Define The Theory of Big Bang.?
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The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.
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In physical cosmology, the Big Bang is the scientific theory that the universe emerged from an enormously dense and hot state about 13.7 billion years ago. The Big Bang theory is based on the observed Hubble's law redshift of distant galaxies that when taken together with the cosmological principle indicate that space is expanding according to the Friedmann-Lemaître model of general relativity. Extrapolated into the past, these observations show that the universe has expanded from a state in which all the matter and energy in the universe was at an immense temperature and density. Physicists do not widely agree on what happened before this, although general relativity predicts a gravitational singularity (for reporting on some of the more notable speculation on this issue, see cosmogony).\n\nThe term Big Bang is used both in a narrow sense to refer to a point in time when the observed expansion of the universe (Hubble's law) began — calculated to be 13.7 billion (1.37 × 1010) years ago (±2%) — and in a more general sense to refer to the prevailing cosmological paradigm explaining the origin and expansion of the universe, as well as the composition of primordial matter through nucleosynthesis as predicted by the Alpher-Bethe-Gamow theory [1].\n\nOne consequence of the Big Bang is that the conditions of today's universe are different from the conditions in the past or in the future. From this model, George Gamow in 1948 was able to predict, at least qualitatively, the existence of cosmic microwave background radiation (CMB) [2]. The CMB was discovered in the 1960s and further validated the Big Bang theory over its chief rival, the steady state theory.\n\nThe Big Bang theory developed from observations and theoretical considerations. Observationally, it was determined that most spiral nebulae were receding from Earth, but those who made the observation weren't aware of the cosmological implications, nor that the supposed nebulae were actually galaxies outside our own Milky Way[3]. In 1927, the Belgian Catholic priest Georges Lemaître independently derived the Friedmann-Lemaître-Robertson-Walker equations from Albert Einstein's equations of general relativity and proposed, on the basis of the recession of spiral nebulae, that the universe began with the "explosion" of a "primeval atom"—what was later called the Big Bang[4].\n\nIn 1929, Edwin Hubble provided an observational basis for Lemaître's theory. He discovered that, relative to the Earth, the galaxies are receding in every direction at speeds directly proportional to their distance from the Earth. This fact is now known as Hubble's law [5]. Given the cosmological principle whereby the universe, when viewed on sufficiently large distance scales, has no preferred directions or preferred places, Hubble's law suggested that the universe was expanding contradicting the infinite and unchanging static universe scenario developed by Einstein.\n\nThis idea allowed for two opposing possibilities. One was Lemaître's Big Bang theory, advocated and developed by George Gamow. The other possibility was Fred Hoyle's steady state model in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time[6]. It was actually Hoyle who coined the name of Lemaître's theory, referring to it sarcastically as "this big bang idea" during a program broadcast on March 28, 1949 by the BBC Third Programme. Hoyle repeated the term in further broadcasts in early 1950, as part of a series of five lectures entitled The Nature of Things. The text of each lecture was published in The Listener a week after the broadcast, the first time that the term "big bang" appeared in print. [7]
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The big bang; the theory that the solar system was created by a large explosion of dust and gas. The dust and gas was pulled together over many years by gravity and formed the planets.
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The discovery of  the universe expansion(doppler red shifted spectrum lines) was the source of the Big Bang theory (i think)\n\nBTW: this is a SCIENCE thread, all you Jesus Freak back off!\nthe theory of the Big Bang is compatible with the concept of a god.\nwhat was there before the big bang ..let there be light....BANG.
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The scientific theory is that the Universe started as a fluctuation of the vacuum. Such vacuum fluctuations make appear a small amount of energy, for a small time. This phenomenon is responsible for the existence of forces, that hold the Universe and matter together.\n\nNormally the bigger the energy fluctuation, the smaller the time it is in existence.\n\nNot so the Big Bang. That was a HUGE fluctuation. So big that a lot of energy came to appearance in the form of mass, elementary particles. These particles started expanding, before the vacuum could reclaim the energy.\n\nAnd it is still expanding today. 14 billion years later.
