The Big Bang Theory is moderncosmologyThe most influential onetheory。Its main point is that the universe had a history of evolution from hot to cold.During this period, the universe system was expanding constantly, making the density of matter evolve from dense to thin, like a huge explosion.
The Big Bang Theory believes that the universe is formed by a dense and hot singularity after a big explosion 13.7 billion years ago.In 1927,BelgiumAstronomers and cosmologistsLemet(Georges Lema î tre) proposed the Big Bang hypothesis for the first time.In 1929, American astronomerHubbleAccording to the hypothesisRedshift amountProportional to the distance between galaxiesHubble's lawAnd deduced the cosmic expansion theory that galaxies are far away from each other.
moderncosmologyOne of the most influential theories in.Its main point is that the universe had a history of evolution from hot to cold.During this period, the universe system is expanding constantly, making the density of matter from dense to thinevolution, like a huge explosion.One of the founders of this theory is Gamov.In 1946, American physicist Gamov formally proposedBig Bang TheoryIt is believed that the universe was formed by a big explosion about 14 billion years ago.At the end of last century, yesIa supernovaOur observations show that the expansion of the universe is accelerating, because the universe may be mostly composed of dark energy.[1]
Production principle
Announce
edit
Big Bang Cosmology
At the beginning of the explosion, matter can only bephotonandneutrinoAnd other basic particle forms exist.[2]The continuous expansion after the cosmic explosion led to a rapid decline in temperature and density.As the temperature decreases and cools, atoms are gradually formedNucleus, molecules, and recombine into ordinary gases.The gas gradually condenses intoNebulaNebula further forms various stars and galaxies, and finally forms the universe we see today.
Basic assumptions
Announce
edit
The establishment of the Big Bang theory is based on two basic assumptions:Laws of physicsUniversality andCosmological principle。Cosmological principle means that the universe is homogeneous and isotropic on a large scale.
These views were initially introduced as apriori axioms, and now there are relevant research efforts to verify them.For example, for the first hypothesis, experiments have confirmed that most of the time since the birth of the universe,Fine structure constantThe relative error value of will not exceed 10 ^ (- 5).In addition, through the study of the solar system andbinary star The general theory of relativity has been verified by very accurate experiments;On a broader cosmological scale, the empirical success of the Big Bang theory in many aspects is also a strong support for general relativity.
Assuming that the large-scale universe is isotropic from the earth,cosmologyThe principle can be changed from a simplerCopernican principle Export in.Copernicus principle means that there is no preferred (or special) observer or observation position.According to the observation of microwave background radiation, the cosmological principle has been confirmed to be on the order of 10 ^ (- 5)establishThe uniformity observed by the universe on a large scale is on the order of 10%.
Research history
Announce
edit
Discovery phase
But since American astronomer Edwin Hubble began to observe the "redshift phenomenon" in 1922“Cosmic expansion”The idea of "is beginning to form.".
In 1929,Edwin Hubble A landmark discovery is summarized, that is, no matter which direction you look, the distant galaxy is rapidly away from us, while the nearby galaxy is approaching us.In other words, the universe is expanding.This means that earlier stars were closer to each other.In fact, it seems that at some time about 10 billion to 20 billion years ago, they were in the same place, so Hubble's discovery suggests that there was abig bangAt that time, the universe was at a singularity with infinite density.[6]
Einstein, who heard about this, soon came to the Wilson Observatory where Hubble worked, and under the leadership of Hubble, he personally carried outRedshift phenomenonObservation of.After the interview, Einstein openly admitted the mistake that his subjective consciousness affected the scientific conclusion, and removed the cosmological constant in the field equation, thus the Einstein Field Equation, as we know it today, came into being.
