 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Natural Science Forum / Physics / Research / July 2009Primordial Nucleon Synthesis and the next 17 ? minutes
I have just been boning up on primordial nucleosynthesis, and the following statement in Wiki (admittedly not always the most reliable source), struck me as incredible:- "there are about seven protons for every neutron at the beginning of nucleogenesis....... This fraction is in favour of protons initially primarily because because lower mass of the proton favors their production." Why my astonishment? 1) The masses of protons and neutrons are almost identical. 2) Two ups and one down seems as likely a bundle to me as two downs and one up when my quark soup starts to cool enough. 3) Proton and electron masses are vastly different but we still end up with them in equal numbers, regardless. Could I be correct in concluding, therefore, that the above given reason for this ratio of 7 to 1 is merely a conjured up excuse for introducing yet a further cosmological fudge factor into the concordance model? Or is there some rational reason why we would genuinely expect twice as many ups as downs in our quark soup? If there is no rational reason, and ups and downs had actually been poured in in equal measure (by a more unbiased chef), what difference, if any, would that then make to the subsequent nucleosynthesis brewing time, and the resultant ratio of protons (hydrogen nuclei) to alpha particles (helium nuclei), eventually? > I have just been boning up on primordial nucleosynthesis, and the > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 26 lines] > time, and the resultant ratio of protons (hydrogen nuclei) to alpha > particles (helium nuclei), eventually? Protons are stable in free space. Neutrons decay with a mean-life of 885.7 seconds or a half-life of 613.9 sec. Roughly equal production rates sustained over about an hour award you your net skew.  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > > I have just been boning up on primordial nucleosynthesis, and the > > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 30 lines] > 885.7 seconds or a half-life of 613.9 sec. Roughly equal production > rates sustained over about an hour award you your net skew. Agreed, entirely. But that is not the point. The bulk of that neutron decay would necessarily occur AFTER the period of primordial nucleosynthesis. Consequently the question is, A) does such an increase in initial neutrons (and corresponding decrease in protons) alter the dynamism sufficiently _during_ the period of primordial nucleosynthesis , to alter the predicted of helium fraction, or B) Did Gamov factor all this in during his original calculation, and Wiki ha just got its summary a bit wrong. On a related point, how robust was Gamov's analysis anyway? I mean to say, I have never seen anyone say, oops, we need to resurrect the cosmological constant, plus alter dark matter proportions, then, oops we now need to check if this alters primordial nucleosynthesis predictions too. > Protons are stable in free space. Neutrons decay with a mean-life of > 885.7 seconds or a half-life of 613.9 sec. Roughly equal production > rates sustained over about an hour award you your net skew. I have just checked the ref again, and quote from just before my earlier quotation: "Combining thermodynamics and the changes brought about by cosmic expansion, one can calculate the fraction of protons and neutrons based on the temperature at this point. The answer is that there are about seven protons for every neutron at the beginning of nucleogenesis, a ratio that would remain stable even after nucleogenesis is over." The authors seem pretty adamant that one needs ~7 protons per neutron _at the start_ of nucleogenesis, for the arithmetic in the Alpher--- Bethe---Gamow paper to work > > Protons are stable in free space. Neutrons decay with a mean-life of > > 885.7 seconds or a half-life of 613.9 sec. Roughly equal production [quoted text clipped - 13 lines] > _at the start_ of nucleogenesis, for the arithmetic in the Alpher--- > Bethe---Gamow paper to work What is the density at inception? Is reverse beta-decay by squeezing Fermi exclusion going to collapse a fraction of hydrogen plasma to neutrons? SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > I have just been boning up on primordial nucleosynthesis, and the > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 8 lines] > > 1) The masses of protons and neutrons are almost identical. On closer examination of the soup, the following statement needs revision: > 2) Two ups and one down seems as likely a bundle to me as two downs > and one up when my quark soup starts to cool enough. Actually, I find two downs and one up is the preferred option because they are electrically neutral. Under charge conservation, every instance of two ups and one down, must have the associated generation of one free electron at the big bang. Diner at the Big Bang Restaurant... "Waiter, what is this strange bug in my soup" Waiter........"With all due respect Sir, those aren't strange bugs in your soup, they are an in house speciality of the Chef...Fishy quarks" > > I have just been boning up on primordial nucleosynthesis, and the > > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 19 lines] > instance of two ups and one down, must have the associated generation > of one free electron at the big bang. Generating free electrons? Seem to be charge consevation bounds why this does not happen. > Diner at the Big Bang Restaurant... "Waiter, what is this strange bug > in my soup" > Waiter........"With all due respect Sir, those aren't strange bugs in > your soup, they are an in house speciality of the Chef...Fishy quarks" > > > I have just been boning up on primordial nucleosynthesis, and the > > > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 22 lines] > Generating free electrons? Seem to be charge consevation bounds why > this does not happen. Two ups and one down quark make a total charge of +e so there must be an electron of charge -e generated to achieve charge conservation. These electrons must be free because it is far too hot for atom formation. At quark soup time, it is even too hot for for nucleon formation. OK? > I have just been boning up on primordial nucleosynthesis, and the > following statement in Wiki (admittedly not always the most reliable > source), struck me as incredible:- [[...]] For a slightly more detailed account, see http://www.astro.ucla.edu/~wright/BBNS.html http://astro.berkeley.edu/~mwhite/darkmatter/bbndetails.html For a detailed review, see Gary Steigman "Primordial Nucleosynthesis in the Precision Cosmology Era" Annual Review of Nuclear and Particle Science 57, 463-491 (2007) http://adsabs.harvard.edu/abs/2007ARNPS..57..463S ciao, Signature-- "Jonathan Thornburg [remove -animal to reply]" <jthorn@astro.indiana-zebra.edu> Dept of Astronomy, Indiana University, Bloomington, Indiana, USA "Washing one's hands of the conflict between the powerful and the powerless means to side with the powerful, not to be neutral." -- quote by Freire / poster by Oxfam On Jun 10, 8:15 pm, "Jonathan Thornburg [remove -animal to reply]" <jth...@astro.indiana-zebra.edu> wrote: > > I have just been boning up on primordial nucleosynthesis, and the > > following statement in Wiki (admittedly not always the most reliable [quoted text clipped - 4 lines] > For a slightly more detailed account, see > http://www.astro.ucla.edu/~wright/BBNS.html Phew! That's all right then. So the ratio of protons to neutrons (or, more precisely, up quarks to down quarks) _is_ ~50/50 initially, as I was originally expecting. > http://astro.berkeley.edu/~mwhite/darkmatter/bbndetails.html Oh dear. "(After 3 minutes) approximately 25 percent by mass of the matter in the universe is now in the form of helium nuclei: the rest consists of protons." So when is all the non baryonic dark matter supposed to arrive, and from where? > For a detailed review, see > Gary Steigman > "Primordial Nucleosynthesis in the Precision Cosmology Era" > Annual Review of Nuclear and Particle Science 57, 463-491 (2007) > http://adsabs.harvard.edu/abs/2007ARNPS..57..463S Yep, that seems to confirm ratio of protons to neutrons (hence ups to downs) does tend to unity as T tends to 0. Thanks for the refs Jonathan, they have been most helpful [and I haven't even finished reading the last one yet] > On Jun 10, 8:15 pm, "Jonathan Thornburg [remove -animal to reply]" > [quoted text clipped - 32 lines] > Thanks for the refs Jonathan, they have been most helpful [and I > haven't even finished reading the last one yet] Of additional potential interest here is the decade earlier http://arxiv.org/PS_cache/astro-ph/pdf/9504/9504082v1.pdf This explicitly covers the non baryonic dark matter constraint. In essence, it concludes that the baryonic mass must be less than ~ 10% of the total mass, for BBN to produce an observationally plausible mix of light elements. Presumably the Harvard ref would lead to similar (and more accurate) conclusions by implication, but, afaict from quick reading, does not explicitly spell this out. On Jun 10, 8:32Â am, Uncle Al <Uncle...