The physics ( physica, via Latin, natural science ' from Greek φυσική physicist, scientific study of the phenomena of nature ', ' natural science ' ) examines the fundamental phenomena in nature. In the intention to declare their properties and behavior based on quantitative models and laws, it is particularly concerned with matter and energy and their interactions in space and time. The operation of the physics consists in a combination of experimental methods and theoretical modeling. Physical theories have proven themselves in the applicability to natural systems by allowing on knowledge of initial states of the same exact possible prediction resulting final states. Advances in physics consist in the provision or development of theories and experimental tools and methods. Example, run on the applicability to other systems, more accurate descriptions, simplifications of the theoretical apparatus or to new or facilitate practical applications.

Disciplines such as chemistry, geology, biology and medicine, and many engineering make intensive use of knowledge and models from physics.

  • 3.1 Classical Mechanics
  • 3.2 Electrodynamics
  • 3.3 Thermodynamics
  • 3.4 Theory of Relativity
  • 3.5 Quantum Physics
  • 4.1 Particle
  • 4.2 Hadron and nuclear physics nuclear
  • 4.3 Atomic and Molecular Physics
  • 4.4 Condensed Matter Physics and Fluid Dynamics
  • 4.5 Astrophysics and Cosmology
  • 4.6 Interdisciplinary topics

History of concept and discipline of physics

The discipline of physics has its origins in the theories and individual studies of ancient scientists. Although the physics is understood here as a branch of philosophy; but she has, for example, in the relevant scheme and implementation in Aristotle, a separate area of ​​knowledge and methodological independence. Middle of the 13th and during the 14th century plead several philosophers and natural scientists - mostly in personal union - for greater autonomy of natural knowledge; - A development that, in fact, could not stop and, leads to uptake of these tendencies in the 16th and 17th centuries in the development of a methodology of physical knowledge, the modern criteria comes to experimental standards close, and especially with Galileo Galilei Isaac Newton.

Thus, the physics has finally established as a discipline in terms of their method, their subject area, their scientific and systematic institutional placing. This new methodology divides the physics essentially into two large areas. Theoretical physics deals mainly with formal descriptions and the laws of nature. It abstracts processes and phenomena in the real nature in the form of a system of models, generally accepted theories and laws of nature as well as intuitively selected hypotheses. In the formulation of theories and laws it uses many of the methods of mathematics and logic. Goal of this analysis is to predict the behavior of a system and the experimental verification of the validity and predictive power of the selected hypotheses by comparing the predicted behavior with the processes and phenomena in the real nature. This verification in the form of reproducible measurements or by observation of natural phenomena constitutes the branch of experimental physics.

The physics is closely related to the engineering and most sciences of astronomy and chemistry to biology and the earth sciences. The demarcation of these sciences arises historically from the origin of physics in philosophy. Especially with the advent of new scientific disciplines a substantive definition of physics to these other fields is made difficult. The physics is often regarded as basic or fundamental science, the stronger than the other natural sciences dealing with the basic principles that govern the natural processes.

In today's physics is especially the border with the chemistry, the transition from the physics of atomic and molecular physics, quantum chemistry, flowing. However, the chemistry tends to concentrate on more complex structures (molecules ), while the physics explores the most fundamental matter. Differentiating it from biology, physics is often referred to as the science of inanimate nature, which is a limitation implied, in physics there is no such. The engineering sciences are delimited by their relationship to practical applications of physics, as in physics, the understanding of the basic mechanisms in relation to the application in the foreground. Astronomy has to carry out any possibility of laboratory experiments and is therefore solely rely on observation of nature, which is used for differentiation from the physics.


The process of gaining knowledge in physics runs in close interaction between experiment and theory, that consists of empirical data collection and analysis and at the same time creating theoretical models to explain them. Nevertheless specializations have emerged during the 20th century that characterize especially the professionally operated physics today. Thus, can be broadly experimental physics and theoretical physics are different.

