The physics is a science , the basic phenomena of nature studied. In order to explain their properties and behavior using quantitative models and laws, she deals in particular with matter and energy and their interactions in space and time .
Explaining here means classifying, comparing, assigning more general phenomena or inferring from general laws of nature . This often requires the formation of new, suitable terms , sometimes also those that are no longer directly accessible. Physics cannot provide explanations in the philosophical sense of “why” nature behaves in this way. Instead, it deals with the "how". For example, she cannot explain why crowds attract one another. This behavior can only be described with different models. Newton did this by assuming that there is an attraction between bodies. Einstein had a completely different idea, who explained gravity by saying that matter bends space-time.
The way physics works consists of a combination of experimental methods and theoretical modeling . Physical theories prove themselves in the application to systems of nature, in that they allow predictions about later states with knowledge of their initial states. Progress in knowledge results from the interplay of observation or experiment with theory. A new or further developed theory can explain known results better or at all for the first time and can also stimulate new experiments and observations, the results of which then confirm or contradict the theory. Unexpected results of observation or experiments give rise to the development of theory in various forms, from gradual improvement to the complete abandonment of a theory that has been accepted for a long time.
History of the concept and discipline of physics
The discipline of physics in its present form has its origins in philosophy , which has been concerned with the reasons and causes of all things in the broadest sense since ancient times. From Aristotle up to the beginning of the 19th century, physics was understood as the branch of philosophy that deals with the realities of nature as natural science, natural history, chemistry or applied mathematics . Compared to the purely philosophical attempts to explain natural processes, the type of knowledge that can be gained through systematic and precise observation, i.e. empirically, played no role for a long time. From the middle of the 13th and in the course of the 14th century, individual philosophers and naturalists - mostly one and the same person such as Roger Bacon - pleaded for greater weight to be given to the knowledge of nature that could be obtained through observation. In the 16th and 17th centuries, with Galileo Galilei and Isaac Newton in particular, these tendencies led to the development of a methodology of physical knowledge that is primarily oriented towards empirical and even experimental standards and, in case of doubt, even gives priority to these over traditional philosophical principles . This approach was initially called " experimental philosophy " and quickly led to significant successes in understanding many different natural processes. Nevertheless, it was not until the 19th century that it finally established itself in physics and thus established it as an independent discipline in its current sense.
With regard to its method, its subject area, its scientific systematic and institutional location, physics is essentially divided into two large areas. The theoretical physics is primarily concerned with formal mathematical descriptions and the laws of nature . It abstracts processes and appearances in real nature in the form of a system of models , general theories and natural laws as well as intuitively chosen hypotheses . When formulating theories and laws, she often makes use of the methods of mathematics and logic . The aim is to theoretically predict the behavior of a system so that this can be checked by comparison with the processes and phenomena in real nature. This verification in the form of reproducible measurements on specifically designed physical experiments or by observing natural phenomena is the field of experimental physics . The result of the check determines the validity and predictive power of the model and the terms, hypotheses and methods chosen in it.
Physics is closely related to engineering and the other natural sciences from astronomy and chemistry to biology and geosciences . Physics is often viewed as a fundamental or fundamental science that deals most closely with the basic principles that determine natural processes. The demarcation to the other natural sciences has arisen historically, but is becoming more and more difficult, especially with the emergence of new scientific disciplines.
In today's physics , the boundary to chemistry marked by atomic and molecular physics and quantum chemistry is fluid. To distinguish it from biology, physics has often been referred to as the science of inanimate versus animate nature, but this implies a limitation that does not exist in physics. The engineering sciences are distinguished from physics by their close relation to practical technical application, since in physics the understanding of the fundamental mechanisms is in the foreground. Astronomy has no way of carrying out laboratory experiments and is therefore solely dependent on observation of nature, which is used here to distinguish it from physics.
The acquisition of knowledge in physics is closely linked between experiment and theory, i.e. it consists of empirical data acquisition and evaluation and, at the same time, the creation of theoretical models to explain them . Nonetheless, specializations developed over the course of the 20th century, which particularly shape professionally operated physics today. Accordingly, experimental physics and theoretical physics can be roughly distinguished from one another.
