Hadean

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https://en.wikipedia.org/wiki/Hadean 

The Hadean (/heɪˈdiːən, ˈheɪdiən/ hay-DEE-ən, HAY-dee-ən) is the first and oldest of the four geologic eons of Earth's history, starting with the planet's formation about 4.6 Ga (estimated 4567.30 ± 0.16 Ma set by the age of the oldest solid material in the Solar System—protoplanetary disk dust particles—found as chondrules and calcium–aluminium-rich inclusions in some meteorites about 4.567 Ga), and ended 4.031 Ga the age of the oldest known intact rock formations on Earth as recognized by the International Commission on Stratigraphy. The interplanetary collision that created the Moon occurred early in this eon. The Hadean eon was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.

Hadean rocks are very rare, largely consisting of granular zircons from one locality (Jack Hills) in Western Australia. Hadean geophysical models remain controversial among geologists: plate tectonics and the growth of cratons into continents may have started in the Hadean, but there is still uncertainty.

Earth in the early Hadean had a very thick hydride-rich atmosphere whose composition likely resembled the solar nebula and the gas giants, with mostly water vapor, methane and ammonia. As the Earth's surface cooled, vaporized atmospheric water condensed into liquid water and eventually a superocean covering nearly all of the planet was formed, turning Earth into an ocean planet. Volcanic outgassing and asteroid bombardments further altered the Hadean atmosphere eventually into the nitrogen- and carbon dioxide-rich, weakly reducing Paleoarchean atmosphere.

Etymology

The eon's name "Hadean" comes from Hades, the Greek god of the underworld (whose name is also used to describe the underworld itself), referring to the hellish conditions then prevailing on early Earth: the planet had just been formed from recent accretion, and its surface was still molten with superheated lava due to that, the abundance of short-lived radioactive elements, and frequent impact events with other Solar System bodies.

The term was coined by American geologist Preston Cloud, originally to label the period before the earliest known rocks on Earth. W.B. Harland later coined an almost synonymous term, the Priscoan period, from priscus, a Latin word for 'ancient'. Other, older texts refer to the eon as the Pre-Archean.

Rock dating

Further information: Oldest dated rocks

Prior to the 1980s and the discovery of Hadean lithic fragments, scientific narratives of the early Earth explanations were almost entirely in the hands of geodynamic modelers.

Backscatter electron micrograph of detrital zircons from the Hadean (4.404 ± 0.008 Ga) metasediments of the Jack Hills, Narryer Gneiss terrane, Western Australia

In the last decades of the 20th century, geologists identified a few Hadean rocks from western Greenland, northwestern Canada, and Western Australia. In 2015, traces of carbon minerals interpreted as "remains of biotic life" were found in 4.1-billion-year-old rocks in Western Australia.

The oldest dated zircon crystals, enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss terrane of Western Australia, date to 4.404 ± 0.008 Ga. This zircon is a slight outlier, with the oldest consistently dated zircon falling closer to 4.35 Ga—around 200 million years after the hypothesized time of Earth's formation.

In many other areas, xenocryst (or relict) Hadean zircons enclosed in older rocks indicate that younger rocks have formed on older terranes and have incorporated some of the older material. One example occurs in the Guiana shield from the Iwokrama Formation of southern Guyana where zircon cores have been dated at 4.22 Ga.

Atmosphere

A sizable quantity of water would have been in the material that formed Earth. Water molecules would have escaped Earth's gravity more easily when the planet was less massive during its formation. Photodissociation by short-wave ultraviolet in sunlight could split surface water molecules into oxygen and hydrogen, the former of which would readily react to form compounds in the then-reducing atmosphere, while the latter (along with the similarly light helium) would be expected to continually leave the atmosphere (as it does to the present day) due to atmospheric escape.

