Wednesday March 26, 2008 5:00 am Lethbridge, Alberta

Chapter 5 The Watchers and the Watched

• "And while many quantum physicists themselves do not feel comfortable about translating the strange abstract properties of the wavefunction to the real world, the mathematical framework and formalism of quantum mechanics has been too successful and is too accurate for there to be much doubt that it is reflecting fundamental truths." [p. 108]
  
  
• One feature of quantum mechanics that is still not well understood is known as the "quantum measurement problem". "Why is it we can never watch the wavefunction - or whatever physical reality it describes - in action when we look? ... how do we understand the way a spread-out wavefunction suddenly transforms into a localized particle as soon as we try to observe it?" [p. 108]
  
  
• "... by the very act of bouncing light off something we are disturbing it and thereby altering it in some small way, either by heating it up a tiny fraction of a degree, or by causing it to recoil ever so slightly from its original position?" [p. 109]

• "... the formalism of quantum mechanics tells us nothing about how to take this step from the Schondinger equation to what we see when we make a specific measurment of the quantum system being studied." [p. 113]
  
  
• "So what constitutes a measurment? What do we mean by an 'observation'? And where is that magical transition from wavefunction to acuality? We do know this much: a measurement must first involve an interaction of some kind between a measuring device , which I have not yet specified, and a quantum system." [p. 123]
  
  
• In the last 30 years physicists have recognized that when "an originally isolated quantum system such as a single atom ... becomes entangled with a macroscopic object ... the superposition of different states forced upon such a complex system involving a trillion trillion atoms simply cannot be maintained and very quickly disappears, or decoheres." [p. 126]
  
  
• "The process of decoherence is still an area of active research and is not yet fully understood." [p. 126]

Chapter 6 The Great Debate

• "... while the formalism of quantum mechanics is not in doubt, nobody has yet found a satisfactory explanation, or interpretation, of the theory that is agreeable to everyone." [p. 132]
  
  
• "No one interpretation of the quantum formalism has been proven to be any better than the rest, other than on aesthetic grounds or personal taste." [p. 133]
  
  
• "... if two people have differing opinions but no way of settling their differences through empirical facts then their conflicting statements are meaningless and they should go have a beer instead." [p. 133]
  
  
• Here are the main alternative explanations that are around today:
  • The Copenhagen interpretation (Niels Bohr, Max Born in the 1920's)
    • we must include the measuring device in the description of the quantum system
    • the role of the observer is central
    • there has to be a clear demarcation between the measurer and the measured
  • The de Broglie-Bohm interpretation (Louis de Broglie, David Bohm)
    • there is a 'real' field that guides the particle
  • The many-worlds interpretation (Hugh Everett, David Deutsch)
    • idea of parallel universe

Tags: physics, science, quantum