A reader writes:

I have always wondered, hypothetically, according to current physical theories (one or more hypothetical theories) _if_ a body (an "object" with mass in space/time, assuming some kind of unobserved QM state)… simply "disappeared".

What would happen? What would be the signature effects?

Would there be any non-local QM side-effects? What happens with "entanglement"? Is unobserved "disappearance" (or collapse to nothing) possible given current hypothetical physical theories?

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And Thomas Aquinas only wanted to know if an angel in going from point A to point B had to travel through the in-between. It’s a good thing the good saint didn’t know about entanglements.

Here is a readable article by Tia Ghose from LiveScience that appeared in the Huffington Post just last month: Quantum Entanglement Experiment Reconfirms Physics Phenomenon Einstein Called ‘Spooky’

Want a brief definition?  This is from a HuffPo mouseover for the above picture:

According to quantum mechanics, two or more particles can become "entangled" so that even after they are separated in space, when an action is performed on one particle, the other particle responds immediately. (Shown here, two entangled mechanical oscillators made up of two pairs of trapped ions.)