Overview:
Trans-Dimensional Nuclear Alchemy (TDNA) is the process of using the energy generated from trans-dimensional travel to trigger a controlled nuclear explosion in which elements are purposefully transmuted and rearranged to form structures derived from the Alchemist's subconscious mind. Elements not used for the Alchemist's structure are affected in the same way elements are affected under normal conditions for a nuclear explosion. However, the leftover matter is left in lower dimensional space to avoid its effects on the third dimension.
We will now go into more detail on each step.
Step 1: Getting kicked out of the party.
The Universe as we know it in three dimensions isn't exactly real. It's more like a 3D projection of a 4D projection of a 5D projection and so on and so on until around 12 or more dimensions. These higher dimensions exist on smaller planes of existence and are very difficult (and maybe impossible) for lower-dimensional beings to enter. The more a lower dimensional being attempts to enter a higher dimensional space, the more that higher dimensional space pushes back. If the Alchemist pushes hard enough, they will be pushed back by an insanely powerful higher-dimensional kick.
Step 2: Falling backward.
Again, it's basically impossible to enter a higher dimensional space. However, it's relatively easy to enter lower dimensional spaces by comparison. Where higher dimensions are smaller, simpler, and more closed off; Lower dimensions are larger, more complicated, and more open. After being pushed backward by the higher-dimensional kick the Alchemist can reorient themselves and accelerate towards the smallest possible dimensional space. An important thing to clear up about dimensional spaces is that there is in fact space between them. These in-between spaces are called Grey Space. Whereas the spaces like the one we live in are called Goldilocks Space. After passing through the first dimension, the Alchemist can quickly approach zero-dimensional space.
Step 3: Stagger a bit.
When we refer to someone (or something) traveling between dimensions we're not talking about their physical body. It's far too dangerous for an Alchemist to travel so close to 0-D space with their actual body. However, certain types of waves can travel into lower dimensions with no effect on their form or composition. Kinetic Wavelengths are wavelengths emitted by biotic entities and can carry material from the third dimension into lower dimensions. As the wave and the material approach 0D space, they are compressed into a smaller space. Small and large are relative terms here. Again, lower dimensional space is bigger than higher dimensional space, but when higher dimensional material enters it has to be squished down/unfolded into lower dimensions. Think of a tennis ball-sized clay sphere. Normally it doesn't seem that big, but if you were to flatten it, then it takes up a lot more area at the expense of its volume. This is why even though the matter is being carried into a larger dimensional space, it begins to heat up due to increasing density. Eventually, this reaches a tipping point, where the material is almost as large as the universe. It's at this point just shy of zero dimensions that the wavelength stops accelerating and turns around once more.
Step 4: Regaining your balance.
On the way back to the third dimension, the Alchemist will once again pass through Grey Space. Grey Space is less defined than Goldilocks Space and is generally empty with a few exceptions. The physical laws within Goldilocks Spaces are more concrete and different for each one. These concrete physical laws go on to support the existence of observers whose observations of physical laws go on to make those physical laws more real. Think of a Utopian city that showcases its laws and the reasons behind them in crystal clarity. The inhabitants of the city gain an understanding of those laws and support for them grows. This leads to more people coming to the city and thus more support for the laws. This is how physics works in Goldilocks Spaces. In comparison, Grey Spaces operates on vague less definable laws that don't support the creation of observers. Due to the lack of observers to observe and support the Grey Space's physical laws, they become weaker and less effective. Like a shady or weak government distrusted by its inhabitants. So when the Alchemist enters a Grey Space it's very easy for them to break its physics. The Alchemist's subconscious mind can override the authority of the dimension and erect physical laws of their own. This level of control allows for the Alchemist to control the transmutation and arrangement of the material brought with them into lower dimensions. All of this happens within a couple of seconds, so anything the Alchemist forms has to be based on pure, simplified ideas of creation.
Step 5: Landing on your feet, and passing the buck.
Finally, the Alchemist's Kinetic Wavelength is brought back to the third dimension along with all the surrounding material taken with it. The transmutation and rearrangement of that matter in Grey Space is completed right before reentry into Goldilocks Space. However, there is pretty much always a tremendous amount of leftover material generated in the Alchemist's transmutation. To avoid causing a nuclear-like explosion the remaining energy and matter are left behind within the lower dimensional area to avoid killing the Alchemist. While it's primarily deposited in Grey Space, the material tends to move toward the more stable Goldilocks Spaces.
There's one main downside to the Alchemic process. Loss of Material.
There is inevitably some sort of loss of material to the lower dimensions. Even if the Alchemist doesn't care about dying in a nuclear explosion some of the material is fundamentally changed by its journey past the 1st dimension. It becomes trapped in these lower dimensional spaces just as we are blocked from entering higher dimensions.
After the discovery that energy turns into dark energy after being pulled into lower dimensions, the idea that the presence of the majority of the dark energy within our dimension was caused by higher dimensional Alchemists redirecting excess energy into lower dimensions rose to prominence. After close observations of the areas in and around super voids, higher dimensional wavelengths that popped in and out of existence were observed. Because of this, we have now been able to effectively map the locations where higher-dimensional civilizations have crossed over into our dimension.
Assuming that there isn't a way to undo the effects of TDNA, then the predictable result is that higher dimensions will eventually lose most of their materials to lower dimensions before collapsing into Grey Space. Additionally, any matter within the dimension will be pushed further and further apart until the entire space falls into a dark and chaotic state similar to the appearance of Grey Space. A state in which higher dimensions are empty and lower dimensions are filled with so much dark energy that even the smallest building blocks of reality are ripped apart. This assumed final form of the Universe has been called Black Space.