WHY IS LITHIUM SO RARE IN THE UNIVERSE?

Presently, astronomers are unsure why lithium is as rare as it is in the Universe. The ‘standard’ model of the Big Bang, using what we know of nuclear physics, can accurately predict the abundances of the chemical elements that were formed between about 100 to 1,000 seconds after the Big Bang. However, although the standard model precisely predicts the primordial hydrogen and helium abundances, it overpredicts the measured primordial abundance of lithium by a factor of three to four. So, either the predictions are inaccurate (and the measurements are correct), or the predictions are accurate (and the measurements are wrong).

Scientists have investigated possible solutions to this so-called ‘lithium problem’. One possibility is that there is something missing in our understanding of nuclear physics — leading us to overestimate the lithium abundance. However, recent research seems to completely discount this possibility.

Perhaps we don’t fully understand the processes going on inside stars – processes which could be destroying lithium out of sight. Although astronomers know that cooler stars have deep convection zones which can drag lithium to the star’s core and destroy it, and that binary stars, or those with planetary systems, can also alter the primordial abundance of lithium, these processes do not seem to be enough to account for the discrepancy. However, some scientists still maintain that there must be other, unknown ways to destroy lithium in the Universe.

Another possible solution to the lithium problem is that there is entirely new physics of which we are unaware. Perhaps mysterious dark matter had an unappreciated effect on the production of elements in the very early Universe. Or perhaps the fundamental constants on which physics is based have not remained constant throughout cosmic time. There are numerous such theories being considered to solve the problem. But, at present, the odd rarity of lithium in the Universe is a complete mystery.