Relativity is more math than physics

Relativity applies to all branches of physics. However, it is more of a geometrical framework – on which the laws of physics can be described. Calling relativity physics would be like calling Euclidean Geometry physics.

Accelerating frames and Special Relativity

Special relativity does not deal with accelerating observers or accelerating reference frames – is a common misunderstanding. In fact, special relativity provides a kinematical framework to describe everything – including forces and accelerations. Hence, it DOES include accelerating observers and reference frames.

Inertial frames and Special Relativity

What IS special about Special Relativity is that it ASSUMES the existence of INERTIAL frames (frames in which Newton’s first law holds). Without such frames, it becomes difficult to discuss STR – and it’s most famous results – such as the Lorentz Transformation – are based on the existence of inertial frames.

Simultaneity is Relative

Two events that occure at the same time t for O – do not occur simultaneously for O’. This means that the time ordering of a system is not fixed – and depends on who is observing the events. It also means that simultaneity has no physical meaning.

All motion is relative

NOTHING is ever moving in its own frame of reference and so nothing ever “experiences” time dilation, for example. It is something that is observed/calculated by someone in a different frame of reference.  You, for example, are MASSIVELY time dilated right now from the frame of reference of an “accelerated” particle at CERN (because it sees itself as motionless and you moving at .999999c)

Invariance of Speed of Light

This is STR’s second postulate – and the most famously known one. It was not Einstein, but Minkowski who cast this  postulate into geometrical terms.

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Summary

Relativity falls under math more than it does under physics.