Maturity stage
Around 1948,GamovFirst establishedThermal explosionThe concept of.The big explosion that created the universe is not the kind of explosion that happens at a certain point on the earth and spreads to the surrounding air, but the kind of explosion that happens everywhere at the same time and fills the whole space from the beginning. Each particle in the explosion is separated from each otherparticleRun fast.In fact, it should be understood asspaceThe rapid expansion of."The whole space" can refer to the whole infinite universe, or a finite universe that can be bent back to its original position just like a sphere.
According to the Big Bang cosmology, the early universe was composed ofMicroparticleThe uniform gas formed has extremely high temperature and density, and is expanding at a very high rate.These gasesheat balanceThere is even temperature under.The unified temperature is the universe at that timestateIs an important symbol ofCosmic temperature。Gas insulationexpandWill reduce the temperatureNucleus、atomand evenfixed starThe system can appear one after another.
Brief history of explosion
Announce
edit
When the Big Bang began: about 15 billion years ago, the points with infinitely small volume, infinitely high density, infinitely high temperature, and infinitely large space-time curvature were called singular points.spaceandtimeBorn in some kind of super space-time - partcosmologyThey call it quantum vacuum（False vacuum）, which is full ofHeisenberg Uncertainty Principle Corresponding quantum energy perturbation.[3]
10 after the big bang-43Seconds（Planck time）: About 10thirty-twoDegrees, the universe fromquantumThe rise and fall background is calledPlanck time。Before that, the density of the universe might exceed 10 per cubic centimeterninety-fourG, exceeding proton density by 10seventy-eightIn physics, all forces are one.（Supersymmetry）At this stage, the universe has cooled togravitationIt can be separated and begin to exist independently, and exist and transmitGravitational interactionOfGraviton。Other forces in the universe (strong, weak interactions andElectromagnetic interaction）Still one.[3]
Big Bang Cosmology
10 after the big bang-35Seconds: about 10twenty-sevenDegrees,Inflationary period（First push）, gravity has been separated, quarkBoson、LeptonFormation.At this stage, the universe has cooled toStrong interactionCan be separated, andWeak interactionAnd electromagnetic interaction are still unified in the so-calledElectroweak interaction。The universe also happenedUpsurge, the boom lasted only 10-33Second, in this instant, the universe experienced 100 times doubling (2one hundred）, the obtained scale is 10% of the previous scalethirty(The universe itself, that is, space and time itself, is soaring, which does not violatelight speedFence).The universe was still there before the explosionphotonAll rough points can be smoothed out within the range of interconnection. When the boom stops, the things detected today have stabilized in their respective small regions, which is calledinflation theory 。[3]
10 after the big bang-12Seconds: about 10fifteenDegree, particle stage,protonandneutronAndAntiparticleFormation, bosonneutrino, electrons, quarks, andGluonStabilize.The universe becomes cold enough, and the weak electric interaction is decomposed into electromagnetic interaction and weak interaction.LeptonFamilies (electrons, neutrinos and corresponding antiparticles) need to wait for the universe to continue cooling 10-4Only seconds can separate from the equilibrium phase of other particles.In which neutrinos onceDecoupling, will freely cross the space, and in principle can detect these original junior high school neutrinos.[3]
0.01 seconds after the big bang: about 100 billion degrees,photon, ElectronicneutrinoThe proton neutron only accounts for one part of one billion. In thermal equilibrium state, the system expands rapidly, and the temperature and density continue to decline.
0.1 seconds after the Big Bang: about 30 billion degrees, the neutron proton ratio decreased from 1.0 to 0.61.
