The Primordial Lithium Problem Persists

by Dr. Danny R. Faulkner on December 4, 2021
Featured in Answers in Depth

The big bang has been the dominant cosmogony for more than a half-century. One supposed evidence for the big bang model is its prediction of the abundances of the light elements, hydrogen, helium, and lithium. According to the model, these three elements—and only these three elements—were synthesized in the first few minutes of the universe’s existence. All other elements, such as the calcium in your bones and the iron in your blood, were forged in stars that formed much later. The claim is that the observations of the abundance ratios of the isotopes of the three lightest elements match the predictions of the big bang model. While it is true that the measured abundances of hydrogen and helium in the universe match the model predictions, the lithium measurements are far less than the abundance predicted by the big bang model, so much so that this mismatch is called the primordial lithium problem.

Cosmologists, astronomers, and nuclear physicists have spent considerable time over the past two decades addressing the primordial lithium problem to no avail.

Why is there a lithium problem? In big bang nucleosynthesis, lithium-7 (the dominant isotope of lithium) is produced through the fusion of tritium (the heaviest but unstable isotope of hydrogen) and a helium-4 nucleus (the most common isotope of helium). At the same time, lithium-7 is destroyed by the fusion of lithium-7 and a proton (a typical hydrogen nucleus) to form two helium-4 nuclei. The efficiencies of these competing processes determine which one dominates, resulting in either more or less lithium-7 in the universe. The efficiency of either process depends upon the physical conditions of the early big bang. Theorists think they have a good understanding of the physical conditions of the early big bang, which permits direct calculation of the predicted abundance of lithium-7. However, comparison with the observed lithium-7 abundance in the universe reveals that the universe contains less than one-third of what is predicted. Cosmologists, astronomers, and nuclear physicists have spent considerable time over the past two decades addressing the primordial lithium problem to no avail.

New Research to the Rescue?

A team of researchers recently reported on this problem. They concentrated on a second nuclear reaction that could have destroyed lithium-7 in the early big bang. That reaction is the fusion of lithium-7 with hydrogen-2 (a rare but stable isotope of hydrogen) to produce a neutron and two helium-4 nuclei. It was thought that this reaction was too inefficient to have destroyed a significant amount of lithium-7, but there was considerable uncertainty in the reaction rate. This team endeavored to improve upon our understanding of the reaction involved using new experimental data. However, they found that the improvement did not significantly change the outcome. Though the researchers didn’t explicitly state in their paper that they initially thought their research might solve the primordial lithium problem, that seemed to be their motivation. Alas, it was not to be, because in their conclusion they wrote, “Therefore, our results confirm the existence of the cosmological lithium problem.”1 Thus, the primordial lithium problem remains.

We at Answers in Genesis are not surprised by such results. We reject the big bang model on the grounds that it does not conform to what the Bible reveals about the history of the world. That is good enough reason to reject the big bang, but it’s good to know that scientific studies provide physical evidence against the big bang as well.


  1. S. Q. Hou, et. al, “New Thermonuclear Rate of 7Li(d,n)24He Relevant to the Cosmological Lithium Problem,” The Astrophysical Journal, 920, no. 2 (2021):145,


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