Thank you Hubble!!!

It is a long time, that I am not writing in Tiyezerk., but undoubtedly I do physics, specially cosmology continuously.

Anyhow I decided to write more frequently here.

Today I was asked what are the main scientific discoveries achieved by Hubble space base telescope.

In the first moment I can't tell much about it, obviously because we owe too much to Hubble telescope, and cosmology really have a rebirth from the discoveries of Hubble telescope.

Anyhow later, I decided to categorize some of the most achievements of it as below:

1)Measurement of Cepheid variable and determination of the Hubble constant, which shows the rate of the expantion of the universe and indirectly determine the age of universe.

2)Astronomers from the High-z Supernova Search Team directed Riess and the Supernova Cosmology Project directed Perlmuter used the telescope to observe distant supernovae and uncovered evidence that, far from decelerating under the influence of gravity, the expansion of the universe may in fact be accelerating and that is the main fingerprint of unknown component of universe.

3)High quality optical spectra and images provide a valuable data for studying the relation of nuclei of galaxies and black holes.

4)Although Hubble telescope is the optical eye of earth, it also detect the optical effect of cosmological events which their peak are in other wavelenght like gamma ray burst.

5)Ultra deep Hubble image focus the telescope and got the furthest optical image of universe, which I wrote about it in a post later.

6)Detection of some objects or events in solar system, like the The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 or the detection of Eris and Pluto

7)Hubble data on proto-planetary disks (proplyds) in the Orion Nebula

and many more...

thanks to Hubble

Shan Baghramian

Interacting Dark Energy Models

Accelerating universe causes to many-many models come to existence.

Whenever we do not have a plausible fundamental theory to describe a phenomena.

Immediately physicists go to phenomenology.

Interacting Dark energy models are one of those trying to describe the Accelerating universe.Recently a nice work done by Authors: Gabriela Caldera-Cabral, Roy Maartens, Bjoern Malte Schaefer with the arxiv address of arXiv:0905.0492 with the
Title: The Growth of Structure in Interacting Dark Energy Models .

Anyhow the interaction is common future in physics and why not to think about the interaction of unknowns!!!(Dark energy-Dark Matter)

Most distance object seen in Universe

The most distant object seen in universe was detected in April 23 by NASA Swift satellite.

A Gamma ray burst detected in redshift of 8.2 is the farthest object ever seen.

GRB 090423 was seen when it is about 630 million years after big-bang!!!

read the news here.

Physics and dimensions

Why physics is so much bizarre in different dimensions.

Starting the course of galactic dynamics in SUT we start to take a look to Poisson equation in two and three dimensions.It is interesting that the dimensionality effect so much on physics of gravitation. A test particle in a 3 dimensional symmetric sphere feels no force.But in 2 dimensions from a homogeneous ring exerts gravitational force on a test particle just because of dimensionality!!

Consequently one can I ask why we are living in 3+1 extended/for believers of higher dimension/ dimensions.Is there any fundamental physical reason behind it?

Design for an asymmetric universe

In the latest issue of Nature Physics Nature Physics 5, 89 - 90 (2009) ,there is a review article about the asymmetric universe by David Wands /
David Wands is at the Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX, UK. /
Wand in this review article describe about the temperature anisotropies asymmetry seen in WMAP5 years data accordig to two hemispheres of CMB sky.Then he concluded that lately with the launch of Planck satellite and more accurate data about this asymmetry will force us to revise and change our inflationary models.
This is because the simplest one field inflation model produce a homogeneous temperature fluctuation,which in this case it is not satisfied.
Anyhow new observations may bring us to asymmetric universe.

Hubble Ultra Deep Field 2004

This picture is the deepest picture of universe in optical wavelenght!!!

Galaxies, galaxies everywhere - as far as NASA's Hubble Space Telescope can see. This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Called the Hubble Ultra Deep Field, this galaxy-studded view represents a "deep" core sample of the universe, cutting across billions of light-years.
The snapshot includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, about 100, may be among the most distant known, existing when the universe was just 800 million years old. The nearest galaxies - the larger, brighter, well-defined spirals and ellipticals - thrived about 1 billion years ago, when the cosmos was 13 billion years old.
In vibrant contrast to the rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. These oddball galaxies chronicle a period when the universe was younger and more chaotic. Order and structure were just beginning to emerge.
The Ultra Deep Field observations, taken by the Advanced Camera for Surveys, represent a narrow, deep view of the cosmos. Peering into the Ultra Deep Field is like looking through an eight-foot-long soda straw.
In ground-based photographs, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is so empty that only a handful of stars within the Milky Way galaxy can be seen in the image.
In this image, blue and green correspond to colors that can be seen by the human eye, such as hot, young, blue stars and the glow of Sun-like stars in the disks of galaxies. Red represents near-infrared light, which is invisible to the human eye, such as the red glow of dust-enshrouded galaxies.
The image required 800 exposures taken over the course of 400 Hubble orbits around Earth. The total amount of exposure time was 11.3 days, taken between Sept. 24, 2003 and Jan. 16, 2004.

