# Matter (physics)

Matter (from the Latin materia , substance ) is a collective term in the natural sciences for everything from which physical bodies can be built, i.e. chemical substances or materials , as well as their building blocks. The description of the composition, structure and dynamics of matter in its various forms is a central objective of physics .

In classical physics , matter is contrasted with the terms vacuum and force field . Here vacuum and force field have no mass , but describe a state of empty space. In classical physics, however, matter is everything that takes up space and has a mass.

In modern physics , the concept of matter has been expanded several times, in particular by the theory of relativity and quantum physics , and its delimitation from the concepts of vacuum and field is no longer standardized today. In the textbooks of physics it is mostly simply assumed without a more precise definition.

In its narrowest sense, the term "matter" today includes all elementary particles with spin , i.e. quarks and leptons , as well as all objects built from them such as atoms , molecules , solid , liquid and gaseous matter, etc. up to stars and galaxies . ${\ displaystyle {\ tfrac {1} {2}}}$

## The development of the physical concept of matter

### Formation

A concrete physical concept of matter was consolidated within the extremely complex philosophical concept of matter when the experimental natural sciences emerged around 1600. In its most general, ontological meaning, the philosophical term “matter” denotes everything that can be shaped in the broadest sense and, in the extreme case, needs to be shaped in order to create something specific that we can recognize. In a narrower sense, it referred to the material matter of which the body is made. The development of physics that began with Galileo concentrated on this matter . The primary properties of material matter, i.e. the most general properties of material bodies, included expansion, divisibility, the ability to rest or move, and resistance to movement. A conservation law has already been adopted for the total amount of matter, which among other things raised the question of how the amount should be determined. The weight of a body was initially ruled out as a measure of the amount of matter it contained, because according to the doctrine, which was still strongly influenced by Aristotle in Galileo's time, weight was not considered a property of all material bodies.

Johannes Kepler approached the desired measure through the inertia of the body in relation to movement, while René Descartes considered the purely geometric property of filling space to be the actual measure. Isaac Newton was an atomist and consequently saw material bodies composed of indivisible particles and empty space in between. He determined the amount of particles ( Latin quantitas materiae ) mathematically by the product of volume and density of the body, the density obviously being understood as the amount of particles per unit volume. In his mechanics he gave the amount of matter a central role under the name "body" or "mass": the mass of a material object entails both its inertia and its weight . Only then did the mass or the amount of matter become a scientifically defined quantity. For the explanation of the mechanical processes on earth as well as the movements of the celestial bodies, Newtonian mechanics , founded in this way, had an overwhelming success, which also contributed significantly to the expansion of the scientific worldview.

In accordance with the everyday handling of material bodies, and with the possibilities of experimental art at the time, their mass and space requirements were considered largely unchangeable, at least with regard to mechanical processes with a given piece of solid matter. Only when it was discovered by Robert Boyle , Edme Mariotte , Blaise Pascal and others that air also has well-defined mechanical properties, including weight, did the gases become physical bodies, which, however, unlike solid and liquid bodies, are no longer the criterion of one certain space requirements, as they strive to occupy every space made available.

Thus, in the 17th century, "chemical" processes such as evaporation , condensation and sublimation also moved into the field of physics. With the assumption of an atomistic structure of matter (according to Pierre Gassendi , Lucretius , Democritus ), Boyle was able to interpret these transformations as purely mechanical processes in the picture that is still valid today: Atoms, which were assumed to be impenetrable again like solid bodies, can arrange themselves in different ways and have a large distance from each other in gases. Boyle also prepared the concepts of the chemical element and the molecule and thus the overcoming of alchemy . He assumed that every homogeneous substance consists of small, identical particles - according to today's name, molecules - and that the molecules themselves are made up of atoms. The molecules of different substances are different, but the arrangement of the atoms in the molecules is precisely defined depending on the substance. Then a few different types of atoms would suffice to explain the great variety of different substances, namely through the variety of possible combinations and spatial arrangements of the atoms in the molecules. After Antoine de Lavoisier had demonstrated the conservation of mass in chemical conversions - especially in reactions with the creation or consumption of gases - towards the end of the 18th century , John Dalton finally made the assumption of immutable and immortal atoms the basis of a new chemistry from 1803 . This was able to explain the multitude of substances and their behavior in detail with extraordinary success and therefore ousted alchemy from science in the course of the 19th century.

