As I mentioned in my last blog post, the remaining doubters of the big bang creation model are atheists and young-earth creationists. Atheists reject the big bang creation model because of its theistic implications and because it makes the universe too young. Young-earth creationists reject it because of what it implies about God (that God spread his creation miracles over long time periods and tolerated thermodynamics, carnivorous activity, and disease before the fall of Adam) and because it makes the universe too old.
Both atheists and young-earth creationists conveniently ignore most of the positive evidence for the big bang. Their tactic is to point out a few anomalies where observations do not yet affirm the big bang and declare that lack of affirmation as a failed prediction of the big bang creation model.
All models have anomalies. Anomalies result from our lack of complete knowledge about the system we are investigating. It is what happens to an anomaly as we press forward with more in-depth research that determines whether or not the anomaly counts as a failed prediction. It will rank as a failed prediction when high quality experiments and/or observations show a marked discrepancy with the model’s predictions where there is no possible reasonable explanation in the context of the model for the discrepancy.
One way we can help big bang skeptics get past their skepticism is by showing them how the anomaly they consider most problematic for the big bang creation model can be straightforwardly resolved in favor or the big bang. I will do so in this post for the most cited big bang anomaly: the primordial abundance of lithium.
Before proceeding, though, let me share what some of the critics are saying. In an article for Answers in Genesis, young-earth creationist astronomer Danny Faulkner referred to primordial lithium as “a big problem for the big bang.”1 He concluded his article by writing, “The predictions and measurements for lithium disagree greatly. Thus, the claims that observed light element abundances prove the big bang model are incorrect.”2 In an article for the Institute for Creation Research, Brian Thomas also referred to the lithium problem as “a big problem for the Big Bang” and is reason enough to “jettison the Big Bang theory altogether.”3
Big Bang Nucleosynthesis Predictions
In the big bang creation model, the universe begins with only one element: hydrogen. As the universe cools from a near infinitely hot initial state as a result of its expansion from the cosmic creation event, it briefly passes through a temperature window (3–4 minutes after creation) where nuclear fusion can occur. According to the big bang model, the amount of fusion that does occur will be precisely determined by the cosmic density of baryons (protons + neutrons).
Based on the cosmic baryon density accurately derived from the Planck map of the cosmic microwave background radiation, the big bang will convert the following fractions of the universe’s original hydrogen into heavier elements:4
- helium: 0.24668 ± 0.00013
- deuterium (heavy hydrogen): 2.606 ± 0.053 x 10-5
- lithium: 4.95 ± 0.39 x 10-10
These amounts are known as the predicted primordial abundances of the universe; that is, the amounts of these elements that the big bang model predicts existed before stars formed. Once stars form and begin nuclear burning, they produce extra helium and consume deuterium and lithium.
Testing the Big Bang Predictions
Astronomers can test these big bang predictions by observing the spectral lines of helium, deuterium, and lithium in stars and gas clouds where little star burning has occurred. Their best tests come from looking at stars and gas clouds that are very distant. The greater the distance, the farther back in time (because of the finite velocity of light) astronomers are making their measurements and, hence, the less time the observed stars have had to produce additional helium and destroy deuterium and lithium.
Astronomers can improve their tests even more by selecting the most metal-poor of the distant stars and gas clouds to observe. In astronomy, metals refer to all the elements in the periodic table above helium. Except for the minuscule amount of lithium produced by the big bang, all metals come from the nuclear burning of stars. The more stars that burn and the longer they burn, the more metals that are exploded by the larger stars into the gas clouds that produce future stars. Thus, the most metal-poor stars and gas clouds are those that are least impacted by the nuclear burning of formerly existing stars.
The most definitive test would be to observe the content of helium, deuterium, and lithium in the universe’s firstborn stars before those stars undergo any significant nuclear burning. Unfortunately, these stars are much too dim for even the most powerful telescopes to detect them. Nevertheless, by observing very distant, very metal-poor stars and gas clouds astronomers can obtain reasonably accurate measurements of the primordial abundances of helium, deuterium, and lithium.
Primordial Helium Abundance Test Results
Two different teams of astronomers have published their determination of the primordial helium abundance from measurements made on distant metal-poor gaseous nebulae. A Mexican-Spanish team obtained a value5 for the primordial helium abundance = 0.2446 ± 0.0029 while an American team produced a value = 0.2449 ± 0.0040.6 This remarkable agreement between prediction and observations today ranks as one of the most spectacular verifications of the big bang creation model and the standard big bang nucleosynthesis theory in particular.
Primordial Deuterium Abundance Test Results
Based on an analysis of the measured deuterium abundance in the most metal-poor damped Lyman alpha systems (large concentrations of hydrogen gas detected in the spectra of quasars) currently known, a team of American and British astronomers determined7 that the primordial deuterium abundance = 2.547 ± 0.033 x 10-5. As the Planck Collaboration team wrote, this agreement between the big bang prediction and observation is “a remarkable success for the standard theory of BBN [big bang nucleosynthesis].”8 In a review paper physicist Brian Fields wrote, “This concordance represents a great success of the hot big bang cosmology.”9
Primordial Lithium Abundance Problem?
Comparing the primordial lithium abundance predicted by the big bang model with the observed primordial lithium abundance is much more challenging than comparing theory and observations for helium and deuterium. The predicted lithium abundance derived from the Planck cosmic microwave background radiation map under the presumption of big bang cosmology is about a factor of a hundred thousand times less than for primordial deuterium and a factor of a billion times less than for primordial helium.
