Fundamental interaction

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Fundamental_interaction

 

In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four fundamental interactions known to exist: the gravitational and electromagnetic interactions, which produce significant long-range forces whose effects can be seen directly in everyday life, and the strong and weak interactions, which produce forces at minuscule, subatomic distances and govern nuclear interactions. Some scientists hypothesize that a fifth force might exist, but the hypotheses remain speculative.

Each of the known fundamental interactions can be described mathematically as a field. The gravitational force is attributed to the curvature of spacetime, described by Einstein's general theory of relativity. The other three are discrete quantum fields, and their interactions are mediated by elementary particles described by the Standard Model of particle physics.

Within the Standard Model, the strong interaction is carried by a particle called the gluon, and is responsible for quarks binding together to form hadrons, such as protons and neutrons. As a residual effect, it creates the nuclear force that binds the latter particles to form atomic nuclei. The weak interaction is carried by particles called W and Z bosons, and also acts on the nucleus of atoms, mediating radioactive decay. The electromagnetic force, carried by the photon, creates electric and magnetic fields, which are responsible for the attraction between orbital electrons and atomic nuclei which holds atoms together, as well as chemical bonding and electromagnetic waves, including visible light, and forms the basis for electrical technology. Although the electromagnetic force is far stronger than gravity, it tends to cancel itself out within large objects, so over large distances (on the scale of planets and galaxies), gravity tends to be the dominant force.

Many theoretical physicists believe these fundamental forces to be related and to become unified into a single force at very high energies on a minuscule scale, the Planck scale, but particle accelerators cannot produce the enormous energies required to experimentally probe this. Devising a common theoretical framework that would explain the relation between the forces in a single theory is perhaps the greatest goal of today's theoretical physicists. The weak and electromagnetic forces have already been unified with the electroweak theory of Sheldon Glashow, Abdus Salam, and Steven Weinberg for which they received the 1979 Nobel Prize in physics. Progress is currently being made in uniting the electroweak and strong fields within what is called a Grand Unified Theory (GUT). A bigger challenge is to find a way to quantize the gravitational field, resulting in a theory of quantum gravity (QG) which would unite gravity in a common theoretical framework with the other three forces. Some theories, notably string theory, seek both QG and GUT within one framework, unifying all four fundamental interactions along with mass generation within a theory of everything (ToE).

The four fundamental interactions of nature

Property/Interaction	Gravitation	Electroweak		Strong
		Weak	Electromagnetic	Fundamental	Residual
Mediating particles	Not yet observed (Graviton hypothesised)	W+, W− and Z0	γ (photon)	Gluons	π, ρ and ω mesons
Affected particles	All particles	Left-handed fermions	Electrically charged	Quarks, Gluons	Hadrons
Acts on	Mass, Energy	Flavor	Electric charge	Color charge
Bound states formed	Planets, Stars, Solar systems, Galaxies	n/a	Atoms, Molecules	Hadrons	Atomic nuclei
Strength at the scale of quarks (relative to electromagnetism)	10−41(predicted)	10−4	1	60	Not applicable to quarks
Strength at the scale of protons/neutrons (relative to electromagnetism)	10−36(predicted)	10−7	1	Not applicable to hadrons	20

History

Classical theory

In his 1687 theory, Isaac Newton postulated space as an infinite and unalterable physical structure existing before, within, and around all objects while their states and relations unfold at a constant pace everywhere, thus absolute space and time. Inferring that all objects bearing mass approach at a constant rate, but collide by impact proportional to their masses, Newton inferred that matter exhibits an attractive force. His law of universal gravitation mathematically stated it to span the entire universe instantly (despite absolute time), or, if not actually a force, to be instant interaction among all objects (despite absolute space.) As conventionally interpreted, Newton's theory of motion modelled a central force without a communicating medium. Thus Newton's theory violated the first principle of mechanical philosophy, as stated by Descartes, No action at a distance. Conversely, during the 1820s, when explaining magnetism, Michael Faraday inferred a field filling space and transmitting that force. Faraday conjectured that ultimately, all forces unified into one.

In 1873, James Clerk Maxwell unified electricity and magnetism as effects of an electromagnetic field whose third consequence was light, travelling at constant speed in a vacuum. The electromagnetic field theory contradicted predictions of Newton's theory of motion, unless physical states of the luminiferous aether—presumed to fill all space whether within matter or in a vacuum and to manifest the electromagnetic field—aligned all phenomena and thereby held valid the Newtonian principle relativity or invariance. 

The Standard Model

The Standard Model of elementary particles, with the fermions in the first three columns, the gauge bosons in the fourth column, and the Higgs boson in the fifth column

 

The Standard Model of particle physics was developed throughout the latter half of the 20th century. In the Standard Model, the electromagnetic, strong, and weak interactions associate with elementary particles, whose behaviours are modelled in quantum mechanics (QM). For predictive success with QM's probabilistic outcomes, particle physics conventionally models QM events across a field set to special relativity, altogether relativistic quantum field theory (QFT). Force particles, called gauge bosons—force carriers or messenger particles of underlying fields—interact with matter particles, called fermions. Everyday matter is atoms, composed of three fermion types: up-quarks and down-quarks constituting, as well as electrons orbiting, the atom's nucleus. Atoms interact, form molecules, and manifest further properties through electromagnetic interactions among their electrons absorbing and emitting photons, the electromagnetic field's force carrier, which if unimpeded traverse potentially infinite distance. Electromagnetism's QFT is quantum electrodynamics (QED).

The electromagnetic interaction was modelled with the weak interaction, whose force carriers are W and Z bosons, traversing the minuscule distance, in electroweak theory (EWT). Electroweak interaction would operate at such high temperatures as soon after the presumed Big Bang, but, as the early universe cooled, split into electromagnetic and weak interactions. The strong interaction, whose force carrier is the gluon, traversing minuscule distance among quarks, is modeled in quantum chromodynamics (QCD). EWT, QCD, and the Higgs mechanism, whereby the Higgs field manifests Higgs bosons that interact with some quantum particles and thereby endow those particles with mass, comprise particle physics' Standard Model (SM). Predictions are usually made using calculational approximation methods, although such perturbation theory is inadequate to model some experimental observations (for instance bound states and solitons.) Still, physicists widely accept the Standard Model as science's most experimentally confirmed theory.

