Dictionary

electron volt

Standard unit of energy in particle physics. One electronvolt is the energy gained by an electron that is being accelerated by an electric potential difference (“electric voltage”) of 1 volt. One electronvolt, in short: 1 eV is equivalent to 1.602176·10^-19 Joule (the Joule being the energy unit of the SI system of units).

Multiples of eV that are commonly used are

kilo-electronvolt: 1 keV = 1000 eV
Mega-electronvolt: 1 MeV = 1,000,000 eV =10⁶ eV
Giga-electronvolt: 1 GeV = 1,000,000,000 eV =10⁹ eV
Tera-electronvolt: 1 TeV = 1,000,000,000,000 eV =10¹² eV.

Making use of the equivalence between mass and energy, eV/c² is commonly used as a unit for particle masses, with c the speed of light. As it is usual in particle physics to use a system of units in which light speed is equal to one, c=1, mass values are often simply given in eV, without explicitly mentioning the factor c².

The energy that is necessary to remove an electron from an atom is typically in the range of between a few and a few dozen eV. Typical energies of x-ray photons are in the keV range. The mass of an electron is 511 keV, that of a proton 938 MeV. Each proton in the proton beams of the Large Hadron Collider, the particle accelerator at the CERN laboratory, is accelerated to an energy of about 7 TeV.

As the temperature is a measure of the average energy with which each component participates in a system’s disordered thermal motion, it can be measured in eV as well, where 1 eV corresponds to 11,604 Kelvin.

Definitioner

TeV

Siehe Elektronenvolt.

MeV

Siehe Elektronenvolt.

Large Hadron Collider (LHC)

Der Large Hadron Collider, zu deutsch etwa die große Maschine, um Kernteilchen zusammenstoßen zu lassen, ist ein Teilchenbeschleuniger am Teilchenforschungszentrum CERN. Aus Sicht der Relativitätstheorie ist er nicht nur interessant, weil die in ihm beschleunigten Protonen so hohe Energien erreichen wie nie zuvor und so neue Tests der relativistischen Quantenfeldtheorien ermöglichen, auf denen die moderne Elementarteilchenphysik beruht, sondern auch, weil sich bei so hohen Energien erste Spuren einer bislang noch nicht experimentell nachgewiesenen Symmetrie der Natur zeigen sollten, der so genannten Supersymmetrie, die eine wichtige Rolle im Zusammenhang mit der Stringtheorie spielt, einem der Ansätze, Allgemeine Relativitätstheorie und Quantentheorie zu einer Theorie der Quantengravitation zu verbinden. Außerdem gibt Physik bei so hohen Energien Aufschluss über die Eigenschaften der Materie des frühen, heißen Universums, die für die Urknallmodelle wichtig sind.

Webseiten des CERN

Large Hadron Collider

Siehe LHC

keV

Siehe Elektronenvolt.

GeV

Siehe Elektronenvolt.

CERN

Europäisches Forschungszentrum für Kern- und Teilchenphysik (Centre Européen pour la Récherche Nucleaire), angesiedelt nahe Genf beidseits der französisch-schweizerischen Grenze, gegründet 1954.

CERN ist nicht nur für seine Teilchenbeschleuniger wie den Large Hadron Collider (LHC) bekannt, sondern auch als Geburtsort des World Wide Web.

Webseiten des CERN

TeV

See electron volt

Tera-electronvolt (TeV)

See electron volt

speed

An object's average speed is the distance it moves during a given period of time, divided by the length of the time interval. If you make the time interval infinitely small, the result is the object's speed at one particular moment in time. The notion of speed can be applied to waves in different ways; for instance, for a simple wave, the phase speed is the speed at which any given wave crest or wave propagates through space. See also the more general entry velocity.

proton

Particle that carries positive electric charge and is comparatively massive; the atomic nuclei consist of protons and neutrons. Protons are not elementary particles, they are compound particles consisting of quarks that are bound together through the strong nuclear interaction . Collectively, protons, neutrons and a number of similar particles are called baryons.

particle physics

The branch of physics that deals with particles that are, to the best of today's knowledge, not made up of more fundamental sub-units, for instance with electrons, quarks or neutrinos. Also included is the study of some species of particles that do have more elementary constitutents, such as protons or neutrons, but not of larger systems such as atomic nuclei (that would be nuclear physics) or, even worse, whole atoms. Questions such as, whether the particles nowadays thought to be elementary really are elementary, or are, for instance, different manifestations of one and the same species of string, fall within the scope of particle physics. The theoretical tools of particle physics are the so-called quantum field theories which allow the description of elementary particles on the basis of both quantum theory and special relativity, while the main experimental tools are particle accelerators in which particles are accelerated and then brought to collision.

particle accelerator

The most important experimental technique of particle physics: accelerating electrically charged particles with the help of electric forces, make them collide with each other and, from the result of the collision, draw conclusions about the properties of elementary particles and their interactions. It is an intriguing possibility, suggested by models based on the ideas of string theory, that particle accelerators such as the LHC might actually produce miniature black holes (for more about this, see the spotlight text Particle accelerators as black hole factories?).