### Classic and everyday concept of matter

The concept of matter in classical physics largely corresponds to the colloquial sense of matter or material , insofar as it is used to denote the difference between physical and non-physical things. A piece of matter has two general and fundamental properties: at any given moment it has a certain mass and a certain shape with which it fills a certain volume . In order to indicate quantities of matter, the quantities mass (colloquially usually expressed as " weight ") and volume are used.

In classical physics, matter forms the opposite of empty space or absolute vacuum and the possibly existing massless force fields . There are numerous special physical and chemical parameters and material properties for a more detailed characterization of macroscopic matter . Such matter can appear to our senses as a perfectly homogeneous continuum , and it is treated that way in parts of physics today. However, matter is always made up of discrete particles of matter that form the microscopic structure of matter. These particles are many orders of magnitude too small for direct perception with our senses or with the light microscope and therefore remained hypothetical for a long time. Specifying the number of particles is the most precise way of determining a quantity of matter. In the case of a macroscopic amount, a specially defined physical quantity is selected , the amount of substance . The indication of the number of particles must always be linked to the information about the type (or types) of particles.

In classical physics and chemistry, the particles that make up matter are the atoms or the molecules composed of certain types of atoms in a fixed way. The atoms were assumed to be indivisible bodies of certain mass and volume. They should - in accordance with the conservation of mass observed at that time in all chemical and physical transformations - also be absolutely stable and in particular neither be able to be created nor destroyed. Together with the scientific proof that atoms really exist, it was discovered at the beginning of the 20th century that these assumptions about their nature are not entirely correct.

### Limits of the classical concept of matter

In modern physics , the atoms were also recognized as composite physical systems . They are made up of even smaller particles of matter, electrons (which belong to the leptons mentioned above ) and quarks . These have mass, but no detectable intrinsic volume. In addition to these building blocks of atoms, there are numerous other types of elementary particles , some with and some without their own mass. Without exception, all elementary particles can be created and destroyed under certain conditions, and that applies accordingly to atoms as well. Thus, the building blocks from which matter is built do not themselves show all of the fundamental properties that were associated with matter in classical physics.

Furthermore, in modern physics the opposition between mass-afflicted matter and massless field has been resolved, namely from both sides: On the one hand, it follows from the equivalence of mass and energy that these fields, when enclosed in an object, form one Contribute to the mass of the object. On the other hand, in quantum field theory, every elementary particle is nothing other than a discrete excitation of a certain field that exists in a vacuum.

This is why there are different views on some quantum physical objects as to whether they should be counted as matter or not. Defining the limit z. B. by the criterion of a non-vanishing mass, then particles such as the W and Z bosons also count as matter. However, they do not take up any specific space and are also clearly in contradiction to the idea that matter is something permanent. In connection with the weak interaction , these particles are viewed as their exchange particles , which therefore allow this interaction to come about at all through their continuous virtual generation and destruction in any number. On the other hand, if one takes the stability of matter as the starting point, then one selects the types of particles to be counted as matter according to the fact that a conservation law applies to the number of particles . Then only quarks and leptons can be regarded as the elementary particles of matter, like their antiparticles, but both only to the extent that their mutual annihilation or pairwise creation is ignored. Furthermore, with all bodies that are counted as matter in everyday life and colloquially, the majority of their mass would have nothing to do with matter. Because over 99% of the mass of these material bodies is contributed by protons and neutrons , which in turn do not get their mass from the masses of the quarks they contain, but almost 99% only from the binding energy between the quarks, which comes from the massless exchange particles of the strong interaction , the gluons .

### The question of the uniformity of matter

The idea of ​​a primordial material , as it had been gleaned from the texts of the pre-Socratics , was further developed under the impression of the Christian belief in creation to the effect that this primordial material should correspond to a uniform substance. In the Middle Ages, however, the question of whether the heavenly bodies also consist of the same kind of substance as the earthly bodies remained controversial. This question was only solved from 1860 with the help of spectral analysis , with which the chemical elements contained in a self-luminous body can be identified. It turned out - after clarifying some doubtful cases such as In the case of helium , for example , the elements that make up the sun and the other stars all occur on earth.

