Understanding The Micro World Of Atoms, Molecules, Elementary Particles And The Macro World Of Cosmos.

The discovery of Higgs Boson (the God Particle), the sub atomic particle was announced by scientists at CERN ,Geneva on 04^th July 2012. The breakthrough has been described as ‘biggest leap in physics’. It will further our understanding the universe.

This article discusses  the growth of ideas in structure of matter from early concepts to the more complex theories of modern times.

In 1987 Sir J J Thomson discovered the electron while doing cathode ray experiments ( the rays which move from cathode to anode when an electric discharge is passed through a gas at low pressure), these are charges of negative electricity. When these cathode rays are deflected onto an electrode of an electrometer, the instrument measured a negative charge. The rays tested also were deflected by application of an electric field. All these results were found irrespective of the gas used. This particle was established basic constituent of all matter.

In 1909 Rutherford investigated the scattering of alpha particles(positively charged particles resulting from radioactive decay) by thin films of heavy metals. A narrow parallel beam of alpha particles impinges on a metal foil and the angular distribution of the scattered particles is obtained by counting the scintillations or light flashes produced on a zinc sulphide screen.

Rutherford analysed the result that an atom has a positively charged core(nucleus) which contains most of the mass of the atom and which is surrounded by orbiting electrons. From scattering measurements it is possible to obtain an estimate for the radius of a typical nucleus (10^-12cm) and the nucleus charge.

The discharge tubes, in which cathode rays are observed also contain positive rays consisting of positively charged particles moving in a direction opposite to that of the cathode rays. These are very much heavier than electrons known as protons. Scientists began to formulate a detailed picture of the atom. It was not difficult to estimate atomic size. It is approximately 10^-8cm.

In 1932 C D Anderson discovered positron (positive electron) which are produced by the interaction of the cosmic rays with matter.

In 1932 J Chadwick showed neutrons are forced when alpha rays from radioactive substances impinge on certain light elements e.g., beryllium ,boron.

When the cathode rays from a discharge tube fall upon metal target a new radiation known as x-rays are produced(Rontgen in1895). These rays differ from cathode rays.They have  greater penetrating power and are not deflected by electric and magnetic field.

Nucleus contain protons and neutrons. The nucleons are held together by one of the four fundamental forces- the strong interactions (the other 3 electromagnet force, weak interaction, gravitational force).strong interactions are strong short range force.

By 1902 it was known that light impinging on a clean metallic surface in vacuum caused the surface to emit electrons (photoelectric effect). In 1905 Einstein postulated on that the photoelectric effect could be explained if light consisted of discrete particles or photons of energy hν. He proposed that when a photon of frequency v and energy hv  impinges on the metallic surface it gives up its energy to an electron . A certain amount of this energy E₀  is used to overcome the attractive forces between the electron and the metal, the rest is available to the ejected electron and appears as kinetic energy ½ mv²

Although Rutherfords   model of the atom was experimentally consistent with the results of the alpha particle scattering experiments there was considerable opposition to its on theoretical grounds. It was  well known when a charged particle is accelerated emits electromagnetic radiation. Atom would cease to exist.

In 1913 Neil Bohr solved this problem by assuming electrons move in circular orbits. The energies of the electrons in an atom can have only certain values( called energy levels of the atom). This was based on spectroscopic observations.  It successfully explained light emission or spectra of atoms. In these experiments the light source is an electrical discharge through the gas to be investigated.

In 1914 de Broglie took some of the equations used earlier by Einstein to describe the photons of light and rearranged them to calculate wavelengths for moving particles. His result was λ=h/mv =h/p. This equation was part of both concept of wave particle duality. That all particles of matter also had wave like properties .  In some experiments they will behave like particles and in other more like waves.

In 1925 quantum mechanics was formulated by Heisinberg and Schrodinger  to describe motion of tiny particles. It included wave like nature of particles. These waves filled the space around each particle and  the position of a particle were determined by wave function. The Schrodinger equation and quantum mechanics further the model of the atom to the concept that we use today.

