Within this posting I plan to give little retrospective regarding Big Bang posts I've writing (6 of them) and make some update and complete the story.  Story is far away from being finished of course - it is open book to say so and it is also step before series of posts about our solar system. Big Bang does not explain how life emerged on Earth, it does explain how Universe started and what conditions where there throughout the timeline before it happened. Big Bang does not say why this happened as that's outside the scope of the theory. Big Bang explains the early development of the Universe only! Everything else is outside the scope of theory as Big Bang theory never tried nor pretended to give any other answers. Big Bang does not try to answer what was before Big Bang as there was no before - time as we know it started with Big Bang. These ideas are sometimes hard to grasp, but what your shoe before it become a shoe? Nothing as its time as shoe started once it become a shoe. Components of your shoe existed before, but similar to your shoe Bog Bang deals with current Universe. If our Universe is cyclic, part of some other universe (multiverse) model or something else - this is something that other theories deal with - not Big Bang. Big Bang is our best theory towards early days of current Universe.




There are many gaps or unknowns in this theory (or even theories as there are several models out there). This is easy to understand. You need to get an idea of how big Universe really is. It's huge. It's so big that you should not bother to comprehend. Yes, no matter how big you imagine it, you will still be wrong and Universe would be bigger. How big is that? We don't know - that big! Current estimate and readings say Universe is 13.75 billion years old. You might not consider billion to be such a big number, but it is if you count years. How old it is does not tell us how big it is though. Well, before we get to that point, I need to mention that our Universe is expanding. It has been expanding since first seconds of Big Bang, but it has increased the speed in its expansion since. Current theoretical models have few explanations for this like negative pressure and likes, but no one will blame you if you say that space has some hormone issue and its belly expanding. This acceleration happened some six billion years ago. This expansion though has impact on size as size at any point in time is no in proportion with other. Which brings us to topic of observable universe - which is universe we can observe since the light had time to reach us.  Light can't go faster than speed of light thus there is theretical limit to how much we can observe. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction - that is, the observable universe is a spherical volume (a ball) centered on the observer, regardless of the shape of the universe as a whole. Every location in the universe has its own observable universe which may or may not overlap with the one centered on the Earth.




So, the age of the universe is about 13.75 billion years, but due to the expansion of space humans are observing objects that were originally much closer but are now considerably farther away than a static 13.75 billion light-years distance. The diameter of the observable universe is estimated to be about 28 billion parsecs (93 billion light-years), putting the edge of the observable universe at about 46-47 billion light-years away. Now, that's a lot. If you really wish to get impressed, clickhere to see sizing model. In your lifetime, which is comparably much smaller of course, there have been events which you would wonder about or simply could not explain them. Universe, big as it is, certainly have such moments too when viewed from our perspective. You can just imagine how many unknowns there are. But, we discovered something that helps us around - rules. There are certain patterns which help us understand why, where and when something happens and we define rules describing those events. Step by step, by probing, calculating and with help of experiments, we are trying to reverse engineer timeline and get an idea of our Universe past, present and consequently future.




The deeper we look into the universe, the deeper we look back in time. When in the night sky you see planets like Jupiter and Saturn, you look about an hour back in time. Look at the stars, and you are looking back in time anywhere from years to several centuries. Bring a binocular to a dark site and you will be able to see galaxies millions of years back in time. Get a decent telescope to the same site and you look even further back. Astronomers can look back down to 380,000 years after the big bang. At the LHC we can recreate the conditions of the universe down to much earlier times of about 0.00000000001 seconds after the big bang. Still earlier times are not experimentally accessible to us, as we lack particle accelerators powerful enough to recreate the energies required. Nobody can claim to know what happened at times and energies not accessible to us. However, we do have theories that go down to much earlier times.