The question of a uniform primordial substance of all matter was hardly touched, because it has been one of the foundations of chemistry since Dalton that the elements cannot be converted into one another and that their atoms are not made up of smaller building blocks. At that time around 30 chemical elements were known and more were being discovered all the time. It has been felt as a lack of theory that one should accept such a large number of different basic types of matter. That is why William Prout made the first attempt at standardization as early as 1815 . He interpreted Dalton's results for the ratios of the atomic masses in such a way that all atoms are composed of hydrogen atoms and consequently one has found the sought-after primary substance in hydrogen. Based on this assumption, attempts were made for decades to interpret the relative atomic masses of the elements in terms of integer ratios to hydrogen, although the increasingly more precise measurements contradicted this more and more. A century after Prout, discoveries by Frederick Soddy and Joseph John Thomson showed that the elements do not necessarily consist of a single type of atom, but of different isotopes , and that the atomic masses of the individual isotopes are actually (almost) whole-number multiples of the hydrogen mass. After Ernest Rutherford discovered around 1920 that larger atomic nuclei contain the nuclei of the hydrogen atom as building blocks, it was considered proven for the next 10 years that all matter is made up of only two building blocks, the protons (hydrogen nuclei) and electrons . (The neutrons that are also required were interpreted as proton-electron pairs with a particularly close bond.)

Then, in 1930 , Paul Dirac took the final step. He noticed that in the context of his theory of particles like electrons there must also be antiparticles, and suggested that the proton be understood as the antiparticle of the electron. The old goal of finding a uniform concept of matter has thus been achieved. However, this picture held up neither the theoretical elaboration nor the more recent experimental findings. On the one hand, the proton and the electron - e.g. B. a whole hydrogen atom - have to annihilate with each other in a very short time, in stark contrast to the stability of matter. On the other hand, numerous other types of particles have been discovered that could also function as matter particles if they were not so short-lived that they practically do not occur in normal matter. All of these types of particles, the number of which have already risen to several hundred and which were ironically referred to as the particle zoo , were brought into a scheme in the Standard Model from around 1970 , in which, as far as we know today, all the properties of matter - both its structure and all physical processes taking place - can be interpreted (with the exception of gravitation ). Accordingly, as far as one means in the original sense the substance of all bodies tangible with the senses, matter consists of three types of particles: electron, up-quark , down-quark . Together with the other leptons and quarks of the Standard Model, which are also called “matter particles” in the narrower sense because of spin , there are already 48 species (including the antiparticles). Finally, if you add the “force particles” for the creation of all kinds of processes and the Higgs boson for the creation of the particle masses, there are 61. ${\ displaystyle {\ tfrac {1} {2}}}$

The search for a uniform basic substance is currently being continued. Approaches to this are provided by the string theory or models, according to which the elementary particles are actually made up of fundamental particles, the " prons ". However, these approaches cannot yet be verified experimentally and are therefore completely hypothetical.

## Macroscopic matter

A “type” of matter that is characterized by its composition and properties is called substance . Chemical elements consist only of atoms with the same atomic number . These are atoms whose nuclei contain the same number of protons . Chemical compounds contain atoms of different elements that combine in certain numerical proportions, be it as uniformly structured molecules or as regularly structured crystals . The properties of a compound are completely different from the properties of the elements from which it is made up. For example, the chemical element oxygen is a colorless gas and silicon is a semi-metal, while the combination of the two, SiO 2, is a transparent, crystalline mineral , namely quartz . Substances that consist of only one element or one compound are called pure substances . If a substance consists of several elements or compounds, it is a mixture of substances . A distinction is made between homogeneous substance mixtures (e.g. solutions ) and heterogeneous substance mixtures (e.g. emulsions , dispersions or aerosols ). Granite, for example, is a conglomerate - i.e. a heterogeneous mixture - of the pure substances quartz, mica and feldspar .

The macroscopic properties of a substance are described by numerous special material properties , e.g. B. density , elasticity , color , breaking strength , thermal conductivity , magnetic properties , electrical conductivity and many others. These values ​​also depend on parameters such as temperature , pressure, etc. These are all intensive quantities , i.e. properties that do not depend on the size of the system under consideration.

A coherent structure of matter is called a body . In addition to the aforementioned intensive properties of the materials from which it is made, its behavior is also largely determined by extensive parameters , for example its mass, spatial extent or external shape.

