Energy level

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Energy levels for an electron in an atom: ground state and excited states. After absorbing energy, an electron may "jump" from the ground state to a higher energy excited state.

A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels. The term is commonly used for the energy levels of electrons in atoms, ions, or molecules, which are bound by the electric field of the nucleus, but can also refer to energy levels of nuclei or vibrational or rotational energy levels in molecules. The energy spectrum of a system with such discrete energy levels is said to be quantized.

In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on farther and farther from the nucleus. The shells correspond with the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with letters used in the X-ray notation (K, L, M, …).

Each shell can contain only a fixed number of electrons: The first shell can hold up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on. The general formula is that the nth shell can in principle hold up to 2(n²) electrons. Since electrons are electrically attracted to the nucleus, an atom's electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a strict requirement: atoms may have two or even three incomplete outer shells.  For an explanation of why electrons exist in these shells see electron configuration.

If the potential energy is set to zero at infinite distance from the atomic nucleus or molecule, the usual convention, then bound electron states have negative potential energy.

If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the ground state. If it is at a higher energy level, it is said to be excited, or any electrons that have higher energy than the ground state are excited. If more than one quantum mechanical state is at the same energy, the energy levels are "degenerate". They are then called degenerate energy levels.

Explanation

Wavefunctions of a hydrogen atom, showing the probability of finding the electron in the space around the nucleus. Each stationary state defines a specific energy level of the atom.

Quantized energy levels result from the relation between a particle's energy and its wavelength. For a confined particle such as an electron in an atom, the wave function has the form of standing waves. Only stationary states with energies corresponding to integral numbers of wavelengths can exist; for other states the waves interfere destructively, resulting in zero probability density. Elementary examples that show mathematically how energy levels come about are the particle in a box and the quantum harmonic oscillator.

History

The first evidence of quantization in atoms was the observation of spectral lines in light from the sun in the early 1800s by Joseph von Fraunhofer and William Hyde Wollaston. The notion of energy levels was proposed in 1913 by Danish physicist Niels Bohr in the Bohr theory of the atom. The modern quantum mechanical theory giving an explanation of these energy levels in terms of the Schrödinger equation was advanced by Erwin Schrödinger and Werner Heisenberg in 1926.

Atoms

Intrinsic energy levels

In the formulas for energy of electrons at various levels given below in an atom, the zero point for energy is set when the electron in question has completely left the atom, i.e. when the electron's principal quantum number n = ∞. When the electron is bound to the atom in any closer value of n, the electron's energy is lower and is considered negative.

Orbital state energy level: atom/ion with nucleus + one electron

Assume there is one electron in a given atomic orbital in a hydrogen-like atom (ion). The energy of its state is mainly determined by the electrostatic interaction of the (negative) electron with the (positive) nucleus. The energy levels of an electron around a nucleus are given by :

${\displaystyle E_{n}=-hcR_{\infty }{\frac {Z^{2}}{n^{2}}}}$

(typically between 1 eV and 10³ eV), where R_∞ is the Rydberg constant, Z is the atomic number, n is the principal quantum number, h is Planck's constant, and c is the speed of light. For hydrogen-like atoms (ions) only, the Rydberg levels depend only on the principal quantum number n.

This equation is obtained from combining the Rydberg formula for any hydrogen-like element (shown below) with E = h ν = h c / λ assuming that the principal quantum number n above = n₁ in the Rydberg formula and n₂ = ∞ (principal quantum number of the energy level the electron descends from, when emitting a photon). The Rydberg formula was derived from empirical spectroscopic emission data.

${\displaystyle {\frac {1}{\lambda }}=RZ^{2}\left({\frac {1}{n_{1}^{2}}}-{\frac {1}{n_{2}^{2}}}\right)}$

An equivalent formula can be derived quantum mechanically from the time-independent Schrödinger equation with a kinetic energy Hamiltonian operator using a wave function as an eigenfunction to obtain the energy levels as eigenvalues, but the Rydberg constant would be replaced by other fundamental physics constants.

Electron-electron interactions in atoms

If there is more than one electron around the atom, electron-electron-interactions raise the energy level. These interactions are often neglected if the spatial overlap of the electron wavefunctions is low.

For multi-electron atoms, interactions between electrons cause the preceding equation to be no longer accurate as stated simply with Z as the atomic number. A simple (though not complete) way to understand this is as a shielding effect, where the outer electrons see an effective nucleus of reduced charge, since the inner electrons are bound tightly to the nucleus and partially cancel its charge. This leads to an approximate correction where Z is substituted with an effective nuclear charge symbolized as Z_eff that depends strongly on the principal quantum number.

