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John Di Stefano
In the beginning was nothing. Then the universe was born in a searing hot fireball of rapidly expanding
space and time called the Big Bang. But what was the Big Bang? Where did it happen? And how have
astronomers come to believe such an incredible thing?
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About 13.82 billion years ago the universe that we inhabit erupted, literally, out of nothing. It expanded
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exponentially in a process known as inflation and everything – matter, energy and even space and time –
came into being at that instant.
In the earliest moments of the Big Bang, the stuff of the universe occupied an extraordinary small volume
and was an unimaginably hot. It was a seething cauldron of electromagnetic radiation mixed with
subatomic particles of matter unlike any found in today’s cold universe. As space expanded it cooled and
more and more structure began to ‘freeze out’.
Step by step the fundamental particles we know today, protons, neutrons and electrons – the building
blocks of ordinary matter – acquired their present identities. The particles condensed into atoms and
under the influence of gravity began to collapse into stars and then into galaxies. About 4.6 billion years
ago a star was born and a planet we call Earth formed about the debris of material expelled by this star we
call our Sun.
It is an extraordinarily picture of creation, many aspects difficult to believe. Yet, astronomers and
physicists, armed with a growing mass of evidence are so confident of the scenario that they believe they
can work out the detailed conditions in the early universe as it evolved, instant by instant.
We can go back in time to a
small fraction of a second
after the Big Bang and
physics can describe when
the universe was 10-35
seconds old. This is an
exceedingly a small interval
of time, but a long way from
zero, the moment of
creation, and much
happened between 0 and
10-35 seconds. In those early
nano and micro seconds the
universe was very hot and
radiation (energetic photons)
and matter particles were
constantly interchanging as
understood through
Einstein’s energy/mass equation E=mc2. As time progressed and expansion cooled the temperature of the
nascent universe quarks, positrons and electrons formed. Protons and antiprotons annihilate, electrons
and positrons annihilate. For reasons yet not understood, a small excess of protons and electrons remain
within a sea of high energy photons. The universe continues to expand and cool and the multitude of
excess photons can no longer be converted to matter. The universe is radiation dominant and it glows like
a single primordial star. Brilliant but opaque.
How far back can physics probe in modern laboratories?
The answer is to a time when the universe was about one trillion (10 -12) of a second old. By then the
universe had cooled to about 1017 oK – still 10 billion degrees hotter than the centre of the sun. In 2012,
physicists at CERN, the European Centre for Particle Physics, recreated these conditions at the Large
Hadron Collider (LHC). They conjured into being a particle we call the Higgs boson that vanished from the
universe a trillion of a second after the Big Bang.
At some point, the building blocks of neutrons and protons, known as quarks, came into being. This period,
known as the quark epoch began approximately 10−12 seconds after the Big Bang. During the quark epoch
the universe was filled with a dense, hot quark–gluon plasma, containing quarks, leptons and their
antiparticles.
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The period when quarks became confined within hadrons – protons and neutrons- is known as the hadron 2
epoch. It started approximately 10−6 seconds after the Big Bang.
Solitary neutrons decay into protons in about 15 minutes. So there was an interval of time from about 1 to
15 minutes in the age of the universe when protons and neutrons were able to combine to form helium
nuclei and a very small quantity of lithium nuclei. After 15 minutes remaining neutrons decayed into
protons2 and element formation stopped. The early universe did not produce any carbon, oxygen,
nitrogen, iron or other elements that we are made of. Where do the heavier elements come from? Where
do we come from?
Hydrogen, Helium and Lithium production in the first 15 minutes of the early universe is one of the
strongest pieces of evidence that the Big Bang did really happen. Theoretical calculations gave the
Hydrogen to Helium ratio as 10:1. Today when astronomers measure the abundance of the elements in
the universe-in stars, galaxies and interstellar space-they still find roughly one Helium atom for every ten
Hydrogen atoms.
The point at which the universe was cool enough for electrons to combine with protons to make the first
atoms was about 380,000 years after the Big Bang when the temperature was about 3000 oK. This cosmic
background "cloud surface" is called the "surface of last scattering".
Until electrons had combined with hydrogen and helium nuclei to make atomic hydrogen and helium
photons could not travel far before being reabsorbed and emitted. Free electrons are very good at
scattering photons. The free electrons and scatted photons created an ionized gas or fog which was
opaque, much like the interior of the sun. The whole universe, in the first 380,000 years was like a single
huge star. As the universe cooled below this temperature the free electrons became bound to the
hydrogen and helium nuclei and photons were free to move freely through the expanse of space, and they
are still doing so, albeit significantly stretched to the microwave region of
electromagnetic spectrum.
