The
Role of Physics in Science and Engineering
We could not even begin to
understand the world around us without having knowledge of the basic rules by
which things behave. Material objects behave and interact in predictable ways –
they move, accelerate, push on each other, heat up, emit light, and make music.
We call these predictable behaviors “laws of physics” – an old fashioned
phrase, but one that reveals how fundamental the science of physics is to our
understanding of the universe that we inhabit, and indeed of ourselves. An
understanding of physics underpins many other scientific endeavors, and the
pursuit of physics research has led to the development of techniques and
technologies that have proved central to advances in other areas and have improved
the quality of our everyday lives.
Much of the physics that
describes everyday phenomena is what we call “classical” physics, the
basics of which have been known for over a hundred years. It enables us to
design everything from roads, dams, bridges, milling machines, airplanes and
automobiles, to clocks, baseball bats, space ships, and sewing machines.
Newton’s mechanics and his theory of gravity were developed in the 17th
century and are still used to design satellites and send spacecraft to
Mars. What is perhaps surprising is the
extent to which the revolutionary and unexpected physics discoveries of the
twentieth century, namely quantum physics, relativity and nuclear and particle
physics, are also all around us.
It may be hard to believe that physics
is essential to the life sciences such as biology and medicine,
since we usually assume that physics is the study of inanimate matter and
energy, not living things. Yet, as
Harold Varmus wrote in 2000, “Medical
advances may seem like wizardry. But pull back the curtain, and sitting at the
lever is a high-energy physicist, a combinational chemist or an engineer.
Magnetic resonance imaging is an excellent example. Perhaps the last century's
greatest advance in diagnosis, MRI is the product of atomic, nuclear and
high-energy physics, quantum chemistry, computer science, cryogenics, solid
state physics and applied medicine.”
Magnetic resonance imaging, which won the 2003 Nobel Prize in
medicine, is based on a phenomenon called nuclear magnetic resonance, which won
the 1952 Nobel Prize in physics. It relies on the nucleus of every atom having
a quantum mechanical property which is called “spin” and which makes the
nucleus behave like a tiny bar magnet. Other medical imaging techniques include
x-rays (which won the very first Nobel Prize and were used by physicians
within months of their discovery), the CT scan, and the PET scan. CT scans use x-rays to image soft tissue,
bone, and blood vessels, and to find tumors, while PET scans use positrons,
which are the anti-particles of electrons and are emitted in the radioactive
decay of certain nuclei, to examine the functioning of cancer cells, the heart,
and the brain.
Radioactive tracers are also used
for medical diagnosis, to see, for example, blood clots or cancerous
tumors. Irradiation by radioactive
emissions, x-rays, or particle beams is used for therapy; about 10,000 cancer
patients are treated every day in the United States with electron beams from
linear accelerators.http://www.sc.doe.gov/henp/henpapplications.htm
- _ftn3 Altogether, nuclear
medicine is now used to diagnose or treat one third of all patients in
United States hospitals.
Medicine and biology also benefit
from tools developed for particle physics research, such as
accelerators. A synchtrotron
light source is a special kind of accelerator developed to provide intense beams
of ultraviolet light and x-rays, allowing the structure of proteins,
enzymes, and viruses to be examined and aiding in the design of drugs. Synchrotron light sources have also been used
to solve the major structure of the ribosome, the cell’s factory for assembling
proteins. In industry, they are used for non-destructive trace elemental and
chemical analysis on samples ranging from art objects to semiconductor
surfaces. The use of beams of atoms from accelerators to embed doped
layers in semiconductors is essential to the multi-billion-dollar semiconductor
industry. The same process is used to
harden surfaces such as those of artificial hip or knee joints, high-speed
bearings, or cutting tools.