Experimental Physics

While some natural sciences such as astronomy and meteorology must be limited methodologically largely on the observations of their object of study, is in physics experiment in the foreground. The Experimental Physics aims to trace regularities in nature and to be described using empirical models through the design, development, implementation and evaluation of experiments. She tries on the one hand to enter physical territory, on the other hand, it examines from theoretical physics, predictions made.

Based on a physical experiment to express the characteristics of a previously prepared physical system, such as a particle accelerator, a vacuum chamber with detectors or a stone thrown by measuring in numerical form, such as a length of a particle track, the pulse height of an electrical voltage pulse or as impact velocity.

Concretely, either only the time-independent ( static ) properties of an object measured or it is the temporal evolution ( dynamics) studied the system, or by continuous intermediate values ​​are about by initial and final values ​​of a measured variable before and are determined by the flow of a process determined.

Theoretical Physics

The task of theoretical physics, in turn, is due to the empirical mathematical models of experimental physics known basic theories or, if that is not possible to develop hypotheses for a new theory, which can then be tested experimentally. You will continue to lead from already known from theories empirically testable predictions.

In developing a model, the reality is idealized principle; firstly focuses only on a simplified image to overlook its aspects and to explore; after the model is mature for these conditions, it is further generalized.

For a theoretical description of a physical system to use the language of mathematics. Its components are represented by this mathematical objects such as scalars or vectors, which are defined by equations relationships. The purpose of the model is to calculate unknown from known quantities and thus, for example, to predict the outcome of an experimental measurement. This concentrated on quantities perspective differs materially from the physics of philosophy and has the consequence that non-quantifiable models, such awareness can not be considered as a part of physics.

The fundamental measure of the success of a scientific theory is the agreement with observations and experiments. By comparing with the experiment, the scope and the accuracy of a theory can be determined, but it can never "prove". In order to refute a theory, or to demonstrate the limits of its validity, is sufficient, in principle, a single experiment, if it is reproducible.

Experimental physics and theoretical physics are therefore in constant interaction with each other. However, it may occur that results of a discipline run ahead of the other: Thus are currently not experimentally verifiable many predictions of string theory; On the other hand, many partially extremely accurate measured values ​​from the field of nuclear physics at the present time (2009) by the associated theory, quantum chromodynamics, not predictable.

Other aspects of

In addition to this basic division of physics sometimes differs even further methodological sub-disciplines, particularly mathematical physics and applied physics. Also working with computer simulations has adopted in recent years, features of a private area of physics.

Mathematical Physics

The mathematical physics is sometimes regarded as a branch of theoretical physics, differs from this, however, is that their object of study are not concrete physical phenomena, but the results of theoretical physics itself abstracting thus from any application, and is interested in instead of the mathematical properties a model, in particular its underlying symmetries. In this way they developed generalizations and new mathematical formulations of known theories, which in turn can be used as working material of the theoretical physicists in the modeling of empirical processes used.

Applied Physics

The physics is applied, however, in ( fuzzy ) definition for experimental physics, partly also to theoretical physics. Its main characteristic is that they are not researched a given physical phenomenon for its own sake, but to use the products resulting from the investigation findings to the solution of a (usually ) non- physical problem. Your applications are in the field of engineering or electronics but also in economics, where it will come in the risk management methods of theoretical solid state physics used. Also there is the interdisciplinary areas of medical physics, physical chemistry, astrophysics and biophysics.

Simulation and Computational Physics

With the progressive development of computing systems has become in the last decades of the 20th century, accelerated since around 1990, developed the computer simulation as a new methodology within physics. Computer simulations are often used as a link between theory and experiment in order to make predictions from a theory, on the other hand, simulations can also take the form of an effective theory, which modeled an experimental result, return a pulse at the theoretical physics. Naturally, this area of ​​physics has numerous links to computer science.