 All these experiments and mathematical formulations and predictions give insight into understanding the nature of physics and its basic principles.

The earliest sources of charged particles and γ rays were provided by the decays of naturally radioactive elements such as radium and thorium. These naturally occurring particles were used as projectiles to bombard matter of various sorts to investigate how they interact with the elements. The realization that some of the electrons surrounding the nucleus are easily removed to yield a charged ion, it became evident that if a very large potential drop existed between electrodes in some sort of electrical machine, these ions might be accelerated to furnish a variety of projectiles for study.

At the beginning of the twentieth century electrons, protons and neutrons were the elementary particles of nature. However, by the 1960s with the advent of huge accelerating machines a list of elementary particles has been uncovered. There were so many fundamental units of nature that confusion existed rather than order. Modern physicists look to mathematical reasoning to provide a thread of continuity and symmetry to all of the elementary particles.

The discovery of elementary particles has been furthered by both theoretical predictions and experimental results.

Atoms are made of e, p and n. They in turn are made of quarks and other sub-atomic particles. Understanding the basic structure of matter explains why the matter behaves the way it does.

The standard model theory explains all observed interactions of elementary particles. This theory says matter particles are 12 in numbers.

Proton and neutron are not elementary but composite particles made up of 3 quarks each. They are also called hadrons. There are 4 bosons already known namely photon,w,z and gluons. One more called Higgs boson has been discovered. Bosons are characterised by their obedience to Bose-Einstein statistics.

The lightest  family of fermions (those particles obeying Fermi-Dirac statistics) is known as the family of leptons and includes four particles and four antiparticles. The lightest of the four are the neutrinos, which have rest mass zero. The two kinds of neutrino known are the electron-neutrino and the muon-neutrino. The two charged members of the lepton family are the electron and the muon.

LHC(Large Hardon Collision) the worlds largest and most powerful particle accelerator was used in the experiment done for discovery of sub atomic particle Higgs boson(god particle).

The LHC smashes beams of sub-atomic particles such as protons virtually at near the speed of light.

The discovery higgs boson the sub atomic particle was announced by scientist at CERN, Geneva on 04^th July. Higgs had predicted the particle’s existence roughly 40 years ago.

Higgs boson last of the 12 particles postulated by standard model of physics, basic building blocks of universe.  How universe has evolved as a function of time and how it looked at various times. This discovered particle is expected to  solve many mysteries.

How we know what we know about universe . How can astronomers tell how far away the stars are, how big they are, how much mass they contain and so on? Mostly the researchers use equipments like  Photometry , telescope, spectroscope. We come to know about distance, size, elements present on stars and other astronomical objects. Important clues also come from the way in which many astronomical objects behave and interact.

Different type of radiations, distinguished by their wavelength and energy, collectively form the electromagnetic spectrum. Distribution map of whole galaxies, stars, planets of planetary systems, clusters and other cosmic masses when compared and different processes observed in laboratories are linked we get idea on how universe has evolved as a function of time and how it looked at various times.

The interaction of the elementary particles may be considered as the direct source of all natural phenomena. The explosion of a star or the growth of a flower all are controlled from instant to instant through particle interactions. A number of interactions are considered in modern physics ( gravitation, weak interaction, electromagnetic interactions, strong interaction.)

The most fundamental question ? how the physical universe has evolved from its beginning to become what we now observe to exist around us.

Nature consists of free elementary particles and chemical elements, with the latter predominating heavily in abundance. How the chemical elements came into existence and in the proportion in which these are now found. How this distribution vary from place to place in the universe. For example is it same on earth as is in the sun and same in all of the stars? If not then why not? How have the elements become distributed from the place where they were made to the places where they are now found.? This subject is a very dynamic one and is developing rapidly. The details of the processes that are involved have been observed in the laboratory.