While some natural sciences, such as astronomy and meteorology , have to restrict themselves methodologically largely to observations of their object of investigation, in physics the focus is on experiment. Experimental physics tries to track down laws through the design, construction, implementation and evaluation of experiments and to describe them using empirical models. On the one hand it tries to break new ground in physics, on the other hand it checks the predictions made by theoretical physics.
The basis of a physical experiment is to express the properties of a previously prepared physical system, for example a thrown stone, an enclosed volume of gas or a particle during an impact process by measuring in numerical form, for example as impact speed, as the resulting pressure (given the boundary conditions) or as Length of the observable particle tracks in the detector.
Specifically, either only the time-independent ( static ) properties of an object are measured or the temporal development ( dynamics ) of the system is examined, for example by determining the start and end values of a measured variable before and after the course of a process or by determining continuous intermediate values.
Theoretical physics seeks to mathematically trace the empirical models of experimental physics back to known basic theories or, if this is not possible, to develop hypotheses for a new theory, which can then be tested experimentally. It also derives empirically verifiable predictions from already known theories.
When developing a model, reality is fundamentally idealized; one concentrates initially only on a simplified image in order to survey and explore its aspects. After the model has matured for these conditions, it is further generalized.
The language of mathematics is used for the theoretical description of a physical system. Its components are represented by mathematical objects such as scalars or vectors , which are related to one another by means of equations . Known variables are calculated from known variables and thus, for example, the result of an experimental measurement is predicted. This view, which is focused on quantities , distinguishes physics significantly from philosophy and has the consequence that non-quantifiable models, such as consciousness , are not regarded as part of physics.
The fundamental measure for the success of a scientific theory is the agreement with observations and experiments. By comparing it with the experiment, the range of validity and the accuracy of a theory can be determined; however, it can never be "proven". In principle, a single experiment is sufficient to refute a theory or to show the limits of its range of validity, provided it proves to be reproducible .
Experimental physics and theoretical physics are therefore constantly interrelated. However, it can happen that the results of one discipline run ahead of the other: For example, many of the predictions made by string theory cannot currently be verified experimentally; on the other hand, many values from the field of particle physics, some of which have been measured very precisely , cannot be calculated at the present time (2009) due to the associated theory, quantum chromodynamics .
In addition to this basic division of physics, a distinction is sometimes made between further methodological sub-disciplines, above all mathematical physics and applied physics . Working with computer simulations also has features in its own area of physics.
Mathematical physics is sometimes viewed as a branch of theoretical physics, but differs from it in that the subject of study is not concrete physical phenomena, but the results of theoretical physics itself. It abstracts from any application and is instead interested in the mathematical properties of a model, especially its underlying symmetries . In this way she develops generalizations and new mathematical formulations of already known theories, which in turn can be used as working material for theoretical physicists in the modeling of empirical processes.
Applied physics is (fuzzy) differentiated from experimental physics, and sometimes also from theoretical physics. Its essential characteristic is that it does not research a given physical phenomenon for its own sake, but rather to use the knowledge obtained from the investigation to solve a (usually) non-physical problem. Its applications are in the field of technology , but also, for example, in economics , where methods of theoretical solid-state physics are used in risk management . There are also the interdisciplinary areas of medical physics , physical chemistry , astrophysics and biophysics .
Simulation and computer physics
With the advancing development of computing systems in the last decades of the 20th century, accelerated since around 1990, computer simulation has developed as a new method within physics. Computer simulations are often used as a link between theory and experiment in order to gain predictions from a theory; on the other hand, simulations can also give an impulse to theoretical physics in the form of an effective theory that models an experimental result. Naturally, this area of physics has numerous points of contact with computer science .
Building of theories
The theoretical structure of physics is based in its origin on classical mechanics . This was supplemented by other theories in the 19th century, in particular electromagnetism and thermodynamics . Modern physics is based on two extensions from the 20th century, the theory of relativity and quantum physics , which generalized certain basic principles of classical mechanics. Both theories contain classical mechanics via the so-called correspondence principle as a borderline case and therefore have a larger area of validity than this. While the theory of relativity is partly based on the same conceptual fundamentals as classical mechanics, quantum physics clearly breaks away from it.
