The Standard Model answers many of the questions about the structure and stability of matter with its six types of quarks, six types of leptons, and four forces. But the Standard Model is not complete; there are still many unanswered questions.

Why do we observe matter and almost no antimatter if we believe there is a symmetry between the two in the universe?

What is this "dark matter" that we can't see that has visible gravitational effects in the cosmos?

Why can't the Standard Model predict a particle's mass?

Are quarks and leptons actually fundamental, or made up of even more fundamental particles?

How does gravity fit into all of this?