The Historical and Conceptual Background of the Special Theory of Relativity

(Last modification: Sep 1^st, 2003)

Among people interested in understanding or in discovering what the Theory of Relativity is about, there are:

• People that believes that Einstein was a genius and he was right in the great majority of its statements.
• People thinking Einstein was a normal person and the circumstances made him famous.
• People that affirms that Einstein and their theories are the biggest scientific fraud in human history.

Independently of personal opinions, the Theory of Relativity is one of the pillars of the modern Physics and it didn't only change our way to see and understand the physical world, but rather it notably influenced the thought of the greater contemporary philosophers.

The non-specialist public associates Relativity with: 

• Loss of absolute referential points ("Everything is Relative")
• The atomic bomb.
• The black holes.
• Clocks that go mad when they move to high speeds.
• Trips in time ....

Most people, also, has no idea about how the work of Einstein can affect his daily life. But, inevitably who feel curiosity for these theories manifest a remarkable necessity to understand the world that surrounds them. Trying to understand the Theory of Relativity is to try to understand what is the Universe.

However the Special Relativity has generated (and generates) several contradictory opinions from scientific people and non scientific "freethinkers" . Besides many publications and books, the Web gives numerous alternative proposals to overcome the so called "logical deficiencies" of the Special Relativity. And, as I mention in another part of this page, this situation doesn't demonstrate that Einstein was mistaken. It only indicates that their concepts are very difficult to be accepted by "common" people.

In consequence I will try to begin by the beginning. Einstein is, without doubt, one of the big humanity geniuses. It was a kind of person able to see things that others were unable to see. And he also had the courage (the strength) of accepting results that his convictions told him that were correct although they were against the line of the dominant thought. And, also, the results of his physical world analyses changed the world where we live. Of course, the theories of Einstein are based on previous developments, made by giants of similar size. But that doesn't subtract merit to his own capacity.

However, Einstein (same as Newton in his moment) tried to avoid the hypotheses or explanatory models. In many cases he took data of experimental reality and elevated them at the postulate level. For his fundamental developments he chose some postulates  coherent with the available information and he studied the consequences.

You can follow the same road that Einstein, appealing to his publications or books, but this is usually an arduous trip. In this page we will try to understand not only ¿How? or ¿What? but ¿Why? . It will obligate us to leave his road but this is the more consistent form of satisfying our necessity of understanding.

In a more marked form, the dominant current in the modern Physics rarely wonders "why". Generally speaking Physics tries to describe "How". 

Example: If an equation is functional, don't care why it works.

However the curious man (like myself) many times wants to understand why the equation works.

Trying to understand the why of something, implies some arrogance. It implies that we feel able to understand the intimate mechanism of things operation. Using an example of the daily life, we are usually interested how to manage an automobile, and not why the motor and the associate mechanism are able to transform the chemical energy in movement.

In this line, in his original development (1905) Einstein postulated, "any ray of light moves in a stationary system with speed " c " so much if the ray is emitted from a body in movement as if it is emitted from the stationary system".

He didn't try to explain why this happens. To explain why, it implies to choose a model adapted to the reality. And the election of a model is a very delicate task. It is simpler (and less objectionable) to say: "things happen in such way", or "everything happens as if...."

Well, one of the questions I will try to answer is: Why the speed of light is the same for all the systems in non-accelerated movements?

In other hand, in Special Relativity, the dilation of time and the contraction of longitudes is only a result of using appropriately the mathematics from some few initial axioms. Well, in my developments I will try to explain why this phenomenon takes place. I will feel very pleased if, as a result of these readings, some of the visitors begin to accept as reasonable the following:

• It is possible that time run at different rhythms for different observers.
• The constant speed of light can be an understandable characteristic of our Universe.

All the Relativity is born linked and in association with the behavior of light. When kids, we hear that matter has atoms and, speed of light is a constant. Those are the type of "truths" that we don't question because everybody takes it for granted. However, to arrive to these statements meant an arduous journey for the humanity.

An important note: Although Relativity analyzes the behavior of clocks and bars employing luminous signs, this doesn't mean that its consequences are only applied to clocks, bar and rays of light. The light is an electromagnetic phenomenon (something like a wave formed by electric and magnetic variable fields). But all the regular physical interactions are electromagnetic interactions. Except for the force of gravity, the whole aspect of the world that surrounds us is modeled by the interactions of external electrons of atoms and the different electromagnetic waves. Example: The aging is a phenomenon associated to the chemical reactions that take place in our cells. And these chemical reactions are the result of electromagnetic interactions. For this reason the biological clocks are affected the same as the mechanical clocks in the analyses of the Special Relativity.

Let us try to answer the following question:.¿ How does light travel?.

