List of unsolved problems in physics

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Some of the most significant unsolved problems in physics are theoretical; H. that the existing theories are unable to explain a certain observed phenomenon or the result of an experiment . The others are experimental in nature; H. that it is difficult to set up an experiment to test a particular theory or to study a particular phenomenon with greater accuracy.

Cosmology and General Relativity

The cosmology deals with the origin, development and the fundamental structure of the universe (cosmos) as a whole and is a branch of astronomy , which is closely related to astrophysics stands.

The general theory of relativity (ART) describes the interaction between matter (including fields ) on the one hand and space and time on the other. She interprets gravity as a geometric property of the curved four-dimensional space - time . The mathematical description of spacetime and its curvature is carried out with the methods of differential geometry .

The Standard Model of Cosmology (SdK) is based on the following assumptions, among others:

The standard model is supported by the following observation results:

However, the standard model has the following problems or open questions:

Cosmological inflation

As cosmological inflation , a period of extremely rapid is the expansion of the universe called. Depending on the underlying assumptions, it began between 10 −43 s, i.e. H. the Planck time (or the beginning of the Big Bang itself), and 10 −35 s and lasted up to a time between 10 −33 s and 10 −30 s after the Big Bang.

  • What is the hypothetically postulated inflaton field that causes this inflation? If the inflation has happened at a certain point in space, is it self-sustaining through the inflation of quantum mechanical fluctuations ( vacuum fluctuations ), and does it therefore possibly continue in distant regions of the universe?

Assuming an inflationary exponential expansion, the following two open questions from the Standard Model of Cosmology can be answered:

  • the horizon problem : During the very short phase of inflation, space-time expands faster than light signals, so that the space accessible to the observer today is causally connected.
  • the flat universe: The inflation "flattens" the curvature of the universe further and further, until finally a Euclidean space is created.

However, the following points speak against the inflation model:

  • Bad inflation or no inflation at all: Bad inflation is more likely than good inflation, where bad inflation means a period of accelerated expansion that leads to a result that contradicts today's observations. And a universe without inflation is more likely than one with inflation (according to Roger Penrose by a factor of 10,100 ).
  • Eternal inflation : once inflation starts, it never stops due to quantum fluctuations. The result is a sea of ​​inflationary expanding space, in which small islands of hot matter and radiation are embedded - each of these islands is an independent universe. According to Alexander Vilenkin , universes form as bubbles, in which physical states with a real vacuum as we know it prevail. These bubbles - our observable universe is such a bubble - remain surrounded by a false vacuum that continues to expand and create new bubbles in the process.

Horizon problem

The horizon problem is the fact that different, distant regions of the universe that are not in contact with each other are so homogeneous (they have the same physical properties despite the great distance), although the Big Bang theory predicts larger, measurable anisotropies of the night sky seems than those that have been observed so far.

  • Are other possible explanations, such as a variable speed of light (Engl. Variable speed of light (VSL): c as a function of time and space, see Variable speed of light ) as a solution may be better suited?

Future of the universe

Which of the possible scenarios best describes the future of the geometry of the space-time of the universe:

  • Eternal expansion , d. H. the universe continues to expand indefinitely without the expansion accelerating or decreasing relevantly.
  • Big Freeze (also called Big Chill or Big Whimper ), d. H. a comparatively sudden transition from expansion to a steady state.
  • Big Rip , d. H. an ever increasing and finally extremely increasing emergence of new space, so that all objects move away from each other faster and faster and can no longer interact.
  • Big Crunch , d. H. the expansion of the universe ends sometime in the future and then turns into an accelerating contraction.
  • Big Bounce : d. That is, when it is contracted to a very small diameter, it expands again.

Baryon asymmetry

The baryon asymmetry is the observed great dominance of matter over antimatter in the universe.

  • Why is there so much more matter than antimatter in the observable universe? There are the following approaches to answer:

1. Proof of the existence of antimatter regions in the universe:

One imagines that the universe consists of spatially separated areas, in which baryonic or antibaryonic matter predominates: The cosmic radiation arriving on earth is examined for antimatter particles, e.g. B. after antihelium or even heavier antibodies. By proving z. B. a single anti-carbon nucleus would prove the existence of stars made of antimatter in the universe, since carbon could not be formed during the Big Bang. However, all previous detection attempts were negative (e.g. through the Pamela experiment or the two AMS experiments). Another argument against the existence of antimatter regions is that extremely high-energy photons, resulting from the mutual annihilation of matter and antimatter, would have to arise in the border areas between matter and antimatter, but this has not yet been observed.

2. The preferred formation of baryons in the early universe:

The Sakharov criteria are necessary conditions for a dynamic generation of the baryon asymmetry in the universe. The CP violation (2nd Sakharov criterion) has so far been proven in four particles, but it alone cannot explain the matter-antimatter asymmetry observed in the universe, as it is too small by a factor of 10 10 . (see also physics beyond the standard model: point 3 )

Theories to explain the baryon asymmetry are e.g. B.