@hate.spam.net> wrote: > Chalky wrote: > [quoted text clipped - 19 lines] > > What is the density at inception? Â Dunno but it should be pretty simple to work out approximately. (Mean density now multiplied by the cube of 13.7 billion years / 3 minutes) > Is reverse beta-decay by squeezing > Fermi exclusion going to collapse a fraction of hydrogen plasma to > neutrons? Quite possibly, if we are starting out with pure hydrogen plasma (or its quark soup equivalent) In this case we are talking about up quark + electron goes to down quark. On the other hand, if we start with pure neutron quark soup, the opposite is far more likely. down quark goes to up quark + electron. I don't know if this reaction rate would be the same in quark soup, but. if it is, your first response suggests you should be able to work out how many neutrons are needed to make 7 protons and 7 electrons in 3 minutes, a lot faster than me. Don't worry 'bout no 'left over' neutrons........Baldrick has a > On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: >> Chalky wrote: >> >> What is the density at inception? > Dunno but it should be pretty simple to work out approximately. (Mean > density now multiplied by the cube of 13.7 billion years / 3 minutes) this assumes the universe mass is the same now and 13.7 billion years ago. Is that valid? Richard D. Saam > > On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: > >> Chalky wrote: [quoted text clipped - 5 lines] > this assumes the universe mass is the same now and 13.7 billion years > ago. No it doesn't. It assumes that the mass now is approximately the same as it was 3 minutes after the big bang > Is that valid? You are welcome to supply a more rigorous analysis if you so wish. >>> On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: >>>> Chalky wrote: [quoted text clipped - 10 lines] > > You are welcome to supply a more rigorous analysis if you so wish. According to Harrison eqn 18.48 density*Universe Radius^(3*gamma) If lambda is other that 1 then mass has to change. The expression 'matter is created during expansion' is used for gamma = 0 > >>> On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: > >>>> Chalky wrote: [quoted text clipped - 12 lines] > > According to Harrison eqn 18.48 Presumably you mean > density*Universe Radius^(3*gamma) =Mass? and gamma = sqrt(1-v^2/c^2)? If so, v is the velocity of what relative to what? > If lambda is other that 1 > then mass has to change. > > The expression 'matter is created during expansion' is used > for gamma = 0 >>>>> On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: >>>>>> Chalky wrote: [quoted text clipped - 14 lines] > > =Mass? No, density*Universe Radius^(3*gamma) = constant density = Mass/volume analogous to adiabatic expression: Pressure*Volume^gamma1 = constant1 > and gamma = sqrt(1-v^2/c^2)? No, gamma is not the Lorentz transform. gamma is another dimensionless constant presented by Harrison, defined in terms of the relativistic equation of state: Pressure = (gamma - 1) density*c^2 in conjunction with the Friedmann-Lemaitre equations result in universe conditions: gamma = 4/3 for radiation dominated universe gamma = 2/3 for static universe gamma = 0 for constant density universe gamma = 1 for a zero pressure universe >> If gamma is other that 1 >> then mass has to change. >> >> The expression 'matter is created during expansion' is used >> for gamma = 0 These are theoretical constructs, but in this context, change 'matter is created during expansion' to 'available energy during expansion' Looks like the possible making of a Carnot cycle in there somewhere. Has anyone theoretically constructed such a thing? Richard D. Saam > >>>>> On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: > >>>>>> Chalky wrote: [quoted text clipped - 18 lines] > density = Mass/volume > analogous to adiabatic expression: Perhaps you should have said that initially > Pressure*Volume^gamma1 = constant1 > [quoted text clipped - 3 lines] > gamma is another dimensionless constant > presented by Harrison, Perhaps you should have also said that initially. Please note;-I still don't know which Harrison you are quoting, or what book. (The most popular Harrison comes up as Harry Harrison, the SF writer) > defined in terms of the relativistic equation of state: > Pressure = (gamma - 1) density*c^2 > in conjunction with the Friedmann-Lemaitre equations result in universe > conditions: > gamma = 4/3 for radiation dominated universe Hmm. This suggests it is not constant. The early universe was radiation dominated whereas the current universe is matter dominated. I note you do not even cover that option, below. > gamma = 2/3 for static universe > gamma = 0 for constant density universe > gamma = 1 for a zero pressure universe These assertions