I was recenlty on the phone with my friend who moved into a new house. The house has been around for a little while...nothing too long. He was on the phone when his mom told him to hang up and look at this. As it turned out, a pane of glass in the bathroom shattered. He looked at it and watched the cracks get longer right in front of him. It began from the middle and worked its way towards the edges. There was no one in that room. The facts that I know are that it was like about room temperature in there. Most of the windows in the house were open. The glass was about ten years old. The water wasn't on and no apparent forces were acting on it. We're really curious to find out what happened considering that we're both really into physics. His guess was that a sudden pressure change from opening a door might have bent the glass slighlty enough to cause it to crack and send small pieces on the floor. More facts....his mom used CLR on the glass to clean it three weeks before the incident. Any help or suggestions would be appreciated, thanks!