Home » Posts tagged 'Newton’s laws of motion'

# Albert Einstein

This name need not be explained. Albert Einstein is considered to be one of the best physicists in the human history.

The twentieth century has undoubtedly been the most significant for the advance of science, in general, and Physics, in particular. And Einstein is the most luminated star of the 20th century. He literally created cm upheaval by the publication, in quick succession, in the year 1905, two epoch-making papers, on the concept of the photon and on the Electrodynamics of moving bodies respectively, with yet another on the Mathematical analysis of Brownian Motion thrown in, in between.

The Electrodynamics of moving bodies was the biggest sensation and it demolished at one stroke some of the most cherished and supposedly infallable laws and concepts and gave the breath takingly new idea of the relativity of space and time.

# What is it?

The word symmetry commonly used in physics has a special meaning. A picture is symmetrical if one side is somehow the same as the other side. Precisely, a thing is symmetrical if one can subject it to a certain operation and it appears exactly the same after the operation.

For Example If we look at a base that is left and right symmetrical, then turn it 180° around the vertical axis it looks the same.

Newton’s laws of motion donot change when the coordinates are moved from one place to other i.e., translated. This is equally true for all other laws. Therefore, we can say that the laws of physics are symmetrical for translational displacements.

The same is true for rotational displacement. Not only Newton’s law, but all the other laws of physics known so far have the two properties which we call invariance (or Symmetry) under translation and rotation of axes.

On the basis of these properties a new mathematical technique has been developed for writing and using physical laws. A very powerful mathematical machinery has been devised called Vector analysis and in fact this is the symmetry of physical laws.

## What I shall discuss now?

### I shall discuss SYMMETRY OPERATIONS & THEIR CONSERVATION !

There are following main symmetry operations in physical laws:
Conservation of Mass-Energy
• Conservation of Momentum
Conservation of Angular Momentum
• Conservation of Electric Charge
• Conservation of Baryon Number
• Conservation of Lepton Number
• Conservation of Strangeness
• Conservation of Hypercharge
• Conservation of Iso-spin
• Conservation of Charge Conjugation
Conservation of Parity.

In this very first post on Symmetry, I shall discuss the last twos:

#### A. Charge Conjugation (C) & its Conservation:–

Charge conjugation C is the operation of changing
• a particle to its anti-particle & vice-versa,
• Positive into negative etc..

For Example:-
• C (π+)= π-
• C (+x²+5x-3) = 3-x²-5x
and so on…

In modern physics, the strong & electromagnetic interactions are symmetrical wrt Charge Conjugation but weak interactions are not symmetrical.

#### B. Parity(P) & its conservation:

The parity operation P is reflection of all coordinates through the origin. Thus
P(r)=-r
where r is the position vector of coordinates.

The wave function (ψ) of elementery particle generally have well defined symmetry under parity operation. Thus it is found that,
P|ψ(p)|= ψ(p)
Here ψ(p) indicates the wave function of particle p.