Cosmological constant

The cosmological constant is a physical constant that was originally introduced by Albert Einstein in general relativity . Today, the cosmological constant is no longer interpreted as a parameter of the general theory of relativity, but as the constant energy density of the vacuum.

Dark matter

The existence of dark matter - invisible matter that does not interact with light - is postulated in cosmology to explain some gravitational effects on visible matter. Their existence is to a large extent certain, because at present this is the only way to explain the speed of stars around the center of their galaxy and the movement of galaxy clusters .

Dark energy

The existence of dark energy is postulated as a hypothetical form of energy to explain the observed accelerated expansion of the universe .

  • Why is the energy density of dark energy of the same order of magnitude as the current density of matter, since the two develop quite differently in time; couldn't it just be that we make the observation at exactly the right time ( anthropic principle )?

What exactly is dark energy? Possible explanations for this are:

Copernican principle

The Copernican principle means that humans do not occupy an excellent, special position in the cosmos, but only a typically average one.

  • Some large structures in the microwave sky, over 13 billion light years away, appear to coincide with both the motion and orientation of the solar system. Is it due to systematic errors in the collection and processing of the data, is it local phenomena or is it a violation of the Copernican principle? (see background radiation: open questions )

The shape of the universe

The local geometry of the universe is determined by the density parameter Ω. From top to bottom: spherical universe (Ω> 1, k> 0); Hyperbolic Universe (Ω <1, k <0); Flat universe (Ω = 1, k = 0).

Concerning. In the shape of the universe, a distinction must be made between local and global geometry:

  • Local geometry: the curvature of the (observable) universe
  • Global geometry: the topology of the universe as a whole (observable and beyond: see also multiverse )

The local geometry of the universe is determined by the value of the density parameter Ω or by the space-time curvature parameter (see Friedmann equation ):

  • Ω> 1: spherical universe, since the energy density of the universe is greater than the critical energy density and thus the curvature of space-time is positive
  • Ω <1: hyperbolic universe, since the energy density is smaller than the critical value and thus the curvature of spacetime is negative
  • Ω = 1: flat (i.e. Euclidean ) universe, since the energy density is exactly as large as the critical energy density and thus space-time has vanishing curvature

The local geometry does not completely determine the global geometry, but it restricts its possible manifestations.

  • What is the 3-manifold of co-moving space (ger .: comoving space ) d. H. a moving space sector of the universe (see also distance measure ), colloquially called the shape of the universe ?
  • Neither the curvature nor the topology are currently known, although it is known that the curvature is close to zero , at least at the observable orders of magnitude . The cosmological inflation hypothesis claims that the shape of the universe may not be ascertainable, but since 2003, Jean-Pierre Luminet et al. suggested that the shape of the universe could be a dodecahedral topology.
  • Is the shape of the universe a Poincare space , another 3-manifold, or is the shape of the universe not ascertainable at all?

Incompatibility of quantum mechanics and general relativity

Both the QT and the ART each have their own problems, and they are fundamentally different because the ART is purely classic. Neither one nor the other theory can claim on its own to give a complete and consistent description of reality. If physics as a whole is to be logically free of contradictions, there must be a theory that unites QT and GTR in some form. A theory of quantum gravity that is supposed to replace QT and GTR must resolve their internal contradictions and contain both theories as borderline cases. It has to make the same statements about nature that the standard models of particle physics and modern cosmology have given us. It also has to answer a key problem in QT: where is the dividing line between the classical and the quantum mechanical world?

Problems of ART:

  • the existence of black holes with a singularity at their center; Points of infinite space curvature and infinite density, which all known laws of physics fail to describe.
  • the big bang singularity with infinite density and temperature
  • Stephen Hawking's discovery that black holes can annihilate - a quantum field theoretical finding that contradicts the predictions of GTR.

QT problems:

  • the appearance of infinitely large terms in mathematical expressions, which must be eliminated with the help of sophisticated rules ( renormalization )

In addition, the question of the nature of space and time at the smallest distances - the so-called Planck length (10 −35 meters) and the Planck time (10 −43 seconds) - must be answered:

  • Are space and time continuous as the GART assumes? Or are space and time quantized? Does the room therefore consist of volume elements that cannot be split up further? And does time run out in tiny, discreet steps? The spacetime would thus have a granular structure of hypothetical spacetime atoms (analogous to the atoms of matter).

A central problem of a theory of quantum gravity would be that the spacetime geometry can no longer be assumed as given (as in QT), but that the spacetime geometry itself is subject to quantum fluctuations.

