Rivers of Time - Principal of Relativity

RIVERS OF TIME THE PRINCIPAL OF RELATIVITY It all started when Galileo Galilei's published his Principal of Relativity in 1639. He wrote that no absolute state of motion could ever be determined among a group of observers who are moving in uniform motion. (Uniformity in motion implies that movement occurs along a straight line path, and at a constant speed.) Later in that century, Sr. Isaac Newton began formulating the classical laws of physics. He did this in such a way as to allow the physical laws of gravity and motion to remain consistent in any frame of reference having uniform motion. To better appreciate the Principal of Relativity, let us embark on an imaginary journey through space and time. Consider the situation where a guy named Albert had been propelled by a spaceship out of the solar system. At some point along the journey, his rocket engines shut down to conserve fuel. He begins drifting through space at a constant speed, and in a never-changing direction. There is no air friction to slow the momentum that had been imparted upon his spaceship by the rocket engines, and there would be negligible gravitational forces to veer his craft from its present course. He and the spaceship would be experiencing uniform motion. While looking through the front and side windows of the spaceship, Albert sees only stars around him. From this unique prospective, there would be no sensation of motion and the stars would all appear stationary due to their great distance from him. His mind becomes tricked into believing that he and his spaceship are at rest... hanging motionless in space. In reality, however, his spacecraft is speeding away from the solar system at a tremendous speed, making its way to the nearest star Alpha Centauri. His journey will cover a distance of 4.37 light years. If Albert carried out experiments inside his spaceship, to test the validity of Newton's three laws of motion -something one might do out of complete boredom- he would discover that the laws of physics hold just as true there, on board his spaceship, as they do on Earth. Interestingly, none of these experiments would reveal anything about his present state of motion. Growing tiered of conducting physics experiments, Albert decides to paint a message on the side of his spaceship. The words say "HELLO. MY NAME IS ALBERT EINSTEIN. I'M AN EMISSARY FROM THE PLANET EARTH!". Much time passes... Suddenly appearing through the front window of his spaceship, Albert sees another spacecraft rapidly approaching and then, in a flash, passing him by. It appears that this alien craft was traveling at a very high speed! He just had time to catch a glimpse of some words painted on the side of the passing spacecraft. The words say "HELLO. MY NAME IS RUEE. I'M AN EMISSARY FROM ALPHA CENTAURI!". I'll shift the focus of the story and tell you a little about the alien Ruee. He is a famous scientist who was launched from Alpha Centauri toward its nearest star called Sol. His rocket engines had long been shut down to conserve fuel, and he and his spacecraft were traveling though space with uniform motion. Ruee peered through the windows of his spacecraft and saw only stars around him. He felt no sensation of motion and the stars all appeared stationary due to their great distance from him. His mind had already been tricked into believing that he and his spacecraft were at rest... hanging motionless in space. Out of pure boredom, Ruee performed several experiments to confirm the physical laws that had been theorized by the greatest minds on his planet. In every case, the experimental results were exactly as they had been predicted. Growing tiered of this, Ruee decided to write a message on the side of his spacecraft. The words say "HELLO. MY NAME IS RUEE.......". Much time passed... Suddenly, through the front window of his spacecraft, Ruee saw a spaceship rapidly approaching and then, in a flash, passing him by. He caught a glimpse of some words painted on the side of the passing spaceship. The words said "HELLO. MY NAME IS ALBERT EINSTEIN. I'M AN EMISSARY FROM THE PLANET EARTH!". Albert and Ruee, each, had their own experiences during that flyby event. Each considered himself to be at rest, and it was his alien counterpart who seemed to be traveling at a very high speed. At the same time, an observer on planet Earth felt herself motionless (completely at rest) as she gazed through a powerful telescope at the two planetary emissaries. She saw both in motion and traveling in opposite directions. Who was correct in believing that he or she was at rest? Can we say that one observer's experience should be trusted over any other observer's experience? The answers are: Everyone was correct in declaring themselves at rest, and no... there was no preferred prospective when witnessing the event. Uniform motion is completely relative. Any one of the observers could have arbitrarily assumed himself or herself to be at rest. Within the scope of mathematical formulation, the net difference in motion is all that matters. Two very important principals came out of the 17th century: Firstly, no absolute state of motion can be determined by a group of observers who are moving in uniform motion; and secondly, the laws of physics are invariant in any frame of reference that is moving in uniform motion. The classical laws of physics, as formalized by Isaac Newton, would rule until the beginning of the 20th century.