Measuring the polarization, or orientation, of the light from the CMB could reveal whether inflation took place. Primordial gravitational waves produced during the epoch of inflation would have alternately stretched and squished space-time in such a way that at the time the CMB was produced, its light would contain B-modes — a swirling pattern — still visible today. If detected by future experiments, these B-modes would provide a clear signature of inflation, as no source other than cosmological gravitational waves can produce them in the CMB. Above is an example of what B-modes look like in a field of polarized light.