Physical constant

From Wikipedia, the free encyclopedia

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

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, which has a fixed numerical value, but does not directly involve any physical measurement.

There are many physical constants in science, some of the most widely recognized being the speed of light in a vacuum c, the gravitational constant G, the Planck constant h, the electric constant ε₀, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed for any object and its dimension is length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.

The term fundamental physical constant is sometimes used to refer to universal-but-dimensioned physical constants such as those mentioned above. Increasingly, however, physicists only use fundamental physical constant for dimensionless physical constants, such as the fine-structure constant α.

Physical constant, as discussed here, should not be confused with other quantities called "constants", which are assumed to be constant in a given context without being fundamental, such as the "time constant" characteristic of a given system, or material constants (e.g., Madelung constant, electrical resistivity, and heat capacity).

Since May 2019, all of the SI base units have been defined in terms of physical constants. As a result, five constants: the speed of light in vacuum, c; the Planck constant, h; the elementary charge, e; the Avogadro constant, N_A; and the Boltzmann constant, k_B, have known exact numerical values when expressed in SI units. The first three of these constants are fundamental constants, whereas N_A and k_B are of a technical nature only: they do not describe any property of the universe, but instead only give a proportionality factor for defining the units used with large numbers of atomic-scale entities.

Choice of units

Whereas the physical quantity indicated by a physical constant does not depend on the unit system used to express the quantity, the numerical values of dimensional physical constants do depend on choice of unit system. The term "physical constant" refers to the physical quantity, and not to the numerical value within any given system of units. For example, the speed of light is defined as having the numerical value of 299792458 when expressed in the SI unit metres per second, and as having the numerical value of 1 when expressed in the natural units Planck length per Planck time. While its numerical value can be defined at will by the choice of units, the speed of light itself is a single physical constant.

Any ratio between physical constants of the same dimensions results in a dimensionless physical constant, for example, the proton-to-electron mass ratio. Any relation between physical quantities can be expressed as a relation between dimensionless ratios via a process known as nondimensionalisation.

The term of "fundamental physical constant" is reserved for physical quantities which, according to the current state of knowledge, are regarded as immutable and as non-derivable from more fundamental principles. Notable examples are the speed of light c, and the gravitational constant G.

The fine-structure constant α is the best known dimensionless fundamental physical constant. It is the value of the elementary charge squared expressed in Planck units. This value has become a standard example when discussing the derivability or non-derivability of physical constants. Introduced by Arnold Sommerfeld, its value as determined at the time was consistent with 1/137. This motivated Arthur Eddington (1929) to construct an argument why its value might be 1/137 precisely, which related to the Eddington number, his estimate of the number of protons in the Universe. By the 1940s, it became clear that the value of the fine-structure constant deviates significantly from the precise value of 1/137, refuting Eddington's argument. A theoretical derivation of the fine structure constant, based on unification in a pre-spacetime, pre-quantum theory in eight octonionic dimensions, has recently been given by Singh.

With the development of quantum chemistry in the 20th century, however, a vast number of previously inexplicable dimensionless physical constants were successfully computed from theory. In light of that, some theoretical physicists still hope for continued progress in explaining the values of other dimensionless physical constants.

It is known that the Universe would be very different if these constants took values significantly different from those we observe. For example, a few percent change in the value of the fine structure constant would be enough to eliminate stars like our Sun. This has prompted attempts at anthropic explanations of the values of some of the dimensionless fundamental physical constants.

Natural units

Main article: Natural units

It is possible to combine dimensional universal physical constants to define fixed quantities of any desired dimension, and this property has been used to construct various systems of natural units of measurement. Depending on the choice and arrangement of constants used, the resulting natural units may be convenient to an area of study. For example, Planck units, constructed from c, G, ħ, and k_B give conveniently sized measurement units for use in studies of quantum gravity, and Hartree atomic units, constructed from ħ, m_e, e and 4πε₀ give convenient units in atomic physics. The choice of constants used leads to widely varying quantities.

Number of fundamental constants

The number of fundamental physical constants depends on the physical theory accepted as "fundamental". Currently, this is the theory of general relativity for gravitation and the Standard Model for electromagnetic, weak and strong nuclear interactions and the matter fields. Between them, these theories account for a total of 19 independent fundamental constants. There is, however, no single "correct" way of enumerating them, as it is a matter of arbitrary choice which quantities are considered "fundamental" and which as "derived". Uzan (2011) lists 22 "unknown constants" in the fundamental theories, which give rise to 19 "unknown dimensionless parameters", as follows:

• the gravitational constant G,
• the speed of light c,
• the Planck constant h,
• the 9 Yukawa couplings for the quarks and leptons (equivalent to specifying the rest mass of these elementary particles),
• 2 parameters of the Higgs field potential,
• 4 parameters for the quark mixing matrix,
• 3 coupling constants for the gauge groups SU(3) × SU(2) × U(1) (or equivalently, two coupling constants and the Weinberg angle),
• a phase for the QCD vacuum.

The number of 19 independent fundamental physical constants is subject to change under possible extensions of the Standard Model, notably by the introduction of neutrino mass (equivalent to seven additional constants, i.e. 3 Yukawa couplings and 4 lepton mixing parameters).

The discovery of variability in any of these constants would be equivalent to the discovery of "new physics".

The question as to which constants are "fundamental" is neither straightforward nor meaningless, but a question of interpretation of the physical theory regarded as fundamental; as pointed out by Lévy-Leblond 1977, not all physical constants are of the same importance, with some having a deeper role than others. Lévy-Leblond 1977 proposed a classification schemes of three types of constants:

• A: physical properties of particular objects
• B: characteristic of a class of physical phenomena
• C: universal constants

The same physical constant may move from one category to another as the understanding of its role deepens; this has notably happened to the speed of light, which was a class A constant (characteristic of light) when it was first measured, but became a class B constant (characteristic of electromagnetic phenomena) with the development of classical electromagnetism, and finally a class C constant with the discovery of special relativity.