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The Big Bang theory does have a good amount of evidence behind it. So we’ll take a look at the three biggies.\n\na) Cosmological Redshift: We can use spectroscopy to determine the rate at which galaxies are moving away from us. Additionally, since it takes light time to travel, the further away we look, the further back in time we are looking.\n\nWhat we find, is that all galaxies in the universe are moving away from us. The further they are, the faster they’re moving away. So if we play the whole thing in reverse, all the galaxies will come back together at a single point in time. This point in time is what we call the Big Bang.\n\nb) The Cosmic Microwave Background (CMB): Figuring that if you played everything back in time like this that all that energy would be crammed into a smaller space, that means the temperature would go up. And also since galaxies couldn’t have formed yet, we’d expect a gaseous sort of universe early on. As I discussed earlier, hot dense gasses emit photons at a peak wavelength corresponding to their temperature. Unfortunately, since things were so dense, photons couldn’t get very far.\n\nHowever, with the available information, astronomers were able to determine at what density and time, photons would finally be able to get far enough that we could observe them. This is called the “surface of last scattering” and has a very specific temperature. So we should be able to look for photons with energy (wavelength) corresponding to that temperature.\n\nBut due to redshift, they will appear at a different wavelength. This radiation should appear from every direction. This was a prediction made by the Big Bang theory that was later confirmed by Penzias and Wilson who stumbled on it accidentally!\n\nNo other theory of the universe has ever been able to make such a profound prediction to the degree of accuracy the Big Bang did in this instance. Making such amazing predictions is one of the highlights of a good theory. None before or since have ever been able to pull off such a feat.\n\nBut the successes of the CMB prediction don’t stop there. Another important piece of the puzzle lies in that the CMB couldn’t be completely even. If it were, then galaxies couldn’t form since there would be no “seeds” with higher mass and thus a stronger gravitational pull to form around.\n\nThus, the Big Bang theory had to predict that the CMB would not be completely homogeneous. It should have some variations to it, and those variations would have to be of a specific size in order to get the universe we see today.\n\nEarly results for the Big Bang didn’t look too good for this prediction and threatened to sink the whole ship. However, the devices used were not actually sensitive enough to pick up these minute variations. But recently, with the Wilkinson Microwave Anisotropy Probe (WMAP), these perturbations have been discovered precisely as predicted.\n\nScore two strong predictions for the Big Bang. Zero for any others.\n\nc) Distribution of Elements: With the conceptual framework intact thanks to the first point, it was also possible to calculate how much of each element should be formed in the initial event. It should be obvious that, given a bunch of protons, electrons, and neutrons, hydrogen should be the easiest to form. Indeed, stick a proton and an electron in a room together and they’ll automatically hook up due to their magnetic attractions.\n\nAdditionally, with such high energies, it would be possible to fuse some of this hydrogen into helium and even a little bit of heavier elements. Since astronomers had a good handle on the energies, it was possible to calculate how much of each there should be. If that number didn’t match up with observations, the Big Bang theory would be shot.\n\nFortunately, the predictions do match up pretty closely. I stated a value earlier of 80% hydrogen, 20% helium, and neglected the rest since it would be statistically insignificant. In the universe today,
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That is what science is trying to figure out.\n\nOne theory is that all matter and energy exploded in a Big Bang from a point particle or singularity.\n\nHowever, current technology prevents us from going back to time zero or the origin of the universe. At a point in time (just s tiny fraction of a second before the Big Bang) all laws of physics break down and yields meaningless answers.\n\nThere are several other theories as well. Another thought (that has been largely abandoned) is that the universe was continually expanding, in cycles, from a Big Bang to a Big Crunch.\n\nThere is another theory that the universe is constantly folding over on itself, continuously annihilating and creating itself.\n\nAnd in quantum physics, the is a concept which even suggest that reality, all of human experience, may be nothing short of a personal subjective concept without substance at all.\n\nQuantum physics is a mysterious world that suggests that many of our concepts are too limited and that there are worlds we can't even imagine (parallel universes, many worlds, branes, dimensions, steady state, etc.)\n\nOur knowledge and understanding of the universe is akin to the knowledge and understanding that an ant has of the world economy.