${\displaystyle E_{n,l}=-hcR_{\infty }{\frac {{Z_{\rm {eff}}}^{2}}{n^{2}}}\ }$

In such cases, the orbital types (determined by the azimuthal quantum number ℓ) as well as their levels within the molecule affect Z_eff and therefore also affect the various atomic electron energy levels. The Aufbau principle of filling an atom with electrons for an electron configuration takes these differing energy levels into account. For filling an atom with electrons in the ground state, the lowest energy levels are filled first and consistent with the Pauli exclusion principle, the Aufbau principle, and Hund's rule.

Fine structure splitting

Fine structure arises from relativistic kinetic energy corrections, spin–orbit coupling (an electrodynamic interaction between the electron's spin and motion and the nucleus's electric field) and the Darwin term (contact term interaction of s shell^[which?] electrons inside the nucleus). These affect the levels by a typical order of magnitude of 10⁻³ eV.

Hyperfine structure

This even finer structure is due to electron–nucleus spin–spin interaction, resulting in a typical change in the energy levels by a typical order of magnitude of 10⁻⁴ eV.

Energy levels due to external fields

Zeeman effect

There is an interaction energy associated with the magnetic dipole moment, μ_L, arising from the electronic orbital angular momentum, L, given by

${\displaystyle U=-{\boldsymbol {\mu }}_{L}\cdot \mathbf {B} }$

with

${\displaystyle -{\boldsymbol {\mu }}_{L}={\dfrac {e\hbar }{2m}}\mathbf {L} =\mu _{B}\mathbf {L} }$.

Additionally taking into account the magnetic momentum arising from the electron spin.

Due to relativistic effects (Dirac equation), there is a magnetic momentum, μ_S, arising from the electron spin

${\displaystyle -{\boldsymbol {\mu }}_{S}=-\mu _{B}g_{S}\mathbf {S} }$,

with g_S the electron-spin g-factor (about 2), resulting in a total magnetic moment, μ,

${\displaystyle {\boldsymbol {\mu }}={\boldsymbol {\mu }}_{L}+{\boldsymbol {\mu }}_{S}}$.

The interaction energy therefore becomes

${\displaystyle U_{B}=-{\boldsymbol {\mu }}\cdot \mathbf {B} =\mu _{B}B(M_{L}+g_{S}M_{S})}$.

Stark effect

Molecules

Chemical bonds between atoms in a molecule form because they make the situation more stable for the involved atoms, which generally means the sum energy level for the involved atoms in the molecule is lower than if the atoms were not so bonded. As separate atoms approach each other to covalently bond, their orbitals affect each other's energy levels to form bonding and antibonding molecular orbitals. The energy level of the bonding orbitals is lower, and the energy level of the antibonding orbitals is higher. For the bond in the molecule to be stable, the covalent bonding electrons occupy the lower energy bonding orbital, which may be signified by such symbols as σ or π depending on the situation. Corresponding anti-bonding orbitals can be signified by adding an asterisk to get σ* or π* orbitals. A non-bonding orbital in a molecule is an orbital with electrons in outer shells which do not participate in bonding and its energy level is the same as that of the constituent atom. Such orbitals can be designated as n orbitals. The electrons in an n orbital are typically lone pairs. ^[3] In polyatomic molecules, different vibrational and rotational energy levels are also involved.

Roughly speaking, a molecular energy state, i.e. an eigenstate of the molecular Hamiltonian, is the sum of the electronic, vibrational, rotational, nuclear, and translational components, such that:

${\displaystyle E=E_{\rm {electronic}}+E_{\rm {vibrational}}+E_{\rm {rotational}}+E_{\rm {nuclear}}+E_{\rm {translational}}\,}$

where E_electronic is an eigenvalue of the electronic molecular Hamiltonian (the value of the potential energy surface) at the equilibrium geometry of the molecule.

The molecular energy levels are labelled by the molecular term symbols.

The specific energies of these components vary with the specific energy state and the substance.

In molecular physics and quantum chemistry, an energy level is a quantized energy of a bound quantum mechanical state.

Energy level diagrams

There are various types of energy level diagrams for bonds between atoms in a molecule.

Examples

Molecular orbital diagrams, Jablonski diagrams, and Franck–Condon diagrams.