Tests on time-independence

Main article: Time-variation of fundamental constants

By definition, fundamental physical constants are subject to measurement, so that their being constant (independent on both the time and position of the performance of the measurement) is necessarily an experimental result and subject to verification.

Paul Dirac in 1937 speculated that physical constants such as the gravitational constant or the fine-structure constant might be subject to change over time in proportion of the age of the universe. Experiments can in principle only put an upper bound on the relative change per year. For the fine-structure constant, this upper bound is comparatively low, at roughly 10⁻¹⁷ per year (as of 2008).

The gravitational constant is much more difficult to measure with precision, and conflicting measurements in the 2000s have inspired the controversial suggestions of a periodic variation of its value in a 2015 paper. However, while its value is not known to great precision, the possibility of observing type Ia supernovae which happened in the universe's remote past, paired with the assumption that the physics involved in these events is universal, allows for an upper bound of less than 10⁻¹⁰ per year for the gravitational constant over the last nine billion years.

Similarly, an upper bound of the change in the proton-to-electron mass ratio has been placed at 10⁻⁷ over a period of 7 billion years (or 10⁻¹⁶ per year) in a 2012 study based on the observation of methanol in a distant galaxy.

It is problematic to discuss the proposed rate of change (or lack thereof) of a single dimensional physical constant in isolation. The reason for this is that the choice of units is arbitrary, making the question of whether a constant is undergoing change an artefact of the choice (and definition) of the units.

For example, in SI units, the speed of light was given a defined value in 1983. Thus, it was meaningful to experimentally measure the speed of light in SI units prior to 1983, but it is not so now. Similarly, with effect from May 2019, the Planck constant has a defined value, such that all SI base units are now defined in terms of fundamental physical constants. With this change, the international prototype of the kilogram is being retired as the last physical object used in the definition of any SI unit.

Tests on the immutability of physical constants look at dimensionless quantities, i.e. ratios between quantities of like dimensions, in order to escape this problem. Changes in physical constants are not meaningful if they result in an observationally indistinguishable universe. For example, a "change" in the speed of light c would be meaningless if accompanied by a corresponding change in the elementary charge e so that the ratio e²/(4πε₀ħc) (the fine-structure constant) remained unchanged.

Fine-tuned universe

Main articles: Fine-tuned universe and Anthropic principle

Some physicists have explored the notion that if the dimensionless physical constants had sufficiently different values, our Universe would be so radically different that intelligent life would probably not have emerged, and that our Universe therefore seems to be fine-tuned for intelligent life. However, the phase space of the possible constants and their values is unknowable, so any conclusions drawn from such arguments are unsupported. The anthropic principle states a logical truism: the fact of our existence as intelligent beings who can measure physical constants requires those constants to be such that beings like us can exist. There are a variety of interpretations of the constants' values, including that of a divine creator (the apparent fine-tuning is actual and intentional), or that ours is one universe of many in a multiverse (e.g. the many-worlds interpretation of quantum mechanics), or even that, if information is an innate property of the universe and logically inseparable from consciousness, a universe without the capacity for conscious beings cannot exist.

The fundamental constants and quantities of nature have been discovered to be fine-tuned to such an extraordinarily narrow range that if it were not, the origin and evolution of conscious life in the universe would not be permitted.

Table of physical constants

Main article: List of physical constants

The table below lists some frequently used constants and their CODATA recommended values. For a more extended list, refer to List of physical constants.

Quantity	Symbol	Value	Relative standard uncertainty
elementary charge	${\displaystyle e}$	1.602176634×10−19 C	Exact by definition
Newtonian constant of gravitation	${\displaystyle G}$	6.67430(15)×10−11 m3⋅kg−1⋅s−2	2.2×10−5
Planck constant	${\displaystyle h}$	6.62607015×10−34 J⋅Hz−1	Exact by definition
speed of light in vacuum	${\displaystyle c}$	299792458 m⋅s−1	Exact by definition
vacuum electric permittivity	${\displaystyle \varepsilon _{0}=1/\mu _{0}c^{2}}$	8.8541878128(13)×10−12 F⋅m−1	1.5×10−10
vacuum magnetic permeability	${\displaystyle \mu _{0}}$	1.25663706212(19)×10−6 N⋅A−2	1.5×10−10
electron mass	${\displaystyle m_{\mathrm {e} }}$	9.1093837015(28)×10−31 kg	3.0×10−10
fine-structure constant	${\displaystyle \alpha =e^{2}/2\varepsilon _{0}hc}$	7.2973525693(11)×10−3	1.5×10−10
Josephson constant	${\displaystyle K_{\mathrm {J} }=2e/h}$	483597.8484...×109 Hz⋅V−1	0
Rydberg constant	${\displaystyle R_{\infty }=\alpha ^{2}m_{\mathrm {e} }c/2h}$	10973731.568160(21) m−1	1.9×10−12
von Klitzing constant	${\displaystyle R_{\mathrm {K} }=h/e^{2}}$	25812.80745... Ω	0

Toxicology

From Wikipedia, the free encyclopedia

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

 

A toxicologist working in a lab (United States, 2008)

Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating exposures to toxins and toxicants. The relationship between dose and its effects on the exposed organism is of high significance in toxicology. Factors that influence chemical toxicity include the dosage, duration of exposure (whether it is acute or chronic), route of exposure, species, age, sex, and environment. Toxicologists are experts on poisons and poisoning. There is a movement for evidence-based toxicology as part of the larger movement towards evidence-based practices. Toxicology is currently contributing to the field of cancer research, since some toxins can be used as drugs for killing tumor cells. One prime example of this is ribosome-inactivating proteins, tested in the treatment of leukemia.

The word toxicology (/ˌtɒksɪˈkɒlədʒi/) is a neoclassical compound from New Latin, first attested circa 1799, from the combining forms toxico- + -logy, which in turn come from the Ancient Greek words τοξικός toxikos, "poisonous", and λόγος logos, "subject matter").

