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72-408: The hypothesis dates back to 1922, with Russian physicist Alexander Friedmann creating a set of equations showing that the end of the universe depends on its density . It could either expand or contract rather than stay stable. With enough matter, gravity could stop the universe's expansion and eventually reverse it. This reversal would result in the universe collapsing on itself, not too dissimilar to

144-664: A Taylor series expansion: z = R ( t 0 ) R ( t e ) − 1 ≈ R ( t 0 ) R ( t 0 ) ( 1 + ( t e − t 0 ) H ( t 0 ) ) − 1 ≈ ( t 0 − t e ) H ( t 0 ) , {\displaystyle z={\frac {R(t_{0})}{R(t_{e})}}-1\approx {\frac {R(t_{0})}{R(t_{0})\left(1+(t_{e}-t_{0})H(t_{0})\right)}}-1\approx (t_{0}-t_{e})H(t_{0}),} If

216-521: A black hole . The ending of the Big Crunch would get filled with radiation from stars and high-energy particles ; when this is condensed and blueshifted to higher energy, it would be intense enough to ignite the surface of stars before they collide. In the final moments, the universe would be one large fireball with a near-infinite temperature, and at the absolute end, neither time, nor space would remain. The Big Crunch scenario hypothesized that

288-399: A redshift velocity , which is the recessional velocity that would produce the same redshift if it were caused by a linear Doppler effect (which, however, is not the case, as the velocities involved are too large to use a non-relativistic formula for Doppler shift). This redshift velocity can easily exceed the speed of light. In other words, to determine the redshift velocity v rs ,

360-464: A "Hubble diagram" in which the velocity (assumed approximately proportional to the redshift) of an object is plotted with respect to its distance from the observer. A straight line of positive slope on this diagram is the visual depiction of Hubble's law. After Hubble's discovery was published, Albert Einstein abandoned his work on the cosmological constant , a term he had inserted into his equations of general relativity to coerce them into producing

432-399: A contracting, yet static universe were dropped for the expanding universe model. A hypothesis called " Big Bounce " proposes that the universe could collapse to the state where it began and then initiate another Big Bang, so in this way, the universe would last forever but would pass through phases of expansion (Big Bang) and contraction (Big Crunch). This means that there may be a universe in

504-583: A decade before Robertson and Walker published their analysis. This dynamic cosmological model of general relativity would come to form the standard for both the Big Bang and Steady State theories. Friedmann's work supported both theories equally, so it was not until the detection of the cosmic microwave background radiation that the Steady State theory was abandoned in favor of the current favorite Big Bang paradigm. The classic solution of

576-500: A discussion of the significance of this): r HS = c H 0   . {\displaystyle r_{\text{HS}}={\frac {c}{H_{0}}}\ .} Since the Hubble "constant" is a constant only in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests that

648-524: A galaxy is at distance D , and this distance changes with time at a rate d t D . We call this rate of recession the "recession velocity" v r : v r = d t D = d t R R D . {\displaystyle v_{\text{r}}=d_{t}D={\frac {d_{t}R}{R}}D.} We now define the Hubble constant as H ≡ d t R R , {\displaystyle H\equiv {\frac {d_{t}R}{R}},} and discover

720-544: A general relativity-based theory called the conformal cyclic cosmology in which the universe expands until all the matter decays and is turned to light. Since nothing in the universe would have any time or distance scale associated with it, it becomes identical with the Big Bang (resulting in a type of Big Crunch that becomes the next Big Bang, thus starting the next cycle). Penrose and Gurzadyan suggested that signatures of conformal cyclic cosmology could potentially be found in

792-417: A lecture on Newton's theories and the rejection of atheism : If we're in a finite universe and all stars attract each other together, would they not all collapse to a singular point, and if we're in an infinite universe with infinite stars, would infinite forces in every direction not affect all of those stars? This question is known as Bentley's paradox , an early predecessor of the Big Crunch. Although, it

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864-406: A low-impact journal. In the 1931 high-impact English translation of this article, a critical equation was changed by omitting reference to what is now known as the Hubble constant." It is now known that the alterations in the translated paper were carried out by Lemaître himself. Before the advent of modern cosmology, there was considerable talk about the size and shape of the universe . In 1920,