Theory building

The theoretical structure of physics is based in its origin to the classical mechanics. This was supplemented in the 19th century to more theories, in particular electromagnetism and thermodynamics. Modern physics rests on two extensions from the 20th century, the theory of relativity and quantum physics, the basic principles of classical mechanics have generalized. Both theories contain classical mechanics via the so-called correspondence principle as a limiting case and therefore have a larger scope than this. While the theory of relativity, in part, on the same conceptual foundations based, like classical mechanics, the quantum physics solves clearly.

Classical Mechanics

Classical mechanics was justified largely by Galileo Galilei and Isaac Newton in the 16th and 17th centuries. Due to the at that time still quite limited technical possibilities are the operations that describes the classical mechanics, largely observable without complicated tools, which makes them appear vividly. Classical mechanics treats systems with a few massive bodies, which distinguishes it from the electrodynamics and thermodynamics. Space and time are not part of the dynamics, but a non-moving background, run in front of the physical processes and bodies move. For very small objects quantum physics takes the place of classical mechanics, while the theory of relativity is suitable for the description of bodies with very large masses and energies.

The mathematical treatment of classical mechanics was unified decisive in the form of the Lagrangian formalism and the Hamiltonian formalism in the late 18th and early 19th centuries. These formalisms are also applicable to the theory of relativity and are therefore an important part of classical mechanics. Although classical mechanics is valid for medium size, descriptive systems, the mathematical treatment of complex systems already in the framework of this theory is mathematically very challenging. Chaos theory is concerned in large part with such complex systems of classical mechanics and is currently (2009) an active area of ​​research.


In electrodynamics phenomena are described with moving electric charges in interaction with time-varying electric and magnetic fields. To merge the development of the theories of electricity and magnetism in the 18th and 19th centuries, an extension of the theory building of classical mechanics was necessary. The starting point was discovered by Michael Faraday 's law of induction and named after Hendrik Antoon Lorentz Lorentz force on a moving electric charge in a magnetic field. The laws of electrodynamics were summarized in the 19th century by James Clerk Maxwell formulated and completely the first time in the form of Maxwell's equations. Basically electrodynamic systems were treated using the methods of classical mechanics, but the Maxwell equations also allow wave solution describing electromagnetic waves such as light. This theory brought, among others, in the form of wave optics also produced its own formalism, the fundamentally different from that of classical mechanics. In particular, the symmetries of electrodynamics are incompatible with those of classical mechanics. This contradiction between the two buildings was solved by the theory of special relativity theory. The wave optics (2011), an active area of ​​research in the form of nonlinear optics today.


At about the same with the electrodynamics developed with the thermodynamics Another theory complex, which is fundamentally different from classical mechanics. In contrast to classical mechanics are not individual bodies in the foreground, but an ensemble of many smallest components, resulting in a radically different formalism in thermodynamics. The thermodynamics is therefore suitable for the treatment of media of all aggregate states. The quantum theory and the theory of relativity can be divided into the formalism of thermodynamics Embed since they only affect the dynamics of the components of the ensemble, but change the formalism for the description of thermodynamic systems can not in principle.

The thermodynamics is suitable for example for the description of heat engines but also for the explanation of many modern research topics such as superconductivity or superfluidity. Especially in the field of solid state physics (2009 ) is therefore worked a lot with the methods of thermodynamics today.

Relativity theory

The founded by Albert Einstein 's theory of relativity introduces an entirely new understanding of the phenomena of time and space. After that, it is in these not universally valid order structures, but spatial and temporal distances are judged differently by different observers. Space and time merge into a four-dimensional space-time. Gravity is attributed to a curvature of the space-time, which is caused by the presence of mass or energy. In the theory of relativity is the cosmology into a science topic for the first time. The formulation of the theory of relativity is considered the beginning of modern physics, even though it is often referred to as a completion of classical physics.

