According to Poe, the initial state of matter was a single
"Primordial Particle". "Divine Volition", manifesting itself as a
repulsive force, fragmented the Primordial Particle into atoms. Atoms
spread evenly throughout space, until the repulsive force stops, and
attraction appears as a reaction: then matter begins to clump together
forming stars and star systems, while the material universe is drawn
back together by gravity, finally collapsing and ending eventually
returning to the Primordial Particle stage in order to begin the process
of repulsion and attraction once again. This part of Eureka describes a
Newtonian evolving universe which shares a number of properties with
relativistic models, and for this reason
Poe anticipates some themes of modern cosmology
[4]
Early 20th century scientific developments
Monseigneur Georges Lemaître, a Belgian Catholic Priest, was the originator of what would become known as the "Big Bang Theory".
Observationally, in the 1910s,
Vesto Slipher and later,
Carl Wilhelm Wirtz, determined that most spiral nebulae (now correctly called
spiral galaxies) were receding from Earth. Slipher used
spectroscopy
to investigate the rotation periods of planets, the composition of
planetary atmospheres, and was the first to observe the radial
velocities of galaxies. Wirtz observed a systematic redshift of nebulae,
which was difficult to interpret in terms of a cosmology in which the
Universe is filled more or less uniformly with stars and nebulae. They
weren't aware of the cosmological implications, nor that the supposed
nebulae were actually galaxies outside our own
Milky Way.
[citation needed]
Also in that decade,
Albert Einstein's theory of
general relativity was found to admit no
static cosmological solutions, given the basic assumptions of cosmology described in the
Big Bang's theoretical underpinnings. The universe (i.e., the space-time metric) was described by a
metric tensor
that was either expanding or shrinking (i.e., was not constant or
invariant). This result, coming from an evaluation of the field
equations of the general theory, at first led Einstein himself to
consider that his formulation of the field equations of the general
theory may be in error, and he tried to correct it by adding a
cosmological constant.
This constant would restore to the general theory's description of
space-time an invariant metric tensor for the fabric of space/existence.
The first person to seriously apply general relativity to cosmology
without the stabilizing cosmological constant was
Alexander Friedmann.
Friedmann derived the expanding-universe solution to general relativity
field equations in 1922. Friedmann's 1924 papers included "
Über die Möglichkeit einer Welt mit konstanter negativer Krümmung des Raumes" (
About the possibility of a world with constant negative curvature) which was published by the Berlin Academy of Sciences on 7 January 1924.
[5] Friedmann's equations describe the
Friedmann–Lemaître–Robertson–Walker universe.
In 1927, the
Belgian Catholic priest
Georges Lemaître proposed an expanding model for the universe to explain the observed redshifts of spiral nebulae, and forecast the
Hubble law. He based his theory on the work of Einstein and
De Sitter,
and independently derived Friedmann's equations for an expanding
universe. Also, the red shifts themselves were not constant, but varied
in such manner as to lead to the conclusion that there was a definite
relationship between amount of red-shift of nebulae, and their distance
from observers.
[citation needed]
In 1929,
Edwin Hubble
provided a comprehensive observational foundation for Lemaître's
theory. Hubble's experimental observations discovered that, relative to
the Earth and all other observed bodies, galaxies are receding in every
direction at velocities (calculated from their observed red-shifts)
directly proportional to their distance from the Earth and each other.
In 1929, Hubble and
Milton Humason formulated the empirical Redshift Distance Law of galaxies, nowadays known as
Hubble's law,
which, once the redshift is interpreted as a measure of recession
speed, is consistent with the solutions of Einstein's General Relativity
Equations for a homogeneous, isotropic expanding space. The isotropic
nature of the expansion was direct proof that it was the space (the
fabric of existence) itself that was expanding, not the bodies in space
that were simply moving further outward and apart into an infinitely
larger preexisting empty void. It was this interpretation that led to
the concept of the expanding universe. The law states that the greater
the distance between any two galaxies, the greater their relative speed
of separation. This discovery later resulted in the formulation of the
Big Bang model.