Part of the ancient planet is theorized to have been disrupted by the impact that created the Moon, which should have caused the melting of one or two large regions of Earth. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses. However, a fair fraction of material should have been vaporized by this impact. The material would have condensed within 2,000 years. The initial magma ocean solidified within 5 million years, leaving behind hot volatiles which probably resulted in a heavy CO
₂ atmosphere with hydrogen and water vapor. The initial heavy atmosphere had a surface temperature of 230 °C (446 °F) and an atmospheric pressure of above 27 standard atmospheres.

Oceans

Hadean and Archean zircons with evaluation of δ¹⁸O

Studies of zircons have found that liquid water may have existed between 4.0 and 4.4 Ga, very soon after the formation of Earth.  Liquid water oceans existed despite the high surface temperature, because at an atmospheric pressure of 27 atmospheres, water remains liquid.

The most likely source of the water in the Hadean ocean was outgassing from the Earth's mantle. Bombardment origin of a substantial amount of water is unlikely, due to the incompatibility of isotope fractions between the Earth and comets.

Asteroid impacts during the Hadean and into the Archean would have periodically disrupted the ocean. The geological record from 3.2 Ga contains evidence of multiple impacts of objects up to 100 kilometres (62 mi) in diameter. Each such impact would have boiled off up to 100 metres (330 ft) of a global ocean, and temporarily raised the atmospheric temperature to 500 °C (932 °F). However, the frequency of meteorite impacts is still under study: the Earth may have gone through long periods when liquid oceans and life were possible.

The liquid water would absorb the carbon dioxide in the early atmosphere; this would not be enough by itself to substantially reduce the amount of CO
₂.

Plate tectonics

Evolution of continental crust and ocean depths (from Korenaga, 2021)

A 2008 study of zircons found that Australian Hadean rock contains minerals pointing to the existence of plate tectonics as early as 4 Ga (approximately 600 million years after Earth's formation). However, some geologists suggest that the zircons could have been formed by meteorite impacts. The direct evidence of Hadean geology from zircons is limited, because the zircons are largely gathered in one locality in Australia. Geophysical models are underconstrained, but can paint a general picture of the state of Earth in the Hadean.

Mantle convection in the Hadean was likely vigorous, due to lower viscosity. The lower viscosity was due to the high levels of radiogenic heat and the fact that water in the mantle had not yet fully outgassed. Whether the vigorous convection led to plate tectonics in the Hadean or was confined under a rigid lid is still a matter of debate. The presence of Hadean oceans is thought to have triggered plate tectonics.

Subduction due to plate tectonics would have removed carbonate from the early oceans, contributing to the removal of the CO
₂-rich early atmosphere. Removal of this early atmosphere is evidence of Hadean plate tectonics.

If plate tectonics occurred in the Hadean, it would have formed continental crust. Different models predict different amounts of continental crust during the Hadean. The work of Dhiume et al. predicts that by the end of the Hadean, the continental crust had only 25% of today's area. The models of Korenaga, et al. predict that the continental crust grew to present-day volume sometime between 4.2 and 4.0 Ga.

Continents

The amount of exposed land in the Hadean is only loosely dependent on the amount of continental crust: it also depends on the ocean level. In models where plate tectonics started in the Archean, Earth has a global ocean in the Hadean. The high heat of the mantle may have made it difficult to support high elevations in the Hadean. If continents did form in the Hadean, their growth competed with outgassing of water from the mantle. Continents may have appeared in the mid-Hadean, and then disappeared under a thick ocean by the end of the Hadean. The limited amount of land has implications for the origin of life.

Possible life

Abundant Hadean-like geothermal microenvironments were shown by Salditt et al. to have the potential to support the synthesis and replication of RNA and thus possibly the evolution of a primitive life form. Porous rock systems comprising heated air-water interfaces were shown to allow ribozyme-catalyzed RNA replication of sense and antisense strands followed by subsequent strand dissociation, thus enabling combined synthesis, release and folding of active ribozymes. A study published in 2024 inferred the last common ancestor of all current life to have emerged during the Hadean, between 4.09 and 4.33 Ga.

