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Nucleosynthesis and Hubble expansion

  1. Jan 13, 2007 #1
    How are Nucleosynthesis and Hubble expansion are considered as an evidence for the Big Bang Theory?
  2. jcsd
  3. Jan 13, 2007 #2


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    The Hubble expansion is predicted by the cosmological solution of the General Relativity field equation. Predicting backwards in time leads to a time when everything was compressed into a very small volume of large density and temperature. If QM effects are not allowed to kick in in this regime then at an even earlier time GR back-predicts a singularity where the present observable universe had zero volume and infinite density and pressure. Expansion from this supposed singularity is called the Big Bang.

    Hubble's observations of a red shift of galaxies that was proportional to their distance confirmed this prediction of GR.

    The baryonic universe appears to consist of "3/4" hydrogen "1/4" helium and 2% everything else.

    The age of the oldest stars in the galaxy is known at around 12Gyrs, also stellar luminosities are known.

    When the required total amount of hydrogen, helium and their products is calculated to produce this total luminosity over this projected age it is found that only the 2% everything else can be accounted for. (2% of the hydrogen turns into helium which then turns into the "2%" of all the other elements.)

    This means that before the stars existed the universe must have consisted of "3/4" hydrogen and "1/4" helium and only trace amounts of other elements.

    It was found that this is precisely what is predicted by the nucleosynthesis processes of the Big Bang. This primordial element relative abundance gave strong verification of the BB theory.

    A third verification of the BB was found in 1965 in the Cosmic Microwave background, that is the isotropic radiation predicted to come from the BB itself, and now much red-shifted so that it is found in the microwave region of the e-m spectrum.

    Last edited: Jan 14, 2007
  4. Jan 13, 2007 #3
    Thanks a lot Garth
  5. Jan 13, 2007 #4
    I have a question. Of the 3/4 hydrogen, is most at this time (before the stars) in the form of the hydrogen atom [P+e-] or deuterium atom [NP+e-) ? And concerning the nucleosynthesis of the neutron [N]--is it more in deuterium [NP+e-] atom at this time (before the stars) or helium-3 [2P+2e- plus N] or just free as unstable [N] ? Thanks for any information.

    {edit: And how does antimatter fit into the picture at this time (before stars). We know antimatter was present (such as in the form of pions which are quark+antiquark)--is it also 3/4 in antihydrogen and 1/4 in antihelium ?}
    Last edited by a moderator: Jan 13, 2007
  6. Jan 14, 2007 #5


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    The "3/4 hydrogen" is in the form of hydrogen!

    Deuterium is very fragile and although created in the BB was also mostly destroyed by it. The trace amount of deuterium in the universe that was left after the universe cooled down gives a handle on constraining the dynamical properties of the BB.

    At an earlier stage matter and antimatter annihiated each other. Because of a slight imbalance there was ~ 108 antiparticles to (108+1) particles.

    No antiparticles survived this process.

    This left 108 photons to every surviving particle. These photons subsequently formed the phtons of the CMB. The photon/particle ratio gives another handle constraining the properties of the BB.

  7. Jan 14, 2007 #6
    Garth, I find your response difficult to get my mind around. First, you say:

    which neatly summarises the observed element abundances. You then go on to say:

    This neatly accounts for the presence of the elements that are heavier than Helium by the nucleosynthesis of such elements in stars and sounds like a plausible argument, as does:



    Despite the reasonableness of what you claim above, it seems to me that it conceals the well-known conflict between the total mass of all matter, as deduced from the presently observed element abundances and well-established nuclear physics, and the total mass of matter, as manifested by its gravity, as in galaxy rotation curves, in virialised galaxy custers and perhaps in the very recent mapping of dark matter via the COSMOS survey (I don't know if this yields an estimate of dark matter density, but it should!).

