Four Fundamental forces

There are 4 fundamental forces are exist in nature.

1. Gravitational force

2. Electromagnetic force

3. Weak nuclear force

4. Strong nuclear force

1.gravitational force :

• Universal : every particles feel force of Gravity according to its mass and energy

• It is weakest of the four forces by long way that we would not notice it

• two special property it has; 1.can act over large distances 2.always attractive

• Other three forces are either short range or are some time attractive and sometime repulsive so they cancel each other.

• In gravitational field force between two metal particles (like earth and sun) is due to the particle of spin 2 called graviton

• Graviton has no mass of its own so the force that it carries its long range

• the gravitational force between the sun and the earth is due to exchange of graviton between the particles that make up these two bodies.

• This graviton are virtual but it have significant measurable effect (like earth around the sun) but real graviton generate gravitational wave and that is also difficult to detect.

2.Electromagnetic force :

• This force interact with electrically charged particle like electron and quark but not with a charged particle like graviton.

• Much stronger than gravitational force Electromagnetic force between two electron is equal to 10^42 times bigger than gravitational force

• As we know like charges repel and unlike charges are attract each other.

• A large body such as earth and sun contain nearly equal number of positive and negative charges so the attractive and repulsive force between individual particle nearly cancel each other and there is very little net electromagnetic force.

• But in small scale like in atom the electromagnetic attraction between negative charge electron and positive charge Proton in nucleus causes electron to orbit nucleus of atom (just like a gravitational force causes Earth to orbit the sun)

• This EM attraction is caused by large number of virtual massless particle with spin 1 called photons.

• But in case when electric charge from one allowed orbit to another one nearer to Nucleus energy is released and real photon is emitted, which is observed by visible light or by Photon detector

• And if real photon collide with atom it may move electron from orbit nearer the nucleus to further away this process use energy of photon so it absorbed.

3. Weak nuclear force :

• This force is responsible for radioactivity and act on all matter particles of spin 1/2 but not on particle of spin 0,1 or 2 such as photon or graviton.

• In 1967 abdus Salam and steven weinberg proposed theory that unified this interaction with electromagnetic force.

• They suggested that in addition to photon there where 3 others spin 1 particles known collectively as massive vector Boson that carried the weak force .these were called W+,W- and Z0.each has mass of around 100 GeV

• The weinberg- Salam theory exhibits property known as spontaneous symmetry breakdown.

• This means that what appear to be number of completely difference particles at low energy are in fact found to be all the same type of particle only in different states.

• At high energies all this particles behave similarly.

4. strong nuclear force :

• This force hold the Quark together in the proton and neutron and hold the proton and neutron together in nucleus of atom.

• This force is carried by spin 1 particles called Gluon - which interact only with itself and quark.

• This force has property called confinement it always bind particle together in to combination that have no colour. one cannot have single quark on its own because it would have colour (R,G or B)

• A red quark has to be join to Green and blue quark by 'string of gluon' so R+G+B = white.such Tripletes constitutes a proton or neutron.

• Another possibilities is pair consisting of quark and antiquark ( red + anti red or green + anti green or blue + antiblue = white) such combination makeup particles known as the Mesons - which are unstable because the quark and antiquark annihilate Each Other producing electron and other particles.

• Similarly confinement prevent one having a single gluon on its own because gluon also have colour so it has to have a collection of gluon whose colour add up to White such collection form an unstable particle called a glueball.

• Another property of strong nuclear force called asymptotic freedom that said that at normal energy strong nuclear force is also strong and it bind quark tightly together,but at high energies the strong force become much weaker & Quark & gluon behave almost like a free particles.

• Strong force get weaker at high energy but EM and weak force which are not asymptotically free get stronger at high energies.

Unification of above 4 forces :

• At some very high energy called Grand unification energy this three forces (electromagnetic,strong and weak) have same strength and so could just be different aspect of single force.

• At this energy 1/2 spin particles like quark and electron would also be essentially same

• energy values is at least thousand million million GeV (giga electron volt) but in particle accelerator like CERN we can only generate energy about few thousand GeV.

• So that is impossible to test grand unified theory in lab because machines required to produce that much energy is about as big as our solar system.

• But in case of EM and weak unified theory there are low energy consequences that can be tested

• The proton which make up much of the mass can spontaneous decay into lighter particle such as antielectron this is because at GUE there is no difference between quark and electron

• 3 Quark inside a Proton normally not have enough energy to change into antielectron but very occasionally one of them a acquire sufficient energy to make transition because of Uncertainty Principle means that energy of quark inside the proton cannot be fixed exactly so proton would then decay.

• Probability of quark gaining sufficient energy is law that wait at least 10^30 year this time much longer since Big Bang which occur at 10^10 year ago.

• But if there is a large amount of matter containing very large amount of protons then we have chance of a decay for that we have 10^31 Proton for a period of 1 years so we can detect a decay.

• But we take an experiment in which we use 8 thousand of water and perform this experiment at Morton salt mine at Ohio but we not detect any spontaneous decay so there is might longer lifetime of decay is possible.