No, not all quantum mechanical objects have to be in a superposition of states. The concept of superposition is a fundamental aspect of quantum mechanics, but it does not apply universally to all quantum systems. Whether or not a system is in a superposition depends on various factors, such as the preparation of the system and the specific observable being measured.
In quantum mechanics, superposition refers to the ability of a quantum system to exist in multiple states simultaneously. This means that the system can be in a combination of different eigenstates of a given observable, with each eigenstate associated with a certain probability amplitude. When a measurement is made on a superposed system, it collapses into one of the eigenstates with a corresponding probability determined by the amplitudes.
However, not all quantum systems are prepared or observed in a way that allows them to exhibit superposition. For example, if a quantum system is prepared in a well-defined eigenstate of an observable, such as a particle in a definite position or a definite energy state, it will not exhibit superposition unless additional interactions or measurements are introduced.
Furthermore, certain macroscopic objects, like everyday objects in our classical world, are typically described using classical physics because the effects of quantum behavior are negligible at large scales. While everything in the universe is ultimately governed by quantum mechanics, the superposition effects become negligible and are not observable at macroscopic scales due to a process called decoherence, which leads to the "classical" behavior we commonly experience.
In summary, while superposition is a fundamental concept in quantum mechanics, not all quantum objects or systems are necessarily in a superposition of states. The presence of superposition depends on the preparation and measurement conditions, as well as the scale of the system being considered.