Warning! Spoilers for Synchronic below.
Synchronic's ending left viewers with a lot of questions, the most pressing of which is what happened to Steve (Anthony Mackie). Synchronic follows paramedics and lifelong friends Steve and Dennis (Jamie Dornan). And throughout the course of the film, the pair run into more and more gruesome accidents during their shifts, which they eventually learn are tied to a designer drug called Synchronic.
Dennis' teenage daughter Brianna goes missing early on in the film, with her disappearance tied to Synchronic. In order to help his grief-stricken friend, Steve vows to find Brianna. He learns that Synchronic allows those with an underdeveloped pineal gland, like teenagers, to literally travel back in time. Early in the movie, Steve discovers he has a brain tumor that led to his pineal gland remaining underdeveloped. Because of that, he is able to take the drug and travel back in time in hopes to find her.
Steve buys out New Orleans' remaining stash of Synchronic in order to perform experiments to help him find Brianna. Those experiments help him to better understand the drug, which leads him to believe that he can travel back and find Brianna. He's eventually successful and manages to find her and bring her back to her parents in the present. But that comes at a devastating price for Steve.
How Synchronic Works
Steve has a run-in with the chemist behind Synchronic who provides convenient exposition as to how the drug works. Dr. Kermani tells Steve that those who take Synchronic are able to see time as is, instead of linear. He uses a needle on a record player to explain this further; one can drop a needle anywhere on a record to play that particular section of music. There's no specific need to go in chronological order because the other parts of the record exist simultaneously. The doctor compares Synchronic to that needle - it allows a user to drop in at any specific moment in time.
Kermani is unsure why, but only users with a non-calcified, underdeveloped pineal gland can experience the effects of the drug. As Steve's cancerous brain tumor stopped his own pineal gland from calcifying, he is able to travel through time with Synchronic, unlike other adults. He learns that the drug physically transports him back in time for seven minutes. The movie never explains why, but the specific location that he stands in his living room dictates which era in time he travels back to. For example, one spot in his living room sends him to a swamp and the other sends him back to the ice age. Steve also discovers he can bring things back in time with him, as long as he is holding on to them when the pill kicks in. But the catch is that things may not return to the present in the same way. Steve uses all the information he gathers in his final mission to rescue Brianna.
What Happened to Brianna
After a series of trial and error, Steve realizes where he needs to go in order to find Brianna. In an earlier scene in Synchronic, Steve and Brianna talk on a boulder in a park during her little sister's birthday party. The boulder notably had "ALLWAYS" carved onto it. After explaining his experiments with Synchronic to Dennis, Steve thought Brianna may have carved that in the past as a message to the two of them. Steve took Synchronic at that exact spot and traveled back to a Civil War-era time period. He found Brianna relatively unharmed and managed to send her to the present in order to be reunited with her dad. Synchronic never reveals what happened to Brianna during or after being sent to the past. That's because, frankly, it doesn't matter. Synchronic is Steve's story; the movie is all about Steve coming to terms with his own mortality in order to see what really matters - saving Brianna helped him to get there.
Steve's Fate Explained
Brianna's safety came at a grave cost to Steve. When he reaches Brianna, she appears to be on a battle field in the middle of the Civil War. They nearly execute their plan to return safely to the present, but Steve is shot in the leg by a soldier who believes he is a slave. The soldier holds Steve at gunpoint while Brianna manages to escape. She is tearfully reunited with her dad when they turn around to see a ghostly version of Steve sitting on the boulder in present day. Steve and Dennis shake hands before Steve fades away into oblivion. Synchronic ends immediately after Steve disappears. While his fate is never spelled out, the movie strongly implies that he is stuck in the past. Not only does he have an aggressive cancer, but he is a Black man stuck in the time of slavery. Sadly, that means Steve likely won't last long in the past. But in his eyes, the sacrifice was worth it. Steve never had a wife or family of his own, so Dennis was like his family. Making sure his fractured family was reunited was more important to Steve than saving himself. So while the mission ultimately cost Steve his life, that outcome would have made it worth it to him.
Who Carved ALLWAYS onto the Boulder
When Steve finds Brianna in the past, he tells her that they found her message on the boulder. She has no clue what he is referring to, meaning that she didn't carve "ALLWAYS". As that location held significance to Steve during Synchronic, he is the most likely candidate for the carver. But ultimately, the identity of the carver doesn't matter — it's the message behind that word. Synchronic directors Aaron Moorhead and Justin Benson told Comic Book Movie that the specific message on the boulder appeared in Synchronic out of sheer coincidence. The pair always knew that some kind of message was going to be carved there. Originally, it was meant to "anything;" whichever word they chose was going to be misspelled in order to make it more memorable. Moorhead and Benson were walking around on location in New Orleans and happened to see a cafe called the All Ways Cafe. That inspired the message on the boulder.
The message represents the fluid way in which time moves. Synchronic deals with the infinite possibilities that time presents, specifically shown in the ways that Steve easily moved through time. Once someone moves beyond the understanding that time moves linearly, the world expands into infinite possibilities — anything is possible. That's exactly what "ALLWAYS" represents in the time travel movie. By sacrificing himself in order to save Brianna in the end of Synchronic, Steve gave back a world of infinite possibilities to his best friend.