Beyond the Standard Model, some theorists work to unite the electroweak and strong interactions within a Grand Unified Theory (GUT). Some attempts at GUTs hypothesize "shadow" particles, such that every known matter particle associates with an undiscovered force particle, and vice versa, altogether supersymmetry (SUSY). Other theorists seek to quantize the gravitational field by the modelling behaviour of its hypothetical force carrier, the graviton and achieve quantum gravity (QG). One approach to QG is loop quantum gravity (LQG). Still other theorists seek both QG and GUT within one framework, reducing all four fundamental interactions to a Theory of Everything (ToE). The most prevalent aim at a ToE is string theory, although to model matter particles, it added SUSY to force particles—and so, strictly speaking, became superstring theory. Multiple, seemingly disparate superstring theories were unified on a backbone, M-theory. Theories beyond the Standard Model remain highly speculative, lacking great experimental support. 

Overview of the fundamental interactions

An overview of the various families of elementary and composite particles, and the theories describing their interactions. Fermions are on the left, and Bosons are on the right.

 

In the conceptual model of fundamental interactions, matter consists of fermions, which carry properties called charges and spin ±​¹⁄₂ (intrinsic angular momentum ±​^ħ⁄₂, where ħ is the reduced Planck constant). They attract or repel each other by exchanging bosons.

The interaction of any pair of fermions in perturbation theory can then be modelled thus:

Two fermions go in → interaction by boson exchange → Two changed fermions go out.

The exchange of bosons always carries energy and momentum between the fermions, thereby changing their speed and direction. The exchange may also transport a charge between the fermions, changing the charges of the fermions in the process (e.g., turn them from one type of fermion to another). Since bosons carry one unit of angular momentum, the fermion's spin direction will flip from +​¹⁄₂ to −​¹⁄₂ (or vice versa) during such an exchange (in units of the reduced Planck's constant).

Because an interaction results in fermions attracting and repelling each other, an older term for "interaction" is force. 

According to the present understanding, there are four fundamental interactions or forces: gravitation, electromagnetism, the weak interaction, and the strong interaction. Their magnitude and behaviour vary greatly, as described in the table below. Modern physics attempts to explain every observed physical phenomenon by these fundamental interactions. Moreover, reducing the number of different interaction types is seen as desirable. Two cases in point are the unification of:

• Electric and magnetic force into electromagnetism;
• The electromagnetic interaction and the weak interaction into the electroweak interaction; see below.

Both magnitude ("relative strength") and "range", as given in the table, are meaningful only within a rather complex theoretical framework. The table below lists properties of a conceptual scheme that is still the subject of ongoing research. 

Interaction	Current theory	Mediators	Relative strength	Long-distance behavior	Range (m)
Weak	Electroweak Theory (EWT)	W and Z bosons	1025	${\displaystyle {\frac {1}{r}}\ e^{-m_{W,Z}\ r}}$	10−18
Strong	Quantum chromodynamics (QCD)	gluons	1038	${\displaystyle {\sim r}}$ (Color confinement	10−15
Electromagnetic	Quantum electrodynamics (QED)	photons	1036	${\displaystyle {\frac {1}{r^{2}}}}$	∞
Gravitation	General relativity (GR)	gravitons (hypothetical)	1	${\displaystyle {\frac {1}{r^{2}}}}$	∞

The modern (perturbative) quantum mechanical view of the fundamental forces other than gravity is that particles of matter (fermions) do not directly interact with each other, but rather carry a charge, and exchange virtual particles (gauge bosons), which are the interaction carriers or force mediators. For example, photons mediate the interaction of electric charges, and gluons mediate the interaction of color charges.

The interactions

Gravity

Gravitation is by far the weakest of the four interactions at the atomic scale, where electromagnetic interactions dominate. But the idea that the weakness of gravity can easily be demonstrated by suspending a pin using a simple magnet (such as a refrigerator magnet) is fundamentally flawed. The only reason the magnet is able to hold the pin against the gravitational pull of the entire Earth is due to its relative proximity. There is clearly a short distance of separation between magnet and pin where a breaking point is reached, and due to the large mass of Earth this distance is disappointingly small.

Thus gravitation is very important for macroscopic objects and over macroscopic distances for the following reasons. Gravitation:

• Is the only interaction that acts on all particles having mass, energy and/or momentum
• Has an infinite range, like electromagnetism but unlike strong and weak interaction
• Cannot be absorbed, transformed, or shielded against
• Always attracts and never repels (see function of geodesic equation in general relativity)

Even though electromagnetism is far stronger than gravitation, electrostatic attraction is not relevant for large celestial bodies, such as planets, stars, and galaxies, simply because such bodies contain equal numbers of protons and electrons and so have a net electric charge of zero. Nothing "cancels" gravity, since it is only attractive, unlike electric forces which can be attractive or repulsive. On the other hand, all objects having mass are subject to the gravitational force, which only attracts. Therefore, only gravitation matters on the large-scale structure of the universe.

The long range of gravitation makes it responsible for such large-scale phenomena as the structure of galaxies and black holes and it retards the expansion of the universe. Gravitation also explains astronomical phenomena on more modest scales, such as planetary orbits, as well as everyday experience: objects fall; heavy objects act as if they were glued to the ground, and animals can only jump so high.

Gravitation was the first interaction to be described mathematically. In ancient times, Aristotle hypothesized that objects of different masses fall at different rates. During the Scientific Revolution, Galileo Galilei experimentally determined that this hypothesis was wrong under certain circumstances — neglecting the friction due to air resistance, and buoyancy forces if an atmosphere is present (e.g. the case of a dropped air-filled balloon vs a water-filled balloon) all objects accelerate toward the Earth at the same rate. Isaac Newton's law of Universal Gravitation (1687) was a good approximation of the behaviour of gravitation. Our present-day understanding of gravitation stems from Einstein's General Theory of Relativity of 1915, a more accurate (especially for cosmological masses and distances) description of gravitation in terms of the geometry of spacetime.

Merging general relativity and quantum mechanics (or quantum field theory) into a more general theory of quantum gravity is an area of active research. It is hypothesized that gravitation is mediated by a massless spin-2 particle called the graviton.

