The broadly accepted theory for the origin and evolution of our universe is the Big Bang model, which states that the universe began as an incredibly hot, dense point roughly So, how did the universe go from being fractions of an inch a few millimeters across to what it is today?
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Here is a breakdown of the Big Bang to now in 10 easy-to-understand steps. It took quite a bit more than seven days to create the universe as we know it today. This is Part 3 in that series. The Big Bang was not an explosion in space, as the theory's name might suggest. Instead, it was the appearance of space everywhere in the universe, researchers have said. According to the Big Bang theory, the universe was born as a very hot, very dense, single point in space. Cosmologists are unsure what happened before this moment, but with sophisticated space missions, ground-based telescopes and complicated calculations, scientists have been working to paint a clearer picture of the early universe and its formation.
This relic of the Big Bang pervades the universe and is visible to microwave detectors, which allows scientists to piece together clues of the early universe. Among other discoveries, WMAP was able to determine the age of the universe — about When the universe was very young — something like a hundredth of a billionth of a trillionth of a trillionth of a second whew!
During this burst of expansion, which is known as inflation, the universe grew exponentially and doubled in size at least 90 times. As space expanded, the universe cooled and matter formed. Light chemical elements were created within the first three minutes of the universe's formation.
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As the universe expanded, temperatures cooled and protons and neutrons collided to make deuterium, which is an isotope of hydrogen. Much of this deuterium combined to make helium. For the first , years after the Big Bang, however, the intense heat from the universe's creation made it essentially too hot for light to shine. The part of the universe we can observe from Earth is filled more or less uniformly with galaxies extending in every direction as far as we can see - more than 10 billion light-years, or about 6 billion trillion miles.
We know that the galaxies must extend much further than we can see, but we do not know whether the universe is infinite or not. When astronomers sometimes refer carelessly! Galaxies are not actually arranged on the surface of a sphere. Many students and teachers mistakenly believe that the galaxies in the universe are arranged on the surface of a sphere. One origin of this misconception is the common demonstration of blowing up a balloon to model the expansion of the universe.
Another is the mistaken belief that during the Big Bang, matter expanded into space from a point see below. A third is the finding that many clusters of galaxies appear to be arranged around the outside of "bubble-like" voids in the universe. But on the largest scales that astronomers have observed, each chunk of space appears to have just as much matter as any other equivalent chunk.
We can see just about as far as nature allows us to see. Two things prevent us from seeing further. First, the universe has been evolving with time. Stars and galaxies did not always exist. Therefore light from MOST of the galaxies in the universe has not yet had time to reach us. Second, the universe has been expanding with time. Again, light from MOST of the universe has not yet had time to reach us.
If you could suddenly freeze time everywhere in the universe, and magically survey all of creation, you would find galaxies extending out far beyond what we can see today.
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But how far, no one knows. Just a hundred years ago, scientists thought of the universe in terms of matter. Space was just the "emptiness" in which matter lived. Today, the situation is reversed. During the twentieth century, scientists learned that space is not "nothingness. In fact, when astronomers talk about the "expansion of the universe," they are referring to the stretching of space between clusters of galaxies - NOT to the motion of galaxies through space. Later, scientists found other properties of space.
For example, matter and anti-matter are routinely created in the laboratory from space itself and an energy source ; the kinds of particles that can exist reflect the structure of space. In fact, there is now evidence that space itself MAY possess some slight amount of energy of its own, of a form previously unknown. If so, space may actually have weight! Discovering the properties of space remains one of the deepest and most important problems in modern science.
Did the Universe expand from a point? The Big Bang was not an explosion IN space. It was a process that involved ALL of space. This misconception causes more confusion than any other in cosmology. Unfortunately, many students, teachers, and scientists! In reality, ALL of space was filled with energy right from the beginning. There was no center to the expansion, and no magical point from which matter hurtled outward. But that primordial pellet of matter and energy was NOT surrounded by empty space In fact, if the whole universe is infinitely large now, then it was always infinite, including during the Big Bang as well.
Thus the Big Bang took place everywhere in space, not at a particular point in space. For much of the twentieth century, astronomers and physicists believed that space might NOT be infinitely large - that is, space might actually curve around on itself to form a "closed universe.
