International Journal of Astronomy and Astrophysics, 2015, 5, 79-89
Published Online June 2015 in SciRes. http://www.scirp.org/journal/ijaa
How to cite this paper: Iqbal, M.Z. (2015) Progress in Physics of the Cosmos. International Journal of Astronomy and As-
trophysics, 5, 79-89. http://dx.doi.org/10.4236/ijaa.2015.52011
Progress in Physics of the Cosmos
M. Zafar Iqbal
Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan
Received 4 March 2015; accepted 5 May 2015; published 8 May 2015
Copyright © 2015 by author and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
Study of the Cosmos, at best, is considered a semi-scientific discipline, primarily because the la-
boratory for carrying out measurements and tests of theories (the Cosmos) has been largely inac-
cessible for centuries. The cosmic vista into the yonder, however, continued to fascinate human-
kind due to its inherent beauty and sheer curiosity. The invention of the optical telescope more
than five centuries back, however, led to the opening of observational cosmology as a scientific
discipline with firm experimental basis. However, the investigations based on visible light posed
obvious limitations for the range of such observational cosmology. The advent of the radio tele-
scope in the first half of the 20th century marked a fundamental new step in the progress of this
branch of science. There has been no looking back in the march of knowledge in the discipline
since then. A whole new vista was laid bare as a result of this development, leading to the discov-
ery of altogether new celestial objects, such as quasars and pulsars and still newer galaxies. The
parallel progress of the physics of fundamental constituents of the material world and their inte-
ractions led to an interesting merger of these two branches of physical sciences, yielding abso-
lutely astounding knowledge of the nature and evolution of the Universe. New concepts of dark
energy and dark matter thought to constitute the dominant share of the Universe were brought to
light as a result of these new observations and theoretical ideas. This brief article aims to provide
an overview of these exciting developments in the field of cosmology and the associated physics.
Radio Astronomy, Cosmic Microwave Background, Dark Energy, Dark Matter, Swirling B Modes
The birth and evolution of the Universe, of which we are one of the tiniest parts, have been an enigma and a
challenge to unravel ever since humankind started taking a rational view of things around him. For a long time,
Cosmology, as a branch of Physics, (Astrophysics) has been regarded more as soft science based on guesswork
M. Z. Iqbal
and heuristic ideas devoid of any solid scientific base, largely due to absence of concrete observational evidence.
However, as the means to explore the Universe came within man’s reach as a result of developments in various
branches of physics and science, in general, more and more hard evidence on the different celestial objects and
the universe beyond our immediate neighborhood in the cosmos started emerging and the revelation of extraor-
dinary nature and properties of these objects fired the imagination of physicists and scientists, in general, to reach
beyond our immediate galaxy, the Milky Way. A brief introduction to how it became possible to do so and with
what scientific tools would be provided in the early part of this report. As amazing new facts about the nature of
the astronomical bodies and systems inhabiting the cosmos emerged as a result of availability of these advanced
means to access distances hitherto thought beyond our means to explore, a coherent picture of the origin and
evolution of the universe started to emerge by the late 20th century, culminating in the so called Standard Mod-
el of Cosmology. This was greatly helped by exciting new developments in the realm of particle physics he-
ralded by the advent of large and expensive accelerator machines, allowing exploration of the structure of the ti-
niest of the constituents of matter and hence of our universe. Although these developments led to a lot of clarity
in our understanding of the science of cosmology, some new enigmas also emerged in their wake. Some of these
unanswered questions will be touched upon towards the end of this article.
2. Historical Background
2.1. Early Explorations
Our understanding of the cosmos has, in general, been impeded by the lack of experimental means to observe it.
These observations were limited to the range of the optical telescope invented by Galileo in 1609, to begin with.
However, this scientific development, momentous though it was, could only extend our knowledge of the cos-
mos (at whatever rudimentary level possible), not far beyond our own solar system or the Milky Way galaxy, in
which it lies. Our observations and, therefore, directly measured data, which are the basis of any scientific un-
derstanding of a system, could, at most, cover a miniscule fraction of the universe as long as we were limited to
the light (radiation) spanning only the visible part of the optical spectrum. Clearly, we had to extend our capabil-
ity of observation to the use of ‘light’ beyond this tiny band of wavelengths, if we intended to explore the ele-
ments of the Universe well beyond, since it was established soon after the discovery of the electromagnetic
waves, which carry information about their origin and whatever lies in between the observer and such sources,
that the cosmos was full of electromagnetic wave signals, harking for research and investigation to establish
their nature and origins, just as visible light gave us a clue of what we were looking at around us and our earth.
