Distinguishing between cold dark matter and modified Newtonian dynamics: Predictions for the microwave background

Two hypothesized solutions for the mass discrepancy problem are cold dark m atter and modified Newtonian dynamics. The virtues and vices of these very different hypotheses are largely disjointed, making the process of distingu ishing between them very dependent on how we weigh disparate lines of evide nce. One clear difference is the nature of the principal mass constituent o f the universe (cold dark matter or baryons). This difference in the baryon fraction (f(b) approximate to 0.1 vs. 1) should leave a distinctive signat ure in the spectrum of fluctuations in the cosmic microwave background. Her e I discuss some of the signatures that should be detectable in the near fu ture. The most promising appears to be the ratio of the amplitudes of the f irst two peaks relative to the intervening trough.