[citation needed]
In 1931, Lemaître proposed in his "
hypothèse de l'atome primitif" (hypothesis of the primeval atom) that the universe began with the "explosion" of the "primeval
atom" — what was later called the Big Bang. Lemaître first took
cosmic rays to be the remnants of the event, although it is now known that they originate within the local
galaxy. Lemaître had to wait until shortly before his death to learn of the discovery of
cosmic microwave background radiation, the remnant radiation of a dense and hot phase in the early Universe.
[6]
Big Bang theory vs. Steady State theory
Hubble's Law suggested that the universe was expanding, contradicting the
cosmological principle
whereby the universe, when viewed on sufficiently large distance
scales, has no preferred directions or preferred places. Hubble's idea
allowed for two opposing hypotheses to be suggested. One was Lemaître's
Big Bang, advocated and developed by
George Gamow. The other model was
Fred Hoyle's
Steady State theory,
in which new matter would be created as the galaxies moved away from
each other. In this model, the universe is roughly the same at any point
in time. It was actually Hoyle who coined the name of Lemaître's
theory, referring to it as "this 'big bang' idea" during a radio
broadcast on 28 March 1949, on the
BBC Third Programme. It is popularly reported that Hoyle, who favored an alternative "
steady state"
cosmological model, intended this to be pejorative, but Hoyle
explicitly denied this and said it was just a striking image meant to
highlight the difference between the two models.
[7] Hoyle repeated the term in further broadcasts in early 1950, as part of a series of five lectures entitled
The Nature of The Universe. The text of each lecture was published in
The Listener a week after the broadcast, the first time that the term "big bang" appeared in print.
[8]
As evidence in favour of the Big Bang model mounted, and the consensus
became widespread, Hoyle himself, albeit somewhat reluctantly, admitted
to it by formulating a new cosmological model that other scientists
later referred to as the "Steady Bang".
[9]
1950 to 1980s
Comparison of the predictions of the standard Big Bang model with
experimental measurements. The power spectrum of the cosmic microwave
background radiation anisotropy is plotted in terms of the angular scale
(or
multipole moment) (top).
From around 1950 to 1965, the support for these theories was evenly
divided, with a slight imbalance arising from the fact that the Big Bang
theory could explain both the formation and the observed abundances of
hydrogen and
helium,
whereas the Steady State could explain how they were formed, but not
why they should have the observed abundances. However, the observational
evidence began to support the idea that the universe evolved from a hot
dense state. Objects such as
quasars
and radio galaxies were observed to be much more common at large
distances (therefore in the distant past) than in the nearby universe,
whereas the Steady State predicted that the average properties of the
universe should be unchanging with time. In addition, the discovery of
the
cosmic microwave background
radiation in 1965 was considered the death knell of the Steady State,
although this prediction was only qualitative, and failed to predict the
exact temperature of the CMB. (The key big bang prediction is the
black-body spectrum of the CMB, which was not measured with high
accuracy until COBE in 1990). After some reformulation, the Big Bang has
been regarded as the best theory of the origin and evolution of the
cosmos. Before the late 1960s, many cosmologists thought the infinitely
dense and
physically paradoxical singularity
at the starting time of Friedmann's cosmological model could be avoided
by allowing for a universe which was contracting before entering the
hot dense state, and starting to expand again. This was formalized as
Richard Tolman's
oscillating universe. In the sixties,
Stephen Hawking and others demonstrated that this idea was unworkable,
[citation needed]
and the singularity is an essential feature of the physics described by
Einstein's gravity. This led the majority of cosmologists to accept the
notion that the universe as currently described by the physics of
general relativity has a finite age. However, due to a lack of a theory
of
quantum gravity,
there is no way to say whether the singularity is an actual origin
point for the universe, or whether the physical processes that govern
the regime cause the universe to be effectively eternal in character. Wk