History

Lithograph of Mathieu Orfila

Dioscorides, a Greek physician in the court of the Roman emperor Nero, made the first attempt to classify plants according to their toxic and therapeutic effect. A work attributed to the 10th century author Ibn Wahshiyya called the Book on Poisons describes various toxic substances and poisonous recipes that can be made using magic. A 14th century Kannada poetic work attributed to the Jain prince Mangarasa, Khagendra Mani Darpana, describes several poisonous plants.

Theophrastus Phillipus Auroleus Bombastus von Hohenheim (1493–1541) (also referred to as Paracelsus, from his belief that his studies were above or beyond the work of Celsus – a Roman physician from the first century) is considered "the father" of toxicology. He is credited with the classic toxicology maxim, "Alle Dinge sind Gift und nichts ist ohne Gift; allein die Dosis macht, dass ein Ding kein Gift ist." which translates as, "All things are poisonous and nothing is without poison; only the dose makes a thing not poisonous." This is often condensed to: "The dose makes the poison" or in Latin "Sola dosis facit venenum".

Mathieu Orfila is also considered the modern father of toxicology, having given the subject its first formal treatment in 1813 in his Traité des poisons, also called Toxicologie générale.

In 1850, Jean Stas became the first person to successfully isolate plant poisons from human tissue. This allowed him to identify the use of nicotine as a poison in the Bocarmé murder case, providing the evidence needed to convict the Belgian Count Hippolyte Visart de Bocarmé of killing his brother-in-law.

Basic principles

The goal of toxicity assessment is to identify adverse effects of a substance. Adverse effects depend on two main factors: i) routes of exposure (oral, inhalation, or dermal) and ii) dose (duration and concentration of exposure). To explore dose, substances are tested in both acute and chronic models. Generally, different sets of experiments are conducted to determine whether a substance causes cancer and to examine other forms of toxicity.

Factors that influence chemical toxicity:

• Dosage
  • Both large single exposures (acute) and continuous small exposures (chronic) are studied.
• Route of exposure
  • Ingestion, inhalation or skin absorption
• Other factors
  • Species
  • Age
  • Sex
  • Health
  • Environment
  • Individual characteristics

The discipline of evidence-based toxicology strives to transparently, consistently, and objectively assess available scientific evidence in order to answer questions in toxicology, the study of the adverse effects of chemical, physical, or biological agents on living organisms and the environment, including the prevention and amelioration of such effects. Evidence-based toxicology has the potential to address concerns in the toxicological community about the limitations of current approaches to assessing the state of the science. These include concerns related to transparency in decision making, synthesis of different types of evidence, and the assessment of bias and credibility. Evidence-based toxicology has its roots in the larger movement towards evidence-based practices.

Testing methods

Toxicity experiments may be conducted in vivo (using the whole animal) or in vitro (testing on isolated cells or tissues), or in silico (in a computer simulation).

Non-human animals

The classic experimental tool of toxicology is testing on non-human animals. Example of model organisms are Galleria mellonella, which can replace small mammals, and Zebrafish, which allow for the study of toxicology in a lower order vertebrate in vivo. As of 2014, such animal testing provides information that is not available by other means about how substances function in a living organism. The use of non-human animals for toxicology testing is opposed by some organisations for reasons of animal welfare, and it has been restricted or banned under some circumstances in certain regions, such as the testing of cosmetics in the European Union.

Alternative testing methods

While testing in animal models remains as a method of estimating human effects, there are both ethical and technical concerns with animal testing.

Since the late 1950s, the field of toxicology has sought to reduce or eliminate animal testing under the rubric of "Three Rs" – reduce the number of experiments with animals to the minimum necessary; refine experiments to cause less suffering, and replace in vivo experiments with other types, or use more simple forms of life when possible.

Computer modeling is an example of alternative testing methods; using computer models of chemicals and proteins, structure-activity relationships can be determined, and chemical structures that are likely to bind to, and interfere with, proteins with essential functions, can be identified. This work requires expert knowledge in molecular modeling and statistics together with expert judgment in chemistry, biology and toxicology.

In 2007 the American NGO National Academy of Sciences published a report called "Toxicity Testing in the 21st Century: A Vision and a Strategy" which opened with a statement: "Change often involves a pivotal event that builds on previous history and opens the door to a new era. Pivotal events in science include the discovery of penicillin, the elucidation of the DNA double helix, and the development of computers. ... Toxicity testing is approaching such a scientific pivot point. It is poised to take advantage of the revolutions in biology and biotechnology. Advances in toxicogenomics, bioinformatics, systems biology, epigenetics, and computational toxicology could transform toxicity testing from a system based on whole-animal testing to one founded primarily on in vitro methods that evaluate changes in biologic processes using cells, cell lines, or cellular components, preferably of human origin." As of 2014 that vision was still unrealized.

The United States Environmental Protection Agency studied 1,065 chemical and drug substances in their ToxCast program (part of the CompTox Chemicals Dashboard) using in silica modelling and a human pluripotent stem cell-based assay to predict in vivo developmental intoxicants based on changes in cellular metabolism following chemical exposure. Major findings from the analysis of this ToxCast_STM dataset published in 2020 include: (1) 19% of 1065 chemicals yielded a prediction of developmental toxicity, (2) assay performance reached 79%–82% accuracy with high specificity (> 84%) but modest sensitivity (< 67%) when compared with in vivo animal models of human prenatal developmental toxicity, (3) sensitivity improved as more stringent weights of evidence requirements were applied to the animal studies, and (4) statistical analysis of the most potent chemical hits on specific biochemical targets in ToxCast revealed positive and negative associations with the STM response, providing insights into the mechanistic underpinnings of the targeted endpoint and its biological domain.

In some cases shifts away from animal studies have been mandated by law or regulation; the European Union (EU) prohibited use of animal testing for cosmetics in 2013.

