Special Relativity, an aesthetically appealing theory was proposed by Albert Einstein after some apparently paradoxical observations related to the speed of electromagnetic radiation. It is concerned with the nature of space and time, and is based on two postulates:
1). The Relativity Postulate : The laws of Physics are the same for all observers, and in all inertial frames.
2). The Speed of Light Postulate: The speed of light in vacuum has the same value in all directions and in all inertial frames. No matter how fast does one moves himself, or the source, the speed of incoming light will always remain the same.
To explain the second postulate, let us assume two observers moving at different speeds while observing light coming from the same source. According to Special Relativity, both these observers measure the same speed irrespective of what the difference in their relative speeds is. This is explained by the basic foundation of Special Relativity - nothing can travel faster than light. The reason why both the obsevers measure the same speed, is that when the speed of the frame of one of the observers increases, his perception of time changes as compared to the other observer who is in a stationary frame. Although the distance measured by these two observers will be different, the time measured by them will also be different, and hence will lead to the same value for the velocity.
This fact was experimentally tested in 1964, at CERN, where the speed of gamma rays emitted by neutral pions moving at 0.99975 times the speed of light was measured, and actually found out to be the same as that emited by a stationary source.
To explain this further, let us now assume a train which moves on the earth, the relative velocities of the train and the earth differing by a considerable factor of the speed of light. In such a case, the time measured by two clocks, one on each frame will at any instant differ, by a factor which can be expressed by
tt = te ( 1 - (v/c)2 )-1/2
Where tt is the time shown by the clock on the train, te is the time shown by the clock on Earth, and the quantity , is known as the Lorentz Factor.
Time dilation at high velocities, was tested in 1977 at CERN, by measuring the lifetime of muons, that were accelarated to a speed od 0.9994 times that of light. The experimentally predicted life-time of 63.5 :s was actually observed to be true. Time dilation was also tested by macroscopic clocks, and confirmed by the results.
This however, is completely different from the 'classical universe' where the difference between two observer's velocity measurements of a third object corresponds with the difference between their own relative velocities. Why such a universe can easliy be accepted, is the fact that in normal life, no object other than light itself attains such high velocities comparable to that of light, and Special Relativity says that they never can, the barrier being the velocity of light itself, which is 299,792,458 ms-1.
Special Relativity theory addresses the relative speed paradox by allowing that time and space occur differently for different observers in such a way that the apparent differences in their observations are reconciled by their measurements of time and space. These two are dependant on the frame of reference of an observer, and not the same for all.
A set rules for transformation of time and space, define the Special Theory of Relativity, some of which are:
> All observers in different inertial frames, measure the same speed of light, irrespective of their relative motion.
> Time and space occur in the same way with respect to each other for all observers in inertial frames.
> The universe behaves like our 'classical' model when we restrict our perspective to situations in which velocities are much less than the speed of light.
Hence, one observer's set of clocks would not appear synchronized to another in another inertial frame and vice-verca. Also, for any pair of simultaneous events, there can always be observers in two different frams that view them at different times. It is important to note that in relativity, an absolute 'present' does not exist and each entity must exist in its own space-time context. In other words, it can be said that if two observers are moving relatively to each other, they will not agree as to whether the two events are simultaneous. However, both of them will be right.
According to Special Relativity, simultaneity is not absolute, but is relative and depends upon the state if the observer.
In conventional representations of Special Relativity, space and time occur as an abstract four-dimensional geometry, three dimensions being for space, and the fourth one for time. Every point in this four-dimensional universe represents an event. This geometrical representation is accurate in its modelling of relativistic relationships, However, the geometry used is truly abstract, non-Euclidean and cannot be visuallised by three dimensional beings like us.
In space-time geometry the "distance" between events is given by sum of the squares of the space co-ordinates minus the square of the difference in the time co-ordinated. The subtraction of the time and space distance terms causes the separation to take on values that do not accord with our ordinary understanding of geometry. For example, when the separation in space equals the separation in time, the distance between the events is zero. Also, when the separation in time exceeds the separation in space, the separation comes out to be an imaginary number. Such geometry of Special Relativity and its abstract space-time geometry is quite different from our 'classical' model. Observations of light and time today provide compelling evidence that the descriptions provided by Einstein are accurate and that our 'classical' model of the universe arises from an illusion, which fits our daily life since we cannot readily achieve speeds that can make relativistic effects in our world.
The views proposed by Einstein in his Special Theory of Relativity are so fundamentally true and contradictory to our classical ideas that there is little possibility that we would revert back to the classical model. Any new interpretation of our universe would have to include the views proposed by the Eintein's model.