936-562: A record-setting balloon flight, reaching the elevation of 7,400 m (24,300 ft). Friedmann's 1924 papers, including " Über die Möglichkeit einer Welt mit konstanter negativer Krümmung des Raumes " ("On the possibility of a world with constant negative curvature of space") published by the German physics journal Zeitschrift für Physik (Vol. 21, pp. 326–332), demonstrated that he had command of all three Friedmann models describing positive, zero and negative curvature respectively,

1008-464: A religious wedding ceremony, though both were far from religious. Together they had a son Alexander Alexandrovich Friedman (1925—1983), born after his father's death. Friedmann died on September 16, 1925, from misdiagnosed typhoid fever . He had allegedly contracted the bacteria on return from his honeymoon in Crimea , when he ate an unwashed pear bought at a railway station. The Moon crater Fridman

1080-415: A smaller velocity than earlier ones. Redshift can be measured by determining the wavelength of a known transition, such as hydrogen α-lines for distant quasars, and finding the fractional shift compared to a stationary reference. Thus, redshift is a quantity unambiguous for experimental observation. The relation of redshift to recessional velocity is another matter. The redshift z is often described as

1152-484: A state of constant Big Bangs and Big Crunches. Cyclic universes were briefly considered by Albert Einstein in 1931. He hypothesized that there was a universe before the Big Bang, which ended in a Big Crunch, which could create a Big Bang as a reaction. Our universe could be in a cycle of expansion and contraction, a cycle possibly going on infinitely. There are more modern models of Cyclic universes as well. The Ekpyrotic model , formed by Paul Steinhardt , states that

1224-436: A supernova brightness, which provides information about its distance, and the redshift z = ∆ λ / λ of its spectrum of radiation. Hubble correlated brightness and parameter z . Combining his measurements of galaxy distances with Vesto Slipher and Milton Humason 's measurements of the redshifts associated with the galaxies, Hubble discovered a rough proportionality between redshift of an object and its distance. Though there

1296-470: A trend line from 46 galaxies, studying and obtaining the Hubble Constant , which he deduced to be 500 km/s/Mpc, nearly seven times than what it is considered today, but still giving the proof that the universe was expanding and was not a static object. After Hubble's discovery was published, Einstein abandoned the cosmological constant. In their simplest form, the equations generated a model of

1368-478: Is attributed to work published by Edwin Hubble in 1929. Hubble's law is considered the first observational basis for the expansion of the universe , and today it serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of astronomical objects due solely to this expansion is known as the Hubble flow . It is described by the equation v = H 0 D , with H 0

1440-414: Is considered a fundamental relation between recessional velocity and distance. However, the relation between recessional velocity and redshift depends on the cosmological model adopted and is not established except for small redshifts. For distances D larger than the radius of the Hubble sphere r HS , objects recede at a rate faster than the speed of light ( See Uses of the proper distance for

1512-465: Is most frequently quoted in km / s / Mpc , which gives the speed of a galaxy 1 megaparsec (3.09 × 10  km) away as 70 km/s . Simplifying the units of the generalized form reveals that H 0 specifies a frequency (SI unit: s ), leading the reciprocal of H 0 to be known as the Hubble time (14.4 billion years). The Hubble constant can also be stated as a relative rate of expansion. In this form H 0  = 7%/ Gyr , meaning that at

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1584-399: Is named after him. Alexander Friedmann International Seminar is a periodical scientific event. The objective of the meeting is to promote contact between scientists working in the field of Relativity, Gravitation and Cosmology, and related fields. The First Alexander Friedmann International Seminar on Gravitation and Cosmology devoted to the centenary of his birth took place in 1988. During

1656-451: Is negligible at low spacetime curvature, but that rises very rapidly in the Planck regime , overwhelming classical gravity and resolving singularities of general relativity . Once the singularities are resolved the conceptual paradigm of cosmology changes, forcing one to revisit the standard issues—such as the horizon problem—from a new perspective. Under this model, due to quantum geometry,

1728-410: Is now known that stars move around and are not static. Albert Einstein favored an unchanging model of the universe. He collaborated in 1917 with Dutch astronomer Willem de Sitter to help demonstrate that the theory of general relativity would work with a static model; Willem demonstrated that his equations could describe a very simple universe. Finding no problems initially, scientists adapted

1800-402: Is some reference time. If light is emitted from a galaxy at time t e and received by us at t 0 , it is redshifted due to the expansion of the universe, and this redshift z is simply: z = R ( t 0 ) R ( t e ) − 1. {\displaystyle z={\frac {R(t_{0})}{R(t_{\text{e}})}}-1.} Suppose

