Historical Hilgenberg globesPotential
reconstruction of continents bordering the Atlantic (left column) and
Pacific (right column) oceans as they might have appeared at different
points, going back in history, using the expanding Earth hypothesis,
based on reconstructions by expanding Earth proponent Neal Adams
The expanding Earth or growing Earthhypothesis argues that the position and relative movement of continents is due at least partially to the volume of Earth increasing. Conversely, geophysical global cooling was the hypothesis that various features could be explained by Earth contracting.
Although it was suggested historically, since the recognition of plate tectonics during the mid 20th century, scientific consensus has rejected the idea of any significant expansion or contraction of Earth.
Different forms of the hypothesis
Expansion with constant mass
In 1834, during the second voyage of HMS Beagle, Charles Darwin investigated stepped plains featuring raised beaches in Patagonia
which indicated to him that a huge area of South America had been
"uplifted to its present height by a succession of elevations which
acted over the whole of this space with nearly an equal force". While
his mentor Charles Lyell
had suggested forces acting near the crust on smaller areas, Darwin
hypothesized that uplift at this continental scale required "the gradual
expansion of some central mass" [of the Earth] "acting by intervals on
the outer crust" with the "elevations being concentric with form of
globe (or certainly nearly so)". In 1835 he extended this concept to
include the Andes
Mountains as part of a curved enlargement of the Earth's crust due to
"the action of one connected force". Not long afterwards, he abandoned
this idea and proposed that as the mountains rose, the ocean floor
subsided, explaining the formation of coral reefs.
In 1889 and 1909 Roberto Mantovani
published a hypothesis of Earth expansion and continental drift. He
assumed that a closed continent covered the entire surface of a smaller
Earth. Thermal expansion caused volcanic
activity, which broke the land mass into smaller continents. These
continents drifted away from each other because of further expansion at
the rip-zones, where oceans currently lie.Although Alfred Wegener noticed some similarities to his own hypothesis of continental drift, he did not mention Earth expansion as the cause of drift in Mantovani's hypothesis.
A compromise between Earth-expansion and Earth-contraction is the "theory of thermal cycles" by Irish physicist John Joly. He assumed that heat flow from radioactive decay inside Earth surpasses the cooling of Earth's exterior. Together with British geologist Arthur Holmes,
Joly proposed a hypothesis in which Earth loses its heat by cyclic
periods of expansion. By their hypothesis, expansion caused cracks and joints in Earth's interior that could fill with magma. This was succeeded by a cooling phase, where the magma would freeze and become solid rock again, causing Earth to shrink.
After initially endorsing the idea of continental drift, Australian geologist Samuel Warren Carey advocated expansion from the 1950s (before the idea of plate tectonics was generally accepted) to his death, alleging that subduction and other events could not balance the sea-floor spreading at oceanic ridges, and describing yet unresolved paradoxes that continue to plague plate tectonics.
Starting in 1956, he proposed some sort of mass increase in the planets
and said that a final solution to the problem is only possible by cosmological processes associated with the expansion of the universe.
Bruce Heezen
initially interpreted his work on the mid-Atlantic ridge as confirming
S. Warren Carey's Expanding Earth Theory, but later ended his
endorsement, finally convinced by the data and analysis of his
assistant, Marie Tharp. The remaining proponents after the 1970s, like the Australian geologist James Maxlow, are mainly inspired by Carey's ideas.
To date no scientific mechanism of action has been proposed for
this addition of new mass. Although the earth is constantly acquiring
mass through accumulation of rocks and dust from space such accretion, however, is only a minuscule fraction of the mass increase required by the growing earth hypothesis.
Decrease of the gravitational constant
Paul Dirac suggested in 1938 that the universal gravitational constant had decreased during the billions of years of its existence. This caused German physicist Pascual Jordan to propose in 1964, a modification of the theory of general relativity, that all planets slowly expand. This explanation is considered a viable hypothesis within the context of physics.
Measurements of a possible variation of the gravitational constant showed an upper limit for a relative change of 5×10−12 per year, excluding Jordan's idea.
