Relativity--Special Theory

From Cassiopedia

The Special Theory Of Relativity is the physical theory of space and time developed by Albert Einstein. It is based on the postulate that all the laws of physics are equally valid in all frames of reference moving at a uniform velocity and that the speed of light from a uniformly moving source is always the same, regardless of how fast or slow the source or its observer is moving.

Albert Einstein first published his special theory of relativity in 1905. It replaced Newtonian notions of space and time, and incorporated electromagnetism as represented by Maxwell's equations. This theory is a special case of Einstein's principle of relativity (hence the name special relativity) where the effects of gravity can be ignored. Ten years later, Einstein published the theory of general relativity, which incorporates gravitation.

The consequences of this theory establish the following:

1) The relativistic mass increase of rapidly moving objects From Wikipedia: The term mass in special relativity is used in a couple of different ways, occasionally leading to a great deal of confusion. Specifically, mass can refer to either the rest mass or the relativistic mass. The rest mass, or invariant mass, is an observer independent quantity, while the relativistic mass, or apparent mass depends on one's frame of reference.

In particular, the relativistic mass increases with velocity while the rest mass stays the same. Both of these terms are somewhat outdated. In the earlier years of relativity, it was the relativistic mass that was taken to be the "correct" notion of mass, and the invariant mass was referred to as the rest mass. Gradually, as special relativity gave way to general relativity and found application in quantum field theory, it was realized that the invariant mass was the more useful quantity and people stopped referring to the relativistic mass altogether.

When particle physicists talk about the mass of an object they always mean the rest mass. They use other terms, like energy, to refer to the relativistic mass (The reason for this is explained in the next section). The terms rest mass and relativistic mass can still be found in elementary textbooks and, especially, in popularizations of physics. There are several arguments, discussed below, as to why this terminology should be dropped. However, the fact that some relativity courses continue to use relativistic mass demonstrates that this is a matter of opinion. In modern usage the term mass, when unqualified, always refers to the invariant (rest) mass.

2)The Lorentz-Fitzgerald contraction: From Wikipedia: Fitzgerald suggested that when a body moves through space it experiences a compression in the direction of the motion. Lorentz showed how such an effect might be expected based on electromagnetic theory and the electrical constitution of matter, that is, when a body moves through space its dimension parallel to the line of motion might become less by an amount dependent on its speed

3)Time Dilatation: From Wikipedia: Time dilation is a consequence of Albert Einstein's theories of relativity. It occurs when one observer finds a clock which is measuring proper time ticking slow with respect to the relative time defined by his own clock (which is also measuring proper time). In special relativity, this occurs for clocks which are moving with respect to an inertial observer. In general relativity this occurs for clocks at lower potentials in a gravitational field, and is called gravitational time dilation. This effect is commonly thought of as being time slowing down for the time dilated clock. This is not the case. Locally, one's proper time always passes at the same rate. Instead what is slowed down is how that proper time passage is perceived by another observer.

4)Mass-Energy equivalence. Mass, momentum, and energy From Wikipedia In addition to modifying notions of space and time, special relativity forces one to reconsider the concepts of mass, momentum, and energy, all of which are important constructs in Newtonian mechanics. Special relativity shows, in fact, that these concepts are all different aspects of the same physical quantity in much the same way that it shows space and time to be interrelated.