Humans have always been curious about the world around
them. The night sky with its bright celestial objects has
fascinated humans since time immemorial. The regular
repetitions of the day and night, the annual cycle of seasons,
the eclipses, the tides, the volcanoes, the rainbow have always
been a source of wonder. The world has an astonishing variety
of materials and a bewildering diversity of life and behaviour.
The inquiring and imaginative human mind has responded
to the wonder and awe of nature in different ways. One kind
of response from the earliest times has been to observe the
physical environment carefully, look for any meaningful
patterns and relations in natural phenomena, and build and
use new tools to interact with nature. This human endeavour
led, in course of time, to modern science and technology.
The word Science originates from the Latin verb Scientia
meaning ‘to know’. The Sanskrit word Vijnan and the Arabic
word Ilm convey similar meaning, namely ‘knowledge’.
Science, in a broad sense, is as old as human species. The
early civilisations of Egypt, India, China, Greece, Mesopotamia
and many others made vital contributions to its progress.
From the sixteenth century onwards, great strides were made
in science in Europe. By the middle of the twentieth century,
science had become a truly international enterprise, with
many cultures and countries contributing to its rapid growth.
What is Science and what is the so-called Scientific
Method? Science is a systematic attempt to understand
natural phenomena in as much detail and depth as possible,
and use the knowledge so gained to predict, modify and
control phenomena. Science is exploring, experimenting and
predicting from what we see around us. The curiosity to learn
about the world, unravelling the secrets of nature is the first
step towards the discovery of science. The scientific method
involves several interconnected steps : Systematic
observations, controlled experiments, qualitative andquantitative reasoning, mathematical
modelling, prediction and verification or
falsification of theories. Speculation and
conjecture also have a place in science; but
ultimately, a scientific theory, to be acceptable,
must be verified by relevant observations or
experiments. There is much philosophical
debate about the nature and method of science
that we need not discuss here.
The interplay of theory and observation (or
experiment) is basic to the progress of science.
Science is ever dynamic. There is no ‘final’
theory in science and no unquestioned
authority among scientists. As observations
improve in detail and precision or experiments
yield new results, theories must account for
them, if necessary, by introducing modifications.
Sometimes the modifications may not be drastic
and may lie within the framework of existing
theory. For example, when Johannes Kepler
(1571-1630) examined the extensive data on
planetary motion collected by Tycho Brahe
(1546-1601), the planetary circular orbits in
heliocentric theory (sun at the centre of the
solar system) imagined by Nicolas Copernicus
(1473–1543) had to be replaced by elliptical
orbits to fit the data better. Occasionally,
however, the existing theory is simply unable
to explain new observations. This causes a
major upheaval in science. In the beginning of
the twentieth century, it was realised that
Newtonian mechanics, till then a very
successful theory, could not explain some of the
most basic features of atomic phenomena.
Similarly, the then accepted wave picture of light
failed to explain the photoelectric effect properly.
This led to the development of a radically new
theory (Quantum Mechanics) to deal with atomic
and molecular phenomena.
Just as a new experiment may suggest an
alternative theoretical model, a theoretical
advance may suggest what to look for in some
experiments. The result of experiment of
scattering of alpha particles by gold foil, in 1911
by Ernest Rutherford (1871–1937) established
the nuclear model of the atom, which then
became the basis of the quantum theory of
hydrogen atom given in 1913 by Niels Bohr
(1885–1962). On the other hand, the concept of
antiparticle was first introduced theoretically by
Paul Dirac (1902–1984) in 1930 and confirmed
two years later by the experimental discovery of
positron (antielectron) by Carl AndersonPhysics is a basic discipline in the category
of Natural Sciences, which also includes other
disciplines like Chemistry and Biology. The word
Physics comes from a Greek word meaning
nature. Its Sanskrit equivalent is Bhautiki that
is used to refer to the study of the physical world.
A precise definition of this discipline is neither
possible nor necessary. We can broadly describe
physics as a study of the basic laws of nature
and their manifestation in different natural
phenomena. The scope of physics is described
briefly in the next section. Here we remark on
two principal thrusts in physics : unification
and reduction.