1872-418: Is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away. For this purpose, the recessional velocity of a galaxy is typically determined by measuring redshift , a shift in the light it emits toward the red end of the visible light spectrum . The discovery of Hubble's law

1944-464: Is true as well, the accelerating expansion of the Universe would inverse to contraction within the cosmic near-future of the next 100 million years. According to an Andrei-Ijjas-Steinhardt study, the scenario fits "naturally with cyclic cosmologies and recent conjectures about quantum gravity ". The study suggests that the slow contraction phase would "endure for a period of order 1 billion y before

2016-507: The 2022 COVID-19 protests in China , Tsinghua University students were seen displaying Friedmann's equation as if it were a protest slogan, which was understood as an evasion of censorship by punning multilingually on "free man" and referring to liberalization and opening via the expansion of the universe. Hubble Constant Hubble's law , also known as the Hubble–Lemaître law ,

2088-564: The Big Bang and Steady State theories of cosmology. In 1927, two years before Hubble published his own article, the Belgian priest and astronomer Georges Lemaître was the first to publish research deriving what is now known as Hubble's law. According to the Canadian astronomer Sidney van den Bergh , "the 1927 discovery of the expansion of the universe by Lemaître was published in French in

2160-531: The Shapley–Curtis debate took place between Harlow Shapley and Heber D. Curtis over this issue. Shapley argued for a small universe the size of the Milky Way galaxy, and Curtis argued that the universe was much larger. The issue was resolved in the coming decade with Hubble's improved observations. Edwin Hubble did most of his professional astronomical observing work at Mount Wilson Observatory , home to

2232-451: The cosmic microwave background ; as of 2020, these have not been detected. There are also some flaws with this model as well: skeptics pointed out that in order to match up an infinitely large universe to an infinitely small universe, that all particles must lose their mass when the universe gets old. Penrose presented evidence of CCC in the form of rings that had uniform temperature in the CMB,

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2304-404: The proportionality constant of Hubble's law. Georges Lemaître independently found a similar solution in his 1927 paper discussed in the following section. The Friedmann equations are derived by inserting the metric for a homogeneous and isotropic universe into Einstein's field equations for a fluid with a given density and pressure . This idea of an expanding spacetime would eventually lead to

2376-509: The Big Bang could have been caused by two parallel orbifold planes, referred to as branes colliding in a higher-dimensional space. The four-dimension universe lies on one of the branes. The collision corresponds to the Big Crunch, then a Big Bang. The matter and radiation around us today are quantum fluctuations from before the branes. After several billion years, the universe has reached its modern state, and it will start contracting in another several billion years. Dark energy corresponds to

2448-678: The Big Bang is replaced by the Big Bounce with no assumptions or any fine tuning. The approach of effective dynamics has been used extensively in loop quantum cosmology to describe physics at the Planck scale, and also the beginning of the universe. Numerical simulations have confirmed the validity of effective dynamics, which provides a good approximation of the full loop quantum dynamics. It has been shown when states have very large quantum fluctuations at late times, meaning they do not lead to macroscopic universes as described by general relativity, but

2520-559: The CMB becomes hotter than M-type stars (about 500,000 years before the Big Crunch in Davies' model), they would no longer be able to radiate away their heat and would cook themselves until they evaporate; this continues for successively hotter stars until O-type stars boil away about 100,000 years before the Big Crunch. In the last minutes, the temperature of the universe would be so great that atoms and atomic nuclei would break up and get sucked up into already coalescing black holes . At

2592-863: The Czech composer Hynek Vojáček). Friedmann was baptized into the Russian Orthodox Church as an infant, and lived much of his life in Saint Petersburg . Friedmann obtained his degree from St. Petersburg State University in 1910, and became a lecturer at Saint Petersburg Mining Institute . From his school days, Friedmann found a lifelong companion in Jacob Tamarkin , who was also a distinguished mathematician. Friedmann fought in World War I on behalf of Imperial Russia , as an army aviator, an instructor, and eventually, under

2664-771: The Einstein field equations that describes a homogeneous and isotropic universe was called the Friedmann–Lemaître–Robertson–Walker metric , or FLRW , after Friedmann, Georges Lemaître , Howard P. Robertson and Arthur Geoffrey Walker , who worked on the problem in the 1920s and 30s independently of Friedmann. In addition to general relativity, Friedmann's interests included hydrodynamics and meteorology . Physicists George Gamow , Vladimir Fock , and Lev Vasilievich Keller were among his students. In 1911, he married Ekaterina Dorofeeva, though he later divorced her. He married Natalia Malinina in 1923. They had