According to our experience, when something moves from a place to another, it is so through two basic mechanisms: 

1. With the independence of a supporting medium. 
2. Propagating through a supporting medium.

It is easy to distinguish both mechanisms: 

• In the first case, the speed of the source is added to that of the object (E.g.: a basketball ball is impelled by a moving player) 
• In the second case the speed of what is emitted is not affected by the speed of the source. (E.g.: The speed of sound doesn't depend on the speed of the emitter).

When was accepted (according to Newton theories) that light was formed by small corpuscles, it was reasonable to suppose that it was not need for a medium allowing the light to move. This situation was in accord  with the experimental observation that light travels on straight line and that crosses the vacuum without difficulty.

However, while developing the Electromagnetic Theory (Maxwell) the concept of a Wave Theory of light was strengthened. And, if light is a wave, it should propagate through some medium that gives support to it. Favoring the existence of this supporting medium (called "ether") were several demonstrations that the speed of light is not affected by the speed of source. Besides numerous laboratory experiences an undeniable source of information exists: The explosions of Supernovas in distant galaxies.

These explosions are almost an instantaneous phenomena at the scale of universe. If the speed of waves were dependant on the speed of source, it would happen that during the explosion, the Star's different parts would emit its signals at different speeds toward us (as example, as a result of the solar rotation, the different parts of the Sun surface would have a component of different speed toward the Earth). Without involving the characteristic speed of the explosion. Considering only the normal speeds of rotation of celestial bodies. Differences of 0.000001 speed of light (speed of sound), are converted in retards of several years when the signal crosses the distance of 10,000,000 light years. And explosions of Supernovas have been observed in much more distant galaxies with a total duration of some few days. The result is conclusive. The speed of the source doesn't affect the speed of light.

Question: ¿Does it exist, then, a medium in which the luminous waves spread?.

Answer: Until the arriving of Special Relativity the answer given by the main scientific stream was YES, in spite of the fact that all the tests for the existence of the "ether" were indirect.

Nevertheless, many Scientifics speculated with regard to the physical properties of " ether ". The following is a translation from an article about the ether included as part of a Hispanic-American encyclopedia, edited at the end of the 19th century.

".... The transformation of motion in light, in heat and in electricity, seems to adduce an additional  test  in pro of the existence of the ether whose main properties are exposed here:

1. It is inert, as it demonstrates the change between him and matter.
2. It is extremely elastic because the propagation of light through a medium varies with the medium elasticity degree: and spreading in the ether with the speed of 298,000 km. per second, it is that the elasticity of this fluid has to be immense.
3. It is discontinuous, in opposition to some affirmations, as demonstrates the polarization phenomenon.
4. It is not the diffusion of the planetary atmospheres because otherwise it would be opposed to the law of Mariotte: the elasticity is proportional to the density.
5. It is a material fluid, opposed the opinion of some physiques that deduce the immaterial of the weightless of ether, without seeing that gravity is not essential to matter, as it is inertia.
6. It is not affirmed neither denied that ether is dense because the density of a body is always relative and, until today, it is not possible to compare the ether to another ponderable substance.
7. Similarly, it is not affirmed that ether is imponderable.

The modern physiques in favor of ether, refer all the forces to only one, the gravity, and the whole matter to ether. Some of these go further and they suppose that gravitation could have its origin in the diverse degrees of condensation of the ethereal mass...."

However, all the intents to determine the properties of the Ether failed.

Is in this scenario where Einstein took the bull by the horns and outlined a development in which the ether stopped to be something to be worry about. The Special Theory of Relativity of Einstein, represents one of the most audacious steps in the human thought. But it is also a symbol of search of the scientific truth, through the simplest postulates.

To develop the Special Relativity, Einstein arrived to the foundations governing the interactions in Physical world. In few words, to derive the transformation formulas among systems in movement, Einstein began to analyze what is simultaneity of two events and synchronism of clocks to observers that are not one beside another.

And this way of outlining the problem is an example of the brightness of Einstein to distinguish between the obvious and what cannot be accepted without a previous analysis. For this reason, any intent of understanding the Special Relativity implies forget preconceptions and open the mind. The effort to carry out is very important and the recompense worth it. At the end of the road, understanding, or not, the entirety of the Theory, we end with a vision of universe, mass, time and space that forces us to reanalyze the philosophical bases of the knowledge.

To analyze the Special Relativity implies, inevitably, to be introduced in philosophical topics. This Theory is very far from being only a mathematical development of the Physical world. It is fundamentally a conception of the Physical world and their interactions.

In the following pages these implications are discussed in detail.

In brief, the main objectives of this site can be summarized in the following points: 

1. Analyze and discuss the main concepts of the Special Relativity. 
2. Distinguish between objective data and speculations. 
3. Give an understandable explanation for the variation of times and lengths with observer's speed.

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