Formation from a gas giant
According to the hypothesis of J. Marvin Herndon (2005, 2013) the Earth originated in its protoplanetary stage from a Jupiter-like gas giant. During the development phases of the young Sun, which resembled those of a T Tauri star,
the dense atmosphere of the gas giant was stripped off by infrared
eruptions from the sun. The remnant was a rocky planet. Due to the loss
of pressure from its atmosphere it would have begun a progressive
decompression. Herndon regards the energy released due to the lack of
compression as a primary energy source for geotectonic activity, to
which some energy from radioactive decomposition processes was added. He
terms the resulting changes in the course of Earth's history by the name of his theory Whole-Earth Decompression Dynamics. He considered seafloor spreading at divergent plate boundaries as an effect of it. In his opinion mantle convection as used as a concept in the theory of plate tectonics is physically impossible. His theory includes the effect of solar wind (geomagnetic storms) as cause for the reversals of the Earth magnetic field. The question of mass increase is not addressed.
Main arguments against Earth expansion
The hypothesis had never developed a plausible and verifiable mechanism of action. During the 1960s, the theory of plate tectonics— based initially on the assumption that Earth's size remains constant, and relating the subduction zones to burying of lithosphere at a scale comparable to seafloor spreading—became the accepted explanation in the Earth Sciences.
The scientific community finds that significant evidence
contradicts the Expanding Earth theory, and that the evidence used for
it is explained better by plate tectonics:
Measurements with modern high-precision geodetic
techniques and modeling of the measurements by the horizontal motions
of independent rigid plates at the surface of a globe of free radius,
were proposed as evidence that Earth is not currently increasing in size
to within a measurement accuracy of 0.2 mm per year.
The main author of the study stated "Our study provides an independent
confirmation that the solid Earth is not getting larger at present,
within current measurement uncertainties".
The motions of tectonic plates and subduction zones measured by a large range of geological, geodetic and geophysical techniques helps verify plate tectonics.
Imaging of lithosphere fragments within the mantle is evidence for lithosphere consumption by subduction.
Paleomagnetic data has been used to calculate that the radius of Earth 400 million years ago was 102 ± 2.8 percent of the present radius.
Examinations of data from the Paleozoic and Earth's moment of inertia suggest that there has not been any significant change of Earth's radius during the last 620 million years.
See Standard Model for the current consensus theory of these particles.
Elementary particles are particles with no measurable internal
structure; that is, it is unknown whether they are composed of other
particles. They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin. All the particles of the Standard Model have been experimentally observed, including the Higgs boson in 2012. Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally.
Fermions have half-integer spin; for all known elementary fermions this is 1⁄2. All known fermions except neutrinos, are also Dirac fermions; that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion. Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the strong interaction or not. In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.
Quarks
Quarks are the fundamental constituents of hadrons and interact via the strong force. Quarks are the only known carriers of fractional charge, but because they combine in groups of three quarks (baryons) or in pairs of one quark and one antiquark (mesons), only integer charge is observed in nature. Their respective antiparticles are the antiquarks, which are identical except that they carry the opposite electric charge (for example the up quark carries charge +2⁄3, while the up antiquark carries charge −2⁄3), color charge, and baryon number. There are six flavors
of quarks; the three positively charged quarks are called "up-type
quarks" while the three negatively charged quarks are called "down-type
quarks".
Leptons do not interact via the strong interaction. Their respective antiparticles are the antileptons, which are identical, except that they carry the opposite electric charge and lepton number. The antiparticle of an electron is an antielectron, which is almost always called a "positron"
for historical reasons. There are six leptons in total; the three
charged leptons are called "electron-like leptons", while the neutral
leptons are called "neutrinos". Neutrinos are known to oscillate, so that neutrinos of definite flavor do not have definite mass, rather they exist in a superposition of mass eigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been omitted.
Bosons are one of the two fundamental particles having integral spinclasses of particles, the other being fermions. Bosons are characterized by Bose–Einstein statistics and all have integer spins. Bosons may be either elementary, like photons and gluons, or composite, like mesons.
