if everything came from nothing, then what created the nothing? It's as old a question as the chicken and the egg.
Well, it seems common sense that there is no need for "nothing" to be created, but the idea that "nothing isn't really nothing"*--at least to cosmologists--is gaining a lot of traction, so that wouldn't really answer your concern. But even if the question is valid for chickens and eggs doesn't mean it's valid for the universe as a whole.
Why can't it come from nothing?: There is no logical or metaphysical reason that the Universe couldn't have come into existence, uncaused. It seems like it would need to, based on our experience of everyday things inside the universe, but that doesn't mean it's the case of the universe itself. The appearance of the universe could just be an uncaused event.
Who says it isn't eternal?: Physicists are not at all convinced that the universe isn't eternal. (In fact, the most simple/best QM models are of an eternal universe, and it's what most cosmologists favor.)
A common paper by a trio of physicists that is often misapplied by a particular apologist/debater concludes that the universe began to exist (and this is coupled with our common-sense notion that all things must begin to exist). But it doesn't really conclude that the universe began to exist, it basically assumes the universe began to exist. One of the two big assumptions of the paper is that the average expansion rate of the universe is greater than 0. If you make that assumption, than a beginning of the classical universe (the "Newtonian" universe we're all used to thinking about, not the Quantum Universe) must follow as a simple result of the math.
But that doesn't mean the universe as a whole began to exist at the Big Bang. The Big Bang marks the expansion of the classical universe. This gets confusing, talking about the Quantum Universe vs the Classical Universe, but we have to keep in mind that Newtonian physics has severe limitations--especially at the high temp/gravity/energy state of the early universe. The Big Bang Model cannot touch the moment of the Big Bang or before it (if there was a before); that's when you need to explore QM.
So, unfortunately, the answer to your question is "That's not a good question." It makes two big--and likely incorrect--assumptions that kind of push it toward a particular answer.
Many physicists are talking now about the 'God particle,' subatomic anomalies that cannot be explained with current scientific models. They operate outside the known laws of physics and perhaps are doorways to other dimensions.
"The God Particle" is the nickname given to the Higgs boson, a particle that gives all matter its mass. It was called that because it is extremely important to arriving at a complete model of reality, but it was very elusive. The Higgs boson was discovered in 2012.
I think these "subatomic anomalies" you're talking about are fluctuations in vacuum energy, but they are explained by scientific models (however, they are unpredictable.) They don't operate outside the laws of physics and don't have anything to do with extra dimensions.
They simply can't express that view publicly, as it would cause them to lose credibility in the scientific community.
I know this is kind of a throwaway line, but it's a bit silly and rather offensive. If you're a good scientist, you'll have credibility. There are tons of scientists who are unabashed theists and it hasn't hurt their careers at all. This seems to me to be nothing more than propaganda started by theists to explain why most scientists (especially in the hard sciences) aren't believers. Kenneth Miller comes to mind as a scientist (biologist at Brown University) who is very vocal about his belief, and yet is very highly regarded as a biologist.
* For a discussion of this, you can read A Universe From Nothing, by Lawrence Krauss, or look for his lectures by that name on YouTube