Quantum physics

Quantum physics describes the laws of nature at the atomic and subatomic level and even more radical breaks with classical notions than the theory of relativity. In quantum physics, and physical quantities are themselves part of the formalism and not merely more parameters that describe a system. Thus, the formalism distinguishes between two types of objects, the observables that describe the variables and the states that describe the system. Similarly, the measurement process is actively involved in the theory. This results in certain situations to quantize the size values ​​. That is, the sizes always accept only certain discrete values. In quantum field theory, the most developed relativistic quantum theory, and matter occurs only in portions, the elementary particles or quanta, in appearance.

The laws of quantum physics beyond largely of human perception, and have dominion over their interpretation is still no consensus. Nevertheless, it is one in terms of their empirical success to the most secure knowledge of mankind.

Topics of modern physics

The theories of physics come in different subject areas used. The division of physics into subtopics is not unique and the delineation of sub-topics is as difficult as the delimitation of physics to other sciences against each other. Accordingly, there is a lot of overlap with each other and mutual relations of the various areas. Here is a collection of topics is displayed on the observed magnitude of the objects and referenced in the course of on topics that are related to it. The topics listed can not be identified with a theory, but operate depending on the investigated subject of various theoretical concepts.

Particle Physics

Particle physics is concerned with elementary particles and their interactions with each other. Modern physics recognizes four fundamental forces:

  • 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 nuclei.

These interactions are described by the exchange of so-called gauge bosons. Particle excluded here from the gravitational moment (2009), since there is no theory of quantum gravity which can describe the gravitational interactions of elementary particles completely. In particle physics, relativistic quantum theories for the description of phenomena are used.

One of the goals of particle physics is to describe all the fundamental forces in a unified concept is (World Formula). So far, however, it is only able to represent the electromagnetic interaction as the union of the electric and the magnetic interaction and also to unify the electromagnetic interaction and the weak interaction to a so-called electroweak interaction. For the union of the electroweak and strong interactions among others, the theory of supersymmetry has been devised, but the date could not be confirmed experimentally. The greatest difficulties were, as already mentioned in the range of the gravitational force, since no theory of quantum gravity exists, but elementary particles can be described only in the context of quantum theory.

Typical experiments to verify the theories of particle physics are performed at particle accelerators with high particle energies. To achieve high collision energies, primarily collider experiments are used in which the particles are to each other and not shoot a fixed target. Hence the concept of high-energy physics is often used almost congruent with the concept of particle physics. The particle accelerator with the current (2011) highest collision energy is the Large Hadron Collider. Neutrino detectors such as Super - Kamiokande the are designed specifically to explore the properties of neutrinos and thus constitute a true special, but still significant experiment class

Hadron and nucleus physics

The elementary particles that are subject to the strong interaction, called quarks, not individually, but always., Only in bound states, the hadrons, above, which include the proton and the neutron are The hadron physics has a lot of overlap with the elementary particle physics, because many phenomena can only be explained by considering that the hadrons are composed of quarks. The description of the strong interaction by quantum chromodynamics, a relativistic quantum field theory, however, the properties of hadrons can not predict, which is why the study of these properties is perceived as a research area. It is therefore sought an extension of the theory of strong interactions for small energies, which exclude the hadrons.

Atomic nuclei are facing elementary the next level of complexity; they consist of several nucleons, ie protons and neutrons, their interactions are investigated. In atomic nuclei dominate the strong and electromagnetic interactions. Research of atomic nuclear physics include radioactive decay and stability of atomic nuclei. The objective is the development of nuclear models that can explain these phenomena. Here, however, no detailed elaboration of the strong interaction as in hadron physics.

To study the properties of hadrons particle accelerators are used, not as in particle physics is the focus here so much on high collision energies. Instead, target experiments are performed, namely supply the lower center of mass energies, but much higher numbers of events. However, collider experiments with heavy ions are used primarily to gain insight into hadrons. In nuclear physics heavy atoms are brought into collision to produce transuranium elements, and radioactive radiation is analyzed with a variety of experimental set-ups.

