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Big Bang ruled out as origin of lithium-6

  1. Sep 11, 2014 #1
    http://physicsworld.com/cws/article/news/2014/sep/02/big-bang-ruled-out-as-origin-of-lithium-6

    The hystory of BB nucleosynthesis is quite busy, Gamow et al. started postulating that all elements were originated in the BB nucleosynthesis process in the late 40s early 50s, it soon became quite evident through the work of Hoyle and others that it couldn't be so and the list was reduced to the light elements, slowly but steadily more elements fell off, now with Lithium ruled out, wich BB origin was a central prediction of BB nucleosynthesis, it seems it's down to two:Hydrogen and Helium. Actually what the nucleosynthesis would predict in principle is their proportion, approx. 1/4 in mass for Helium, wich is in basic accordance with its observed abundance.
    That the BB nucleosynthesis theory actually came up with this proportion(1/4) has been critiziced in the past by Hoyle(and others) who claimed that other theories without Big-bang, including his, also predicted it.

    Now BB nucleosynthesis used to be one of the three pillars of the Big-bang theory(the others being cosmological redshift and the CMB), is the ruling out of Lithium as originated in the Big-bang a big blow or just a scratch to the theory?
     
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  3. Sep 11, 2014 #2

    phyzguy

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    You're selling BBN short. It very accurately predicts the abundances of H, D, He-3, and He-4. The question is why the measured abundance of Li-7 in old stars is 2-4X lower than BBN predicts. There are a number of possible explanations, the most likely being (IMHO) that some of the Li-7 is consumed by nuclear reactions in these stars. This interpretation is supported by this Nature paper, which measured the abundance of Li-7 in interstellar gas (not in stars) in the SMC, and found about the amount predicted by BBN. I suspect it will be some time before this is all sorted out, but I predict that the standard Lambda-CDM model of cosmology will emerge unscathed.
     
  4. Sep 11, 2014 #3
    "First Direct Measurement of the H2(α,γ)Li6 Cross Section at Big Bang Energies and the Primordial Lithium Problem"
    Phys. Rev. Lett. 113, 042501 – Published 21 July 2014
    M. Anders et al. (LUNA Collaboration)

    This is the paper that the article linked above refers to. This specific issue seems to have already been sorted out.

    I'm not selling anything short, just presented some apparently not controversial scientific facts and wondered how they affect the theory. I don't think this gets solved simply by appeals to faith in the current concordance model, wich has been changed several times thru the years, the last important one as recently as 1998, to accomodate new facts.
     
  5. Sep 11, 2014 #4

    phyzguy

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    When I said you were "selling BBN short", I was referring to your statement that, "it seems it's down to two:Hydrogen and Helium", meaning ( I think) that BBN only successfully predicts the abundance of two elements. However, it really successfully predicts the abundances of four nuclei, H, D, He-3, and He-4, and only misses on one - Li-7. Given this, it seems more logical to suspect the Li-7 measurements than BBN itself. But time will tell.
     
  6. Sep 11, 2014 #5
    Ok, but I was obviously referring to the 2 elements generically(as it's done in the physicsworld article), D and He-3 are obviously isotopes of H and He respectively. But it doesn't make much difference if it's down to 2 or 4 isotopes, because the abundances are closely connected in BB nucleosynthesis in the sense that it is a process and therefore abundances of some influence the others. That's the reason why the observed discrepancy in abundance of Lithium-6 and -7 is a real problem for the whole BBN model.
     
  7. Sep 22, 2014 #6

    CKH

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    My reading of the article is that the BB nucleosynthesis calculations agree with experiment (at least under the conditions of this experiment). So this is just a verification of the problem. My understanding is that in stellar measurements there a consistency, quite different from BBN that needs to be explained. That is, the lithium level doesn't seem to depend on precise stellar age or precise mass.

    I've only read the abstract in the Nature article. I'm skeptical that some measurement of gas in the Magellanic cloud can be taken as primordial.