Although the early part of the Late Heavy Bombardment happened during the Hadean, the impacts were frequent only on a cosmic scale, with thousands or even millions of years between each event. As Earth already had oceans, life would have been possible, but vulnerable to extinction events caused by those impacts. The risk would not be on the frequency, but on the size of the impactor, and remains on the Moon suggest impactors bigger than the Chicxulub impactor that caused the extinction of dinosaurs. An impactor big enough may erase all life on the planet, although some models suggest that microscopic life may still survive if underground or in the oceanic depths.

Origin of water on Earth

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Origin_of_water_on_Earth

Water covers about 71% of Earth's surface.

Life timeline
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 —	Water   Single-celled life   Photosynthesis   Multicellular life   Plants   Arthropods Molluscs Flowers Dinosaurs   Mammals Birds Primates Hadean Archean Proterozoic Phanerozoic	← Earth formed ← Earliest water ← LUCA ← Earliest fossils ← Atmospheric oxygen ← Sexual reproduction ← Earliest fungi ← Neoproterozoic oxygenation event ← Ediacaran biota ← Cambrian explosion ← Earliest tetrapods ← Earliest hominoid
(million years ago)

The origin of water on Earth is the subject of a body of research in the fields of planetary science, astronomy, and astrobiology. Earth is unique among the rocky planets in the Solar System in having oceans of liquid water on its surface. Liquid water, which is necessary for all known forms of life, continues to exist on the surface of Earth because the planet is at a far enough distance (known as the habitable zone) from the Sun that it does not lose its water, but not so far that low temperatures cause all water on the planet to freeze.

It was long thought that Earth's water did not originate from the planet's region of the protoplanetary disk. Instead, it was hypothesized water and other volatiles must have been delivered to Earth from the outer Solar System later in its history. Recent research, however, indicates that hydrogen inside the Earth played a role in the formation of the ocean. The two ideas are not mutually exclusive, as there is also evidence that water was delivered to Earth by impacts from icy planetesimals similar in composition to asteroids in the outer edges of the asteroid belt.

History of water on Earth

One factor in estimating when water appeared on Earth is that water is continually being lost to space. H₂O molecules in the atmosphere are broken up by photolysis, and the resulting free hydrogen atoms can sometimes escape Earth's gravitational pull. When the Earth was younger and less massive, water would have been lost to space more easily. Lighter elements like hydrogen and helium are expected to leak from the atmosphere continually, but isotopic ratios of heavier noble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses. In particular, xenon is useful for calculations of water loss over time. Not only is it a noble gas (and therefore is not removed from the atmosphere through chemical reactions with other elements), but comparisons between the abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water, a volume of water approximately equal to modern ocean volume, early in its history. This is likely to have occurred between the Hadean and Archean eons in cataclysmic events such as the moon forming impact.

Any water on Earth during the latter part of its accretion would have been disrupted by the Moon-forming impact (~4.5 billion years ago), which likely vaporized much of Earth's crust and upper mantle and created a rock-vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majority carbon dioxide atmosphere with hydrogen and water vapor. Afterward, liquid water oceans may have existed despite the surface temperature of 230 °C (446 °F) due to the increased atmospheric pressure of the CO₂ atmosphere. As the cooling continued, most CO₂ was removed from the atmosphere by subduction and dissolution in ocean water, but levels oscillated wildly as new surface and mantle cycles appeared.

This pillow basalt on the seafloor near Hawaii was formed when magma extruded underwater. Other, much older pillow basalt formations provide evidence for large bodies of water long ago in Earth's history.

Geological evidence also helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption) was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence has yet to be discovered (which may be because such potential evidence has been destroyed by geological processes like crustal recycling). More recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.