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I hope that most of the previous answerers were joking. The Big-Bang theory is the best theory of the origin of the Universe that we have so far. It was formulated based on the expansion of the Universe, that we know because everywhere we look on the sky, on average, the galaxies are getting away from us, not because the "red radiation" but because of redshift, the light emitted by the galaxies is redshifted, which means that they are getting away form us (check at the Dopler effect to understand this), and the farther away the faster they are getting away, check: Hubble law. This means that the expansion is accelerated, then is natural to thing that going to the past the galaxies were closer together and there was a moment when they actually were in a single point of infinite density and energy, a singularity. The big bang states then that something caused this singularity to explode producing the accelerated Universe we see today with all the things inside. Now, Science can tell more or less how the Universe has evolved since a brief moment (less than one second) after big-bang until know, but it can not tell what happened at the "zero time" because general relativity breaks down in the singularity. Nobody know what triggered this big explosion.
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Steady state theory has no answers for two major astronomical observations.\n\n1. Cosmic microwave background radiation (CMB)\n2. Hubble expansion.\n\nAs a result the theory has been discarded by the majority of professional astronomers.  The Big Bang theory does provide answers for those two bits of observation.  It may not be perfect but it is the best we got.  That's what theories are...the best explanation until something better comes along.
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this is actually a common misconception about the big bang.  the big bang theory says that spacetime itself originated in that event.  the big bang theory is supported by evidence very well.  no other theory or hypothesis is.\n\nread these:\nhttp://www.sciam.com/print_version.cfm?articleID=0009F0CA-C523-1213-852383414B7F0147\nhttp://map.gsfc.nasa.gov/m_uni.html
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the big bang is just another theory that scientists came up with. it's not proven, just like many other theories are not proven, but it is the most supported by scientists because it says that a molecule (atom) the size of alittle dot exploded 10-17 billion years ago, and kept expanding. this is mostly supported because today, we still see other objects in space red shifted on doppler system, which means that objects are moving away from us, and expanding the border of the universe.
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No one "discoverd" the Big Bang - it is a theory, not a fact - just like evolution.\n\nIf you believe in God and believe that God created the universe you can still believe in the Big Bang theory - it may be the method in which He created the universe. \n\nBut to believe in the Big Bang theory without believing in God is a Big Mistake. "Nothing" cannot begat something, whether it is the universe, or life. To believe that out of nothing all of a sudden something came into existence defies good science. Even science iteself had to start somwhere - it could not come out of nothing!\n\nLife did not begin in some premordial ooze as the result of a reaction between certain chemicals catalyzed by sunlight. That theory is sheer stupidity and requires more faith to believe than it does to believe in God.
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You could start with the Wikipedia entry for the Big Bang.
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One of the more popular theories is the "bottom-up" model.  Basically what the theory states is that once the universe cooled down enough it was lumpy.  The initial condition of, and right after, the big bang created slighty denser regions than others in space.\n\nThese over dense regions began to collect matter and that matter formed stars.  As more of these groups formed the began to merge together.  It is through the merger of these objects that we form galaxies.\n\nA competing theory has a "top-down" model.  It hold that the larger objects formed first and then fragmented into the smaller ones.  Righ now physics and the thermal evolution of the universe favor the "bottom-up" model.