Dose response complexities

Most chemicals display a classic dose response curve – at a low dose (below a threshold), no effect is observed. Some show a phenomenon known as sufficient challenge – a small exposure produces animals that "grow more rapidly, have better general appearance and coat quality, have fewer tumors, and live longer than the control animals". A few chemicals have no well-defined safe level of exposure. These are treated with special care. Some chemicals are subject to bioaccumulation as they are stored in rather than being excreted from the body; these also receive special consideration.

Several measures are commonly used to describe toxic dosages according to the degree of effect on an organism or a population, and some are specifically defined by various laws or organizational usage. These include:

• LD50 = Median lethal dose, a dose that will kill 50% of an exposed population
• NOEL = No-Observed-Effect-Level, the highest dose known to show no effect
• NOAEL = No-Observed-Adverse-Effect-Level, the highest dose known to show no adverse effects
• PEL = Permissible Exposure Limit, the highest concentration permitted under US OSHA regulations
• STEL = Short-Term Exposure Limit, the highest concentration permitted for short periods of time, in general 15–30 minutes
• TWA = Time-Weighted Average, the average amount of an agent's concentration over a specified period of time, usually 8 hours
• TTC = Threshold of Toxicological Concern have been established for the constituents of tobacco smoke

Types

"Clinical toxicology" redirects here. For the journal, see Clinical Toxicology.

Medical toxicology is the discipline that requires physician status (MD or DO degree plus specialty education and experience).

Clinical toxicology is the discipline that can be practiced not only by physicians but also other health professionals with a master's degree in clinical toxicology: physician extenders (physician assistants, nurse practitioners), nurses, pharmacists, and allied health professionals.

Forensic toxicology is the discipline that makes use of toxicology and other disciplines such as analytical chemistry, pharmacology and clinical chemistry to aid medical or legal investigation of death, poisoning, and drug use. The primary concern for forensic toxicology is not the legal outcome of the toxicological investigation or the technology utilized, but rather the obtainment and interpretation of results.

Computational toxicology is a discipline that develops mathematical and computer-based models to better understand and predict adverse health effects caused by chemicals, such as environmental pollutants and pharmaceuticals. Within the Toxicology in the 21st Century project, the best predictive models were identified to be Deep Neural Networks, Random Forest, and Support Vector Machines, which can reach the performance of in vitro experiments.

Occupational toxicology is the application of toxicology to chemical hazards in the workplace.

Toxicology as a profession

A toxicologist is a scientist or medical personnel who specializes in the study of symptoms, mechanisms, treatments and detection of venoms and toxins; especially the poisoning of people.

Requirements

To work as a toxicologist one should obtain a degree in toxicology or a related degree like biology, chemistry, pharmacology or biochemistry. Bachelor's degree programs in toxicology cover the chemical makeup of toxins and their effects on biochemistry, physiology and ecology. After introductory life science courses are complete, students typically enroll in labs and apply toxicology principles to research and other studies. Advanced students delve into specific sectors, like the pharmaceutical industry or law enforcement, which apply methods of toxicology in their work. The Society of Toxicology (SOT) recommends that undergraduates in postsecondary schools that do not offer a bachelor's degree in toxicology consider attaining a degree in biology or chemistry. Additionally, the SOT advises aspiring toxicologists to take statistics and mathematics courses, as well as gain laboratory experience through lab courses, student research projects and internships.

Duties

Toxicologists perform many different duties including research in the academic, nonprofit and industrial fields, product safety evaluation, consulting, public service and legal regulation. In order to research and assess the effects of chemicals, toxicologists perform carefully designed studies and experiments. These experiments help identify the specific amount of a chemical that may cause harm and potential risks of being near or using products that contain certain chemicals. Research projects may range from assessing the effects of toxic pollutants on the environment to evaluating how the human immune system responds to chemical compounds within pharmaceutical drugs. While the basic duties of toxicologists are to determine the effects of chemicals on organisms and their surroundings, specific job duties may vary based on industry and employment. For example, forensic toxicologists may look for toxic substances in a crime scene, whereas aquatic toxicologists may analyze the toxicity level of water bodies.

Compensation

The salary for jobs in toxicology is dependent on several factors, including level of schooling, specialization, experience. The U.S. Bureau of Labor Statistics (BLS) notes that jobs for biological scientists, which generally include toxicologists, were expected to increase by 21% between 2008 and 2018. The BLS notes that this increase could be due to research and development growth in biotechnology, as well as budget increases for basic and medical research in biological science.

Reparations for slavery in the United States

From Wikipedia, the free encyclopedia

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

 

Reparations for slavery is the application of the concept of reparations to victims of slavery or their descendants. There are concepts for reparations in legal philosophy and reparations in transitional justice. In the US, reparations for slavery have been both given by legal ruling in court and/or given voluntarily (without court rulings) by individuals and institutions.

The first recorded case of reparations for slavery in the United States was to former slave Belinda Royall in 1783, in the form of a pension, and since then reparations continue to be proposed and/or given in a variety of forms. The 1865 Special Field Orders No. 15 ("Forty acres and a mule") is the most well known attempt to help newly freed slaves integrate into society and accumulate wealth. However, President Andrew Johnson reversed this order, giving the land back to its former Confederate owners.

Reparations have been a recurring idea in the politics of the United States, most recently in the 2020 Democratic Party presidential primaries. The call for reparations has intensified in 2020, amidst the protests against police brutality and the COVID-19 pandemic, which both kill Black Americans disproportionately. Calls for reparations for racism and discrimination in the US are often made by black communities and authors alongside calls for reparations for slavery. The idea of reparations remains highly controversial, due to questions of how they would be given, how much would be given, who would pay them, and who would receive them.

Forms of reparations which have been proposed or given in the United States by city, county, state, and national governments or private institutions include: individual monetary payments, settlements, scholarships, waiving of fees, and systemic initiatives to offset injustices, land-based compensation related to independence, apologies and acknowledgements of the injustices, token measures (such as naming a building after someone), and the removal of monuments and streets named to slave owners and defenders of slavery.

