The Observer in Modern Physics
Some Personal Speculations

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.