Why Gravity Is the Ultimate Space Telescope (forbes.com)

TheAlexKnapp writes: Ethan Siegel has written a nice overview of gravitational lensing, and how taking advantage of it has enabled to study parts of the universe that otherwise would've require the construction of massive telescopes. From his Forbes article: "Although the first gravitational lens wasn't discovered for some 40 years after it was first theorized, it's now the most prolific tool for weighing distant (foreground) galaxies, and discovering ultra-distant (background) galaxies. Although this isn't a technique we have precision control over — the Universe puts the lenses and the lensed objects where they are, and all we can do is watch — there's a spectacular amount of material that's out there."