Relative direction
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The most common relative directions are: Left, right, forward, backward, up, and down.
There is no universal direction which can be said to be either one of them. Scientifically this is expressed as that there is no absolute inertial frame of reference. One famed attempt to discern what is the "real" up and down in the universe was the Michelson-Morley experiment. The fame comes from the experiment's complete failure, something which eventually led up to the Albert Einstein's theories of relativity. These conclude that it is not possible to find an absolute up or down.
The upshot of this is that the most basic concepts of direction known to mankind cannot be scientifically defined. They are - in effect - defined through tradition and word of mouth. This also means that in order to use these directions to express oneself one first has to define a reference.
The easiest relative directions to define are up and down. The most common definition uses gravity and the planet Earth as a frame of reference. Since there is a very noticeable force of gravity acting between the Earth and any other object, down is defined as that direction which an object moves in reference to the Earth when the object is left to fall freely. Up is then defined as the opposite direction of down.
Another common definition uses a human body, standing upright, as a frame of reference. In that case, up is defined as the direction from feet to head, peripendicular to the surface of the Earth.
Forward and backward are most commonly defined by referring to an object or person's motion. Forward is defined as the direction in which the object is moving. Backwards is then defined as the opposite of forward.
The terms left and right are derived from the fact that some 90% of the population use the hand of the same side of their body for writing and other manual tasks. Through cognate of the word right in the meaning correct or good, the side with the hand most used was defined as the right side. The word left comes from the Old English lyft, meaning weak. This dichotomy can also be seen in the words dextrous and sinister, from the Latin words for right and left. In order to figure out which hand is which you will need a compass and the sun. Face the sun before solar noon and check the compass. The hand on the south side is right. Left is then defined as the opposite of right.
In the vast majority of the population, the heart is slightly to the left of the body's centre line and the liver is to the right. Less visibly, the two hemispheres of the brain differ in function.
In nautical usage, the halves of a ship are designated port (left) and starboard (right), relative to a person looking forward (towards the bow of the ship).
In politics, "left" and "right" are labels applied to parts of a theoretical spectrum of opinion:
- Left is associated with socialism, and, in the United States, with liberalism and the Democratic Party. In the extreme, "left" can be associated with communism and anarchism.
- Right is associated with conservatism, and, in the United States, with the Republican Party; elsewhere in the world it is also often associated with liberalism. In the extreme, "right" can be associated with fascism.
This usage derives from the seating of parliamentary partisans during the French Revolution; see Left-Right politics.
Example
In this diagram, showing a road with right-hand traffic, the red car is to the left of the blue car. The blue car is, therefore, on the right-hand side. Should the blue car move backward, it would reach the position of the yellow car. For the red car to be where the green car is, it would have to move forward.
The lane containing the green and red cars is the left lane, the lane with the yellow and blue cars is the right lane.de:Links de:Rechts fr:Gauche he:ימין ושמאל (כיוונים במרחב) nl:Links en rechts (richting) zh:相对方位