I don't believe in the Big Bang, not solely because I am religious person; but because the Big Bang theory itself makes no sense. Before time, an explosion occurred and expanded from nothing. First of all, nothing contains no energy, therefore, there would be no result which equals = 0. Its impossible for a matter to happen if there is nothing caused it. Currently, there is no evidence to support the results of the Big Bang theory, so the theory is moot.
You're referring to the law of conservation of energy. Thanks to Albert Einstein's work on the equivalence of energy and matter, this law now incorporates the old conservation of matter. If the energy is not converted to matter, it is converted to another form of energy. That new form is monotonically less "useful" than the old one. That's the essence of entropy, a measure of "disorder". The field that studies this is thermodynamics. When you ask about energy created from 'nothing', a scientist may talk about a quantum singularity. When you ask about matter being created from energy, a scientist may talk about a photon 'decaying' into an electron and a positron. They may also talk about the zero-point field. They may hypothesize the formation of the universe from the intersection of M-branes. They may acknowledge that big bang cosmology is based upon such extreme extrapolation that they can't say this is what happened. All they can say is, we have worked out all the equations and done the math for all the physical laws we know about, and we can't prove it could not have happened this way. Sometimes the even hypothesize new physical laws. They may acknowledge that extrapolation isn't even valid to the point of singularity, and definitely not valid beyond that point. They should say they can't prove the universe was 'created' by some intelligent entity. But they should also say they can't disprove it, either. See Dr. Alan Guth's later chapters in his book, The Inflationary Universe. That's where he talks about the possibility that the total energy of the universe is zero, due to the reasoning that gravitational potential energy is negative. That's how the idea of "the universe out of nothing" is plausible. Perhaps the creation event was the sudden removal by God of a huge amount of entropy. See thermodynamics.
That's not a contradiction, that's a paradox.
As for your question. The Big Bang answers it quite well.
Rapid inflation nano-seconds after the happening of the big bang caused massive expansion which created the universe (which has been expanding for billions of years itself). The energy itself was "created" and or exerted from the big bang itself because the core of the big bang was originally extremely condensed and very hot; heat produces energy in the form of heat energy which is transferred in a process called "enthalpy" (heat exchange). This is further proven by the post above by Trap Lord. Stars themselves are radiated with heat energy and are extremely hot. Once the star dies out, it collapses on the gravity that held it up and the gravitational force (measured in g or better known as "gravitons") is EXTREME. Like on Earth, it is roughly 1 g, which is relative to our normal weight we have on Earth but we'd be lighter/heavier on a planet that has higher or lower gravitational pull; the force of gravity at the center of a black hole (which is just the star collapsing) is something like 40 Million gravitons, which is immense beyond comprehension. Following the Big Bang Theory, that's where energy came from. There's also evidence from the spontaneous appearance and disappearance of random particles observed in a laboratory over time.
Oh Dimitri... Read these responses.
Read them and none of them explains previous events before the Big Bang. But even then, I wouldn't bother reading them, since its common sense you don't get results from 0. Basic and simple.
Everything we have... what we are and how we are; it's all essentially, the result of chance.
The Big Bang would have been a transformation, as is everything that comes from nothing.