# Galilean Invariance and the Special Principle of Relativity

• mangaroosh
In summary, the PoR is an extension of the Galilean PoI, where both principles state that inertial observers cannot determine by experiment if they are "in motion" or "at rest". However, the Galilean PoI was only applied to massive bodies while the Lorentz Transformation was applied to light, resulting in two different PoR's. Einstein's contribution in Special Relativity was to apply a single PoR to both massive bodies and light, as seen in his 1905 paper. His PoR does not extend to accelerating frames, which is addressed in General Relativity.
mangaroosh
To what extent is the PoR an extension of the galilean PoI?

A stated consequence of the Galilean PoI is that inertial observers cannot determine by experiment if they are "in motion" or "at rest", with a similar consequence being mentioned for the PoR - to what extent to these differ, does anyone know?

Does the special PoR extend the Galilean PoI to accelerating reference frames also?

In general, to what extent are the two principles the same and different?

mangaroosh said:
To what extent is the PoR an extension of the galilean PoI?

A stated consequence of the Galilean PoI is that inertial observers cannot determine by experiment if they are "in motion" or "at rest", with a similar consequence being mentioned for the PoR - to what extent to these differ, does anyone know?

Does the special PoR extend the Galilean PoI to accelerating reference frames also?

In general, to what extent are the two principles the same and different?
I think it would be helpful for you to read the wikipedia article on the History of Lorentz Transformations. There you will see that PoI is based on the Galilean Transformation and was accepted as fundamental for massive bodies up until the time of Einstein while the Lorentz Transformation was applied only to light. Thus, in effect, they had two different PoR's in operation at the same time because they didn't know how to reconcile them. Einstein's great contribution was to apply a single PoR to both massive bodies and to light, which is the reason for the name of his 1905 paper, "On the Electrodynamics of Moving Bodies".

Einstein's PoR in Special Relativity does not extend to accelerating frames--General Relativity takes care of that.

## What is Galilean Invariance?

Galilean invariance, also known as Galilean relativity, is the principle that the laws of physics should remain the same for all observers in uniform motion. This means that the laws of physics should not depend on the velocity of the observer or the reference frame they are in.

## What is the Special Principle of Relativity?

The Special Principle of Relativity, also known as the Special Theory of Relativity, is a fundamental principle in physics that states the laws of physics should remain the same for all observers in uniform motion. It was developed by Albert Einstein and is based on the idea that the speed of light is constant for all observers, regardless of their relative motion.

## How are Galilean Invariance and the Special Principle of Relativity related?

Galilean invariance and the Special Principle of Relativity are both based on the idea that the laws of physics should remain the same for all observers in uniform motion. However, the Special Principle of Relativity goes beyond Galilean invariance by including the constant speed of light as a fundamental principle.

## What is the significance of Galilean Invariance and the Special Principle of Relativity?

Galilean invariance and the Special Principle of Relativity have played a crucial role in modern physics and our understanding of the universe. They have led to the development of the theory of relativity and have helped to explain many phenomena, such as time dilation and length contraction, that were previously unexplained by classical physics.

## Are Galilean Invariance and the Special Principle of Relativity still applicable today?

Yes, Galilean invariance and the Special Principle of Relativity are still applicable today and are considered fundamental principles in physics. They have been confirmed by numerous experiments and continue to be used in modern theories and calculations.

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