Inflation predicts that quantum fluctuations determine the large scale structure of the Universe .
This raises the striking possibility that quantum mechanics , developed to describe nature at short distances , can be tested by studying nature at its most immense – cosmology .
In this note , we realize this possibility .
A nonlinear generalization of quantum mechanics modifies predictions for the cosmological power spectrum .
Observational cosmology is sufficiently precise to place a stringent limit , b < 3 \times 10 ^ { -34 } eV , on the size of the nonlinear term .