Very early days of our Universe are best estimate based on what we gathered so far. At very smallish time interval, the one we refer today as Planck Epoch, Universe starts as dense and hot miniature dot if you want to. Temperature is sky high and we know little about physics under such conditions, but we believe conditions are such that all known forces of today (weak, strong, electromagnetism and gravity) are united into one single force. At this point Universe has what we call Plack size and Planck temperature. Following Planck epoch is the grand unification epoch, which begins when gravitation separates from the other forces of nature. At this time the earliest elementary particles (and antiparticles) begin to be created. Inflationary epoch is something many people today have problems to swallow still. It is epoch which caused fabric of cosmos to expand at speeds way beyond speed of light for example. For cosmologists inflation answers the classic puzzle of the big bang cosmology: why does the universe appear flat (that is the geometry of space we are used to), homogeneous (or is the same everywhere) and isotropic (which means the same in all directions) and so fits with all the cosmological ideas a big bang scientist would expect if you have this inflation event. As fabric stretches at unimaginable scale, this dense ball of energy is distributed equally. The rapid expansion of space meant that elementary particles remaining from the grand unification epoch were now distributed very thinly across the universe. However, the huge potential energy of the inflation field was released at the end of the inflationary epoch, repopulating the universe with a dense, hot mixture of quarks, anti-quarks and gluons as it entered the electroweak epoch. There are some theories which place electroweak epoch at the start of inflation, but important to say is that this epoch is separation of strong force from electroweak one (electromagnetism and weak force united). Finally, baryogenesis phase starts in which symmetry among particles breaks and thanks to them, we have matter today. The excess of baryons over antibaryons in the present universe is thought to be due to non-conservation of baryon number in the very early universe, though this is not well understood. At the end of this epoch, existing particles acquire mass through Higgs mechanism.


Today distribution of matter across the universe is not that big. It is faintly small. We may be surrounded by matter, but put that into perspective of observable universe and it faints away quickly. In those early days Universe was in state of quark-gluon plasma. Most recently we succeeded to reproduce this state too. Next phase is speculative, but many theorists require its existence - supersymmetry breaking phase. At this point bond is breaken and particles take different masses. This is followed by quark epoch where universe was filled with a dense, hot quark-gluon plasma, containing quarks, leptons (electrons and neutrinos) and their antiparticles. Quarks and antiquarks annihilate each other upon contact, but due to baryogenesis, a surplus of quarks (about one for every billion pairs) survives, which will ultimately combine to form matter. This temperature of the universe is still too high to allow quarks to bind together to form hadrons (collisions are far too energetic for any of those). The following period, when quarks became confined within hadrons, is known as the hadron epoch. Here some familiar hadrons like protons and neutrons form. In this era neutrinos decouple too.


Now, bare in mind that all these above happened up to 1 second after Big Bang.  That's a lot of thrill for such a shor time (at least at our own human scale). Anyway, it continues with lepton phase which is similar to handron phase except electrons tend to play major role here. Finally, we have photon epoch which is rather important and takes longish period of time to complete. Within this period we differentiate nucleosynthesis (neutron and protons start to combine atomic nuclei), matter domination (more precisely dark matter domination which makes 63% of total mass-energy), recombination (ionized hydrogen and helium atomic nuclei capture electrons and first neutrally charged atoms appear and most important photons are set free in what we call decoupling) and finally dark ages - which will last until first light by stars is not ignited.


We do not have exact estimate as to where first stars and galaxies along with black holes appeared, but flow was that we had pristine gas first which formed stars in nebulaes (interstellar cloud of dust, hydrogen, helium and other ionized gases). That may have happened at earliest some 480 million years after Big Bang according to estimates. We have records of this pristine gas clouds 12 billion years ago being observed, but some early galaxy observations indicate large scale structures might have appeared as early as 480 million years after Big Bang. From these gas first stars have formed - earliest estimates today suggest 30 million years after Big Bang. Those were massive stars and short-lived (compared to current standards). Epoch in which first stars appeared is called reionization. Astronomers think that the only molecule that could cool down a forming star in that particular time was so called H3+. In Big Bang cosmology, reionization is the process that reionized the matter in the universe after the "dark ages", and is the second of two major phase changes of gas in the universe. As the majority of baryonic matter is in the form of hydrogen, reionization usually refers to the reionization of hydrogen gas. The primordial helium in the universe experienced the same phase changes, but at different points in the history of the universe, and is usually referred to as Helium reionization. We can say that during this long phase the first quasars and stars form from gravitational collapse, and the intense radiation they emit reionizes the surrounding universe. From this point on, most of the universe goes from being neutral back to being composed of ionized plasma and galaxies which form on the way and Universe starts to take shape as we know it.


In June 2012 the faint, lumpy glow given off by the very first objects in the universe may have been detected with the best precision yet, using NASA's Spitzer Space Telescope. These faint objects might be wildly massive stars or voracious black holes. They are too far away to be seen individually, but Spitzer has captured new, convincing evidence of what appears to be the collective pattern of their infrared light.