Atomic and Molecular Physics

Atoms consist of a nucleus and usually several electrons and provide the next level of complexity of matter dar. goal of nuclear physics is to explain, among other things, the line spectra of atoms, for which an exact quantum-mechanical description of the interaction of the electrons of the atoms is necessary. Since molecules are made ​​up of several atoms, molecular physics works with similar methods, however, provide particularly large molecules usually much more complex systems is what makes the necessary calculations much more complicated and often the use of computer simulations.

The atomic and molecular physics are on the investigation of the optical spectra of atoms and molecules with the optics in close relationship. For example, expanding the functional principle of the laser, a significant technical development, largely on the results of atomic physics. Since the molecular physics also deals extensively with the theory of chemical bonds, overlap with the chemical are present in this subject area.

An important experimental approach consists in the exposure to light. For example, optical spectra of atoms and molecules with their quantum mechanical properties are set in conjunction. Conversely, then with spectroscopic methods, the composition of a substance mixture to be examined and on the basis of the star light statements about the elements in the star atmosphere are taken. Other methods of investigation consider the behavior under the influence of electric and magnetic fields. Examples are the mass spectroscopy or the Paul trap.

Condensed Matter Physics and Fluid Dynamics

The condensed matter physics and fluid dynamics are in this collection, the area with the greatest range of topics, from the solid state physics to plasma physics. All these areas have in common that they deal with macroscopic systems of very many atoms, molecules or ions. Accordingly, in all areas of this subject area thermodynamics is an important part of the theoretical foundation. Depending on the problem but they are also quantum theory and relativity theory are used to describe the systems. Also, computer simulations have become an integral component of the development of these many-body systems.

Due to the range of topics exist overlaps with almost all other fields of physics, for example, with the optics in the form of laser-active media or non-linear optics, but also with the acoustics, atomic, nuclear and particle physics. In astrophysics, the fluid dynamics plays a major role in the creation of models for the formation and structure of stars, as well as in the modeling of many other effects. Many research areas are very application-oriented, such as materials research, plasma physics, or the study of high-temperature superconductors.

The range of experimental methods in this area of physics is very large, making it easy to specify no typical methods for the whole area. The quantum mechanical effects such as superconductivity and superfluidity, which have gained a certain notoriety, is allocated to the low-temperature physics, which is accompanied by typical cooling methods.

Astrophysics and Cosmology

Astrophysics and cosmology are interdisciplinary fields of research that strongly overlap with astronomy. Almost all other topics of physics are included in the astrophysical models to model processes at different scales. The goal of this model is to explain astronomical observations on the basis of the known physics.

The cosmology is based in particular on the foundations of the general theory of relativity, however, the quantum theories are in the framework of quantum cosmology very important to explain the evolution of the universe at much earlier stages. The current (2009) most represented cosmological standard model builds largely on the theories of dark matter and dark energy. Neither dark matter nor dark energy has yet to be directly detected experimentally, but there are a variety of theories as to what these objects are accurate.

As in astrophysics experiments are possible only to a very limited extent, this branch of physics is highly dependent on the observation unbeeinflussbarer phenomena. It also knowledge of nuclear physics and particle physics and typical methods of measurement of these subject areas will apply, to draw conclusions on astrophysical or cosmological contexts. For example, give the spectra of starlight information about the element distribution of the stellar atmosphere, the study of cosmic rays allows conclusions on cosmic rays and neutrino detectors measure after a supernova increased neutrino flux that is observed simultaneously with the light of a supernova.

Interdisciplinary topics

Methods of physics in many subject areas application that does not belong to the core topic of physics. Some of these applications have already been addressed in the previous chapters. The following list gives a short overview of the most important interdisciplinary topics.