Classical mechanics was largely founded in the 16th and 17th centuries by Galileo Galilei and Isaac Newton. Due to the still quite limited technical possibilities at that time, the processes described by classical mechanics can largely be observed without complicated aids, which makes them clear. Classical mechanics deals with systems with a few massive bodies, which distinguishes them from electrodynamics and thermodynamics. Space and time are not part of the dynamics, but an immobile background against which physical processes take place and bodies move. For very small objects, quantum physics takes the place of classical mechanics, while the theory of relativity is suitable for describing bodies with very large masses and energies.
The mathematical treatment of classical mechanics was decisively unified in the late 18th and early 19th centuries in the form of the Lagrange formalism and the Hamilton formalism . These formalisms can also be used with the theory of relativity and are therefore an important part of classical mechanics. Although classical mechanics is only valid for medium-sized, descriptive systems, the mathematical treatment of complex systems is mathematically very demanding even within the framework of this theory. The chaos theory is concerned in large part with such complex systems of classical mechanics and is currently (2009) an active area of research.
Electrodynamics and optics
In electrodynamics, phenomena with moving electrical charges in interaction with time-varying electrical and magnetic fields are described. In order to bring together the development of the theories of electricity and magnetism in the 18th and 19th centuries, it became necessary to expand the theoretical structure of classical mechanics. The starting point was the law of induction discovered by Michael Faraday and the Lorentz force, named after Hendrik Antoon Lorentz , on a moving electrical charge in a magnetic field. The laws of electrodynamics were summarized by James Clerk Maxwell in the 19th century and formulated in full for the first time in the form of the Maxwell equations . Basically, electrodynamic systems were treated with the methods of classical mechanics, but the Maxwell equations also enable a wave solution that describes electromagnetic waves like light. Among other things, this theory produced its own formalism in the form of wave optics , which is fundamentally different from that of classical mechanics. Especially the symmetries of electrodynamics are incompatible with those of classical mechanics. This contradiction between the two theoretical buildings was resolved by the special theory of relativity. Wave optics is still an active research area today (2011) in the form of non-linear optics .
At about the same time as electrodynamics, another set of theories developed, thermodynamics, which is fundamentally different from classical mechanics. In contrast to classical mechanics, in thermodynamics it is not individual bodies that are in the foreground, but an ensemble of many tiny building blocks, which leads to a radically different formalism. Thermodynamics is therefore suitable for the treatment of media of all aggregate states . The quantum theory and the relativity theory can be embedded in the formalism of thermodynamics, since they only affect the dynamics of the building blocks of the ensemble, but do not fundamentally change the formalism for describing thermodynamic systems.
Thermodynamics is suitable, for example, for describing heat engines but also for explaining many modern research subjects such as superconductivity or superfluidity . Especially in the area of solid state physics , a lot of work is still done with the methods of thermodynamics today (2009).
theory of relativity
The theory of relativity founded by Albert Einstein introduces a completely new understanding of the phenomena of space and time. According to this, these are not universally valid order structures, but spatial and temporal distances are assessed differently by different observers. Space and time merge into a four-dimensional space - time . The gravitation is attributed to a curvature of this space-time, which is caused by the presence of mass or energy . In the theory of relativity, cosmology becomes a scientific topic for the first time . The formulation of the theory of relativity is considered to be the beginning of modern physics , even if it is often referred to as the completion of classical physics .
Quantum physics describes the laws of nature in the atomic and subatomic realm and breaks even more radically with classical ideas than the theory of relativity. In quantum physics, physical quantities are themselves part of the formalism and are no longer mere parameters that describe a system. The formalism differentiates between two types of objects, the observables , which describe the quantities, and the states , which describe the system. The measurement process is also actively included in the theory. In certain situations, this leads to the quantization of the size values. This means that the quantities always only take on certain discrete values . In quantum field theory , the most developed relativistic quantum theory, matter appears only in portions, the elementary particles or quanta .
