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?

Quantum Space by Jim Baggott, Preface

1. My book buying is really out of control. My goal, unattainable, is to read a chapter of something each day and blog it. I've bought too many recently to go one by one. I'm going to wander.

Today I read the Preface of Jim Baggott's recent 2018 book, Quantum Space: Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe. I've read/listened to much of another book of his on the Higgs boson. I've also read more than one book by one of the key players in this book, Carlo Rovelli. It was well written.

Every once and a while I find what I consider a really good science book. The best for me was The Perfect Theory, on relativity. Rovelli's book, Reality Is Not What It Seems, is pretty good. There are others I like. I'm hoping Quantum Space is another winner. I've bought plenty that didn't hold my attention.

2. Quantum loop gravity. I don't like the name. I don't like some of its terms (like "spinfoam"). It doesn't capture the imagination. It's a PR loser.

But God has told me it's right and string theory is wrong. OK, maybe it was that sausage pizza. I do like pasta, but I don't like string theory. Never have. I'm afraid I'm with Leslie Winkle on this one. Reality is loopy.

The basic difference is that string theory sees reality as made up of vibrating strings in something like 10 dimensions. Quantum loop gravity sees reality as made up of space quanta. Neither theory can be experimentally tested or verified.

3. In the Preface, Baggott introduces the issue:

• "There is not one single piece of observational or experimental evidence to support it" (ix).
• "The quantum theory of gravity is simply the greatest scientific problem of our age."

The problem is that both the theory of relativity and quantum mechanics are both incredibly successful theories. Yet they are incompatible with each other. Quantum mechanics assumes that spacetime is absolute. Relativity does not. 

If string theorists tend to start with quantum mechanics and move toward relativity, loopies like me start with relativity and move toward quantum mechanics. LQG (loop quantum gravity) assumes that space is quantized. These "lumps" of space then interlink into a fabric of interlocking loops, a "spin network." (xii). The changing connections between these networks give rise to a spin foam. This foam added together gives us spacetime.

I think I could come up with better lingo.

4. Two key players form the heart of the story of the last twenty five years of LQC's existence. I've mentioned Carlo Rovelli. In addition to Reality Is Not What It Seems, I also have his Introduction to Quantum Gravity and Spinfoam Theory. The other player is Lee Smolin. I have a couple of his books too--The Trouble with Physics and Three Roads to Quantum Gravity. They are both pretty good with PR.

So I'm excited to read this book.