Energy level transitions

An increase in energy level from E₁ to E₂ resulting from absorption of a photon represented by the red squiggly arrow, and whose energy is h ν

 

A decrease in energy level from E₂ to E₁ resulting in emission of a photon represented by the red squiggly arrow, and whose energy is h ν

Electrons in atoms and molecules can change (make transitions in) energy levels by emitting or absorbing a photon (of electromagnetic radiation), whose energy must be exactly equal to the energy difference between the two levels. Electrons can also be completely removed from a chemical species such as an atom, molecule, or ion. Complete removal of an electron from an atom can be a form of ionization, which is effectively moving the electron out to an orbital with an infinite principal quantum number, in effect so far away so as to have practically no more effect on the remaining atom (ion). For various types of atoms, there are 1st, 2nd, 3rd, etc. ionization energies for removing the 1st, then the 2nd, then the 3rd, etc. of the highest energy electrons, respectively, from the atom originally in the ground state. Energy in corresponding opposite quantities can also be released, sometimes in the form of photon energy, when electrons are added to positively charged ions or sometimes atoms. Molecules can also undergo transitions in their vibrational or rotational energy levels. Energy level transitions can also be nonradiative, meaning emission or absorption of a photon is not involved.

If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the ground state. If it is at a higher energy level, it is said to be excited, or any electrons that have higher energy than the ground state are excited. Such a species can be excited to a higher energy level by absorbing a photon whose energy is equal to the energy difference between the levels. Conversely, an excited species can go to a lower energy level by spontaneously emitting a photon equal to the energy difference. A photon's energy is equal to Planck's constant (h) times its frequency (f) and thus is proportional to its frequency, or inversely to its wavelength (λ).^[3]

ΔE = h f = h c / λ,

since c, the speed of light, equals to f λ^[3]

Correspondingly, many kinds of spectroscopy are based on detecting the frequency or wavelength of the emitted or absorbed photons to provide information on the material analyzed, including information on the energy levels and electronic structure of materials obtained by analyzing the spectrum.

An asterisk is commonly used to designate an excited state. An electron transition in a molecule's bond from a ground state to an excited state may have a designation such as σ → σ*, π → π*, or n → π* meaning excitation of an electron from a σ bonding to a σ antibonding orbital, from a π bonding to a π antibonding orbital, or from an n non-bonding to a π antibonding orbital. ^{[3] [4]} Reverse electron transitions for all these types of excited molecules are also possible to return to their ground states, which can be designated as σ* → σ, π* → π, or π* → n.

A transition in an energy level of an electron in a molecule may be combined with a vibrational transition and called a vibronic transition. A vibrational and rotational transition may be combined by rovibrational coupling. In rovibronic coupling, electron transitions are simultaneously combined with both vibrational and rotational transitions. Photons involved in transitions may have energy of various ranges in the electromagnetic spectrum, such as X-ray, ultraviolet, visible light, infrared, or microwave radiation, depending on the type of transition. In a very general way, energy level differences between electronic states are larger, differences between vibrational levels are intermediate, and differences between rotational levels are smaller, although there can be overlap. Translational energy levels are practically continuous and can be calculated as kinetic energy using classical mechanics.

Higher temperature causes fluid atoms and molecules to move faster increasing their translational energy, and thermally excites molecules to higher average amplitudes of vibrational and rotational modes (excites the molecules to higher internal energy levels). This means that as temperature rises, translational, vibrational, and rotational contributions to molecular heat capacity let molecules absorb heat and hold more internal energy. Conduction of heat typically occurs as molecules or atoms collide transferring the heat between each other. At even higher temperatures, electrons can be thermally excited to higher energy orbitals in atoms or molecules. A subsequent drop of an electron to a lower energy level can release a photon, causing a possibly colored glow.

An electron farther from the nucleus has higher potential energy than an electron closer to the nucleus, thus it becomes less bound to the nucleus, since its potential energy is negative and inversely dependent on its distance from the nucleus.^[5]

Crystalline materials

Crystalline solids are found to have energy bands, instead of or in addition to energy levels. Electrons can take on any energy within an unfilled band. At first this appears to be an exception to the requirement for energy levels. However, as shown in band theory, energy bands are actually made up of many discrete energy levels which are too close together to resolve. Within a band the number of levels is of the order of the number of atoms in the crystal, so although electrons are actually restricted to these energies, they appear to be able to take on a continuum of values. The important energy levels in a crystal are the top of the valence band, the bottom of the conduction band, the Fermi level, the vacuum level, and the energy levels of any defect states in the crystal.

Metaphysical naturalism

From Wikipedia, the free encyclopedia

Metaphysical naturalism, also called ametaphysicalism, ontological naturalism, philosophical naturalism, scientific materialism and antisupernaturalism is a philosophical worldview, which holds that there is nothing but natural elements, principles, and relations of the kind studied by the natural sciences. Methodological naturalism is a philosophical basis for science, for which metaphysical naturalism provides only one possible ontological foundation. Broadly, the corresponding theological perspective is religious naturalism or spiritual naturalism. More specifically, metaphysical naturalism rejects the supernatural concepts and explanations that are part of many religions.

