The Role of Physics in Science and Engineering

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.