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Big Bang theory \n\nIn astronomy, a theory according to which the universe began billions of years ago in a single event, similar to an explosion. There is evidence for the Big Bang theory in the observed red shift of distant galaxies, which indicates that they are moving away from the Earth, in the existence of cosmic microwave background, and from other data. The Big Bang theory of the origin of the universe is accepted by most astronomers today. \n\n\nScientists have recently found that the expansion of the universe is actually speeding up. This effect is attributed to the presence of dark energy.
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Hi bornsmartgal\n\nOther possible explanations for the observations which support big bang theory are numerous.  They tend to focus on trying to explain the redshift observations, and they include tired light, strange compton scattering, large hydrogen clouds, etc.  The thing is that no single explanation (other than big bang theory) explains *all* the observations.  For example very few of them explain the time dilation of distant supernovas.  There's also the Tolman surface brightness test which distinguishes between big bang models and other models by a factor of z^4 (this is a nice test because it gives a very large discrepancy).  Only an expanding universe passes the test.\n\n\nHope this helps!\nThe Chicken
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The Big Bang \n\nAbout fifty years ago, American astronomers studying the galactic star clusters, stumbled on evidence that the entire Universe is blowing up before our eyes. According to their observations, all the galaxies in the Universe are moving away from us and from one another at very high speeds, and the most distant are receding at the extraordinary speed of hundreds of millions of miles an hour.\n\nFirst there was nothing and it blew up and then there was everything and scientists have calculated that it all happened in 1043 of a second. [The] echo of that explosion can still be heard bouncing around in space. Scientists claim that in the big bang all of the fundamental particles necessary for life were formed. All of the complexity we see around us is the result of this massive explosion.\n\n"The new finding hit the scientific world like a thunderclap." It meant that the idea of an ultimate beginning was no longer merely religious dogma. Science itself now indicated that the universe burst into existence at a particular time in the remote past.\n\nIn 1992 measurements by the Cosmic Background Explorer (COBE) and by the Hubble Space Telescope seemed to confirm beyond any reasonable doubt that the Big Bang cosmology is indeed correct. George Smoot, Professor at the University of California at Berkeley and Principle Investigator of the COBE team which made the discovery, said regarding these new observations, "What we have found is evidence for the birth of the universe . . . It's like looking at God."\n\nWorking backwards, the evidence implies that there was a time when the universe was infinitesimally small. The evidence from general relativity also indicates that it was not merely a case of the matter in the universe being concentrated at a particular location, but that space itself was this tiny. At a sudden instant in time all of the energy and mass in the universe was located at this infinitesimally small point and exploded. The currently observed outbound motion of the galaxies from each other is a continuing effect of that explosion.\n\n"The scientific community is prepared to consider the idea that God created the universe is a more respectable hypothesis today than at any time in the last 100 years," Frederic B. Burnham, science historian, declared.\n\nHowever, some die-hard secularists propose that the universe goes through endless cycles of expansions and collapses. Hence, eternity becomes nothing more than an eternal succession of big bangs followed by big crunches followed by big bangs followed by big crunches over and over again and again forever.\n\nBut this violates the second law of thermodynamics, the law of decay, that implies that the universe is in a process of gradual disintegration - running down, like a wound-up clock. And if it is running down, then there must have been a time when it was wound up. Once the big bang takes place and the universe begins its expansion, entropy starts to increase. From this point on it will never be able to go back to its original state.\n\nWhat's more, the first law of thermodynamics (the conservation of matter) implies that matter cannot just pop into existence or create itself. And therefore, if the universe had a beginning, then something external to the universe must have caused it to come into existence - something, or Someone, transcendent to the natural world.\n\nThe facts clearly indicate that the universe is not eternal, and it cannot originate itself The implication is that the universe began at a definite moment in time, in a flash of light and energy. Science has begun to sound eerily like Genesis 1: "And God said, 'Let there be light"' (1:3).\n\nThe evidence requires that we believe God formed the universe at His command, pointing to the importance of taking God at His word literally - from the beginning both of time and the Bible. Second, there is such a striking parallel between the Hebrews 1