Why?

They did not "come from" anywhere. If matter-energy can neither be created nor destroyed, what does that tell you?

There was never literally nothing. That would violate the first law of thermodynamics and overturn all of physics as we understand it. Somthing NEVER comes from literally nothing.

It is theists who insist upon a creation ex nihlo, from literally nothing. Are you now positing that God didn?t create the universe from nothing, that He didn?t simply say ?Let there be Light? and make it so, or that God Himself must have had a creator? No, I think not. The theist position IS one of creation ex nihlo, an atheist wouldn?t be caught dead believing something that foolish.
What baffles me, is that you?ve actually answered your own question here, and are simply too thick to realize it. You?ve simply projected your own problems onto the atheist, which is sadly typical.

Atheists are very well aware of the first law of thermodynamics, and it is this very concept that makes what theists propose, a creation ex nihlo, ridiculous.

Creation ex nihlo is a classic failure of human perception.

No painting comes to exist without a painter, no building is built without an architect, etc. Seems logical enough, but do these people create from literally nothing or is it more accurate to say they assemble existing materials? For no painter starts with nothing - they start with blank canvass and paint. No builder starts with nothing, they start with brick, mortar and blueprints. Something never comes from literally nothing.

Looking at things from the perspective of a First Cause argument, which theists are quite fond of, for something to exercise influence on the universe this causal agent must have already existed. Something nonexistent can't serve as a causal agent; thus causality must assume existence. Theists arguing for a creation of the universe ex nihlo, however have their logic backward - that existence assumes causation.

What the atheist can offer is a scientific explanation that meshes with conventional logic.

If we take matter-energy to be eternal, uncaused - as our best science seems to suggest (see the first law again), then existence is simply axiomatic. The universe just is, and the Big Bang becomes more or less a transitional event. The universe as we know it began with the Big Bang, but the matter-energy was always there, it must have been - to say otherwise turns all of physics as we understand it on its head.

We know that matter-energy is conserved - always, in every instance we have ever observed or theorized about. It is but a simple and very reasonable extrapolation to then say that matter-energy has always been, and it is empirically evident. There is no need to postulate a creator or a creation ex nihlo.

Not only does science point to existence being axiomatic, but simple logic does as well, because ?nothing? is an incoherent concept. ?Nothing? is not lack, not empty, not the void, not darkness, not the absence of anything, because the absence of anything would still be something. So again, the concept of creation from literally nothing makes no sense, because ?nothing? quite literally cannot exist.

In the end, the theist is reduced to demanding to know why there is something rather than nothing ? but this too begs the question, because it presumes that nothing or non-existence ought to be the natural state of things. This is like presuming the sky is supposed to be green and then citing the fact that it is blue as evidence for a Creator.

A scientist does not ask "why is there something rather than nothing", but rather "why SHOULDN'T there be something rather than nothing". There isn't anything about the universe that suggests it shouldn't be here and be exactly as we observe it be.

All of that aside, current quantum theories may in fact have room for our universe coming from what would be perceptually (not literally) nothing. Such theories included the universe arising from a quantum vacuum fluctuation that propagated itself, proposed by Ed Tyron in the early 1970s and a variation upon this proposed by Alex Vilenkin in the 80s that was dubbed quantum tunneling. There is also chaotic inflation theory and Smolin selection theory that posit similar natural "origins" to the universe.

Personally I think that the most lucid theory going at the moment was proposed by Stephen Hawking and James Hartle, and is often dubbed the ?no boundary proposal?. Their view provides a description of the universe in its entirety, viewed as a self-contained entity, with no reference to anything that might have come before it ? pretty much what I?ve laid out above. For Hawking, this description is timeless, for as one looks at earlier and earlier times, they find that the universe is not eternal, but has no creation event either. Instead, at times of the order of Planck time (10-43 seconds), our classical understanding of space-time is reduced to quantum soup. In Hawking's exact words:

?The boundary condition of the universe is that it has no boundary.' The universe would be completely self-contained and not affected by anything outside itself. It would neither be created nor destroyed. It would just BE.? - A Brief History of Time (New York: Bantam, 1988), p. 136.

I'm a skinhead, so i'm a dedicated bald person as well .

And yeah, that pretty much melted my brain, but it is a very good point.
Never really looked at it that way. Dark matter in the universe is emptiness, but it's not really empty because nothing is there, but nothing is something. O_O