On September 28, 2006, I made the case that telescopic power is indeed an accelerating technology, set to improve at an estimated rate of 26% a year for the next 30 years. I believe that increasingly more powerful telescopes will ensure that we discover the first genuinely Earth-like planet in another star system by 2011, and that by 2025, we will have discovered thousands of such planets.
In support of this thesis of accelerating telescope improvement, I had to bring attention to one particular prospective technology that greatly increases the chances of this predicted rate of improvement holding true : Liquid mirrors that could at some point replace glass in the largest telescopes (from MIT Technology Review).
The mirror is a pool of salt-based liquids that only freeze at very lower temperatures, coated with a silver film. While practical usage is at least 20 years away, the details reveal a technology that is brilliantly simple, yet tantalizingly capable of addressing almost all of the problems facing the construction of giant telescopes. Glass mirrors are exceedingly difficult to scale to larger sizes, and even the most minor defect can render a mirror useless. Reflective liquid, by contrast, can be scaled up almost indefinitely, limited only by the perimeter of the enclosure it is placed in. External blows that would crack or scratch a glass mirror would have no effect on a liquid that could quickly return to the original shape.
I don't expect updates on this technology in the near future, but the next logical step would be for a smaller telescope to be demonstrated to use this technology. If that succeeds, the ultimate goal would be, by 2030, a massive telescope more than 200 meters in diameter placed on the Moon, where the sky is free of atmospheric distortions, and the ground is free of tiny seismic shaking. This would enable us to observe Earth-like planets at a distance of up to 100 light years, as well as observe individual stars near the center of the Milky Way galaxy (30,000 light years away).