Definition

According to Steven Schafersman, geologist and president of Texas Citizens for Science metaphysical naturalism is a philosophy that maintains that; 1. Nature encompasses all that exists throughout space and time; and 2. Nature (the universe or cosmos) consists only of natural elements, that is, of spatiotemporal physical substance—mass–energy. Non-physical or quasi-physical substance, such as information, ideas, values, logic, mathematics, intellect, and other emergent phenomena, either supervene upon the physical or can be reduced to a physical account; and 3. Nature operates by the laws of physics and in principle, can be explained and understood by science and philosophy; and 4. the supernatural does not exist, i.e., only nature is real. Naturalism is therefore a metaphysical philosophy opposed primarily by Biblical creationism".^[1]

Carl Sagan put it succinctly: "The Cosmos is all that is or ever was or ever will be."^[2]

According to Danto, Naturalism, in recent usage, is a species of philosophical monism according to which whatever exists or happens is natural in the sense of being susceptible to explanation through methods which, although paradigmatically exemplified in the natural sciences, are continuous from domain to domain of objects and events. Hence, naturalism is polemically defined as repudiating the view that there exists or could exist any entities which lie, in principle, beyond the scope of scientific explanation.^[3]

Regarding the vagueness of the general term "naturalism", David Papineau traces the current usage to philosophers in early 20th century America such as John Dewey, Ernest Nagel, Sidney Hook, and Roy Wood Sellars: "So understood, 'naturalism' is not a particularly informative term as applied to contemporary philosophers. The great majority of contemporary philosophers would happily accept naturalism as just characterized—that is, they would both reject 'supernatural' entities, and allow that science is a possible route (if not necessarily the only one) to important truths about the 'human spirit'".^[4] Papineau remarks that philosophers widely regard naturalism as a "positive" term, and "few active philosophers nowadays are happy to announce themselves as 'non-naturalists'", while noting that "philosophers concerned with religion tend to be less enthusiastic about 'naturalism'" and that despite an "inevitable" divergence due to its popularity, if more narrowly construed, (to the chagrin of John McDowell, David Chalmers and Jennifer Hornsby, for example), those not so disqualified remain nonetheless content "to set the bar for 'naturalism' higher".^[4]

Philosopher and theologian Alvin Plantinga, a well-known critic of naturalism in general, comments: "Naturalism is presumably not a religion. In one very important respect, however, it resembles religion: it can be said to perform the cognitive function of a religion. There is that range of deep human questions to which a religion typically provides an answer ... Like a typical religion, naturalism gives a set of answers to these and similar questions".^[5]

Methodological naturalism

Metaphysical naturalism is an approach to metaphysics or ontology, which deals with existence per se. It should not be confused with methodological naturalism, which sees empiricism as the basis for the scientific method.^{[citation needed]}

Regarding science and evolution, Eugenie C. Scott, a notable opponent of teaching creationism or intelligent design in US public schools, stresses the importance of separating metaphysical from methodological naturalism:

If it is important for Americans to learn about science and evolution, decoupling the two forms of naturalism is essential strategy. ... I suggest that scientists can defuse some of the opposition to evolution by first recognizing that the vast majority of Americans are believers, and that most Americans want to retain their faith. It is demonstrable that individuals can retain religious beliefs and still accept evolution as science. Scientists should avoid confusing the methodological naturalism of science with metaphysical naturalism.^[6]

— Eugenie C. Scott, Creationism, Ideology, and Science

Lack of necessity for worship

The historian Richard Carrier, in his book Sense and Goodness without God: A Defense of Metaphysical Naturalism, describes metaphysical naturalism thus: as a philosophy "wherein worship is replaced with curiosity, devotion with diligence, holiness with sincerity, ritual with study, and scripture with the whole world and the whole of human learning". Carrier wrote that it is the naturalist’s duty "to question all things and have a well-grounded faith in what is well-investigated and well-proved, rather than what is merely well-asserted or well-liked".^[7]