Unlike rocks, minerals called zircons are highly resistant to weathering and geological processes and so are used to understand conditions on the very early Earth. Mineralogical evidence from zircons has shown that liquid water and an atmosphere must have existed 4.404 ± 0.008 billion years ago, very soon after the formation of Earth. This presents somewhat of a paradox, as the cool early Earth hypothesis suggests temperatures were cold enough to freeze water between about 4.4 billion and 4.0 billion years ago. Other studies of zircons found in Australian Hadean rock point to the existence of plate tectonics as early as 4 billion years ago. If true, that implies that rather than a hot, molten surface and an atmosphere full of carbon dioxide, early Earth's surface was much as it is today (in terms of thermal insulation). The action of plate tectonics traps vast amounts of CO₂, thereby reducing greenhouse effects, leading to a much cooler surface temperature and the formation of solid rock and liquid water.

Earth's water inventory

Where water is found on earth and in what proportions.

While the majority of Earth's surface is covered by oceans, those oceans make up just a small fraction of the mass of the planet. The mass of Earth's oceans is estimated to be 1.37 × 10²¹ kg, which is 0.023% of the total mass of Earth, 6.0 × 10²⁴ kg. An additional 5.0 × 10²⁰ kg of water is estimated to exist in ice, lakes, rivers, groundwater, and atmospheric water vapor. A significant amount of water is also stored in Earth's crust, mantle, and core. Unlike molecular H₂O that is found on the surface, water in the interior exists primarily in hydrated minerals or as trace amounts of hydrogen bonded to oxygen atoms in anhydrous minerals. Hydrated silicates on the surface transport water into the mantle at convergent plate boundaries, where oceanic crust is subducted underneath continental crust. While it is difficult to estimate the total water content of the mantle due to limited samples, approximately three times the mass of the Earth's oceans could be stored there. Similarly, the Earth's core could contain four to five oceans' worth of hydrogen.

While not considered to be one of the major sources of water on the planet, it should also be noted that biological processes such as photosynthesis and respiration are key factors in the hydrologic cycling of water on earth. These processes may have also had a more vital role on the early earth, and as such, they could impact the amount of available water present in a given location at a given time. This is due to one of these aforementioned processes consuming water, and the other generating water, and the balance between them is therefore what truly determines their impact. If photosynthesis occurs in higher degrees than respiration, earth's water inventory would decrease, while if respiration occurs in higher degrees than photosynthesis, earth's water inventory would increase.

Hypotheses for the origins of Earth's water

Extraplanetary sources

Water has a much lower condensation temperature than other materials that compose the terrestrial planets in the Solar System, such as iron and silicates. The region of the protoplanetary disk closest to the Sun was very hot early in the history of the Solar System, with temperatures ranging from 500-1500 Kelvin or 227-1227 Celsius, and therefore, it is not feasible that oceans of water condensed with the Earth as it formed. Further from the young Sun where temperatures were lower, water could condense and form icy planetesimals, which accumulated to form the Oort cloud. The boundary of the region where ice could form in the early Solar System is known as the frost line (or snow line), and is located in the modern asteroid belt, between about 2.7 and 3.1 astronomical units (AU) from the Sun. It is therefore necessary that objects forming beyond the frost line–such as comets, trans-Neptunian objects, and water-rich meteoroids (protoplanets)–delivered water to Earth. However, the timing of this delivery is still in question.

One hypothesis claims that Earth accreted (gradually grew by accumulation of) icy planetesimals about 4.5 billion years ago, when it was 60 to 90% of its current size. In this scenario, Earth was able to retain water in some form throughout accretion and major impact events. This hypothesis is supported by similarities in the abundance and the isotope ratios of water between the oldest known carbonaceous chondrite meteorites and meteorites from Vesta, both of which originate from the Solar System's asteroid belt. It is also supported by studies of osmium isotope ratios, which suggest that a sizeable quantity of water was contained in the material that Earth accreted early on. Measurements of the chemical composition of lunar samples collected by the Apollo 15 and 17 missions further support this, and indicate that water was already present on Earth before the Moon was formed.

