The current physical model
Current model
Today’s standard model of physics comprises of two main parts: General relativity[1][2][3][4] and the standard model of particle physics[5][6][7][8][9]:
General relativity describes gravitation as the curvature of spacetime. It is the decisive theory for astronomy since macroscopic motion is dominated by gravitation.
It is exactly the other way round for the standard model of particle physics: it describes the smallest constituents of matter and their interactions. Alas, the standard model of particle physics is not compatible with general relativity so far. This is an unsatisfactory situation, yet it does not influence the description of many physical effects, since in most cases gravitation is negligible for the considered particles and is clearly superimposed by the other interactions.
Let us consider the standard model of particle physics more precisely:
The particles in the standard model of particle physics
The standard model of particle physics describes all effects through point-like particles, even interactions: If two matter particles exert forces onto each other («interact») then the model describes this as the transfer of an exchange particle.
This contains already the first classification of particles in matter and exchange particles:
The graphic of the elementary particles has been adapted from [11]
A few aspects of the standard model of particle physics
Stable particles
For nature, the stable particles are especially important:
The up (u) and down (d) quark, which in different combinations build up the proton (uud) and neutron (udd) found in the nucleus of atoms.
The electron, which forms the atomic shell around nuclei.
And the photon, which we perceive as light or electromagnetic radiation (radio, cellphones, microwaves etc.).
Three generations
It is interesting that all matter particles are found in groups of three generations. This means that for each particle there are two others, which in certain cases are up to a thousand times heavier than the original particle and decay after a short time, but which otherwise have the same properties: same charge, same spin, same interaction properties, etc.
The heavy (high-energy) particles from the higher generations decay in the lighter particles of the lower generations, yet only under the effect of the weak force. A decay through pure energy emission by photons is not possible.
Why the particles from the different generations are so similar and why there are precisely three generations of particles are two big questions of today’s physics.
The interactions
Gravitation is not considered in the standard model of particle physics, yet masses are present. They are introduced as the rest energy of each particle. A big question is whether neutrinos have mass or not.
The electromagnetic interaction is, together with gravitation, the second force with an unlimited range. Yet in the macro cosmos it plays a lesser role since there are positive and negative charges, which cancel each other out on macroscopic scales.
The electromagnetic interaction is entirely described by the standard model of particle physics. It is transmitted by the photon. All charged particles are subject to the electromagnetic interaction (all elementary particles except for neutrinos). Especially interesting is the question as to why the elementary charge plays such an important role and shows up in all - yet otherwise particularly distinct - particles.
The weak force is the only interaction which can transform particles from one generation to another and therefore determines decays of the heavy particles from the second and third generations. It is transmitted through the W+, W- and Z bosons. They possess a particularly big mass, which is why the force has only a short range (hence «weak» force).
The strong force acts only on quarks and not on leptons. It «glues» many particles together, which can move almost freely within a certain radius. The exchange particles are correspondingly called «gluons». This gluing effect is very strong and becomes even stronger with increasing distance, hence the name «strong» force. Composite particles underlying the strong interaction are also called hadrons.
Neutrinos and their oscillations
Neutrinos are uncharged particles. They are also leptons, so they interact only very weakly since the electromagnetic and strong forces are omitted. In the proper standard model of particle physics, they do not even have a mass, so they are only subject to the weak interaction.
Yet it has been observed that neutrinos which are emitted from the sun, transform into one another. This means that, on the way, the original electron neutrino of the first generation turns into a mu or tau neutrino and back. It oscillates between the generations.
In the standard model, this effect is only possible for particles which possess mass. The oscillations, their corresponding models and the size and type of the neutrino masses were and are yet today subject to intensive research.
Literature
- ↑ Allgemeine Relativitätstheorie, E. Schachinger, Universität Graz, 8. Oktober 2004 [1]
- ↑ Allgemeine Relativitätstheorie, Jörg Frauendiener, Universität Tübingen - Institut für Theoretische Astrophysik, 21. Juli 2005 [2]
- ↑ Elektrodynamik & Relativitätstheorie, Peter Eckelt, Universität Münster - Institut für theoretische Physik, SS 2003 [3]
- ↑ The Meaning of Einstein's Equation, John C. Baez & Emory F. Bunn, American Journal of Physics - AMER J PHYS. 73, 2005, DOI 10.1119/1.1852541 [4]
- ↑ Das Standardmodell in der Elementarteilchenphysik, Thomas A. Terényi, Akademisches Gymnasium Wien I [5]
- ↑ Das Standardmodell der Elementarteilchenphysik, Robert Harlander, CERN, TH Division, Mai 2000 [6]
- ↑ Das Standardmodell der Teilchenphysik, André S. Indenhuck, RWTH Aachen University, Februar 2004 [7]
- ↑ The Standard Model Lagrangian, Diego Bettoni, Istituto Nazionale di Fisica Nucleare, Academic Year 2011-12 [8]
- ↑ The Standard Model, Thomas Teubner, University of Liverpool, September 2008 [9]
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