Benjamin O’Connor

May 5, 1999

STS-003

 

Modern Physics and Philosophical Problems

 

Throughout the history of science, natural philosophers have dealt with different bases of natural human knowledge.  Some believed that the only true way to “know” was through experience and observation.  Others believed that true knowledge arose not from the senses, but through rational reflection and mathematical certainty.  During the 20th century, developments such as quantum theory and Einstein’s theory of relativity necessitated certain changes in philosophical concepts and the closer examination of several longstanding philosophical problems of natural philosophy.  These changes in the classical theories of physics caused reexaminations and changes in the classical methods of observation, and changes in our perception of the limits of human knowledge and empiricism. 

The quantum theory and uncertainty principles of the 20th century point out that for some phenomenon, accurate description through experience and observation is impossible.  The philosophical implications of the quantum theory are staggering. Quantum theory suggests that the very nature of an experiment will determine which state of reality is to be observed. The implications of this concept suggest that it is not possible to observe reality without changing it. Therefore, quantum logic assumes, in a certain sense, that we create our own reality by choosing which aspect we wish to observe. The concept of “observation” took on an entirely different meaning altogether.  In classical physics, the error of observation and observed values was a major consideration.  In quantum physics, this error of observation is unavoidable, and has probability functions associated with it.  Because of these effects, we can’t “know” any property in quantum physics.  We can, however, predict the probability distribution of a given property or event.  For example, the exact position of an electron about a certain atom at a given time cannot be known.  We can, however, predict a probability of finding the electron at a given point in a cloud. 

            Observation plays a definite role in the result of quantum effects.  A good example of this is the famous “light through two slits” experiment.  Shining a light through a screen with two slits onto a photographic plate will develop interference patterns on the plate indicative of the representation of light as waves.  According to the uncertainty principle, we can never know more than an approximate location and energy for any particle, so it is observed by us as a wave spread out over a small region of space and a variety of energy levels.  These waves represent the probability that the particle (in this case, a photon of light) will be found at a given spot.  While we never see these actual probability waves, the interference pattern from the two-slit experiment is indicative of their existence.  If the two-slit experiment is repeated with light again, but only releasing one at a time through the slits, it would be expected that the wave interference patterns would not appear, since there would only be one discreet wave with nothing to cancel it out.  However, even with one photon, the pattern remains on the photographic plate as a representation of a probability distribution.  But, if a detector is set up behind the screen to observe which slit each photon went through, the pattern disappears.  By finding out which path it took, the probability that it took the other path becomes zero, and so there is nothing to interfere with. 

The quantum theory presents us with certain limits on the possibilities of human knowledge.  In fact, the quantum theory suggests that the human mind is not capable of completely comprehending reality under any circumstances. Physicists of the 20th century, including Bohr, Einstein, Planck and Heisenberg, have discovered logically that our rational ideas about the world around us are terminally deficient.  Physicists have developed certain concepts in an attempt to describe that which cannot be expressed in terms of classical mechanics.

The concepts of classical physics form the language by which we describe the arrangement of our experiments and state the results.  We cannot and should not replace these concepts by any others.  Still the application of these concepts is limited by the relations of uncertainty. (Heisenberg 44)

The advent of the quantum theory dealt a blow for the strict interpretation of classical mechanics. Classically, if the exact position and momentum of a particle are known, and all the forces acting upon it at a specific instant are also known, then the exact position and momentum of that same particle can be determined at a later time. Quantum theory denotes that we are unable to determine the exact position and momentum of a particular particle, even if we have the most precise instrumentation available. The Heisenberg Uncertainty Principle has determined that as one measurement is being made, the exactness of the other measurement becomes greatly reduced. Thus the quantum theory can only predict the probability, and with great accuracy, of a particle being at a particular point at some later time.

Einstein’s theory of relativity questions the effectiveness of accumulating knowledge through observation.  A fundamental theory of relativity with respect to Newton’s laws of motion has been around for ages.  No experiment can tell if an object is moving.  If an object appears to be moving, there is no way to tell if the object itself is moving, or if the observer and everything else is moving in the opposite direction.  In a concrete example, a passenger on a train in a station adjacent to another train cannot tell at first if it is his train that is moving, or if his train is stationary and the other train is pulling out of the station.  Taking this one step further, while any train can be “observed” as traveling along a train track, we cannot be immediately certain that the track, or the rest of the universe for that matter, is traveling around the train.  All of the laws of Newton’s mechanics appear the same to an observer in motion as to one standing still. 

Einstein proposed that the concepts of “observed” time and distance actually differ as the “observer” or the “observed” approach the speed of light.  This is the concept of “time dilation.”  That is, a moving clock appears to tick more slowly than a stationary one.  However, each observer thinks that all clocks but his own have been slowed down because of motion, even if the observer himself is in motion.  This “time dilation” effect makes events that appear simultaneous to one observer appear to occur at different times to another.  This lack of absolute simultaneity goes against intuition, and is not perceptible at the speeds dealt with in everyday life.  However, a variable concept of time, depending on the state of the observer, shakes the very foundations of scientific observation. 

Einstein called his theory of relativity a “principle theory.” He said of “principle theories”:

“These employ the analytic, not the synthetic method.  The elements which form their basis and starting-point are not hypothetically constructed but empirically discovered ones, general characteristics of natural processes, principles that give rise to mathematically formulated criteria which the separate processes or the theoretical representations of them have to satisfy." Einstein 228)

Mathematical formulation and completeness is the only way to construct and fully understand Einstein’s theory, as well as quantum theory and other developments in the field of subatomic physics.  All future developments in this “new physics” must arise from this rational and mathematical reflection since observation is not possible.  These modern developments in physics clearly signify the limits of human knowledge through observation and experience. 


Bibliography

 

Albert Einstein, “What is the Theory of Relativity?” The London Times (1919)

 

Niels Bohr, Atomic Theory and the Description of Nature. Cambridge University Press, Cambridge, (1960)

 

Werner Heisenberg, Physics and Philosophy. Harper and Row, New York, (1962)