The singularity from the FLRW metric is interpreted to mean that current theories are inadequate to describe what actually happened at the start of the Big Bang itself. It is widely believed that a correct theory of quantum gravity may allow a more correct description of that event, but no such theory has yet been developed.
After that moment, all distances throughout the universe began to increase from perhaps zero because the FLRW metric itself changed over time, affecting distances between all non-bound objects everywhere. For this reason it is said that the Big Bang "happened everywhere". During the earliest moments of cosmic time, the energies and conditions were so extreme that current knowledge can only suggest possibilities, which may turn out to be incorrect. To give one example, eternal inflation theories propose that inflation lasts forever throughout most of the universe, making the notion of "N seconds since Big Bang" ill-defined.
Therefore the earliest stages are an active area of research and based on ideas which are still speculative and subject to modification as scientific knowledge improves. The inflationary period marks a specific period when a very rapid change in scale occurred, but does not mean that it stayed the same at other times.
More precisely, during inflation, the expansion accelerated. After inflation, and for about 9. About 4 billion years ago, it began slightly speeding up again. Initially, the universe was inconceivably hot and dense. It has cooled over time, which eventually allowed the forces, particles, and structures currently seen to manifest as they do today.
The Planck epoch is an era in traditional non-inflationary Big Bang cosmology immediately after the event which began the known universe. During this epoch, the temperature and average energies within the universe were so high that everyday subatomic particles could not form, and even the four fundamental forces that shape the universe — gravitation, electromagnetism , the weak nuclear force , and the strong nuclear force — were combined and formed one fundamental force.
Little is understood about physics at this temperature; different hypotheses propose different scenarios. Traditional big bang cosmology predicts a gravitational singularity before this time, but this theory relies on the theory of general relativity , which is thought to break down for this epoch due to quantum effects. Models that aim to describe the universe and physics during the Planck epoch are generally speculative and fall under the umbrella of " New Physics ".
Examples include the Hartle—Hawking initial state , string theory landscape , string gas cosmology , and the ekpyrotic universe. As the universe expanded and cooled, it crossed transition temperatures at which forces separated from each other. These phase transitions can be visualized as similar to condensation and freezing phase transitions of ordinary matter. This is not apparent in everyday life, because it only happens at far higher temperatures than we usually see in our present universe.
These phase transitions in the universe's fundamental forces are believed to be caused by a phenomenon of quantum fields called " symmetry breaking ". In everyday terms, as the universe cools, it becomes possible for the quantum fields that create the forces and particles around us, to settle at lower energy levels and with higher levels of stability.
In doing so, they completely shift how they interact. Forces and interactions arise due to these fields, so the universe can behave very differently above and below a phase transition.
For example, in a later epoch, a side effect of one phase transition is that suddenly, many particles that had no mass at all acquire a mass they begin to interact differently with the Higgs field , and a single force begins to manifest as two separate forces. Assuming that nature is described by a so-called Grand Unified Theory GUT , the grand unification epoch began with a phase transitions of this kind, when gravitation separated from the universal combined gauge force.
This caused two forces to now exist: gravity , and an electrostrong interaction. There is no hard evidence yet, that such a combined force existed, but many physicists believe it did. The physics of this electrostrong interaction would be described by a Grand Unified Theory. The grand unification epoch ended with a second phase transition, as the electrostrong interaction in turn separated, and began to manifest as two separate interactions, called the strong and the electroweak interactions.
Depending on how epochs are defined, and the model being followed, the electroweak epoch may be considered to start before or after the inflationary epoch. In some models it is described as including the inflationary epoch. The electroweak interaction will also separate later, dividing into the electromagnetic and weak interactions. The exact point where electrostrong symmetry was broken is not certain, because of the very high energies of this event.
At this point of the very early universe, the metric that defines distance within space suddenly and very rapidly changed in scale , leaving the early universe at least 10 78 times its previous volume and possibly much more. This change is known as inflation. Although light and objects within spacetime cannot travel faster than the speed of light , in this case it was the metric governing the size and geometry of spacetime itself that changed in scale. Changes to the metric are not limited by the speed of light.
There is good evidence that this happened, and it is widely accepted that it did take place. But the exact reasons why it happened are still being explored. So a range of models exist that explain why and how it took place—it is not yet clear which explanation is correct. In several of the more prominent models, it is thought to have been triggered by the separation of the strong and electroweak interactions which ended the grand unification epoch.