Although general relativity has been experimentally confirmed (at least for weak fields) on all but the smallest scales, there are rival theories of gravitation. Those taken seriously by the physics community all reduce to general relativity in some limit, and the focus of observational work is to establish limitations on what deviations from general relativity are possible.

Proposed extra dimensions could explain why the gravity force is so weak.

Electroweak interaction

Electromagnetism and weak interaction appear to be very different at everyday low energies. They can be modelled using two different theories. However, above unification energy, on the order of 100 GeV, they would merge into a single electroweak force.

Electroweak theory is very important for modern cosmology, particularly on how the universe evolved. This is because shortly after the Big Bang, the temperature was approximately above 10¹⁵ K, the electromagnetic force and the weak force were merged into a combined electroweak force.

For contributions to the unification of the weak and electromagnetic interaction between elementary particles, Abdus Salam, Sheldon Glashow and Steven Weinberg were awarded the Nobel Prize in Physics in 1979.

Electromagnetism

Electromagnetism is the force that acts between electrically charged particles. This phenomenon includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other. 

Electromagnetism has infinite range like gravity, but is vastly stronger than it, and therefore describes a number of macroscopic phenomena of everyday experience such as friction, rainbows, lightning, and all human-made devices using electric current, such as television, lasers, and computers. Electromagnetism fundamentally determines all macroscopic, and many atomic levels, properties of the chemical elements, including all chemical bonding. 

In a four kilogram (~1 gallon) jug of water there are 

${\displaystyle 4000\ {\mbox{g}}\,H_{2}O\cdot {\frac {1\ {\mbox{mol}}\,H_{2}O}{18\ {\mbox{g}}\,H_{2}O}}\cdot {\frac {10\ {\mbox{mol}}\,e^{-}}{1\ {\mbox{mol}}\,H_{2}O}}\cdot {\frac {96,000\ {\mbox{C}}\,}{1\ {\mbox{mol}}\,e^{-}}}=2.1\times 10^{8}C\ \,\ }$

of total electron charge. Thus, if we place two such jugs a meter apart, the electrons in one of the jugs repel those in the other jug with a force of 

${\displaystyle {1 \over 4\pi \varepsilon _{0}}{\frac {(2.1\times 10^{8}C)^{2}}{(1m)^{2}}}=4.1\times 10^{26}N.}$

This force is larger than the planet Earth would weigh if weighed on another Earth. The atomic nuclei in one jug also repel those in the other with the same force. However, these repulsive forces are canceled by the attraction of the electrons in jug A with the nuclei in jug B and the attraction of the nuclei in jug A with the electrons in jug B, resulting in no net force. Electromagnetic forces are tremendously stronger than gravity but cancel out so that for large bodies gravity dominates.

Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 19th century James Clerk Maxwell discovered that electricity and magnetism are two aspects of the same fundamental interaction. By 1864, Maxwell's equations had rigorously quantified this unified interaction. Maxwell's theory, restated using vector calculus, is the classical theory of electromagnetism, suitable for most technological purposes. 

The constant speed of light in a vacuum (customarily described with a lowercase letter "c") can be derived from Maxwell's equations, which are consistent with the theory of special relativity. Einstein's 1905 theory of special relativity, however, which flows from the observation that the speed of light is constant no matter how fast the observer is moving, showed that the theoretical result implied by Maxwell's equations has profound implications far beyond electromagnetism on the very nature of time and space.

In another work that departed from classical electro-magnetism, Einstein also explained the photoelectric effect by utilizing Max Planck's discovery that light was transmitted in 'quanta' of specific energy content based on the frequency, which we now call photons. Starting around 1927, Paul Dirac combined quantum mechanics with the relativistic theory of electromagnetism. Further work in the 1940s, by Richard Feynman, Freeman Dyson, Julian Schwinger, and Sin-Itiro Tomonaga, completed this theory, which is now called quantum electrodynamics, the revised theory of electromagnetism. Quantum electrodynamics and quantum mechanics provide a theoretical basis for electromagnetic behavior such as quantum tunneling, in which a certain percentage of electrically charged particles move in ways that would be impossible under the classical electromagnetic theory, that is necessary for everyday electronic devices such as transistors to function.

Weak interaction

The weak interaction or weak nuclear force is responsible for some nuclear phenomena such as beta decay. Electromagnetism and the weak force are now understood to be two aspects of a unified electroweak interaction — this discovery was the first step toward the unified theory known as the Standard Model. In the theory of the electroweak interaction, the carriers of the weak force are the massive gauge bosons called the W and Z bosons. The weak interaction is the only known interaction which does not conserve parity; it is left-right asymmetric. The weak interaction even violates CP symmetry but does conserve CPT.

Strong interaction

The strong interaction, or strong nuclear force, is the most complicated interaction, mainly because of the way it varies with distance. At distances greater than 10 femtometers, the strong force is practically unobservable. Moreover, it holds only inside the atomic nucleus.

After the nucleus was discovered in 1908, it was clear that a new force, today known as the nuclear force, was needed to overcome the electrostatic repulsion, a manifestation of electromagnetism, of the positively charged protons. Otherwise, the nucleus could not exist. Moreover, the force had to be strong enough to squeeze the protons into a volume whose diameter is about 10⁻¹⁵ m, much smaller than that of the entire atom. From the short range of this force, Hideki Yukawa predicted that it was associated with a massive particle, whose mass is approximately 100 MeV.

The 1947 discovery of the pion ushered in the modern era of particle physics. Hundreds of hadrons were discovered from the 1940s to 1960s, and an extremely complicated theory of hadrons as strongly interacting particles was developed. Most notably:

• The pions were understood to be oscillations of vacuum condensates;
• Jun John Sakurai proposed the rho and omega vector bosons to be force carrying particles for approximate symmetries of isospin and hypercharge;
• Geoffrey Chew, Edward K. Burdett and Steven Frautschi grouped the heavier hadrons into families that could be understood as vibrational and rotational excitations of strings.

While each of these approaches offered deep insights, no approach led directly to a fundamental theory. 