The laws of quantum physics largely elude human perception , and even today there is still no consensus on their interpretation . Nevertheless, in terms of its empirical success, it is one of the best-established knowledge of mankind.
Subject areas of modern physics
The theories of physics are used in various subject areas. The division of physics into subtopics is not clear and the delimitation of the subtopics from one another is just as difficult as the delimitation of physics from other sciences. Accordingly, there is a great deal of overlap and mutual relationships between the various areas. Here, a collection of subject areas is presented according to the size of the objects considered and in the course of this, reference is made to subject areas that are related to them. The topics listed cannot be clearly assigned to a theory, but rather make use of various theoretical concepts depending on the subject examined.
Particle physics deals with elementary particles and their interactions with one another. Modern physics knows four basic forces :
- The gravitation or gravity,
- the electromagnetic interaction ,
- the weak interaction that is responsible, for example, for certain radioactive decay processes and
- the strong interaction that holds the atomic nuclei together.
These interactions are described by the exchange of so-called calibration bosons . Particle physics currently excludes gravity, as there is still no theory of quantum gravity that can fully describe the gravitational interactions of elementary particles. In particle physics, relativistic quantum theories are used to describe the phenomena.
One of the goals of particle physics is to describe all basic forces in a unified overall concept ( world formula ). So far, however, it has only been possible to represent the electromagnetic interaction as a combination of the electrical and the magnetic interaction and also to combine the electromagnetic interaction and the weak interaction into a so-called electroweak interaction . To combine the electroweak and the strong interaction, among other things, the theory of supersymmetry was devised, which, however, has not yet been confirmed experimentally. As already mentioned, the greatest difficulties arise in the area of gravitational force, as there is no theory of quantum gravity yet, but elementary particles can only be described within the framework of quantum theory.
Typical experiments to test the theories of particle physics are carried out at particle accelerators with high particle energies. In order to achieve high collision energies, collider experiments are used in particular , in which particles are shot against each other and not at a fixed target. Therefore, the term high-energy physics is often used almost congruently with the term particle physics. The particle accelerator with the currently (2011) highest collision energy is the Large Hadron Collider . Neutrino detectors such as the Super-Kamiokande are specially designed for researching the properties of neutrinos and thus represent a special, but important class of experiments.
Hadron and Atomic Nuclear Physics
The elementary particles that are subject to the strong interaction, the so-called quarks , do not occur individually, but always only in bound states, the hadrons , which include the proton and the neutron . Hadron physics has many overlaps with elementary particle physics, as many phenomena can only be explained by taking into account that hadrons are made up of quarks. However, the description of the strong interaction by quantum chromodynamics, a relativistic quantum field theory, cannot predict the properties of hadrons, which is why the investigation of these properties is regarded as an independent research area. The aim is to expand the theory of strong interaction for small energies at which the hadrons are formed.
Atomic nuclei represent the next level of complexity compared to elementary particles. They consist of several nucleons , i.e. protons and neutrons, whose interactions are examined. In atomic nuclei, the strong and the electromagnetic interaction predominate. Research areas in atomic nuclear physics include radioactive decay and stability of atomic nuclei. The aim is to develop core models that can explain these phenomena. However, there is no detailed elaboration of the strong interaction as in hadron physics.
Particle accelerators are used to research the properties of hadrons, although the focus here is not as much on high collision energies as in particle physics. Instead, target experiments are carried out, which yield lower center of gravity energies but a much higher number of events. However, collider experiments with heavy ions are mainly used to gain knowledge about hadrons. In nuclear physics, heavy atoms are brought to collision to generate transuranium elements and radioactivity is investigated with a variety of experimental setups.
Atomic and Molecular Physics
Atoms consist of the atomic nucleus and usually several electrons and represent the next level of complexity of matter. One of the aims of atomic physics is to explain the line spectra of the atoms, which requires an exact quantum mechanical description of the interactions between the electrons of the atoms. Since molecules are made up of several atoms, molecular physics works with similar methods, but large molecules in particular usually represent significantly more complex systems, which makes the calculations much more complicated and often requires the use of computer simulations.
