If the theory of relativity dealt with the very large and led us to the spatially and temporally comprehensible "ends" of the universe, then quantum theory takes us into the realm of the very small, into the world of atomic nuclei and subatomic particles.197 Important steps in the development of quantum theory included Max Planck's study of black-body radiation in 1900, his discovery of the quantum of action and the derivation of the so-called Planck's Constant connected with it, as well as Einstein's 1905 article on light quanta. After the wave theory of light had ruled for a century, the discussion then shifted to photons and light quanta, whereby individual atomic processes were ascribed a discontinuity that was foreign to classical physics.198 It became clear that light, depending upon which measuring process is used, exhibits two different modes of behavior. It acts like a wave and like a small, solid object. The two modes of behavior cannot be observed simultaneously and apply not only to photons, but also to particles in general. Each object of quantum theory is therefore as much a particle as it is a wave. Bohr summarized these findings in the complementarity principle, which had a great impact, and not only on physics. The concept of complementarity that was new to physics had repercussions on philosophy as a model for understanding dichotomies.199
Complementarity thus describes two sides of one and the same object that contradict each other and never occur simultaneously, but that complete each other to create a structural connection: "The very nature of the quantum theory thus forces us to regard the space-time co-ordination and the claim of causality, the union of which characterises the classical theories, as complementary but exclusive features of the description, symbolising the idealisation of observation and definition respectively."200
Even if quantum physics has existed as a theory for over sixty years, its interpretation is still the subject of discussion. Thus, for example, the status of reality is interpreted in various ways. Positions range from the view that observations only describe already existing reality to the standpoint that reality is created only through observation or that only statements regarding phenomena and their behavior are possible, but not statements about reality as a whole. The Copenhagen interpretation of quantum theory, which was developed primarily by Bohr and Heisenberg, is thus not the only one, but it is certainly the most common.201
The heartbeat of quantum theory lies in the indeterminacy principle, which was formulated by Heisenberg.202 It says that perfect precision in the measurement of the momentum (= velocity X mass) and position of a particle is impossible, and this is not because the measurement equipment is defective, but rather because nature is the way it is. If we know where a particle is, we cannot simultaneously know what it is doing and vice versa. Mathematically expressed, this means: The uncertainty of the measurement of the position of a particle multiplied by the uncertainty of the measurement of its velocity can never result in a smaller value than h/^Km, where h is Planck's Constant, and m is the mass of the particle in question. Thus, the larger the particle mass, the smaller the uncertainty; the smaller the particle mass, the larger the uncertainty.
What applies to the uncertainty relation of impulse or velocity and position is also valid for the relationships of time and energy or time and mass. Analogous to the minimum values in the relationship of position and impulse, minimum values also exist here, i.e., a value below which one cannot go, for the time that is interpreted as the measuring time.203 The world of the very small thus confronts us, in relation to the expressive possibilities of concrete language, with a blurred image of reality. It is possible to conclude from this "that in the deep layers of the particle waves, the essence of space and time itself is imprecise and only vaguely defined."204
The quantum field theory developed by Paul Dirac in 1927 enabled a rational understanding of the duality of waves and particles. In contrast, the structure of the measurement process is still open to varying interpretations. As long as it is not measured, a system is in the state of superposition, i.e., a particle is in a state that is a mixture of "here" and "there." The mixture does not mean that the particle is somewhere between "here" and "there," but rather that its position can be determined only according to probability. Only the measurement forces a decision, which is the same as saying that the wave function suffers a collapse. The principle of superposition is therefore the cause for the statistical character of the quantum world.
In quantum physics, one is confronted with two different shapes of time. On the one hand, there are reversible quantum states and equations that do not define a direction of time. On the other hand, observations or measurements are performed that transform the quantum system, which is indifferent to directions of time, into an irreversible event, because conclusions cannot be drawn on the past of the quantum system based on an observational finding.205 With regard to the measuring process, it should be noted that each measuring instrument is exposed to quantum physical processes. Even the most precise clocks are objects that are subject to quantum uncertainty.
Even if quantum theory appears to contradict the intuitive understanding of reality, it neither allows the interpretation that everything is possible, nor does it permit any indiscriminately far-reaching metaphysical conclu-sions.206 In a direct sense, it concerns only the area of the subatomic order; the effects of quantum phenomena, however, affect the entire range from atom to cosmos.207
Initially, quantum theory appeared to cause radical disillusionment for the hopes that were linked to the progress in the field of atomic theory. With regard to lucidity and the description of causal correlations, it virtually led to resignation. This "resignation," however, was very soon regarded as epistemological progress,208 and one of the reasons for the successful application of quantum theory lies precisely in this manner of viewing things.
