This is my view:
synchronicity is a real thing and depends on the viewer. For it to occur, the following chain of events needs to take place:
1) People or whatever need to share a common association to something in the environment, say an object or the juxtaposition of objects. These things are used by the brain as a memnemonic device, it's an extension of the persons memory, a filing system.
2) This association is defined as a cultural standard of some sort. A dynamic representation is the single mindedness of a group of fighters or players making the score. A child and parent or sibling sharing the same idea. A pack of dogs, A flock of birds.
3) The memory of those involved is triggered by something like the same configuration of brain synapses. Like a group of people seeing the same thing. For this to take place, the neuron transition from sense to interpretation requires a memory input which is taken from the environment. The interpretation is made on a learned standard, but the neuron calling for a standard (some kind of similar previous experience) excites more than just the brain, so that others sharing the association, form the same conclusion or mental imagery. This is the point of this note. It goes beyond-mind (para-noid)*: "Brain Waves" happen. When the previous experience is not exact, one is synthesized from approximate experiences using a creative association. The new association is learning taking place, and may involve someone elses experience.
"Brain waves" between people are, as far as I know, only a theoretical explanation for synchronistic phenomena. However I point to the following evidence: Alpha wave (bio feedback) sensors detect a particular pattern between two people who are mutually a ttracted to each other: a double beep, like a heart beat but missing the third beat (beep-beep, beep-beep, etc.). How come? Possibly to be in contact with the other person?
Situational awareness (the opposite of visualization) still depends on so me kind of feedback. When the environment changes in an unfamiliar manner, like in dreams, one tends to act in a dream manner: fainting, laughing, or standing agog. widdershins etc.
1 Feb 2016:
Continuation of the brain waves hypothesis:
This article about Synchronized brain waves in distant regions combine memories (science daily) says
"Humans have the remarkable ability to integrate information from multiple memories and infer indirect relationships. How does our brain support this important function? Neuroscientists have now shown that rhythmic brain waves, called theta oscillations, engage and synchronize the brain regions that support the integration of memories."Also: How brain oscillations might respond to teleportation
An extenuation of the same phenomenon could be that a bunch of people doing the same thing might also be sensitive to the theta osculations of those around them amplified by the group, causing them to act in a similar way. please comment if you have any thoughts :)
*A note on paranoia:
The process of paranoia is common, as described above. But popular definition of paranoia implies that something is wrong, and could just as well be defined as fear. The wrongness is actually a lack of confidence in the cultural standard. Psychologists and Therapists tend to exploit and reinforce the phenomena to make a buck. Any ones compassion can wear thin, but it seems shameless for them to continue, though they are probably unaware and are only supporting their own reality.