This event had the effect of making the universe transparent and the
microwaves we detect and measure are referred to as the cosmic microwave
background, CMB1. The picture of the CMB looks like this and signifies small
variations in temperature (of the order of 1 part in 10,000) of deep space over
all of space. Analysis of the CMB leads to many interesting results which we will explore further.
The CMB photons started their journey when they were 3000 oK. Since then the universe has expanded
1100 times and correspondingly the temperature has cooled by a proportionate amount to approximately
3 degrees above absolute zero.
When the early universe cooled to 3000 oK it signified another
important event; the point at which the energy of the photons fell
below that of matter. From then on the universe became dominated
by matter and by the force of gravity acting on that matter. Gravity
caused clumps of slightly dense volumes of space to accumulate into
large stars and later galaxies. At one point, about 9 billion years ago
after the Big Bang, an inconspicuous yellow star was born in a
common spiral galaxy that we call the Milky Way. The star was our Sun and one of the planets it spawned
was Earth.
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2
CMB Photons: According to calculations, the comoving distance of photons from the CMB, which represent the radius of the
visible universe, is about 45.7 billion light years.
n0 → p+ + e− + νe
Modern Cosmology
In the presentation by Guy Consolmagno ‘Making Sense of the Universe’, we heard of the importance of
earlier cosmologies, from ancient Greece, the Middle Ages and into the 17th and 18th centuries and how
these cosmologies framed or instructed the thinking of the times.
In the 20th century, beginning with a new theory of gravity in 1915, Einstein’s
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General Theory of Relativity, science begins to replace humanist and religious
cosmologies with mathematical and physical interpretations within the framework 3
of General Relativity.
(Gravity/Curvature of Space-time) = 8 π G × (Energy Content).
Using the equations of General Relativity, Einstein and various other physicist
developed models on how gravity might work on the universe as a whole.
Prominent among these was Alexander Freedman and Georges Lamaitre. Their
solution to the equations of General Relativity gave us a model of an evolving universe. A universe with a
beginning; a beginning of space and time. A hot dense beginning expanding and cooling ever since.
The basic hypothesis of the Friedmann-Lemaître model
The first hypothesis of a cosmological model rests on the cosmological principle: the Earth has no reason for standing
at the centre of the Universe, or in any privileged area. According to this hypothesis the universe is considered as:


Homogeneous On a large scale (about 200 million light years) the universe looks the same
everywhere.
Isotropic
The universe looks the same in all direction.
The second necessary hypothesis is the universality of the laws of physics. These laws are the same in any place and
any time in the Universe.
The parameters of the Friedmann-Lemaître model
In order to completely describe a model, in accordance with these previous
hypothesis, the Friedmann-Lemaître models use three parameters which totally
characterize the evolution of the universe:



The Hubble constant, which characterizes the rate of expansion of
the universe,
The mass density parameter, noted Ω, which measures the ratio
between the density ρ of the studied universe and a particular density, called the critical density ρc.
(Ω = ρ/ ρc )
The current value of this parameter is noted Ωo.
The cosmological constant, Λ, (the fudge term Einstein added to his equations to make the universe
static) which represents a force opposing gravity.
Ω Omega,
ρ Rho,
 Lamda
The density of matter within the universe is the key parameter for the
development of its evolution. If it is very dense (Ωo > 1), gravity will be able
to win against expansion, and the universe will go back to its initial state.
In the opposite case, the expansion will continue forever.
Intuitively, we can realize the evolution of the universe, according to
the amount of matter inside:



A great quantity of matter will result in a closed universe and the
universe will finally collapse to its initial state.
A low amount of matter will result in an open universe, with an
infinite expansion.
The value Ωo = 1 leads to the particular case of a
flat universe.
The value of the critical density ρc is about 6x10-27 kg/m3,
that is two atoms of hydrogen per cubic meter. This very
low figure explains why some cosmological models
which suppose an empty universe are not such a bad
approximation.
Edwin Hubble
Einstein too arrived at the same conclusion of a
dynamic universe but rejected these results as
inconsistent with current accepted thinking and
modified his equations to conform to a static, non
changing universe. He soon realised this was a big mistake.
