"A mirror much larger than eight meters, made of a single piece of glass, would be too expensive and too hard to handle." Glass was used 20 years ago because i

"A mirror much larger than eight meters, made of a single piece of glass, would be too expensive and too hard to handle." Glass was used 20 years ago because it has favorable stiffness to weight ratio. Change to carbon fiber was speculated, but it's not transparent and it would be more difficult to polish. Carbon fiber backed glass might be the future.