The development of electronic technology and the sensitive tools to detect even weak signals around us first
brought us to the advent of radio astronomy. This made it possible for mankind to extend his sphere of explora-
tion of the Cosmos to the ‘invisible’ (to the human eye or the optical telescope) part of the universe.
2.2. Radio Astronomy
Radio astronomy started with a serendipitous discovery in 1932 by Jansky , a scientist at the Bell Telephone
Laboratories, of radio waves coming from space. Development of radar and allied technology during the 2nd
World War led to a boost to this branch of science, bringing into limelight focused studies to look for radio wave
sources from around the Universe, using specially designed high resolution radio telescopes, yielding remarka-
ble results to enrich our knowledge of the universe. The power of radio astronomy is well demonstrated by the
well-resolved structure, with much enhanced clarity, in the equatorial plane of our Milky Way galaxy, as ob-
served by a radio telescope in comparison to that observed by visible light, as shown in Figure 1. Unlike visible
light, radio waves are not absorbed by clouds, interstellar dust, or the atmosphere of the Earth. They, thus, pro-
vide a superior means of exploring distant celestial objects in the universe, as compared to the ordinary visible
light waves. The original radio wave signal picked up by Jansky turned out to originate from the centre of the
Milky Way. Large diameter dish antennae telescopes had to be constructed to achieve relatively high resolutions
for meaningful exploration of the cosmos. Whereas radio wave emission from the Sun was first observed  in
1942, the first distant objects, i.e., the galaxies Centaurus A and M87 and the Crab Nebula, shown in Figure 2,
were identified as strong radio sources in 1949 .
Planetary science of our solar system benefitted from the development of the radio telescope greatly, since,
although planets only reflect visible light, they may, however, emit radio waves, leading to their detailed studies
M. Z. Iqbal
Figure 1. (Top) The Milky Way galactic plane under visible light. (Bottom) The
structures of galactic plane become clear in 21 cm hydrogen spectral line observa-
tions. (Photo credit: NASA). Source: The National Radio Astronomy Observatory
using the new type of telescopes. The surface temperature of Venus was measured from such observations  as
were some initial explorations made on radio wave emissions, both continuous and pulsed, from Jupiter .
Studies based on the 21 cm hydrogen line emission, first detected in 1951   have been extremely useful for
the exploration of the interstellar matter, which largely consists of neutral hydrogen gas. Such studies, for exam-
ple, led to the observation of the many spiral arms of our galaxy - finer than those of other galaxies. The
formation and evolution of stars from regions of interstellar space containing other gases, which are the sources
of radio waves, have been widely studied with radio telescopes, yielding exceptionally useful information on
star birth. New galaxies, such as Cygnus A, have been found to be a million times brighter than Milky Way in
radio-wave region   of emission spectrum, with large lobes of radio-wave emission (Figure 3) around
the central region emitting in the optical domain—detailed studies showed that the outer radio wave lobes are
only 3 million years old as compared to the central region going back to 10 billion years. Radio astronomy has
revealed altogether new facts about the Cosmos, such as the existence of quasi-stellar objects (quasars) in 1960
-, which emit brightly both in the visible and the radio frequency region of the electromagnetic wave
spectrum. These strange objects were at the centre of fascinating studies by astronomers, as well as physicists,
during the 1960s; detailed redshift studies indicated them to be just about the farthest objects in the universe at
the time, some 12 billion light years from Earth. As such, they held the promise of yielding information on the
early stages of the Universe. The discovery of pulsars , following in 1967, showed how rotating neutron stars,
some of the most densely packed material objects in the universe, could lead to the emission of pulses of radio
waves at such an amazingly regular interval (33 milliseconds for the crab nebula pulsar), that they can be used
as “astronomical clocks” with the highest precision. These wonderful lighthouse-like objects have inspired a
great, in-depth understanding of the Universe by providing detailed insight into the life cycle of the stars. The
M. Z. Iqbal
Figure 2. Hubble Space Telescope photograph of the Crab Nebula
Figure 3. 5-GHz radio image of Cygnus A (3C405). http://en.wikipedia.org/wiki/Cygnus_A#cite_note-3
1This is a mosaic image, on e of the largest ever taken by NASA’s Hubble Space Telescope of the Crab Nebula, a six-light-year-wide e
panding remnant of a star’s supernova explosion. Japanese and Chinese astronomers recorded this violent event nearly 1000 years ago
1054, as did, almost certainly, Native Americans. The orange filaments are the tattered remains of the star and consist mostly of
The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula’s eerie interior bluish glow.
blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star,
a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star’s rotation. A neutron star is
crushed ultra-dense core of the exploded star. The Crab Nebula derived its name from its appearance in a drawing made by Irish
Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the
Southern Observatory’s Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular
demise of a star, 6500 light-years away. The newly composed image was assembled from 24 individual Wide Field and Planetary Camera
exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were e
pelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur
and red indicates doubly-ionized oxygen.
