eldavojohn writes "Want to make a great concave mirror for your telescope? Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now. The key problem in this situation is that the bowl will always have to point straight up. MIT's Technology Review is analyzing a team's success in combating problems with bringing liquid mirrors into the practical applications of astronomy. To fight the gravity requirement, the team used a ferromagnetic liquid coated with a metal-like film and very strong magnetic fields to distort the surface of that liquid as they needed. But this introduces new non-linear problems of control when trying to sync up several of these mirrors similar to how traditional glass telescopes use multiple hexagonal mirrors mounted on actuators. The team has fought past so many of these problems plaguing liquid mirrors that they produced a proof of concept liquid mirror just five centimeters across with 91 actuators cycling at one kilohertz and the ability to linearize the response of the liquid. And with that, liquid mirrors take a giant leap closer to practicality."