According to the Standard Model, the elementary bosons are:
The Higgs boson is postulated by the electroweak theory primarily to explain the origin of particle masses. In a process known as the "Higgs mechanism", the Higgs boson and the other gauge bosons in the Standard Model acquire mass via spontaneous symmetry breaking of the SU(2) gauge symmetry. The Minimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons. On 4 July 2012, the discovery of a new particle with a mass between 125 and 127 GeV/c2
was announced; physicists suspected that it was the Higgs boson. Since
then, the particle has been shown to behave, interact, and decay in many
of the ways predicted for Higgs particles by the Standard Model, as
well as having even parity and zero spin, two fundamental attributes of a
Higgs boson. This also means it is the first elementary scalar particle
discovered in nature.
The graviton is a hypothetical particle that has been included in some extensions to the standard model to mediate the gravitational
force. It is in a peculiar category between known and hypothetical
particles: As an unobserved particle that is not predicted by, nor
required for the Standard Model,
it belongs in the table of hypothetical particles, below. But
gravitational force itself is a certainty, and expressing that known
force in the framework of a quantum field theory requires a boson to mediate it.
If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current,
a first-order tensor). Additionally, it can be shown that any massless
spin-2 field would give rise to a force indistinguishable from
gravitation, because a massless spin-2 field would couple to the
stress–energy tensor in the same way that gravitational interactions do.
This result suggests that, if a massless spin-2 particle is discovered,
it must be the graviton.
Particles predicted by supersymmetric theories
Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally.
Introduced by many extensions of the Standard Supermodel, and may be needed to explain the LSND results. A special role has the sterile sneutrino, the supersymmetric counterpart of the hypothetical right-handed neutrino, called the "sterile neutrino".
Just as the photon, Z boson and W± bosons are superpositions of the B0, W0, W1, and W2 fields, the photino, zino, and wino± are superpositions of the bino0, wino0, wino1, and wino2.
No matter if one uses the original gauginos or this superpositions as a
basis, the only predicted physical particles are neutralinos and
charginos as a superposition of them together with the Higgsinos.
Other hypothetical bosons and fermions
Other
theories predict the existence of additional elementary bosons and
fermions, with some theories also postulating additional superpartners
for these particles:
Unidentified scalar force-carrier that is presumed to have physically caused cosmological “inflation” – the rapid expansion from 10−35 to 10−34seconds after the Big Bang.
Kaluza–Klein towers
of particles are predicted by some models of extra dimensions. The
extra-dimensional momentum is manifested as extra mass in
four-dimensional spacetime.
Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks "aces"), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons. (The interaction between quarks and gluons is described by the theory of quantum chromodynamics.) A "sea" of virtual quark-antiquark pairs is also present in each hadron.
Baryons
A combination of three u, d or s-quarks with a total spin of 3⁄2 form the so-called "baryon decuplet".Proton quark structure: 2 up quarks and 1 down quark.
Ordinary baryons (composite fermions) contain three valence quarks or three valence antiquarks each.
Nucleons are the fermionic constituents of normal atomic nuclei:
Protons, composed of two up and one down quark (uud)
Neutrons, composed of two down and one up quark (ddu)
Hyperons, such as the Λ, Σ, Ξ, and Ω particles, which contain one or more strange quarks, are short-lived and heavier than nucleons. Although not normally present in atomic nuclei, they can appear in short-lived hypernuclei.
A number of charmed and bottom baryons have also been observed.
Pentaquarks consist of four valence quarks and one valence antiquark.
At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed.
A tetraquark consists of two valence quarks and two valence antiquarks;
A glueball is a bound state of gluons with no valence quarks;
Hybrid mesons consist of one or more valence quark–antiquark pairs and one or more real gluons.
Atomic nuclei
A semi-accurate depiction of the helium
atom. In the nucleus, the protons are in red and neutrons are in
purple. In reality, the nucleus is also spherically symmetrical.
Atomic nuclei typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such as hypertriton which contains a hyperon.
These baryons (protons, neutrons, hyperons, etc.) which comprise the
nucleus are called nucleons. Each type of nucleus is called a "nuclide", and each nuclide is defined by the specific number of each type of nucleon.