Science and naturalism

Metaphysical naturalism is the philosophical basis of science as described by Kate and Vitaly (2000) "There are certain philosophical assumptions made at the base of the scientific method — namely, 1) that reality is objective and consistent, 2) that humans have the capacity to perceive reality accurately, and that 3) rational explanations exist for elements of the real world. These assumptions are the basis of naturalism, the philosophy on which science is grounded. Philosophy is at least implicitly at the core of every decision we make or position we take, it is obvious that correct philosophy is a necessity for scientific inquiry to take place."^[8] Steven Schafersman, agrees that methodological naturalism is "the adoption or assumption of philosophical naturalism within scientific method with or without fully accepting or believing it ... science is not metaphysical and does not depend on the ultimate truth of any metaphysics for its success, but methodological naturalism must be adopted as a strategy or working hypothesis for science to succeed. We may therefore be agnostic about the ultimate truth of naturalism, but must nevertheless adopt it and investigate nature as if nature is all that there is."^[1] Contrary to other notable opponents of teaching Creationism or Intelligent Design in US public schools such as Eugenie Scott, Schafersman asserts that "while science as a process only requires methodological naturalism, I think that the assumption of methodological naturalism by scientists and others logically and morally entails ontological naturalism".^[1] as well as the similarly controversial assertion: "I maintain that the practice or adoption of methodological naturalism entails a logical and moral belief in ontological naturalism, so they are not logically decoupled."^[1] On the other hand, Scott argues:

that a clear distinction must be drawn between science as a way of knowing about the natural world and science as a foundation for philosophical views. One should be taught to our children in school, and the other can optionally be taught to our children at home. Once this view is explained, I have found far more support than disagreement among my university colleagues. Even someone who may disagree with my logic or understanding of philosophy of science often understands the strategic reasons for separating methodological from philosophical materialism—if we want more Americans to understand evolution.^[6][9]

— Eugenie C. Scott, Science and Religion, Methodology and Humanism

However, there are other controversies, Arthur Newell Strahler embeds peculiar anthropic distinctions in the name of naturalism: "The naturalistic view is that the particular universe we observe came into existence and has operated through all time and in all its parts without the impetus or guidance of any supernatural agency. The naturalistic view is espoused by science as its fundamental assumption."^[10] Variously known as background independence, the cosmological principle, the principle of universality, the principle of uniformity, or uniformitarianism, there are important philosophical assumptions that cannot be derived from nature. As noted by Stephen Jay Gould: "You cannot go to a rocky outcrop and observe either the constancy of nature's laws or the working of unknown processes. It works the other way around. You first assume these propositions and "then you go to the out crop of rock."^[11][12] "The assumption of spatial and temporal invariance of natural laws is by no means unique to geology since it amounts to a warrant for inductive inference which, as Bacon showed nearly four hundred years ago, is the basic mode of reasoning in empirical science. Without assuming this spatial and temporal invariance, we have no basis for extrapolating from the known to the unknown and, therefore, no way of reaching general conclusions from a finite number of observations. (Since the assumption is itself vindicated by induction, it can in no way "prove" the validity of induction—an endeavor virtually abandoned after Hume demonstrated its futility two centuries ago)."^[13] Gould also notes that natural processes such as Lyell's "uniformity of process" are an assumption: "As such, it is another a priori assumption shared by all scientists and not a statement about the empirical world."^[14] Such assumptions across time and space are needed for scientists to extrapolate into the unobservable past, according to G.G. Simpson: "Uniformity is an unprovable postulate justified, or indeed required, on two grounds. First, nothing in our incomplete but extensive knowledge of history disagrees with it. Second, only with this postulate is a rational interpretation of history possible, and we are justified in seeking—as scientists we must seek—such a rational interpretation."^[15] and according to R. Hooykaas: "The principle of uniformity is not a law, not a rule established after comparison of facts, but a principle, preceding the observation of facts ... It is the logical principle of parsimony of causes and of economy of scientific notions. By explaining past changes by analogy with present phenomena, a limit is set to conjecture, for there is only one way in which two things are equal, but there are an infinity of ways in which they could be supposed different."^[16]

Various associated beliefs

Contemporary naturalists possess a wide diversity of beliefs within metaphysical naturalism. Most metaphysical naturalists have adopted some form of materialism or physicalism.^[17]

Undesigned universe

Metaphysical naturalists argue that the scientific facts and theories that we have to explain the origins of the universe provide no evidence for supernatural beings or deities.^[18] As Richard Carrier explains:

...no other worldview is directly and substantially supported by any scientific evidence, whereas all scientific evidence so far does support Metaphysical Naturalism, often directly, sometimes substantially. Though naturalism has not yet been proved, it is the best bet going.^[18]

One might say that either it has always existed or it had a purely natural origin, being neither created nor designed.

Abiogenesis and evolution

Since nature is all there is, and there was once no life, abiogenesis is implied: that life arose spontaneously from natural causes. Naturalists reason about how, not if evolution happened. They maintain that humanity's existence is not by intelligent design but rather a natural process of emergence.