Matter that is present as a pure substance in macroscopic quantities has one of the three physical states of solid , liquid and gaseous , or is a plasma , i.e. H. a mixture of ionized atoms and free electrons. Solid and liquid substances are collectively referred to as condensed matter . In contrast to gases, condensed matter is only very slightly compressible. Liquids and gases are collectively referred to as fluids . In contrast to solid matter, fluids do not have a permanent spatial shape. B. the container walls.

In the particle model, the difference in aggregate states has a simple explanation. One only needs to consider different types of spatial arrangement and bonding between the particles: In the gas, the molecules (in the case of noble gases : the atoms) fly around individually and in a disordered manner. The attractive or repulsive forces between them only play a role in their accidental collisions and are otherwise weak and largely negligible due to the average distance between the particles. A gas becomes a plasma when the kinetic energy of the particles is increased so much that individual electrons are torn off when they collide. In the solid state, on the other hand, the atoms or molecules have much lower energy, are much closer together and maintain a largely fixed arrangement. The distances to their nearest neighbors are determined by the balance of forces of strong attraction and repulsion and can only be changed little by external pressure or tension. In a liquid the particles are at similar distances as in a solid, which is why the liquid is only slightly compressible. However, the particles have a higher kinetic energy, on average not enough to fly away individually and form a gas, but enough to easily switch to another neighboring particle. Therefore, the amount of liquid as a whole does not have a solid form.

## Further names for forms of matter

Between macroscopic and microscopic matter, the research area of clusters and nanoparticles , known as mesoscopic matter, has emerged in recent decades . They are grains of matter that consist of up to tens of thousands of atoms or molecules and are therefore already described using the terms typical for macroscopic bodies. They are less than about 100 nm in size and therefore remain individually invisible to the eye. Both individually and in larger quantities, these particles sometimes show completely different behavior than the same substance in homogeneous macroscopic quantities due to their small size.

In nuclear physics and elementary particle physics, a distinction is made between matter on the basis of the types of particles that occur, e.g. B. nuclear matter , strange matter , quark-gluon-plasma , antimatter . Antimatter is a form of matter that is made up of the antiparticles of those elementary particles that make up “normal” matter. According to the laws of elementary particle physics, antimatter and normal matter each show exactly the same behavior. However, they annihilate each other as soon as they meet, producing annihilation radiation.

In astronomy and cosmology , dark matter is considered. The dark matter is documented by its gravitational effect, but has so far remained invisible in all other attempts at observation. Apart from their mass, nothing is known about their nature. To distinguish it from dark matter, "normal" matter is collectively referred to as baryonic matter .

Particle radiation consists of fast moving particles of matter. This form of matter does not belong to any particular physical state and is far out of thermal equilibrium. Particle radiation can be electrically charged (e.g. cathode radiation , ion radiation , alpha radiation , beta radiation ) or electrically neutral (e.g. neutron radiation , molecular radiation ).

Under conditions that are far removed from the everyday, matter can behave so unfamiliarly that it is given its own name. A state of macroscopic matter is called warm, dense matter , which corresponds as much to an extremely condensed plasma as it does to an extremely hot solid. Of degenerate matter is when special quantum mechanical effects are the properties of a material amount of strongly from the "normal" behavior according to classical physics differ. Examples can be found at very low temperatures in the Bose-Einstein condensate and in superfluidity , and under normal conditions also in the Fermi gas of the metallic conduction electrons .

## Occurrence

Stars and the Milky Way in the night sky. There are about 10 22 to 10 23 stars in the universe .

The total mass of baryonic matter in the observable universe , which is distributed in a spherical volume with a radius of approx. 46 billion light years , is estimated at 1.5 · 10 53 kg (including dark matter it would be almost exactly 10 54 kg).

According to the Lambda CDM model , the current standard model of cosmology , about 17% of the total mass is in the form of baryonic matter, i.e. matter in which protons and neutrons make up the largest part of the mass.

Some of the baryonic matter is found in the total of around 10 22 to 10 23 stars , which in the form of galaxies , galaxy clusters and super clusters form the structure of the cosmos . After the gravitational collapse of the pre-existing star, a small part of the matter is in one of the numerous black holes and is only noticeable through gravity.

The rest of the baryonic matter is called interstellar matter or intergalactic matter , depending on whether it is within a galaxy or between the galaxies. It is gas, dust and larger lumps, such as B. Planets . The gas, mostly hydrogen, is atomic or ionized.

