We reconsider the predictions of inflation for the spectral index of scalar ( energy density ) fluctuations ( n _ { s } ) and the tensor/scalar ratio ( r ) using a discrete , model-independent measure of the degree of fine-tuning required to obtain a given combination of ( n _ { s } , r ) .
We find that , except for cases with numerous unnecessary degrees of fine-tuning , n _ { s } is less than 0.98 , measurably different from exact Harrison-Zel ’ dovich .
Furthermore , if n _ { s } \gtrsim 0.95 , in accord with current measurements , the tensor/scalar ratio satisfies r \gtrsim 10 ^ { -2 } , a range that should be detectable in proposed cosmic microwave background polarization experiments and direct gravitational wave searches .