THE 

FUNDAMENTAL FORCES 

- INTRODUCTION


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Every interaction taking place in the universe can be explained by 4 fundamental types of interactions that are also known as the fundamental forces -
  • Gravity/ Gravitational force
  • Electromagnetism/ Electromagnetic force
  • Weak Interaction/ Weak Nuclear Force
  • Strong Interaction/ Strong Nuclear force 


GRAVITY:

  • Has the farthest reach i.e. the longest range of the four fundamental forces.
  • Weakest in magnitude (yes, it is even weaker than the weak force!)
  • A purely attractive force that even reaches through an 'empty' void of space to draw two masses towards each other.
  • Keep planets in orbit around the sun and the moon in orbit around the earth.
  • Described under the Theory of General Relativity.
  • Its boson, which is believed to be the graviton has not yet been proven.
The Theory of General Relativity defines Gravity as the "curvature of spacetime around an object of mass." This curvature creates a situation where the path of least energy is toward the other object of mass.

ELECTROMAGNETISM:

  • Interaction of particles with an electric charge
  • Charged particles at rest interact through electrostatic forces that are attractive or repulsive forces between particles that are caused by their electric charges.
  • In motion, the charged particles interact through electrical and magnetic forces.
  • Its boson is the photon. However, there are two types of photons - virtual and real. I will be explaining this in more detail in my future posts!
For a long time, electric and magnetic forces were considered to be different. They were unified by James Clerk Maxwell in 1864. In the 1940s, electrodynamics consolidated electromagnetism with quantum physics.
(Know more about electrodynamics in the next article!)
  • The electromagnetic force is the most prevalent in our world as it can affect things at a reasonable distance with a fair amount of force.

WEAK INTERACTION:

(There are separate articles on the weak interaction as well as the beta decay.)
  • A powerful force that acts on the scale of the atomic nucleus.
  • Has been consolidated with electromagnetism as a single interaction - "electroweak interaction."
  • Mediated by the W boson (W+ and W- bosons) as well as the Z boson. 
  • This force causes phenomena such as beta decay.
Beta decay is a type of radioactive decay in which a beta particle (i.e. a fast energetic electron or positron) is emitted from an atomic nucleus, transferring the original nuclide to an isobar of that nuclide.

BETA-DECAY:

Beta particles are electrons or positrons (positrons are electrons with a positive charge; also known as antielectrons).

Beta-decay occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transferred into the other.

Beta minus decay: Neutron decays to proton and in the process, creates an electron and an electron antineutrino.

Beta plus decay: Proton decays into a neutron and in the process, creates a positron and an electron neutrino.

STRONG INTERACTION:

  • Strongest of the forces.
  • Short-range.
  • The force that keeps nucleons (protons and neutrons) bound together.
    • The same strong interaction force that binds quarks within a nucleon also binds protons and neutrons together to form a nucleus, called the nuclear force (or residual strong force).
E.g. - The helium atom. This force is strong enough to bind the protons together though their positive electrical charges cause them to repel each other.
  • This interaction allows particles called gluons to bind together quarks. This creates nucleons in the first place!
Gluons can also interact with other gluons, which gives the strong interaction a theoretically infinite distance, although its major manifestations are all at the subatomic level. 
Then why does the strong interaction have a short range?
This is because - 
  • Gluons carry attractive force between quarks.
  • But particles called mesons (you can know more about mesons in an article on hadrons!) carry the attractive force between nucleons.
  • The pi mesons, also known as the pions, are the lightest particles involved in this. 
  • But pi mesons exist only for a short time. Thus, it covers a shorter range.

UNIFYING THE FUNDAMENTAL FORCES:

Physicists believe that all four fundamental forces are the manifestations of a single underlying/ unified force that is yet to be discovered.
E.g. - Electricity, magnetism and weak force are unified into electroweak interaction.

The current quantum mechanical interpretation of these forces is that particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions.
  • Quantum mechanics, in simple words, is a physical theory developed in the 1920s to accounts for the behaviour of matter on the atomic scale.
As discussed earlier, gravity is not a part of the Standard Model. (This is because the existence of the boson for gravity i.e. believed to be the graviton has not yet been proven).

Efforts to unify gravity with other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called graviton which would be the mediating element in gravity interactions.

To date, gravitons have not yet been detected, and no theories of quantum gravity have been successful or universally adopted. 

Can you think of any theory which could solve this?

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I am still learning Particle physics, but will try my best to answer your questions :)

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With Warm Wishes,
Lavanya

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