Moving closer to a resolution of the cosmological lithium problem

Galaxy cluster MACS J0416.1-2403, courtesy Hubble Frontier Fields

(—There’s not as much lithium in the universe as predicted, and scientists aren’t sure why. According to the theory of big bang nucleosynthesis (BBN), isotopes of the three lightest elements—hydrogen, helium, and lithium—were created within the first 20 minutes after the big bang. The theory predicts with remarkable accuracy the observed amounts of hydrogen and helium, but its estimate for lithium is three times too high.

The problem has frustrated scientists working in cosmology, since almost any modification to the BBN theory that corrects the lithium abundance inadvertently throws off the hydrogen or helium abundances, or contradicts other constraints on the theory. The situation may be compared to trying to solve a Rubik’s cube that has only one square of the wrong color.


Constraints on the primordial lithium abundance. A loophole in the way that electromagnetic cascades are computed opens up the possibility of solutions to the [cosmological] lithium problem. Credit: Poulin and Serpico. Copyright: 2015 American Physical Society

Now in a new paper published in Physical Review Letters, physicists Vivian Poulin and Pasquale Dario Serpico at Université Savoie Mont Blanc, CNRS, in Annecy-le-Vieux, France, have suggested that the lithium problem may be connected to an overlooked loophole in another theory: that of electromagnetic cascades. Although addressing the lithium problem is not the main result of the paper, it illustrates the potential impact of these broader findings. “The general result we found in our paper is not specifically related to the lithium problem, rather to the inaccuracy of an approximation used to describe perfectly standard physics, related to cascades,” Serpico told

The paper is Vivian Poulin and Pasquale Dario Serpico,  “Loophole to the Universal Photon Spectrum in Electromagnetic Cascades and Application to the Cosmological Lithium Problem”, Physical Review Letters. DOI: 10.1103/PhysRevLett.114.091101. The full article explains more and continues:

“A consequence of our results is that it is easier to solve the lithium problem in a broad class of new physics models, so to speak,” Serpico said. “More in general, we would say that the importance of the lithium problem is due to its long-standing nature; it goes back to the beginning of the millennium and, despite several alternatives (both standard and exotic), none of them has been conclusively argued to be ‘the one.’ Concerning implications: If the solution is due to new physics, there will be profound implications for theories beyond the standard model as well as their impact on the early universe. Alternative classes of solutions may involve subtle aspects of stellar astrophysics, for instance. Hence, even more mundane explanations are typically not trivial at all.” In the future, the scientists plan to apply the results to other situations that may be affected by the loophole, and consider some of these cases even more urgent than the lithium problem. “In particular, an obvious case is provided by big bang nucleosynthesis constraints on unstable relics, based on deuterium and helium measurements and for photons having a broader energy range (from a few MeV to hundreds of MeV),” they wrote. “This is a calculation we are currently completing. “Of course, given its importance, we are also thinking about particle physics models that may ‘exploit’ the features we have pointed out, in order to provide a more efficient solution to the lithium problem. Linking these results to the problem of the nature of dark matter or other signatures of particle physics beyond the standard model (for instance in the neutrino sector) is certainly on our medium-term agenda.”

On a new topic: Was the Europan plume just an impact? Article in and abstract.


5 Responses to “Moving closer to a resolution of the cosmological lithium problem”

  1. Lithium problem, solve it(hypothesis): 7Li(p,y)8Be*(a,y)12C* nuclear reaction.

    • Some lithium was indeed produced in the Big Bang and is therefore primordial.

      • “The theory predicts with remarkable accuracy the observed amounts of hydrogen and helium, but its estimate for lithium is three times too high.”

        7Li=12C-16O (7Li(p,y)8Be*(a,y)12C*, 7Li(p,y)8Be*(8Be*,y)16O*)

        The theory is that carbon and oxygen primordial!
        Conclusion : The “problem with lithium”, a consequence of life Universe. This is a new Anthropic principle. But it has yet to be proven. 🙂

        Regards nyemi

  2. What do you think about this hypothesis?
    You are given explain the amount of carbon and oxygen in the universe?
    Thank you in advance for your reply.

    Regards nyemi

    • I think that Fred Hoyle found his 7.7 MeV line for excited carbon (i.e. an excited state of the carbon nucleus) which showed that 12C could form about a billion times faster than without the excited intermediary) in the 1950s and that this nuclear processing (the triple alpha process) formed the basis of the CNO cycle in hot, massive stars. Your hypothesis demands a calculation of the amount of 12C and 16O and other isotopes that might have been formed in a hot big bang, along with a consideration of lithium, and also observational evidence for C and O in Population III stars, which would be a surprise. Also, lithium abundances aren’t totally understood in all stars.

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