Cluster of Galaxies

Cluster of galaxies are the largest and massive structure in universe which are gravitationally bound together.Each cluster of galaxy contain 10 to 1000 galaxies.Galaxies in cluster have a very large peculiar velocity of 800-1000 km/s to be virialized in cluster.

Beside the galaxies it is found that there is a hot plasma gas in the clusters with the name of ICM "Inter cluster mass" which is approximately 2 times massive that the baryonic matter in galaxies.

The mysterious aspect of clusters is that if this structures are in hydrostatic equilibrium they need Dark matter with mass of 6 times more than baryonic matter in cluster.

So in this case there are three main constituents in each cluster:

1)5% galaxies 2)10% X-ray emitting hot gas 3)Dark matter.

It seems that the dark matter ,galaxies and ICM has approximately the same distribution in clusters.

Cluster of galaxies are the most massive and lately formed structure in the hierarchical structure formation model.They masses vary from 10^14 to 10^ 15 solar masses and the diameter of this clusters are from 2 to 10 Mpc.

The nearby important clusters are Virgo cluster, Hercules cluster and Coma cluster.

The galaxy clusters are a rich regions for observational cosmology and consequently theoretical cosmology.

Accreation disks

Accretion disks arises when materials in universe usually being transformed from one celestial to the other object.Accretion means the collecting of additional matter.

The place that accretion disk take place is Binary stars and active galaxy nuclei.

For example consider a white dwarf that a simple star like ours rotate around it.

because of the conservation of angular momentum and gravitational pull from White dwarf to interstellar medium and sun ,spirals appear in disk.

gas become very hot in disk due to friction and being tugged on by white dwarf and eventually looses angular momentum and falls into WD.

The important of accretion disk is that the first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc.

Neutron Star

Collapse of stars,type II supernovae and type Ib and type Ic SN caused to have neutron stars.This stars whic are completely/dominantly/ composed of neutrons have masses between 1.35~2.1 solar mass and radius of 12 km which means that neutron stars have high densities of 3.7~5.9 * 10^17 kg/m^3 .At the very high pressures involved in this collapse, it is energetically favorable to combine protons and electrons to form neutrons plus neutrinos. The neutrinos escape after scattering a bit and helping the supernova happen, and the neutrons settle down to become a neutron star, with neutron degeneracy/Pauli exclusion principle/ managing to oppose gravity.

The neutron stars are formed by high rotation speed because of conservation of angular momentum.Also because of the high speed of stars they can escape from disk of galaxies and can be found in perpendicular direction of disk galaxies.

The high density of neutron star cause to have a escape velocity of about 33% of light speed as a comparison a teaspoon of neutron star has a mass of 5*10^12 kg.

Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula (or check out this cool X-ray image of the nebula, from the Chandra X-ray Observatory).

up to today there are 2000 known neutron stars are found in milky way and Magellanic clouds.

it is also worth that they appear in binary type with 5%.

Some good links for neutron stars.

http://www.astro.umd.edu/~miller/nstar.html#formation

http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html

6 puzzles for LCDM

Recently a nice review article appeared in arxivarXiv:0811.4684 by Perivolaropoulos from Greece.

The title is 6 puzzles for LCDM .In this article author pay attention to 6 problems /observational ones/that the LCDM model have problem with them.

In literature always we confront with the two problems of fine tuning and coincidence problem for LCDM ,but there are more to confront.

1)Large scale velocity flow: LCDM predicts smaller amplitude and scale for the flow.

2)Brightness of type I SuperNova at high redshifts :LCDM predicts fainter SuperNova in high redshifts.

3)Emptiness of voids:LCDM predicts more dwarf or irregular galaxies in voids.

4)Profile of Halo clusters:LCDM predicts low and shallower concentration and density.

5)Profile of galaxy halos:LCDM predicts cuspy core and low outer density while lensing and other observations predicts central core of constant density.

6)Size able population of disk galaxies:LCDM predicts less disk galaxies.