2736-463: The Hubble law: v r = H D . {\displaystyle v_{\text{r}}=HD.} From this perspective, Hubble's law is a fundamental relation between (i) the recessional velocity associated with the expansion of the universe and (ii) the distance to an object; the connection between redshift and distance is a crutch used to connect Hubble's law with observations. This law can be related to redshift z approximately by making

2808-523: The Universe, or "Gnab Gib", as it is referred to, as they dine. The term is sometimes used in the mainstream, for example (as "gnaB giB") in Physics I For Dummies and in a posting discussing the Big Crunch. Alexander Friedmann Alexander Alexandrovich Friedmann (also spelled Friedman or Fridman ; / ˈ f r iː d m ə n / ; Russian : Алекса́ндр Алекса́ндрович Фри́дман ; June 16 [ O.S. June 4] 1888 – September 16, 1925)

2880-444: The constant of proportionality—the Hubble constant —between the "proper distance" D to a galaxy (which can change over time, unlike the comoving distance ) and its speed of separation v , i.e. the derivative of proper distance with respect to the cosmic time coordinate. (See Comoving and proper distances § Uses of the proper distance for discussion of the subtleties of this definition of velocity. ) The Hubble constant

2952-490: The current rate of expansion it takes one billion years for an unbound structure to grow by 7%. Although widely attributed to Edwin Hubble , the notion of the universe expanding at a calculable rate was first derived from general relativity equations in 1922 by Alexander Friedmann . Friedmann published a set of equations, now known as the Friedmann equations , showing that the universe might be expanding, and presenting

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3024-427: The density of matter throughout the universe is sufficiently high that gravitational attraction will overcome the expansion that began with the Big Bang. The FLRW cosmology can predict whether the expansion will eventually stop based on the average energy density , Hubble parameter , and cosmological constant . If the expansion stopped, then contraction will inevitably follow, accelerating as time passes and finishing

3096-650: The distance is not too large, all other complications of the model become small corrections, and the time interval is simply the distance divided by the speed of light: z ≈ ( t 0 − t e ) H ( t 0 ) ≈ D c H ( t 0 ) , {\displaystyle z\approx (t_{0}-t_{\text{e}})H(t_{0})\approx {\frac {D}{c}}H(t_{0}),} or c z ≈ D H ( t 0 ) = v r . {\displaystyle cz\approx DH(t_{0})=v_{r}.} According to this approach,

3168-485: The effective dynamics departs from quantum dynamics near bounce and the later universe. In this case, the effective dynamics will overestimate the density at bounce, but it will still capture qualitative aspects extremely well. If a form of quintessence driven by a scalar field evolving down a monotonically decreasing potential that passes sufficiently below zero is the (main) explanation of dark energy and current data (in particular observational constraints on dark energy)

3240-518: The end, the cosmological constant , the name for the anti-gravity force, was added to the theory of relativity. Edwin Hubble working in the Mount Wilson Observatory took measurements of the distances of galaxies and paired them with Vesto Silpher and Milton Humason 's measurements of red shifts associated with those galaxies. He discovered a rough proportionality between the red shift of an object and its distance. Hubble plotted

3312-467: The expansion of the universe is accelerating ( see Accelerating universe ), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at

3384-433: The expansion speed if that were the case. Before Hubble, German astronomer Carl Wilhelm Wirtz had, in two publications dating 1922 and 1924, already deduced with his own data that galaxies that appeared smaller and dimmer had larger redshifts and thus that more distant galaxies recede faster from the observer. Then Georges Lemaître , in a 1927 article, independently derived that the universe might be expanding, observed

3456-519: The force between the branes, allowing for problems, like the flatness and monopole in the previous models to be fixed. The cycles can also go infinitely into the past and the future, and an attractor allows for a complete history of the universe. This fixes the problem of the earlier model of the universe going into heat death from entropy buildup. The new model avoids this with a net expansion after every cycle, stopping entropy buildup. There are still some flaws in this model, however. The basis of