Nuclear physics has a role
in energy production and national security, but in fact it has much broader
relevance. Besides powering reactors to
generate electricity, nuclear reactions are what makes smoke detectors
work, what makes the sun shine, and what keeps the inside of the earth
hot and molten – volcanoes are powered by radioactive decay deep in the
core of the earth. Nuclear physics is
crucial for astrophysics, since the source of energy for stars is
nuclear fusion. The fusion of hydrogen in
stars also produces other atomic nuclei, and stars are the source of all
elements up to iron. The heavier nuclei
are produced when a star explodes in a supernova, and scattered throughout the
universe. Caught in orbit around other
stars, this nuclear stardust gradually accumulates, attracted by gravity, and
forms some rocky planets like ours, with all the elements needed for life.
The twentieth century discoveries
of the structure of the atom, and the fact that atomic phenomena are governed
by quantum mechanics, brought a profound revolution in the understanding
of chemistry. Modern chemistry is based on atomic physics: chemical properties
and reactions are determined by the organization and interactions of atomic
electrons. This allows new substances
and processes to be designed from a fundamental understanding of atoms and
molecules. Quantum mechanics, which
seems remote from everyday life, is actually vital to it. Apparently weird quantum phenomena, such as
the idea that electrons behave both as a particle and a wave, are what enabled
the invention of semiconductors, and hence the integrated circuits –
chips and microprocessors – that are used in a vast array of electronic devices
from cell phones to computers to the engine in your car. The next time you go to the supermarket,
department store or music shop, notice how lasers and electronics
have revolutionized our way of doing business, our economy, and our lives. It
is has been estimated that
about one third of the world’s manufacturing economy is actually based in some
way on the principles of quantum mechanics.
Physical laws and methods are
important for biochemistry and the processing of information inside
cells. Biophysicists study the basic physical properties of biological systems
(such as elasticity of DNA and DNA-protein interactions) and apply physical techniques
to the modeling of neural, genetic and metabolic networks.
Classical mechanics is essential
to civil, mechanical, and aeronautical engineering
and, together with the physics of fluids and sound transmission,
it underlies geology and gives an understanding of earthquakes
and other processes that shape the earth.
When Michael Faraday, one of the
discoverers of electricity and magnetism, was asked by the prime
minister "But what is the use of it?" he is said to have answered
"Sir, some day you may come to put a tax on it." And indeed, electricity is universal - and
taxed - in our society. Electrical
engineers use the physics of electromagnetism to build electric power
plants and transmission lines, while electric motors and batteries power
everything from medical implants to Game Boys. Radio waves and radar
have revolutionized communications, making television sets and cell phones
possible, but they also power the microwave oven. They have revolutionized astronomy,
allowing us to detect radio waves from very distant, but very violent galaxies,
and indeed from the Big Bang itself.
Thermodynamics – the way
in which heat and energy are stored and transferred – was also developed in the
19th century, and yet its principles remain essential to such
diverse areas as refrigeration, chemical engineering, internal
combustion engines, and earth science. Driving a hybrid-powered automobile is in fact
a daily lesson in energy transfer and storage. Heat transfer is what drives the
weather, and understanding the heat balance of the Earth is critical to
knowing what should be done about global warming.
In the early twentieth century,
Albert Einstein’s general theory of relativity provided a remarkable new
explanation for the apparent force of gravity as a due to a curvature of space
itself, caused by the matter and energy it contains, such as stars and
planets. General relativity and particle
physics come together at the heart of modern cosmology, the study of
the origin and evolution of the universe.
Cosmology is now one of the most exciting fields of science, due to the
recent discovery that the expansion of the universe is speeding up rather than slowing
down, as expected from gravitational attraction. This acceleration requires an “antigravity”
force, which must be caused by a mysterious new form of energy, often called
“dark energy.” Einstein’s esoteric
theory of gravity is also used for a much more practical matter. It is needed to help a GPS system to
locate your precise position by correcting for the small speed-up of time in
the weaker gravitational field at the altitude of a satellite.
The extremely broad range and
depth of physics make it both important and fascinating. Physics continues to explore its own very
fundamental questions, such as the unification of the forces of nature, the
behavior of nanoparticles, the
dynamics of chemical reactions. At the same time, it provides the foundations
for much of modern science and engineering, and explains why almost all the
things we take for granted in our everyday lives work. Truly, physics is
everywhere.