The solar system's layout; which can help explain why incoming icy planetesimals from the outer solar system can be filtered out by the gaseous planets before they can reach the terrestrial planets.

One problem with this hypothesis is that the noble gas isotope ratios of Earth's atmosphere are different from those of its mantle, which suggests they were formed from different sources. To explain this observation, a so-called "late veneer" theory has been proposed in which water was delivered much later in Earth's history, after the Moon-forming impact. However, the current understanding of Earth's formation allows for less than 1% of Earth's material accreting after the Moon formed, implying that the material accreted later must have been very water-rich. Models of early Solar System dynamics have shown that icy asteroids could have been delivered to the inner Solar System (including Earth) during this period if Jupiter migrated closer to the Sun. Jupiter's relatively quick development however, made it difficult for the inner solar system to receive matter from the outer solar system, limiting the accumulation of water on the terrestrial planets. This is in addition to other factors, such as the conditions for the goldilocks zone, where liquid water, and by extension life as we know it, can exist, as opposed to solid ice forming snowball planets or gaseous water vapor forming gas giants.

Yet a third hypothesis, supported by evidence from molybdenum isotope ratios from a 2019 study, suggests that the Earth gained most of its water from the same interplanetary collision that caused the formation of the Moon. Albeit, as mentioned above, the majority of this water would have remained in a gaseous phase until significant planetary cooling occurred.

The evidence from 2019 shows that the molybdenum isotopic composition of the Earth's mantle originates from the outer Solar System, likely having brought water to Earth. The explanation is that Theia, the planet said in the giant-impact hypothesis to have collided with Earth 4.5 billion years ago forming the Moon, may have originated in the outer Solar System rather than in the inner Solar System, bringing water and carbon-based materials with it.

Geochemical analysis of water in the Solar System

Carbonaceous chondrites such as the Allende Meteorite (above) likely delivered much of the Earth's water, as evidenced by their isotopic similarities to ocean water.

Isotopic ratios provide a unique "chemical fingerprint" that is used to compare Earth's water with reservoirs elsewhere in the Solar System. One such isotopic ratio, that of deuterium to hydrogen (D/H), is particularly useful in the search for the origin of water on Earth. Hydrogen is the most abundant element in the universe, and its heavier isotope deuterium can sometimes take the place of a hydrogen atom in molecules like H₂O. Most deuterium was created in the Big Bang or in supernovae, so its uneven distribution throughout the protosolar nebula was effectively "locked in" early in the formation of the Solar System. By studying the different isotopic ratios of Earth and of other icy bodies in the Solar System, the likely origins of Earth's water can be researched.

Earth

The deuterium to hydrogen ratio for ocean water on Earth is known very precisely to be (1.5576 ± 0.0005) × 10⁻⁴. This value represents a mixture of all of the sources that contributed to Earth's reservoirs, and is used to identify the source or sources of Earth's water. The ratio of deuterium to hydrogen has increased over the Earth's lifetime between 2 and 9 times the ratio at the Earth's origin, because the lighter isotope is more likely to leak into space in atmospheric loss processes. Hydrogen beneath the Earth's crust is thought to have a D/H ratio more representative of the original D/H ratio upon formation of the Earth, because it is less affected by those processes. Analysis of subsurface hydrogen contained in recently released lava has been estimated to show that there was a 218‰ higher D/H ratio in the primordial Earth compared to the current ratio. No process is known that can decrease Earth's D/H ratio over time. This loss of the lighter isotope is one explanation for why Venus has such a high D/H ratio, as that planet's water was vaporized during the runaway greenhouse effect and subsequently lost much of its hydrogen to space.

Asteroids

Comet Halley as imaged by the European Space Agency's Giotto probe in 1986. Giotto flew by Halley's Comet and analyzed the isotopic levels of ice sublimating from the comet's surface using a mass spectrometer.

