First of all, English is not my native language, so I hope, that text below is readable. Please help me to correct my “translation mistakes”. And please fell free to share this text on other forums (I didn’t find many Half-life active forums. Maybe you find them? But write to this topic, if you shared this post somewhere). It is very sad, that Marc Laidlaw retired, I wanted to share my thoughts with him. But anyway… Scientific basis of Half-Life universe I must say, I'm not professional physicist. Moreover, I understand that Half-life lore writers could just use scientific terms for "game cleverness", without understanding them. But it is not a reason not to speculate about the game, isn’t it? Physics in Half-Life, apparently assumes the correctness of string theory, at least, Calabi-Yau space – is term from that theory, moreover Mossman tells us that combine "teleport" based on string technologies. Therefore, in the future, we will be based on string theory, more precisely, in its new "branch" - M-theory. The "world" of M-theory consists of different dimension branes. String (one-dimensional object) - 1-brane, the membrane - 2-brane, our three-dimensional universe - 3-brane. It is assumed the presence of other 3-branes (in fact, other universes), placed in the space of higher dimensions (there are 11 dimensions including time in M-theory). Where are they located? We can observe only three-dimensional objects, we "cling" to our 3-brane. All our senses perceive only what is happening on our 3-brane. Additional dimensions are very close to us (the distance to them, in fact, minimal - the Planck length), but we just can’t observe them. What is Xen? As I mentioned, there may be other 3-branes. Moreover, the physics laws in these universes can be different from our physics laws. Xen is unlikely in our universe. Xen could be regarded as a conglomeration of asteroids orbiting the gas giant (the green slime at the Xen bottom is gas giant’s atmosphere). But this is unlikely. Objects in orbit are weightless, but Xen “islands” are not weightless. If they held near planet, for example, by Xen crystals, they must feel horrible gas giant’s gravitation, but in Xen gravitation even weaker, than on Earth. And it is hardly possible to describe "sky" in Xen in terms of our universe. Most likely, Xen is just a "neighbour" 3-brane. Our brane and other branes including Zen, separated by a space of higher dimensions. This can be represented as two sheets of paper (2-dimensional objects), separated by a space of higher dimension – third dimension. If we want to move some body from one sheet of paper to another it is necessary to give to that body some energy (momentum) - "tear" the body from a sheet and move in 3-dimensional space to another sheet (for two-dimensional "residents" in the sheets our three-dimensional space will be hyperspace - a space of higher dimension). How "Teleports" work. To get from one point to another in our brane, we can move inside the brane as we do in everyday life. But in this case there is a limit - the speed of light. But if you travel through space of higher dimensions - you can work around this limit. For example, if we want to pass from point A to point B on a two-dimensional sheet, there is the maximum speed and minimum travel time (if the object is moving at the speed of light). But if you move in the third dimension, it is possible to reach the destination quicker - bent sheet approaching the point in the third dimension and move in three dimensions, instead of two. Visually shown here:https://upload.wikimedia.org/wikipedia/commons/7/7b/Wormhole-demo.png So back to our three-dimensional world. Traveling in “higher” dimensions – fourth, fifth etc (let’s call them simply - hyperspace), we can reach our destination inside our 3-brane faster. And "teleports" are simply doing that. They "tear off" the object of the three-dimensional brane (give to it some energy – initial momentum), moving it into hyperspace, and then body “fall” to our brane with other coordinates. This is simple, like you take a stone and throw it. Why I write "teleport" instead than teleport? This device isn’t teleport, it is likely hyperdrive (it doesn’t move the object in hyperspace instantly. Travel time depends on the initial momentum, which we give to the object). Combine "Teleport" and Rebel one differs by only one thing - the amount of energy that must be applied to the object. Rebel "teleport" also uses our neighbour 3-brane - Xen, like sling (very much like space probe, executing gravity assist maneuver around some planet), so we can give much smaller initial energy (momentum) to the object in “teleport”. Combine “teleport” doesn’t use Xen and move objects simply through hyperspace. I wrote, that voyages in hyperspace takes time depends on initial teleported body energy (momentum). You can give to the object smaller initial momentum and moving in hyperspace will be slower. In fact, the slow "teleport" - this is it. Apparently, the explosion of combine “teleport” take some energy from teleportation process, which resulted in a week delay in Gordon arrival . Stasis - veeeeery slow "teleport" with very low initial momentum giving to the object. The only difference - it does not just move the object by 3-brane through hyperspace, it also moves the object in the time dimension, not only with respect to the 3-brane (our universe), but also with respect to the object time.