Most common misconception:
"...the big bang started as a point which led to an explosion of space and matter.."
There are many misconceptions associated with a statement of this nature. One, The Big Bang Model that is currently used by most cosmologists, is one that doesn't describe the universe expanding 'from a point' as that would imply a center of the universe. Second, nowhere will you find a legitimate model of the Big Bang Theory which depicts a 'chemical explosion' of some kind which Creationist's seem to believe is the case.
There are plenty of
older models which depicted a 'point', an 'explosion', etc. which relied on specific conditions which have since then been proven false. In mainstream cosmology, you will get laughed at for trying to push the idea of a 'point' and an 'explosion'.
It is not that 'all things are expanding from a point,' rather, all things are moving away from each other as space-time stretches.
"The big bang is the expansion or stretching of space. It is not that things are flying out from a point. Rather, all things are moving away from each other. It is like having an infinite rubber sheet with people sitting on it. Stretch the rubber sheet, and all the people move away from one another. Each thinks they are at the center of an explosion. It is an optical illusion - everybody moves away from everybody else and there is no center.
Run the story going back in time and the sheet was more and more unstretched and the people were closer together. When everybody is so close they are on top of one another, that is is the beginning of the big bang picture - the cosmic singularity. At that time, the universe has nearly infinite density and temperature. "
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http://wwwphy.princeton.edu/~steinh/
The Big Bang Theory is NOT about the origin of the universe -- it's primary focus is the development of the universe over time. We measure the Big Bang Theory through numerous different methods (expansion of the CMB, COBE measurements, Doppler-effect and frequency shift of light, etc.) and we can derive certain information based on observations.
The Big Bang Model does not imply that the universe was ever 'point-like' and that the origin of the universe was an explosion of matter into already existing space. It's not thought of as an 'explosion' or a 'point' anywhere, by cosmologists.
There are plenty of theorists out there that use the data collected from the Big Bang Model, to produce 'possible' explainations regarding our universes origin, however, no one claims these are fact. Also, there are many many explainations for our universe which lie at the heart of Quantum Mechanics (such as "inflationary" theory), which if you are familiar with, you would understand the truly strange nature of The Explicate Order, or physical reality, in comparison with the Implicate Order, or Quantum Reality.
Evidence for the Big BangUniverse: Cosmology 101