Astrophysics problems and solutions

The lithium problem or lithium discrepancy refers to the discrepancy between the primordial abundance of lithium as inferred from observations of metal-poor halo stars in our galaxy and the amount that should theoretically exist due to Big Bang nucleosynthesis+WMAP cosmic baryon density predictions of the CMB.Namely

The most widely accepted models of the Big Bang suggest that three times as much primordial lithium

Should exist.This contrasts with the observed abundance of isotopes of hydrogen and helium that are consistent with predictions.The discrepancy is highlighted in a so-called Schramm plot

Named in honor of astrophysicist David Schramm

Which depicts these primordial abundances as a function of cosmic baryon content from standard BBN predictions.

An exact solution is a solution of the Einstein field equations whose derivation does not invoke simplifying assumptions

Though the starting point for that derivation may be an idealized case like a perfectly spherical shape of matter.Mathematically

Finding an exact solution means finding a Lorentzian manifold equipped with tensor fields modeling states of ordinary matter

1. Such as :
2. A fluid

Or classical non-gravitational fields such as :

The electromagnetic field.

The flatness problem is a cosmological fine-tuning problem within the Big Bang model of the universe.Such problems arise from the observation that some of the initial conditions of the universe appear to be fine-tuned to very 'special' values

And that small deviations from these values would have extreme effects on the appearance of the universe at the current time.