- Slides: 15
Quantum Theory of What? What does quantum theory describe?
In classical physics, we assume that objects exist objectively • Classical physics describes classical objects, which are those that are assumed to be directly observable with the human senses. • Classical objects are assumed to exist whether or not they are being observed because different observers agree that they exist. • This is the definition of objective reality. • If there is no agreement, there is no objective reality!
But, what does quantum theory describe? • That is the big question! • Quantum objects are not assumed to be observable with the human senses. • Quantum theory predicts the probability of obtaining a specific result, such as position or velocity, in a specific measurement on a specific quantum object. • That’s all it says. • But there is no agreement on what a quantum object is!
So, what is a quantum object? • Is it objectively real—i. e. , does it exist whether or not it is being observed? • Or is it only the mathematical prediction of the probability of obtaining a specific result in an observation?
If it is objectively real… • We should be able to verify that it exists whether or not it is being observed. • But, how can this be verified? • The only verification we have is that, if two different observers agree on the results of their measurements, then they assume that something exists on which the measurements are being made. • This is verification by agreement. • However, in quantum theory there is no agreement on what that something is!
For example: • Suppose we devise an apparatus to measure either a position or a velocity. • Quantum theory tells us the probability of measuring a specific position or velocity. • Measurements can then be made and the experimental results can be compared with the predicted probabilities.
But, is there a self-existent object that is being measured? • How would we know? • All we can do is make observations with whatever tools we have and compare them with the predicted probabilities. • Anything more requires an interpretation in terms of what might exist objectively.
In both classical and quantum physics, an interpretation is needed • In classical physics, we regard the interpretation to be self-evident because the objects are assumed to be directly perceivable with the human senses. • In quantum physics, the interpretation is not self-evident because the objects are not assumed to be directly perceivable with the human senses.
There is no single agreed-on interpretation in quantum physics • Remember, quantum theory consists only of the mathematical probabilities of obtaining specific results if specific observations are made. • The basic theory tells us nothing more. • It does not say anything about the object, if any, whose properties are being observed.
Problem: Too many interpretations! Examples of classes of interpretations: 1. Statistical (predicts the probability distribution of the results of many observations on identical systems, not of a single observation. All other interpretations may apply to a single observation as well as to many). 2. Copenhagen with consciousness (objective wavefunction is collapsed by consciousness of observer to give a subjective result). 3. Copenhagen without consciousness (objective wavefunction is collapsed by some unknown objective process into classical physical state).
More interpretations… 4. Hidden variables (classical particles, objective quantum force, no collapse, no consciousness). 5. Many worlds (objective wavefunction, no collapse, conscious observation mysteriously causes branching into many noncommunicating objective worlds). 6. Many minds (objective wavefunction, no collapse, conscious observation mysteriously causes branching into many noncommunicating objective brain states).
Still more interpretations… 7. Transactional (objective wavefunction, no collapse, observer emits retarded wave that cancels advanced wave emitted by observed object). 8. Relational (subject and object represented by entangled objective wavefunctions, no collapse). 9. Mostly subjective (Christopher Fuchs) (external object but no objective wavefunction, quantum probabilities interpreted as subjective Bayesian probabilities).
Problem: How does consciousness fit into all of this? • Consciousness as essentiality is required in some versions of Copenhagen to collapse the wavefunction. • Consciousness as an emergent property is required in many worlds and many minds (to cause a branching, the mechanism of which is unexplained), but the wavefunction is assumed to be objective. • Consciousness is not a necessary part of the other interpretations.
Another problem! • In quantum theory, objective time and space form a fixed background in which everything happens. • In general relativity (gravity theory), objective time, space, matter, and energy depend on each other and evolve in time together. • How to unify such disparate theories into a quantum theory of gravity? • One possibility: Eliminate objective time and space!
A nondualistic interpretation might solve all interpretation problems: 1. Awareness would be the essential source, background, and substance of the mind. 2. There would be no external objective reality, and no objective time and space. (Objective reality implies separation between subject and object, and causes interpretation paradoxes. ) 3. A major problem would be to find a mechanism by which Awareness is essential to the arising of the mind. 4. Quantum theory would describe the arising of subjective mind states (not brain states) in Awareness, plus the subjective process of decision making. 5. While a big step forward, the interpretation of Christopher Fuchs is a theory of subjective mind states that requires an external, objective system to be observed; but Awareness is only implied, not essential.