I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level.

This is supposed to be big news, but I don't understand why (my ignorance, of course).

For instance, with an index of 0.96, can we say how many e-foldings occured during inflation ? What else does it tell us  ?

I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level.

This is supposed to be big news, but I don't understand why (my ignorance, of course).

For instance, with an index of 0.96, can we say how many e-foldings occured during inflation? What else does it tell us?