He was a good man. You need only to look at a photograph of him with his large, luminous eyes and humble expression to perceive the tremendous passion that made this man great, as well as the human kindness that made this man good. But upon close examination of Albert Einstein, you will also find things that might surprise you: a sense of humor, an understanding of human flaws, a stubborn unselfconsciousness, an irreverence toward authority. Needless to say, this guy was one of a kind.
Although he is regarded as one of the most brilliant mathematical physicists of the century, Einstein thought of himself as much as a philosopher as a scientist. Certainly his theories relating matter, energy, space, time and gravity have guided much of the work in theoretical physics since 1905. His famous "thought experiments," based on intuition and imagination rather than laboratory work, propelled us beyond the mechanistic, unchanging "clockwork universe" of Newton and the other classical physicists into a relativistic universe. Here clocks run slower or faster depending on the speed of travel or location in the universe, and "true" distances are stretched or shrunk by gravity.
Einstein's legacy is a universe in which space and time are woven into a single fabric -- spacetime. It is matter that causes spacetime to curve and whose motion and properties are, in turn, altered by that curvature. If all this seems a bit baffling, relax. With a bit of persistence you'll get the gist.
The two fundamental concepts of special relativity are the inertial frame and the principle of relativity. An inertial frame of reference is any region in which all objects have uniform velocity and move in straight lines. The principle of relativity states that the laws of physics must have the same form in every inertial frame, and similarly, the speed of light must be the same in any inertial frame regardless of the speed of its source or that of the observer. Essentially all the laws and consequences of special relativity can be derived from these concepts.
An important consequence of special relativity is the relativity of simultaneity (two events happening at the same time). Any definition of simultaneous events at different locations involves the sending of signals between them, so two events that are simultaneous in one inertial frame may not be simultaneous when viewed from a frame moving relative to the first. This observation helped abolish the long-held Newtonian concept of an absolute, universal time.
Special relativity quickly became a vital tool for theorists and experimentalist in the nascent fields of atomic and nuclear physics and quantum mechanics. However, general was not so readily accepted. General relativity did not appear to have as much experimental potential as the special theory; with most of its applications only observable on astronomical scales. Also, the mathematics of the theory were thought to be so difficult for even most physicists to tackle. The British astronomer Sir Arthur Eddington, one of the first people to fully comprehend theory, when asked if it was true that only three people in the world understood general relativity, was said to have replied, "Who is the third?"
Around 1960, however, General Relativity acquired widespread interest again that has made it an important of physics and astronomy. This was probably the result of the new mathematical techniques applied to the study of general relativity that streamlined calculations and allowed the significant concepts to be isolated as well as the discovery of exotic astronomical phenomena, including quasars, microwave background radiation, and possible black holes, which general relativity could play an important role in describing.
The first person to use the General Theory of Realativity for a practical purpose was the German astrophysicist Karl Schwarzschild. Immediately after reading Einstein's theory, Schwarzchild started figuring its consequences for the gravitational fields of stars.
Because of the difficult calculations involved in General Relativity, Schwarzschild simplified the problem to the situation of a perfectly spherical, stationary star. He sent his preliminary solution to Eistein, and in January of 1907 Einstein reported his results at a physics meeting. The prediction of spacetime curvature calculated by Schwarzschild became known as the Schwarzschild geometry and greatly influenced research on gravitation and cosmology.
A few weeks later, Schwarzschild produced a second paper describing the spacetime curvature inside a star and sent it to Einstein. Although Schwarzchild died of an illness a few months later, his legacy lives on through this groundbreaking second paper. The paper described a singularity, a point in spacetime with infinite curvature that theoritically lies within a black hole. Although Einstein resisted the idea of the "Schwarzschild singularity" and black holes until his death, there has been mounting evidence showing a very high possibility for the existence of black holes in the universe, possibly within our own galaxy.
Atrophysicists have now used supercomputers to extend the Schwartschild's calculations to include complex spacetime geometries like spinning, non-symmetrical objects.
One of the first applications of general relativity was in the field of cosmology. theory predicts that the universe could be expanding from an initial, infinitely dense state, a process called the big bang. In 1965, a background radiation with a uniform temperature of about 2.7K that fills the universe was discovered. Background radiation had been proposed by general relativity as the remaining trace of an early, hot phase of the universe following the big bang. The observed cosmic abundance of helium also agreed with the conditions predicted by relativity theory.