Ethics and meta-ethics

Some embrace virtue ethics and many see no compelling argument against ethical naturalism. Some may advocate for a Science of morality. One example of an attempt to ground a naturalist Meta-Ethical system is Richard Carrier's chapter "Moral Facts Naturally Exist (and Science Could Find Them)" which was peer reviewed by four philosophers. It sets out to prove a Moral realism centered around human satisfaction. Alexander Rosenberg has expressed a contrary position that naturalists, in general, have to accept moral nihilism.^[22]

The mind is a natural phenomenon

If any variety of metaphysical naturalism is true, any mental properties that exist are caused by and ontologically dependent upon nature. However, some metaphysical naturalists consider the mental to be out-of-bounds, just like the supernatural.

Metaphysical naturalists do not believe in a soul or spirit, nor in ghosts, and when explaining what constitutes the mind they rarely appeal to substance dualism. If one's mind, or rather one's identity and existence as a person, is entirely the product of natural processes, three conclusions follow according to W.T. Stace. First, all mental contents (such as ideas, theories, emotions, moral and personal values, or aesthetic response) exist solely as computational constructions of one's brain and genetics, not as things that exist independently of these. Second, damage to the brain (regardless of how) should be of great concern. Third, death or destruction of one's brain cannot be survived, which is to say, all humans are mortal. Stace, however, believes that ecstatic mysticism calls into question the assumption that awareness is impossible without data processing.^[24]

Utility of reason

Metaphysical naturalists hold that reason is the refinement and improvement of naturally evolved faculties. The certitude of deductive logic remains unexplained by this essentially probabilistic view. Nevertheless, naturalists believe anyone who wishes to have more beliefs that are true than are false should seek to perfect and consistently employ their reason in testing and forming beliefs. Empirical methods (especially those of proven use in the sciences) are unsurpassed for discovering the facts of reality, while methods of pure reason alone can securely discover logical errors.^[25]

Value of society

Humans are social animals, which is why humanity developed culture and civilization. In terms of evolution, this means that differential reproductive success somehow depended on traits that permit the development and maintenance of a healthy and productive culture and civilization.^{[citation needed]}

History

Ancient period

Metaphysical naturalism appears to have originated in early Greek philosophy. The earliest presocratic philosophers, such as Thales, Anaxagoras or especially the atomist Democritus, were labeled by their peers and successors "the physikoi" (from the Greek φυσικός or physikos, meaning "natural philosopher," borrowing on the word φύσις or physis, meaning "nature") because they investigated natural causes, often excluding any role for gods in the creation or operation of the world. This eventually led to fully developed systems such as Epicureanism, which sought to explain everything that exists as the product of atoms falling and swerving in a void.^{[citation needed]}

Plato's world of eternal and unchanging Forms, imperfectly represented in matter by a divine Artisan, contrasts sharply with the various mechanistic Weltanschauungen, of which atomism was, by the fourth century at least, the most prominent... This debate was to persist throughout the ancient world. Atomistic mechanism got a shot in the arm from Epicurus... while the Stoics adopted a divine teleology... The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or inject intelligence into the system. This was how Aristotle (384–322 bc), when still a young acolyte of Plato, saw matters. Cicero (On the Nature of the Gods 2. 95 = Fr. 12) preserves Aristotle's own cave-image: if troglodytes were brought on a sudden into the upper world, they would immediately suppose it to have been intelligently arranged. But Aristotle grew to abandon this view; although he believes in a divine being, the Prime Mover is not the efficient cause of action in the Universe, and plays no part in constructing or arranging it... But, although he rejects the divine Artificer, Aristotle does not resort to a pure mechanism of random forces. Instead he seeks to find a middle way between the two positions, one which relies heavily on the notion of Nature, or phusis.^[26]

— R. J. Hankinson, Cause and Explanation in Ancient Greek Thought

Metaphysical naturalism is most notably a Western phenomenon, but an equivalent idea has long existed in the East. Though unnamed and never articulated into a coherent system, one tradition within Confucian philosophy embraced a form of metaphysical naturalism dating to the Wang Chong in the 1st century, if not earlier, but it arose independently and had little influence on the development of modern naturalist philosophy or on Eastern or Western culture.^{[citation needed]}

Middle ages to modernity

With the rise and dominance of Christianity in the West and the later spread of Islam, metaphysical naturalism was generally abandoned by intellectuals. Thus, there is little evidence for it in the Middle Ages. The reintroduction of Aristotle's empirical epistemology as well as previously lost treatises by Greco-Roman natural philosophers during the Renaissance contributed to Scientific Revolution which was begun by the medieval Scholastics without resulting in any noticeable increase in commitment to naturalism. It was not until the early modern era and Age of Enlightenment that naturalism, like that of Benedict Spinoza, David Hume, Denis Diderot, Julien La Mettrie, and Baron d'Holbach, among others, started to emerge again in the 17th and 18th centuries.^{[citation needed]}