M. Z. Iqbal
development of radio astronomy, thus, expanded the horizon of our knowledge and understanding of the Un-
iverse from the elements of our own solar system and its planets to stars and other objects in our galaxy, to in-
terstellar space and galaxies far beyond.
3. Cosmic Microwave Background
The discovery of cosmic microwave background (CMB) radiation in 1964  is one of the most significant
milestones in the development of the science of cosmology in the modern era, based on observations in radio as-
tronomy. The serendipitous detection of this all pervading diffuse microwave radiation, found to have isotropic
distribution over entire space, corresponding to a black body temperature of 2.73 Kelvin, although a mind bog-
gling puzzle to start off with, was soon interpreted as the remnant of the massive explosion that accompanied the
creation of the Universe, estimated to have taken place some 13.7 billion years ago. This event, heralding enorm-
ous release of energy, came to be dubbed as the big bang with time. The point in space of this event corresponded
to a singularity from which radiation emanated in all directions, eventually transforming into matter (elementary
particles of all descriptions constituting the material universe) as it cooled down. The material universe is be-
lieved to be expanding as per a law attributed to Hubble, but first derived from Einstein’s equations of General
Relativity by Georges Lemaître in 1927, which states that all cosmological bodies are receding from each other
with a velocity proportional to their distance from each other. The proportionality constant which was first meas-
ured by Hubble in 1929 has come to be known as the Hubble constant and its most recent and accurate value is
H0 = 74.3 ± 2.1 (km/s)/Mpc, pc being the symbol for a parsec, an astronomical unit of distance equal to 3.09 ×
1013 km. The crab nebula, for instance, is receding from us at a rate of ~1500 km/s. The discovery of the cosmic
microwave background radiation was the first definitive evidence for the big bang origin of our expanding un-
4. Structure of the Universe
Whereas the uniformity of CMB in all directions in the cosmos seemed to be a striking feature of its discovery,
detailed later studies based on COBE (Cosmic Background Explorer), a satellite in the Explorer series launched
by NASA on November 18, 1989 in a sun-synchronous orbit, revealed strong evidence for an all important ani-
sotropy in CMB, first announced on April 23, 1992 . The famous full map of this anisotropic distribution of
CMB obtained by COBE is shown in Figure 4. These fluctuations in CMB around the sky are extremely weak
(about one part in 100,000 as compared to the 2.73 Kelvin average temperature of the radiation field), explain-
ing why the initial measurements found a virtually isotropic microwave background, regardless of the position
in the Cosmos. This anisotropy, clearly, hinted at the local density fluctuations of the Universe at or close to the
time of the big bang, as evidenced today by the existence of galaxies interspersed by empty space. This was the
first indication of the reason for the existence of today’s structure in the Universe. This important observation
led to very significant advances in our understanding of the formation of stars, galaxies of stars and their clusters
and, hence, the evolution of the Universe. This significance of the discovery has been recognized by the award
of the Nobel Prize for Physics in 2006 to John C. Mather of the NASA Goddard Space Flight Center and George
F. Smoot at the University of California, Berkeley, two of COBE’s principal investigators. According to the
Nobel Prize committee, “the COBE-project can also be regarded as the starting point for cosmology as a preci-
sion science” .
The COBE mission was followed by the Wilkinson Microwave Anisotropy Probe (WMAP) launched on June 30,
2001 with the objective of obtaining a more precise full sky map of the anisotropy of CMB distribution with a
resolution of 13 arcminute - 45 times more sensitive and with 33 times the angular resolution of COBE. These
precise data were expected to help understand the geometry, content, and evolution of the Universe, providing
finer tests of the Big Bang model. WMAP’s measurements played the key role in establishing the current Stan-
dard Model of cosmology and have led to the most precise value, till then, of the age of the Universe at 13.75 ±
0.11 billion years; the full timeline of the Universe according to the standard model is given in Figure 5.
M. Z. Iqbal
Temperature of the Cosmic Microwave Background (CMB) radiation spectrum as determined with the COBE satellite during the first two
years of the Differential Microwave Radiometer (DMR) observation. The plane of the Milky Way Galaxy is horizontal across the middle of
each picture: (top) uncorrected; (middle) corrected for the dipole term due to our peculiar velocity; (bottom) further corrected to remove the
contribution of our galaxy. Note: This map is based on data collected over the two first years of the four-year COBE mission. Therefore, it
has been superseded by the four-year map (shown below).
