Physics behind the Theory of Relativity

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  • Topic: Special relativity, Speed of light, Spacetime
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Physics Behind
The Theory of special relativity
Related Concepts


Prior to albert Einstein’s theory of special relativity there was always an idea about relativity. Through Galilean transformations, which worked perfectly with the newton’s laws of motion, people had formed a vague idea that all motion in this world is relative to something else. There came up the mysterious thing called aether — the medium through which light propagated. The belief in aether had caused a mess of things, in Einstein’s view, by introducing a medium that caused certain laws of physics to work differently depending on how the observer moved relative to the aether. In 1905, Albert Einstein published the theory of special relativity, which explains how to interpret motion between different inertial frames of reference — that is, places that are moving at constant speeds relative to each other. Einstein explained that when two objects are moving at a constant speed as the relative motion between the two objects, instead of appealing to the aether as an absolute frame of reference that defined what was going on. If you and your friend, say AA, are moving in different spaceships and want to compare your observations, all that matters is how fast you and AA are moving with respect to each other. Special relativity includes only the special case (hence the name) where the motion is uniform. The motion it explains is only if you’re traveling in a straight line at a constant speed. As soon as you accelerate or curve — or do anything that changes the nature of the motion in any way — special relativity ceases to apply. That’s where Einstein’s general theory of relativity comes in, because it can explain the general case of any sort of motion. Einstein’s theory was based on two key principles:

* The principle of relativity: All objects move in a motion relative to one another. No motion except the speed of light is fixed. And the laws of physics don’t change, even for objects moving in inertial (constant speed) frames of reference. * The principle of the speed of light: The speed of light is the same for all observers, regardless of their motion relative to the light source. (Physicists write this speed using the symbol c.)

Explaining theory of relativity and related concepts

Classical Relativity (mechanics theory)
Experiment: (Self thought and practically conducted)
An everyday life situation when you are moving in a straight escalator. Standing on next to an escalator, I measured the speed of my mother, who was standing still on the straight escalator, using a Doppler’s radar. Speed measured by the radar= 3 km/h

Then standing on the same escalator I measured the speed of my mother a few meters from me. Speed Measured by the radar= 0 km/h
Classical relativity states that all motion in this universe is relative to one another. Nothing is fixed. As measured by the radar the escalator and hence my stationary mother on it was moving at a speed of 3km/h. But when I measured the speed with myself on the escalator, the radar measured 0 km/h. This is because although my mother was still moving with the escalator’s speed her state of motion with respect to mine was stationary.

Maxwell’s theory and the abolishment of aether theory
Maxwell was a scientist who gave various laws with respect to electromagnetic radiation. He, through his equations, proposed that like all other EMRs even the speed of light could be calculated.  James Clark Maxwell (1884) devised his famous equation, showing that the four basic equations of electromagnetism (one of which Maxwell invented so his equation would work, but it turned out to be correct), can be combined into a single wave equation. The speed of the wave is determined solely by a term involving known...
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