One of the theoretical products of this phase transition was a scalar field called the inflaton field. As this field settled into its lowest energy state throughout the universe, it generated an enormous repulsive force that led to a rapid expansion of the metric that defines space itself.
Inflation explains several observed properties of the current universe that are otherwise difficult to account for, including explaining how today's universe has ended up so exceedingly homogeneous similar on a very large scale, even though it was highly disordered in its earliest stages.
The rapid expansion of space meant that elementary particles remaining from the grand unification epoch were now distributed very thinly across the universe. However, the huge potential energy of the inflation field was released at the end of the inflationary epoch, as the inflaton field decayed into other particles, known as "reheating".
This heating effect led to the universe being repopulated with a dense, hot mixture of quarks, anti-quarks and gluons. In other models, reheating is often considered to mark the start of the electroweak epoch, and some theories, such as warm inflation , avoid a reheating phase entirely. Therefore, in inflationary cosmology, the earliest meaningful time "after the Big Bang" is the time of the end of inflation. After inflation ended, the universe continued to expand, but at a much slower rate.
About 4 billion years ago the expansion gradually began to speed up again. This is believed to be due to dark energy becoming dominant in the universe's large-scale behaviour. It is still expanding today. On 17 March , astrophysicists of the BICEP2 collaboration announced the detection of inflationary gravitational waves in the B-modes power spectrum which was interpreted as clear experimental evidence for the theory of inflation.
As the universe's temperature continued to fall below a certain very high energy level, a third symmetry breaking occurs. So far as we currently know, it was the penultimate symmetry breaking event in the formation of our universe, the final one being chiral symmetry breaking in the quark sector.
In the Standard Model of particle physics, electroweak symmetry breaking happens at a temperature of This has two related effects:. After electroweak symmetry breaking, the fundamental interactions we know of—gravitation, electromagnetic, weak and strong interactions—have all taken their present forms, and fundamental particles have their expected masses, but the temperature of the universe is still too high to allow the stable formation of many particles we now see in the universe, so there are no protons or neutrons, and therefore no atoms, atomic nuclei , or molecules.
More exactly, any composite particles that form by chance, almost immediately break up again due to the extreme energies. If supersymmetry is a property of our universe, then it must be broken at an energy that is no lower than 1 TeV , the electroweak scale. The masses of particles and their superpartners would then no longer be equal.
This very high energy could explain why no superpartners of known particles have ever been observed. After cosmic inflation ends, the universe is filled with a hot quark—gluon plasma , the remains of reheating. From this point onwards the physics of the early universe is much better understood, and the energies involved in the Quark epoch are directly accessible in particle physics experiments and other detectors.
This was the period in the evolution of the early universe immediately after electroweak symmetry breaking, when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but the temperature of the universe was still too high to allow quarks to bind together to form hadrons. During the quark epoch the universe was filled with a dense, hot quark—gluon plasma, containing quarks, leptons and their antiparticles.
Collisions between particles were too energetic to allow quarks to combine into mesons or baryons. Baryons are subatomic particles such as protons and neutrons, that are composed of three quarks. It would be expected that both baryons, and particles known as antibaryons would have formed in equal numbers. However, this does not seem to be what happened—as far as we know, the universe was left with far more baryons than antibaryons.
In fact, almost no antibaryons are observed in nature. It is not clear how this came about. Any explanation for this phenomenon must allow the Sakharov conditions related to baryogenesis to have been satisfied at some time after the end of cosmological inflation.
Current particle physics suggests asymmetries under which these conditions would be met, but these asymmetries appear to be too small to account for the observed baryon-antibaryon asymmetry of the universe.
The quark—gluon plasma that composes the universe cools until hadrons, including baryons such as protons and neutrons, can form. A comparatively small residue of hadrons remained at about 1 second of cosmic time, when this epoch ended. Theory predicts that about 1 neutron remained for every 7 protons. We believe this to be correct because, at a later stage, all the neutrons and some of the protons fused , leaving hydrogen, a hydrogen isotope called deuterium, helium and other elements, which we can measure.
A ratio of hadrons at the end of this epoch would indeed produce the observed element ratios in the early as well as current universe. At approximately 1 second after the Big Bang neutrinos decouple and begin travelling freely through space.