One second after the big bang: about 10 billion degrees, neutrinos escape outward, and positron and negative electron annihilation reactions appear,Nuclear forceNot enough restraintneutronandproton。
10 seconds after the big bang: about 3 billion degrees, during the nuclear period,hydrogen、heliumQuasi stableNucleus(chemical element) forming.When the universe cools to 10nineBelow Kelvin (about 100 seconds later), particle transformation is impossible.Nuclear synthesis calculation indicates that,baryonDensity only accounts fortopology2%~5% of the material required for the flat universe strongly implies the energy form of other materials (non baryonsdark substanceAnd dark energy) filled the universe[3]。
10 after the big bangelevenSeconds (10fourYear), the temperature is about 10fiveKelvin, material period.In the early history of the universe, light dominated various forms of energy.along withCosmic expansion，electromagnetic radiationThe wavelength of the photon is lengthened, and the corresponding photon energy decreases.radiationenergy density And scale (R) and volume (4 π Rthree/3) The product of is inversely reduced, i.e. safety 1/RfourAnd the energy density of the material is simply 1/R of the volumethreeInverse scalereduce.Ten thousand years later, the density of matter caught up with that of radiation and exceeded it. Since then, the universe and its dynamics have become dominated by matter.[3]
300000 years after the Big Bang: about 3000 degrees, neutral due to chemical combinationatomThe main component of the universe is gaseous matter, which gradually condenses into a gas cloud with high density under the action of self gravity untilfixed starandStellar system。
The quantum vacuum reached its peak in the boom period, and then it spread throughout the universe in the form of dark energy. With the rapid reduction of the density of matter and radiation, the dark energy became more and more obvious.Dark energy may account for 2/3 of the total energy density of the universe[1], thus promotingCosmic acceleration。[3]
On June 1, 2021, the European team of scientists used the Large Hadron Collider (LHC) to reveal the new details of the first 0.000001 second of the Big Bang, that is, what happened to a special plasma in the first microsecond. This plasma is not only the "first substance" in the history of the universe,Its relevant details also provide an important "puzzle" for the evolution of the universe as we know it today.[5]
On April 4, 2023, an international team of astronomersTwo papers published in Nature Astronomy pointed out that they discovered four of the oldest known galaxies by James Webb Space Telescope, one of which formed 320 million years after the Big Bang, when the universe was still in its infancy[7]。
Observational fact
Announce
edit
The scientific nature of the Big Bang theory is compelling.The most direct evidence comes from the study of the light characteristics of distant galaxies.In the 1920s, astronomersEdwin Hubble (Edwin Hubble) studiedVesto Slipher (Vesto Slipher).He noticed that the color of the far galaxy was slightly redder than that of the near galaxy.Hubble carefully measured this reddening and made a map.He found that this reddening（red shift）It is systematic. The farther away a galaxy is from us, the redder it appears.
lightThe color of is related to its wavelength.staywhite lightIn the spectrum, the blue light is at the short wave end, and the red light is at thelong waveEnd.The reddening of distant galaxies means that theirlight waveThe wavelength has become slightly longer.In carefully measuring the spectra of many galaxiesCharacteristic spectral lineHubble confirmed the effect.He believes that light waves grow longer because the universe isexpandResults.This great discovery of Hubble has laid the foundation for modern timescosmologyThe foundation of.
The nature of the expanding universe has puzzled many people.From the Earth's point of view, it seems that distant galaxies are rapidly moving away from us.However, this does not mean that the earth is the center of the universe.On average, the expansion image is the same in different parts of the universe.It can be said that every point is the center, and no point is the center (the best explanation is a painting: cutting of three-dimensional space).We'd better think of it as intergalacticspaceThey are stretching or expanding, rather than galaxies moving in space.This is different from the explosion from a point seen in our daily life.
The fact that space can stretch may seem odd, but it was 1915EinsteingeneralizedrelativityThe concept that scientists have known for a long time since its publication.General relativityIt is believed that gravity is actually space (strictly speakingspace-time）A form of bending or deformation.In a sense, space is elastic and can be bent or extended in a certain way, depending on the arrangement of materials.This idea has been fully confirmed by observation.
