Transcript SAND Quantum Theory of What

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.