Quantum Gravity Theory

There are different approaches:

  • Canonical quantization tries to quantize space-time geometry directly . This leads to the Wheeler-DeWitt equation , which describes the entire universe by a single wave function of the universe . In this case, not only subatomic particles would have to be described quantum mechanically as probability waves, but the entire cosmos. The problem with this is that the quantum mechanical peculiarities in the classical world are not observed: how does our classical world emerge from a purely quantum mechanical system?
  • Loop quantum gravity: According to loop quantum gravity, space consists of discrete volume pieces of the minimum size of a Planck volume (10 −99 cubic centimeters), and time progresses in leaps of the order of magnitude of a Planck time (10 −43 seconds) (see also quantum foam and Spin foam ). However, the question of how (and whether) this structure merges into a smooth space-time continuum at macroscopic distances remains unresolved - only in this case the GTR can be included in the theory as a borderline case.
  • Would a consistent theory contain a force whose carrier is the hypothetical graviton (see also string theory ) or would it be the result of the quantized structure of space-time itself (as in loop quantum gravity )?
  • Are there any deviations from the predictions of general relativity in the microscopic as well as in the macroscopic range, or under other extreme conditions that arise from a theory of quantum gravity ? According to the loop quantum gravity z. B. does light of different wavelengths propagate at different speeds. The smaller the wavelength, the more the spacetime grid, consisting of spacetime atoms , distorts the wave. Is experimental evidence possible?

Vacuum disaster

A vacuum catastrophe is the fact that the theoretically predicted value of the vacuum energy of the universe is greater than the actually observed value by a factor of 10 120 . (see also the unsolved problem : cosmological constant )

  • What is the cause of this huge discrepancy?
  • Why does the predicted mass of the quantum vacuum have little effect on the expansion of the universe?

Information paradox of black holes

According to the no-hairs theorem , the behavior of a black hole towards the outside is completely determined by its mass , its electrical charge and its angular momentum . In addition, there can be no loss of information in the context of quantum physics . What then happens to the information contained in the objects that have been absorbed by a black hole? This black hole information paradox is closely related to the question of how quantum physics and general relativity can be reconciled.

Cosmic censorship

Roger Penrose hypothesized in 1969 that naked singularities cannot exist in the universe . Is it possible to derive this hypothesis from more general physical principles? Or can naked singularities arise from realistic initial conditions?

Additional dimensions

Are there more than four spacetime dimensions in nature? If so, what is their number and size? The following theories postulate more than 4 spacetime dimensions:

Are dimensions a fundamental property of the universe or are they the result of other physical laws?

Can we experimentally prove higher spatial dimensions?

Locality

In physics, locality describes the property of a theory that processes only have an impact on their direct spatial environment. In the case of non-locality or locality, the main question is whether or under what conditions an event can influence another event.

According to Bell's inequality , a physical theory is local if, in the case of two spatially separated particles, the choice of what is measured for one particle does not directly affect the other particle during the measurement. Quantum mechanics violates Bell's inequality .

  • Can information and properties also be transmitted in a non-local way?
  • Under what conditions are non-local phenomena observed?
  • What does the existence or non-existence of non-local phenomena say about the fundamental structure of spacetime ?

Presumption to protect the time order

The presumption for protecting the order of time or the time sequence (engl. Chronology protection conjecture or CPC) was obtained from Stephen Hawking formulated as in some solutions to the equations of the general theory of relativity closed time-like curves (engl. Closed time like curves or CTC) appear and these include the possibility of time travel backwards on the time axis .

High energy physics / particle physics

The Standard Model of Particle Physics (SM) is a physical theory that describes the currently known elementary particles and the interactions between them. The three interactions described by the SM are the strong interaction , the weak interaction, and the electromagnetic interaction .

The SM has the following inherent problems:

  • The SM requires that all particles be massless, but particles obviously have mass. So what is the origin of mass?

Is the introduction of the Higgs mechanism and the Higgs boson the solution? The Higgs boson was postulated almost 50 years ago for purely theoretical reasons. The Higgs mechanism is the simplest known possibility to take into account the masses of the fundamental particles in the SM in a mathematically consistent manner. According to this, all particles with mass interact with a field that fills the entire space. It is therefore said that the Higgs mechanism creates the masses of the particles . However, the spin of the Higgs boson is zero, which in turn poses problems, because none of the particles without spin observed so far are not elementary particles and theoretical arguments suggest that particles without spin should be much heavier than the Higgs boson that has just been discovered.

  • The SM contains 18 or 25 (if neutrinos have mass) or 27 free parameters, which are not determined by theory and must first be determined by measurements.

The 18 free parameters are:

In addition there are 7 further parameters (3 masses and 4 mixing angles) if neutrinos have mass.

  • Why are there three generations of elementary particles?

The 12 particles of matter can be classified into three almost identical groups, which mainly differ in the masses of the associated particles. Why do these three generations exist and what is the cause of the huge differences between the masses? The top quark has a mass of about 1.73 · 10 11 eV and the electron neutrino of <2 eV. The Higgs mechanism creates masses, but does not provide any explanation for these differences.

  • What is the relationship between quarks and leptons? The proton and the electron have the same elementary charge ( or ), but otherwise different properties.
  • The SM is a consistent mathematical theory in the energy range of current experiments, but diverges at high energies.

The SM also leaves the following questions unanswered:

  • The gravity does not occur in the SM.
  • What is the dark matter?
  • What is the dark energy?

Higgs mechanism

The Higgs mechanism interprets the mass of the fundamental particles, a property that was previously considered to be original, as the result of a new type of interaction.

