Science Chronology

Notes for "Three Roads to Quantum Gravity " (2001) by Lee Smolin

Chapter Two: "In the Future We Shall Know More" [p. 26 - 32]

• The following two statements are wideley accepted by physicists and cosmologists today:
  
  
  • Nothing can travel faster than light.
    
    
  • The universe is approximately 14 billion years old.
    
    
• From these two statements Smolin deduces that we can only see light that has travelled less than 13 billion light-years. Any light that is travelling from further away than that has yet to reach us.
  
  
• He then points out that there is no evidence that the universe is either bounded or shrinking and thus concludes that we can only see a small fraction of what exists.
  
  
• Finally, in the future the universe will be even older and hence we will be able to see further and thus we shall "know more" about what is out there.
  

This is a very short chapter, but it makes perfect sense.

Chapter Three: "Many Observers, Not Many Worlds" [p. 33 - 48]

• "... doing cosmology requires a radical revision of our way of doing science - a revision that goes even to the foundations of logic." [p. 33]
  
  
• "We must acknowledge that each observer can have only a limited amount of information about the world, and that different observers will have access to different information." [p. 33]
  
  
• "We are constructing a pluralistic version of quantum cosmology in which there is one universe. That universe has, however, many different mathematical descriptions, each corresponding to what a different observer can see when they look around them." [p. 48]
  
  
• The mathematics/logic for this description is relatively new and is called topos theory.

I have googled "topos theory" and located a number of articles on the topic. But, as Smolin says, this is very difficult material to understand. I will leave it for the moment and simply assume that such mathematics exists.

Chapter Four: The Universe is Made of Processes, Not Things [p. 49 - 65]

• "The idea of a state in Newtonian physics shared with classical sculpture and painting the illusion of the frozen moment. This gives rise to the illusion that the world is composed of objects. ... But relativity and quantum theory each tells us that this is not how the world is. They tell us - no, better, they scream at us - that our world is a history of processes. Motion and change are primary." [p. 53]
  
  
• "From this point of view, the universe consists of a large number of events. An event may be thought of as the smallest part of a process, a smallest unit of change." [p. 53]
  
  
• "The universe of events is a relational universe. That is, all its properties are described in terms of relationships between the events." [p. 53]
  
  
• "The most important relationship that two events can have is causality." [p. 53]