In May 2023, an astronomer team led by the University of Southampton in the UK captured the largest ever cosmic explosion, which is believed to be caused by a huge gas cloud swallowed by a supermassive black hole.[8]
Related concepts
Announce
edit
Expansion space
The basic concept of expansion space can be understood through a simple simulation.Imagine sewing a row of buttons on an elastic band.Suppose you lengthen the elastic belt from both ends, and all the buttons will be far away from each other.No matter which button we choose, the buttons on its adjacent side seem to be far away, and the expansion is the same everywhere, without a special center.Of course, when we draw this row of buttons, it has a central button, but this has nothing to do with the expansion mode of the system.As long as the elastic belt with buttons is infinitely lengthened or looped into a circle, the center will no longer exist.
Judging from any button, the button closest to it regresses at a certain speed, and the next button regresses at a double degree, and so on.In your opinion, the farther away the button is, the faster it will recede.So this expansion means that the retrogression speed is proportional to the distance - this is a very important relationship.With this image, we can imagine that light waves are, no wonder Hubble found that,Redshift amountIt is proportional to the distance, which is completely consistent with the result of this simple image simulation.
Horizon
An important feature of the Big Bang space-time isHorizonThe existence of: Because the universe has a limited age and light has a limited speed, there may be some past events that cannot pass information to us through light.From this analysis, we can see that there is such a limit or past horizon, and only events within this limit distance can be observed.On the other hand, because space is constantly expanding, and the more distant objects recede at a greater speed, the light emitted from us may never reach there.From this analysis, we can see that there is such a limit or future horizon, and only events within this limit distance can be affected by us.The existence of the above two horizons depends on the specific form of the FLRW model describing our universe: our existing understanding of the very early universe means that there should be a past horizon for the universe, but our observations in experiments are still limited by the opacity of the early universe to electromagnetic waves,As a result, we can not observe the events in the longer term through electromagnetic waves even though the horizon has retreated due to space expansion in the past.On the other hand, if the expansion of the universe continues to accelerate, the universe will also have a future horizon.
Microwave radiation (1978 Nobel Prize in Physics)
Cosmic microwave background radiation
As early as the late 1940s, the originator of the Big Bang cosmologyGamovIt is believed that our universe is bathed in the residual radiation of the early high-temperature universe, whose temperature is about 6K.Just as a stove can emit a little hot gas even though it no longer has a fire.
In 1964, a young engineer of Bell Telephone Company——PenziasandWilsonWhen debugging their huge horn antenna, they unexpectedly received a kind of millimeter wave microwave interference, and the signal strength in all directions was the same, which lasted several months without change.
Is there something wrong with the instrument itself?Or is it caused by pigeons perched on the antenna?They disassembled and reassembled the antenna, and still received the inexplicable millimeter wave.The wavelength of this wave is several millimeters, and in the microwave band, it corresponds toEffective temperatureRadiated by 3.5K blackbodyelectromagnetic wave(Its spectrum is exactly consistent with the luminescence in the furnace that reaches a certain thermal equilibrium state. This radiation is known to physicists“Blackbody radiation”）。After their analysis, they think that this millimeter wave is definitely not fromArtificial satellite, or from the sunGalaxyOr someExtragalactic galaxyRadio source, because the millimeter wave intensity is always constant when the antenna is rotated.
Later, after further measurement and calculation.The radiation temperature is 2.7K, which is generally called 3K cosmic microwave background radiation.This discovery has greatly encouraged many scientists engaged in the study of Big Bang cosmology.Because Penzias and Wilson's observations are so close to the temperature predicted by the theoryBig BangOn a very strong support!This is after Hubble's discovery in 1929Galactic spectral linered shiftAfter that, another major astronomical discovery was made.
The discovery of cosmic microwave background radiation has opened up a new field for observing the universe, and also provided a new observation constraint for various cosmic models. Therefore, it was listed as one of the four major discoveries in astronomy in the 1960s.Penzias and Wilson obtained theThe nobel prize in physics。The Swedish Academy of Sciences pointed out in the award decision that this discovery enables us to obtain information about the cosmic processes that took place long ago during the creation of the universe.
