Q: What exactly is the vacuum catastrophe and what effects does this have upon our understanding of the universe?
In a nutshell: if a particle definitely has zero energy, then it’s definitely not moving and its momentum is zero. That little bit of energy is called the “ground state energy” or just “ground energy”. These form the ground state energy density, which is more commonly known as the “zero point energy”. Looking at all the frequencies up to you find that the ground state energy density is proportional to (again, not obvious). As far as we know, there may be no upper limit, which would imply that the ground state energy is infinite.