RELATIVITY: The Special and General Theory
The theory of relativity was introduced by Albert Einstein around the early nineteen hundereds. It is a theory which enables the human mind to understand the possible actions of the universe. The theory is divided into two parts, the special, and the general. In each part, there is a certain limit to which it explains and helps to comprehend. In the special, Einstein explains ways of understanding the atom and other small objects, while the general is designed for the study of large objects, such as planets. The theory of relativity having being created, succeeded the two hundred year old mechanics of Isaac Newton, thus showing Einstein as more of a futuristic thinker and adapter.
Einstein introduced the concept of Relativity, which means that there is no absolute motion in the universe. Einstein showed that humans are not in a flat, absolute time of everyday experience, but in a curved space-time. Take for example the Earth as a whole. The earth has a circumference of around twenty five thousand miles, and it can be covered within a twenty-four hour time frame. Having this completion of distance covered within the set amount of time, shows that the Earth rotates a little over one-thousand miles per hour. it can be assumed that something in the solar system is not moving, and we can measure how fast the earth is moving by relative to the object. However, no matter what object is chosen, it is moving as well, thus showing that nothing is fixed and that everything is moving, and it is unknown how fast or in what direction. The Theory of Relativity is a theory compressing mechanics, gravitation, and space-time. Having known this, it is seen so that all things are related, but can not be thought of as individual.
The Theory of Relativity is known for having two parts to it. The first part is the special relativity; the other is the general relativity. Special relativity is known for it’s publication in 1906; it is used for microscopic physics, such as atoms and small objects. The other type of relativity, the general, is known for its publication in 1916, well after the birth of it’s counterpart. The general half of the theory is intended for astrophysics and cosmology, such as solar systems, planets, and large objects. A British Astronomer named Sir Arthur Eddington, was one of the first to fully understand the Theory of Relativity. A little humor about his intelligence can be seen to when he was asked about there being three people who understood the Theory of Relativity, his response was “who is the third?” The discovery of Quasars, the 3 kelvin microwave background radiation, pulsars, and possibly blackholes were studied with to see the accuracy of the Theory of Relativity with gravity. This led the development of the space program, telescopes, computers, etc…to make better calculations of the accuracy of the theory.
The Theory of Relativity has two main parts, the special and the general. The internal part of the special theory is in reference to any region, such as a free falling laboratory, in which objects move in straight lines and have uniform velocities. In the lab, nothing would appear to be moving if everything in the lab was falling, the movement of the lab is relevant to the person that is in the lab. The principle of relativity theorizes that experiments in an internal frame, is independent from uniform velocity of the frame. An example of this is the speed of light. The speed of light within the internal frame is the same for all, regardless of the speed of the observer. Two events that are simultaneos in one frame, may not be simultaneos when viewed from a frame moving relative to the first one. Movement looks different depending on where the observer is located, how fast it is moving, and in what direction. An interesting fact about the special relativity, is that the mechanical foundations of special relativity were researched in 1908 by a german mathmetician named, Hermann Minkowski. Minkowski ler einstein to postulate the vanishing of gravity in free fall. In any free fall, laws of physics should take on special relitavistic forms, this is what led to the EEP(Eisteins Equivalence Principle.)
A consequence of EEP is that the space time must be curved. It is techinical, consider two frames falling freely, but on opposite sides of the Earth. According to Minkowski, spare time is valid locally in each frame, but since the frames are accelerating towards each other, the two Minkowski space-times can not be extended untill they meet. Therefor, with gravity, space time is not flat locally, but spaced globally. Any theory of gravity that fulfills EEP, is called a metric theory.