The shape was later favored by Einstein as a possible shape for the universe. Such a closed universe would have a finite volume, yet no boundaries or edges. Although closed universes cannot be visualized from the outside, they CAN be visualized from the inside. For example, the image at right gives an idea of what a tiny closed universe might look like.
In a real closed universe, you cannot see the back of your head, the way you can here. And the collapse of some of the first stars may have seeded the growth of supermassive black holes that formed in the hearts of galaxies and became the spectacular power sources of quasars. In short, the earliest stars made possible the emergence of the universe that we see today—everything from galaxies and quasars to planets and people. The age of each object can be determined by the redshift of its light, which shows how much the universe has expanded since the light was produced.
The oldest galaxies and quasars that have been observed so far date from about a billion years after the big bang assuming a present age for the universe of 12 billion to 14 billion years. Researchers will need better telescopes to see more distant objects dating from still earlier times.
Cosmologists, however, can make deductions about the early universe based on the cosmic microwave background radiation , which was emitted about , years after the big bang. The uniformity of this radiation indicates that matter was distributed very smoothly at that time. Because there were no large luminous objects to disturb the primordial soup, it must have remained smooth and featureless for millions of years afterward. As the cosmos expanded, the background radiation redshifted to longer wavelengths and the universe grew increasingly cold and dark.
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Astronomers have no observations of this dark era. But by a billion years after the big bang, some bright galaxies and quasars had already appeared, so the first stars must have formed sometime before. When did these first luminous objects arise, and how might they have formed? Many astrophysicists, including Martin Rees of the University of Cambridge and Abraham Loeb of Harvard University, have made important contributions toward solving these problems.
The recent studies begin with the standard cosmological models that describe the evolution of the universe following the big bang. Although the early universe was remarkably smooth, the background radiation shows evidence of small-scale density fluctuations—clumps in the primordial soup. The cosmological models predict that these clumps would gradually evolve into gravitationally bound structures.
Smaller systems would form first and then merge into larger agglomerations. The denser regions would take the form of a network of filaments, and the first star-forming systems—small protogalaxies—would coalesce at the nodes of this network.
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In a similar way, the protogalaxies would then merge to form galaxies, and the galaxies would congregate into galaxy clusters. The process is ongoing: although galaxy formation is now mostly complete, galaxies are still assembling into clusters, which are in turn aggregating into a vast filamentary network that stretches across the universe. According to the cosmological models, the first small systems capable of forming stars should have appeared between million and million years after the big bang.
These protogalaxies would have been , to one million times more massive than the sun and would have measured about 30 to light-years across. These properties are similar to those of the molecular gas clouds in which stars are currently forming in the Milky Way , but the first protogalaxies would have differed in some fundamental ways.
But in the protogalaxies, the ordinary matter would still have been mixed with the dark matter. The second important difference is that the protogalaxies would have contained no significant amounts of any elements besides hydrogen and helium. The big bang produced hydrogen and helium, but most of the heavier elements are created only by the thermonuclear fusion reactions in stars, so they would not have been present before the first stars had formed.
The young metal-rich stars in the Milky Way are called Population I stars, and the old metal-poor stars are called Population II stars; following this terminology, the stars with no metals at all—the very first generation—are sometimes called Population III stars. In the absence of metals, the physics of the first star-forming systems would have been much simpler than that of present-day molecular gas clouds. Furthermore, the cosmological models can provide, in principle, a complete description of the initial conditions that preceded the first generation of stars. In contrast, the stars that arise from molecular gas clouds are born in complex environments that have been altered by the effects of previous star formation.
Therefore, scientists may find it easier to model the formation of the first stars than to model how stars form at present. In any case, the problem is an appealing one for theoretical study, and several research groups have used computer simulations to portray the formation of the earliest stars. Norman now at Pennsylvania State University, the Massachusetts Institute of Technology and the University of California at San Diego, respectively has made the most realistic simulations.
In collaboration with Paolo Coppi of Yale University, we have done simulations based on simpler assumptions but intended to explore a wider range of possibilities.
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Toru Tsuribe, now at Osaka University in Japan, has made similar calculations using more powerful computers. Fumitaka Nakamura and Masayuki Umemura now at Niigata and Tsukuba universities in Japan, respectively have worked with a more idealized simulation, but it has still yielded instructive results.
Although these studies differ in various details, they have all produced similar descriptions of how the earliest stars might have been born.