In the early 1920s, while working at the Mt. Wilson
Observatory with the most advanced telescope of the time,
Edwin Hubble showed that some of the numerous distant,
faint clouds of light in the universe were actually entire
galaxies—much like our own Milky Way. The realization that
the Milky Way is only one of many galaxies forever changed
the way astronomers viewed our place in the universe.
But perhaps his greatest discovery came in 1929, when Hubble
determined that the farther a galaxy is from Earth, the faster it
appears to move away. This notion of an "expanding" universe
formed the basis of the Big Bang theory, which states that the
universe began with an intense burst of energy at a single
moment in time — and has been expanding ever since.
Cosmic Microwave Background
The entire universe is awash with microwaves. The CMB, or cosmic Microwave Background is an
undercurrent of radiation coming from every direction of space. The CMB is critical in understanding how
the cosmos was created and is probably one of the most important astronomical discovery of the 20 th
century.
Where did this ever present radiation come from?
In the first few hundred thousand years after the Big Bang the entire universe was filled with plasma, a
state of nuclei (hydrogen and Helium) and free electrons, similar to the interior of the sun and lots and lots
of photons, particles of light, like UV, X-Rays and Gamma Rays. This condition of matter will readily absorb
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and re-emit photons so any light created was almost instantly absorbed. Even though the universe was
filled with light, it was so short lived that you couldn’t see it – the universe was opaque.
That all changed 380,000 after the Big Bang when the universe cooled below 3000 oK. At this temperature
and below the free nuclei and electrons can combine into stable neutral atoms. Once that happened the
photons could move
through the
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universe, in every
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direction, virtually
unimpeded and they
have been doing so
ever since. As space
has expanded this
light has also
stretched out and its
wavelength has now
reached the
microwave region, 1 to 10 mm wavelength.
At first glance the CMB is the same in every direction. That was certainly the case when Penzias and Wilson
inadvertently discovered this radiation in 1965. However in 1992, NASA’s Cosmic Background Explorer
(COBE) mapped the CMB for the whole sky and gave us a picture of the early universe. The slight variations
in microwaves are converted to temperature differences in the sky to create a whole sky map. In 2003 the
Wilkinson Microwave Anisotropy Probe (WMAP) measured the CMB with much greater accuracy. Planck,
a space observatory operated by the European Space Agency (ESA) from 2009-2013, again mapped
the anisotropies of the CMB at higher sensitivity and smaller angular resolution.
Each set of data improved and extended on the previous set. This field of study is not complete and in the
coming decades it is hoped to extend these measurements to measuring gravity waves.
Planck 2013 data release
On 21 March 2013, the European-led research team behind
the Planck cosmology probe released the mission's all-sky map of the cosmic
microwave background. This map suggests the universe is slightly older than
previously thought. According to the map, subtle fluctuations in temperature
were imprinted on the deep sky when the universe was about 380,000 years
old. The imprint reflects ripples that arose as early in the existence of the
universe as the first nonillionth (10−30) of a second. It is currently theorised
that these ripples gave rise to the present vast cosmic web of galactic
clusters and dark matter. According to the Planck team, the universe
is 13.819 billion years old, and contains 4.82% ordinary matter, 25.8% dark
matter and 69% dark energy. The Hubble constant was also measured to
be 67.80 (km/s)/Mpc.
Dark Matter, Dark Energy
It used to said that cosmologists, the scientists who study the universe as a whole, are 'often in error but never in
doubt.' Today, they are less often in error, but their doubts have grown large. After decades of research involving
new and better telescopes, better and bigger cameras and much better computers, cosmologists can now state with
high precision that the universe was born 13.8 billion years ago, most likely in a bubble of space no bigger than an
atom. For the first time they have mapped the cosmic microwave background radiation - light released when the Page |
universe was 380,000 thousand years old - to an accuracy of 1 part in a 1000. But they have also concluded that all 6
the stars and galaxies they see in the sky make up 5 percent of the observable universe. The invisible ma jority
comprises 27 percent dark matter and 68 percent dark energy. Both of them are mysteries - scientists
conducting numerous experiments around the world have yet not been able to detect what these substances are.
Dark matter is thought to be responsible for sculpting the
glowing sheets and tendrils of galaxies that make up the
large scale structure of the universe. Dark energy is even
more mysterious. The term, coined to describe whatever
is accelerating the rate at which the universe is expanding,
is also, virtually an unknown quantity.
