There are lots of theories existing at any given time (in time). Often they are disproven. Sometimes they convey an image of authority to the people that advocate the most popular theory.
A Higgs field and an inflaton that arises about simultaneously splitting off from an unstable field at T=0 from a singularity is a popular theory. It is thought to have existed carefully balanced in a vacuum balanced between positive and negative energy. After the expansion of all that energy in the Higgs field and a win for matter over anti-matter the sub-luminal mass of the Universe continued along with gravity, stellar synthesis and biological evolution. People tend to accept those general parameters as a valid theory of the origin of everything in this Universe back to a singularity.
Then there are meta-theories that have the initial energy before expansion as pure spirit- in the mind of God as it were, with the expansion pre-determined in accordance with His will. Some people have tossed blind random chance into a meta-theory to explain the existence of life, and have postulated a profusion of Universes existing in a Multiverse along the lines of Everett’s every possible universe that could exist does exist principal. That is a good approach for a defining theory that allows for the Universe to be in several forms with several explanations for its existence depending upon where one starts or orients the beginning.
If mass and energy are at the most fundamental level secondary phenomena of mathematical or spiritual construction made by a thinking being, or alternatively is a Super-string theory supports the profusion of Universes, or if the Universes are something like a static field with mind switching between the appropriate Universe that corresponds to what the sentient, primary being thinks (a phenomenon of mind) in a deterministic field with free will determining the destination of the traveler through the moral or soteriological facts, or if one appeals to quantum simulation theory with the idea of origin coinciding with some sort of Schrodinger wave function collapse into self-awareness the definition of the origin of the Universe might appear equally valid to the sentient observer even tested with some measure of falsifiability.
Therefor a definition of the origin of the Universe these days tends to be a process. The genesis of being and nothingness has an in God we trust element to it for those of us that regard an omniscient being and Creator of every possible Universe at some stage of the way, and a logical point to purpose and utility- again a process.
Language itself is a process of associating words and objects, meanings and ideas with definitions and objects each changing in the temporal field of common human experience. God, alternatively, is constant forever and before any temporal field that he manifests.