  • Do the decay channels of the Higgs boson agree with the Standard Model?
  • Are the Higgs boson and its (hypothetical) anti-particle responsible for the baryon asymmetry ? (see also the unsolved problem : baryon asymmetry )

Hierarchy problem

In particle physics , the hierarchy problem describes the question why gravity is so significantly weaker (by a factor of 10 −32 ) than the electroweak interaction .

  • For elementary particles, gravitation only becomes strong on the Planck scale , at approx. 10 19 G eV , a multiple of the order of magnitude of the weak interaction . However, the Planck scale is 16 orders of magnitude above the electroweak scale (order of magnitude 10 3 G eV ). The effective (i.e. experimentally accessible) Higgs mass, the value of which is required for the Higgs mechanism in the range of the electroweak scale, is therefore not at its natural value in the vicinity of the Planck mass ( naturalness problem ).

Magnetic monopoly

A magnetic monopole is an imaginary magnet that has only one pole. By Paul AM Dirac speculation comes, it could the magnetic monopole as elementary particles give that the magnetic counterpart of the electron would be.

  • Do elementary particles exist that carry a magnetic charge (analogous to the electrical charge ) or did they exist in the past?

There are two arguments in favor of this idea:

  • The asymmetry between the otherwise similar phenomena magnetism and electricity - visible e.g. B. in Maxwell's equations - would be fixed, electrical and magnetic phenomena would be strictly "dual" to each other.
  • According to Dirac, the presence of magnetic monopoles would explain the quantization of the electric charge .

proton

Proton decay

  • Is the proton basically stable? Or does it only have a very long half-life (greater than 10 31 years) and therefore decays within a finite period of time? The proton decay is of some variants of the grand unified theory predicted (GUT).

Spin crisis

The total spin of the proton is made up of the spins of the valence quarks , the sea ​​quarks and the gluons as well as the angular momenta of the quarks and gluons. To date, however, it has not yet been possible to divide the total spin of the proton exactly into these components. Theoretical models and experiments also seem to show different contributions of the quarks to the total spin of the proton. According to the following source, the spin of the proton is composed as follows: the quark spin contributes approximately , while the proportions of gluon spin, quark angular momentum and gluon angular momentum are unknown.

Charge radius of the proton

When measuring the Lamb shift on the muonic hydrogen , i.e. on the bound system of muon and proton, it became apparent in 2010 that the charge radius of the proton of muonic hydrogen - the proton is surrounded by a muon instead of the electron - is 841.84 ( 67) 10 −18  m results. The CODATA value, on the other hand, is 8.414 (19) · 10 −16  m. In 2013 the same research group determined the value  even more precisely at 840.87 (39) · 10 −18 m. While measurement errors were initially suspected, the research group (at the Paul Scherrer Institute ) is now certain that the proton in muonic hydrogen is smaller than in normal hydrogen. If this turns out to be correct, various consequences are possible: Does the Rydberg constant have to be adjusted? Are the QED calculations correct for muonic hydrogen? Does the proton have an unexpectedly complex structure that only becomes clear under the influence of the heavy muon? Or is this an indication of a phenomenon beyond the Standard Model of particle physics? In order to get to the bottom of the proton puzzle, muonic helium is to be measured spectroscopically. In 2017, the deviation in the proton radius was also confirmed with laser spectroscopy for ordinary hydrogen (with 3.3 instead of 4 standard deviations).

Supersymmetry

The Super symmetry is a hypothetical symmetry of the particle , the bosons (particles with integer spin) and fermions converts (particles with half-integer spin) into each other. Most of the Great Unified Theories and Superstring Theories are supersymmetric. However, to date no experimental evidence has been found that supersymmetry actually exists in nature.

  • Does space-time supersymmetry occur in the range of T eV ? If so, what mechanism causes the supersymmetry to be broken?

Generations

In particle physics, the twelve known elementary matter particles are divided into three so-called generations of four particles each plus their antiparticles . The existence of a fourth, fifth etc. generation with corresponding elementary particles that have not yet been experimentally proven cannot be ruled out, but no indications are known for further generations.

  • Is there a theory that can explain the mass of certain quarks and leptons in certain generations on the basis of superordinate principles (e.g. based on a theory of Yukawa coupling)?

Neutrinos

In today's standard model of particle physics , neutrinos have no mass . However, experiments on neutrino oscillation have shown that neutrinos have a mass other than zero. There are also theories that describe a non-zero mass.

  • How big are the neutrino masses? Is the mass hierarchy normal or inverted?

Confinement

In particle physics, confinement denotes the phenomenon that particles with a color charge - quarks and gluons - do not isolate, i.e. H. do not occur as free particles, but only in elementary particles made up of them, such as B. mesons and baryons .

Strong CP problem

Under CP violation (C for engl. Batch charge; P for parity parity ) is understood to mean the violation of the CP invariance . The latter says that the physical relationships and laws in a system should not change if all particles are replaced by their antiparticles and all spatial coordinates are mirrored at the same time.

