String theory is an attempt to explain the phenomena of current physics as emergent behavior of some underlying objects. The details are beyond my understanding of physics.

> How does the Higgs boson come into play here? Is it merely hypothetical or has it been widely accepted as something that exists?

The Higgs was hypothetical for a long time, but was observed by the LHC in 2012. It's now generally accepted that it exists.

> What I can remmeber, it was the particle responsible for granting all sorts of matter their mass.

More or less, yes. Specifically, it's (among other things) why the W and Z bosons have mass but the photon doesn't.

Recall that mass and energy are two different expressions of the same thing. Potential energy stored in one of the physical fields underlying the universe is mass, and in fact about 99% of the mass of the objects around you comes from the potential energy of quark-quark attraction, not in the bare mass of the quarks themselves. The Higgs mechanism gives some particles mass by effectively "tangling" the Higgs field (one of the underlying physical fields) with the field underlying the weak interaction (one of the four fundamental physical forces) in such a way that neither of them can settle into the zero-energy state that they "want" to settle into.

Again, the details here are extremely complicated.

> Doing some diving into wikipedia there are tons of things like gravitons and fermions and whatnot that make it seem like it's a massive iceberg out there. My question is, what is the most widely accepted theory for quantum mechanics and what subatomic particles have been proved to actually exist?

The basic accepted theory of particle physics today is the Standard Model, which contains the following particles:

• Six quarks, two of which (the "up" and "down" quark, no relation to everyday directions) make up protons (two up, one down) and neutrons (one up, two down) respectively. The others (the charm, strange, bottom, and top quarks) are unstable under normal conditions and are only observed briefly in particle accelerators.

• Six leptons: the electron and its two heavier cousins, and the three types of neutrino. The muon and tau (the two heavier cousins of the electron) are unstable. The three neutrinos are sort of stable, but they actually oscillate (change from one type of neutrino to another) as they travel. Neutrinos are rarely important to everyday events because they interact very weakly with the matter humans are made of.

• The bosons, particles that carry the underlying physical forces of the Universe. These are the photon (carries electromagnetism), the W+, W-, and Z bosons (which carry the weak interaction), the eight types of gluon (which carry the strong interaction), the Higgs boson (which carries the Higgs field, or more properly one component of it), and the still-unobserved graviton (which carries gravity).

Of these, only the graviton has not been observed.

The Standard Model is, however, known to be incomplete. It can't explain some physical phenomena, and it's incompatible with relativity in conditions where both gravity and quantum mechanics become relevant. Theories like string theory are attempts to expand the standard model in ways that cover these gaps.

> Is it theoretically possible to split a subatomic particle? If so, how much energy would it release?

Subatomic, sure, but not fundamental. The only subatomic particles currently known not to be fundamental are protons and neutrons, and you could in principle split them apart...

...but the properties of the strong interaction make the behavior of such a split a bit weird. Instead of seeing free quarks, you'd see new protons and neutrons!

The reason is that the strong interaction (in its full form, not to be confused with the residual strong force that holds the nuclei of atoms together) doesn't fall off with distance the way that electromagnetism or gravity do. The potential energy of two separated charges in electromagnetism, for example, is -1/r, but the potential energy of two separated strong-interacting particles is, roughly, just r. So once quarks get very far apart, it's actually energetically-favorable to just spontaneously produce new quarks from the void to bind them up into protons and neutrons again.

In any case, protons and neutrons are very tightly bound, so you wouldn't release energy by splitting them (you'd have to input a huge amount of energy). The same is true of nuclei, by the way, it's just that sometimes splitting a nucleus results in more tightly bound nuclei.

> Is it true that many subatomic particles are believed to interact with parallel universes (like basically exist in both simultanoeusly)?

This is speculative and depends on your interpretation of quantum mechanics. Unless you're doing the math, this sort of question is more "whooaa duuuuuude" stoner speculation than science.