Since further injustices and discrimination have continued since slavery was outlawed in the US, some black communities and civil rights organizations have called for reparations for those injustices as well as for reparations directly related to slavery. Some suggest that the U.S. prison system, starting with the convict lease system and continuing through the present-day government-owned corporation Federal Prison Industries (UNICOR), is a modern form of legal slavery that still primarily and disproportionately affects black populations and other minorities via the war on drugs and what has been criticized as a school-to-prison pipeline.

U.S. historical context

In colonial times

The debate on reparations reaches as far back as the eighteenth century. Quakers, who were some of the first abolitionists in the United States, almost unanimously insisted that freed slaves were entitled to compensation from their former owners. If an owner repented of his sin of owning a chattel slave, he needs to atone for it by making amends. Quakers cited the book of Deuteronomy, in which owners were exhorted to share their goods with former slaves.

During the Revolutionary War, Warner Mifflin advocated for restitution for freed ex-slaves as early as 1778, in the form of cash payments, land, and shared crop arrangements. Gary B. Nash writes that, "he may fairly be called the father of American reparationism".

Before the Civil War

Well before slavery was abolished nationally in 1865, abolitionists presented suggestions on what could or should be done to compensate the enslaved workers after their liberation.

Early in 1859, in a book dedicated to "Old Hero" John Brown, James Redpath declared himself a "reparationist", and implies that in his view, the lands of the Confederacy should be given to the ex-slaves. He also quotes an earlier poem, by William North, that refers to "the course of reparation".

Later that year, after Brown's execution, Redpath reported in the first biography of Brown that he "was not merely an emancipationist, but a reparationist. He believed, not only that the crime of slavery should be abolished, but that reparation should be made for the wrongs that had been done to the slave. What he believed, he practiced. On this occasion [Missouri raid, 1859], after telling the slaves that they were free, he asked them how much their services had been worth, and—having been answered—proceeded to take property to the amount thus due to the negroes."

Calls for permanent confiscation and redistribution of plantation lands had already been made by Representatives George W. Julian and Thaddeus Stevens, both of the Radical Republican faction.

The Reconstruction period

The arguments surrounding reparations are based on the formal discussion about many different reparations, and actual land reparations received by African Americans which were later taken away. In 1865, after the Confederate States of America were defeated in the American Civil War, General William Tecumseh Sherman issued Special Field Orders, No. 15 to both "assure the harmony of action in the area of operations" and to solve problems caused by the masses of freed slaves, a temporary plan granting each freed family forty acres of tillable land in the sea islands and around Charleston, South Carolina for the exclusive use of black people who had been enslaved. The army also had a number of unneeded mules which were given to freed slaves. Around 40,000 freed slaves were settled on 400,000 acres (1,600 km²) in Georgia and South Carolina. However, President Andrew Johnson reversed the order after Lincoln was assassinated, the land was returned to its previous owners, and the blacks were forced to leave. In 1867, Thaddeus Stevens sponsored a bill for the redistribution of land to African Americans, but it did not pass.

Reconstruction came to an end in 1877 without the issue of reparations having been addressed. Thereafter, a deliberate movement of segregation and oppression arose in southern states. Jim Crow laws passed in some southeastern states to reinforce the existing inequality that slavery had produced. In addition white extremist organizations such as the Ku Klux Klan engaged in a massive campaign of terrorism throughout the Southeast in order to keep African Americans in their prescribed social place. For decades this assumed inequality and injustice was ruled on in court decisions and debated in public discourse.

In one anomalous case, a former slave named Henrietta Wood successfully sued for compensation after having been kidnapped from the free state of Ohio and sold into slavery in Mississippi. After the American Civil War, she was freed and returned to Cincinnati, where she won her case in federal court in 1878, receiving $2,500 in damages. Though the verdict was a national news story, it did not prompt any trend toward additional similar cases.

2020

The topic became a prominent theme during the 2020 Democratic Party presidential primaries as concerns surrounding race were heightened due to current events. It was further amplified due to the African American people dying prematurely and disproportionately due to the COVID-19 pandemic. Ongoing systemic racism and police brutality also sparked outrage across the country, notably the killing of Breonna Taylor, a 26-year-old African-American emergency medical technician, fatally shot by Louisville Metro Police Department in her home; the murder of Ahmaud Arbery, shot while out for a run by three white men in Georgia; and the murder of George Floyd, a Black American killed during an arrest by Minneapolis police after allegedly passing a counterfeit $20 bill, that sparked the nationwide George Floyd protests.

Candidates that endorsed the idea included:

• Andrew Yang said that he supports H.R. 40, the Commission to Study and Develop Reparation Proposals for African-Americans Act, sponsored by Rep. Sheila Jackson Lee, while speaking on the Karen Hunter show.
• Marianne Williamson detailed a plan for reparations in an interview for Ebony Magazine.
• Senators Elizabeth Warren and Cory Booker have both indicated some level of support for reparations, according to NPR.
• Tulsi Gabbard is a cosponsor of H.R. 40, the only piece of legislation in Congress to study and develop reparations proposals and Bernie Sanders is a co-sponsor for the Senate version of the bill.

Kamala Harris declared in April 2019 she supports reparations.

Beto O'Rourke is "open to considering some form of reparations," according to U.S. News & World Report.

Tom Steyer in the 2020 Democratic Primaries Debate in South Carolina voiced his support for reparations.

Proposals for reparations

United States government

Some proposals have called for direct payments from the U.S. government. Various estimates have been given if such payments were to be made. Harper's Magazine estimated that the total of reparations due was about "$97 trillion, based on 222,505,049 hours of forced labor between 1619 and 1865, regardless the United States wasn't a recognized independent country until after the Revolutionary War in 1787, compounded at 6% interest through 1993". Should all or part of this amount be paid to the descendants of slaves in the United States, the current U.S. government would only pay a fraction of that cost, since it has been in existence only since 1789.

