Predicting big bang deuterium

We present new upper and lower bounds to the primordial abundances of deuterium and He-3 based on observational data from the solar system and the interstellar medium. Independent of any model for the primordial production of the elements we find (at the 95% C.L.): 1.5 x 10(-5) less than or equal to (D/H)(p) less than or equal to 10.0 x 10(-5) and (He-3/H)(p) less than or equal to 2.6 x 10(-5). When combined with the predictions of standard big bang nucleosynthesis, these constraints lead to a 95% C.L. bound on the primordial abundance deuterium: (D/H)(best) = (3.5(-1.8)(+2.7)) x 10(-5). Measurements of deuterium absorption in the spectra of high-redshift QSOs will directly test this prediction. The implications of this prediction for the primordial abundances of He-4 and Li-7 are discussed, as well as those for the universal density of baryons.