    We measure only the stellar surface (outer atmosphere). Yet it seems that these abundances are taken as uniform throughout the star. That seems unlikely in that mass and atomic size ought to have some migration effects. Are these effects somehow taken into account?

    Regarding "more logical to suspect Li-7 measurements than BBN itself". That's interesting because it's like saying that the theory trumps measurement. The theory is apparently considered so well proven that usually when there is disagreement with measurement, it is called "tension" and everyone scrambles to find a way to relieve it. Many, if not most, papers that find discrepancies focus on reducing this "tension" by searching for other effects to bridge the gap. On the other hand, measurements apparently in agreement with theory, don't get much focus. That is we don't usually look for other effects to explain a result in agreement with theory, even though such effects may well exist.
     
  8. Sep 23, 2014 #7

    Drakkith

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    That's simply not true. Theories are developed to explain observations and measurements. New observations and measurements are taken and old ones are refined, and if the theory disagrees with the observations then we have to figure out why. Many times it turns out that our measurements are either wrong, or our understanding of how the measurement applies to the theory is wrong. In addition, many times competing theories are explored even though the observations don't contradict the accepted mainstream theory. A good example is the various alternatives to special relativity: http://en.wikipedia.org/wiki/Special_relativity_(alternative_formulations)

    I think the problem is that people rarely hear of alternative theories that have been explored or all the experiments that are performed to verify that current theories are correct.

    Also, remember that science is a work in progress and if you aren't one of the ones actively working in a field you're extremely unlikely to understand all the work going on and how it affects the current working theory.
     
  9. Sep 24, 2014 #8

    CKH

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    I agree with what you say above, but I don't see how it contradicts what you quoted.

    I often see the phrase in papers "in good agreement with LCDM" referring to observations and their interpretation supporting LCDM. However when the conclusion is "in substantial tension with LCDM", that paper is going to draw at lot more attention. The observation and it's analysis are going to scrutinized. Researchers are going to pick it apart piece by piece. If the result of this scrutiny is that the paper is valid, then researchers are going to put considerable effort into explaining that discrepancy in the context of LCDM.

    Even if they cannot explain such a discrepancy, they expect that an answer will come that is consistent with the theory. The decades old Lithium discrepancy is a case in point.

    Right now, as far as I know, there is no alternative theory that agrees with cosmological observations as well as LCDM. However it is also true that LCDM has many problems on the scale of galaxies which could mean something is wrong despite the agreement at the level of the entire cosmos..
     
  10. Sep 26, 2014 #9

    e.bar.goum

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    It's worth noting that those 6Li abundance measurements published by Asplund in 2006 disappear if you go to a 3D NLTE model of the solar atmosphere (see Lind, Asplund, Collet, Melendez 2012). This is hardly surprising if you know how measurements of 6Li in stellar atmospheres are made - they manifest as a slight asymmetry in the Li line shape.

    I don't think anyone really thinks there's a "primordial 6Li problem" any more.

    Now, the 7Li problem, on the other hand, is somewhat more intractable. My personal bias is that it will be solved by a combination of increased mixing in stars (which gets you about half-way to BBN abundances), with maybe a variation of nuclear reaction rates associated with 7Be destruction.
     
  11. Oct 28, 2014 #10
    Hi TrickyDicky! Thinking about your question, how much "the ruling out of Lithium as originated in the Big-bang" affects the theory's track record regarding predictions, and phyzguy brought up hydrogen and helium, we should also keep in mind its prediction on antimatter.