This are really interesting probes for dark energy problem

Sweet molecule in our galaxy

An interesting article with id number of 0811.3821 in arXiv is uploaded.

A group of astronomers in University Collage of London found the simplest monosacharite ,

"glycolaldehde" in a distant of 9 kpc in a hot molecular cloud in our galaxy.

The discovery is so interesting because this monosacharite is the block for generating Ribose which is the main block of RNA.

lately there are evidence for glycolaldeyde in the center of galaxy ,but because of high interaction rate and density of this part of galaxy it seemed natural to found it there.

But the detection of spectral line of glycolaldehde by IRAM radio telescope in France in region which star forming is probable is an interesting news for exoearth life science.

molecule

News in science daily:

http://www.sciencedaily.com/releases/2008/11/081125090344.htm

arXiv:0811.3821v1

Reionization

Today in IPM/Tehran/There is a lecture talk about the law frequency radio astronomy.

In the conclusion part, the lecturer state that one of the applications of law frequency radio astronomy is detecting objects in reionization era.

Now what is reionization era.

Let me do a little job to describe it.

In the history of universe two major phase transition occurred for hydrogen.

First of it was in the time of recombination/redshift z~1100 / 400,000years after big bang when the rate of combination of electron to protons became higher than the ionization of hydrogen atom so in consequence of this the hydrogen atoms formed and the universe become transparent for photons.This is the last scattering surface and the photons coming from this redshift are the cosmic microwave background radiation photons.

The second phase transition occurred in reionization era, 150 million to 1 billion year after big band/redshift of 20 to 6/ because of formation of structures high energy became free and the universe /the intergalactic medium /changes it phase and from neutral become ionized and transformed to plasma.In this case the protons and electrons which are not bound can not capture the photons so they become transparent to it.

There are different techniques to found out about this era,which in future posts I will introduce them first of all for my self like.

Techniques are:

Quasars and the Gunn-Peterson trough

CMB anisotropy and polarization

21-cm line

Ph.D.

Now it is November 2008!
I start to plan all the way for my Ph.D. thesis
The general title will be accelerating universe:Theory and phenomenology.
In this work I should take a look and do my research in theoretical models generally Dark energy and modified gravity ones,and also use cosmological observations like Supernova, CMB,large scale structure,local tests of gravity to investigate the mystery of 70% of our universe.
I think that I should finish my work in September 2011!!!
It seems interesting time for me.
Go on...

Scintillation of light curves and Dark matter

In the last two weeks, in physics department of SUT, in our weekly cosmology seminars we have Frahang Habibi as a speaker. In this two sessions he describes for us a general view of his Ph.D thesis. Farhang is a joint Ph.D. student of sharif university and IAP in Paris.
He is working on dark matter detection in form of hydrogen molecule gas.

Now what is the story?
As we know 23% of our universe is composed of dark matter/means no electromagnetism interaction/but gravitationally is resemble to ordinary baryonic matter.
There are many many candidates for Dark matter starting from super symmetric particles to unseen baryonic matter.
Now what is Farhangs and Mark Moniez/his french side supervisor/ idea ?It is about a cloud of hydrogen molecule distrubeted in clusters which are not radiating because of there internal structure of hydrogen molucule ,but can be a candidate of unseen matter.
In this thesis they introduce a type of a test in order to detect them.
If there is a cloud of hydrogen molecules, they can effect optically on the light coming from stars beyond it.This cloud can scatter and diffract the light coming.So if in an experiment / observation/we can see an effect of scintillation in the light curves of the stars., it shows that there is something there that cause the amplification of light and maybe if the characteristics of our observation seems to our models match, it could be a cloud of hydrogen.

This is the good part of the story.But the bitterly hard part remains,the simulation of this effect and then observation of a known cluster and after that data reduction in order to find the best candidate stars which their light curves shows the effect of scintillation is Farhangs hard task.

6+1 lesson from f(R)-gravity

Last Monday 3 of November a nice talk-article was appeared in arXiv with the title of:

6+1 lessons from f(R) gravity with the arxiv address arXiv:0810.5594

In this article Thomas P. Sotiriou a postdoc in Meryland, describe the 7 lessons that we learn from studing the straightforward form of modification of gravity.

Thomas P. Sotiriou received his Ph.D. in SISSA in September 2007 under supervision of Stefano Liberati and John Miller with the title of Modified Actions for Gravity: Theory and Phenomenology with the address of arXiv:0710.4438 .

He is the great expert of modified gravity.Tracking his articles in recent years help me lot even in preparing my Master thesis.

