When Michael Burnham returned to her ship in Star Trek: Discovery season 3, she provided new details about the Burn, which only deepens the mystery.
Warning: SPOILERS for Star Trek: Discovery season 3, episode 3, "People of Earth".
Star Trek:Discovery has offered tantalizing new information about the Burn that completely altered the galaxy of the 32nd century. The Burn is the central mystery of Star Trek: Discovery season 3 and finding out what caused it is one of the missions of Commander Michael Burnham (Sonequa Martin-Green), who has reunited with the U.S.S. Discovery one year after she arrived in the year 3188.
Michael and the Discovery saved all organic life in the galaxy when they left their proper 23rd century time period and jumped 930 years into the future. But while Burnham did ensure life would continue, she didn't expect to arrive in a different and darker reality where the United Federation of Planets has collapsed and the galaxy is fractured and isolated. The cause of the Alpha and Beta Quadrants' new status quo was the Burn, a cataclysmic event sometime between 3068-3088 that affected the galaxy's dilithium, which is the heart and power source of every warp-capable starship. The Burn caused the destruction of thousands of starships and killed everyone aboard. Even starbases and outposts were affected and, without warp-capable starships and viable means of long-range communications, the Federation broke apart.
With the help of Cleveland "Book" Booker (David Ajala), Burnham became a courier and spent the next year delivering goods in exchange for bits of dilithium from the Orions and Andorians, who united to take control of the dwindling supplies of crystals that still remained. Michael, unfortunately, learned little about what caused the Burn or why, but she did glean more crucial information that she shared with her crewmates of the Discovery when she returned to the starship in 3189.
Dilithium Became Scarce 200 Years Before The Burn
Michael discovered that about a century before the Burn happened, the galaxy's dilithium supply was already dwindling. As Burnham told Captain Saru (Doug Jones) and the Discovery's bridge crew, "700 years after we left, dilithium supplies dried up". This means that in the 2900s, the planets that the galaxy relied upon and mined for their dilithium stopped producing the vital element.
A handful of worlds were known to be sources of dilithium, including Coridan, Corvan II, Troyius, the Halkan homeworld, Rura Penthe, Remus (which was destroyed along with Romulus by the supernova of the 2380s), and Xahea. It's unknown if an unnatural event occurred on those worlds that affected their dilithium production or if a thousand years of relentless mining for a galaxy that insatiably needed the element to power thousands upon thousands of starships simply overwhelmed what the dilithium-producing planets could provide. In either case, dilithium was already becoming a scarce commodity a hundred years before the Burn took place.
The Federation Tried & Failed To Create Alternative Warp Drive Designs
Naturally, the Federation was aware of the problem and tried to solve it - but they failed. According to Burnham, the Federation's best scientific minds attempted to invent alternative warp drive designs but "none proved reliable." So, there was no alternative that could substitute for the matter-antimatter containment warp cores that were part of every starship, or, at least, nothing that could equal the results of dilithium-powered warp drives.
Curiously, it's not clear what happened to the Federation's technology for recrystallizing dilithium after the element had been drained. Me Hani Ika Hali Ka Po (Yadira Guevara-Prip), the Queen of Xahea who befriended Ensign Sylvia Tilly (Mary Wiseman) in Star Trek: Discovery season 2, invented an incubator to recrystallize dilithium, and her technology is now used aboard the U.S.S. Discovery. Further, by the 2280s, the Federation also had the means to recrystallize dilithium, and Spock (Leonard Nimoy) and Scotty (James Doohan) even innovated a means to revive inert dilithium using plutonium collected from a nuclear vessel when they time traveled to 1986 in Star Trek IV: The Voyage Home.
In the TNG era, Starfleet had the technology to recrystallize dilithium while still in its warp core. And in 3188, Book asked Michael if she could whip up a new dilithium recrystallizer when they first met, so the technology is still available in the 32nd century. Yet dilithium recrystallization somehow wasn't a viable option to service the multitude of starships in the entire galaxy, which lacked a consistent source of new dilithium after the 2900s.
The Burn Happened Simultaneously Across The Galaxy
Michael also learned more of what the Burn actually did to starships when it happened: "In an instant, all dilithium went inert." This happened everywhere in the galaxy simultaneously and "any ship with an active warp core detonated." The term "active warp core" is confusing, however; Captain Saru (Doug Jones) took it to mean that a starship had to be at warp to explode when the Burn hit. However, that contradicts Michael's belief that every starship detonated simultaneously since not every vessel could have been traveling at warp the exact instance the Burn happened.
It's possible that starships didn't necessarily need to be traveling at warp at the moment the Burn took place, just that their warp core had to be "active" - which would essentially be every starship in service. This would also mean starships docked in starbases that had active warp cores also exploded, which would explain why Federation space stations were also destroyed. Regardless, the death toll was in the millions.
Was The Burn Manmade?
The logistics of the Burn would seem to be improbable. As Michael described it, "devastation flashed in an instant across all known space." But as Lt. Paul Stamets (Anthony Rapp) pointed out, "That's impossible. Nothing could affect all dilithium all at once." So, something managed to render every piece of dilithium inert everywhere at the exact same time. Over a hundred years later, still "no one knows" what caused the Burn or how it happened, and this is because without long-range sensors and warp-capable ships - or the Federation - the brilliant minds who might have been able to find answers were cut off from each other or the means to study and pursue those answers. And by 3189, only a few long-lived species are still alive who actually remember the Burn while everyone else grew up in a post-Burn reality.
But if the possibility of the Burn as a natural, one-in-a-million phenomena was eliminated then the remaining answer would be that the Burn was a man-made event caused by someone or something. This becomes a compelling chapter in the story because it would mean the Burn happened by design and there was (or is) a culprit somewhere in the galaxy.
On Instagram, the @startreklogs feed features the private logs of Star Trek: Discovery's characters after each season 3 episode. In Emperor Philippa Georgiou's (Michelle Yeoh) log after Star Trek: Discovery episode 2, "Far From Home", the former ruler of the Mirror Universe mused that "Whoever was responsible may be cunning enough to keep me from being bored here... I can only hope they are still alive... a worthy adversary if there ever was one..." Given Georgiou's instincts and the fact that she was also an agent of Section 31, this could be a clue that there was a villain behind the Burn and that Star Trek: Discovery season 3 could eventually lead right to a mastermind who literally rewrote the story of Star Trek's future.