Temperature of the Cosmic Microwave Background (CMB) radiation spectrum as determined with the COBE satellite during the full four
years of the Differential Microwave Radiometer (DMR) observation. The plane of the Milky Way Galaxy is horizontal across the middle of
each picture. This map shows the 53 GHz channel: (top) prior to dipole subtraction; (middle) after dipole subtraction (due to the solar system
movement); (bottom) after subtraction of a model of the Galactic emission.
Figure 4. Source: The COBE datasets were developed by the NASA Goddard space flight center under the guidance of the
COBE science working group. http://en.wikipedia.org/wiki/Cosmic_Background_Explorer
M. Z. Iqbal
Figure 5. The timeline of the Universe, from inflation to the WMAP.
5. Dark Energy and Dark Matter
This insight into the nature of the Universe has led to two remarkable new concepts. The first is to do with the
expansion of the Universe referred to above. It has all along been expected that the speed of this expansion
would slow down as we move farther and farther out in the Universe, since the galaxies would gravitationally
pull each other. It was, therefore, to every body’s astonishment that, to the contrary, this expansion was found to
be accelerating rather than slowing down as we move outwards. This amazing recent discovery based on the
observations of the distant Type 1a Supernovae—a late-in-life, dying state of a star—in 1998   caused a
great stir among astronomers and physicists alike, leading to the award of the 2011 Nobel Prize in Physics. This
novel phenomenon led to the idea of some mysterious “dark energy”, which pulls the space apart . The
question of the precise nature of this dark energy is one of the hotly debated subjects in astrophysics and of on-
going research in both observational cosmology and theoretical physics.
Another subject of immense current research is an equally, if not more, mysterious object called the “dark
matter”. This is matter proposed to provide the gravitational glue binding the galaxies together in the cosmos.
The original idea for this type of matter arose from the fact that galaxies in some clusters are found to move too
fast to be allowed to hold together among themselves; even some stars within some individual galaxies move
way too fast for gravity to hold them in these galaxies. Some mysterious invisible “dark matter” was, therefore,
proposed to provide the missing gravitational pull in these systems, as early as 1933 . Recent WMAP mea-
surements provided a more direct evidence for this dark matter, however, suggesting that some 83% of the Un-
iverse constituted in “dark matter”, while the ordinary matter we see and feel around us in the entire cosmos
makes only about 4.56% of the mass of the Universe -.
5.1. Observation of Dark Matter
The European Space Agency’s (ESA) Planck mission, launched to study the cosmic microwave background
(CMB), released the first results after the initial 15 months in March 2013 . These observations revealed
new structure in temperature fluctuations of the CMB on a far finer scale than known hitherto (Figure 6). Planck
has scanned the entire sky in microwave and submillimeter range of the electromagnetic spectrum, materializing
high resolution pictures of the temperature fluctuations since the Universe was very young. The slightly slower
expansion rate of the Universe sensed by Planck has extended the age of the Universe slightly, in comparison
with the previous estimates—to 13.81 ± 0.05 billion years from 13.77 billion years proposed by the WMAP
mission and allied observations.
With the initial, opaque plasma state of the Universe after the Big Bang, the excessive energy present did not
allow formation of stable atoms until a cooling period of 380,000 years, when an event known as recombination
set in. The transparent universe followed with a huge outflow of photons, into the modern era. The initial ultra-
violet photons resulting from recombination, however, converted to the microwave spectral region as the un-
iverse cooled further down to its current level. The power spectrum of the fluctuations over the sky, revealed by
M. Z. Iqbal
Figure 6. The cosmic microwave background—temperature fluctuations left
over from 380,000 thousand years after the Big Bang. This new map is based on
data from the Planck mission. ESA/Planck Collaboration/D. Ducros
Planck mission, Figure 7, yields crucial information on the structure and composition of the Universe. The most
prominent fluctuations are due to the total energy content of the Universe, while the smaller ones are associated
with the distribution of matter alone, both ordinary and dark. The relative magnitudes of the ordinary and dark
matter and the conglomeration of the latter are revealed by the smaller fluctuations. Comparison of the Planck
data with theoretical models led to finer, but significant adjustments in the hitherto known estimates of ener-
gy/matter composition of the Cosmos (Figure 8): dark energy lowered to 68.3% from 72.8%; dark matter up
from 22.7% to 26.8%; ordinary matter also up from 4.5% to 4.9%.