As neutrinos rarely interact with matter, these neutrinos still exist today, analogous to the much later cosmic microwave background emitted during recombination, around , years after the Big Bang.
One of these predictions is that neutrinos will have left a subtle imprint on the CMB. It is well known that the CMB has irregularities. Some of the CMB fluctuations were roughly regularly spaced, because of the effect of baryonic acoustic oscillations. In theory, the decoupled neutrinos should have had a very slight effect on the phase of the various CMB fluctuations.
In , it was reported that such shifts had been detected in the CMB. Moreover, the fluctuations corresponded to neutrinos of almost exactly the temperature predicted by Big Bang theory 1. Primordial black holes are a hypothetical type of black hole proposed in ,  that may have formed during the so-called radiation-dominated era , due to the high densities and inhomogeneous conditions within the first second of cosmic time.
Random fluctuations could lead to some regions becoming dense enough to undergo gravitational collapse, forming black holes. Current understandings and theories place tight limits on the abundance and mass of these objects. The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons such as the electron , muons and certain neutrinos and antileptons, dominating the mass of the universe.
The lepton epoch follows a similar path to the earlier hadron epoch. Initially leptons and antileptons are produced in pairs. About 10 seconds after the Big Bang the temperature of the universe falls to the point at which new lepton—antilepton pairs are no longer created and most remaining leptons and antileptons quickly annihilated each other, giving rise to pairs of high energy photons, and leaving a small residue of non-annihilated leptons.
After most leptons and antileptons are annihilated at the end of the lepton epoch, most of the mass-energy in the universe is left in the form of photons. Therefore, the energy of the universe, and its overall behaviour, is dominated by its photons.
These photons continue to interact frequently with charged particles, i. They continue to do so for about the next , years. Between about 2 and 20 minutes after the Big Bang, the temperature and pressure of the universe allowed nuclear fusion to occur, giving rise to nuclei of a few light elements beyond hydrogen "Big Bang nucleosynthesis". Atomic nuclei will easily unbind break apart above a certain temperature, related to their binding energy.
From about 2 minutes, the falling temperature means that deuterium no longer unbinds, and is stable, and starting from about 3 minutes, helium and other elements formed by the fusion of deuterium also no longer unbind and are stable. The short duration and falling temperature means that only the simplest and fastest fusion processes can occur.
Only tiny amounts of nuclei beyond helium are formed, because nucleosynthesis of heavier elements is difficult and requires thousands of years even in stars. The next most common stable isotopes produced are lithium-6 , beryllium-9, boron , carbon , nitrogen and oxygen "CNO" , but these have predicted abundances of between 5 and 30 parts in 10 15 by mass, making them essentially undetectable and negligible.
The amounts of each light element in the early universe can be estimated from old galaxies, and is strong evidence for the Big Bang. A few isotopes, such as lithium-7, were found to be present in amounts that differed from theory, but over time, these differences have been resolved by better observations.
Until now, the universe's large scale dynamics and behaviour have been determined mainly by radiation—meaning, those constituents that move relativistically at or near the speed of light , such as photons and neutrinos. This occurs because the energy density of matter begins to exceed both the energy density of radiation and the vacuum energy density.
According to the Lambda-CDM model , by this stage, the matter in the universe is around However the total matter in the universe is only There is overwhelming evidence that dark matter exists and dominates our universe, but since the exact nature of dark matter is still not understood, the Big Bang theory does not presently cover any stages in its formation.
From this point on, and for several billion years to come, the presence of dark matter accelerates the formation of structure in our universe. In the early universe, dark matter gradually gathers in huge filaments under the effects of gravity, collapsing faster than ordinary baryonic matter because its collapse is not slowed by radiation pressure.
This amplifies the tiny inhomogeneities irregularities in the density of the universe which was left by cosmic inflation. Over time, slightly denser regions become denser and slightly rarefied emptier regions become more rarefied.
Ordinary matter eventually gathers together faster than it would otherwise do, because of the presence of these concentrations of dark matter. The properties of dark matter that allow it to collapse quickly without radiation pressure, also mean that it cannot lose energy by radiation either. Losing energy is necessary for particles to collapse into dense structures beyond a certain point. Therefore dark matter collapses into huge but diffuse filaments and haloes, and not into stars or planets.