In this period, some metaphysical naturalists adhered to a distinct doctrine, materialism, which became the only category of metaphysical naturalism widely defended until the 20th century, when advances in physics resulted in widespread abandonment of prior formulations of materialism. 19th century physics added electromagnetic force fields, and in the 20th century matter was found to be a form of energy and therefore not fundamental as materialists had assumed. (See History of physics.) In philosophy, renewed attention to the problem of universals, philosophy of mathematics, the development of mathematical logic, and the post-positivist revival of metaphysics and the philosophy of religion, initially by way of Wittgensteinian linguistic philosophy, further called the naturalistic paradigm into question. Developments such as these, along with those within science and the philosophy of science brought new advancements and revisions of naturalistic doctrines by naturalistic philosophers into metaphysics, ethics, the philosophy of language, the philosophy of mind, epistemology, etc., the products of which include physicalism and eliminative materialism, supervenience, causal theories of reference, anomalous monism, naturalized epistemology (e.g. reliabilism), internalism and externalism, ethical naturalism, and property dualism, for example.

Currently, metaphysical naturalism is more widely embraced than in previous centuries, especially but not exclusively in the natural sciences and the Anglo-American, analytic philosophical communities. While the vast majority of the population of the world remains firmly committed to non-naturalistic worldviews, prominent contemporary defenders of naturalism and/or naturalistic theses and doctrines today include J. J. C. Smart, David Malet Armstrong, David Papineau, Paul Kurtz, Brian Leiter, Daniel Dennett, Michael Devitt, Fred Dretske, Paul and Patricia Churchland, Mario Bunge, Jonathan Schaffer, Hilary Kornblith, Quentin Smith, Paul Draper and Michael Martin, among many other academic philosophers.

According to David Papineau, contemporary naturalism is a consequence of the build-up of scientific evidence during the twentieth century for the "causal closure of the physical", the doctrine that all physical effects can be accounted for by physical causes.^[27]

According to Steven Schafersman, president of Texas Citizens for Science, an advocacy group opposing creationism in public schools,^[28] the progressive adoption of methodological naturalism—and later of metaphysical naturalism—followed the advances of science and the increase of its explanatory power.^[29] These advances also caused the diffusion of positions associated with metaphysical naturalism, such as existentialism.^[30]

By the middle of the twentieth century, the acceptance of the causal closure of the physical realm led to even stronger naturalist views. The causal closure thesis implies that any mental and biological causes must themselves be physically constituted, if they are to produce physical effects. It thus gives rise to a particularly strong form of ontological naturalism, namely the physicalist doctrine that any state that has physical effects must itself be physical.

From the 1950s onwards, philosophers began to formulate arguments for ontological physicalism. Some of these arguments appealed explicitly to the causal closure of the physical realm (Feigl 1958, Oppenheim and Putnam 1958). In other cases, the reliance on causal closure lay below the surface. However, it is not hard to see that even in these latter cases the causal closure thesis played a crucial role.^[31]

— David Papineau, "Naturalism" in the Stanford Encyclopedia of Philosophy

Marxism, Objectivism, and secular humanism

A number of politicized versions of naturalism have arisen in the Western world, most notably Marxism in the 19th century and Objectivism in the 20th century. Marxism is an expression of communist or socialist materialism within a naturalistic framework. Objectivism is an expression of capitalist idealism within a naturalistic framework. Most proponents of metaphysical naturalism in First World countries, however, are neither Marxists nor Objectivists, and instead embrace the more moderate political ideals of secular humanism or cultural moral relativism.^{[citation needed]}

Arguments for metaphysical naturalism

In the context of creation and evolution debates, Internet Infidels co-founder Jeffery Jay Lowder argues against what he calls "the argument from bias", that a priori, the supernatural is merely ruled out due to an unexamined stipulation. Lowder believes "there are good empirical reasons for believing that metaphysical naturalism is true, and therefore a denial of the supernatural need not be based upon an a priori assumption".^[32]

Richard Carrier argues in Sense and Goodness Without God: A Defense of Metaphysical Naturalism that Metaphysical Naturalism is true. Topics covered include metaphilosophy, semantics, epistemology, the nature and origin of the universe (including a proposal that spacetime may be the ground of all being and a rejection of the logical possibility for any ultimate answer), free will compatibilism, the nature of mind, abstract objects, ontological reductionism, the nature of emotions, the meaning of life, the nature of reason, atheism, aesthetics, morality (including ethical naturalism and a recommendation for a science of morality), and politics.

