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Three Roads to Quantum Gravity

I suspect that the difficulty of the book and the concept in general contributed to the small group showing to discuss Lee Smolin's “Three Roads to Quantum Gravity”. I also had a hard time getting through the book as I felt many concepts were touched upon too briefly. I think that since the author approached the theory of quantum gravity from three different perspectives and each had its own terminology and history, the book would have been three times as long if he had tried to go into more detail. The fact that the book is billed as “It would be hard to imagine a better guide to this difficult subject. -- Scientific American” makes me wonder how bad other books on the topic are.

The book focuses on the history and current state of research into quantum gravity. It is not out to answer all of the questions and assures you that there is still much to be done. This is a very different outcome from many of the other books we have read in the group that had a distinct viewpoint and a definitive ending. The author does maintain a good level of objectivity when talking about the competing theories that are outside of his field of research. He makes a point towards the end of mentioning that in doing so he upset all camps, which in his mind means he found the proper balance between them.

Having read other book about quantum physics in the past I found this book more challenging and felt that for many of the concepts introduced I didn't grasp them. I'd be tempted to read it again, but think that with the general objections raised about the author's approach to the subject I might find a second read more infuriating than rewarding. Instead I'd probably delve into the extensive list of recommended further readings the author includes after the very helpful glossary. Some of the scientific concepts I did pick up are that space and time are defined of discrete indivisible units, black holes emit radiation and as such shrink over time, and that there is the concept of the horizon which hides information from the observer.

I collected a few more notes and references than usual while reading this book and they are listed below:

2: Human perception is too coarse to see the building blocks of nature.
3: Quantum theory was invented to explain why atoms are stable.
9: The three roads are:
1.From quantum theory: based on string theory
2.From relativity: based on loop quantum gravity
3.From new ground: based on questioning the base assumptions, more philosophical, “What is time?”
17: There is nothing outside the universe.
20: The world is nothing but an evolving network of relationships.
27: We will never be able to see the entire universe. Based on the size of the universe and speed of light.
34: Only one mathematical model for quantum theory, but a multitude of interpretations.
48: One universe, sen by many observers, rather than many universes, seen by one mythical observer outside the universe.
51: Stories are best to describe processes (like humans) that unfold over time, versus a description of an object like a rock.
52: Artists cannot turn a process into a thing.
52: But even rocks have stories that just take place over longer time periods.
58: The cone of light determines what events could possibly influence or be influenced by other events.
59: Relationships between events is the causal structure of a universe.
62: Smoothness of space and time are illusions; really discrete events that can be counted.
62: Plank scale: 10^-23 cm, 10^-43 second.
63: Big bang is really the big freeze as the Plank temperature is hotter than anything in the universe.
75: Black holes stretch the wavelengths of light that are close but don't get sucked into into.
79: Mass increases as you approach the speed of light.
92: Black hole evaporation is the process in which a black hole decreases in mass due to Hawking radiation.
93: Entropy is a measure of missing information.
94: What is the nature of the information trapped in a black hole?

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