A

**static universe**, also referred to as a "stationary" or "Einstein" universe, is a model in which space is neither

expandingThe metric expansion of space is the increase of distance between distant parts of the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...

nor contracting.

Albert EinsteinAlbert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

proposed such a model as his preferred

cosmologyPhysical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...

in 1917 . He added a positive

cosmological constantIn physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...

to his equations of

general relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

to counteract the attractive effects of gravity on ordinary matter, which would otherwise cause the universe to either

collapseIn physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity.- Overview :...

or expand forever. This motivation evaporated after the discovery by

Edwin HubbleEdwin Powell Hubble was an American astronomer who profoundly changed the understanding of the universe by confirming the existence of galaxies other than the Milky Way - our own galaxy...

that the universe is in fact not static, but expanding; in particular, Hubble discovered a relationship between

redshift and distanceHubble's law is the name for the astronomical observation in physical cosmology that: all objects observed in deep space are found to have a doppler shift observable relative velocity to Earth, and to each other; and that this doppler-shift-measured velocity, of various galaxies receding from...

, which forms the basis for the modern

expansion paradigmThe metric expansion of space is the increase of distance between distant parts of the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...

. According to Gamow this led Einstein to declare this cosmological model, and especially the introduction of the cosmological constant, his "biggest blunder".

Even after Hubble's observations,

Fritz ZwickyFritz Zwicky was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy.- Biography :Fritz Zwicky was born in Varna, Bulgaria to a Swiss father....

proposed that a static universe could still be viable if there was an alternative explanation of

redshiftIn physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

due to a mechanism that would cause light to lose

energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

as it traveled through

spaceSpace is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

, a concept that would come to be known as "

tired lightTired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship. These models have been proposed as alternatives to the metric expansion of space of which the Big Bang and the Steady State cosmologies are the most...

". However, subsequent cosmological observations have shown that this model is not a viable alternative either, leading nearly all astrophysicists to conclude that the static universe is not the correct model of our universe.

## Einstein's universe

Einstein's static universe is closed (i.e. has hyperspherical topology and positive spatial curvature), and contains uniform dust and a positive

cosmological constantIn physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...

with value precisely

, where

is Newtonian gravitational constant,

is the energy density of the matter in the universe and

is the

speed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...

. The

radius of curvatureIn geometry, the radius of curvature, R, of a curve at a point is a measure of the radius of the circular arc which best approximates the curve at that point. If this value taken to be positive when the curve turns anticlockwise and negative when the curve turns clockwise...

of space of the Einstein universe is equal to

The Einstein universe is one of Friedmann's solutions to Einstein's field equation for dust with density

, cosmological constant

, and radius of curvature

. It is the only non-trivial static solution to Friedmann's equations .

Because the universe is now known to be expanding the Einstein universe is no longer regarded as a viable model for our universe. Moreover, it is unstable in the sense that any change in either the value of the cosmological constant, the matter density, or the spatial curvature will result in a universe that either expands and accelerates forever or re-collapses to a big crunch.

After observations indicated that the universe was expanding, most physicists of the twentieth century assumed the cosmological constant is zero. If so (absent some other form of

dark energyIn physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

), the expansion of the universe would be decelerating. However, with the discovery of the

accelerating universeThe accelerating universe is the observation that the universe appears to be expanding at an increasing rate, which in formal terms means that the cosmic scale factor a has a positive second derivative, implying that the velocity at which a given galaxy is receding from us should be continually...

, a positive cosmological constant has been revived as a simple explanation for

dark energyIn physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

.

## Other problems with the model

Aside from

Hubble's lawHubble's law is the name for the astronomical observation in physical cosmology that: all objects observed in deep space are found to have a doppler shift observable relative velocity to Earth, and to each other; and that this doppler-shift-measured velocity, of various galaxies receding from...

, the

cosmic microwave background radiationIn cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....

is used as empirical evidence of the

Big BangThe Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

model. A static universe model has to explain this radiation in some other way. Also there has to be some process of "recreation of Hydrogen" since if the universe was not created some finite time ago, as in the Big Bang model, the stars would otherwise all have run out of fuel (Hydrogen) by now.