This is a post.
Let's start with a brief, somewhat simplified explanation of the ten dimensions of string theory. Obviously we have the first, second, and third spatial dimensions that we perceive the world in. But then we have the fourth, which represents time as a single line spanning from past to present. Because we are three-dimensional beings, we can only see little cross-sections of the fourth dimension as we progress through our lives, and can't see the entirety of the dimension at one time (as we can with the lower three dimensions).
If we think of time as a tree, with different "points of causality" at the base branching off into countless outcomes, the fourth dimension is only a single path. It traces one timeline, one set of outcomes - the one we know as reality. The fifth dimension, however, encompasses the entire tree, spanning all outcomes emerging from a single cause. If one were able to traverse the fifth dimension, you could cross multiple timelines similar to yours, and travel backward and forward in each "parallel universe."
This is where the Vex come in. Like guardians (more on that later), they are higher dimensional beings, capable of crossing the fourth and fifth dimensions at will. They are attempting to write themselves into time itself, making themselves a part of the universe. The Vex are able to do this by building multi-dimensional constructs like those found on Venus (Vault of Glass) in the far past, effectively incorporating themselves into history. This explains the Vex's emphasis on construction, and the fact that they clearly aren't built for all-out war. Take the Cyclops for example - it malfunctions frequently when shot at. And Vex weapons function more as energy terminals than actual combat tools.
For example, when we try to kill Atheon in the Vault, we are "teleported" to a different location at a different time. These are actually different timelines, orthogonal to our own (a trait characteristic of fifth-dimensional spacetime), where the Vex have established a firm foothold in reality. The time gates we use to escape pull us through the fifth dimension, and even though we don't perceive it, we are actually jumping THROUGH time.
Supercomputers like Gorgons and Oracles can literally write us out of existence by bending the fourth dimension, via the fifth, such that reality takes a different course than expected. With the ability to bend spacetime as they see fit, they are almost invincible, capable of simulating, then choosing and executing a timeline out of the near-infinity available in which the Vex experience a favorable future.
However, the Vex are not infallible. Once again, imagining time as a tree, the fifth dimension represents a single causal event with multiple outcomes. The sixth, however, represents an infinity of causal events, or an infinite amount of trees. Both the light and the darkness are manifest in the universe, and thus are ten-dimensional (encompassing the sixth).
We Guardians are sixth-dimensional, allowing us to defy a pre-ordained chain of causality and "make our own fate." By manipulating the light, we make ourselves invulnerable to mere fifth-dimensional simulation. With the right strategy, we are able to completely bend Vex simulation to our will by inserting a different causal event in their chain, screwing with their simulations and giving us the upper hand. This also explains why the Vex are unable to simulate Oryx by the time he's taken in the Worms and the Darkness - he too is sixth-dimensional, and can defy causality completely.
Note: In the Paradox mission, the Vex predict their own annihilation because they can't stand up to a sixth dimensional being like Oryx or his Taken. They cannot simulate a higher dimensional being, therefore, they cannot predict what will happen and are put at a huge disadvantage.
Guardians can throw balls of Void and create guns out of thin air because we are not bound by mere law. Neither is Oryx. We can unconsciously picture a different chain of events, a different chain of causality, and shape the universe as we see fit. That's why we can destroy Time's Conflux, and triumph over the impossibility of the Vault. Thanks for reading all of that. I'll probably edit this post quite a bit, as this theory explains...a lot about how the Destiny universe works. Let me know what you guys think in the comments.
-Totally The Architects