what would make a patio glass table just shatter?
Unless you're talking about pyrex glass, most glass panes, tabletops, etc, are full of stresses that are trapped within the glass. It seems unlikely to have "shattered by itself," because it usually takes some form of energy to liberate the stresses. The energy we normally think of is mechanical, such as a hammer. Most of this type of energy is generated by human activity. I can think of one that might occur without apparent cause, and that would result from the "sonic boom" of an aircraft traveling faster than the speed of sound, but I have never heard of one shattering a glass table top, though sonic booms can produce damage to many kinds of structures, some damage may be to windows, etc. Do you live near a military air base? There are ways to submit claims for damage such as from sonic booms of military aircraft. See the base legal office for guidance.
There is a third possibility, the normal heating and cooling of the weather, which causes most things to expand or contract as they warm up or cool off. That glass top may have been too tightly enclosed in its metal support structure, and the two (glass and support structure) have different expansion rates when they warm up or cool down. There needs to be some space for expansion and contraction in such things, of they will expand or contract different amounts, put the glass in a mechanical bind, and cause what seems to be a spontaneous shattering. Sounds impossible to you, but might be the cause.
Having raised children, dogs, horses, etc, I would most likely suspect one of them of perhaps an accidental mechanical act that shattered the glass. Remember, too, that it could be as simple as a lawn mower throwing up a stone or other object, and probably wouldn't be noticed by someone operating a noisy machine. Hope you find the cause, and would be interested to know if you do.
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