Nobody knows and anyone claiming to know is a liar (whether they claim that it's quantum fluctuations, brane theory, God, etc.).
All I can do is point you to different ideas about why it came into existence:
Quantum Fluctuations: http://www.colbertnation.com/the-colbert…
(this is an interview with Lawrence Krauss on the Colbert Report which, at one point, discusses how quantum fluctuations can explain the Big Bang).
Brane Theory: http://en.wikipedia.org/wiki/Membrane_%2…
"...On this conception, our universe may not be so special, since membrane collisions could cause big bangs all the time..."
Then I did recently hear about the oscillating universe on "Through the Wormhole". I find this difficult to believe since everything I had heard prior to this is that we have the worst possible type of universe (a saddle universe) meaning that it will expand forever and ever until eventually there is basically no particles, no energy, just flat space.
http://en.wikipedia.org/wiki/Cyclic_mode…
Edit:
If you are REALLY interested in this topic then I suggest watching this video where Lawrence Krauss goes through a pretty lengthy discussion on the current state of cosmology:
http://www.youtube.com/watch?v=7ImvlS8PL…
this is VERY LONG and I, myself, have NOT watched the whole thing. But realize that this is, obviously, an EXTREMELY complicated topic so expecting to get a satisfying answer in a 5 minute interview or here on Y!A is clearly NOT possible. I think Krauss does a VERY good job of presenting the material in an understandable way.
...of course, ultimately, the only TRUE understanding comes from understanding the underlying mathematics.
All I can do is point you to different ideas about why it came into existence:
Quantum Fluctuations: http://www.colbertnation.com/the-colbert…
(this is an interview with Lawrence Krauss on the Colbert Report which, at one point, discusses how quantum fluctuations can explain the Big Bang).
Brane Theory: http://en.wikipedia.org/wiki/Membrane_%2…
"...On this conception, our universe may not be so special, since membrane collisions could cause big bangs all the time..."
Then I did recently hear about the oscillating universe on "Through the Wormhole". I find this difficult to believe since everything I had heard prior to this is that we have the worst possible type of universe (a saddle universe) meaning that it will expand forever and ever until eventually there is basically no particles, no energy, just flat space.
http://en.wikipedia.org/wiki/Cyclic_mode…
Edit:
If you are REALLY interested in this topic then I suggest watching this video where Lawrence Krauss goes through a pretty lengthy discussion on the current state of cosmology:
http://www.youtube.com/watch?v=7ImvlS8PL…
this is VERY LONG and I, myself, have NOT watched the whole thing. But realize that this is, obviously, an EXTREMELY complicated topic so expecting to get a satisfying answer in a 5 minute interview or here on Y!A is clearly NOT possible. I think Krauss does a VERY good job of presenting the material in an understandable way.
...of course, ultimately, the only TRUE understanding comes from understanding the underlying mathematics.