Murray Gell-Mann along with George Zweig first proposed fractionally charged quarks in 1961. Throughout the 1960s, different authors considered theories similar to the modern fundamental theory of quantum chromodynamics (QCD) as simple models for the interactions of quarks. The first to hypothesize the gluons of QCD were Moo-Young Han and Yoichiro Nambu, who introduced the quark color charge and hypothesized that it might be associated with a force-carrying field. At that time, however, it was difficult to see how such a model could permanently confine quarks. Han and Nambu also assigned each quark color an integer electrical charge, so that the quarks were fractionally charged only on average, and they did not expect the quarks in their model to be permanently confined. 

In 1971, Murray Gell-Mann and Harald Fritzsch proposed that the Han/Nambu color gauge field was the correct theory of the short-distance interactions of fractionally charged quarks. A little later, David Gross, Frank Wilczek, and David Politzer discovered that this theory had the property of asymptotic freedom, allowing them to make contact with experimental evidence. They concluded that QCD was the complete theory of the strong interactions, correct at all distance scales. The discovery of asymptotic freedom led most physicists to accept QCD since it became clear that even the long-distance properties of the strong interactions could be consistent with experiment if the quarks are permanently confined. 

Assuming that quarks are confined, Mikhail Shifman, Arkady Vainshtein and Valentine Zakharov were able to compute the properties of many low-lying hadrons directly from QCD, with only a few extra parameters to describe the vacuum. In 1980, Kenneth G. Wilson published computer calculations based on the first principles of QCD, establishing, to a level of confidence tantamount to certainty, that QCD will confine quarks. Since then, QCD has been the established theory of the strong interactions. 

QCD is a theory of fractionally charged quarks interacting by means of 8 bosonic particles called gluons. The gluons interact with each other, not just with the quarks, and at long distances the lines of force collimate into strings. In this way, the mathematical theory of QCD not only explains how quarks interact over short distances but also the string-like behavior, discovered by Chew and Frautschi, which they manifest over longer distances. 

Beyond the Standard Model

Numerous theoretical efforts have been made to systematize the existing four fundamental interactions on the model of electroweak unification.

Grand Unified Theories (GUTs) are proposals to show that the three fundamental interactions described by the Standard Model are all different manifestations of a single interaction with symmetries that break down and create separate interactions below some extremely high level of energy. GUTs are also expected to predict some of the relationships between constants of nature that the Standard Model treats as unrelated, as well as predicting gauge coupling unification for the relative strengths of the electromagnetic, weak, and strong forces (this was, for example, verified at the Large Electron–Positron Collider in 1991 for supersymmetric theories).

Theories of everything, which integrate GUTs with a quantum gravity theory face a greater barrier, because no quantum gravity theories, which include string theory, loop quantum gravity, and twistor theory, have secured wide acceptance. Some theories look for a graviton to complete the Standard Model list of force-carrying particles, while others, like loop quantum gravity, emphasize the possibility that time-space itself may have a quantum aspect to it.

Some theories beyond the Standard Model include a hypothetical fifth force, and the search for such a force is an ongoing line of experimental research in physics. In supersymmetric theories, there are particles that acquire their masses only through supersymmetry breaking effects and these particles, known as moduli can mediate new forces. Another reason to look for new forces is the discovery that the expansion of the universe is accelerating (also known as dark energy), giving rise to a need to explain a nonzero cosmological constant, and possibly to other modifications of general relativity. Fifth forces have also been suggested to explain phenomena such as CP violations, dark matter, and dark flow.

Debunked: the number of phytoplankton in the oceans have decreased by 40% - out of date research from 2010

Robert Walker, BSc (1st Class), MHum, York Uni, Postgrad Study at Wolfson College, Oxford

https://www.quora.com/q/duzzmyeobxjljrpq/Debunked-the-number-of-phytoplankton-in-the-oceans-have-decreased-by-40-out-of-date-research-from-2010?fbclid=IwAR1qcJ0wRLahDTVd5QtlTceXttg09jVBtkw5YyzfNig60t2Az1_u_L3t7D0

Short summary: This is out of date research. If there is a decrease it is by a much smaller amount, and it may be an increase. There is no effect on the oxygen we breathe as we have enough for thousands of years. The plankton do however seem to be decreasing somewhat in tropical regions and increasing in polar regions, on the whole.

The main question is about what it does to carbon sequestration as a third of our CO2 emissions are absorbed by the sea. As of a review in 2018 it was impossible to know if the amount of CO2 sequestered will increase or decrease in a warming world due to the complexity of the problem.

The original 40% decrease was really a change of colour rather than a decrease in the numbers. In a warmer ocean then the phytoplankton need less chlorophyll because they spend more time near the surface. That’s because a warmer ocean has less mixing of surface layers. Taking account of that reduces the decrease to a sixth of that figure, but then they also were confused by natural variability.

I looked at the latest high level review from 2018 that I could find. In their surey of the literature they were not able to decid whether numbers overall are increasing or decreasing. They did however find good evidence of an increase in polar regions and a decrease in tropical regions and some temperate regions.

If you are worried about running out of oxygen, please check my article:

• We will NOT run out of oxygen to breathe, even if we cut down all the forests and the ocean plankton disappear - they are not the lungs of the planet in any literal sense

IN DETAIL

Phytoplankton refer to any of the microscopic organisms that use light for photosynthesis in the sea.

To find out more: What are Phytoplankton? and Phytoplankton - Wikipedia

70 to 80% of our oxygen comes from green algae The Most Important Organism? | Ecology Global Network - and they also play an important role sequestering carbon dioxide. Marine sinks take up up to a third of the anthropogenic emissions, similar in effect to terrestrial ecosystems. This is a result of the combined effect of the solubility of CO2 in the oceans and the biological pump which pumps the CO2 into the deap sea as the dead plankton sink to the bottom.

See: Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate

Incidentally, whales also help with CO2 sequestration. When they die their bodies fall to the bottom carrying all that carbon with them. Also phytoplankton feed on their feces and this helps encourage phytoplankton to grow.

• Whales and Climate Change: Our Gentle Giants are Natural CO2 Regulators

The study I’m debunking, from 2010, used chlorophyll directly to estimate phytoplankton abundance came to the dramatic conclusion that the oceans had lost 40 per cent of their phytoplankton since the 1950s.

