General Relativity BasicsAuthor: Zion
General Relativity Basics
At the age of 25, Albert Einstein (1879-1955) has come up with his Theory of Relativity, actually, the theory of Special relativity. This was at the year of 1905.
Ten years latter, at the year of 1916, after lots of mental effort did he published his theory of General Relativity.
Both theories did make a huge change in the perception of Energy, Matter, and Space. The Special relativity deals with bodies and particles moving in a uniform, constant velocity relative to each other, while the General Relativity deals with accelerated bodies.
We will discuss here the General Relativity only, and will leave the Special Relativity for another article.
Well, what are the basics behind the General Relativity?
General Relativity actually deals with gravitational interaction between objects. It thus deals with the rules that govern the giant universe and the galaxies within.
It all started when Einstein tried to express accelerated motions in terms of gravitational field. He claimed that the acceleration of "falling" object can be formulated in terms of a movement of the object in the gravitational "field", rather due to the gravitational "force" the object sense, as claimed the classical laws of mechanical physics. Einstein said: there are no gravitational forces out there. There is a gravitational field that causes objects to move in an accelerated motion (i.e. falling or travelling in a certain orbit).
What was that gravitational field that Einstein had defined? He claimed that the space-time domain is actually curved. Where ever there is a giant mass, it distorts the space (like creating a deep curve in space) to which objects fall if they are sufficiently close.
To clearly understand this, imagine the following commonly used example: suppose there a bit flat rubber tissue held well stretched. Now put a metal ball on this rubber tissue. The metal ball will create a curve in the tissue. Another object that travels on this tissue, when sufficiently close, will be trapped by this curve and will accelerate toward the metal ball. This is actually the gravitational field, consisting of curved space trying to trap any moving object out there.
This example, although understandable for a two-dimensional rubber tissue case, is not so easily understood for the space-time four-dimensional domain.
Anyway, Einstein needed about ten years of hard mental effort, and using complicated mathematic and a different geometry principles in order to formulate his new revolutionary theory.
This was of course a revolution. This postulate undermined the 300-year classical Newton mechanics that ruled the cosmos motion, which actually did a great job, reflected in amazing travels in space and man landing on the moon.
In contrast to the Special relativity that was quite simple to understand and adopt, even for the regular people, and had quite simple mathematics to support it, the General Relativity was really a new hard concept to digest. The idea of a curved universe, and the complicated geometry and mathematics behind, made this theory unique to very few scientist.
Although the new theory did succeed to explain some abnormal orbits of certain cosmic objects, and although one of the world wide scientific experiment done in 1919 did prove that light is bent at the vicinity of a big cosmic object, as the general relativity equation predicted, still it took many years later till the general relativity did gain its appropriate importance in the science world.
The general relativity was in full compliance with the Newton mechanics, and was found to be more accurate when enormous object are in concern, and near-light velocity is handled. The Newton's mechanics for example could not specifically explain how the graviton forces act, and how there are transmitted. It also stated that the force act between object at no time. For example, if the sun vanishes all of a sudden, the earth will immediately sense this change, and immediately its track will change. However, according to General relativity, the disappearance of the sun will be sensed by Erath only after about eight minutes, the time that the wave of gravitational change will make its way from the sun to earth, and only then will earth orbit start to react to the change.
Within the years more and more evidence to the general relativity predictions were found, and more theories were developed on top. Black holes, universe expansion/inflation, big bang, and other funny notions are based on the General relativity.