Q1: Quantum theory, as it is being taught in colleges, is a theory for atoms and molecules. It is seldom connected with our personal and social life. Why do you think quantum theory is relevant to our daily life?
Quantum theory has first been invented to describe the behaviors of atoms and molecules. Later it is found that it can be used to describe the beginning of the universe. So it is valid for the very small and the very big. It is equally able to describe the medium size objects like human beings.
Q2: The normal wisdom among physicists is that all large human size object the appropriate theory is classical physics and not quantum theory?
One proper logical way to look at physics is that classical theory is an approximation of quantum theory. Classical theory can be derived from quantum theory. Quantum theory on the other hand cannot be derived from classical theory. It has been shown almost a hundred year ago that Newton equation is an approximation of Schrodiger’s equation, which is the equation of motion in quantum theory.
We often time use classical physics such as Newton equation for large objects because it is easier to do calculations.
Q3: What are the essential features of quantum theory that anyone can learn that will be useful to guide his personal and social life?
A: There are at least seven features of quantum theory, I believe, that are relevant to our daily life. Therefore these seven features are useful guide for us to lead a successful and happy life.
Q4: What are these seven features?
The seven features are:
- Probability
- Duality
- Ways to influence an event
- Macro-variables
- Five independent variables
- Symmetries
- Action principle
These seven features of quantum theory can explain many important human behavior.
Q5. Before we get to the much more complicate problems of describing the complex human behavior with quantum theory, let us stay in the much simpler area of atoms and molecules. Can you elaborate these seven features of quantum theory more in the area of atoms and molecules?
Let us start with probability. The behavior of atoms and molecules are not deterministic. Their behavior is probabilistic. We cannot predict the future trajectory of a free atom completely.
Q6. What do you mean by duality?
Duality features prominently in quantum theory. For one aspect of physical nature, there is an opposite aspect. The first one discovered is the particle wave duality. Every particle has some wave property. Every wave has particle properties.
For us to describe the decay of an excited neon atom in a helium-neon laser, we need to specify the initial and final states of the neon atom before we calculate how probable such kind of decay will occur. If we only specify the initial state of an excited neon atom, there are in general many final states that it could decay into. Only after we specify which specific final state of its decay then we can calculate its decay probability.
For any initial state of an event that is measurable, it must have a final state. Conversely for any known final state of a measurable event, there must be an initial state. Initial state is dual to final state.
The duality of quantum theory is best described by the tai chi diagram with yin and yang as two opposite sides of the same entity.
Q7. Can you influence how an excited atom decays? If you can, how do you do it?
Yes, we can influence how an excited atom decays. In a laser we can choose one particular decay mode of the excited atom by having the right size resonance cavity. We change the boundary where the excited atom is it, we can change the favored decay mode of an excited atom, and we have a particular wave length of light from the decay of that excited atom.
Q8. How do you describe a big system like a laser which contains a few trillion trillions atoms?
For system with size much bigger than that of atoms and molecules, we need macroscopic variables or macro-variables in short. We need to specify the pressure, temperature, and volume of the laser cavity say in the neon-helium laser that we talk about. Pressure, temperature and volume are macroscopic variables that have little meaning when we talk about several atoms or molecules.
Q9. For atoms and molecules, what are the minimum independent variables that we need to describe them?
To describe a traveling electron, we need to specify its time, space, energy and momentum. For a complete quantum description of a traveling electron, we need a plane wave function. A plane wave function is an exponential function exp (-ip.x + iEt), where t, x, E, p are time, space, energy and momentum. For momentum we shall call it is one kind of matter flow with mass. For a plane wave function there is an uncertainty of an arbitrary phase, which is associated with the electron number.
There are in general five kinds of independent variables for any given quantum system. They are: numbers, time, space, energy, and flow.
Q10. What is the relevance of symmetries to quantum systems like atoms and molecules?