However a later study found that global warming leads to less mixing of surface layers, so that surface plankton get more sunlight and need less chlorophyll. The 40% decrease was over estimated about six-fold.

The warming has winners and losers, the increased CO2 as well. Higher acidity is bad for many, but good for some types. Also, the decreased mixing at the poles can mean phytoplankton there stay at the surface longer in the low ight conditions.

• Ocean’s hidden green plankton revealed by fixing glitch in model

Then a later review in 2016 found that these studies had a question mark too as they had been confused by natural variability of the oceans.

"Some analyses of satellite data have revealed large-scale declines in productivity from 1998 to the early 2000s (Gregg et al. 2005, Behrenfeld et al. 2006), with the proposed mechanism being increased stratification caused by climate warming. This mechanism remains under debate (Lozier et al. 2011, Behrenfeld et al. 2016). Ocean biogeochemical models indicate that the trends observed to date show decadal variability and cannot be attributed to global climate change(Henson et al. 2010). Projections of the future impacts of climate warming on ocean productivity generally suggest reduced subtropical and increased high-latitude productivity (Sarmiento et al.2004, Bopp et al. 2013)."

Natural Variability andAnthropogenic Trends in the Ocean Carbon Sink

In that quote, Behrenfeld et al. 2016 is the New Scientist paper.

Their future projection is reduced productivity in subtropical regions, and increased levels at high latitudes.

A 2019 study using foraminifera finds that the average community of plankton has shifted 602 km poleward since pre-industrial times. However the amount of displacement varies between 45 and 2,557 km depending on the amount of the sea surface temperature change.

2018 REVIEW

There are many other changes. A 2018 review of the literature concluded that the strength of the biological pump is likely to change, but that it is difficult to predict the direction of the change, whether more or less will be sequestered as the oceans warm.

• Elevated CO2 and light levels stimulate larger organisms like diatons increasing the amount of CO2 removed by biology,
• Warmer oceans and depleted nutrients favour smaller organisms such as the cyanobacteria, decreasing the amount of CO2 removed by biology,

They concluded:

“This makes it difficult to currently predict whether the biological pump will strengthen orweaken in the next 100 years”

They go on to say that to add to the difficulty of predicting it, then the temperature, light, nutrient availability and the carbonate system will vary in different regions, and may work together to create conditions more beneficial or more hostile to phytoplankton.

This means they have to study the effects of multiple stressors working together. This vastly increases the complexity of the problem.

Another issue is the timescale. Most laboratory studies look at effects of acidification of the oceans over timescales too short for the organisms to adapt through evolution, but they would do this rapidly in the sea (short lives, much larger population and longer timescale).

Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate

So, there are winners and losers. But even if we destroyed all phytoplankton in some unimaginable eco-catastrophe we'd still be able to breath the air due to the oxygen that is still in it, leaving centuries for the Earth to recover and start creating oxygen again.

Even if impossibly plant life worldwide somehow stopped producing oxygen and the phytoplankton too, and animals continued to breathe it, we have so much in the atmosphere, even taking account of processes that remove it, that we would not run out of oxygen for thousands of years.

This is one of the sections of my article:

• We will NOT run out of oxygen to breathe, even if we cut down all the forests and the ocean plankton disappear - they are not the lungs of the planet in any literal sense

---

SEVEN TIPS FOR DEALING WITH DOOMSDAY FEARS

If you are scared: Seven tips for dealing with doomsday fears which also talks about health professionals and how they can help.

If in the middle of a panic attack, see

• Robert Walker's post in Debunking Doomsday
• Tips from CBT - might help some of you to deal with doomsday anxieties
• STOPP skill

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• Search Doomsday Debunked (Facebook)
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Tip, bookmark those links to search for debunks more easily. Here is a screenshot of my bookmarks

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There are many others in the group who are available to support scared people via PM and who can also debunk fake Doomsday “news” for you if you get scared of a story and are not sure if it is true. See our debunkers list

If you are suicidal don’t forget there’s always help a phone call away with the List of suicide crisis lines - Wikipedia

Virtual particle (updated)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Virtual_particle

 

In physics, a virtual particle is a transient quantum fluctuation that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the uncertainty principle. The concept of virtual particles arises in perturbation theory of quantum field theory where interactions between ordinary particles are described in terms of exchanges of virtual particles. A process involving virtual particles can be described by a schematic representation known as a Feynman diagram, in which virtual particles are represented by internal lines.

Virtual particles do not necessarily carry the same mass as the corresponding real particle, although they always conserve energy and momentum. The longer the virtual particle exists, the closer its characteristics come to those of ordinary particles. They are important in the physics of many processes, including particle scattering and Casimir forces. In quantum field theory, even classical forces—such as the electromagnetic repulsion or attraction between two charges—can be thought of as due to the exchange of many virtual photons between the charges. Virtual photons are the exchange particle for the electromagnetic interaction.

The term is somewhat loose and vaguely defined, in that it refers to the view that the world is made up of "real particles": it is not; rather, "real particles" are better understood to be excitations of the underlying quantum fields. Virtual particles are also excitations of the underlying fields, but are "temporary" in the sense that they appear in calculations of interactions, but never as asymptotic states or indices to the scattering matrix. The accuracy and use of virtual particles in calculations is firmly established, but as they cannot be detected in experiments, deciding how to precisely describe them is a topic of debate.

Properties

The concept of virtual particles arises in the perturbation theory of quantum field theory, an approximation scheme in which interactions (in essence, forces) between actual particles are calculated in terms of exchanges of virtual particles. Such calculations are often performed using schematic representations known as Feynman diagrams, in which virtual particles appear as internal lines. By expressing the interaction in terms of the exchange of a virtual particle with four-momentum q, where q is given by the difference between the four-momenta of the particles entering and leaving the interaction vertex, both momentum and energy are conserved at the interaction vertices of the Feynman diagram.

A virtual particle does not precisely obey the energy–momentum relation m²c⁴ = E² − p²c². Its kinetic energy may not have the usual relationship to velocity–indeed, it can be negative. This is expressed by the phrase off mass shell. The probability amplitude for a virtual particle to exist tends to be canceled out by destructive interference over longer distances and times. As a consequence, a real photon is massless and thus has only two polarization states, whereas a virtual one, being effectively massive, has three polarization states.

