{"word_count": 2424, "character_count": 15525}
Now that I have described how modern physics was founded by Galileo Galilei as a new science, I will follow the path of physics in the following and show how the legacy of the pre-Socratics and ancient mathematicians has borne fruit. After a decline of the ancient culture one could, after about 2000 years, revive it and reach new heights of knowledge. The fact that it took so long may has many reasons - if one can speak of reasons at all in history. However, I do not wish to take part in such considerations. First, I want togive an overview of the theories that have been developed and established inphysics over the course of time. The fact that they always had to provethemselves in competition with other theories than the "better ones"in each case was explained, for example, in (Honerkamp, 2017, p. 111ff). In thenext chapters I will show what role the questions raised by the pre-Socraticshave played in the development of these theories. In particular, I will discussthe development of the theories and their relationships to each other. EspeciallyI will pursue the path along which there have always been mergers orunifications of theories. Thus, today we are only talking about two greattheories and are out to recognize these two as parts of a single "theoryfor everything". This would answer the most noble question of thepre-Socratics, the question of a "One", albeit in a completelydifferent way than one could imagine at that time.The developmentand establishment of a physical theory always involved the explanation ofphenomena of a certain type. We have already seen that the phenomenon of"motion" was the first theme that interested people in antiquity andagain in the Renaissance. It is the most original and probably also the mostgeneral phenomenon that we know.&#160; We encounter the phenomenon of "light" in a similarly direct way.&#160; So, it is no wonder that at the beginning of modern physics not only the phenomenon of motion was dealt with, but also experiments with light were carried out, as we know them from Isaac Newton, for example. A century later, people began to study other, seemingly quite different phenomena, electrical or magnetic. Finally, at the turn of the 20th century, they discovered sorts of radiation which obviously differed greatly from light rays, and among these new rays there were also different types. The space of phenomenaIn short, thehistory of physical theories is a history of discoveries in a "space ofphenomena" where there have always been certain objects in play. In thisspace, one can identify large areas in which there are phenomena that seem tobe so similar to each other that one might be tempted to invoke the same reasonfor their explanation. Thus, over time, the idea of fundamental forces actingbetween planets and the sun, electrons and other found or discovered objectsemerged. Over time, four such interactions were distinguished: Gravitational,electromagnetic, strong and weak interaction. This distinction is still veryhelpful for an overview of the set of the theories developed in the 400 yearssince Galileo.There are,however, two other categories in respect of which one should distinguish thetheories. It is not only the interaction or the force that can be decisive fora phenomenon. This can also be the range on a length scale. Thus, phenomena canbe distinguished according to the scale of length on which the phenomenonappears, whether in the world of the smallest dimensions, the largestdimensions or the middle dimensions. Finally, an aspect will become important that has to do with our cognitive abilities, namely the question of whether we must describe the phenomenon as a complex one, namely as one in which it is not sufficient for an understanding to consider only a few objects with few important properties. Many or very many objects can represent a system that has new properties that are not inherent to the individual objects themselves, but only "emerge" through the interaction of the objects. Water, for example, has the property of being liquid. However, this does not apply to its components, the H2O molecules. With these two characteristics, spatial size and complexity, we can already consider aspects that allow us to have an overview in the form of a landscape of phenomena. If one enters the characteristic length of some objects, which play a role in physical theories, into a coordinate system, in which this size is plotted against the complexity of the objects, then one obtains e.g. Fig.4.2.  Fig.4.2: Rough classification of certain objects according to size and  complexity. Objects like planets can appear at different places,  depending on how much of their properties you want to consider (R stands  for order of magnitude, N for number of degrees of freedom or  complexity resp.).  