  • Strong CP problem (. Engl strong CP problem- ): Why could not for the strong interaction no CP violation - which should be possible in principle - be detected experimentally?
  • Axion : Is the Peccei – Quinn theory and the hypothetical elementary particle Axion the solution to the strong CP problem? Can axions be proven experimentally?

Anomalous magnetic moment

  • Why does the experimentally measured value of the anomalous magnetic moment of the muon (| g | −2) differ from the value theoretically predicted by the Standard Model ?

Astronomy and astrophysics

Accretion disk

In astrophysics, an accretion disk is a disk rotating around a central object that transports (accretes) matter towards the center. It can consist of atomic gas or dust or of different degrees of ionized gas ( plasma ).

  • Jets : Why are jets formed perpendicular to the plane of rotation of certain astronomical objects, such as B. galactic nuclei or black holes that collect matter by means of a rotating accretion disk ?
  • Quasi-periodic oscillations (Engl. Quasi-periodic oscillations ): Why in many accretion disks occur quasi-periodic oscillations? Why is the period of oscillation inversely proportional to the mass of the central object? Why are there sometimes harmonics and why do they occur in different objects in different frequency ratios?

Solar corona

The solar corona is the area of ​​the sun's atmosphere that lies above the chromosphere and is characterized by significantly lower densities and higher temperatures compared to the deeper layers of the sun's atmosphere.

  • Heating the corona : Why is the temperature of the corona (typically a few million Kelvin ) significantly hotter than the temperature of the underlying layers of the sun such as the chromosphere and photosphere (surface of the sun)?

Possible explanatory models for the heating of the corona include the dissipation of plasma waves , reconnection of continuously restructured magnetic field configurations, shock-dominated dissipation of electrical currents, heating by shock waves and other possible processes.

  • Reconnection : Why is magnetic reconnection many orders of magnitude faster than predicted by standard models?

Supermassive black holes

The M – sigma relation (M– relation) is an empirically determined relationship between the mass M of a supermassive black hole (comprising up to several billion solar masses) in the center of a galaxy and the velocity dispersion of stars in the dense central region of a spiral galaxy ( bulge ) .

  • What is the reason for the M – sigma relation?
  • How did the most distant quasars accumulate their supermassive black holes so early in the history of the universe?

UHECR

  • Whence originated ultra-high energy cosmic rays (Engl. Ultra-high-energy cosmic ray or UHECR)?
  • Why is there cosmic radiation with an incredibly high energy (see OMG particles )? The particles of cosmic rays can travel a maximum of 50 Mpc , but none of the possible sources are located in such a radius around the earth.
  • Why does cosmic radiation from distant sources obviously have energies above the GZK cutoff ?

Others

  • Kuiper cliff (. English Kuiper cliff ): Why is it that the number of objects in the Kuiper belt of the solar system beyond a limit of 50 AE from unexpected and fast?
  • Supernova : What is the exact mechanism to describe the transition from the collapse of the core (implosion) to the actual explosion of the star?
  • Magnetar : What causes the extremely strong magnetic field of a magnetar?
  • Rotation rate of Saturn : why does the magnetosphere of Saturn show a slowly changing periodicity that is similar to the rotation rate of clouds on Saturn? What is the rate of rotation of the inner part (or solid core) of Saturn?
  • Roar of space (. Engl roar space ): Why is the roar of space six times louder than expected? What is the source for this?
  • Age metallicity relationship : is there a universally valid relationship between age and metallicity in galaxies ?
  • Lithium problem : The theory of primordial nucleosynthesis describes the formation of atomic nuclei in the time up to three minutes after the Big Bang. However, the lithium-7 abundance predicted by the theory does not match the observed abundance in ancient stars. It is not clear what causes this discrepancy.

Nuclear physics

The nuclear physics is the branch of physics that deals with the structure and behavior of atomic nuclei busy. Your most important theoretical aid is quantum mechanics .

Quantum chromodynamics

The quantum (QCD) is a quantum field theory to describe the strong interaction . It describes the interaction of quarks and gluons , the fundamental building blocks of atomic nuclei. Like quantum electrodynamics (QED), QCD is a calibration theory . However, the description of nucleons is an open problem. The quarks have only 5% of the mass of the nucleons, the remaining 95% of the nucleon mass comes from the binding energy of the strong interaction and the kinetic energy of the quarks and gluons, which build up the nucleons.

  • What are the phases of strongly interacting matter and what role do they play in the cosmos? What does the internal structure of the nucleons look like? What does the QCD predict with regard to the properties of strongly interacting matter?
  • What role do gluons and interactions between gluons play in nucleons and atomic nuclei? Do glueballs exist (hypothetical, color-charge-neutral particles that only consist of gluons)? Do gluons gain mass dynamically within hadrons , although no mass is formally assigned to them in QCD?
  • What determines the main features of QCD and how do they relate to gravity and space-time?
  • Why has no CP violation been proven for the QCD ? Does the QCD really have no CP violation? (see also the unsolved problem : strong CP problem )

Atomic nuclei and nuclear astrophysics

The strong interaction serves to explain the bond between the quarks in the hadrons . Before the introduction of the quark model, the force of attraction between the nucleons ( protons and neutrons ) of the atomic nucleus was referred to as the strong interaction . This attraction between the nucleons is nowadays referred to as residual interaction or nuclear force . A complete description of this nuclear force from quantum chromodynamics is not yet possible.

