A physics major typically includes quantum mechanics courses, as they are essential for understanding various fields within physics, including cosmology. Most undergraduate programs require at least one semester of quantum mechanics. While it is possible to enroll in a PhD program with just a bachelor's degree, students will still need to complete master's level coursework, although not all programs confer a master's degree. The requirements for entering a PhD program can vary significantly by country; in the US, a bachelor's degree is generally sufficient, but other educational systems may have different prerequisites. Understanding quantum mechanics is crucial for many areas of physics, including observational cosmology, which relies on quantum principles to interpret spectra.