Quantum Space chapter 1 -- Special Relativity

Last week I did a post on the Preface of Quantum Space. It tells the story of quantum loop gravity.

Chapter one gives a snapshot of Einstein's theory of special relativity, which he published in 1905. The title is "The Laws of Physics Are the Same for Everyone."

1. The late 1800s left us with two contradictory truths. The first is that the laws of physics are the same in every frame of reference. The second is that the speed of light is the same in every frame of reference. The contradiction comes if space and time are a fixed and absolute background. 

If a duck in a frame of reference is moving and the frame of reference (say the earth) itself is moving relative to an absolute background, then the speed of the duck is its speed plus the speed of the frame of reference. But this doesn't work if the speed of light is the same no matter what. If a spaceship is moving at near the speed of light and someone shines a flashlight from the top forward, Newton would say the speed relative to the absolute background should be spaceship speed + light speed.

But it's not, nearly light speed + light speed = light speed.

2. Einstein suggested that there is no absolute background. Space and time expand or contract as you approach the speed of light. Here's the formula:

As velocity (v) gets closer to the speed of light (c), the apparent length outside a frame of reference gets smaller.

It was also at this time that Einstein formulated his famous E=mc².

3. This was part 1. But Einstein was assuming constant speed here. What happens if a body is accelerating? And what about gravity?