  • What is the nature of the residual interaction that holds the protons and neutrons together in stable nuclei (see also magic nuclei ) and isotopes ?
  • What is the origin of simple structures in complex cores? What is the nature of exotic excitations in nuclei at the limit of stability and their role in the physical processes of stars?
  • What is the nature of neutron stars and densely packed matter? What are the physical processes of stars and star explosions?

Atomic physics

The atomic physics is the branch of physics that deals with the physics of the atomic shell and the processes occurring in their operations. Atomic physics regards the atomic nucleus as a building block that cannot be further subdivided.

Hydrogen / helium

Condensed Matter Physics

The physics of condensed matter differs significantly from free particles ( elementary particle physics , atomic physics ) due to the mutual interaction of the building blocks of matter . The theoretical description is based on many-body theory .

High temperature superconductors

As a high-temperature superconductor materials are referred to whose superconductivity - unlike conventional superconductors - not by the electron- phonon interaction is established. The cause has not been clarified for more than 25 years.

  • What is the mechanism that causes some materials to show superconductivity at temperatures well above 25 Kelvin?
  • Is it possible to manufacture a material that is superconducting at room temperature (20 ° C or 293 K)?

Amorphous materials

An amorphous material is a substance in which the atoms do not form an ordered structure but an irregular pattern and only have short-range order, but not long-range order. In contrast to amorphous materials, regularly structured materials are called crystals .

  • Which physical processes are responsible for the properties of glasses and the glass transition?

Sonoluminescence

Under sonoluminescence is meant a physical phenomenon ultrashort in which a liquid under high pressure fluctuations that emits high-energy light flashes.

  • What is the cause of these short, high-energy flashes of light that emanate from imploding cavitation bubbles in a liquid, if these bubbles have previously been artificially generated with ultrasound of suitable strength and frequency?

turbulence

Turbulence is the movement of liquids and gases in which eddies occur on all size scales. This form of flow is characterized by mostly three-dimensional, apparently random movements of the fluid particles (see also turbulence model ).

  • Can a theoretical model be created to describe the statistics of a turbulent flow (especially its internal structure)?
  • Under what conditions do exact solutions of the Navier-Stokes equations exist ? This problem is also one of the Millennium Problems in mathematics.

Others

  • Topological order : Is the topological order stable at temperatures above 0 K?
  • Quantum dot : what is the cause of the nonparabolicity in the conduction band of quantum dots?

World formula

A world formula should link and precisely describe all physical phenomena in the known universe. It is unclear what such a world formula could look like and whether it can be found.

Problems solved in the 21st century

Some problems could be solved in the recent past. This list is sorted by the date of the solution, the period in which this was an unresolved question is given in brackets (if clear).

  • Where do short gamma-ray bursts (1993–2017) come from? These can arise from the merging of two neutron stars , first observed in 2017 when gravitational waves emitted at the same time could be measured.
  • Missing baryonic matter (1998–2017): The known contributions to baryonic matter added up to a value that was too low. The missing portion was found as hot interstellar gas.
  • Do time crystals exist (2012–2016)? Yes, first observed experimentally in 2016.
  • Do gravitational waves exist (1916–2016)? Yes, first found by LIGO in 2016.
  • Can Bell's inequality be tested without loopholes (1970–2015)? Yes, as three research groups demonstrated in 2015.
  • Do pentaquarks exist (1964–2015)? Yes, found by LHCb .

