- "Yes, but quantum mechanics blows that out of the water. According to the Heisenberg Uncertainty Principle it is impossible to look at a sub-atomic particle and know both where it is and where it's going at the same time. The more accurately you fix its position, the more uncertain you make its velocity and vice versa. The best we can do is calculate probabilities."
- ―Samantha Carter to Jonas.[src]
Jonas's precognitive ability was relatively uncontrollable, giving him brief glimpses of the future that he was apparently unable to control or change, and it was also soon established that the visions were caused by excess brain mass that was turning into a tumour that would eventually kill him. However, by using Kelno'reem shortly before the tumour reached the point where it would have to be removed, Jonas was able to deliberately induce a specific vision of events taking place back on a planet controlled by Mot while he was at the SGC. Having seen an upcoming ambush that would capture O'Neill, Teal'c, and the rest of the SGC members on the planet, Jonas was able to advise the SGC to warn O'Neill, setting up a chain of events that prevented the ambush from taking place and led to Mot's death. (SG1: "Metamorphosis", "Prophecy")
The Seer, Davos, was also able to perceive the future through unknown means, and could also share his visions with others. Unlike with Jonas, his visions always came to pass even with his awareness of them, such as witnessing a Wraith attack that destroyed his village but managing to save his people, or witnessing the destruction of Atlantis while unaware that he was actually seeing the destruction of the Asuran copy of Atlantis (SGA: "The Seer", "This Mortal Coil").
- Precognition on Wikipedia