Greenwich falls on the environs of the British capital. It can be reached by a one-hour bus journey, or by boat. Although it is famous for its astronomical observatory -which was turned into a museum after it was moved to another location due to pollution in the capital – its large maritime museum and the Cutty Sark Ship sitting at its dock and which is a tourist attraction and a reminder of Britain’s trade and naval glories, it is necessary to visit Greenwich for those who wish to see for themselves the birth of mean solar time to measure standards of time and space.  

In the observatory’s old yard, where science’s oldest masters, like Isaac Newton, Edmond Halley and John Flamsteed once stood, a visitor sees a line that crosses the yard and divides the earth in two. An amazing feeling overcome you in the middle of the world at zero degrees of longitude and the  central time zone. For a few pounds sterling, you will receive from the ATM machine a card that immortalizes your visit. All this, and the line is illusionary and the halves of the earth are relative.

What we call lines of longitude and latitude are in fact nothing more than a genius, defining addition. It is difficult to picture civilization without it. Neither trade nor communications would have been possible. At the beginning, they were used to demarcate the globe and to facilitate finding cities, places and distances. After that everything on the earth became identified through a series of curvatures that encircle the globe in opposing directions. When astronomy evolved, scientists used the same method for the celestial sphere to determine the locations of stars and calculate distances. 

It was a simple yet magnificent invention.

Around 150 AD, astronomer and geographer Ptolemy of Alexandria challenged this school of inventions in documented references and translated them into 27 maps that formed the first known atlas in the world. But being a scientist who shunned travelling, he did not double check much of what he wrote and prominently said that everything that lives below the equator is at risk of melting due to the heat. When Ptolemy drew the lines of longitude he was free to choose the line that halved all these lines (prime meridian). He selected the islands, known today as the Canary and Madeira islands, off the northern-western coast of Africa. The line then respectively moved between the Azure islands, Cape Verde islands, Rome, Copenhagen, Jerusalem, Cairo (reference to the Grand Pyramids of Giza), Saint Petersburg, Pisa (reference to its tower), Paris, Philadelphia until it settled in Greenwich. A degree in the line of longitude at the equator is equivalent to its value at the line of latitude i.e. 110 kilometers (since it is the outcome of 1 divided by 360 degrees of the earth’s circumference.

At 40 degrees of longitude, which forms a circle that is smaller than the line of longitude that crosses the equator, a degree equals 84.8 kilometers only while at 60 degrees, a degree equals 55.5 kilometers. Meanwhile, at the two poles where all lines of longitude meet, a degree equals zero. Here also, the value of the longitude lines is similar to the latitude lines and each degree is divided into 60 minutes and each minutes into 60 seconds.

Since the earth’s rotation around its axis takes 24 hours, this means it rotates 360 degrees every 24 hours. As such, one hour is equivalent to 15 degrees and every two points 15 degrees apart are at an hour’s distance in the time cycle.

On this basis, a system for the standards of space was set. As for time, Greenwich was chosen in an 1884 conference as a referral point to a new timing system that divided the world into 24 time intervals which helped put an end to all the commotion over time differences. With that, the United States was divided into eight time zones compared to 300 before the agreement. Implementation was not smooth since a similar attempt had previously failed when American farmers feared that this new timing will hinder chickens from laying their eggs or cause the milk to dry up in the cows. Chicago workers also went on strike because the new system would force them to work nine extra minutes. 

This system continued to represent reality until Einstein appeared with his theory of relativity which annulled the concept of time and space as absolute values. The time length of an event and its space dimension, according to relativity, are not constant values and can only be determined according to the observer. Therefore, the relativity theory replaced space and time, which are the main pillars of the traditional system, as two individual factors with one encompassing factor which is space-time.

The widespread Newtonian conception stipulates that for a light beam sent from one place to another, observers, irregardless of how many there are, will agree on the time length for the light journey, because time, according to Newton, is an absolute. As for Einstein, this is not true because the theory of relativity does not recognize real time for an event that two persons, one of immobile and the other mobile, are trying to intercept each from their own location and circumstance.

As evidence, Einstein gives the following example: A set of twins, one lives in an earth station and another takes a distant space journey at high speed then reverses course and returns. Of course the twins will disagree over the timing since it is a distant event, meaning that a specific time of an incident inside a spaceship is determined by the immobile twin in the earth station with a time difference than that determined by the twin in the ship. Since the difference relies on speed, then the difference will not fade away upon the ship’s return but will double since the return journey is a second trip. The result is that when the twins meet they will not be of the same age but the traveler twin will find himself younger than his brother. This concept turned around science in one of the greatest scientific revolution. What does that signify scientifically and what are its consequences? This is what we will address in the following issue.