See also

Web links

Individual evidence

  1. ↑ a b c d e f Archived copy ( memento of the original from August 9, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Pp. 1–2, p. 15 @1@ 2Template: Webachiv / IABot / www.physik.uni-regensburg.de
  2. ↑ a b c d e Archived copy ( memento of the original dated August 8, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.physik.uni-regensburg.de
  3. ^ A b Paul J. Steinhardt: Cosmic Inflation on the Test Stand, Spectrum of Science 8/11 - August 2011, pages 40-48
  4. ↑ Archived copy ( memento of the original from September 23, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.bild-der-wissenschaft.de
  5. ↑ a b http://www.si-journal.de/index2.php?artikel=jg13/heft2/sij132-4.html
  6. ↑ http://amscimag.sigmaxi.org/4Lane/ForeignPDF/2004-03Cline_Ger.pdf p. 35
  7. ↑ a b http://press.web.cern.ch/press-releases/2013/04/lhcb-experiment-observes-new-matter-antimatter-difference It is only the fourth subatomic particle known to exhibit such behavior. [..] “We also know that the total effects induced by Standard Model CP violation are too small to account for the matter-dominated Universe,” says Campana.
  8. ↑ http://iktp.tu-dresden.de/~schubert/talks/tud-ringvorlesung-0211.pdf p. 26
  9. ↑ http://www.spektrum.de/alias/higgs-boson/beeinflsse-das-higgs-teilchen-die-materieverkauf-im-universum/1209561
  10. ↑ http://www.wissenschaft.de/home/-/journal_content/56/12054/1164662/
  11. ↑ http://arxiv.org/abs/astro-ph/0310253 http://physicsworld.com/cws/article/news/2003/oct/08/is-the-universe-a-dodecahedron
  12. ↑ a b c d e f Hermann Nicolai: On the way to physics of the 21st century, Spectrum of Science, November 2008, p. 33.
  13. ↑ a b Lee Smolin : Quantum Space-Time, Spectrum of Science, May 2005, p. 34.
  14. ^ A b Hermann Nicolai : On the way to physics in the 21st century, Spectrum of Science, November 2008, p. 31.
  15. ↑ a b Martin Bojowald : The Ur-Sprung des Alls, Spectrum of Science, 05/2009, p. 27.
  16. ↑ a b c Hermann Nicolai: On the way to physics of the 21st century, Spectrum of Science, 11/2008, p. 32.
  17. ↑ Lee Smolin : Quantum of Space-Time, Spectrum of Science, May 2005, p. 33.
  18. ^ Hermann Nicolai : On the way to physics of the 21st century, Spectrum of Science, November 2008, p. 34.
  19. ↑ Lee Smolin : Quantum of Spacetime, Spectrum of Science, May 2005, p. 32.
  20. ↑ http://www.wissenschaft.de/home/-/journal_content/56/12054/1164662/
  21. ↑ Remigiusz Augusiak, Maciej Demianowicz, Antonio Acín: Local hidden - variable models for entangled quantum states
  22. ↑ http://www.wissenschaft.de/home/-/journal_content/56/12054/54728/ Hawking believes the latter, and has formulated a "presumption to protect the order of time": Time machines could not be built or could arise by themselves and if so yes, quantum gravity effects would destroy them again immediately.
  23. ↑ http://www-ekp.physik.uni-karlsruhe.de/~deboer/html/Lehre/HS_WS0809/Standardmodell_Praesentation.pdf p. 19
  24. ↑ a b c d e http://www.physik.uni-dortmund.de/~paes/Masterclasses.pdf pp. 4–5
  25. ↑ http://www.hep.physik.uni-siegen.de/~grupen/MNUVortrag.pdf p. 17
  26. ↑ a b c d e f g http://www.hep.physik.uni-siegen.de/~grupen/MNUVortrag.pdf p. 32
  27. ↑ a b Archived copy ( Memento of the original from April 17, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.weltderphysik.de
  28. ↑ a b c d e http://adweb.desy.de/~klanner/Lehre/WS0506/Kapitel10.pdf ( Memento from May 2, 2014 in the Internet Archive )
  29. ↑ a b c d Archived copy ( Memento of the original from April 14, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.weltderphysik.de
  30. ↑ a b http://www2.uni-wuppertal.de/FB8/groups/Teilchenphysik/oeffentlichkeit/Prinzipien.html
  31. ↑ a b c d http://www-ekp.physik.uni-karlsruhe.de/~deboer/html/Lehre/HS_WS0809/Standardmodell_Praesentation.pdf p. 23
  32. ↑ http://www.fsp102-cms.de/higgs_teilchen_am_cern_entdeck_/higgs_results/index_ger.html The question of which is the best decay channel for the search for the Higgs particle is not only decided by the frequency of a certain decay. It is also important how well such a decay of the Higgs particle can be distinguished from other reactions (background processes).
  33. ↑ https://www.weltderphysik.de/gebiet/teilchen/baussteine/higgs/ursprung-der-masse/ So how do you recognize a Higgs boson? Higgs bosons disintegrate almost immediately (after about 10–22 seconds) back into known particles - in the range preferred by the LEP experiments for the Higgs mass, about eighty percent into the heavy b-quarks. Although b-quarks can be easily identified at the LHC, they are so omnipresent in other processes that b-quarks cannot be isolated from Higgs decays. [..] Further searches exploit the decay of the Higgs boson into a pair of tau leptons. If the Higgs boson is heavier than about 140 GeV / c², the decay into a pair of Z bosons, which in turn can each decay a pair of electrons or muons, offers a reliable signature for the Higgs discovery.
  34. ↑ http://www.spektrum.de/alias/higgs-boson/beeinflsse-das-higgs-teilchen-die-materieverkauf-im-universum/1209561
  35. ↑ http://www.desy.de/~troms/teaching/WiSe1011/talks/Reitz_SUSY.pdf p. 5
  36. ↑ Archived copy ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. That means the natural mass of a scalar particle . For the electroweak theory, however, the Higgs mass must be of the order of magnitude of the electroweak scale . This is also called the naturalness problem: the Higgs mass is not at its natural value. @1@ 2Template: Webachiv / IABot / www.physik.uzh.ch
