Is there a natural process by which hydrogen is generated from heavier elements in the cosmos?

Question

we know that stars fuse hydrogen into helium starting at 3 MK; 13 MK in the Sun's core; carbon fusion starts at above 500 million K, and silicon fusion starts at over 2700 million K for comparison; we know fusion stops at iron, because a star has to use more energy to fuse that than it gets back; so heavier elements are created mostly in a supernova (but also possible in small quantities by special processes like neutron capture); finally sun-like stars end up as white dwarfs, bigger stars as neutron stars, quark stars, black holes; and black holes ultimately convert themselves into radiation, in the far distant future when the stable black hole mass limit goes up high enough that even the most massive black holes evaporate;

http://en.wikipedia.org/wiki/Vacuum_Diagrams

so my question is, will it be like Stephen Baxter said, that in the future only radiation will be left in the universe? Specifically, is there a natural process out there by which hydrogen is spewed into the cosmos, converted back from heavier elements, to regenerate the fuel for stars so that they may shine in the far distant future as well?

Of course we don't need to worry about this for the time being. This is only considering our concern with what will be 10^70 years from now.

Answer 1

There are a couple of relevant questions one would want to ask:

1) Do protons decay, and if so, what do they decay into? The answer appears to be no, or at least the theoretical lifetime of the proton must increase as a results of these experiments. If they do, eventually the universe could end up in a state of radiation (and dark energy, and dark matter, unless they also decay).

2) Is Hydrogen a bi-product of any natural decay process? Below is a table of all known nuclides.

As you can see, the majority of the elements (not necessarily by number or mass in the universe) do decay through some type of process. There exists a 'stable' ridge (called the island of stability, surrounded by the sea of instability) of elements which will happily exist forever.

The question is, which modes of decay produce protons (Hydrogen nuclei)? Well, there is proton decay (not the proton itself decaying), which is colored in red, though I have to admit that I don't know exactly what this refers to. Fission bi-products are gamma rays (high energy photons), neutrons, and daughter nuclei (see Decay chain). Though, I should mention that free neutrons produced from this type of radioactive decay are not long lived, decaying into a proton and an electron (this process takes on average approximately 11 minutes). By this logic, also isotopes which decay by emitting neutrons, colored purple, would also eventually produce protons. $\beta^{-}$ and $\beta^{+}$ refer to the beta decay process, where the minus sign refers to the emission of an electron and the plus sign refers to the emission of a positron (the anti-particle of the electron). $\alpha$ decay is the emission of a Helium nucleus, which is stable.

Now, given that there are ways for heavy elements to naturally produce protons, the question I would ask is what is the rate of these processes in the universe compared to fusion processes occurring at the centers of stars. I'm not sure that I could give you an answer to this question (or even point you to the appropriate material), but in principle these rates are known. I'd imagine that it'd be quite a lot of bookkeeping to get it correct.

Answer 2

It is not possible to split a larger nucleus into hydrogen nuclei without expending a greater amount of energy that you receive back. This is because Hydrogen has (by far) the lowest nuclear binding energy per nucleon (protium has zero nuclear binding energy, though deuterium and tritium do have some). Therefore, such a process would decrease the entropy of the universe - a violation of the laws of thermodynamics.

I could not speak for if these laws would still hold true were there a "big crunch" (though current observations support an expanding universe).

There is a scenario called heat death, where the universe simply has no energy left to do anything - that is, everything is completely uniform. There would be no gradients or anisotropies in the distribution of energy or matter.

Answer 3

It seems that primordial black holes produce anti protons, and it is implied in the linked article that they are capable of producing all kinds of other particles. So maybe even protons.

Also, I guess that during natural fission or nucleues collision reactions, there may be fragments being produced that are also single protons.

Cosmic rays seem to consist primarily of protons. The question is, whether these protons were produced in the big bang, or if they stem from other sources. The article states that lots of cosmic rays stem from supernovae. However, this does not answer the question if the protons were produced in the supernova from heavier elements.

Since I am not an astrophysicist, I am gladly waiting for comments or other answers!

Edit: I read about another mechanism on how to create electrons and protons: Two-Photon interaction. I cite the Wikipedia article:

The law of conservation of energy sets a minimum photon energy required for creation of a pair of fermions: this threshold energy must be greater than the total rest energy of the fermions created. To create an electron-positron pair the total energy of the photons must be at least 2mec2 = 2 × 0.511 MeV = 1.022 MeV (me is the mass of one electron and c is the speed of light in vacuum), an energy value that corresponds to soft gamma ray photons. The creation of a much more massive pair, like a proton and antiproton, requires photons with energy of more than 1.88 GeV (hard gamma ray photons).

First calculations of rate of e+–e− pair production in photon-photon collision was done by Lev Landau in 1934.1 It was predicted that the process of e+–e− pair creation (via collisions of photons) dominates in collision of ultra-relativistic charged particles—because those photons are radiated in narrow cones along the direction of motion of original particle greatly increasing photon flux.

In high-energy particle colliders, matter creation events have yielded a wide variety of exotic heavy particles precipitating out of colliding photon jets (see two-photon physics). Currently, two-photon physics studies creation of various fermion pairs both theoretically and experimentally (using particle accelerators, air showers, radioactive isotopes, etc.).

So, in small amounts electron-positron pairs and proton anti-proton pairs should be created by soft and hard gamma radiation respectively (or other Fermion particles). The problem here again is that this event will happen only very rarely, not significantly producing new matter. The article goes on to say that this was the method in which matter was created during the Big Bang. But only one in $10^{10}$ Fermions would have survived to form the current matter in the universe.

All in all these processes will probably be not enough to form new stars.