This extremely low abundance of lithium is affirmed by astronomical observations. Lithium spectral lines in astronomical sources are so weak that astronomers are unable to obtain a useful detection in any star outside our galaxy. They are limited to observing lithium in metal-poor stars in our galaxy. That is, unlike for helium and deuterium, astronomers presently have no access to lithium abundance measures in either very distant or very metal-poor stars.
This lack of access explains why astronomers do not view the lithium abundance problem as a serious challenge to the big bang creation model. Where the primordial abundance observations are adequate (helium and deuterium) to test the big bang, the big bang model passes with flying colors. Where such observations are not adequate (lithium), an understandable discrepancy remains. Where young-earth creationists are being disingenuous in their critique of the big bang model is in their ignoring the big bang’s predictive successes where the observational tests are robust and their hyping the big bang’s predictive “failure” where the observational tests are marginal.
The story of the past decade on this issue is one of astronomers doing whatever they can to make the marginal observational test of the primordial lithium abundance less marginal and seeing what their efforts do to the predictive discrepancy.
Observations published in 2005 of a sample of metal-poor stars in the halo of our galaxy yielded a ratio of lithium to hydrogen = 1.66 ± 0.35 x 10-10. This value is a factor of 2.98 times less than the big bang predicted value.10
Subsequent observations published in 2012 by two different teams of astronomers produced lithium to hydrogen ratios = 1.91–2.88 x 10-10 and 3.80 ± 0.77 x 10-10 respectively.11 Two sets of observations of stars in metal-poor Milky Way Galaxy globular clusters produced lithium to hydrogen ratios = 3.72 ± 0.96 x 10-10 and 1.95–2.24 x 10-10 respectively.12
All the observational values lie below the predicted value. While one could argue that the two larger values are in statistical agreement with the predicted value, the other measurements depart from the predicted value by a factor of 1.72–2.59 times.
The announced detection of the lithium-6 isotope in three galactic halo stars13 makes the lithium problem much worse. However, a follow-up study revealed that “none of the three analysed stars have a significant detection of 6Li.”14
Astronomers have proposed several reasonable solutions to what remains of the lithium problem. The most obvious is that all observations to date measure the present lithium abundance, not the lithium abundance at epochs close to the cosmic creation event. As astronomers Corinne Charbonnel and Francesca Primas deduced, “We are then left with the conclusion that the Li abundance along the plateau is not the pristine one, but that halo stars have undergone surface depletion during their evolution.”15 Astronomers Elisabeth Vangioni and Alain Coc add that since it is well known that stellar burning consumes lithium, it may be a mistake to presume “that lithium has not been depleted at the surfaces of these stars” and that “the presently observed abundance can be assumed to be equal to the initial one.”16 Astronomer Brian Fields demonstrated that if at any time during a star’s youth, its near surface layers experienced temperatures exceeding 2.5 x 106 kelvin, that exposure would cause substantial destruction of lithium.17
That stellar destruction of lithium likely explains the lithium abundance problem finds strong support from the recent observation of interstellar lithium in the Small Magellanic Cloud (SMC). The SMC is a dwarf galaxy located 197,000 light-years away. Compared to the Milky Way Galaxy, the interstellar gas in the SMC is metal-poor. High-resolution spectra of the SMC’s interstellar medium seen as absorption lines in the light of the bright SMC star, SK 143, revealed a lithium to hydrogen ratio = 4.79 ± 1.48 x 10-10 respectively.18 This value is fully consistent with the predicted primordial lithium abundance, although clearly higher precision measurements would be desirable.
If needed, there may be a nuclear physics solution to the lithium problem. If beryllium-7 destruction in nucleosynthesis is greater than what current models predict, that destruction by itself could solve the lithium problem. Presently, the relevant nucleosynthesis resonances that determine rates of beryllium-7 destruction are poorly measured.19 There is also the possibility of an unknown resonance.
Possible cosmological solutions to the lithium problem include long-term exposure of stellar surfaces to cosmic rays,20 the decay of a relatively long-lived negatively charged exotic mass particles (the most likely candidate being the second lightest supersymmetric particle),21 photon cooling,22 and a weak primordial magnetic field.23 Long-term exposure to cosmic rays definitely occurs. The degree to which this exposure destroys lithium has yet to be determined. The observational upper limits on a primordial magnetic field (1–2 nanogauss on size scales of several million light-years)24 is close to the value required, by itself, to solve the lithium problem.
A team of Japanese and American astronomers pointed out that three of the above-mentioned possible solutions (higher past stellar surface temperatures, cosmic rays, primordial magnetic field) are known to have at least some impact on lowering the lithium abundance on stellar surfaces from the primordial value.25 Thus, they propose that the most reasonable solution to the lithium problem is a combination of these three factors plus possibly small contributions from photon cooling and the decay of exotic particles.
Lithium abundance would only be “a big problem for the big bang” if
- there was no other observational support for what the big bang model predicts,
- the observational measurements determining the primordial lithium abundance were getting progressively more discordant rather than less discordant, and
- there were no reasonable scenarios in the context of the big bang model for explaining why a discrepancy exists.
None of these three “ifs” apply. Therefore, lithium is not a big problem for the big bang model. In fact, over the past five decades the observational evidence establishing the validity of the big bang creation model has become both progressively and consistently stronger and more comprehensive. However, long before astronomers discovered that the universe manifests a history and features consistent with the big bang model, thousands of years ago the Bible described its fundamental features.26
Featured image credit: chemwiki.ucdavis.edu