    If there is no such conflict, why then is has there been such a fuss about dark matter consisting of unobserved exotica like axions, etc? It seems to me that you are neatly sweeping this difficulty under the carpet, perhaps for didactic reasons.
  8. Jan 14, 2007 #7
    :confused: If no antiparticles survived this process (eg., before the stars were formed), then how do you explain the existence of the various pions (with quark+antiquark) that now exist ? Are you saying pions (and other entities with antimatter that we know) were formed "from the stars", and not before ?

    Also, in the last response was no mention of nucleosynthesis of the "neutron". If as you say, the 3/4 hydrogen was mostly in the form of the hydrogen atom [P+e-], and only trace amounts of deuterium were present, (both of which are stable), then how do we explain the synthesis of the neutron--again, is it formed "from the stars" and not before.
  9. Jan 14, 2007 #8


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    oldman The density allowed by the model is determined by the requirement to produce the right amount of helium and correct traces of deuterium and other 'metals'.

    This is a function of the temperature and pressure or the universe and the time taken for the universe to cool off below nucleosynthesis temperatures. This in turn is determined by the scale factor rate of expansion of the universe, R(t).

    In the standard model R(t) ~ t1/2 and it works out that in order to get the correct primordial relative abundances there could have been no more than 4% of the critical density in the form of baryonic matter.

    Other considerations, as you mention galaxy rotation curves, cluster lensing and the WMAP data are consistent with another matter component of exotic non-baryonic Dark Matter - of 23% critical density.

    Cosmic acceleration and spatial flatness from the CMB anisotropies data require another component of Dark Energy to bring the total density up to the critical density or just above it.

    If you are happy to accept this DM and DE, which has not yet been discovered in the laboratory, then there is no conflict.

    Rade Neutrons and protons are formed and destroyed and reformed in the first three minutes of the BB. After that the number of neutrons is frozen out at around 12% neutron and 88% protons by number. Although other processes were present the majority of the neutrons formed helium nuclei producing about 23%-24% He-4 by mass.

  10. Jan 15, 2007 #9
    I don't see how anyone can be happy about such ad hoc solutions to such serious problems. The following quote is relevant:

    (A physical) “theory must not contradict empirical facts. However evident this demand may in the first place appear, its application turns out to be quite delicate. For it is often, perhaps even always, possible to adhere to a general theoretical foundation by securing the adaptation of the theory to the facts by means of additional artificial assumptions.” ...........

    Einstein, A.: 1949, in Albert Einstein: Philosopher Scientist, P. A. Schilpp (ed.), Harper & Row, New York. p. 23.
  11. Jan 15, 2007 #10


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    Well, laying my cards on table, actually I am not happy with these additional assumptions, that is, not until they are independently confirmed in 'the laboratory'.

    Perhaps the LHC, coming online this year, will provide the necessary confirmation?

    The cosmological community as a whole is convinced that the Higgs Boson/Inflaton necessary for Inflation, the non-baryonic DM particle and DE are all real and about to be discovered. The peaks of the CMB anisotropy power spectrum was a prediction of the standard model subsequently confirmed by observation, the need for DE comes both from the apparent spatial flatness of the universe and the distant SN Type Ia data, and exotic DM is concordant with both the WMAP data and large scale structure formation. SpaceTiger is the person to convince you of these.

    If you want to know what I really think read my Self Creation Cosmology thread. As an alternative gravitational theory SCC has a mountain to climb.

    Perhaps after April things will be clearer? Alternative theories being tested by Gravity Probe B

    Last edited: Jan 15, 2007
  12. Jan 15, 2007 #11
    Thanks for this informative post, Garth. I now understand better the current consensus and your own position.

    I have browsed through your "new" SCC post, and I'm aware of the predictions you've made. But I'm not competent to fully understand your thoroughly worked out alternative views, which are sadly unlikely on their own to overturn the consensus, human nature neing what it is.

    All I can do is wish you well and hope that some startling (for some) results do turn up in the near future --- or at least before my perch gives way!