We've proven quantum entanglement and it's been demonstrated experimentally with photons, electrons, top quarks, molecules and even small diamonds. The use of entanglement in communication, computation and quantum radar is an active area of research and development I'm interested in. Einstein referred to the effects of entanglement as "spukhafte Fernwirkung" or "spooky action at a distance", meaning the acquisition of a value of a property at one location resulting from a measurement at a distant location.

If you want to go down a fun rabbit hole, search for the double slit experiment. One of the most intriguing aspects of the experiment is that even when particles like electrons are fired one at a time through the slits, they still create an interference pattern, suggesting that the act of observing the particle (just looking at them) somehow affects its behavior! The double slit experiment is an example of the counterintuitive nature of quantum mechanics, where particles can behave like waves and the outcome of an experiment can be influenced by the sheer act of observation.