Symmetries in humanly observable sized objects are easier to describe. A spherical ball is spherically symmetric. It has rotational symmetry. No matter which direction you look at a spherical ball, it looks the same. The spherical ball emits rotational symmetric light, which does not give a preferred direction to our eyes.
Atoms also have rotational symmetry. The light emitted by the spherical atom comes from their rotational symmetric interaction.
Let us come back the example of the neon atom in the neon-helium laser. The excited neon decays to emit light. There is the rotational symmetry of the atom-light interaction. It does not matter which direction we look at the excited neon atom it is the same. Rotational symmetry determines the shape of interaction.
There is another more subtle symmetry, which is related to the conservation of the number of entities, and is called gauge symmetry. Electrons in the neon atom are conserved. The number of electrons does not change when the excited neon atom decays. The conservation of electron number is the result of the arbitrary phase in the wave function of electron. Should the number of electrons become not conserved, then the electrons will disappear. Symmetry is broken.
Symmetry is always accompanied with the consideration of symmetry breaking.
Symmetry and symmetry breaking are two opposite sides of the same issue.
Number conservation or gauge symmetry is quite general in our universe. The survival of any entity in our universe means the number of that entity is conserved. The survival of a human means the number of human being is conserved. When a human being dies, the number conservation or gauge symmetry is broken.
Symmetry and symmetry broken represents two aspect of a human being: his survival and his death.
Q11: We come to the last feature of quantum theory: the action. We all like action in our life. Without action nothing happens. What does action mean for atoms and molecules?
Action in physics has precise meaning in physics. To avoid misunderstanding, let us call action in physics as action S from now on.
When neon atom emits light, it has a very precise action S, which is universal to all charged particles that emit light. How does an excited neon evolve in time is determined by optimizing its action S. Optimization of the action S is called the principle of action S. We optimize S with some constraint like conservation of energy and conservation of number. Or the action has to obey symmetry principles that we discuss above. S should be rotation symmetric, and obey gauge principle.
We propose that human being also has an action S. Human actions are determined by optimizing action S through the principle of action. From optimization of human S our actions are to be determined in a probabilistic way. The principle of ethics of human behavior is related to the principle of action.
If we want to focus on the action of an individual, the action S for the individual will contain his own action with an additional interaction term from the environment.
If we want to understand the relation of two individuals on equal footing, we shall have an action S that contains the actions of each individual and an interaction of these two individual.
For very simple atom like hydrogen we have an exact action S that we can use to predict the exact behavior of hydrogen atom with light that agrees with experimental data to one part in trillions. But for a complicate atom like neon we do not have exact knowledge of the motions of all electrons inside the neon atom to predict its exact behavior when emitting light. Nevertheless we have a workable action S that gives very precise answer for the emission of light by an excited neon atom that agrees with experiment. As our system gets more complicate like an organic molecule, we have less and less precise action S that we can use. Eventually we shall have the idea of optimization of an S, the form of which is invented on a trial and error basis. Even such qualitative and empirical ways of progressing have helped us greatly in our understanding and prediction of how a complicate organic molecule emits light.
When we get to human sized object, we do not have a precise action for human. But the qualitative feature of action S and the principle of S will help us to clarify many issues in a semi-quantitative way. We can also propose experiments that give quantitative answers that guide us forward in our understanding and our prediction of human behavior. We have elaborated this more in our lecture series of Quantum theory of life.
Q12 Can you summarize your position of quantum theory as related to our world?
Quantum theory is the correct fundamental theory to describe every object of our world. The object could be as big as the universe. It could be as small as electrons and photons. It could be of the middle size like human beings. Since we are human beings, it seems the major thrust of improvement of our knowledge is to apply quantum theory to human body and human society.
The essential features of quantum theory can be summarized to be seven:
There is only one world, which is probabilistic, and two sides to every event or objects like yin and yang in a tai chi diagram.
We have three ways to influence how an event to proceed and four macro-variables to describe the behavior of every human beings in a group.
There are five independent variables: number, time, space, energy and flow; six kinds of symmetries and seven characteristics of actions
By SYL on Feb 2, 2007
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