The past, present and future are 'local' not global phenomena. Modern science owes this revelation to Albert Einstein.
One month before his own death the physicist wrote a letter to the sister of his recently departed friend Michele Besso, in which he noted that the fact that one person passes before another 'means nothing' and that all our experience of time is in a sense, illusory.
Nevertheless, Italian pointy-head Carlo Rovelli has warned us against treating this memetic soundbite out of context, as something vocalised by an oracle. Einstein, he notes, was grieving and attempting to offer a shared comfort.
Nevertheless, a sentence within that letter forms the basis of the premise of Synchronic, which has the potential to be profound, yet limits itself to the shallowest of implementations — there's a new designer drug which messes with our pineal gland, apparently the part of our brain responsible for the conscious experience of the very personal, if not illusory, present. Younger people, whose pineal glands have yet to calcify, not only experience potentially dangerous temporal commingling, but actually travel back in time physically...for seven minutes.
From this point onwards, the more I try to explain this premise, the more arbitrary and generally silly it is going to sound. If chronology is an illusion established inside our minds, why would the physical body itself hop between times, for if the disappearing human form can be seen and filmed, then there is inherently a shared, objective element to all this. Exit Einstein.
The protagonist is at one point left trying to explain why his dog's lead, minus the actual dog, has returned to his original present, and says something remarkably similar to 'It's quantum, baby'. This is just lazy.
Still, as B movies go, and there do seem to be a lot of them around right now, this one is fairly engaging. On some levels it works better as horror than sci-fi. One is left with the impression that there is no point in the history of New Orleans that was anything other than a nightmarish ordeal. Even contemporary NOLA, garden district and all, is presented as a penumbral mind-trip.