Are there any conditions under which glass cracks spontaneously? Just now, my mother's rear windshield cracked spontaneously. The story according to her: Slowly approaching a stop sign. No busy traffic. No trees/animals in sight. Few people. Suddenly, the rear windshield cracked with a loud boom with no evidence as to what caused it. A police officer happened to be directing traffic and saw it occur. The officer did nothing about it since there was no indications as to what caused it. This is very strange! I don't believe that this could have just happened without a something hitting the window. I suspect it happened so quickly no one saw it. But, apparently, there were no cars, and few people, so they believe that the object impacting the glass scenario is not possible. My question now is: is it possible that the glass cracked spontaneously? For reference, the temperature outside was 34 degrees Fahrenheit, the temperature inside about 70 degrees Fahrenheit. Thanks for any replies/insight! In this picture above, you can see the indications that some impact occurred.