Welcome ...
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Friday, September 29, 2006
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 Nature of the subject ...
Physics is the most fundamental of the experimental sciences as it seeks to explain the universe itself,
from the very smallest particles—quarks (perhaps 10-17 m in size) which may be truly fundamental—
to the vast distances between galaxies (1024 m).
Classical physics, built upon the great pillars of Newtonian mechanics, electromagnetism and
thermodynamics, went a long way in deepening our understanding of the universe. From Newtonian
mechanics came the idea of predictability in which the universe is deterministic and knowable. This
led to Laplace’s boast that by knowing the initial conditions—the position and velocity of every
particle in the universe—he could, in principle, predict the future with absolute certainty. Maxwell’s
theory of electromagnetism described the behaviour of electric charge and unified light and
electricity, while thermodynamics described the relation between heat and work and described how all
natural processes increase disorder in the universe.
However, experimental discoveries dating from the end of the nineteenth century eventually led to the
demise of the classical picture of the universe as being knowable and predictable. Newtonian
mechanics failed when applied to the atom and has been superseded by quantum mechanics and
general relativity. Maxwell’s theory could not explain the interaction of radiation with matter and was replaced by quantum electrodynamics (QED). More recently, developments in chaos theory, in which
it is now realized that small changes in the initial conditions of a system can lead to completely
unpredictable outcomes, have led to a fundamental rethinking in thermodynamics.
While chaos theory shows that Laplace’s boast is hollow, quantum mechanics and QED show that the
initial conditions Laplace required are impossible to establish. Nothing is certain and everything is
decided by probability. But there is still much that is unknown and there will undoubtedly be further
paradigm shifts as our understanding deepens.
Despite the exciting and extraordinary development of ideas throughout the history of physics, certain
things have remained unchanged. Observations remain essential at the very core of physics, and this
sometimes requires a leap of imagination to decide what to look for. Models are developed to try to
understand the observations and these themselves can become theories which attempt to explain the
observations. Theories are not directly derived from the observations but need to be created. These
acts of creation can sometimes compare to those in great art, literature and music, but differ in one
aspect which is unique to science: the predictions of these theories or ideas must be tested by careful
experimentation. Without these tests a theory is useless. A general or concise statement about how
nature behaves, if found to be experimentally valid over a wide range of observed phenomena, is
called a law or a principle.
The scientific processes carried out by the most eminent scientists in the past are the same ones
followed by working physicists today and, crucially, are also accessible to students in schools. Early
in the development of science physicists were both theoreticians and experimenters (natural
philosophers). The body of scientific knowledge has grown in size and complexity and the tools and
skills of theoretical and experimental physicists have become so specialized that it is difficult (if not
impossible) to be highly proficient in both areas. While students should be aware of this, they should
also know that the free and rapid interplay of theoretical ideas and experimental results in the public
scientific literature maintains the crucial links between these fields.
At the school level both theory and experiments should be undertaken by all students. They should
complement one another naturally, as they do in the wider scientific community. The Diploma
Programme physics course allows students to develop traditional practical skills and techniques and
increase facility in the use of mathematics, which is the language of physics. It also allows students to
develop interpersonal skills, and information and communication technology skills which are essential
in modern scientific endeavour and are important life-enhancing, transferable skills in their own right.
Alongside the growth in our understanding of the natural world, perhaps the more obvious and
relevant result of physics to most of our students is our ability to change the world. This is the
technological side of physics in which physical principles have been applied to construct and alter the
material world to suit our needs, and have had a profound influence on the daily lives of all human
beings; for good or bad. This raises the issue of the impact of physics on society, the moral and ethical
dilemmas and the social, economic and environmental implications of the work of physicists. These
concerns have become more prominent as our power over the environment has grown, particularly
amongst young people for whom the importance of the responsibility of physicists for their own
actions is self-evident.
Physics is therefore, above all, a human activity and students need to be aware of the context in which
physicists work. Illuminating its historical development places the knowledge and the process of
physics in a context of dynamic change in contrast to the static context in which physics has
sometimes been presented. This can give students insights into the human side of physics: the
individuals; their personalities, times and social milieux; and their challenges, disappointments and
triumphs.
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