The first inkling of dark matter’s pervasive presence
came in the 1930’s when the Swiss astronomer Fritz
Zwicky , while working at the Mount Wilson
Observatory measured the speed at which galaxies in
the Coma cluster, 321 million light years from away,
orbit the centre of the cluster. He calculated that unless the cluster contained mush more mass than was
visible, the galaxies would long since have flown off into space. That the Coma cluster was still intact can
only mean, that the Coma cluster must contain other matter that cannot be seen. Subsequent
investigations by Vera Rubes in the 1970’s and many others since, all indicate that galaxies never would
have formed if gravity, generated by dark matter, were not present to gathered primordial materials when
the universe was young.
Dark matter cannot just be inconspicuous normal atomic matter because there isn’t enough of that.
Trillions of dim, normal matter objects are surely out there – among them black holes, cold stars, cold gas
and dust and rouge planets, ejected by their stars to wonder the cold dark places of the cosmos. But in no
detailed accounting of all this material can scientist find enough of these objects to add up to 5 times the
mass of the bright stuff. Hence scientists think that dark matter is made or some particle not yet
discovered, generally termed a Wimp, for weakly interacting massive particle.
Theorists working on an extension of the Standard Model of Particle physics, called Super Symmetry,
predict a supersymmetric particle for every known particle, and one or more of these might turn out to be
dark matter. This new theory is very speculative since evidence is just not yet available.
Strange and perplexing as dark matter might appear, it looks somewhat ordinary in comparison to the
mysterious phenomenon of dark energy. Dark energy is believed to be a property of space itself and
therefore difficult to conduct direct studies. Astrophysicist
Michael Turner nominates dark energy as the ‘most
profound mystery in all of science’. Turner coined the term
‘dark energy’ after two teams of astronomers announced in
1998 that the rate at which the universe was expanding
appeared to be accelerating. The astronomers reached this
conclusion by studying a class of exploding stars that are
bright enough and consistent in their brightness to make
them useful in measuring distances of very distant galaxies
– Type 1A supernova.
Common wisdom had it before 1998 that the mutual tug of gravity among all galaxies would serve as a
brake on the expansion of the universe, and so astronomers expected it to be slowing down. Two
independent teams conducting the experiment in 1998 found the opposite. Their results showed, to
everyone’s surprise, that the universe was expanding ever faster as time goes by and has been doing so for
about 5 billion years.
Astronomers today are busy mapping the universe looking for evidence of just when dark energy emerged and
whether it has since remained constant in strength or is growing ever stronger. They are limited though by the
capacity of the current telescopes and digital detectors. So more accurate cosmological data requires better
equipment. See the document ‘Giant Telescopes’ for a description of some of the new telescopes to be built in the
next 10 years. In addition, there are current experiments and sky surveys, such as the Dark Energy Survey, using the Page |
Blanco 4 metre telescope in the Chilean Andes, which is collecting data on 300 million galaxies. The European Space 7
Agency’s Euclid Space Telescope, scheduled to launch in 2020 is designed to make precise measurements of cosmic
dynamics over the past 10 billion years.
Mission Statement from the Euclid web site: http://sci.esa.int/euclid/
Euclid is an ESA mission to map the geometry of the dark Universe. The mission will
investigate the distance-redshift relationship and the evolution of cosmic structures
by measuring shapes and redshifts of galaxies and clusters of galaxies out to redshifts
~2, or equivalently to a look-back time of 10 billion years. In this way, Euclid will
cover the entire period over which dark energy played a significant role in
accelerating the expansion.
The Víctor M. Blanco Telescope is a 4m telescope located at the Cerro Tololo
Observatory, Chile. Commissioned in 1974 and completed in 1976. In 1995 it was
dedicated and named in honour of Víctor Manuel Blanco, the Puerto Rican astronomer.
The newly installed DECam (Dark Energy Camera) on the telescope is the main-research
instrument in the Dark Energy Survey, and began to take measurements in September
2012.
DECam has one of the widest field of view (2.2 degrees) available for ground-based
optical and infrared imaging. The survey will image 5,000 square degrees of the southern
sky. The survey will take five years to complete, and the survey footprint will be covered
several times in five photometric bands.
From Wikipedia, the free encyclopaedia
http://www.phys-astro.sonoma.edu/people/faculty/tenn/cosmologysince1900.html
http://www.preposterousuniverse.com/blog/2006/03/16/wmap-results-cosmology-makes-sense/
http://nrumiano.free.fr/Ecosmo/cg_model.html
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