strike me as highly cosmology dependent. > >> If gamma is other that 1 > >> then mass has to change. [quoted text clipped - 8 lines] > to > 'available energy during expansion' That seems somewhat more credible > Looks like the possible making of a Carnot cycle in there somewhere. > Has anyone theoretically constructed such a thing? Dunno (as in my original response that you objected to). To cut to the chase, I suggested, in that response, a simple approach to determining density as a function of time, to a first approximation, and invited you to provide a more rigorous analysis. AFAICT you have not yet done so. I still don't know what your approach is supposed to predict at 1 second, or 3 minutes, or any other time, for that matter. > Please note;-I still don't know which Harrison you are quoting, or > what book. > > (The most popular Harrison comes up as Harry Harrison, the SF > writer) In the context of cosmology, the default meaning of "Harrison" can reasonably be taken to be the (superb) book Edward R Harrison "Cosmology: The Science of the Universe" Cambridge U.P., 1981 (I believe there is a 2nd edition of available, but I don't have publication info for it.) If it doesn't mean this, then it might mean the classic paper by the same author http://adsabs.harvard.edu/abs/1993ApJ...403...28H Title: The redshift-distance and velocity-distance laws Authors: Harrison, Edward Publication: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 403, no. 1, p. 28-31. Publication Date: 01/1993 ciao, Signature-- "Jonathan Thornburg [remove -animal to reply]" <jthorn@astro.indiana-zebra.edu> Dept of Astronomy, Indiana University, Bloomington, Indiana, USA "Washing one's hands of the conflict between the powerful and the powerless means to side with the powerful, not to be neutral." -- quote by Freire / poster by Oxfam > > On Jun 10, 8:32 am, Uncle Al <Uncle...hate.spam.net> wrote: > >> Chalky wrote: [quoted text clipped - 7 lines] > > Is that valid? I note from line 15 of page 87 of "The accidental universe"# that density (of particles) is actually supposed to be inversely proportional to time squared. This should make things nice and simple. (Not least because temperature is also inversely proportional to time squared, in the early [radiation dominated] universe.] # http://books.google.co.uk/books?id=s2s4AAAAIAAJ&pg=PA87&lpg=PA87&dq=density+time +relationship+universe&source=bl&ots=ZkvDYkyjrd&sig=VhWIM8lhsBTPiP4HJuQA6u21BzE& hl=en&ei=Dyw_SuqmFtm4jAf2_5wY&sa=X&oi=book_result&ct=result&resnum=5 On Jun 22, 5:22 pm, "John Bell (Change John to Liberty for email)" <john.b...@accelerators.co.uk> wrote: > I note from line 15 of page 87 of "The accidental universe"# that > density (of particles) is actually supposed to be inversely > proportional to time squared. Does this apply for time after recombination as well as before? > This should make things nice and simple. (Not least because > temperature is also inversely proportional to time squared, in the > early [radiation dominated] universe.] > > #http://books.google.co.uk/books?id=s2s4AAAAIAAJ&pg=PA87&lpg=PA87&dq=d... On Jun 22, 5:23 pm, Ian Parker <ianpark...@gmail.com> wrote: > On 22 June, 10:41, "Chalky (OR)" <chalky.or...@accelerators.co.uk> > wrote: [quoted text clipped - 3 lines] > I am afraid I must eat a little humble pie here. Plotting the curve > from the present to 3min gives T = t^(-2/3). Interesting. This does seem to give the correct result from the present to the surface of last scattering (matter dominated era). > T is proportional to Density. (Assuming no other degrees of freedom) Can this be confirmed, Temperature is proportional to density, now too, not just in the early radiation dominated era? (I don't really understand your degrees of freedom argument) > Speed of recession (km/s per MPs) = sqrt(Density) Is left hand side supposed to have dimensions of 1/time, or distance/ time ? if 1/time, we have time is proportional to Temperature^-1/2 This is the formula which seems to work for the peeriod before recombination > This on integration gives T^(-3/2) prop t. or T prop 1/(t^(2/3)) Now you have lost me again. Integrating what WRT what? On 23 June, 21:39, "Chalky (OR)" <chalky.or...