Homepage of Thomas Sotiriou

http://terpconnect.umd.edu/~sotiriou/mysite/About_Me.html

Chameleon mechanism

Tuesday 28 of October I gave a small!!! talk in physics department,in series of cosmology weekly seminars.

The general title of talk is the Accelerating universe,Theory and phenomenology and the subtitle is Chameleon scalars mechanism and modified gravity.

The general title is the field which I want to be engaged in my Ph.D.thesis.

And what about the chameleon theories?

The accelerating universe open a new paradigm in cosmology.

There are many many models trying to describe this phenomena,but generally we can divided all the models in 2 general subdivisions.

If we accept the context of general relativity, which means that we know gravity well, we will come to the realization that new physical entity needed to describe the accelerating universe,such as cosmological constant or scalar fields generally named quintessence.

The second main models come to existence from the assumption that the general relativity needed to be modified in long ranges and small curvatures.This models named Modified gravity.

But what is chameleon?

The point is that we know that general relativity works well in solar system and local tests of gravity.So if we change the action of Einstein -Hilbert to have new effects in cosmological scales also we will affect the local tests of gravity, so we need a mechanism! in order to conceal this effect in local tests and disappear it and bring it back to existence in cosmological scales. This mechanism is called Chameleon mechanism after the name of lizard!!!like animal which changes its skin color with environment.So the scalar field equivalent to modified gravity /We know about the equivalence of modified gravity with scalar field theories/

changes its behaviour with respect of the density of environment like Chameleons.

BUT

in theoretical point of view this mechanism needs more investigations to be reliable,I will study it more...

Ads/CFT

It is about a year that in our physics department in Sharif university, each Tuesday held a seminar among the three active theoretical groups of department.

1)Particle physics 2)Cosmology 3)Conformal field theory group

The idea and the motivation of seminars is nice:it is to be connected and aware of the work of each other.Last Tuesday particle group talk about really complex subject.I want to respell the ideas of it in order to have a snapshot of this.

The talk is given by Mohsen Alishahia and is about about Ads/CFT correspondence more vastly Anti de sitter space/Conformal field theory correspondence which is also called after Maldacena the Argentinian physicists MAldacena duality.What is all about?

The theory shows that the string theory in a Anti desitter space plus a sphere or orbifold is physically equivalent to a conformal field theory with out gravity defined in its boundary.

It seems complicated anyhow it is interesting because of presenting a way to solve the quantum gravity theory and also it is inspired by the holographic principle which claim that you can extract the physics of a volume from its boundary.Holographic principle is a a speculative idea about quantum gravity originally proposed by Gerard 't Hooft and improved and promoted by Leonard Susskind.

Finally the lecturer imposed the probability that maybe this correspondence first of all can be used to describe the gravitational effects on inflationary models.

Let me show up some important papers on this genius work.

Reminding you that In about five years, Maldacena's article had 3000 citations and became one of the most important conceptual breakthroughs in theoretical physics of the 1990s, providing stark new insight into both quantum gravity and QCD.

1)Maldacena, The Large N Limit of Superconformal Field Theories and Supergravity, arΧiv:hep-th/9711200.
2)Witten, Anti-de Sitter Space and Holography, arΧiv:hep-th/9802150.
3)Gubser, Klebanov and Polyakov, Gauge Theory Correlators from Non-Critical String Theory, arΧiv:hep-th/9802109.
4)Aharony et al, Large N Field Theories, String Theory and Gravity, arΧiv:hep-th/9905111.
AdS/CFT correspondence on arxiv.org.

2008 Physics Nobel Prize

Finally the 2008 Physics Nobel prize goes to Japanese.

Yoichiro Nambu from Chicago University /http://physics.uchicago.edu/research/areas/particle_t.html#Nambu /for his contribution to the finding of the mechanism of spontaneous broken symmetry in subatomic physics get 1/2 of the Nobel prize and the other half goes to Makoto Kobayashi and Toshihide Maskawa for for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature.

One another Nobel prize goes to particle physicists campaign,although their are hope to see the prize in cosmology for the discovery Accelerating universe by Supernovas but ...

Anyhow in the upcoming posts I will try to describe the work of Nobel prize winners...

MOND vs Dark Matter

A couple of weeks ago, there was a Ph.D. thesis defence in Sharif University of Technology by Hossein Haghi **,***under supervision of Dr. Sohrab Rahvar/He is my supervisor too!:)/, in physics department with the title of MOND* in ... : Modified Newtonian Dynamics.

