# I Special Relativity

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1. Jun 18, 2016

### Alpha1

In Galilean Relativity, laws of mechanics are invariant across frames. In all the frames they are the same.

So, in Dynamics and Relativity by W.D.McComb, it is written that this implies you cannot perform any experiment in an inertial frame that can tell whether an inertial frame is moving or at rest with respect to another frame.

My question is suppose laws of Physics are different in different frames, then if we are in a frame, can we perform mechanical experiments to determine its speed with respect to other inertial frames.

2. Jun 18, 2016

### jfizzix

If the laws of physics were different between every inertial reference frame depending on speed, there would be measurable consequences.
If some measurable thing did change with your reference frame's speed, then you could tell your speed by measuring that thing.

3. Jun 18, 2016

### Alpha1

Hi , thank you for your response.
The change will happen if the frame of reference in which you, changes its speed. I totally agree we can measure that change.
However, if we are just in our frame, what does it mean to determine the speed of other frame ? We do not even know of their existence
I am not able to understand this.

4. Jun 18, 2016

### Ibix

Imagine that the speed of light varied with direction (i.e. light behaved like a wave in a medium), except in one frame in which it is isotropic. That would hint that there was something special about the frame where the speed is isotropic, and how much the speed varied in your chosen frame would tell you how fast you were going with respect to that special frame.

In our universe, you can't do this (or anything analogous) by any means we are aware of.