"Isotopes" are nuclides which have the same number of protons but differing numbers of neutrons.
Conversely, "isotones" are nuclides which have the same number of neutrons but differing numbers of protons.
"Isobars" are nuclides which have the same total number of nucleons but which differ in the number of each type of nucleon. Nuclear reactions can change one nuclide into another.
Atoms are the smallest neutral particles into which matter can be divided by chemical reactions.
An atom consists of a small, heavy nucleus surrounded by a relatively
large, light cloud of electrons. An atomic nucleus typically consists of
1 or more protons and 0 or more neutrons. Protons and neutrons are, in
turn, made of quarks. Each type of atom corresponds to a specific chemical element. To date, 118 elements have been discovered or created.
Exotic atoms
may be composed of particles in addition to or in place of protons,
neutrons, and electrons, such as hyperons or muons. Examples include pionium ( π− π+ ) and quarkonium atoms.
Leptonic atoms
Leptonic atoms, named using -onium, are exotic atoms constituted by the bound state of a lepton and an antilepton. Examples of such atoms include positronium ( e− e+ ), muonium ( e− μ+ ), and "true muonium" ( μ− μ+ ). Of these positronium and muonium have been experimentally observed, while "true muonium" remains only theoretical.
Molecules
are the smallest particles into which a substance can be divided while
maintaining the chemical properties of the substance. Each type of
molecule corresponds to a specific chemical substance.
A molecule is a composite of two or more atoms. Atoms are combined in a
fixed proportion to form a molecule. Molecule is one of the most basic
units of matter.
Ions
Ions are charged atoms (monatomic ions) or molecules (polyatomic ions). They include cations which have a net positive charge, and anions which have a net negative charge.
Quasiparticles are effective particles that exist in many particle systems. The field equations of condensed matter physics
are remarkably similar to those of high energy particle physics. As a
result, much of the theory of particle physics applies to condensed
matter physics as well; in particular, there are a selection of field
excitations, called quasi-particles, that can be created and explored. These include:
Anyons are a generalization of fermions and bosons in two-dimensional systems like sheets of graphene that obeys braid statistics.
Dislons are localized collective excitations of a crystal dislocation around the static displacement.
Polarons are moving, charged (quasi-) particles that are surrounded by ions in a material.
Skyrmions are a topological solution of the pion field, used to model the low-energy properties of the nucleon, such as the axial vector current coupling and the mass.
The following categories are not unique or distinct: For example, either a WIMP or a WISP is also a FIP.
A WIMP (weakly interacting massive particle) is any one of a number of particles that might explain dark matter (such as the neutralino or the sterile neutrino)
A WISP (weakly interacting slender particle) is any one of a number of low mass particles that might explain dark matter (such as the axion)
A GIMP (gravitationally interacting massive particle) is a particle
which provides an alternative explanation of dark matter, instead of the
aforementioned WIMP
A SIMP (strongly interacting massive particle) is a particle that interact strongly between themselves and weakly with ordinary matter and could form dark matter
A SMP (stable massive particle) is a particle that is long-lived and has appreciable mass that could be dark matter
A FIP
(feebly interacting particle) is a particle that interacts very weakly
with conventional matter and could account for dark matter
Calorons, finite temperature generalization of instantons.
Dyons are hypothetical particles with both electric and magnetic charges.
Geons
are electromagnetic or gravitational waves which are held together in a
confined region by the gravitational attraction of their own field of
energy.
Goldstinos are fermions produced by the spontaneous breaking of supersymmetry; they are the supersymmetric counterpart of Goldstone bosons.
Sphalerons are a field configuration which is a saddle point of the Yang–Mills field equations. Sphalerons are used in nonperturbative calculations of non-tunneling rates.
Instantons,
a field configuration which is a local minimum of the Yang–Mills field
equation. Instantons are used in nonperturbative calculations of
tunneling rates.
Meron,
a field configuration which is a non-self-dual solution of the
Yang–Mills field equation. The instanton is believed to be composed of
two merons.