The majority of the mass of the universe, 83%, is made up of non-baryonic dark matter , which does not glow and has so far only been inferred from its gravitational effects. Their large-scale distribution seems to be very similar to the distribution of luminous matter. According to the cosmological standard model, this is understood to mean that dark matter was able to accumulate first and form halos , in whose gravitational field the baryonic matter could then concentrate and stars. So far, there is no reliable knowledge about the nature of dark matter. In the interpretations suggested for this, the still speculative supersymmetric partners of the known particles play a role.

## Formation of matter

In the cosmological standard model, the big bang is imagined as the hot, high-energy beginning of space-time and, through the energy content, also as the beginning of matter. Since the previous physical theories depend on the existence of spacetime, the state of the universe can only be described from the end of the Planck era after the Big Bang. The temperature is estimated at around 10 30  K and the universe has been expanding and cooling since then. Gradually, in successive symmetry breaks, the elementary particles freeze out, react and recombine until, after baryogenesis and the extensive mutual annihilation of particles with antiparticles, the predominance of matter over antimatter prevails today . The nuclei of the heavy hydrogen isotopes deuterium and tritium as well as the isotopes of helium and lithium are then formed . After further cooling, the resulting nuclei can combine with electrons to form neutral atoms. The matter is then in gas or dust form until the first stars are formed by gravity. With sufficient values ​​of pressure and density inside, the nuclear fusion ignites and leads to the formation of the elements up to iron . Heavier elements are generated by neutron capture and subsequent beta decays, partly in AGB stars , partly in supernovae .

## literature

• Stephen G. Brush : Statistical Physics and the Atomic Theory of Matter : From Boyle and Newton to Landau and Onsager. Princeton University Press, Princeton, NJ, 1983.
• Max Jammer : The concept of mass in physics. 3rd edition, Wissenschaftliche Buchgesellschaft, Darmstadt 1981, ISBN 3-534-01501-0 .
• Erwin Schrödinger : What is matter? In: Scientific American. 189, 1953, pp. 52-57 ( PDF ).
• Klaus Stierstadt : Physics of Matter . VCH Verlagsgesellschaft, Weinheim 1989. ( online )
• Hermann Weyl : What is matter? - two essays on natural philosophy. Springer, Berlin 1924
• Hermann Weyl: Space, Time, Matter - Lectures on General Theory of Relativity. 8th edition, Springer 1993 (first 1918, 5th edition 1922) online
• Roberto Toretti : The Philosophy of Physics , esp. Chap. 1.3 Modern Matter , Cambridge University Press 1999

Wikiquote: Matter  - Quotes
Wiktionary: matter  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. P. Hucklenbroich: The physical concept of matter . In: Article 'Materie' in the Historical Dictionary of Philosophy . tape 5 , 1980, pp. 922 .
2. Max Jammer The Concept of Mass in Physics Scientific Book Society, Darmstadt 1964 (Concepts of Mass in Classical and Modern Physics, Harvard 1961).
3. ^ Isaac Newton: Philosophiae Naturalis Principia Mathematica , preface to the 3rd edition, explanations. German translation
4. ^ Marie Boas Hall: Robert Boyle and Seventeenth-Century Chemistry , Cambridge University Press, 1958.
5. Roberto Toretti: The Philosophy of Physics . Cambridge University Press, Cambridge 1999, ISBN 0-521-56259-7 , pp. 13 ff .
6. Silvia Donati: Aegidius von Roms criticism of Thomas Aquinas doctrine of the hylemorphic composition of the heavenly bodies . In: Albert Zimmermann (ed.): Thomas Von Aquin - work and effect in the light of recent research . Walter de Gruyter, Berlin 1988, p. 377 .
7. ^ PAM Dirac: The Proton . In: Nature . tape 126 , 1930, pp. 605 , doi : 10.1038 / 126605a0 .
8. For a discussion of the method of counting see Jörn Bleck-Neuhaus: Elementary Particles. From the atoms to the Standard Model to the Higgs boson (Section 15.12) . 2nd Edition. Springer, Heidelberg 2013, ISBN 978-3-642-32578-6 , doi : 10.1007 / 978-3-642-32579-3 .
9. Planck Mission 2013
10. Weinberg calls in Cosmology 16.828% from measurements of the anisotropy of the background radiation Steven Weinberg: Cosmology . Oxford University Press, Oxford 2008, ISBN 978-0-19-852682-7 , pp. 356 .