Helium abundance
Finally, there is another proof of incandescence and high densityThe origin of the universeTheoretical evidence.Just know todaythermal radiationAccording to the thermal big bang theory, it is easy to calculate that the temperature everywhere is about 10 billion degrees one second after the birth of the universe, which is too high for the synthesis of existing atomic nuclei.At that time, matter must be torn into the most basic components, forming a potQuark gluon soup, such asproton、neutronAnd electronics.But as the soup cools,nuclear reactionIt may appear.
The big bang model can be used to calculateHelium-4、helium-3 、deuteriumAnd lithium-7, etcLight elementRelatively ordinaryHydrogen elementThe proportion of content in the universe.All these light elementsabundanceIt all depends on a parameter, that is, the ratio of photons to baryons in the early universe, and the calculation of this parameter is independent of the specific details of the microwave background radiation fluctuations.Big Bang TheoryThe inferred proportion of light elements (here it is the ratio of the total mass of elements rather than the ratio of quantity) is about: helium-4/hydrogen=0.25, deuterium/hydrogen=10 ^ - 3, helium-3/hydrogen=10 ^ - 4, and lithium-7/hydrogen=10 ^ - 7.
The light element abundances measured in practice are roughly consistent with the theoretical values calculated from the photon baryon ratio.Among them, deuterium is the best match between the theoretical value and the measured value, helium-4 is close to but still different from the measured value, and lithium-7 is twice the difference. There is a large systematic random error for the calculation of the latter two elements.Nevertheless, the light element abundances predicted by the Big Bang nucleosynthesis theory can be considered as basically consistent with the actual observations, which is a strong support for the Big Bang theory.So far, no other theory can explain and give the relative abundance of these light elements.At the same time, the content of helium in the universe predicted by the Big Bang theory, which can be "regulated", cannot exceed or be lower than 20% to 30% of the existing abundance.In fact, many observation results can only be explained by the Big Bang theory today, for example, why the abundance of helium in the early universe is higher than deuterium, and the content of deuterium is higher than helium-3, and the proportion is constant.
Main evidence
Announce
edit
On March 17, 2014, American physicists announced that they had discovered direct evidence for the existence of the primordial gravitational waves of the universe for the first time.
primaryGravitational waveIt was proposed by Einstein in the general theory of relativity published in 1916. It is a kind of space-time wave generated at the beginning of the universe, which is weakened with the evolution of the universe.Scientists say that the original gravitational waves, like the "afterglow" of the Big Bang of Genesis, will help people trace back to an extremely short period of rapid expansion at the beginning of the creation of the universe, the so-called "inflation".
However, since the general theory of relativity was put forward nearly a hundred years ago, other important predictions derived from it, such as the bending of light, the perihelion precession of Mercury, and the gravitational redshift effect, have been confirmed one by one, while gravitational waves have never been directly detected. The problem is that their signals are extremely weak and difficult to measure technically.
The Harvard Smithsonian Center for Astrophysics and other institutional physicists use the BICEP2 telescope set up in the South Pole to observe the "embers" of the Big Bang - microwave background radiation.The microwave background radiation is formed by the microwave background photons diffused in the cosmic space. The calculation shows that a special polarization mode called mode B will be generated when the original gravitational wave acts on the microwave background photons, and other forms of disturbance can not produce this mode B polarization, so the mode B polarization becomes the "unique mark" of the original gravitational wave.The observed B mode polarization means the existence of gravitational waves.
The South Pole is one of the best places on Earth to observe the microwave background radiation.The researchers found a polarization signal of mode B that was "much stronger than expected" here. After more than three years of analysis, they excluded other possible sources and confirmed that it was caused by the original gravitational wave.
At the beginning of 2016, scientists from the American Laser Interference Gravitational Wave Observatory (LIGO) and the European Gravitational Wave Observatory (VIRGO) jointly announced that they had detected the gravitational waves generated by the merger of two black holes about 30 times the mass of the sun 1.3 billion years ago. This discovery is called "the discovery of the epoch".
