DOE Office of Science:
Heir to the Revolutionary Work of Albert Einstein
In 1905, Albert Einstein, then an unknown patent clerk in Bern, Switzerland, published four papers that laid the foundations of much of physics, as we know it today. Indeed it can be said that the research programs supported by the Office of Science at the Department of Energy are the scientific grandchildren and great grandchildren of these papers.
Each paper dealt with a specific topic. One helped to establish the modern view that all matter and material objects are composed of individual atoms and molecules attracted to one another by the fundamental forces of Nature. Another paper, for which Einstein was awarded the 1921 Nobel Prize, was an important step in the development of quantum mechanics, the theory that
provides us with the fundamental understanding of molecules, atoms, and atomic nuclei. His most famous paper, entitled "On the electrodynamics of moving bodies," introduced the special theory of relativity and led to the universally known equation, E = mc², which he derived in a fourth paper in the same "miracle year" of 1905.
Brownian Motion
Robert Brown, in 1827, discovered that tiny particles of pollen suspended in a liquid were not stationary, but jiggled around in a random motion that could actually be seen under a microscope. Over the years, many attempts were made to explain this phenomenon, but none of them succeeded, in part because the dominant view of matter was that it was continuous and static in structure.
In 1905, Einstein adopted what was then a minority view that matter was composed of very large numbers of discrete particles, called molecules, which were in random motion within the liquid. He attributed the motion discovered by Brown (and known as Brownian motion) to collisions between the pollen particle and the much smaller, but rapidly moving molecules of the liquid, and he successfully calculated the properties of the motion and the number and size of the molecules. This work refuted continuous theories of matter and established the view that all material objects are composed of discrete units, molecules and atoms. This point of view is the starting point for all the research of the Department of Energy's Office of Science - and indeed of all research in the physical and chemical sciences.
Today, Einstein's theory of Brownian motion has widespread applications to the phenomena of diffusion and osmosis, to medical imaging and robotics and to aerosol particles, all of which are relevant to Office of Science research programs in Basic Energy Sciences and Biological and Environmental Research. The theory is even applicable to such worldly activities as manufacturing and stock market analysis.
Photoelectric Effect
At the time Einstein was writing his paper on the photoelectric effect, the electron had already been discovered, but the nucleus of the atom had not. Max Planck had introduced the idea that light behaves like discrete "bundles," or quanta, whose energy is proportional to the frequency of the light, and Einstein used it to explain the photoelectric effect.
He argued that in order to eject an electron from the surface of a metal, the frequency of the light had to exceed a certain minimum value, which varied from one metal to another, say silver, or cesium, or sodium. In this way each "bundle" of light could transfer sufficient energy to the electron to free it from the surface of the metal. It is not the intensity of light that is key, as many had thought, but rather its color: if the color matches the minimum frequency, electrons will be ejected and the number of electrons ejected increases with intensity, but if the color corresponds to a frequency below the minimum, no electrons will be ejected no matter how intense the light may be.
Subsequent experiments by Robert Millikan and others confirmed Einstein's theory and laid the foundation for quantum mechanics as the basic physics of atomic and molecular phenomena. Today quantum mechanics is the basis of many everyday things, including lasers, X-rays and CT scans, computers, microwave ovens and laptop screens. It is the foundation of much of the research in the Office of Science's Nuclear Physics, High Energy Physics, and Basic Energy Sciences research programs.
Special Relativity
Special relativity, the subject of Einstein's third paper, completely revised our notions of space and time, and it reconciled apparent conflicts between Isaac Newton's theory of mechanics, which had dominated physics for more than two hundred years, and James Clerk-Maxwell's late 19th Century theory of electromagnetism, which required the speed of light to be the same for all observers, no matter how fast they might be moving, and which predicted the existence of electromagnetic waves, the basis for radio, television and all wireless communications.
The equivalence of mass and energy, embodied in the equation E = mc², has the most profound consequences for us here on Earth, and for the entire Universe in which we live. It provides the basis for our research in Nuclear Physics, High Energy Physics, and Fusion Energy Sciences.
Fusion of light nuclei and fission of heavy ones provide copious sources of energy. The sun generates most its energy by fusing four hydrogen nuclei into one helium nucleus, while reactors on Earth break up heavy uranium nuclei into pairs of lighter ones. Stars carry on the fusion processes of the sun to become ovens that "cook" hydrogen into all the elements up to,
and beyond iron.
E = mc² is also behind the phenomenon of radioactivity which has many applications in medicine; for example, PET scans, or positron emission tomography, are a significant medical diagnostic technique.