The great cosmic discovery - IX

Prof H Nandakumar Sarma *

The discovery of microwave background radiation, neutron star, pulsar; trying to understand the cosmic forces, the discovery of anisotropy of cosmic microwave background radiation, the discovery of Higgs boson ( God's particle ), the detection of gravitational wave and black hole etc are some of the exciting moments in the understanding of the universe.

In this series, we trace some of the great cosmic discovery made from the beginning of the 20th century to the present day.

Einstein laboured for the last quarter century of his life to Unified Field Theory. The purpose of a Unified Field Theory is to construct a bridge between electromagnetic force and gravitational force.

Believing in the harmony and uniformity of space, Einstein looked for a single edifice of physical laws to encompass both the phenomena of atom and phenomena of outer space.

Ultimately the features of the universe distilled down to a few basic quantities space, time, matter, energy, and gravitation. Einstein’s Unified Field Theory sought to culminate and climax this coalescing process.

The forces of nature can be divided into four distinct groups. One of the forces that due to gravity was recognized hundred of years ago by natural philosophers. Gravity seems to exert a large influence in our experience of life. Rather paradoxically, the gravitational force is least understood.

Another force, that due to electricity and magnetism (electromagnetic forces) is also within the realm of common human experience. Electromagnetic forces bind atoms to form molecules and thus are responsible for all chemistry and biology. Anyone who has seen a lightning bolt or has received an electric shock knows something about electromagnetism.

The other two forces of nature- weak force and strong force fall into the realm of nuclear interactions and not so familiar in day to day life. Example of weak interactions is nuclear beta decay and the slow decays of elementary particles.

Strong forces are those that bind the protons and neutrons in the nucleus etc. They are very short range. Although gravitation is the only universal force- that is, it is experienced by all particles without exception, it is still least understood.

A complete Grand Unified Theory of gravitation, electromagnetism with strong nuclear forces will touch the “grand aim of all science, it will be loftiest passion of the human intellect”.

Gravity (Gravitation)

Chief cosmic roles: binding planets, stars, and galaxy. Extremely weak in atoms; very strong in collapsed stars, infinite range, acts on everything (matter and energy) carried by gravitons.

Electric Force (Electromagnetic Interaction)

Hans Oersted proved experimentally that the flow of electric current in a wire would affect a compass needle by producing magnetism. Michael Faraday had constructed electromagnetic devices and later developed laws of electromagnetic induction.

Magnetism having to do with compass needle and picking up iron filings with permanent magnet was originally quite separate from electricity. Electricity is all about sparks, shocks, lightning chemical batteries etc.

James Clerk Maxwell who was born in 1831 at Edinburgh, Scotland was appointed the first Cavendish Professor of Experimental Physics in 1871 of the University of Cambridge. The old Cavendish laboratory is situated at the Free School Lane of the University.

After many years of thought, research and experiment, Maxwell developed his electromagnetic theory, which is still valid even today as they were in 1873. As an integral part of his theory, Maxwell identify light as an electromagnetic radiation.

Maxwell further extended his reasoning by suggesting and predicting the existence of other electromagnetic radiation which is not sensitive to our eyes and body ( as light and heat are) but travelling through space with the same speed as that of light.

We now know that light occupies a relatively narrow band in the spectrum, which also includes gamma rays, X-rays, ultra violet, visible light, microwave, radio wave etc. many objects of the universe emit different radiations of the electromagnetic spectrum.

Chief cosmic roles of electromagnetic interaction are: binding atoms; creating magnetism, strong in atoms, weak over cosmic distances because matter is neutral, infinite in range, acts on all charged particles, carried by photons

Strong nuclear force (Strong interaction)

Chief cosmic roles: binding atomic nuclei; burning in stars, about 100 times strength of electric force, short range (~10-13), carried by gluons.

Weak force (weak interaction)

Chief cosmic roles: altering basic particles, effective in exploding stars, strength about ~10-11 of electromagnetic force, very short range (10-15cm ), acts on all basic particles (quarks and lepton family), carried by W+, W-, neutral current Z.

Steven Weinberg of Harvard University told how the various cosmic forces have come into operation As he put it:

“To build a universe may be a good deal easier than you think. I suspect that at the beginning of Big Bang, which took place sometimes 12-15 billion years ago, nature was very simple. Then the incredible temperature began to cool down, all the variety of forces and particles that we know about today began to appear. The electric force, strong force and weak forces all had about the same strength and same range. They were all in effect the same force.”