@accelerators.co.uk> wrote: > Can this be confirmed, Temperature is proportional to density, now > too, not just in the early radiation dominated era? (I don't really > understand your degrees of freedom argument) At about 3 min there were only electron positron pairs, which soon recombined. From then until now the amount of antimatter in the Universe was negligible and photons existed in just two degrees of freedom (polarization). Let us suppose there was some process that could absorb photons. The temperature of the Universe would clearly fall. Let us visualize a temperature of 10MeV. This is not sufficiently hot for quarks to be produced, but is hot enough for electron positron pairs. We have now effectively doubled the volume of our phase space. We may assume the pairs to be travelling at something like 0.9c. In my undergraduate Physics course the Stephan Boltzmann law was derived using a (gedanken) box which contained the radiation. A box containing pairs therefore emits twice the energy of the photons alone, and has twice the energy. This means in fact that if we extrapolate t^(2/3) to 10MeV we will get the same amount of energy. The temperature will in fact be 10*(0.5^(1/4))MeV. The precise form before 3min depends to some extent on what theory of elementary particle physics you subscribe to. In a quark soup, quarks, electrons and photons will coexist. It should I think be pointed out that in a dense quark soup the particles will behave differently from how they behave in isolation. Remember that each individual quark is heavier than a proton. - Ian Parker On Jun 23, 9:39 pm, "Chalky (OR)" <chalky.or...@accelerators.co.uk> wrote: > On Jun 22, 5:22 pm, "John Bell (Change John to Liberty for email)" > [quoted text clipped - 4 lines] > > Does this apply for time after recombination as well as before? It looks like it. I have quickly posted up the classical cosmological relationships given in Google's disclosed portions of quoted books, at http://global.accelerators.co.uk/CCR/ I have inserted 'therefore' symbols for the formulae derived from the given formulae, and additionally disambiguated the employed symbols for temperature and time. If anyone sees any errors, please advise. > On 23 June, 21:39, "Chalky (OR)" <chalky.or...@accelerators.co.uk> > wrote: > > > Can this be confirmed, Temperature is proportional to density, now > > too, not just in the early radiation dominated era? I refer again to http://global.accelerators.co.uk/CCR/ Apparently, density is proportional to the cube of temperature in matter dominated region, but the fourth power in radiation dominated. Again, if anyone sees any errors, please advise. On 25 June, 17:56, "John Bell (Change John to Liberty for email)" <john.b...@accelerators.co.uk> wrote: > I refer again tohttp://global.accelerators.co.uk/CCR/ > Apparently, density is proportional to the cube of temperature in > matter dominated region, but the fourth power in radiation dominated. > > Again, if anyone sees any errors, please advise. I don't know if this could be regarded as an error or not, but if matter is travelling at relativistic speeds, ie. close to c it follows the radiation law Momemtum (prop 1/wavelength) = Ec where E is the energy of the particle. Particle is travelling, near as no matter at c. By the nature of how pairs (of anything) are formed, if antimatter is in equilibrium with matter it must be travelling at an appreciable fraction of c at least. Remember the early Universe was not matter, but matter and antimatter with an eventual predominance of matter. How is still a mystery. - Ian Parker > On 25 June, 17:56, "John Bell (Change John to Liberty for email)" > [quoted text clipped - 10 lines] > energy of the particle. Particle is travelling, near as no matter at > c. I don't know for sure either, but suspect that this is all part and parcel of what is meant by 'radiation dominated era' > By the nature of how pairs (of anything) are formed, if antimatter is > in equilibrium with matter it must be travelling at an appreciable > fraction of c at least. > Remember the early Universe was not matter, but matter and antimatter > with an eventual predominance of matter. How is still a mystery. You seem to be conflating two different things here (and are by no means alone in this). There is, firstly, the mechanism for creating the big bang and its immediate products. This is still unknown (at least in the published domain). Then there is the mechanism for creating particle/ antiparticle pairs from photons, and vice versa. This is well known, and, imo, we have no valid grounds for concluding other than that those particles/antiparticles are both created and annihilated in equal numbers. The question of why there are so many high energy photons around in the early universe (and hence so many [eventually destroyed] matter/ antimatter pairs), is probably worthy of further discussion in its own right, and so I am starting a separate thread on that subject (moderator permitting). JB |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2010 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.