Ordinary matter, which can lose energy by radiation, forms dense objects and also gas clouds when it collapses. At around , years, the universe has cooled enough for helium hydride, the first molecule, to form.
About , years after the Big Bang, two connected events occurred: recombination and photon decoupling. Recombination describes the ionized particles combining to form the first neutral atoms, and decoupling refers to the photons released "decoupled" as the newly formed atoms settle into more stable energy states.
Just before recombination, the baryonic matter in the universe was at a temperature where it formed a hot ionized plasma. Most of the photons in the universe interacted with electrons and protons, and could not travel significant distances without interacting with ionized particles.
As a result, the universe was opaque or "foggy". Although there was light, it was not possible to see, nor can we observe that light through telescopes. At around , years, the universe has cooled to a point where free electrons can combine with the hydrogen and helium nuclei to form neutral atoms. Directly combining in a low energy state ground state is less efficient, so these hydrogen atoms generally form with the electrons still in a high energy state, and once combined, the electrons quickly release energy in the form of one or more photons as they transition to a low energy state.
This release of photons is known as photon decoupling. Some of these decoupled photons are captured by other hydrogen atoms, the remainder remain free. By the end of recombination, most of the protons in the universe have formed neutral atoms. This change from charged to neutral particles means that the mean free path photons can travel before capture in effect becomes infinite, so any decoupled photons that have not been captured can travel freely over long distances see Thomson scattering.
The universe has become transparent to visible light , radio waves and other electromagnetic radiation for the first time in its history. Red shifting describes the photons acquiring longer wavelengths and lower frequencies as the universe expanded over billions of years, so that they gradually changed from visible light to radio waves.
These same photons can still be detected as radio waves today. They form the cosmic microwave background, and they provide crucial evidence of the early universe and how it developed.
Around the same time as recombination, existing pressure waves within the electron-baryon plasma—known as baryon acoustic oscillations —became embedded in the distribution of matter as it condensed, giving rise to a very slight preference in distribution of large-scale objects.
Therefore, the cosmic microwave background is a picture of the universe at the end of this epoch including the tiny fluctuations generated during inflation see 9-year WMAP image , and the spread of objects such as galaxies in the universe is an indication of the scale and size of the universe as it developed over time.
After recombination and decoupling, the universe was transparent and had cooled enough to allow light to travel long distances, but there were no light-producing structures such as stars and galaxies. Stars and galaxies are formed when dense regions of gas form due to the action of gravity, and this takes a long time within a near-uniform density of gas and on the scale required, so it is estimated that stars did not exist for perhaps hundreds of millions of years after recombination.
New Living Translation Before daybreak the next morning, Jesus got up and went out to an isolated place to pray. English Standard Version And rising very early in the morning, while it was still dark, he departed and went out to a desolate place, and there he prayed. Berean Study Bible Early in the morning, while it was still dark, Jesus got up and slipped out to a solitary place to pray. Berean Literal Bible And having risen up very early, still much in night, He went out and departed into a solitary place, and there He was praying.
New American Standard Bible In the early morning, while it was still dark, Jesus got up, left the house, and went away to a secluded place, and was praying there. New King James Version Now in the morning, having risen a long while before daylight, He went out and departed to a solitary place; and there He prayed. King James Bible And in the morning, rising up a great while before day, he went out, and departed into a solitary place, and there prayed.
Christian Standard Bible Very early in the morning, while it was still dark, he got up, went out, and made his way to a deserted place; and there he was praying. Contemporary English Version Very early the next morning before daylight, Jesus got up and went to a place where he could be alone and pray. Good News Translation Very early the next morning, long before daylight, Jesus got up and left the house.
He went out of town to a lonely place, where he prayed. People should follow the guidelines put in place by their local health organizations to ensure they keep themselves and others safe. A person can protect themselves from coronavirus by following the CDC guidelines.
COVID is a highly infectious disease that will usually produce symptoms a person can manage at home. However, it can occasionally cause severe illness. People with a coronavirus infection should ensure they follow guidelines and self-isolate for 14 days from when they become sick. If a person with COVID has trouble breathing, or experiences other concerning symptoms, they should call and seek medical attention.
Researchers are now working on developing a coronavirus vaccine. Learn more here. The symptoms of the flu and the coronavirus are similar, but there are differences. Learn more about the other symptoms and what to expect here.
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