    An extensive search for the antimatter predicted by the BB ended with a paper in the Astrophysics Journal concluding that "a matter-antimatter symmetric universe is empirically excluded" with the journal Science reporting a physicist's assessment that, "The work is extremely compelling and gives me fresh pessimism" that the theory's prediction has failed, i.e., that there is not an entire universe's worth of antimatter out there. Fermi lab produced a short video to explain the problem:



    TD, you also mention the BB's CMB prediction. That's an interesting one because it was more of a post-diction, made after observations had already indicated the data. In his lecture given on the very occasion of sharing the Nobel Prize for discovering the Cosmic Microwave Background Radiation, Robert Wilson, admitted that, "The first confirmation of the microwave cosmic background that we knew of, however, came from a totally different, indirect measurement. This measurement had, in fact, been made thirty years earlier by [Mount Wilson Observatory's] Adams and Dunhan... from the first rotationally excited state. McKellar using Adams' data... calculated [via absorption lines from cyanide detected in outer space] that the excitation temperature of CN was 2.3 K. This rotational transition occurs at 2.64mm wavelength, near the peak of a 3 K black body spectrum." [Robert Wilson, Nobel Lecture, see more..., and see also Arno Penzia's lecture]

    So TD, if lithium-6 is a scratch, antimatter must be another scratch. :) Now I'm wondering about phyzguy's statement about hydrogen and helium.
     
  12. Oct 28, 2014 #11
    I'm a bit confused over what you are trying to say here.

    - The Li-7 problem is an observation with stress re cosmology, but as the thread notes it is spurious, likely partial (only in stars, where nucleosynthsis is less well understood), and small (less than an oom).

    - Matter/anti-matter asymmetry on the other hand is a big problem. Not too big, since the basic mechanism was discovered by Sakharov. But AFAIU the lack of predicted constraints puts it many oom from the matter content that is observed.

    - Incidentally, the observed matter/anti-matter asymmetry is perfectly consistent with the CMB relict photons. Yes, its existence was a post-diction according to the timeline [ http://en.wikipedia.org/wiki/Cosmic_microwave_background#History ], but the characterization of its anisotropy has many features that are predicted (multipole moments vs total energy, dark energy, dark matter and matter; polarization).

    TL;DR: Not much of a problem with cosmology as such. But the matter/anti-matter symmetry is a long-standing open question.
     
  13. Oct 28, 2014 #12
    Hello Torbjorn_L! These two, Anders and Johnston, are more qualified than I am to put the lithium problem in perspective.

    After M Anders' Physics Review Letters paper concluded that "The much higher Li6/Li7 values reported for halo stars will likely require a nonstandard physics explanation," Physics World's Hamish Johnston wrote:

    The BBN model predicts that lithium-6 should account for about two out of every 100,000 lithium nuclei in "metal-poor" stars, which are believed to be among the first stars to have formed and so should reflect the composition of the early universe. However, observations... suggest that the abundance of lithium-6 is more than a thousand times greater in such stars, accounting for about 5% of all the lithium present.
    And so Johnston, who is the editor of Physics World, summed it up this way: "Big Bang nucleosynthesis (BBN) theory... fails miserably when it comes to the two stable lithium isotopes: lithium-6 and lithium-7."

    So when TrickyDicky asked, "is the ruling out of Lithium as originated in the Big-bang a big blow or just a scratch to the theory?", I was thinking that when folks talk about predictions as evidence in support of the big bang, they should also just as readily acknowledge where the predictions were actually post-dictions, and where other predictions, like with antimatter and lithium, just haven't held up.

    Then there's phyzguy's statement about the BB predictions of abundances of hydrogen and helium. As with all of science history of course, there's an interesting story there too.
     
  14. Oct 28, 2014 #13

    mfb

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    If you expect to measure 0 (as deviation from a theory from example) and 99 measurements are compatible with 0 while one gives a significant deviation, it should be obvious that this one gets the most attention. It is clear evidence that something is not understood. Sure, there could be smaller errors in the other experiments, but the chance that two significant problems happen at the same time (to give a null result again) is very small.
     
  15. Oct 28, 2014 #14

    e.bar.goum

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    I need to emphasize again that no-one (apart from Anders and Johnston, apparently) really thinks there is a 6Li problem after re-analysis of the measurements in 2012 by Lind, Asplund, Collet and Melendez (Mem. S.A.It. Suppl. 22, 142). Martin Asplund the second author is the the guy who made the original 6Li measurements (APJ 644 2006), by the way. ETA: And he says that he was never as certain about the 6Li measurements as other people were, in the first place, FTR.