  • Astrophysics uses physical methods to the study of astronomical phenomena.
  • In biophysics, the physical laws are examined, which are living organisms and their interaction with nature.
  • In physical chemistry methods of physics are applied to the samples related to chemistry.
  • Geophysics uses physical models and methods for explanation of geo-scientific processes and issues.
  • The Technical Physics deals with the technical applications physical knowledge. Important parts of the quantum electronics and the theory of quantum computers.
  • The environmental physics deals in their research, especially with the energy and climate.
  • Socio physics and physical contact econophysics and statistical methods to social, economic, cultural and political phenomena.

Limits of physical knowledge

The current state of physics is still faced with unresolved issues. Firstly, it involves the less basic case of problems whose solution is at best approachable possible in principle, but with the current mathematical ways. On the other hand there are a number of problems for which it is still unclear whether a solution in the conceptual framework of today's theories will ever be possible. So it is not so far been able to formulate a unified theory that describes both phenomena, the subject of electro-weak as the strong interaction, as well as those which are subject to gravity. Only when such a union of quantum theory and gravitation theory ( general relativity ), all four fundamental forces could be treated uniformly, so that a unified theory of elementary particles resulted.

The previous candidate of quantum gravity theories, supersymmetry and supergravity, string and M- theories try to achieve such standardization. In general, it is a practical conductive target today's physicists to describe all the operations of nature by the smallest possible number of simple laws of nature as possible. This should describe the behavior of basic properties as possible 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 is achievable in practice or in principle, is actually no longer the subject of the individual physical science for knowledge, any more than there are general questions about what degree of certainty can achieve physical findings in principle or in fact have achieved. Such questions are the subject of epistemology and philosophy of science. This will bring very different positions to be defended. Is relatively undisputed that scientific theories in the sense are only hypotheses that one can not know with certainty whether this is true and justified opinions. One can be cautious in more specific way here by relying on the theory and concept mediation of all empirical findings or to the fact that man indeed falls as knowing subject under the subject area of physical theories, but only as a truly outsider have certain knowledge could. Because for observers who interact with their object of knowledge, there are basic limits of predictability in the sense of indistinguishability of the present state - a limit that would also be true if the person would know all the laws of nature and the world would be deterministic. This limit has practical significance for deterministic processes, for which small changes in the initial state lead to large deviations in the sequelae - processes as they are described by the theory of chaos. But not only a practical predictability is very limited in many cases, also is considered by some philosophers of science, a statement disputed ability of physical models of reality at all. This is true in various elaborations of a so-called epistemological anti-realism in varying degrees: for different types of physical concepts a real reference is denied or held for unknowable. Also, a principled or probable Zusammenführbarkeit individual theories is disputed by some philosophers of science.

Relationship to other sciences

Relations with the philosophy have traditionally closely, has yet the physics of classical philosophy developed, without ever having to face up to in principle in opposition to it, and were by today's Categories numerous important physicists are also major philosophers and vice versa. According to today's philosophical discipline distinctive physics is especially based on the ontology, which attempts to describe the basic structures of reality in general possible terms, in addition to the theory of knowledge, which tries to capture the quality criteria for knowledge at all, specific yet on the philosophy of science, which attempts to determine the general methods of scientific knowledge and of course works on the philosophy of nature and philosophy of physics, which is often treated as a sub-discipline of ontology or philosophy of science, but in any case specific based just on the individual findings of physics, analyzes their system of concepts and ontological interpretations of physical theories discussed.

Physics in Society

Since physics is considered the basic science, physical knowledge and thought are already taught in school, generally as part of a separate school subject. As part of the school system physics is generally taught as a minor subject from Grade 5-7, and is often performed in high school as a credit course.

  • Most universities offer the subject physics.
  • Since 1901, the Swedish Academy of Sciences annually awards the Nobel Prize in Physics.
  • The question of the ethics of scientific research was first explicitly raised hindeuteten as physical discoveries in the late 1930s to the possibility of an atomic bomb. This theme is taken up Physicists in the literature, such as in Friedrich Dürrenmatt's play.
  • 2005 was the Year of Physics.