Occasionally, I come across a religious person who suggests that I, as an atheist, must believe that the universe and everything within it came into existence from nothing at all, and that the belief that everything came from nothing on its own accord requires greater faith than does belief in an eternal creator that caused everything to come into existence. The entire basis of this argument hinges on the notion that there existed a time when matter and energy, and indeed the universe itself, did not exist. Not only is this unprovable, but is highly unlikely given what we know of the existence of matter, energy, and the universe.
The law of conservation of matter and energy states simply that matter and energy cannot be created nor destroyed, only changed from one state to another. It also states that the total quantity of matter and energy available in the universe is a fixed amount and never any more or less. Consider the burning of a match: The wood fibers of a match are converted into heat and light energy, as well as carbon; the heat and light energy that was the source of the wood is essentially released, as the wood that the match was made from occurred as a conversion into matter of light and heat energy from the sun, as well as carbon from the environment. Of course, there's more to these events than that, but for the sakes of describing this law in a way that is easily understood, I chose to simplify the process.
What we understand of the universe is that it is composed of matter and energy that is continually changing from one state to another of stuff that cannot be created nor destroyed, going through natural cycles governed by physical laws that we still have a lot to learn about. I don't know about you, but I consider that which cannot be created nor destroyed to exist infinitely. That which exists infinitely, by a believer's own definition of the god they believe, requires no creator.
At this point, the believer scrambles from their cherished beliefs back to the realm of science and asks, "But what of the big bang?" It's at this point that the believer requires yet another lesson in science; that lesson being that the big bang theory is a theory which explains how the matter and energy in the known universe has come to its current arrangement, and does not state where that matter and energy came from. It assumes that all matter and energy in the universe existed as a singularity prior to the event, and does not suggest a violation of the law of conservation of matter and energy.
The big bang theory will most likely continue to go through revisions, and may even be superseded by an entirely new theory as our knowledge grows. However, the law of conservation of matter and energy is a safe bet, because it is something we can test and observe today. Therefore, given our current understanding, I propose that it takes more faith to believe that energy, matter, and the universe needed to be created than it does to believe it had always existed without needing a creator.