A very interesting essay from Alex Vilenkin on whether the universe has a beginning and what this implies. If you want my opinion, “nothing” does not equal “physical system with zero energy”.
Alexander Vilenkin on The Beginning of the Universe
November 13, 2015 by lukebarnes
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Letters to Nature 
If you want my opinion, “nothing” does not equal “physical system with zero energy.
Indeed. Even if energy conservation is necessary in the creation of the universe, it is certainly not sufficient. Also, energy doesn’t seem to be conserved in cosmology anyway, so the whole stuff about the kinetic and potential energy balancing out is a red herring.
From the article:
The energy of the gravitational field is negative;17 it is conceivable that this negative energy could compensate for the positive energy of matter, making the total energy of the cosmos equal to zero. In fact, this is precisely what happens in a closed universe, in which the space closes on itself, like the surface of a sphere. It follows from the laws of general relativity that the total energy of such a universe is necessarily equal to zero.
Whether or not this argument is relevant, one often hears it, but usually with the example of the Einstein-de Sitter universe, not a spatially closed universe. What am I missing?
I strongly recommend reading Aron Wall on this. The links are here: https://letterstonature.wordpress.com/2014/08/05/did-the-universe-have-a-beginning-carroll-vs-craig-review-part-1/
Newtonian gravity: zero energy = Einstein-de Sitter
General relativity: zero energy = closed universe.
And that’s if it makes sense to talk about total energy at all in GR.
In the main article Alexander Vilenkin has written that the universe can pop out of nothing, and for this to happen no cause is needed. The quote is here:
“What causes the universe to pop out of nothing? No cause is needed.”
The theory that the universe can originate from nothing has been critiqued in the following two links:
1) https://sekharpal.wordpress.com/2015/10/23/a-fundamental-flaw-in-the-thesis-a-universe-from-nothing-part-I/
2) https://sekharpal.wordpress.com/2015/10/23/a-fundamental-flaw-in-the-thesis-a-universe-from-nothing-part-II/
Vilenkin says “We have no viable models of an eternal universe. The BGV theorem gives us reason to believe that such models simply cannot be constructed. “ What is he talking about? It seems to me that thinking you have tackled three models (Eternal Inflation, Ekpyortic and the Emergent Model) that it is impossible to construct a model of the universe that is eternal. But these are not the only models of early universe cosmology.
Most cosmologists agree we are unlikely to understand the big bang without a quantum theory of gravity. The leading candidates for this are string theory, loop quantum gravity and Horava-Lifshitz gravity. We see again and again in all these different approaches the same result; the hourglass universe i.e a period of contraction mirroring a period of expansion. This clearly violates the BGV theorem. Don’t believe me, ask Aron Wall, here are his words:
“Carroll’s secondary point that the assumptions of the theorem might not hold seems even more devastating. It says that there must be a beginning if the universe is always expanding. So maybe have it contract first, and then expand. That’s an easy way around the BGV theorem, and (as Carroll points out) there are a number of models like that. On this point I agree with Carroll that the BGV theorem is not by itself particularly strong evidence for a beginning.”
The reason as to why the universe cannot have originated from nothing is that the existence of nothing is self-contradictory. That means only something can exist and not nothing. For further details please see the link here:
https://sekharpal.wordpress.com/2015/11/30/is-there-a-god/
There’s a story, probably apocryphal, that captures the problem with “something from nothing” better than anything else I’ve ever seen… A philosophy professor gave an exam to a class of some 300 students. He arrived at the lecture hall carrying a desk chair, which he placed in front of the podium before giving the following instructions;
“This exam has only one question. Provide the best proof you can for the non-existence of this chair. The only rule is that you must write something–I won’t accept anything so trite as a blank piece of paper intended to make a statement of some kind. You have two hours beginning now…”
Everyone went to work furiously producing various and sundry arguments… except for one student near the back. He just sat there looking puzzled. The first hour passed, and still he sat like a deer in headlights. The professor noticed this with interest. After two hours he announced that time was up and called for papers to be turned in. At that very moment the student grabbed his pencil and quickly scribbled something before turning his in. The following Monday the professor stood before the class and announced, “The exams have been graded. One of you got an A+. Everyone else flunked. To the consternation of everyone, the professor proudly pointed out the student who had sat through the entire exam until the end. The task had been to provide a proof for the non-existence of the chair. And the student’s answer was…
“What chair?”
The moral of the story is clear. Once you treat nothing as though it was a noun–that is, something that can be discussed and even considered to have potency of some sort–by definition, it ceases to be nothing. In the 4th Century B.C. Parmenides said, “Nihil fit ex nihilo” (Out of nothing, nothing comes). Since then, no scientist or philosopher of any repute has ever disputed this… until the present age, when a handful of overly confident physicists decided that one could practice sound philosophy without any training in the subject, or for that matter even an understanding of the English language.
Some physicists love to say that their nothing is not the same as philosophers’ nothing and that the philosophers’ nothing is not the real nothing at all. But how do they come to know that their nothing was there before the beginning of the universe? Is there any evidence in support of it? Or, is it just a guesswork? This is because their nothing was created within the existing universe. How is it possible to know what probable shape and properties would this nothing have when there would be no universe?