Universe

The Tetrian definition of the universe is "all space, time, matter, energy, and other as-yet-unknown constructs that are causally-interconnected by natural means". Since Tetrians are open to the possibility that at some future point, they may discover a way to interact with another universe, the "natural means" qualification allows for such a universe to still be considered separate and not simply amalgamated onto ours because of an artificial or unnatural causal relation between the two.

History
Tetrian physicists have not been able to determine how the universe came into existence, if it did at all. A proposal similar to the "Big Bang" theory was put forward at one point, but it was set aside since it could not be conclusively proved. Known facts about the history of the universe include that a type of energy known as microwave radiation first appeared approximately 13.7 billion Earth-years ago, and another known as light appeared a few hundred thousand Earth-years later.

Structure
The smallest known structures in the universe are quantum waves, which make up all subatomic particles including protons, neutrons, and electrons. These subatomic particles are the components of atoms, the building blocks of all matter. Atoms bond to form structures known as molecules. Most of the universe's molecular matter is contained in stars, giant spheres of gas that emit vast amounts of radiation through nuclear fusion reactions. Stars tend to group together in gravitationally-bound disks called galaxies, which in turn group together in galaxy clusters. The largest known structures in the universe are superclusters, collections of clusters that are gravitationally bound into spherical shapes and filamental strands.

Physical Laws
Physical phenomena in the universe can be observed to adhere to specific principles, and can be described through mathematical models; the discipline of physics deals with the nature of these principles. Circumstantial evidence has shown that the physical laws are generally consistent throughout the universe. However, many of these laws contain variables which are drastically skewed near the edges of the universe due to extreme curvature of spacetime in these regions, as explained by the Grand Theory Of Relativity.