Both Spectator and Actor in the Great Existential Drama209— The Role of the Observer The theory of relativity had already bestowed upon the observer a more important position than ever before by making time dependent upon the respective reference systems of one or another observer. Quantum theory increased this tendency into the almost unimaginable. First, it brought disorder into the distinction between "objective" and "subjective" that was apparently so self-evident in natural science. Thus, for example, the concept "objective observation" becomes contradictory in itself, because in quantum theory, it must be assumed that we can observe only that which cannot be separated from us.210 Quantum physics also robbed empirical measurement processes of their innocence by asserting that any observation of a process represents an influence on that process. In the words of Bohr: "Now the quantum postulate implies that any observation of atomic phenomena will involve an interaction with the agency of observation not to be neglected. Accordingly, an independent reality in the ordinary physical sense can neither be ascribed to the phenomena nor to the agencies of observation."211
Bohr thus goes so far as to question the very existence of an independent reality. Neither the phenomena nor the observations can be described with a simple "that's how it is." Each observation requires an intervention into the course of phenomena in a way that deprives us of the basis for a causal description.212
It may sound improbable that the intense observation of a clock slows down its movement, but that is precisely what happens when the clock is regarded as a quantum system. It has been shown on atoms that normally disintegrate with regularity that continuous observation prevents these atoms from disintegrating.213 During uninterrupted observation of a quantum system, time, then, principally stands still. For physicists, this is not entirely unproblematic: Their definition of time as being that which is shown by the clock works only when they do not look at the clock too often.
So far, this presentation of quantum physics has focused on probability and uncertainty only. The inclusion of the observer makes clear that, in quantum theory, one is dealing with a massive triad of probability, complementarity, and observation. Neither probability nor complementarity becomes clear without measurement. This means that even when uncertainty cannot be traced back to a fault of the observer and his or her equipment, but is rather a feature of nature per se, uncertainty becomes evident only through the act of measurement that is performed by an acting subject. The extent to which a distinction can be maintained between an observing subject and a quantum system as the observed object is the subject of an ongoing discussion.214 Some interpretations can go so far that, finally, "everything" is dependent upon the observer. What "everything" means in this context can be clarified by the thought experiment with Erwin Schrodinger's famous cat. This is the attempt to work out the epistemologi-cal consequences of quantum theory by transposing a quantum system onto the macroscopic level. The thought experiment goes like this: A cat is in a closed, opaque crate together with an ampoule of lethal poison. A hammer is affixed above the ampoule and crushes the ampoule when it falls down, thus leading to the instant death of the cat. The release of the hammer is dependent upon the random disintegration of a radioactive atom. As long as no one looks into the crate, the cat is not, as would be assumed, either alive or dead, but it is rather in a "both dead-and-alive condition," which corresponds to a wave function that contains both possibilities. Only at the moment when an observer looks into the box does the one possibility disappear and the other become reality, which is synonymous with the collapse of the wave function for the unrealized possibility.215
Generally speaking, one can say that a measurement causes a collapse at a point when the condition of all possible measurement results passes into the state of a factual result. This condition then holds true at the same moment in the entire universe.216 To what extent such measurements require the presence and activity of human consciousness continues to be debated.
The highly subject-oriented interpretation of the measurement process that is outlined here has significance for the conceptions of the beginning and end of the universe, or of time. It can be understood in such a way that an external observer causes the collapse of a wave function by measuring and thus calls a concrete reality into existence. Formulated differently: If this interpretation is correct, a universe without an external observer would be inconceivable. The mathematician Andrej A. Grib217 goes so far as to characterize the universe as a creation out of nothing, a vacuum state, by an external observer who decided upon a special measurement. Somewhat in the manner of Frank J. Tipler,218 he infers a general resurrection from quantum cosmology.
Understandably, such interpretations are extremely controversial in the scientific camp, for they go far beyond what can be called a general consensus. According to Grib, "All events in spacetime will be reorganized or 'resurrected' but not in such a way that they will be in time."219 He thereby identifies neither God with the "Ultimate Observer" or the Resurrection with the collapse of the wave function in the great final collapse of the universe, but he postulates both as possibilities.220 Another possible interpreta-
tion that dispenses with an external observer propagates the notion that all quantum physical possibilities are of equal value. Each of these possibilities is realized in its own universe, which leads to an infinite number of parallel universes.
These thoughts belong to the realm of what are, in part, highly speculative cosmological theories that will be discussed in more detail in 3.5.3. First, however, I shall consider the significance of quantum theory for the relationship between language and reality.
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