General relativity has also suggests many kinds of celestial phenomena that could possibly exist. For example, according to relativistic theory, neutron stars would be small stellar bodies primarily composed of neutrons with densities comparable that of an atomic nucleus. Since these stars were first proposed in the 1930's, a mounting collection of data has been gathered concerning the possible existence of neutron stars, and most astrophysicists agree on their existence.
Black holes are among the most fascinating of the predictions of general relativity, although the concept itself dates back more than a century. These theorized objects are most likely to be produced in the supernovae of extremely massive stars. After the outer layers of these stars are expelled in the supernovae, gravity pulls the remaining central material together and collapses the matter in on itself into an infinitely dense, mathematical point. The gravitational field of the resulting black hole is so strong that radiation emitted from it becomes infinitely [redshifted], and thus ceases to exist. Much evidence now exists that black holes exist at the center of many massive galaxies.
The concept of gravitational lenses is based on the relativistic prediction that light from a celestial object is deflected when passing near a very massive object. Based on this, a very massive galaxy could act as the equivalent of an optical lens to see objects still further away. An actual gravitational lens was first discovered in 1979.
Einstein's theory of relativity demanded the equivalence of mass and energy, as demonstrated by the most famous equation in the history and science, E = mc^2 . In this equation, E is energy, m is mass, and c^2 is the sqaure of the speed of light. All action and creation in the whole universe is summed up in this simple, elegant little equation.
One of its most important results was the discovery of the nature of the Sun's energy, a question that had eluded physicists for centuries. The answer lay in the nuclear fusion hydrogen, the simplest and most abundant element in the universe. The energy from nuclear fusion was actually taken from hydrogen's mass, so the resulting helium nucleus had less mass than the two original hydrogen nuclei, agreeing with Einstein's equation. Although the loss of mass is comparatively small, about seven tons for every one thousand tons of hydrogen used, nuclear fusion releases far more energy than ordinary chemical reactions such as burning fossil fuels and metabolizing food.
Another type of nuclear process, nuclear fission, is also bound up in E = mc^2. The heaviest natural elements, such as radium and uranium, have energy added to their nuclei from the stellar exlosions that created them, so certain isotopes are naturally radioactive and spontaneously eject small pieces of nuclei to achieve stability. Thus, these heavy elements constantly emit small particles until they change into lead or bismuth, the heaviest stable elements. This gradual release of radioactive energy seeps into rocks and causes earthquakes and volcanoes, but are otherwise unspectatular.
However, uranium-235, a radioactive isotope of uranium, will explosively undergo fission, a splitting into two pieces, when struck by a low-energy neutron. This explosion triggers the fission of other uranium-235 atoms, causing a brief, uncontrolled thermonuclear reaction. The A-bombs dropped on Hiroshima and Nagasaki used the fusion of uranium and plutonium, respectvely, for their nuclear fuel.
Increasing the potential for global devastation, scientists later invented the H-bomb, a bomb based on both nuclear fission and the fusion of hydrogen. Many different types of H-bombs exist, all based on variations of the same reaction. First, an A-bomb is detonated, and this in turn triggers nuclear fusion in a container of various isotopes of hydrogen and lithium. With these awesome weapons, mankind attempts to recreate the nuclear fusion by which the stars shine and takes control of the destiny of Earth. But even these intense nuclear reactions can only unleash at most one percent of the total rest-energy of the fuels, showing that it is not easy, to put it mildly, to change conventioal mass into other forms of energy. However, physicists can now set up the ultimate demonstration of E = mc^2: the creation of matter out of energy. Using high-energy gamma rays [link to electromagnetic spectrum], fresh sub-atomic particles can be made. The number of particles in the universe, however, is not so easily changed, so an antiparticle counterpart must be made also. Thus, when a particle meets its anti-particle, they both completely annihilate into a burst of gamma rays (100% energy efficiency!).
So in summary, E = mc^2 governs the secrets of solar energy and nuclear weapons, the radioactive decay, and the creation of all the particles from which we are made. Pretty neat, huh?
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|This homepage was constructed for ThinkQuest 1998.