With every year that goes by, the total amount of knowledge that humanity accumulates only grows and grows. At the start of 2015, humanity had never detected a gravitational wave; at present, we've detected 11, and full expect to find perhaps hundreds more in 2019. In the early 1990s, we didn't know whether there were any planets outside our own Solar System; today, we have thousands, some of which are almost good enough to be considered Earth-like.
We've found all the particles in the Standard Model; we've discovered that the Universe is not only expanding,...
Read more about 2019 Science Breakthrough of the Year: Imaging the Event Horizon