> I've seen several people here mention that it's not "measured directly" - does it mean something else in this case? As far as I can see from the article (cou

> I've seen several people here mention that it's not "measured directly" - does it mean something else in this case? As far as I can see from the article (couldn't find the paper detailing the experiment), they observed an artifact that could have been caused by primordial gravitational waves. This is different from using a thermometer to measure temperature because we're not sure yet whether that is the only possibility (or our instruments are not sensitive/too sensitive, it's a different mechanism of inflation etc.), it's the best explanation, but we're not extremely sure yet. (Although as I say this it occurred to me that it's probably much more certain than before because of the discovery.) The key takeaway here is that the inflationary model is almost certainly the right one and gravitational waves are almost certainly real. (This is similar to the first Higgs Boson announcement, where we were almost certain it was the Higgs, but not sure enough to claim discovery; because we hadn't determined all the properties of the observed particle)