On this figure we can show how far we have explored the space of natural phenomena today with our physical theories. It also makes it clear that in addition to the physics of fundamental interactions, there is also a very large area of complex systems for which areas of physics such as thermodynamics or statistical mechanics, solid state physics, etc. are responsible. This should be kept in mind, even if we do not deal with it here and we mainly consider the wide range of spatial scales in the area of "simple" systems - from 10-15 to 1020 m.The world of the middle dimensions in the range of about 10-4 to 1010 m is most accessible to us intellectually, because we ourselves, as participants of this world, can have direct experiences with it. Thus, the phenomena of this world are also the subject of the earliest physical theories; they are also called classical theories. The exploration of the space of phenomena thus started in the world of the middle dimension. At the beginning of the 20th century, phenomena of the world's smallest dimensions were discovered. One had to state that the concepts of the world of the middle dimensions are no longer suitable here. A completely different concept, a "quantum", replaced the concept of a material object and gave physics on this scale the name "quantum physics". At the same time a modern cosmology and astrophysics began to emerge. Today we hear of particularly spectacular discoveries in this field of the largest dimensions. Classicalphysics, quantum physics and cosmology: this is a classification that can alsobe described as physics of medium, smallest and largest dimensions. Cosmologytoday has not yet required its own conceptual apparatus, as quantum physicsdoes, which is why it is also added to classical physics, if one wants toemphasize the methodological aspect.With adistinction regarding the spatial size alone one has of course not yetexhausted the space of phenomena. There are other quantities which, measured bythe conditions of our world of daily experiences, can be small or large.Particularly prominent in this context is speed; but the strength offundamental forces, in particular of gravity, will also be significant for thenature of physical theories. The landscape sketched in Fig.4.2 must thereforeonly be imagined as a slice from the whole space of phenomena.The explorationof this space of phenomena resembles the exploration of our earth in the timeof the great discoveries in the 16th century. One spoke thereby of thediscovery of the "world", although it were only new ranges of theplanet earth, which one discovered at that time gradually. Today one knowsalmost every corner of the earth and "reaches for the stars".&#160; Thus, one alsoknows all laws of nature in the world of the middle dimensions, but only on thefundamental level. The more complex the systems are in these dimensions, theless familiar they are to us today. But the more we limit ourselves to thefundamental side, the further we have advanced into the world of the smallestand also the largest dimensions. Even if it werepossible in several years or decades to establish a theory for all fundamentalinteractions, physics would not be at its end. In the direction of complexsystems there are still many questions waiting for an answer. The transition tochemistry, biology and cognitive science will be fluent. Also, in theexploration of life and consciousness one will not be able to ignore physicalconditions. The theories of classicalphysicsClassicalphysics is dominated by three large phenomenon areas: the phenomenon of motionand the two areas in which we encounter the fundamental forces of gravity andelectromagnetism, respectively. Phenomena fromthese areas have been known since ancient times. "Nothing is older thanmotion," we may quote Galileo once again. For the pre-Socratics, motion ornon-motion always played a role, Aristotle distinguished different types ofmotion and formulated a first kind of theory of motion. Even in the Middle Agesthere were always natural philosophers who wanted to trace the nature ofmotion.Gravity was alsoan everyday phenomenon. With Aristotle it was a quality that made all bodies ofthe sublunar world strive for the centre of the world. Also, the sphericity ofthe earth was later explained by such a "natural striving". We read lessabout magnetic and electrical forces in early sources, but magnetic andelectrical phenomena were already known in ancient times. If you rubbed anamber, it would attract dust or shreds of wool. Iron was attracted by amagnetis stone and it was discovered that splinters of such stones alwaysrotate in a north-south direction. The physicaltheories, which today explain all basic phenomena from these three phenomenonareas, are - for motion: Newton's and Einstein's theory of motion, - for gravitation: Newton's and Einstein's theory of gravitation, - for electrical and magnetic phenomena: Maxwell's theory of electromagnetism.Normally,Newton's theory of motion and gravitation is subsumed under the name classicalmechanics. Newton's theory of gravity essentially consists of a law for theforces between two material bodies. Newton was able to use this law to explainthe motion of the planets within the framework of his theory of gravity.Einstein's theory of motion is the special theory of relativity, Einstein's theory of gravity is the general theory of relativity. Both represent extensions of the corresponding Newtonian theories to a larger range of phenomena: for motions to "higher" velocities, for gravitation to "higher" velocities and to "stronger" gravitational forces. It will still be necessary to make precise what the terms "higher" or "larger" mean in each case.Maxwell's theoryof electromagnetism serves to explain all electrical and all magnetic phenomenaas well as those phenomena in which electrical and magnetic effects aremutually dependent. It is the result of a unification of two earlier theories,one for electricity and one for magnetism. Gravity and electromagnetic forces act over long distances. Otherwise, we wouldn't have felt it all the time. They are therefore called long-range, in contrast to the short-range forces that were only discovered in the world of the smallest dimensions. They hold the world "together at its innermost" and their reach does not go beyond that. Of course, the long-range forces can affect even at short distances, electromagnetic forces are even quite important for understanding structure of atoms. However, gravitational forces at the level of atoms have not yet been registered. The masses of the building blocks of the atoms are obviously much too small.The theories of quantumphysicsTheestablishment of Maxwell's theory, in particular by the discovery ofelectromagnetic waves in 1886, increasingly drew physicists to the question ofhow an electric current and how electromagnetic radiation can be generated inmatter. In the end, the question of the structure of matter stood in the centerof attention. From apre-Socratic Leukipp and his follower Democritus one knew the concept of anatom, a smallest indivisible particle (άτομος gr. indivisible). The chemistsused this idea in the 19th century with great profit for the explanation of thelaws in the reactions of different chemical elements. But there were alsovehement opponents, because one had not yet "really seen" an atom andthe idea of indivisibility only raised new questions.But otherquestions also came to mind. In the "golden years of physics" from1895 to 1898 further rays were discovered, such as X-rays, cathode rays, α-, β-or γ-rays. Finally, there were the heat rays, a phenomenon that had been knownfor some time: All bodies become red, light red and finally white-yellow withconstant heating; and one feels that heat emanates from them.The origin andnature of these rays had to be understood. It was a very fruitful time forphysics, and during this time the idea of atoms should establish itself asbuilding blocks of matter, but only as a milestone on the way to ever smallerbuilding blocks. One could then obtain an explanation for all these rays andthereby gain a consistent picture of the structure of matter and the atom. In an attempt todevelop this picture into a consistent theory success was only achieved afterdaring to describe the discovered relationships between the experimentalresults with a completely different mathematical conceptual apparatus.A test case foreach approach of a theory for the structure of an atom was the calculation ofthe possible energy states of a hydrogen atom. The success or failure of amathematical calculation thus now decided on the success of a theory in thisworld of the smallest dimensions. The building blocks of an atom such aselectrons, protons or neutrons could then no longer be regarded as particles inthe sense of classical physics and the living world. They were soon called"quanta", like the energy packages Max Planck had talked about in alecture on 14 December 1900 when he gave an explanation of thermal radiation.By the way, the date of this lecture is regarded today as the birthday ofquantum physics. The quantumtheories responsible for all the fundamental phenomena of the world's smallestdimensions are first of all- quantummechanics, to a certain extent the replacement for classical mechanics - quantumelectrodynamics, the continuation of electrodynamics on the atomic level.An explanationof the origin and nature of α- and β-rays could only be achieved by introducingtwo completely new types of forces, the "strong" force, which isresponsible for the binding of the building blocks of the atomic nucleus, andthe "weak" force, which can cause the transformation of a neutroninto a proton, but also serves to describe the decays of other later discovered"particles". Thus - theories ofweak and of strong interaction were created.These two theories were constructed according to the model of quantumelectrodynamics. This soon led to the desire to describe these threeinteractions within a unified theory. As an intermediate step the- theory ofelectroweak interaction, a unification ofthe electromagnetic and weak interaction was found, and finally - the unifiedtheory of electrical, weak and strong interaction, the so-called standardmodel. Today, thismodel is regarded as the basic quantum theory. Quantum mechanics now plays therole of a theory for a limited range of phenomena in which relativistic effectsdo not have to be taken into account and in which there is no decay and nogeneration of particles. Figure 4.3 shows the development of the individual theories over the course of time. Fig.4.3: Timetable for the emergence of physical theories of fundamental interactions 