One thing people usually make mistake is to believe big bang was explosion with center. It was not.  While you can imagine dot as something from where all it came from, as it was really small during Planck epoch, inflation stretched fabric so much that what we observe today is flat. Perhaps geometry is wrong, but for distances observable to us - it is flat. This is similar to Earth - while Earth is not flat, distance I can see and measure makes it flat and there is no need for my sight to take curvature into account. With all these points in Universe being stretched and still expanding, it is fair to say that each point in Universe would be equally old. So it comes as no surprise recent discovery of two white dwarf stars considered the oldest and closest known. Astronomers identified these 11- to 12-billion-year-old white dwarf stars only 100 light years away from Earth. These stars are the closest known examples of the oldest stars in the Universe forming soon after the Big Bang. Known as WD 0346+246 and SDSS J110217, 48+411315.4 (J1102), these stars are located in the constellations Taurus and Ursa Major, respectively.




With collapse of big stars came first supernovas and black holes. Recent study shows black holes came thus before galaxies formed and surely those are super massive black holes. Earlier studies had revealed an intriguing link between the masses of black holes and the central "bulges" of stars and gas in galaxies. Generally, the black hole's mass was seen to be about 1000th that of the mass of the surrounding galactic bulge. This indicated an interactive relationship between the black hole and the bulge. Recently, hoewever, new evidence from NASA's Chandra X-ray Observatory challenges prevailing ideas about how black holes grow in the centers of galaxies. Astronomers long have thought that a supermassive black hole and the bulge of stars at the center of its host galaxy grow at the same rate - the bigger the bulge, the bigger the black hole. However, a new study of Chandra data has revealed two nearby galaxies with supermassive black holes that are growing faster than the galaxies themselves - bringing to focus once again role of dark matter.


Supernovas on the other hand were five times more frequent 10 billion years ago than they are today (and those most likely came from collapse of massive stars). After supernova explosion, we can expect either neutron star to form or black hole. When a massive star explodes they tend to have internal factors that distort that nice, smooth expansion. One big factor is that the actual point of explosion is off-center in the star, not at its exact heart. That can create a massively asymmetric explosion, blasting vast amounts of material and energy off to one side. The core itself in such a star still collapses to become a super-dense neutron star (or a black hole), but the sideways nature of the explosion can give a kick to the leftover ball of neutrons. In fact, the energies are so titanic that an off-center supernova explosion can blast the neutron star in the other direction, screaming away from the explosion site like a shell out of the muzzle of a battleship gun. Astronomers may have found the most extreme example of this (what looks to be just such a neutron star barreling away from a supernova at high speed):



See that comet-looking thing? You can see a dot at the head of the "comet". Astronomers think that might be the runaway neutron star from the explosion that created SNR MSH 11-16A. Tail of gas pointing right back to the center of the supernova gas cloud. A hot, young neutron star blows out a high-energy wind of subatomic particles called a pulsar wind, and that pushes against gas floating out in space. As a runaway neutron star blasts through space, it would leave a glowing trail like that. The X-rays appear to be coming from a single, tiny point, just what you'd expect for a neutron star, and observations using optical and infrared don't see it; again, just what you'd expect since neutron stars are tiny and don't glow visibly. They're brightest in X-rays due to their phenomenally strong magnetic fields whipping particles around at high energies. If that dot is the ejected neutron star, it’s screaming away from the explosion site at a mind-numbing 10 million kilometers per hour. Other runaway neutron stars have been seen moving away from supernovae at high speeds, but none this fast.


Neutron stars are extremely dense ball of matter only a few kilometers across. Imagine taking a mountain and crushing down in size to where it could fit in your hand. Or think of it this way: a cubic centimeter (roughly the size of a sugar cube or dice) of neutron star material would have about the same mass as all the cars in the US combined. Go even more denser and you get black hole - where gravitational pull is so string that even light can't escape it thus the name. Very close to neutron star is term pulsar; a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. They appear to pulse because the magnetic axis is not aligned with the axis of rotation, so the pole comes in and out of view as the neutron star rotates. This produces a very precise interval, between pulses that range from roughly milliseconds to seconds for an individual pulsar. The precise periods of pulsars makes them useful tools - sort of space lighthouse. Coming back to black holes, they are interesting to many theorists due to holographic principle too. No one has ever been inside black and back, but theories exist which tend to explain inner part of black hole after horizon have been passed (see here for more). Black holes are extremely powerful and efficient engines that not only swallow up matter, but also return a lot of energy to the Universe in exchange for the mass they eat. When black holes attract mass they also trigger the release of intense X-ray radiation and power strong jets. But not all black holes do this the same way. This has long baffled astronomers.