Multiple geochemical studies have concluded that asteroids are most likely the primary source of Earth's water. Carbonaceous chondrites—which are a subclass of the oldest meteorites in the Solar System—have isotopic levels most similar to ocean water. The CI and CM subclasses of carbonaceous chondrites specifically have hydrogen and nitrogen isotope levels that closely match Earth's seawater, which suggests water in these meteorites could be the source of Earth's oceans. Two 4.5 billion-year-old meteorites found on Earth that contained liquid water alongside a wide diversity of deuterium-poor organic compounds further support this. Earth's current deuterium to hydrogen ratio also matches ancient eucrite chondrites, which originate from the asteroid Vesta in the outer asteroid belt. CI, CM, and eucrite chondrites are believed to have the same water content and isotope ratios as ancient icy protoplanets from the outer asteroid belt that later delivered water to Earth.

A further asteroid particle study supported the theory that a large source of earth's water has come from hydrogen atoms carried on particles in the solar wind which combine with oxygen on asteroids and then arrive on earth in space dust. Using atom probe tomography the study found hydroxide and water molecules on the surface of a single grain from particles retrieved from the asteroid 25143 Itokawa by the Japanese space probe Hayabusa.

Comets

Comets are kilometer-sized bodies made of dust and ice that originate from the Kuiper belt (20-50 AU) and the Oort cloud (>5,000 AU), but have highly elliptical orbits which bring them into the inner solar system. Their icy composition and trajectories which bring them into the inner solar system make them a target for remote and in situ measurements of D/H ratios.

It is implausible that Earth's water originated only from comets, since isotope measurements of the deuterium to hydrogen (D/H) ratio in comets Halley, Hyakutake, Hale–Bopp, 2002T7, and Tuttle, yield values approximately twice that of oceanic water. This is also supported by analysis using the comparison of isotopic ratios for both carbon and nitrogen isotopes, which attribute only a few percent of the water present on earth to comet sources, indicating a much higher reliance on incoming asteroid matter. Using the cometary D/H ratio, models predict that less than 10% of Earth's water was supplied from comets.

Other, shorter period comets (<20 years) called Jupiter family comets likely originate from the Kuiper belt, but have had their orbital paths influenced by gravitational interactions with Jupiter or Neptune. 67P/Churyumov–Gerasimenko is one such comet that was the subject of isotopic measurements by the Rosetta spacecraft, which found the comet has a D/H ratio three times that of Earth's seawater. Another Jupiter family comet, 103P/Hartley 2, has a D/H ratio which is consistent with Earth's seawater, but its nitrogen isotope levels do not match Earth's.

Why is there anything at all?

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

This question has been written about by philosophers since at least the ancient Parmenides (c. 515 BC).

"Why is there anything at all?" or "Why is there something rather than nothing?" is a question about the reason for basic existence which has been raised or commented on by a range of philosophers and physicists, including Gottfried Wilhelm Leibniz, Ludwig Wittgenstein, and Martin Heidegger, who called it "the fundamental question of metaphysics".

Introductory points

There is something

No experiment could support the hypothesis "There is nothing" because any observation obviously implies the existence of an observer.

Defining the question

The question is usually taken as concerning practical causality (rather than a moral reason for), and posed totally and comprehensively, rather than concerning the existence of anything specific, such as the universe or multiverse, the Big Bang, God, mathematical and physical laws, time or consciousness. It can be seen as an open metaphysical question, rather than a search for an exact answer.

The circled dot was used by the Pythagoreans and later Greeks to represent the first metaphysical being and the metaphysical life, the Monad or the Absolute.

On timescales

The question does not include the timing of when anything came to exist.

Some have suggested the possibility of an infinite regress, where, if an entity cannot come from nothing and this concept is mutually exclusive from something, there must have always been something that caused the previous effect, with this causal chain (either deterministic or probabilistic) extending infinitely back in time.

Arguments against attempting to answer the question

The question is outside our experience

Philosopher Stephen Law has said the question may not need answering, as it is attempting to answer a question that is outside a spacetime setting while being within a spacetime setting. He compares the question to asking "what is north of the North Pole?"

