Physics: Thinking Back and Forward

Physicists Contemplate Their Impact over the Last 75 Years as Their Science Expands into Diverse Frontiers

May 3, 2006--As the American Institute of Physics (AIP) celebrates its 75th anniversary this year, physicists think about how much their science has evolved and how far it has expanded into new territory. Several busy physicists have taken the time to step back from their work to reflect upon events that have transpired since that occasion in 1931 when AIP first set up shop in New York City.

"In the past 75 years, breakthroughs in physics have led to life-saving medical imaging, ubiquitous computers, inexpensive worldwide telecommunications, and an ever-deepening knowledge of matter, the Earth and the universe," says Marc H. Brodsky, AIP's Executive Director and CEO.

What have been the most important events in physics during this relatively short period of time? AIP senior historian and physicist Spencer Weart suggests two discoveries which took place in the early 20th century that have had tremendous influence on how we not only see and understand our world, but also how we live in it.

Quantum mechanics and Einstein’s general theory of relativity, he says, have laid down the "new physics" of our age.

Matter and Light at Its Tiniest: Controlling Electrons

Quantum mechanics is the name given to the development of new rules of physics applicable to matter and radiation at an atomic level. Application of these principles has led to development of such devices as lasers, the atomic clock, magnetic resonance imaging, the electron microscope, transistors, computer chips and high-speed communications with fiber optics.

A laser controls the way that energized electrons release photons (packets of light energy). When the photon is released, the amount of its energy determines its individual wavelength or color.

Today, lasers are used all around us, for a multitude of purposes. In practical applications they are focused beams of radiation energy that can be aimed and pointed in a specific direction with a controlled intensity.

In addition to being used in manufacturing and industrial applications of every kind, lasers play a big part in many present day medical procedures on a very individualized and personal level. Lasers are common in everything from cosmetic dermatology, in which a two-hour laser treatment can eradicate or reduce the appearance of the skin's aging, to removing a tumor in the body.

While an ordinary clock measures time through the motion of a balance wheel and a tiny, precise spring, an atomic clock uses the oscillation between the nucleus of an atom and the surrounding electrons to keep track of time. Since time kept by an atomic clock is so precise, it is used to provide our national time standard. By having such a precise standard scientists were able to invent the Global Positioning System (GPS).

And has anything more revolutionized society than the development of the digital computer with its capacity for data manipulation, transfer and storage? It too would not be possible without quantum theory, which explains how to control the electrons in the materials that make computer chips.

Another challenge ahead is the application of quantum mechanics to the development of a quantum computer, a machine that will perform certain computational tasks exponentially faster than present computers.

Einstein Showed Us Where We Are

In the general theory of relativity, Einstein determined the relationship between space and time, while considering the effect of gravity.

Gravity has its biggest effect at large scales, holding together galaxies. Applying general relativity enables us to do such things as predict, with incredible precision, the position of the planets and other objects in space.

On a more local level, Einstein's theories ensure the precision of the Global Positioning System. GPS helps users determine their precise position on Earth by relying on a network of satellites each of which contains atomic clocks to synchronize their signals with one another.

Through his general theory of relativity, Einstein explained that gravity slows time down ever so slightly for an observer bound to the Earth compared to a satellite less encumbered by gravity. Through his special theory of relativity, Einstein showed that time moves slower for a moving object such as a satellite relative to one at rest such as a GPS user on Earth. Both effects must be taken into account for GPS to work accurately.

The Future of Physics: A Wrestling Match

Unfortunately even these two theories (general relativity and quantum mechanics) are incompatible with one another. They fail, for example, when scientists combine them to explain behavior inside black holes, the most compact objects imaginable having such strong gravity that nothing (not even light) can escape their grip or gravity.

Combining these two modern pictures of the universe into a "unified" theory is one of the major challenges still facing physicists, says Judy Franz, Executive Officer of the American Physical Society.

"We're trying to unite these different ideas," Franz said. "I'm confident it will be done in the future," she says, "but how it will be done," she adds, is the big question, sure to reveal some wonderful new physics.

Physics Explains the World Today

Though physicists think a lot about the very large and the very small, they have applied their tools to all size scales, including the environment of our planet. New theories in the areas of global warming, plate tectonics and continental drift will improve our ability to better predict future climate variations, as well as the location and timing of earthquakes and volcanic eruptions.

"Science," says Jim Gates, a professor of physics at the University of Maryland, is "a determined flight from fantasy. Physics is not about the truth, it is about making our systems of beliefs less false."

Even the "simple" concept of automobile power has progressed from the combustion engine using fossil fuel to ever more practical engines driven by fuel cells.

Advances in medicine and space exploration have both relied upon the development of new instruments, from microscopes that can see and move individual atoms and molecules to NASA's Hubble Space Telescope, which has revealed that the universe is expanding at an ever-increasing rate, providing a glimpse of the future of the cosmos billions of years from now.

And then there's the Internet. It was physicists who invented the World Wide Web only 15 years ago, as a way for researchers at different locations to share their data. Thank the existence of lasers, and fiber optics, for the ability to transport data at breakneck speeds over long distances.

Society has rarely seen exponential advances like the ones in the past 75 years. What will science and the next 75 years bring?

At left: In the early 1930's, particle accelerators -- a type of device used to smash atoms together to find out what's inside -- took up the space of a room in a lab. Today, the largest accelerator forms an underground 17-mile (27-km) loop.

References

More on the impact of physics on society and the economy in the AIP's Physics Success Stories

Contact:

Chris Rowe
American Institute of Physics
Tel: 301-209-3136
crowe@aip.org