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According to Inflation for Beginners,

... quantum physics allows the entire Universe to appear, in this supercompact form, out of nothing at all, as a cosmic free lunch. The idea that the Universe may have appeared out of nothing at all, and contains zero energy overall, was developed by Edward Tryon, of the City University in New York, who suggested in the 1970s, that it might have appeared out of nothing as a so-called vacuum fluctuation, allowed by quantum theory.

Based on my layman's understanding, quantum mechanics allows for energy to spontaneously appear, provided it disappears later. But matter, with its positive energy, is offset by the negative energy gravitational field it creates -- netting zero energy that therefore doesn't have to disappear.

Does this mean that matter/antimatter (say, an electron and a positron) may be created and annihilate each other, or maybe some amount of matter on its own (with gravity and thus a net energy of zero) could appear and exist forever? In the latter case, how does a small amount of matter compare with this supercompact form that leads to inflation? Presumably there are isolated hunks of matter with corresponding gravity out there that quantum mechanics created but that didn't expand into their own universes?

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  • $\begingroup$ Quantum mechanics, in absence of other circumstances, does not allow for matter to appear. It only gives rise to virtual particles. In order to generate real particles we need real energy. That energy has to come from somewhere, even with QM being at work. One can, pro forma, account for the positive energy of matter with a negative energy term assigned to the background to make a zero balance, but that's just an accounting trick to make the current cosmological model work. It is by no means clear where this energy term comes from or what physical meaning it has. $\endgroup$ – CuriousOne Dec 14 '14 at 7:18
  • $\begingroup$ So I'm totally off in my thinking that the matter that spawned our universe in the big bang came from this quantum mechanical 'free lunch'? $\endgroup$ – alexdelarge Dec 14 '14 at 7:27
  • $\begingroup$ Inflation is an infinite class of classical hypotheses that take care of a few problems in the current cosmological model. There are serious attempts to narrow these models down by linking them to quantum field theory and measured (or indirectly deduced) properties of the vacuum, but all of that is very early and none of it is, to my best knowledge, sufficiently covered by data from accelerators or cosmic particle observations. If we can find dark matter particles and gravitational waves, we will probably know more. I would suggest to wait for 20 years before buying into too much of the hype. $\endgroup$ – CuriousOne Dec 14 '14 at 7:38
  • $\begingroup$ Is there a generally accepted theory, then, on where the matter for our universe came from? Or is it wide-open across all of cosmology (not just quantum physics)? $\endgroup$ – alexdelarge Dec 14 '14 at 7:47
  • $\begingroup$ Quantum mechanics and general relativity are widely accepted theories, but on their own they are not sufficient to build a unique cosmological model, even together they leave too many possibilities open, which is probably a consequence of the fact that they can not even be merged into a single self-consistent theory, at the moment. We are missing one new theory (usually assumed to be the theory of quantum gravity) that can bridge the gap and make unique predictions about cosmology. This leaves us with collecting poorly fitting puzzle pieces, which we then mold into models, not theories. $\endgroup$ – CuriousOne Dec 14 '14 at 7:53
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Does this mean that matter/antimatter (say, an electron and a positron) may be created and annihilate each other,

This is called vacuum fluctuations as stated by Quantum Field Theory. In this case energy has to be supplied so that the electron positron pair out of the vacuum would materialize. This does happen at laboratory energies in experiments with strong laser beams . It is also supposed to happen with the energy supplied by the gravitational field of black holes, one lepton falling in the black hole the other leaving: Hawking radiation

or maybe some amount of matter on its own (with gravity and thus a net energy of zero) could appear and exist forever? In the latter case, how does a small amount of matter compare with this supercompact form that leads to inflation? Presumably there are isolated hunks of matter with corresponding gravity out there that quantum mechanics created but that didn't expand into their own universes?

You must not have read the article you link to the end:

The idea of chaotic inflation led to what is (so far) the ultimate development of the inflationary scenario. The great unanswered question in standard Big Bang cosmology is what came "before" the singularity. It is often said that the question is meaningless, since time itself began at the singularity. But chaotic inflation suggests that our Universe grew out of a quantum fluctuation in some pre-existing region of spacetime, and that exactly equivalent processes can create regions of inflation within our own Universe. In effect, new universes bud off from our Universe, and our Universe may itself have budded off from another universe, in a process which had no beginning and will have no end. A variation on this theme suggests that the "budding" process takes place through black holes, and that every time a black hole collapses into a singularity it "bounces" out into another set of spacetime dimensions, creating a new inflationary universe -- this is called the baby universe scenario.

So in the active research front of cosmology model spontaneous gravitational creations are being proposed.

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  • $\begingroup$ I would disagree about your last sentence. There is no "research front" of spontaneous gravitation creation models. We are nowhere close to experimentally observing the effects of gravity even at 1MeV, the minimum energy it would take to create an electron-positron pair. I have yet to see a single experimental proposal that dares to suggest a method to get us there, lest there are macroscopic hidden dimensions, which I think not even Nima Arkani-Hamed is betting on, any more. I would be honestly disappointed, if he did, I think he is way too smart and level headed for that. $\endgroup$ – CuriousOne Dec 14 '14 at 8:01
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    $\begingroup$ @CuriousOne Did you read the quote? It is not about electron positron pairs but of bubble universes that there are models proposed, of course theoretical ones. $\endgroup$ – anna v Dec 14 '14 at 8:05
  • $\begingroup$ All physics is experimental... pretty much everything that you are proposing, while necessary theoretical grunt work, is theoretical modeling without any foundation in experimental data. As an experimentalist whose field is asking for the next $10 billion (or so) for an accelerator that will barely get us more than a precision characterization of the Higgs, I find it a poor strategy to pretend to the people who are paying for our research instruments that we can do more than what we actually can. $\endgroup$ – CuriousOne Dec 14 '14 at 8:10
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    $\begingroup$ @CuriousOne I do not know if you are characterizing yourself as an experimentalist, but I am a retired experimental particle physicists. I am not making any proposals, I am answering a question by a newbie on what is being discussed in cosmology, and a lot of it is theoretical speculations. $\endgroup$ – anna v Dec 14 '14 at 9:43
  • $\begingroup$ I am simply saying that we shouldn't portray speculative theoretical models as scientific theory. Our theorists are decades ahead of our experimental capability. Inflation is a hypothesis, nothing more. We do not know where the energy came from that has created matter. We can attempt to model it on a phenomenological level, but that's about it. $\endgroup$ – CuriousOne Dec 14 '14 at 10:21

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