Argument from physical minds

Several Metaphysical Naturalists have used the trends in scientific discoveries about minds to argue that no supernatural minds exist. For instance, Lowder says, "Since all known mental activity has a physical basis, there are probably no disembodied minds. But God is conceived of as a disembodied mind. Therefore, God probably does not exist."^[33] Lowder argues the correlation between mind and brain implies that supernatural souls do not exist because the theist position, according to Lowder, is that the mind depends upon this soul instead of the brain.^[32]

Cosmological argument for naturalism

[Elegance] goes directly to the question of how the laws of nature are constructed. Nobody knows the answer to that. Nobody! It's a perfectly legitimate hypothesis, in my view, to say that some extremely elegant creator made those laws. But I think if you go down that road, you must have the courage to ask the next question, which is: Where did that creator come from? And where did his, her, or its elegance come from? And if you say it was always there, then why not say that the laws of nature were always there and save a step?^[34]

— Carl Sagan, Conversations with Carl Sagan

There is no plausible reason why an Almighty would need billions of years and trillions of galaxies to accomplish his ends through long, deterministic causal processes. But that is exactly what we should expect if there is no god, but only nature.^[35]

— Richard Carrier, Sense And Goodness Without God

Arguments against

Arguments against metaphysical naturalism include the following examples.

Evolutionary argument against naturalism

Alvin Plantinga is the John A. O'Brien Professor of Philosophy Emeritus at the University of Notre Dame, and the inaugural holder of the Jellema Chair in Philosophy at Calvin College. He is a Christian, and a well-known critic of naturalism. He argues, in his evolutionary argument against naturalism, that the probability that evolution has produced humans with reliable true beliefs, is low or inscrutable, unless their evolution was guided, for example, by God. According to David Kahan of the University of Glasgow, in order to understand how beliefs are warranted, a justification must be found in the context of supernatural theism, as in Plantinga's epistemology.
Plantinga argues that together, naturalism and evolution provide an insurmountable "defeater for the belief that our cognitive faculties are reliable", i.e., a skeptical argument along the lines of Descartes' evil demon or brain in a vat.^[39]

Take philosophical naturalism to be the belief that there aren't any supernatural entities—no such person as God, for example, but also no other supernatural entities, and nothing at all like God. My claim was that naturalism and contemporary evolutionary theory are at serious odds with one another—and this despite the fact that the latter is ordinarily thought to be one of the main pillars supporting the edifice of the former. (Of course I am not attacking the theory of evolution, or anything in that neighborhood; I am instead attacking the conjunction of naturalism with the view that human beings have evolved in that way. I see no similar problems with the conjunction of theism and the idea that human beings have evolved in the way contemporary evolutionary science suggests.) More particularly, I argued that the conjunction of naturalism with the belief that we human beings have evolved in conformity with current evolutionary doctrine... is in a certain interesting way self-defeating or self-referentially incoherent.^[39]

— Alvin Plantinga, "Introduction" in Naturalism Defeated?: Essays on Plantinga's Evolutionary Argument Against Naturalism

Branden Fitelson of the University of California, Berkeley and Elliott Sober of the University of Wisconsin–Madison argue that Plantinga must show that the combination of evolution and naturalism also defeats the more modest claim that "at least a non-negligible minority of our beliefs are true", and that defects such as cognitive bias are nonetheless consistent with being made in the image of a rational God. Whereas evolutionary science already acknowledges that cognitive processes are unreliable, including the fallibility of the scientific enterprise itself, Plantinga's hyperbolic doubt is no more a defeater for naturalism than it is for theistic metaphysics founded upon a non-deceiving God who designed the human mind: "[neither] can construct a non-question-begging argument that refutes global skepticism."^[40] Plantinga's argument has also been criticized by philosopher Daniel Dennett and historian Richard Carrier who argue that a cognitive apparatus for truth-finding can result from natural selection.^[41]

Pre-Modern philosophy

Edward Feser, in his book The Last Superstition: A Refutation of the New Atheism, lays a plenary case against naturalism by re-examining pre-Modern philosophy. Beginning in the second chapter, Feser cites the Platonic^[42] and Aristotelian^[43] answers to the problem of universals—that is, realism. Feser also offers arguments against nominalism.^[44] And by defending realism and rejecting nominalism, he rejects eliminative materialism—and thus naturalism.

In the third chapter, Feser summarizes three of Thomas Aquinas's arguments for the existence of God.^[45] These include arguments for an unmoved mover,^[46] first, uncaused cause ^[47] and (supernatural) supreme intelligence,^[48] concluding that these must exist not as a matter of probability—as in the intelligent design view, particularly of irreducible complexity^[49]—but as a necessary consequence of "obvious, though empirical, starting points".