    There are three approaches to solutions to the primordial lithium-7 problem:

    1: We don't understand the mechanisms for 7Li depletion in metal poor halo stars. Perhaps there is more diffusion and turbulent mixing between the surface layers and burning layers than we previously thought. Scatter in the low metalicity end of abundances suggests there is some mechanism of depletion we don't fully understand. See for example, Pinsonneault et. al. 2002, Pizzone et. al. 2007. Lind 2009 is another good one. There are hundreds of papers on this.

    2: We don't fully understand the nuclear reactions that go into BBN. While all significant reactions (we think) have been measured, large uncertainties exist for some reaction rates. Measurements at BBN energies are very challenging. Is there perhaps, some resonance that we're missing, or some mechanism that we've not investigated fully? See for example, Coc, A. 2011, Civitarese, 2013 & 2014, Broggini 2012, Chakraborty, 2011. Kirsebom 2011. Again, hundreds of papers on this possibility.

    3: There is some new physics solution. These include Axion dark matter (Ereken 2012), SUSY (so many papers. Look at Pospelov 2010 or Fields 2011 for an overview) , late-time neutron injection (through any mechanism the authors can think of e.g. Vasquez 2012), variation of fundamental constants (Coc 2007), cosmic rays during BBN (Kang 2011)... it goes on.

    But, it is important to note that these new physics mechanisms are not replacing BBN, but modifying it, and modifying it in a small way, otherwise you lose the nice agreement with other BBN elements. And options 1 and 2 are not yet ruled out, either, allowing for unmodified BBN to be true.

    It is a bit of a stretch to say that because the 7Li abundances are 3-4 times larger in BBN than in metal poor halo stars, that they provide evidence against the Big Bang. In fact, I'd say it is flat out wrong.
     
    Last edited: Oct 28, 2014
  16. Oct 28, 2014 #15

    e.bar.goum

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  17. Oct 29, 2014 #16
    Ah, thanks Bob! Now I understand what your comment is intending. Well, I don't really know anything about primordial nucleosynthesis or the observation problems, but what I read in this thread is encouraging: 6Li is no longer an obvious problem (if it ever where), if I understand e.bar.goum's comments with its many good references which I haven't had time to read. (While your reference neatly supports the BBN prediction.)

    The other stuff you mention seems plain - "flat out" in the parlance of this thread - wrong. (Wikipedia clearly states the post-diction timeline; there is no finalized antimatter prediction - they are still measuring cross-sections in the standard model for particles (and see e.bar.goum's comment on this) - except that the observed asymmetry not necessarily need new physics for its prediction).
     
  18. Oct 29, 2014 #17
    Hello mfb! Yes, that's true. What's also true, I'm sure everyone here would agree, is the importance of having an objective assessment of how often the bb predictions of primordial abundances have actually matched actual observations, and how often, like with the CMB, we are seeing post-dictions and after-the-fact adjustments. An open letter was published in New Scientist, signed by dozens (and since by hundreds) of researchers working at prestigious institutions, including the Max-Planck Institute for Astrophysics, Sheffield University, George Mason University, Jet Propulsion Laboratory at CalTech, Cambridge University, Lawrenceville Plasma Physics, Penn State, Cal State Fullerton, University of Virginia, European Southern Observatory, and scores of others, affirming the opinion published in the journal Nature, that:

    It is commonly supposed that the so-called primordial abundances of D (Deuterium, i.e., heavy hydrogen, N+P), 3He (Helium N+2P), and 4He (2N+2P) and 7Li (Lithium 3P+4N) provide strong evidence for Big Bang cosmology. But a particular value for the baryon-to-photon ratio needs to be assumed ad hoc to obtain the required [predicted] abundances.
    - 1990 Nature http://www.nature.com/nature/journal/v346/n6287/pdf/346807a0.pdf