Atomic and molecular physics are closely related to optics through the study of the optical spectra of atoms and molecules. For example, the functional principle of the laser , a major technical development, is largely based on the results of atomic physics. Since molecular physics also deals intensively with the theory of chemical bonds , this subject area overlaps with chemistry.
An important experimental approach is exposure to light. For example, optical spectra of atoms and molecules are related to their quantum mechanical properties. Conversely, spectroscopic methods can then be used to examine the composition of a mixture of substances and to make statements about the elements in the star's atmosphere using starlight. Other investigation methods consider the behavior under the influence of electric and magnetic fields. Examples are mass spectroscopy or the Paul trap .
Condensed Matter and Fluid Dynamics
The physics of condensed matter and fluid dynamics are the areas with the greatest thematic range in this list, from solid-state physics to plasma physics . What all these areas have in common is that they deal with macroscopic systems made up of a large number of atoms, molecules or ions . Accordingly, thermodynamics is an important part of the theoretical foundation in all areas of this subject area. Depending on the problem, quantum theory and relativity are also used to describe the systems. Computer simulations are also an integral part of research on such many-body systems.
Due to the range of topics, there are overlaps with almost all other areas of physics, for example with optics in the form of laser-active media or non-linear optics, but also with acoustics, atomic, nuclear and particle physics. In astrophysics, too, fluid dynamics plays a major role in the creation of models for the formation and structure of stars and in the modeling of many other effects. Many research areas are very application-oriented, such as materials research , plasma physics or research into high-temperature superconductors .
The range of experimental methods in this area of physics is very large, so that no typical methods can be given for the whole area. The quantum mechanical effects such as superconductivity and superfluidity , which have become known to a certain extent, are attributed to the low-temperature physics associated with typical cooling methods .
Astrophysics and cosmology
Astrophysics and cosmology are interdisciplinary research areas that strongly overlap with astronomy. Almost all other subject areas of physics are included in the astrophysical models in order to model processes on different size scales. The aim of these models is to explain astronomical observations on the basis of previously known physics.
Cosmology is based in particular on the fundamentals of the general theory of relativity, however, within the framework of quantum cosmology , quantum theories are also very important to explain the development of the universe in much earlier phases. The cosmological standard model currently (2009) most represented is based largely on the theories of dark matter and dark energy . So far, neither dark matter nor dark energy has been directly demonstrated experimentally, but there are a number of theories as to what exactly these objects are.
Since experiments are only possible to a very limited extent in astrophysics, this branch of physics is very dependent on the observation of phenomena that cannot be influenced. Findings from atomic physics and particle physics and typical measurement methods from these disciplines are also used to draw conclusions about astrophysical or cosmological relationships. For example, give the spectra of starlight information about the distribution of elements of the star atmosphere, the study of the height radiation allows conclusions to cosmic rays and neutrino detectors measure for a Super Nova increased neutrino stream which is simultaneously observed with the light of Super Nova.
Interdisciplinary subject areas
Methods of physics are used in many subject areas that do not belong to the core subject area of physics. Some of these applications have already been addressed in the previous chapters. The following list gives a brief overview of the most important interdisciplinary subject areas.
- The astrophysics uses physical methods to the study of astronomical phenomena.
- In biophysics , the physical laws that living beings and their interaction with nature are subject to are examined.
- The Medical Physics uses physical phenomena such as lasers, radioactivity, X-rays and magnetic resonance for medical diagnostics and therapy.
- In physical chemistry , methods of physics are applied to the objects of illustration in chemistry.
- The Geophysics uses physical models and methods to explain geoscientific processes and issues.
- The Technical Physics deals with the technical applications physical knowledge. Important areas are quantum electronics and the theory of quantum computers .
- In its research, environmental physics is primarily concerned with the areas of energy and climate .
- Sociophysics and econophysics apply physical and statistical methods to social, economic, cultural and political phenomena.
Limits of physical knowledge
The current state of physics is still faced with unresolved problems. On the one hand, there is the less fundamental case of problems, the solution of which is possible in principle, but at best can be approximated with the current mathematical possibilities. On the other hand, there are a number of problems for which it is still unclear whether a solution in the context of today's theories will be possible at all. So far it has not been possible to formulate a unified theory that describes phenomena that are subject to electroweak and strong interaction as well as those that are subject to gravity. Only with such a union of quantum theory and theory of gravity (general theory of relativity) could all four basic forces be treated uniformly, resulting in a unified theory of elementary particles.