3528-552: The galaxies in the neighborhood recede at a rate proportional to their distance, formalizing an observation made earlier by Carl Wilhelm Wirtz . Unaware of Friedmann's work, in 1927 Belgian astronomer Georges Lemaître independently formulated an evolving Universe. In June 1925 Friedmann was given the job of the director of the Main Geophysical Observatory in Leningrad. In July 1925 he participated in

3600-420: The idea being that these rings would be the signature in our aeon—An aeon being the current cycle of the universe that we're in—was caused by spherical gravitational waves caused by colliding black holes from our previous aeon. Loop quantum cosmology is a model of the universe that proposes a "quantum-bridge" between expanding and contracting universes. In this model quantum geometry creates a brand-new force that

3672-425: The model to describe the universe. They ran into a different form of Bentley's paradox. The theory of general relativity also described the universe as restless. Einstein realized that for a static universe to exist—which was observed at the time—an anti-gravity would be needed to counter the gravity contracting the universe together, adding an extra force that would ruin the equations in the theory of relativity. In

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3744-481: The model, branes, are still not understood completely by string theorists, and the possibility that the scale invariant spectrum could be destroyed from the big crunch. While cosmic inflation and the general character of the forces—or the collision of the branes in the Ekpyrotic model—required to make vacuum fluctuations is known. A candidate from particle physics is missing. Physicist Roger Penrose advanced

3816-439: The most general principles to the nature of the universe yielded a dynamic solution that conflicted with the then-prevalent notion of a static universe . In 1912, Vesto M. Slipher measured the first Doppler shift of a " spiral nebula " (the obsolete term for spiral galaxies) and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at

3888-515: The observational basis for modern cosmology. The cosmological constant has regained attention in recent decades as a hypothetical explanation for dark energy . The discovery of the linear relationship between redshift and distance, coupled with a supposed linear relation between recessional velocity and redshift, yields a straightforward mathematical expression for Hubble's law as follows: v = H 0 D {\displaystyle v=H_{0}\,D} where Hubble's law

3960-417: The observed and emitted wavelengths respectively. The "redshift velocity" v rs is not so simply related to real velocity at larger velocities, however, and this terminology leads to confusion if interpreted as a real velocity. Next, the connection between redshift or redshift velocity and recessional velocity is discussed. Suppose R ( t ) is called the scale factor of the universe, and increases as

4032-689: The proportionality between recessional velocity of, and distance to, distant bodies, and suggested an estimated value for the proportionality constant; this constant, when Edwin Hubble confirmed the existence of cosmic expansion and determined a more accurate value for it two years later, came to be known by his name as the Hubble constant. Hubble inferred the recession velocity of the objects from their redshifts , many of which were earlier measured and related to velocity by Vesto Slipher in 1917. Combining Slipher's velocities with Henrietta Swan Leavitt 's intergalactic distance calculations and methodology allowed Hubble to better calculate an expansion rate for

4104-403: The relation: v rs ≡ c z , {\displaystyle v_{\text{rs}}\equiv cz,} is used. That is, there is no fundamental difference between redshift velocity and redshift: they are rigidly proportional, and not related by any theoretical reasoning. The motivation behind the "redshift velocity" terminology is that the redshift velocity agrees with

4176-450: The revolutionary regime, as the head of an airplane factory. Friedmann in 1922 introduced the idea of an expanding universe that contained moving matter. Correspondence with Einstein suggests that Einstein was unwilling to accept the idea of an evolving Universe and worked instead to revise his equations to support the static, eternal Universe of Newton's time. In 1929 Hubble published the redshift vs distance relationship showing that all

4248-400: The static solution he previously considered the correct state of the universe. The Einstein equations in their simplest form model either an expanding or contracting universe, so Einstein introduced the constant to counter expansion or contraction and lead to a static and flat universe. After Hubble's discovery that the universe was, in fact, expanding, Einstein called his faulty assumption that

4320-424: The time it was highly controversial whether or not these nebulae were "island universes" outside the Milky Way galaxy. In 1922, Alexander Friedmann derived his Friedmann equations from Einstein field equations , showing that the universe might expand at a rate calculable by the equations. The parameter used by Friedmann is known today as the scale factor and can be considered as a scale invariant form of

4392-457: The time of the Big Crunch, all the matter in the universe would be crushed into an infinitely hot, infinitely dense singularity similar to the Big Bang . The Big Crunch may be followed by another Big Bang, creating a new universe. In The Restaurant at the End of the Universe , a novel by Douglas Adams , the concept is that a restaurant, Milliways, is set up to allow patrons to observe the end of

