Special Theory of Relativity Part 2 - The Postulates

In the first part of this series of blogs, we discussed the various mysteries of light such as, why doesn't it have relative motion, is it a wave or a particle and why can't one reach the speed of light. We also talked about reference frames which in simple terminology, is the place where one observes from. Today we will discuss the consequences or postulates of the special theory of relativity.
The First Postulate of Special Relativity
The first postulate of the theory of special relativity is: The laws of physics hold true for observers in all uniformly moving frames of reference.
This is the simplest of all relativistic concepts to grasp. The physical laws help us understand how and why our environment reacts the way it does. They also allow us to predict events and their outcomes. Consider a wooden pencil. If you measure the length of the pencil, you will get the same result regardless of whether you are standing on the ground or riding a bus. Next, measure the time it takes a pendulum to make 10 full swings from a starting height of 10 inches above its resting point. Again, you will get the same results whether you are standing on the ground or riding a bus. Note that we are assuming that the bus is not accelerating but travelling along at a constant velocity on a smooth road.
 Now if we take the same examples as above, but this time measure the length of the pencil and time the pendulum swings as they ride past us on the bus, we will get different results than our previous results. The difference in the results of our experiments occurs because the laws of physics remain the same for all frames of reference. It is important to note that just because the laws of physics are constant, it does not mean that we will get the same experimental results in differing frames. That depends on the nature of the experiment. For example, if we crash two cars into each other, we will find that the energy was conserved for the collision regardless of whether we were in one of the cars or standing on the sidewalk. Conservation of energy is a physical law and therefore, must be the same in all reference frames.
The Second Postulate of Special Relativity
The second postulate of the special theory of relativity is quite interesting and unexpected because of what it says about frames of reference. The postulate is: The speed of light is measured as constant in all frames of reference (i.e. the speed of light is independent of the motion of the observer).
This can really be described as the first postulate in different clothes. If the laws of physics apply equally to all frames of reference, then light (electromagnetic radiation) must travel at the same speed regardless of the frame of reference. Speed is the distance traveled in a given amount of time. For e.g. if you travel at 60 miles in one hour, your speed is 60 miles/hour. We can easily change our speed by accelerating or decelerating. For the speed of light to be constant, even if the light is "launched" from a moving object, only two things can be happening. Either something about our notion of distance and/or something about our notion of time must be skewed, i.e., distorted. As it turns out, both are skewed. This is called length contraction and time dilation which we will discuss in the next blog.
Part 3 will come out soon.
Reference:
1. https://www.howstuffworks.com
2. Physics for the Rest of Us by Roger Jones

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