In Physics, we attempt to explain diverse
physical phenomena in terms of a few concepts
and laws. The effort is to see the physical world
as manifestation of some universal laws in
different domains and conditions. For example,
the same law of gravitation (given by Newton)
describes the fall of an apple to the ground, the
motion of the moon around the earth and the
motion of planets around the sun. Similarly, the
basic laws of electromagnetism (Maxwell’s
equations) govern all electric and magnetic
phenomena. The attempts to unify fundamental
forces of nature (section 1.4) reflect this same
quest for unification.
A related effort is to derive the properties of a
bigger, more complex, system from the properties
and interactions of its constituent simpler parts.
This approach is called reductionism and is
at the heart of physics. For example, the subject
of thermodynamics, developed in the nineteenth
century, deals with bulk systems in terms of
macroscopic quantities such as temperature,
internal energy, entropy, etc. Subsequently, the
subjects of kinetic theory and statistical
mechanics interpreted these quantities in terms
of the properties of the molecular constituents
of the bulk system. In particular, the
temperature was seen to be related to the average
kinetic energy of molecules of the system.
1.2 SCOPE AND EXCITEMENT OF PHYSICS
We can get some idea of the scope of physics by
looking at its various sub-disciplines. Basically,
there are two domains of interest : macroscopic
and microscopic. The macroscopic domain
includes phenomena at the laboratory, terrestrial
and astronomical scales. The microscopic domain
includes atomic, molecular and nuclearphenomena*. Classical Physics deals mainly
with macroscopic phenomena and includes
subjects like Mechanics, Electrodynamics,
Optics and Thermodynamics. Mechanics
founded on Newton’s laws of motion and the law
of gravitation is concerned with the motion (or
equilibrium) of particles, rigid and deformable
bodies, and general systems of particles. The
propulsion of a rocket by a jet of ejecting gases,
propagation of water waves or sound waves in
air, the equilibrium of a bent rod under a load,
etc., are problems of mechanics. Electrodynamics
deals with electric and magnetic phenomena
associated with charged and magnetic bodies.
Its basic laws were given by Coulomb, OerstedAmpere and Faraday, and encapsulated by
Maxwell in his famous set of equations. The
motion of a current-carrying conductor in a
magnetic field, the response of a circuit to an ac
voltage (signal), the working of an antenna, the
propagation of radio waves in the ionosphere, etc.,
are problems of electrodynamics. Optics deals
with the phenomena involving light. The working
of telescopes and microscopes, colours exhibited
by thin films, etc., are topics in optics.
Thermodynamics, in contrast to mechanics, does
not deal with the motion of bodies as a whole.
Rather, it deals with systems in macroscopic
equilibrium and is concerned with changes in
internal energy, temperature, entropy, etc., of the
system through external work and transfer of
heat. The efficiency of heat engines and
refrigerators, the direction of a physical orchemical process, etc., are problems of interest
in thermodynamics.
The microscopic domain of physics deals with
the constitution and structure of matter at the
minute scales of atoms and nuclei (and even
lower scales of length) and their interaction with
different probes such as electrons, photons and
other elementary particles. Classical physics is
inadequate to handle this domain and Quantum
Theory is currently accepted as the proper
framework for explaining microscopic
phenomena. Overall, the edifice of physics is
beautiful and imposing and you will appreciate
it more as you pursue the subject.You can now see that the scope of physics is
truly vast. It covers a tremendous range of
magnitude of physical quantities like length,
mass, time, energy, etc. At one end, it studies
phenomena at the very small scale of length
(10-14 m or even less) involving electrons, protons,
etc.; at the other end, it deals with astronomical
phenomena at the scale of galaxies or even the
entire universe whose extent is of the order of
1026 m. The two length scales differ by a factor of
1040 or even more. The range of time scales can
be obtained by dividing the length scales by the
speed of light : 10–22 s to 1018 s. The range of
masses goes from, say, 10–30 kg (mass of an
electron) to 1055 kg (mass of known observable
universe). Terrestrial phenomena lie somewhere
in the middle of this range.