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4464-552: The universe expands in a manner that depends upon the cosmological model selected. Its meaning is that all measured proper distances D ( t ) between co-moving points increase proportionally to R . (The co-moving points are not moving relative to their local environments.) In other words: D ( t ) D ( t 0 ) = R ( t ) R ( t 0 ) , {\displaystyle {\frac {D(t)}{D(t_{0})}}={\frac {R(t)}{R(t_{0})}},} where t 0

4536-497: The universe in a kind of gravitational collapse , turning the universe into a black hole. Experimental evidence in the late 1990s and early 2000s (namely the observation of distant supernovas as standard candles ; and the well-resolved mapping of the cosmic microwave background ) led to the conclusion that the expansion of the universe is not getting slowed by gravity but is instead accelerating . The 2011 Nobel Prize in Physics

4608-481: The universe is static his "greatest mistake". On its own, general relativity could predict the expansion of the universe, which (through observations such as the bending of light by large masses , or the precession of the orbit of Mercury ) could be experimentally observed and compared to his theoretical calculations using particular solutions of the equations he had originally formulated. In 1931, Einstein went to Mount Wilson Observatory to thank Hubble for providing

4680-411: The universe that expanded or contracted. Contradicting what was observed, hence the creation of the cosmological constant. After the confirmation that the universe was expanding, Einstein called his assumption that the universe was static his "biggest mistake". In 1931, Einstein visited Hubble to thank him for "providing the basis of modern cosmology". After this discovery, Einstein's and Newton's models of

4752-535: The universe transitions to a new phase of expansion". Paul Davies considered a scenario in which the Big Crunch happens about 100 billion years from the present. In his model, the contracting universe would evolve roughly like the expanding phase in reverse. First, galaxy clusters , and then galaxies, would merge, and the temperature of the cosmic microwave background (CMB) would begin to rise as CMB photons get blueshifted . Stars would eventually become so close together that they begin to collide with each other. Once

4824-493: The universe. Though the Hubble constant H 0 is constant at any given moment in time, the Hubble parameter H , of which the Hubble constant is the current value, varies with time, so the term constant is sometimes thought of as somewhat of a misnomer. A decade before Hubble made his observations, a number of physicists and mathematicians had established a consistent theory of an expanding universe by using Einstein field equations of general relativity . Applying

4896-530: The velocity from a low-velocity simplification of the so-called Fizeau–Doppler formula z = λ o λ e − 1 = 1 + v c 1 − v c − 1 ≈ v c . {\displaystyle z={\frac {\lambda _{\text{o}}}{\lambda _{\text{e}}}}-1={\sqrt {\frac {1+{\frac {v}{c}}}{1-{\frac {v}{c}}}}}-1\approx {\frac {v}{c}}.} Here, λ o , λ e are

4968-511: The world's most powerful telescope at the time. His observations of Cepheid variable stars in "spiral nebulae" enabled him to calculate the distances to these objects. Surprisingly, these objects were discovered to be at distances which placed them well outside the Milky Way. They continued to be called nebulae , and it was only gradually that the term galaxies replaced it. The parameters that appear in Hubble's law, velocities and distances, are not directly measured. In reality we determine, say,

5040-410: Was a Russian and Soviet physicist and mathematician . He originated the pioneering theory that the universe is expanding , governed by a set of equations he developed known as the Friedmann equations . Alexander Friedmann was born to the composer and ballet dancer Alexander Friedmann (who was a son of a baptized Jewish cantonist ) and the pianist Ludmila Ignatievna Voyachek (who was a daughter of

5112-491: Was awarded to researchers who contributed to this discovery. The Big Crunch hypothesis also leads into another hypothesis known as the Big Bounce , in which after the big crunch destroys the universe, it does a sort of bounce, causing another big bang. This could potentially repeat forever in a phenomenon known as a cyclic universe. Richard Bentley, a churchman and scholar, sent a letter to Isaac Newton in preparation for

5184-530: Was considerable scatter (now known to be caused by peculiar velocities —the 'Hubble flow' is used to refer to the region of space far enough out that the recession velocity is larger than local peculiar velocities), Hubble was able to plot a trend line from the 46 galaxies he studied and obtain a value for the Hubble constant of 500 (km/s)/Mpc (much higher than the currently accepted value due to errors in his distance calibrations; see cosmic distance ladder for details). Hubble's law can be easily depicted in

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