The Rev. M.J. Divine, better known as Father Divine, was one of the earliest leaders to argue clearly for "retroactive compensation", and the message was spread via International Peace Mission publications. On July 28, 1951, Father Divine issued a "peace stamp" bearing the text: "Peace! All nations and peoples who have suppressed and oppressed the under-privileged, they will be obliged to pay the African slaves and their descendants for all uncompensated servitude and for all unjust compensation, whereby they have been unjustly deprived of compensation on the account of previous condition of servitude and the present condition of servitude. This is to be accomplished in the defense of all other under-privileged subjects and must be paid retroactive up-to-date".

At the first National Reparations Convention in Chicago in 2001, a proposal by Howshua Amariel, a Chicago social activist, would require the federal government to make reparations to proven descendants of slaves. In addition, Amariel stated "For those blacks who wish to remain in America, they should receive reparations in the form of free education, free medical, free legal and free financial aid for 50 years with no taxes levied," and "For those desiring to leave America, every black person would receive a million dollars or more, backed by gold, in reparation." At the convention Amariel's proposal received approval from the 100 or so participants. Nevertheless, the question of who would receive such payments, who should pay them and in what amount, has remained highly controversial, since the United States Census does not track descent from slaves or slave owners and relies on self-reported racial categories.

On July 30, 2008, the United States House of Representatives passed a resolution apologizing for American slavery and subsequent discriminatory laws.

Nine states have officially apologized for their involvement in the enslavement of Africans. Those states are:

• Alabama – April 25, 2007
• Connecticut
• Delaware – February 11, 2016
• Florida – 2008
• Maryland – 2007
• New Jersey – 2008
• North Carolina – 2007
• Tennessee
• Virginia – 2007

Private institutions

Private institutions and corporations were also involved in slavery. On March 8, 2000, Reuters News Service reported that Deadria Farmer-Paellmann, a law school graduate, initiated a one-woman campaign making a historic demand for restitution and apologies from modern companies that played a direct role in enslaving Africans. Aetna Inc. was her first target because of their practice of writing life insurance policies on the lives of enslaved Africans with slave owners as the beneficiaries. In response to Farmer-Paellmann's demand, Aetna Inc. issued a public apology, and the "corporate restitution movement" was born.

By 2002, nine lawsuits were filed around the country coordinated by Farmer-Paellmann and the Restitution Study Group—a New York non-profit. The litigation included 20 plaintiffs, demanding restitution from 20 companies from the banking, insurance, textile, railroad, and tobacco industries. The cases were consolidated under 28 U.S.C. 1407 to multidistrict litigation in the United States District Court for the Northern District of Illinois. The district court dismissed the lawsuits with prejudice, and the claimants appealed to the United States Court of Appeals for the Seventh Circuit.

On December 13, 2006, that court, in an opinion written by Judge Richard Posner, modified the district court's judgment to be a dismissal without prejudice, affirmed the majority of the district court's judgment, and reversed the portion of the district court's judgment dismissing the plaintiffs' consumer protection claims, remanding the case for further proceedings consistent with its opinion. Thus, the plaintiffs may bring the lawsuit again, but must clear considerable procedural and substantive hurdles first:

If one or more of the defendants violated a state law by transporting slaves in 1850, and the plaintiffs can establish standing to sue, prove the violation despite its antiquity, establish that the law was intended to provide a remedy (either directly or by providing the basis for a common law action for conspiracy, conversion, or restitution) to lawfully enslaved persons or their descendants, identify their ancestors, quantify damages incurred, and persuade the court to toll the statute of limitations, there would be no further obstacle to the grant of relief.

In October 2000, California passed the Slavery Era Disclosure Law requiring insurance companies doing business there to report on their role in slavery. The disclosure legislation, introduced by Senator Tom Hayden, is the prototype for similar laws passed in 12 states around the United States.

The NAACP has called for more of such legislation at local and corporate levels. It quotes Dennis C. Hayes, CEO of the NAACP, as saying, "Absolutely, we will be pursuing reparations from companies that have historical ties to slavery and engaging all parties to come to the table." Brown University, whose namesake family was involved in the slave trade, has also established a committee to explore the issue of reparations. In February 2007, Brown University announced a set of responses to its Steering Committee on Slavery and Justice. While in 1995 the Southern Baptist Convention apologized for the "sins" of racism, including slavery.

In December 2005, a boycott was called by a coalition of reparations groups under the sponsorship of the Restitution Study Group. The boycott targets the student loan products of banks deemed complicit in slavery—particularly those identified in the Farmer-Paellmann litigation. As part of the boycott, students are asked to choose from other banks to finance their student loans.

Pro-reparations groups such as The National Coalition of Blacks for Reparations in America advocate for compensation to be in the form of community rehabilitation and not payments to individual descendants.

Black Lives Matter

Many groups under the Black Lives Matter organization have laid out a list of demands, some of which include: reparations, for what they say are past and continuing harms to African-Americans, an end to the death penalty, legislation to acknowledge the effects of slavery, a move to defund the police, as well as investments in education initiatives, mental health services and jobs programs. These calls for reparations have been bolstered amidst the COVID-19 pandemic and the high rates of police brutality against Blacks.

Arguments for reparations

Accumulated wealth

Housing discrimination played a big role in creating the racial wealth gap that exists today. After the Great Migration of southern blacks to Chicago in the 1940s, redlining was used to keep former slaves segregated from whites and to prevent black families from getting a mortgage. Thus they were forced to buy houses on contracts from real estate speculators, which were a scam. Not only did this cause thousands of Black Americans to lose their homes and their money, it also created what is known today as ghettos and prevented Blacks from accumulating wealth. Today, the average white family has roughly 10 times the amount of wealth as the average black family, and white college graduates have over seven times more wealth than Black college graduates.

The wealth of the United States was greatly enhanced by the exploitation of African American slave labor: some argue it is the bedrock for the U.S. economy and capitalism. However, former slaves and their descendants are among the poorest demographic in America. According to this view, reparations would be valuable primarily as a way of correcting modern economic imbalances.