What is it about?and what is the story of modification...

During last century, in physics history usually we observed new phenomenas in experiments which could not be described by approved and used models and physical laws of the day.So what happened? Immediately the situation is divided in two ways

1)In the same frame of our known laws and models, we defined new physical entities to describe the experiment. or

2)We concluded that we do not know the laws well, and we start to change and modify them.

This scenario was happened several times, as a famous example is the problem of missing mass in beta decay in late 20's and beginning of 30's ,as I mentioned there were two solution 1)The law of conservation of energy is not correct or

2)there is a new mysterious unseen particle that we do not know about it and can not detect in experiment.

The history in this case shows that the second solution, the famous Neutrino predicted by Pauli was the right answer.

Now we have such a situation in galactic scale cosmology too.

The rotation curves of stars rotating in galaxy contradict with the prediction of Newtonian Mechanic, and we get flat rotational curves.

Immediately there is two solutions to the problem

1)Modifying the Newtonian law:Which means we do not understand it well,or there is more complete theory standing there.MOND as an example.

2)There is a new mysterious,only gravitationally interacting particle which named DARK MATTER ,which is responsible for this new missing mass in galaxy.

Finally what I want to mention is about the always existing two perspectives as a solution of the problem.

1)Modifying the laws or 2)Introducing New physical entity, are always teasing physicists minds.

But which one is seems more plausible is not yet well established but it will be fair to mention that the DARK MATTER campaign is so large /because of its success in cosmological model for structure formation models as CDM and there is a huge Hope to find light supersymmetric particles (LSP) in LHC arXiv:0807.2244 as a candidate for this entities as DARK MATTER.

But the story is not happy ended yet .Anyhow let us see what experiments unreveal for us.

*Nice web site about MOND related papers: http://www.astro.umd.edu/~ssm/mond/

**arXiv:astro-ph/0606246

***arXiv:astro-ph/0504171

Timeline of General Relativity and Cosmology from 1905

The new semester in Sharif university begins.This term Dr. Reza Mansouri,/ http://en.wikipedia.org/wiki/Reza_Mansouri /one of the prominent scientists of Iran teach General relativity and gravitation. Dr. Mansouri which recieved his Ph.D. in Austria in begining of 1970s is the first one who taught general relativity in Iran.
In first session he take a look on history of general relativity and cosmology.
The below is a more complete list of the happenings since the foundation of Special relativity in 1905.


1905 - Albert Einstein , special relativity

1907 - Albert Einstein introduces the principle of equivalence of gravitation and inertia

1915 - Albert Einstein - general relativity.

1915 - Karl Schwarzschild - Schwarzschild metric ,first solution to the Einstein field

1916 - Albert Einstein - field equations of general relativity admit wavelike solutions

1917 - Willem de Sitter derives an isotropic static cosmology with a cosmological constant, as well as an empty expanding cosmology with a cosmological constant, termed a de Sitter universe.

1918 - J. Lense and Hans Thirring find the gravitomagnetic precession of gyroscopes GR

1919 - Arthur Eddington -solar eclipse expedition- detection gravitational deflection of light

1921 - Theodor Kaluza 5-dimensional version of GR equations unifies gravitation and EM

1922 - Alexander Friedmann finds a solution to the Einstein field equations which suggests a general expansion of space

1927 - Georges Lemaître discusses the creation event of an expanding universe governed by the Einstein field equations.

1929 - Edwin Hubble demonstrates the linear redshift-distance relation and thus shows the expansion of the universe

1933 - Edward Milne names and formalizes the cosmological principle 1934 - Georges Lemaître interprets the cosmological constant as due to a vacuum energy with an unusual perfect fluid equation of state

1937 - Fritz Zwicky states that galaxies could act as gravitational lenses

1937 - Albert Einstein, Leopold Infeld, and Banesh Hoffmann -geodesic equations of GR can be deduced from its field equations

1938 - Paul Dirac suggests the large numbers hypothesis, that the gravitational constant may be small because it is decreasing slowly with time.

1948 - Hermann Bondi, Thomas Gold, and Fred Hoyle propose steady state cosmologies based on the perfect cosmological principle.

1948 - George Gamow predicts the existence of the cosmic microwave background radiation by considering the behavior of primordial radiation in an expanding universe

1950 - Fred Hoyle derisively coins the term "Big Bang".

1957 - John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity.

