The Observer in Modern Physics
Some Personal Speculations
The phenomena of
the cosmos require an observer in order to be learned about and understood
by us. The observer can take many forms, for example:
1. A person watching
amoeba through a microscope
2. A person watching an ocean sunset
3. A spacecraft monitoring a distant asteroid (and transmitting data
to earth)
4. A person conducting an experiment in a laboratory
The ideal observer
is one who causes no unnecessary perturbations to the system being observed.
An observation made by such an observer is called an objective observation.
In our school physics and chemistry, we routinely assume that our observations
are objective.
But reality seldom,
if ever, provides us with ideals. The real observer always causes an
unnecessary perturbation of some kind. Scientists must remain alert
in their efforts to minimize the magnitudes of these perturbations.
The extent to which they succeed determines the level of confidence
they can claim in their results and, therefore, the certainty they can
expect in their knowledge of things.
In the 20th century,
physics was forced into the position of re-evaluating the role of the
observer, both in relativity and in quantum mechanics. In relativity,
the absolutes of Newtonian physics were banished, and observations obtained
by observers in different frames of reference became all that was available.
These observations were linked through a system of coordinate transformations.
In quantum mechanics,
the observer and the system being observed became mysteriously linked
so that the results of any observation seemed to be determined in part
by actual choices made by the observer. This situation is represented
by the wave function, a function in the complex domain that contains
information about both the cosmos at large and the observer's apparent
state of knowledge.
I have long been
fascinated by these developments and have developed a model to help
me both to understand them and to explain them to others. I wish to
share this model with you...
Let us ask a simple
question: When you look up at night and "see" a star, what
is "really" going on? A Newtonian philosopher might answer
that you are "really seeing" the star, since, in Newtonian
physics, the speed of light is reckoned as being infinite. An Einsteinian
philosopher, on the other hand, would answer that you are seeing the
star as it was in a past epoch, since light travels with finite velocity
and therefore takes time to cross the gulf of space between the star
and your eye. To see the star "as it is right now" has no
meaning since there exists no means for making such an observation.
A quantum philosopher
would answer that you are not seeing the star at all. The star sets
up a condition that extends throughout space and time-an electromagnetic
field. What you "see" as a star, is actually the result of
a quantum interaction between the local field and the retina of your
eye. Energy is being absorbed from the field by your eye, and the local
field is being modified as a result. You can interpret your observation
as pertaining to a distant object if you wish, or concentrate strictly
on local field effects.
This line of argument
brings us to an interesting notion: that of the interaction boundary.
Let us assume an observer and a system to be observed-any observer and
any system. Between them, imagine a boundary, and call it an interaction
boundary. This boundary is strictly mathematical; it has no necessary
physical reality. In order for the observers to learn about the system,
they must cause at least one quantum of "information" (energy,
momentum, spin, or what-have-you) to pass from themselves through the
boundary. The quantum of information is absorbed by the system (or it
might be reflected back) and the system is thereby perturbed. Because
it has undergone a perturbation, it causes another quantum of information
to pass back through the boundary to the observer. The "observation"
is the observer's subjective response to receiving this information.
In a simple diagram, the situation looks like this:
O | S
where O and S represent
the observer and the system, the vertical line represents the interaction
boundary, and the arrows represent the information exchanged in the
act of observation.
In this scheme,
no observation can be made without first perturbing the system. The
observation is never one of the system "at rest," but of the
system perturbed. If
represents the state of the system before the perturbation and
±
represents the state immediately after, then the observation approaches
the ideal only if
<<
.
If I is the information
selected by the observer to send across the interaction boundary, then
it is apparent that
must be a function of I: i.e.,
= (I).
Thus, the observation
is affected by choices made by the observer, as quantum mechanics seems
to teach. In the case of atomic and some molecular phenomena, the inequality
<<
does not hold; in
fact
so that the perturbation is comparable in magnitude to the state itself.
Because all information is exchanged in quanta (modern physics does
not allow for the "smooth exchange" of arbitrarily small pieces
of information), this situation necessarily gives rise to an inescapable
uncertainty in such observations. The quantum theory takes this uncertainty
into account as the Heisenberg Uncertainty Principle.
Uncertainty is not
strictly a law of Nature, but is a result of natural laws that reveal
a kind of granularity at certain levels of existence. Observers in modern
physics truly become participants in their observation, whatever that
observation might be.