Figure 7. The power spectrum measured by Planck, showing the fluctuations in temperature
at a range of size scales on the sky. The anomaly previously seen by WMAP lies at the left
edge. The three major peaks show the relative contributions of dark energy, ordinary matter,
and dark matter. ESA/Planck Collaboration/D. Ducros
Figure 8. The composition of the cosmos, before and after Planck data release. ESA/Planck
M. Z. Iqbal
5.2. Polarization Studies of CMB
The ultimate evidence for or against dark matter is expected to emerge from the polarization studies of the CMB
radiation over the Universe and its anisotropy signature. A great excitement was recently generated by positive
news on that count, coming from a telescope station located at the South Pole of the earth. On March 17, 2014
came the announcement of the observation of the so called primordial B-modes by BICEP2 detector of the tele-
scope. These are swirling polarization patterns, Figure 9, in the tiny (1 part in 100,000) fluctuations in CMB
temperature across the Universe. These miniscule variations in temperature are interpreted to be due to varia-
tions in the density of the primordial gas at the time of emission of the black body radiation, thus reflecting the
evolutionary process of the Universe. These fluctuations are thought to be magnified by the gravitational pull of
matter, leading to formation of galaxies and clusters of galaxies, now observed in the cosmos. The development
of ultrasensitive detectors about a decade back made it possible to provide precise measurements of the polariza-
tion, calling in a new era in experimental cosmology and in studies of structure and evolution of the Universe. In
particular, the swirling B modes would provide information on the inflationary development—proposed as early
as 1980—of the very early Universe, during the first 10−36 to 10−32 seconds of the Big Bang, during which the
Cosmos grew by a factor of 1026. The gravitational waves during this period are supposed to generate this pola-
rization pattern. Dust and magnetic fields in our galaxy were expected to easily mask the tiny polarization signal
being sought after. Scales of 1˚ used for the initial measurement of B modes were concluded to be large enough
to avoid interference due to signals from intervening galaxies. The sceptics found these signals to be far stronger
than those predicted or even beyond the limits set by Planck mission on the power of the gravitational waves to
generate the CMB temperature fluctuations.
Figure 9. B-mode polarization in the Cosmic Microwave Background (source: BICEP2 Collaboration).
However, it did not take too long to realize that the twisting CMB polarization pattern could easily be caused
by the cosmic dust in the Milky Way galaxy . It has been concluded that the BICEP2 team underestimated
M. Z. Iqbal
the contribution of this dust to the swirl polarization pattern, which could almost entirely be accounted for by the
latest dust pattern data revealed by Planck mission.
This reversal of the evidence for the detection of primordial gravitational waves applies brakes to the progress
in the quest for experimental proof of Big Bang inflationary model, to the idea of multiverse and, of course, to a
definitive proof of the existence of dark matter. However, this may signal a temporary hiatus, since, at least,
eight experiments, including BICEP3, the Keck Array and Planck, are already focused on this problem.
Mean-while, a new perception has emerged regarding the inflationary model, which makes this theoretical mod-
el valid irrespective of the experimental evidence for the primordial gravitational waves—the paradigm of infla-
tion would, in that perspective, appear to be unfalsifiable and, therefore, scientifically meaningless .
6. Concluding Remarks
The brief review above shows clearly how far we have travelled in unraveling the secrets of the Cosmos and the
Universe in which we live, over less than a century. It is equally manifest that this rapid progress has been made
possible by the enormous advancements in the experimental instrumentation and techniques available for ob-
serving the Cosmos. The huge progress in telescopy and the remarkable developments in space technology have
made a tremendous impact on the achievable knowledge with high precision and accuracy. While the astronom-
ical knowledge of the cosmos has witnessed impressive progress, the analysis of these observations has opened
new frontiers in our understanding of the fundamental physics and nature and evolution of the Universe.
It is clear from the above brief description of the current state of our knowledge of the Universe that the age
old maxim, the more we know, less we conclude we actually know, appears to be perfectly valid. However, such
is perhaps the nature of all human knowledge. But how exciting the ever expanding frontiers of this field of
fundamental physics are can be gauged from this brief narrative. It is also clear that our quest for the knowledge
of the Universe will be a continuing chapter in the story of human search and discovery for the years to come
and may yet raise more questions than it can answer. Thanks to the remarkable developments in technology, and
hence the tools of observational astronomy, many new frontiers of the unknown may yet be opened for even
more extensive exploration of the Cosmos than the territory conquered hitherto.
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