In Oliver Stone's "The Untold History of the United States", he claims that there is actual evidence that the atomic bombs were not the reason the Japanese surrendered.
This is obviously a theory we've all heard, but he does not go on to claim it was the Soviet invasion either. His claim is that the Japanese offered to surrender if their emperor wasn't deposed. The US denied this, bombed them, and then offered them a surrender at that exact deal they had originally wanted, meaning the emperor wasn't deposed in the end.
I had personally never heard anything like this before anywhere. If true, it seems like a piece of information that would settle this long debate once and for all. If what he said was true to a "T", we would have had no reason to drop the bombs at all.
So is this factually accurate? Or is there even evidence that suggests anything like this is true?
If you search on here for "Hasegawa thesis" and "Untold History of the United States" you'll find a lot of threads that discuss this. E.g. here or here or here.
Short version is: the end of World War II was complicated and most scholars think it was probably a mixture of factors and circumstances. The Stone version cherry picks some aspects of this out, and makes it look more straightforward than it was. The "it was the atomic bombs and that was that" story that most people know isn't correct either.
A more succinct version of the above would be: the US knew Japan was hung up on the Emperor question; some members of the Japanese high command (including the Emperor) were searching for diplomatic ends to the war; the US deliberately chose to not give the Japanese the reassurances they knew it wanted; the atomic bomb may have had some impact on Japanese thinking but the Soviet invasion of Manchuria seems to have had a lot of impact as well; the Japanese offered a conditional surrender, the US rejected it; the Japanese then (a few days later) offered unconditional surrender, and the war ended; in the end, the US Occupation decided to give Japan the conditions it had originally wanted anyway, but that decision was made a lot later.
As for whether the bombs were "needed" — it's unclear. It depends on how much weight you give them relative to the other factors. There's no easy way to know this. Even Hasegawa, whose book has the most evidence for the "Soviet invasion was a big deal" thesis thinks that the bombs were part of the surrender decision. But one can speculate about what would have happened without them; there's no easy way to disentangle the events, though, so it's hard to know.