# Portal talk:Special relativity

## Archive of material that should not be on this topic page

This is a Wikiversity:topics page, so i've removed the following material from it. Please incorporate it into another learning resource if you think it's useful. i disabled the section headers. Boud 12:38, 21 June 2011 (UTC)

Archive begins

The Special relativity (SR) or Special relativity theory (SRT) is the physical theory published in 1905 by Albert Einstein. It replaced Newtonian notions of space and time, and incorporated electromagnetism as represented by Maxwell's equations. The theory is called "special" because the theory does not include a description of gravity. Ten years later, Einstein published the theory of general relativity, which incorporates gravitation.

== Introduction

Before special relativity can be understood it is wise to revise Newtonian Mechanics paying close attention to its assumptions. This course will first re-examine classical mechanics in 3 dimensions whilst introducing relativistic notation. Specifically, students are used to using x,y,z to specify spacial position, whereas this course will talk about dimensions 1,2,3 instead. This is not to confuse you, but to train you into thinking in terms of dimensions. Already you may be guessing where this is leading, to the use of a number 4. The course continues on to describing the observations which demand a re-thinking of our basic assumptions about time and space and how electromagnetism was found to be inconsistant with classical mechanics. The student will find it satisfying to derive Einstein's famous equation relating mass and energy and gain a fuller understanding of the nature of space and time. It is anticipated that this course will be one of the most popular in Wikiversity.

== Motivation for the theory of special relativity

The principle of relativity was introduced by Galileo. Overturning the old absolute views of Aristotle, it held that motion, or as least uniform motion in a straight line only had meaning relative to something else, and that there was no absolute reference frame by which all things could be measured. Galileo also assumed a set of transformations called the Galilean transformations. These seem like common sense today. Galileo produced five laws of motion. Newton accepted the principle of relativity when constructing an improved set of only three laws of motion.

While these seemed to work well for everyday phenomena involving solid objects, light was still problematic. Newton believed that light was "corpuscular", but later physicists found that a transverse wave model of light was more useful. Mechanical waves travel in a medium, and so it was assumed for light. This hypothetical medium was called the " luminiferous aether". It seemed to have some conflicting properties, such as being extremely stiff, to account for the high speed of light, while at the same time being insubstantial, so as not to slow down the Earth as it passes through. The idea of an aether seemed to reintroduce the idea of an absolute frame of reference, one that is stationary with respect to the aether.

In the early 19th century, light, electricity, and magnetism began to be understood as aspects of the electromagnetic field. Maxwell's equations showed that accelerating a charge produced electromagnetic radiation which always traveled at the speed of light. The equations showed that the speed of the radiation did not change based upon the speed of the source. This is consistent with analogies to mechanical waves. Presumably, however, the speed of the radiation would change based on the speed of the observer. Physicists tried to use this idea to measure the speed of the Earth with respect to the aether. The most famous attempt was the Michelson-Morley experiment. While these experiments were controversial for some time, a consensus emerged that the speed of light does not vary with the speed of the observer, and since

== Newtonian Assumptions on the nature of Space and Time

=== Assumption 1

Archive ends