Theoretical Award
Announce
edit
American Saul Perlmutter and Adam Reese, as well as Brian Schmidt, who holds dual nationality of the United States and Australia, won the 2011 Nobel Prize in Physics.The jury of the Nobel Prize in Physics commented on the 4th that the three winners "studied dozens of exploding stars, namely 'supernovae', and found that the universe is expanding at an accelerating rate".At the Swedish Academy of Sciences in Stockholm, Sweden, the Nobel Prize in Physics was announced at 11:45 local time (17:45 Beijing time).
The research object of Perlmutter, Riess and Schmidt is a phenomenon that occurs with the separation of the core and the shell of some massive stars in the late evolution period, that is, the super large explosion.A star whose mass is 8 to 25 times that of the sun ends its "life" in a supernova explosion, while the gas packet outside the star is thrown away at a high speed, showing an absolute luminosity 10 billion times higher than that of the sun.When analyzing the explosions of certain types of supernovae, the research team of Perlmutter, Rhys and Schmidt found that more than 50 supernovae appeared dimmer than previously expected.The explanation for this result is that the universe is accelerating its expansion.This discovery was called "shaking the foundation of cosmology" by the Royal Swedish Academy of Sciences.NobelThe review committee of the Physics Prize recognized that the research results obtained by the three winners have changed the human understanding of the universe."Nearly a century ago, it was generally accepted that the universe was expanding, about 14 billion years ago‘big bang’Results. "The review committee said."However, it is amazing to find that the expansion of the universe is accelerating." The review committee said, "If the expansion continues to accelerate, the universe will end in a frozen state." In addition, the research of three people confirmed a theory originally proposed by Albert Einstein, a scientist, that is, the theory he called "cosmological constant".In 1998, Perlmutter presided over a research group, and Schmidt presided over another research group, including Reese.The two groups work hard and "compete" with each other, and the observation results can be described as "coincidental".The evaluation committee announced a prize of 10 million yuanSwedenKronor (about 1.46 million US dollars), Perlmutter got one half, Schmidt and Rhys got the other half.
Existing problems
Announce
edit
For the first few minutes after the Big Bang, there was a serious lack of relevant observations, and the actual form of the earliest cosmic matter energy was still only a guess to a large extent.grand unified theory Predicted specific types of particles (such as elusiveMagnetic monopole）, andSuperstring、Supersymmetry、SupergravityAnd othersMultidimensionalBoth theories predict their primary particles and forces.
Substance pairAntimatterThe absolute advantage of is also an empirical fact that needs to be explained thoroughly.
Other major issues are related to the generation and nature of dark matter and dark energy (generally, quantum vacuum is considered as the main provider of both).[3]
Modern debate
Announce
edit
American scientists proved that "black holes do not exist" by mathematical method on September 28, 2014.[4]
According to the website of the American Physicists Organization, Laura Melcini Horton, a theoretical physicist at the University of North Carolina at Chapel Hill, published an article in the online physics knowledge base ArXiv, saying that she had proved that "black holes do not exist" with mathematics.Once her view has been proved correct by the scientific community, modern physicsOriginSaid they would be overthrown[4]。
The report points out that Laura's theory uses mathematical methods to harmoniously integrate the theory of gravity and quantum mechanics: the conclusion is that "black holes do not exist".She andHawkingIt is believed that when a star dies and collapses, it will release the radiation proposed by Hawking.In this process, the stars themselves will also lose a large part of their mass. Finally, the density of the dead stars is not enough to form black holes.
If this theory is proved to be correct, the Big Bang theory may be overthrown, and even the origin theory of modern physics for the universe may be overthrown, or the new theory integrating the theory of universal gravitation and quantum mechanics may set that "black holes do not exist".