In 2008 the American Humanist Association published an article which argued that if emancipated slaves had been allowed to possess and retain the profits of their labor, their descendants might now control a much larger share of American social and monetary wealth. Not only did the freedmen not receive a share of these profits, but they were stripped of the small amounts of compensation paid to some of them during Reconstruction. Therefore, many scholars and activists call for reparations to eliminate "racial disparities in wealth, income, education, health, sentencing and incarceration, political participation, and subsequent opportunities to engage in American political and social life".

Health care

In 2019, VICE magazine published an article that argued racial health disparities, from slavery through Jim Crow until today, have cost Black Americans a significant amount of money in health care expenses and lost wages, and should be paid back. Ray and Perry state in a Brookings article that the lack of a social safety net and the wealth gap are particularly highlighted during the COVID-19 pandemic. They explain that “disparities in access to health care along with inequities in economic policies combine,” making this inequality a life or death situation for black Americans.

Current discrimination

Many argue that giving reparations for slavery is too complicated, but there is a strong basis for them on the past and current discrimination that blacks in America face. Ta-Nehisi Coates explains it in "The Case for Reparations" article in The Atlantic as "ninety years of Jim Crow, sixty years of separate but equal, and thirty-five years of racist housing policy". The legacy of these policies have kept African Americans from opportunities to build wealth, while slavery "enriched white slave owners and their descendants". Today, the district of North Lawndale in Chicago, where redlining was the strongest, is the poorest neighborhood in the city with an unemployment rate of 18.6% and 42% of residents living below the poverty line.

The discriminatory practices of 1940 through 1970 still reverberate today, as the average White family has roughly ten times the amount of wealth as the average Black family. As Bittker claims in his book The Case for Black Reparations, "as slavery faded into the background, it was succeeded by a caste system embodying white supremacy". Many argue that while reparations may be a first step towards amending the harms caused by slavery, the systemic racism that exists in many institutions will not be fixed as easily. Malcolm X stated: "If you stick a knife in my back nine inches and pull it out six inches, there's no progress. If you pull it all the way out that's not progress. Progress is healing the wound that the blow made."

Precedents

Advocates have used other examples of reparations to argue that victims of institutional slavery should be similarly compensated.

In several cases the federal government has formally apologized to or compensated minority groups for past actions:

• Under the Civil Liberties Act of 1988, signed into law by President Ronald Reagan, the U.S. government apologized for Japanese American internment during World War II and provided reparations of $20,000 to each survivor, to compensate for loss of property and liberty during that period. No compensation was given to the descendants of affected individuals though.
• The Alaska Native Claims Settlement Act transferred land, federal money, and a portion of oil revenues to native Alaskans.
• The Apology Resolution of 1993 apologized for the overthrow of the Kingdom of Hawaii, but gave no compensation.

U.S. state governments have made reparations in some specific circumstances:

• Virginia established a compensation fund for victims of involuntary sterilization in 2015.

Other countries have also opted to pay reparations for past grievances, such as:

• Reparations for the Holocaust, including the Reparations Agreement between Israel and West Germany and various programs under the Conference on Jewish Material Claims Against Germany.

Arguments against reparations

Statute of limitations

Most state and federal laws under which parties can sue for damages have a statute of limitations which sets a deadline for filing; these have all long since passed, which prevents courts from granting relief under existing laws. This has been used effectively in several suits, including In re African American Slave Descendants, which dismissed a high-profile suit against a number of businesses with ties to slavery.

Technical complications

The technical side of reparations is very complex, and could be a reason why they have not yet been implemented. Some argue against the idea of putting a monetary value on the traumas that Black Americans have faced, dubbing it "transactionalism". On the other hand, some dismiss the case for reparations entirely due to practical concerns, such as who would receive these financial payments, why should the current generation pay for wrongs for which they are not responsible, and how much should be paid.

The estimates of the monetary value of stolen slave labor and subsequent discrimination vary “from an outrageously low $3.2 million to $4.7 billion,” and to as much as $12 trillion. This also raises the question of who is responsible for paying. Generally, three actors are agreed upon: federal and state governments, who supported and protected the institution of slavery; private companies that benefited from it; and “rich families that owe a good portion of their wealth to slavery”.

Some claim that closing the wealth gap involves paying descendants of slaves “individual cash payments in the amount that will close the Black-white racial wealth divide”. Another suggestion is for reparations to "come in the form of wealth-building opportunities that address racial disparities in education, housing, and business ownership". For example, in the city of Asheville, North Carolina, reparations have been implemented in the form of "investments in areas where Black residents face disparities". However, the complications that surround this are significant, and others argue that putting the money into communities is not efficient, due to people moving and gentrification.

In his book, Bittker lays out some of the practical and constitutional problems that would likely arise in an attempt to execute a program of reparations to Blacks. Would it be the same payment to every person? Would they have to prove ancestry to an African slave, or would it be any black person who was subject to racism? There are no real answers to these questions, as this is an unprecedented case. Other cases of reparations, such as to the Jewish people who survived the Holocaust or the Native Americans in the United States, are very different in the way that it is much easier to identify the group who should receive them, and the reparations were paid more quickly than in the case of reparations for slavery.

Additional arguments and opinions

Steven Greenhut, the western region director for the R Street Institute, has suggested that reparations would make racism worse.

Republican Senator Mitch McConnell of Kentucky,(who is a descendant of slave owners) while acknowledging that slavery was an "original sin" of the United States, opposes providing reparations because "none of us currently living are responsible."

One publication against reparations is David Horowitz, Uncivil Wars: The Controversy Over Reparations for Slavery (2002). Other works that discuss problems with reparations include John Torpey's Making Whole What Has Been Smashed: On Reparations Politics (2006), Alfred Brophy's Reparations Pro and Con (2006), and Nahshon Perez's Freedom from Past Injustices (Edinburgh University Press, 2012).