Researchers at the SRON Netherlands Institute for Space Research have reported in June 2012 evidence that suggests that each black hole can change between two different regimes, like changing the gears of an engine. Their work suggests that changing gear might be common among black holes. They also found that the switch between gears happens at a similar X-ray luminosity for all observed black holes.


Finally, another component of Universe, are quasars. Quasar is a compact region in the center of a massive galaxy surrounding its central supermassive black hole. Quasars are believed to be powered by accretion of material onto supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. As stars and interstellar gas fall into the black holes, they swirl around them and then are swallowed up - but not before giving off bright light at nearly all wavelengths of the electromagnetic spectrum.


But while above appear to me small components of big Universe (or big picture if you want), there are much larger structures (or grouping if you want) that exist out there. Stars have their planets and they form solar system. Solar system (stars and planets) tend to form galaxies which are determined by their radius which somehow is related to size of supermassive black hole in galaxy center. Galaxies form groups and cluster of galaxies which further leads to filaments. And that's where the story ends. At least as far as we can see within our observable patch of Universe (it is not hard to get your imagination going here and imagine our Universe being part of multiverse). What is beyond horizon we have no idea nor we know any mechanism which could help us probe those distances even in theory. But we know there are parts of universe without any known matter - so called voids. We know there is dark matter and dark energy as two mass-energy components we still didn't figure out. There are certain gravitational pulls coming outside visible horizon - so called dark flow. It is fair to say that small fluctuation is dense fabric what Universe was during first moments of time may have caused certain asymmetry which further caused large structures to be scattered across Universe (otherwise you would expect uniform distribution and universe would be one large structure as such).


In June 2012 astronomers at Arizona State University have found an exceptionally distant galaxy, ranked among the top 10 most distant objects currently known in space. Light from the recently detected galaxy left the object about 800 million years after the beginning of the universe. Below is the false color image of the galaxy LAEJ095950.99+021219.1 . In this image, blue corresponds to optical light (wavelength near 500 nm), red to near-infrared light (wavelength near 920 nm), and green to the narrow range of wavelengths admitted by the narrow bandpass filter (around 968 nm). LAEJ095950.99+021219.1 appears as the green source near the center of the image cutout. The image shows about 1/6000 of the area that was surveyed. (btw, if you wonder how Milky Way looks at different wavelenghts just click here)




Baby galaxies from the young Universe more than 12 billion years ago evolved faster than previously thought, shows new research from the Niels Bohr Institute. They discovered not only that the galaxies from the very early Universe had a surprisingly large quantity of heavier elements, but also that one of the galaxies in particular was especially interesting. For one of the galaxies, they observed the outer regions and here there was also a high element content. This suggests that large parts of the galaxy are enriched with a high content of heavier elements and that means that already in the early history of the Universe there was potential for planet formation and life. How and when did galaxies with hundreds of billions of stars form and evolve? The sun, which is the center of the solar system in which we live, is also only one of the countless stars contained within a galaxy. In brief, it can be said that we need to understand the evolution of galaxies to understand the world we live in.


Couple months ago, a team of researchers from the Laboratoire Univers et Théorie (LUTH) coordinated by Jean-Michel Alimi has performed the first-ever computer model simulation of the structuring of the entire observable universe, from the Big Bang to the present day. The simulation has made it possible to follow the evolution of 550 billion particles. For more details check here.


Going back to the beginning, I said there is nothing before Big Bang as notion of time did begun with Big Bang itself. There are mathematical models, one by famous Leonard Susskind, which tend to indicate there has to be some kind of beginning. For details, check here and here. We continue to uncover the facts and based on them patterns and rules. We are young civilization with few primitive steps made outside Earth, but smart enough - hopefully - to make much bigger things. I will finish this with picture infographic by astrophysicist Invader Xan who made nice side by side overview of our missions to space - the final frontier (maybe).