Quantum tunnelling may be considered a manifestation of virtual particle exchanges. The range of forces carried by virtual particles is limited by the uncertainty principle, which regards energy and time as conjugate variables; thus, virtual particles of larger mass have more limited range.

Written in the usual mathematical notations, in the equations of physics, there is no mark of the distinction between virtual and actual particles. The amplitude that a virtual particle exists interferes with the amplitude for its non-existence, whereas for an actual particle the cases of existence and non-existence cease to be coherent with each other and do not interfere any more. In the quantum field theory view, actual particles are viewed as being detectable excitations of underlying quantum fields. Virtual particles are also viewed as excitations of the underlying fields, but appear only as forces, not as detectable particles. They are "temporary" in the sense that they appear in calculations, but are not detected as single particles. Thus, in mathematical terms, they never appear as indices to the scattering matrix, which is to say, they never appear as the observable inputs and outputs of the physical process being modelled.

There are two principal ways in which the notion of virtual particles appears in modern physics. They appear as intermediate terms in Feynman diagrams; that is, as terms in a perturbative calculation. They also appear as an infinite set of states to be summed or integrated over in the calculation of a semi-non-perturbative effect. In the latter case, it is sometimes said that virtual particles contribute to a mechanism that mediates the effect, or that the effect occurs through the virtual particles. 

Manifestations

There are many observable physical phenomena that arise in interactions involving virtual particles. For bosonic particles that exhibit rest mass when they are free and actual, virtual interactions are characterized by the relatively short range of the force interaction produced by particle exchange. Examples of such short-range interactions are the strong and weak forces, and their associated field bosons. 

For the gravitational and electromagnetic forces, the zero rest-mass of the associated boson particle permits long-range forces to be mediated by virtual particles. However, in the case of photons, power and information transfer by virtual particles is a relatively short-range phenomenon (existing only within a few wavelengths of the field-disturbance, which carries information or transferred power), as for example seen in the characteristically short range of inductive and capacitative effects in the near field zone of coils and antennas.

Some field interactions which may be seen in terms of virtual particles are:

• The Coulomb force (static electric force) between electric charges. It is caused by the exchange of virtual photons. In symmetric 3-dimensional space this exchange results in the inverse square law for electric force. Since the photon has no mass, the coulomb potential has an infinite range.
• The magnetic field between magnetic dipoles. It is caused by the exchange of virtual photons. In symmetric 3-dimensional space, this exchange results in the inverse cube law for magnetic force. Since the photon has no mass, the magnetic potential has an infinite range.
• Electromagnetic induction. This phenomenon transfers energy to and from a magnetic coil via a changing (electro)magnetic field.
• The strong nuclear force between quarks is the result of interaction of virtual gluons. The residual of this force outside of quark triplets (neutron and proton) holds neutrons and protons together in nuclei, and is due to virtual mesons such as the pi meson and rho meson.
• The weak nuclear force—it is the result of exchange by virtual W and Z bosons.
• The spontaneous emission of a photon during the decay of an excited atom or excited nucleus; such a decay is prohibited by ordinary quantum mechanics and requires the quantization of the electromagnetic field for its explanation.
• The Casimir effect, where the ground state of the quantized electromagnetic field causes attraction between a pair of electrically neutral metal plates.
• The van der Waals force, which is partly due to the Casimir effect between two atoms.
• Vacuum polarization, which involves pair production or the decay of the vacuum, which is the spontaneous production of particle-antiparticle pairs (such as electron-positron).
• Lamb shift of positions of atomic levels.
• The Impedance of free space, which defines the ratio between the electric field strength | E | and the magnetic field strength | H |: Z₀ = | E | / | H |.
• Much of the so-called near-field of radio antennas, where the magnetic and electric effects of the changing current in the antenna wire and the charge effects of the wire's capacitive charge may be (and usually are) important contributors to the total EM field close to the source, but both of which effects are dipole effects that decay with increasing distance from the antenna much more quickly than do the influence of "conventional" electromagnetic waves that are "far" from the source. ["Far" in terms of ratio of antenna length or diameter, to wavelength]. These far-field waves, for which E is (in the limit of long distance) equal to cB, are composed of actual photons. Actual and virtual photons are mixed near an antenna, with the virtual photons responsible only for the "extra" magnetic-inductive and transient electric-dipole effects, which cause any imbalance between E and cB. As distance from the antenna grows, the near-field effects (as dipole fields) die out more quickly, and only the "radiative" effects that are due to actual photons remain as important effects. Although virtual effects extend to infinity, they drop off in field strength as 1/r² rather than the field of EM waves composed of actual photons, which drop 1/r (the powers, respectively, decrease as 1/r⁴ and 1/r²). See near and far field for a more detailed discussion. See near field communication for practical communications applications of near fields.

Most of these have analogous effects in solid-state physics; indeed, one can often gain a better intuitive understanding by examining these cases. In semiconductors, the roles of electrons, positrons and photons in field theory are replaced by electrons in the conduction band, holes in the valence band, and phonons or vibrations of the crystal lattice. A virtual particle is in a virtual state where the probability amplitude is not conserved. Examples of macroscopic virtual phonons, photons, and electrons in the case of the tunneling process were presented by Günter Nimtz and Alfons A. Stahlhofen.

Feynman diagrams

One particle exchange scattering diagram

 

The calculation of scattering amplitudes in theoretical particle physics requires the use of some rather large and complicated integrals over a large number of variables. These integrals do, however, have a regular structure, and may be represented as Feynman diagrams. The appeal of the Feynman diagrams is strong, as it allows for a simple visual presentation of what would otherwise be a rather arcane and abstract formula. In particular, part of the appeal is that the outgoing legs of a Feynman diagram can be associated with actual, on-shell particles. Thus, it is natural to associate the other lines in the diagram with particles as well, called the "virtual particles". In mathematical terms, they correspond to the propagators appearing in the diagram.