Reparations in the U.S. have never gained widespread public support. Often in these conversations, the White reaction is to claim that this is a form of unjustifiable "reverse racism", or that demands for reparations are an example of the "Black refusal to move beyond the memory of slavery". A 2020 poll from The Washington Post showed that "63% of Americans don't think the U.S. should pay reparations to the descendants of slaves". Notably, 82% of Black Americans support reparations, while 75% of White Americans do not. Some arguments also highlight the complications behind reparations, such as "not all Black Americans are descendants of slaves" or that the people alive today are not responsible for the harms of slavery. Others still argue that reparations will do nothing in the face of racism, and that structural and policy changes would be more effective. In the midst of America's current racial reckoning in 2020, these tensions are particularly exposed.

Reparations and COVID-19

The call for reparations has amplified due to the coronavirus pandemic, which has exposed the underbelly of American inequality in many ways, with people of color disproportionately likely to be laid off, to struggle financially, and to die from the virus. For example, 40% of black-owned businesses have closed permanently since March due to the pandemic, compared to 17% of white-owned businesses during the same period. This relates back to the fact that white families have roughly ten times the wealth of black families. This limits black-owned businesses' access to credit and loans, and they do not have the safety net in times of crises that many white-owned businesses do.

In addition, African Americans continue to get infected and die from COVID-19 at rates more than 1.5 times their share of the population. In August 2020, the CDC released data showing that Blacks, Latinos, and American Indians are experiencing hospitalizations at rates 4.5 to 5.5 times higher than non-Hispanic whites, and that African Americans are dying at 2.4 times the white rate.

Legislation and other actions

Federal government

On July 30, 2008, the United States House of Representatives passed a resolution apologizing for American slavery and subsequent discriminatory laws. The Senate has never passed such a resolution.

States

• California – Adopted legislation requiring insurance companies to determine whether they have records going back to when slavery existed in this country and, if so, to provide information on insurance policies held by slaveholders on slaves to the state's insurance department.
• Illinois – Adopted legislation requiring insurance companies to determine whether they have records going back to when slavery existed in this country and, if so, to provide information on insurance policies held by slaveholders on slaves to the state's insurance department.
• Maryland – Adopted legislation requiring insurance companies to determine whether they have records going back to when slavery existed in this country and, if so, to provide information on insurance policies held by slaveholders on slaves to the state's insurance department.
• Iowa: Adopted legislation asking the insurance commissioner to request if insurance companies they have records going back to when slavery existed in this country and, if so, to provide information on insurance policies held by slaveholders on slaves to the state's insurance department.
• Alabama – Apologized for its involvement in the enslavement of Africans on April 25, 2007.
• Connecticut – In 2009 apologized for its involvement in the enslavement of Africans.
• Delaware – Apologized for its involvement in the enslavement of Africans on February 11, 2016.
• Florida – In 2008, apologized for its involvement in the enslavement of Africans in America.
• Maryland – In 2007, apologized for its involvement in the enslavement of Africans in America.
• New Jersey – In 2007, apologized for its involvement in the enslavement of Africans in America.
• North Carolina – In 2007, apologized for its involvement in the enslavement of Africans in America.
• Tennessee – In 2007, the Tennessee House of Representatives voted in unanimous support on a resolution stating that it "regrets" its involvement in the enslavement of Africans. The House had specifically removed any "apology" language from the resolution.
• Virginia – Apologized for its involvement in the enslavement of Africans on February 26, 2007.

Counties

• Buncombe County, North Carolina: On June 16, 2020, in a 7–0 vote, Buncombe County Commissioners decided to remove several Confederate monuments including the Vance Monument which is named after North Carolina Governor Zeb Vance, a slave owner who used convict labor to build the railroad to Western North Carolina. Significant community involvement led to the decision. Leading up to the vote, the board received 549 supporting messages and 19 opposing.

Cities

• Chicago, Illinois: "In 2015, Chicago enacted a reparations ordinance covering hundreds of African Americans tortured by police from the 1970s to the 1990s. The law calls for $5.5 million in financial compensation, as well as hundreds of thousands more for a public memorial, and a range of assistance related to health, education and emotional well-being."
• Evanston, Illinois: "The City Council of Evanston, Illinois, voted to allocate the first $10 million in tax revenue from the sale of recreational marijuana (which became legal in the state on January 1, 2020) to fund reparations initiatives that address the gaps in wealth and opportunity of black residents."
• Asheville, North Carolina: The city council approved reparations on a 7–0 vote on July 14, 2020. "[B]udgetary and programmatic priorities may include but not be limited to increasing minority home ownership and access to other affordable housing, increasing minority business ownership and career opportunities, strategies to grow equity and generational wealth, closing the gaps in health care, education, employment and pay, neighborhood safety and fairness within criminal justice," the resolution reads. The resolution establishes the Community Reparations Commission which will make concrete recommendations for programs and resources allocations to ultimately carry out the reparations. The Asheville City Council also voted unanimously on June 9, 2020, to remove two confederate monuments as a result of demands made by a group called "Black Asheville Demands" and the work of the Racial Justice Coalition with led the push for the effort. The City Council meeting had so much community engagement public comment was extended for an extra hour beyond the normal meeting time.

Organizations and institutions

• Georgetown University: "In 2016 [the university agreed] to give admissions preference to descendants of the 272 slaves[,] formally apologized for its role in slavery [and] [renamed] two buildings on its campus to acknowledge the lives of enslaved people". In April, 2019 students at Georgetown University voted to increase their tuition by $27.20 to benefit the descendants of the 272 slaves sold by the Jesuits who ran the school in 1838. The student-led referendum was non-binding. Later that year, after further pressure and follow up from the Georgetown University Student Association the university eventually moved forward with a similar proposal without the students' covering the cost with a tuition increase.
• Princeton Theological Seminary: In 2019 the Seminary announced a $27 million commitment for various initiatives to recognize how it benefited from black slavery. This is the largest monetary commitment by an educational institution.
• Virginia Theological Seminary: Set aside $1.7 million to pay reparations to descendants of African Americans who were enslaved to work on their campus, first distributed in 2021
• Wachovia: Apologized for its connection to slavery in 2005.
• JP Morgan Chase: Apologized for its connection to slavery in 2005.
• University of Alabama: Apologized for the history of slavery at the university in 2004.