2-57. It Was A Ghost


It started with a bang! At first, I wasn’t sure what happened. As I was sitting alone and quietly on a couch 17 stories in the air, I couldn’t imagine what glass had broken. I could tell it was tempered glass by the sound. It was dull, and didn’t ring. But the only tempered glass I could think of was the sliding glass door. Did a bird slam into it? Was someone shooting at it?

Without moving, I examined the doors and could see no evidence that they had shattered. In fact, despite the noise, I couldn’t see broken glass anywhere. And then I took a closer look at the pinball machine.

There were small diamonds of broken glass all around it. But it wasn’t the glass covering the play field that was broken, it was the glass where the score is displayed. Somehow, this 26 x 18 section had shattered into thousands of pieces.

A bit too much magic.

A bit too much magic.

This glass is called a back glass, and it usually features some art associated with the machine. In our 1995 Theatre of Magic machine, there is an illustration of a magician throwing steel balls. But why had the glass shattered? My first thought was that something had hit the glass. But I was in a sealed room, alone. Though there were three parakeets in there, they were safely in their cage 15 feet from the pinball machine. There were no cats to blame, and no windows were open. I was motionless when it happened.

So maybe the sun was hitting it? No, it was cloudy and the top of the machine would have been room temperature. I should add that the machine was off as well, so there was nothing going on inside the machine that could have caused it.

I knew a bit about tempered glass and how it spontaneously shattered sometimes, but I decided to head to Google for a better explanation. And a common one that I saw was… ghosts. Yep, that’s right, if something unexplained happens, the explanation is always ghosts. Case closed. You can stop reading or listening now. Or you can keep on and learn some interesting things about tempered glass.

Tempered glass is made of normal glass treated with heat to make it stronger. Water is used to cool the outside of the glass quickly, while the hotter inside is left to cool slowly. This creates tension in the glass, and that tension gives the glass strength against blunt impacts. If you were to take a baseball bat to a sliding glass door, you might be surprised how hard it was to break.

As a bonus, when tempered glass does break, it forms tiny pieces, making it much less dangerous.

But there’s a problem. Because the glass is under tension, it can spontaneously shatter. A small scratch or a chip near the edge, where the tension is most easily released, can cause the glass to shatter in spectacular fashion. There can be as much as 10,000 PSI stored in a sheet of window glass, and when it breaks, it does so at speeds up 14x the speed of sound.

People have tried to take slow motion videos of tempered glass with their smartphones only to find that the glass goes from whole to entirely shattered in just one frame.

The sound you’re hearing now is the broken glass popping ten minutes after the original explosion. Some pieces were actually jumping onto the floor.

So did a ghost do this? Probably not. The glass was twenty years old, and it probably had some very minor damage that gave way. A minuscule crack could have been spreading until it finally attained the geometry necessary to release all that pressure.

So it’s Physics: 1 and Ghosts: 0. If the ghosts want to prove it was them, they can simply put all the glass back together again. Then I might believe.

This glass broke at 14 times the speed of sound.

This glass broke at 14 times the speed of sound.

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