1960 - Robert Pound and Glen Rebka test the gravitational redshift predicted by EP the approximately 1%

1961 - Robert Dicke argues that carbon-based life can only arise when the gravitational force is small, because this is when burning stars exist; first use of the weak anthropic principle

1962 - Robert Dicke, Peter Roll, and R. Krotkov use a torsion fiber balance to test the weak equivalence principle to 2 parts in 100 billion

1964 - Irwin Shapiro predicts a gravitational time delay of radiation travel as a test GR

1965 - Joseph Weber puts the first Weber bar gravitational wave detector into operation

1965 - Martin Rees and Dennis Sciama analyze quasar source count data and discover that the quasar density increases with redshift.

1965 - Arno Penzias and Robert Wilson, astronomers at Bell Labs discover the 2.7 K microwave background radiation, which earns them the 1978 Nobel Prize in Physics. Robert Dicke, James Peebles, Peter Roll and David Todd Wilkinson interpret it as relic from the big bang.

1966 - Stephen Hawking and George Ellis show that any plausible general relativistic cosmology is singular

1966 - James Peebles shows that the hot Big Bang predicts the correct helium abundance

1967 - Andrei Sakharov presents the requirements for baryogenesis, a baryon-antibaryon asymmetry in the universe

1968 - Irwin Shapiro presents the first detection of the Shapiro delay

1968 - Kenneth Nordtvedt studies a possible violation of the weak equivalence principle for self-gravitating bodies and proposes a new test of the weak equivalence principle based on observing the relative motion of the Earth and Moon in the Sun's gravitational field.

1969 - Charles Misner formally presents the Big Bang horizon problem 1969 - Robert Dicke formally presents the Big Bang flatness problem.

1974 - Robert Wagoner, William Fowler, and Fred Hoyle show that the hot Big Bang predicts the correct deuterium and lithium abundances

1976 - Robert Vessot and Martin Levine use a hydrogen maser clock on a Scout D rocket to test the gravitational redshift predicted by the equivalence principle to approximately 0.007%

1976 - Gravity Probe A experiment confirmed slowing the flow of time caused by gravity matching the predicted effects to an accuracy of about 70 parts per million.

1979 - Dennis Walsh, Robert Carswell, and Ray Weymann discover the gravitationally lensed quasar Q0957+561

1981 - Viacheslav Mukhanov and G. Chibisov propose that quantum fluctuations could lead to large scale structure in an inflationary universe 1981 - Alan Guth proposes the inflationary Big Bang universe as a possible solution to the horizon and flatness problems

1982 - Joseph Taylor and Joel Weisberg show that the rate of energy loss from the binary pulsar PSR B1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5%

1990 - Preliminary results from NASA's COBE mission confirm the cosmic microwave background radiation is an isotropic blackbody to an astonishing one part in 105 precision, thus eliminating the possibility of an integrated starlight model proposed for the background by steady state enthusiasts.

1990s - Ground based cosmic microwave background experiments measure the first peak, determine that the universe is geometrically flat

1998 - Controversial evidence for the fine structure constant varying over the lifetime of the universe is first published.

1998 - Adam Riess, Saul Perlmutter and others discover the cosmic acceleration in observations of Type Ia supernovae providing the first evidence for a non-zero cosmological constant.

1999 - Measurements of the cosmic microwave background radiation (most notably by the BOOMERanG experiment see Mauskopf et al., 1999, Melchiorri et al., 1999, de Bernardis et al. 2000) provide evidence for oscillations (peaks) in the anisotropy angular spectrum as expected in the standard model of cosmological structure formation. These results indicates that the geometry of the universe is flat. Together with large scale structure data, this provides complementary evidence for a non-zero cosmological constant.

2002 - The Cosmic Background Imager (CBI) in Chile obtained images of the cosmic microwave background radiation with the highest angular resolution of 4 arcmin. It also obtained the anisotropy spectrum at high-resolution not covered before up to l ~ 3000. It found a slight excess in power at high-resolution (l > 2500) not yet completely explained, the so-called "CBI-excess".

2003 - NASA's WMAP obtained full-sky detailed pictures of the cosmic microwave background radiation. The image can be interpreted to indicate that the universe is 13.7 billion years old (within one percent error) and confirm that the Lambda-CDM model and the inflationary theory are correct. 2003 - The Sloan Great Wall is discovered.

2004 - The Cosmic Background Imager first obtained the E-mode polarization spectrum of the cosmic microwave background radiation.

2006 - The long-awaited three-year WMAP results are released, confirming previous analysis, correcting several points, and including polarization data.

2007 - End of Gravity Probe B experiment.