  37. ↑ a b https://lp.uni-goettingen.de/get/text/7042
  38. ↑ https://www.fwf.ac.at/de/wissenschaft-konkret/projektvorektiven-archiv/2007/pv200712/ This is how common models explain that 60 percent of the spin of the protons must come from the spin of the quarks. [..] But experiments on some of the most powerful particle accelerators in the world come to the result that a maximum of 30 percent of the spin of the protons comes from the spin of the quarks.
  39. ↑ http://www.dpg-physik.de/veroeffnahmung/themenhefte/highlights-2013.pdf P. 9–10 The spin of the proton should result from the sum of its building blocks, i.e. the spin of three quarks. At the end of the 1980s, however, experiments at CERN found that the three quarks only provided about a quarter of the value.
  40. ↑ Archived copy ( Memento of the original from February 21, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. P. 15 @1@ 2Template: Webachiv / IABot / www.nuclear.gla.ac.uk
  41. ↑ a b c http://www.nature.com/nature/journal/v466/n7303/full/nature09250.html
  42. ↑ CODATA Recommended Values. National Institute of Standards and Technology, accessed July 21, 2019 . CODATA 2014 value.
  43. ↑ a b c http://www.psi.ch/media/weiter-raetsel-um-das-proton
  44. ↑ a b c http://www.spektrum.de/alias/kernphysik/das-proton-paradox/1256117
  45. ↑ a b c https://www.organische-chemie.ch/chemie/2010/jul/proton.shtm
  46. ↑ Shrunken Proton , Pro Physik, October 6, 2017
  47. ↑ http://www.weltderphysik.de/gebiet/astro/kosmische-strahl/detektoren/cast/ fundamental problem of particle physics: the preservation of the "CP symmetry" in quantum chromodynamics (QCD). This theory describes the strong interaction between quarks and actually suggests the break of the fundamental CP symmetry principle. [..] The violation of the CP symmetry was observed, but not in connection with the QCD.
  48. ↑ http://www.weltderphysik.de/gebiet/astro/kosmische-strahl/detektoren/cast/ [..] axions would thus be more or less stable particles that cannot decay. These properties make it difficult to prove experimentally.
  49. ↑ http://www.astropage.eu/index_news.php?id=944 The researchers also performed similar calculations to give a more accurate estimate of the anomalous magnetic moment of the muon. Your improved value confirms the previous result, which does not exactly match the value predicted by the standard model. The scientists believe that this discrepancy between the measurement and the theoretical prediction could lead to new insights that go beyond the standard model of elementary particles.
  50. ↑ http://arxiv.org/pdf/1311.2198.pdf These improvements would halve the uncertainty on the difference between experiment and theory, and should clarify whether the current difference points toward New Physics, or to a statistical fluctuation. At present, the (g-2) result is arguably the most compelling indicator of physics beyond the Standard Model and, at the very least, it represents a major constraint for speculative new theories such as supersymmetry, dark gauge bosons or extra dimensions.
  51. ↑ http://www.pro-physik.de/details/news/1721901/Woher_stammt_die_ultrahochenergetische_kosmische_Strahlung.html Astroparticle physicists have known about the existence of ultra-high energy particles for a long time, but their exact origin is still a mystery.
  52. ↑ http://www.wissenschaft.de/erde-weltall/astronomie/-/journal_content/56/12054/1221555/Riesencrash-im-All-k%C3%B6nnte-Herkunft-hochenergetischer-kosmischer-Strahlung-erkl%C3 % A4ren / The greatest difficulty is the explanation of the ultra-high energy cosmic rays. “No process in our Milky Way can create it,” says Roger Clay from the University of Adelaide.
  53. ↑ Archived copy ( Memento of the original from March 22, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Many of the best computer models of supernova explosions fail to produce an explosion. Instead, according to the simulations, gravity wins the day and the star simply collapses. [..] Something must be helping the outward push of radiation and other pressures overcome the inward squeeze of gravity. To figure out what that "something" is, scientists need to examine the inside of a real supernova while it's exploding @1@ 2Template: Webachiv / IABot / science1.nasa.gov
  54. ↑ http://www.weltderphysik.de/gebiet/astro/sterne/elemententstehung/ Here, the star sheds its outer shell and hurls the nuclides that have been produced during the various hydrostatic combustion phases into space. The dynamics of the collapse are largely determined by the electron capture rate at nuclei. Their measurement and theoretical determination is one of the primary tasks of nuclear astrophysics today .
  55. ↑ http://www.hcm.uni-bonn.de/homepages/prof-dr-benjamin-schlein/teaching/graduate-seminar-on-pdes-in-the-sciences/ To prove the existence of Bose-Einstein condensation for interacting systems is, in general, a major open problem in mathematical physics.
  56. ↑ Archived copy ( memento of the original from October 11, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. The relatively small energy gap of some semiconductors such as B. InAs leads to a pronounced non-parabolic nature of the energy-momentum dispersion relation due to the strong coupling of neighboring bands. This is expressed, for example, in a clear energy dependence of the effective mass of the charge carriers in such systems. @1@ 2Template: Webachiv / IABot / www.nano.physik.uni-muenchen.de