In the adjacent image, the solid lines correspond to actual particles (of momentum p₁ and so on), while the dotted line corresponds to a virtual particle carrying momentum k. For example, if the solid lines were to correspond to electrons interacting by means of the electromagnetic interaction, the dotted line would correspond to the exchange of a virtual photon. In the case of interacting nucleons, the dotted line would be a virtual pion. In the case of quarks interacting by means of the strong force, the dotted line would be a virtual gluon, and so on.

One-loop diagram with fermion propagator

 

Virtual particles may be mesons or vector bosons, as in the example above; they may also be fermions. However, in order to preserve quantum numbers, most simple diagrams involving fermion exchange are prohibited. The image to the right shows an allowed diagram, a one-loop diagram. The solid lines correspond to a fermion propagator, the wavy lines to bosons. 

Vacuums

In formal terms, a particle is considered to be an eigenstate of the particle number operator a^†a, where a is the particle annihilation operator and a^† the particle creation operator (sometimes collectively called ladder operators). In many cases, the particle number operator does not commute with the Hamiltonian for the system. This implies the number of particles in an area of space is not a well-defined quantity but, like other quantum observables, is represented by a probability distribution. Since these particles do not have a permanent existence, they are called virtual particles or vacuum fluctuations of vacuum energy. In a certain sense, they can be understood to be a manifestation of the time-energy uncertainty principle in a vacuum.

An important example of the "presence" of virtual particles in a vacuum is the Casimir effect. Here, the explanation of the effect requires that the total energy of all of the virtual particles in a vacuum can be added together. Thus, although the virtual particles themselves are not directly observable in the laboratory, they do leave an observable effect: Their zero-point energy results in forces acting on suitably arranged metal plates or dielectrics. On the other hand, the Casimir effect can be interpreted as the relativistic van der Waals force.

Pair production

Virtual particles are often popularly described as coming in pairs, a particle and antiparticle which can be of any kind. These pairs exist for an extremely short time, and then mutually annihilate, or in some cases, the pair may be boosted apart using external energy so that they avoid annihilation and become actual particles, as described below. 

This may occur in one of two ways. In an accelerating frame of reference, the virtual particles may appear to be actual to the accelerating observer; this is known as the Unruh effect. In short, the vacuum of a stationary frame appears, to the accelerated observer, to be a warm gas of actual particles in thermodynamic equilibrium.

Another example is pair production in very strong electric fields, sometimes called vacuum decay. If, for example, a pair of atomic nuclei are merged to very briefly form a nucleus with a charge greater than about 140, (that is, larger than about the inverse of the fine structure constant, which is a dimensionless quantity), the strength of the electric field will be such that it will be energetically favorable to create positron-electron pairs out of the vacuum or Dirac sea, with the electron attracted to the nucleus to annihilate the positive charge. This pair-creation amplitude was first calculated by Julian Schwinger in 1951.

Compared to actual particles

As a consequence of quantum mechanical uncertainty, any object or process that exists for a limited time or in a limited volume cannot have a precisely defined energy or momentum. For this reason, virtual particles – which exist only temporarily as they are exchanged between ordinary particles – do not typically obey the mass-shell relation; the longer a virtual particle exists, the more the energy and momentum approach the mass-shell relation.

The lifetime of real particles is typically vastly longer than the lifetime of the virtual particles. Electromagnetic radiation consist of real photons which may travel light years between the emitter and absorber, but (Coulombic) electrostatic attraction and repulsion is a relatively short-range force that is a consequence of the exchange of virtual photons.

Passive infrared sensor

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Passive_infrared_sensor

 

Typical residential/commercial PIR-based motion detector (PID).

 

A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications. PIR sensors detect general movement, but do not give information on who or what moved. For that purpose, an active IR sensor is required. 

PIR sensors are commonly called simply "PIR", or sometimes "PID", for "passive infrared detector". The term passive refers to the fact that PIR devices do not radiate energy for detection purposes. They work entirely by detecting infrared radiation (radiant heat) emitted by or reflected from objects. 

Operating principles

All objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation isn't visible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose. 

Construction

Infrared radiation enters through the front of the sensor, known as the 'sensor face'. At the core of a PIR sensor is a solid state sensor or set of sensors, made from pyroelectric materials—materials which generate energy when exposed to heat. Typically, the sensors are approximately 1/4 inch square (40 mm²), and take the form of a thin film. Materials commonly used in PIR sensors include gallium nitride (GaN), caesium nitrate (CsNO₃), polyvinyl fluorides, derivatives of phenylpyridine, and cobalt phthalocyanine. The sensor is often manufactured as part of an integrated circuit.

PIR-based motion detector

A PIR motion detector used to control an outdoor, automatic light.

 

An indoor light switch equipped with PIR-based occupancy sensor

 

A PIR-based motion detector is used to sense movement of people, animals, or other objects. They are commonly used in burglar alarms and automatically-activated lighting systems. 

Operation

A PIR sensor can detect changes in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of the objects in front of the sensor. When an object, such as a person, passes in front of the background, such as a wall, the temperature at that point in the sensor's field of view will rise from room temperature to body temperature, and then back again. The sensor converts the resulting change in the incoming infrared radiation into a change in the output voltage, and this triggers the detection. Objects of similar temperature but different surface characteristics may also have a different infrared emission pattern, and thus moving them with respect to the background may trigger the detector as well.

PIRs come in many configurations for a wide variety of applications. The most common models have numerous Fresnel lenses or mirror segments, an effective range of about 10 meters (30 feet), and a field of view less than 180°. Models with wider fields of view, including 360°, are available, typically designed to mount on a ceiling. Some larger PIRs are made with single segment mirrors and can sense changes in infrared energy over 30 meters (100 feet) from the PIR. There are also PIRs designed with reversible orientation mirrors which allow either broad coverage (110° wide) or very narrow "curtain" coverage, or with individually selectable segments to "shape" the coverage. 

Differential detection

Pairs of sensor elements may be wired as opposite inputs to a differential amplifier. In such a configuration, the PIR measurements cancel each other so that the average temperature of the field of view is removed from the electrical signal; an increase of IR energy across the entire sensor is self-cancelling and will not trigger the device. This allows the device to resist false indications of change in the event of being exposed to brief flashes of light or field-wide illumination. (Continuous high energy exposure may still be able to saturate the sensor materials and render the sensor unable to register further information.) At the same time, this differential arrangement minimizes common-mode interference, allowing the device to resist triggering due to nearby electric fields. However, a differential pair of sensors cannot measure temperature in this configuration, and therefore is only useful for motion detection. 