Causation may not apply

The ancient Greek philosopher Aristotle argued that everything in the universe must have a cause, culminating in an ultimate uncaused cause. (See Four causes.)

However, David Hume argued that a cause may not be necessary in the case of the formation of the universe. Whilst we expect that everything has a cause because of our experience of the necessity of causes, the formation of the universe is outside our experience and may be subject to different rules. Kant supports and extends this argument.

We may only say the question because of the nature of our minds

Kant argues that the nature of our mind may lead us to ask some questions (rather than asking because of the validity of those questions).

The brute fact approach

In philosophy, the brute fact approach proposes that some facts cannot be explained in terms of a deeper, more "fundamental" fact. It is in opposition to the principle of sufficient reason approach.

On this question, Bertrand Russell took a brute fact position when he said, "I should say that the universe is just there, and that's all." Sean Carroll similarly concluded that "any attempt to account for the existence of something rather than nothing must ultimately bottom out in a set of brute facts; the universe simply is, without ultimate cause or explanation."

The question may be impossible to answer

Roy Sorensen has discussed that the question may have an impossible explanatory demand, if there are no existential premises.

Explanations

Something may exist necessarily

Philosopher Brian Leftow has argued that the question cannot have a causal explanation (as any cause must itself have a cause) or a contingent explanation (as the factors giving the contingency must pre-exist), and that if there is an answer, it must be something that exists necessarily (i.e., something that just exists, rather than is caused).

Natural laws may necessarily exist, and may enable the emergence of matter

Philosopher of physics Dean Rickles has argued that numbers and mathematics (or their underlying laws) may necessarily exist. If we accept that mathematics is an extension of logic, as philosophers such as Bertrand Russell and Alfred North Whitehead did, then mathematical structures like numbers and shapes must be necessarily true propositions in all possible worlds.

Physicists, including popular physicists such as Stephen Hawking and Lawrence Krauss, have offered explanations (of at least the first particle coming into existence aspect of cosmogony) that rely on quantum mechanics, saying that in a quantum vacuum state, virtual particles and spacetime bubbles will spontaneously come into existence. The actual mathematical demonstration of quantum fluctuations of the hypothetical false vacuum state spontaneously causing an expanding bubble of true vacuum was done by quantum cosmologists in 2014 at the Chinese Academy of Sciences.

A necessary being bearing the reason for its existence within itself

Gottfried Wilhelm Leibniz attributed to God as being the necessary sufficient reason for everything that exists (see: Cosmological argument). He wrote:

"Why is there something rather than nothing? The sufficient reason... is found in a substance which... is a necessary being bearing the reason for its existence within itself."

A state of nothing may be impossible

The pre-Socratic philosopher Parmenides was one of the first Western thinkers to question the possibility of nothing, and commentary on this has continued.

A state of nothing may be unstable

Nobel Laureate Frank Wilczek is credited with the aphorism that "nothing is unstable." Physicist Sean Carroll argues that this accounts merely for the existence of matter, but not the existence of quantum states, space-time, or the universe as a whole.

It is possible for something to come from nothing

See also: A Universe from Nothing

Some cosmologists believe it to be possible that something (e.g., the universe) may come to exist spontaneously from nothing. Some mathematical models support this idea, and it is growing to become a more prevalent explanation among the scientific community for why the Big Bang occurred.

Other explanations

Robert Nozick proposed some possible explanations.

1. Self-Subsumption: "a law that applies to itself, and hence explains its own truth."
2. The Nothingness Force: "the nothingness force acts on itself, it sucks nothingness into nothingness and produces something..."

Mariusz Stanowski explained: "There must be both something and nothing, because separately neither can be distinguished".

Humour

Philosophical wit Sidney Morgenbesser answered the question with an apothegm: "If there were nothing, you'd still be complaining!", or "Even if there was nothing, you still wouldn't be satisfied!"