Along with the special side of the theory, is the genral side of it. The principle to show space-time curved by presence of matter. To determine curvature, requires a specific metric theory of gravity, such as general relativity. Einsteins aim was to find the simplist equations, he found a set of 10. To test the general theory Einstein performed three tests. Gravitational red shift, light deflection, and perihelion shift of mercury. To test light deflection, Einstein used the curve space-time of the sun light; it shoul be deflected 1.75 seconds of arc if it glazes the solar surface. The concept of gravitational lenses is based on the already discussed and proven relativistic prediction that when light from a celestial object passes near a massive body such as a star, its path is deflected. The amount of deflection depends on the massiveness of the intervening body. From this came the notion that very massive celestial objects such as galaxies could act as the equivalent of crude optical lenses for light coming from still more distant objects beyond them. An actual gravitational lens was first identified in 1979. Another of the early successes of general relativity was its ability to account for the puzzle of Mercury’s orbit. After the perturbing effects of the other planets on Mercury’s orbit were taken into account, an unexplained shift remained in the direction of its perihelion (point of closest approach to the Sun) of 43 seconds of arc per century; the shift had confounded astronomers of the late 19th century. General relativity explained it as a natural effect of the motion of Mercury in the curved space-time around the Sun. Recent radar measurements of Mercury’s motion have confirmed this agreement to about half of 1 percent.
One of the remarkable properties of general relativity is that it satisfies EEP for all types of bodies. If the Nordtvedt effect were to occur, then the Earth and Moon would be attracted by the Sun with slightly different accelerations, resulting in a small perturbation in the lunar orbit that could be detected by lunar laser ranging, a technique of measuring the distance to the Moon using laser pulses reflected from arrays of mirrors deposited there by Apollo astronauts. One of the first astronomical applications of general relativity was in the area of cosmology. The theory predicts that the universe could be expanding from an initially condensed state, a process known as the big bang. For a number of years the big bang theory was contested by an alternative known as the steady state theory, based on the concept of the continuous creation of matter throughout the universe. Later knowledge gained about the universe, however, has strongly supported the big bang theory as against its competitors. Such findings either were predicted by or did not conflict with relativity theory, thus also further supporting the theory. Perhaps the most critical piece of evidence was the discovery, in 1965, of what is called background radiation. This “sea” of electromagnetic radiation fills the universe at a temperature of about 2.7 K (2.7 degrees C above absolute zero). 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 (20 to 30 percent by weight) is also a required result of the big-bang conditions predicted by relativity theory.
In addition, general relativity has suggested various kinds of celestial phenomena that could exist, including neutron stars, black holes, gravitational lenses, and gravitational waves. According to relativistic theory, neutron stars would be small but extremely dense stellar bodies. A neutron star with a mass equal to that of the Sun, for example, would have a radius of only 10 km (6 mi). Stars of this nature have been so compressed by gravitational forces that their density is comparable to densities within the nuclei of atoms, and they are composed primarily of neutrons. Such stars are thought to occur as a by-product of violent celestial events such as supernovae and other gravitational implosions of stars. Since neutron stars were first proposed in the 1930s, numerous celestial objects that exhibit characteristics of this sort have been identified. In 1967 the first of many objects now called pulsars was also detected. These stars, which emit rapid regular pulses of radiation, are now taken to be rapidly spinning neutron stars, with the pulse period represent the period of rotation.
Black holes are among the most exotic of the predictions of general relativity, although the concept itself dates from long before the 20th century. These theorized objects are celestial bodies with so strong a gravitational field that no particles or radiation can escape from them, not even light–hence the name. Black holes most likely would be produced by the implosions of extremely massive stars, and they could continue to grow as other material entered their field of attraction. Some theorists have speculated that supermassive black holes may exist at the centers of some clusters of stars and of some galaxies, including our own. While the existence of such black holes has not been proven beyond all doubt, evidence for their presence at a number of known sites is very strong.
in conclusion, relativity is a way of looking at things, keeping in mind that everything is moving, and that we really have no way of know just how fast. This theory, along with complex equations developed many years ago, helped to explain certain long misunderstood things about planets and their movements. But the same thinking about very large objects, in motion, like stars, planets, solar sysems, simply does not work accurately when you look at microscopic things, like atoms. Too, since the development of the theory of relativity, we have made many technological advances that have allowed us to make accurate measurements, and to basically confirm the theory is correct.