The previous candidate of quantum gravity theories, supersymmetry and supergravity - string and M-theories try to achieve such standardization. In general, it is a practically leading goal of today's physicists to describe all processes in nature by the smallest possible number of the simplest possible laws of nature . These should describe the behavior of the most fundamental properties and objects (such as elementary particles ) so that higher-level ( emergent ) processes and objects can be reduced to this level of description.
Whether this goal can be achieved in principle or in practice is actually no longer the subject of individual scientific physical knowledge efforts, just as there are general questions about the degree of certainty physical knowledge can in principle achieve or have actually achieved. Such questions are the subject of epistemology and philosophy of science . Very different positions are defended. It is relatively undisputed that scientific theories are only hypotheses in the sense that one cannot know with certainty whether they are true and justified views. One can be even more specific here, by referring to the theoretical and conceptual mediation of all empirical knowledge or to the fact that the human being as a knowing subject falls under the subject area of physical theories, but only as a really outsider have certain knowledge could. Because for observers who interact with their object of knowledge , there are fundamental limits to predictability in the sense of indistinguishability of the present state - a limit that would also apply if man knew all natural laws and the world were deterministic. This limit is of practical importance in deterministic processes for which small changes in the initial state lead to large deviations in subsequent states - processes as described by chaos theory . But not only a practical predictability is only possible to a limited extent in many cases, some scientific theorists also dispute the ability of physical models to make any statements about reality at all. This applies in different drafts of a so-called epistemological antirealism to varying degrees: for different types of physical concepts is denied a real reference or deemed unknowable. A fundamental or probable merging of individual theories is also contested by some theorists of science.
Relationship to other sciences
The relationship to philosophy is traditionally close, since physics developed from classical philosophy without ever fundamentally contradicting it, and according to today's categories numerous important physicists were also important philosophers and vice versa. According to today's philosophical disciplinary distinction, physics is particularly related to ontology , which tries to describe the basic structures of reality in terms that are as general as possible, furthermore to epistemology , which tries to grasp the quality criteria of knowledge at all, and more particularly to the philosophy of science , which Tries to determine the general methods of scientific knowledge and of course to the natural philosophy or philosophy of physics , which is often treated as a sub-discipline of ontology or philosophy of science, but in any case works more specifically based on the individual knowledge of physics, analyzes their system of terms and analyzes ontological interpretations of physical theories discussed.
Relations with mathematics are also close. All physics uses the mathematical language. Many important physicists were also important mathematicians in today's categories, and vice versa.
According to today's mathematical disciplinary distinction, physics is particularly related to geometry , which tries to describe the basic structures of space in as general terms as possible, and also to algebra , more specifically to algebraic geometry , to differential geometry and mathematical physics .
Physics in Society
Since physics is considered the fundamental natural science, physical knowledge and thinking are usually taught in school as part of a separate school subject. As part of the school system, physics is usually taught as a minor subject from grades 5–7 and is often offered as an advanced course in the upper grades.
- Most universities offer physics as a subject.
- The Swedish Academy of Sciences has awarded the Nobel Prize in Physics annually since 1901 .
- The question of the ethics of scientific research was first explicitly raised when physical discoveries in the late 1930s suggested the possibility of an atomic bomb. This topic is also taken up in literature , for example in Friedrich Dürrenmatt's play The Physicists .
- There have been attempts to instrumentalize physics in an ideological way. For example, in the time of National Socialism there was German physics, turned against Einstein, and military physics as applied physics. Representatives of such endeavors were the physics didactic and school politician Erich Günther († 1951), whose textbook Wehrphysik (a manual for teachers) was used until 1975, and Karl Hahn (1879-1963), who was appointed an honorary doctor of the University of Gießen in 1959, who worked as the Reich clerk Erased theories of Jewish physicists from his textbooks and whose textbooks were widespread until the 1960s.
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