MeV

See electron volt

Mega-electronvolt (MeV)

See electron volt

mass

In classical physics, mass plays a triple role. First of all, it is a measure for how easy it is to influence the motion of a body. Imagine that you're drifting in emtpy space. Drifting by are an elephant and a mouse, and you give each of them a push of equal strength. The fact that the mouse abruptly changes its path, while the elephant's course is as good as unaltered, is a sure sign that the mass (or, in the language of physics, the inertia or inertial mass) of the elephant is much greater than that of the mouse. Secondly, mass is a measure of how many atoms there are in a body, and of what type they are. All atoms of one and the same type have the same mass, and adding up all those tiny component masses, the total mass of the body results. Thirdly, in Newton's theory of gravity, mass determines how strongly a body attracts other bodies via the gravitational force, and how strongly these bodies attract it (in this sense, mass is the charge associated with the gravitational force). In special relativity, one can also define a mass that is a measure for a bodies resistance to changing its motion. However, the value of this relativistic mass depends on the relative motion of the body and the observer. The relativistic mass is the "m" in Einstein's famous E=mc² (cf. equivalence of mass and energy). The relativistic mass has a minimum for an observer that is at rest relative to the body in question. This value is the so-called rest mass of the body, and when particle physicists talk of mass, this is usually what they mean. Just as in classical physics, the rest mass is a kind of measure for how much matter the body is made up of - with one caveat: For composite bodies, the energies associated with the forces holding the body together contribute to the total mass, as well (another consequence of the equivalence of mass and energy). In general relativity, mass still plays a role as a source of gravity; however, it has been joined by physical quantities such as energy, momentum and pressure.

light

Light in the strict sense of the word is electromagnetic radiation the human eye can detect, with wave-lengths between 400 and 700 nano metres. In relativity theory and in astronomy, the word is often used in a more general sense, encompassing all kinds of electromagnetic radiation. For instance, astronomers might talk about "infrared light" or "gamma light"; in this context, light in the stricter sense is referred to as "visible light". Within classical physics, the properties of light are governed by Maxwell's equations; in quantum physics, it turns out that light is a stream of energy packets called light quanta or photons. In the context of relativistic physics, light is of great interest, and for a number of reasons. First of all, the speed of light plays a central role in both special and general relativity. Also, there are a number of interesting effects in general relativity which are associated with the propagation of light, namely deflection, the Shapiro effect and the gravitational redshift.

light speed

See speed of light.

Large Hadron Collider

The Large Hadron Collider is a particle accelerator in the research centre CERN. From the point of view of relativity theory, it has several points of interest: First of all, it accelerates protons to higher energies than ever, allowing new tests of the relativistic quantum field theories that are at the core of modern particle physics. Secondly, at such high energies, there should be first traces of an as-yet unproven symmetry of nature called supersymmetry, which plays an important role in string theory, one of the candidates for a theory of quantum gravity (the quantum theory version of Einstein's general relativity). Finally, the high energies are interesting because they give information about the very early high temperature universe, and about the physics that should be included in the big bang models of relativistic cosmology. CERN website

keV

See electron volt

kilo-electronvolt (keV)

See electron volt

GeV

See electron volt

Giga-electronvolt (GeV)

See electron volt

energy

Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, thermal energy and the energy carried by electromagnetic radiation. Processes that transform one form of energy into another take place in all machines we use in everyday life, from the engine of a subway train (electrical energy into kinetic energy of the train) to an electric blanket (electrical energy into thermal energy). One important consequence of special relativity is that energy and mass are completely equivalent - two different ways to define what is, on closer inspection, one and the same physical quantity. See the keyword equivalence between mass and energy.

CERN

European research centre for nuclear and particle physics (Centre Européen pour la Récherche Nucleaire - pardon my French), located near Geneva on both sides of the franco-swiss border, founded 1954. CERN isn't famous just because of particle accelerators like its proton synchrotron, the Large Electron Positron Collider (LEP) and the Large Hadron Collider (LHC), but also as the birthplace of the World Wide Web. > CERN website

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electron volt

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