Practical Implementation

When a PIR sensor is configured in a differential mode, it specifically becomes applicable as a motion detector device. In this mode when a movement is detected within the "line of sight" of the sensor, a pair of complementary pulses are processed at the output pin of the sensor. In order to implement this output signal for a practical triggering of a load such as a relay or a data logger, or an alarm, the differential signal is rectified using a bridge rectifier and fed to a transistorized relay driver circuit. The contacts of this relay close and open in response to the signals from the PIR, activating the attached load across its contacts, acknowledging the detection of a person within the predetermined restricted area. 

Product design

The PIR sensor is typically mounted on a printed circuit board containing the necessary electronics required to interpret the signals from the sensor itself. The complete assembly is usually contained within a housing, mounted in a location where the sensor can cover the area to be monitored. 

PIR motion sensor design

 

The housing will usually have a plastic "window" through which the infrared energy can enter. Despite often being only translucent to visible light, infrared energy is able to reach the sensor through the window because the plastic used is transparent to infrared radiation. The plastic window reduces the chance of foreign objects (dust, insects, etc.) from obscuring the sensor's field of view, damaging the mechanism, and/or causing false alarms. The window may be used as a filter, to limit the wavelengths to 8-14 micrometres, which is closest to the infrared radiation emitted by humans. It may also serve as a focusing mechanism; see below. 

Focusing

Different mechanisms can be used to focus the distant infrared energy onto the sensor surface. 

Lenses

The plastic window covering may have multiple facets molded into it, to focus the infrared energy onto the sensor. Each individual facet is a Fresnel lens.

• Multi-Fresnel lens type of PIR
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  PIR motion detector housing with cylindrical faceted window. The animation highlights individual facets, each of which is a Fresnel lens, focusing light on the sensor element underneath.
  
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  PIR front cover only (electronics removed), with point light source behind, to show individual lenses.
  
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  PIR with front cover removed, showing location of pyroelectric sensor (green arrow).
  
  

Mirrors

Some PIRs are manufactured with internal, segmented parabolic mirrors to focus the infrared energy. Where mirrors are used, the plastic window cover generally has no Fresnel lenses molded into it.

• Segmented mirror type of PIR
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  Typical residential/commercial PID using an internal segmented mirror for focusing.
  
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  Cover removed. Segmented mirror at bottom with PC (printed circuit) board above it.
  
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  Printed circuit board removed to show segmented mirror.
  
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  Segmented parabolic mirror removed from housing.
  
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  Rear of circuit board which faces mirror when in place. Pyroelectric sensor indicated by green arrow.
  
  

Beam pattern

As a result of the focussing, the detector view is actually a beam pattern. Under certain angles (zones), the PIR sensor receives almost no radiation energy and under other angles the PIR receives concentrated amounts of infrared energy. This separation helps the motion detector to discriminate between field-wide illumination and moving objects.

When a person walks from one angle (beam) to another, the detector will only intermittently see the moving person. This results in a rapidly changing sensor signal which is used by the electronics to trigger an alarm or to turn on lighting. A slowly changing signal will be ignored by the electronics.

The number, shape, distribution and sensitivity of these zones are determined by the lens and/or mirror. Manufacturers do their best to create the optimal sensitivity beam pattern for each application.

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  Motion detector with superimposed beam pattern. The length of the beams is a measure of the detectors sensitivity in that direction.
  
  

Automatic lighting applications

When used as part of a lighting system, the electronics in the PIR typically control an integral relay capable of switching mains voltage. This means the PIR can be set up to turn on lights that are connected to the PIR when movement is detected. This is most commonly used in outdoor scenarios either to deter criminals (security lighting) or for practical uses like the front door light turning on so you can find your keys in the dark. Additional uses can be in public toilets, walk-in pantries, hallways or anywhere that automatic control of lights is useful. This can provide energy savings as the lights are only turned on when they are needed and there is no reliance on users remembering to turn the lights off when they leave the area. 

Security applications

When used as part of a security system, the electronics in the PIR typically control a small relay. This relay completes the circuit across a pair of electrical contacts connected to a detection input zone of the burglar alarm control panel. The system is usually designed such that if no motion is being detected, the relay contact is closed—a 'normally closed' (NC) relay. If motion is detected, the relay will open the circuit, triggering the alarm; or, if a wire is disconnected, the alarm will also operate.

Placement

Manufacturers recommend careful placement of their products to prevent false alarms (i.e., any detection not caused by an intruder).

They suggest mounting the PIRs in such a way that the PIR cannot "see" out of a window. Although the wavelength of infrared radiation to which the chips are sensitive does not penetrate glass very well, a strong infrared source (such as from a vehicle headlight or sunlight) can overload the sensor and cause a false alarm. A person moving on the other side of the glass would not be "seen" by the PID. That may be good for a window facing a public sidewalk, or bad for a window in an interior partition.

It is also recommended that the PIR not be placed in such a position that an HVAC vent would blow hot or cold air onto the surface of the plastic which covers the housing's window. Although air has very low emissivity (emits very small amounts of infrared energy), the air blowing on the plastic window cover could change the plastic's temperature enough to trigger a false alarm.

Sensors are also often designed to "ignore" domestic pets, such as dogs or cats, by setting a higher sensitivity threshold, or by ensuring that the floor of the room remains out of focus.

Since PIR sensors have ranges of up to 10 meters (30 feet), a single detector placed near the entrance is typically all that is necessary for rooms with only a single entrance. PIR-based security systems are also viable in outdoor security and motion-sensitive lighting; one advantage is their low power draw, which allows them to be solar-powered.

PIR remote-based thermometer

Designs have been implemented in which a PIR circuit measures the temperature of a remote object. In such a circuit, a non-differential PIR output is used. The output signal is evaluated according to a calibration for the IR spectrum of a specific type of matter to be observed. By this means, relatively accurate and precise temperature measurements may be obtained remotely. Without calibration to the type of material being observed, a PIR thermometer device is able to measure changes in IR emission which correspond directly to temperature changes, but the actual temperature values cannot be calculated.