Theory of meaning is a part of the disciplines of philosophy and psychology. 'Meaning' or ultimate truth is what we seek in our attempt to understand what is. Homo sapiens needs to know whatever there is to know. We have sex and life and birth and death and eating, drinking, defecating and pain and pleasure and rain and dry spells; we also have minds and desires and emotions and thoughts and angst, a pang, a worry, fostered by our ignorance. Like Socrates, we know that there is much we do not know. So . . . science, we have the scientific enterprise, the attempt to know in certainty what is out there, in here (inside ourselves) and everywhere, even beyond the universe. [What was before the big bang?]
Philosophy and psychology are partly unscientific disciplines in that they involve some guesswork and are content to leave hypothesis in place in their teaching as if it were fact. Science doesn't countenance this, but tries to turn hypothesis into fact with experiment. Nobody has ever discovered ego in the brain, yet it is an accepted psychological term. So anyway what do you think? Is there an ultimate truth behind the cosmos? Is human life meaningful in the cosmic scale?
Sunset
Addenda: Search for meaning is also part of literary study as stories are told to entertain and to provoke thought or answer questions about why or how came something. From olden myth to modern novel, storytelling has included the purpose of finding meaning, large and small. Religious studies too, traverse this terrain.