    The many astrophysicists and similarly qualified scientists at scores of leading institutions claimed in that New Scientist open letter that:

    the big bang theory can boast of no quantitative predictions that have subsequently been validated by observation. The successes claimed by the theory's supporters consist of its ability to retrospectively fit observations with a steadily increasing array of adjustable parameters...​

    Of course, they may be wrong mfb. But they are many. And unlike much of the difficulties that cosmology faces, these scientists are making claims that are verifiable, or falsifiable, via something as relatively simplistic as history. The more I look into actual bb predictions, including that there should be no "mature" galaxies among those that that are most distant, but per Science, observation has shown otherwise; and that gravity should have enabled less galaxy clustering far away, and more clustering nearby, yet Hubble keeps finding clusters that defy that patter, and not to delve into the unexpected anisotropy of the Axis of Evil and the apparent quantized redshift from hundreds of thousands of galaxies, much of the cosmos doesn't seem to fit neatly into the predictions of the theory, which might be why even a group like the National Academy of Sciences would publish as recently as in 2003 an alternative cosmological model for a bounded universe.
     
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  19. Oct 29, 2014 #18

    Drakkith

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    I'm not sure why adjusting a theory to match observations is looked down on, especially in the case of cosmology, which requires knowledge of macroscopic physics, microscopic physics, the conditions of the very early universe, and the ability to compute massive amounts of data representing both short term and long term changes. It seems obvious to me that the chances of coming up with a near-perfect theory that requires no adjusting is effectively zero.
     
  20. Oct 29, 2014 #19
    Drakkith, hi! It seems obvious to me that you are EXACTLY CORRECT:
    Adjusting a theory to match observations is properly done all the time. And equally obvious, we should not be revisionists and claim that a theory predicted something when it did not, because then our revisionism itself becomes misinterpreted as actual evidence for the validity of the theory.

    The long-predicted shadow of the big bang is a handy example. A 2006 paper in the Astrophysical Journal reported on a "vital test of the present cosmological paradigm" that "taken at face value, one may even hold the opinion that there is in fact no strong evidence" for the CMB's shadow from behind 31 nearby galaxy clusters. About this, Hunstville's Univ of Alabama professor of physics Richard Lieu said in Science Daily, that, "These shadows are a well-known thing that has been predicted for years. If you see a shadow… it means the radiation comes from behind the cluster. If you don’t see a shadow, then you have something of a problem", and so, "Either... the Big Bang is blown away or ... there is something else going on."

    Of course, something else may be going on. Regardless though, regarding evidence, we should let the chips fall where they may. Once the wheel stops, so to speak, nobody gets to move their chips. So based on the current state of our knowledge,
    - if major predictions appear to be simply wrong, like with a 50% antimatter universe, or
    - if they weren't predictions but post-dictions, like with the CMB, or
    - if they require secondary adjustments after-the-fact, like with initial abundances, or
    - if they require significant secondary assumptions, like with lithium, or
    - if they even require the supposition of multiple hypothetical entities,
    then rather than overselling one's claims, a more frank assessment might not present the theory's predictive powers as reason to squelch challenges.
     
    Last edited: Oct 29, 2014
  21. Oct 29, 2014 #20

    Drakkith

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    I think there may be some confusion with the word "prediction" here. If I input a set of conditions into my model and get a result, then that model "predicts" the results. Similarly, the standard model of cosmology (based on the big bang theory) predicts certain things like the CMB, nucleosynthesis, etc. Changing the parameters of the model alters the prediction.

    From wiki: http://en.wikipedia.org/wiki/Prediction#Prediction_in_science

    In science, a prediction is a rigorous, often quantitative, statement, forecasting what will happen under specific conditions; for example, if an apple falls from a tree it will be attracted towards the center of the earth by gravity with a specified and constant acceleration.

    So a "prediction" does not necessarily mean that we predicted something prior to discovery, though that may happen.
     
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