While quantum theory allows for the concept of particles, such as electrons, to exhibit behaviors such as superposition and being in multiple states simultaneously, this phenomenon does not extend to macroscopic objects or complex systems like humans.
The principle of superposition in quantum mechanics describes how particles can exist in multiple states or locations simultaneously. However, this behavior is only observed at the microscopic level, specifically in the realm of particles that exhibit wave-particle duality, such as electrons and photons.
Macroscopic objects, including humans, are made up of an enormous number of particles and are subject to different physical principles that dominate at larger scales. These objects do not exhibit wave-particle duality in the same way as individual particles. The behavior of macroscopic objects is governed by classical physics, which does not incorporate the same quantum phenomena.
Additionally, macroscopic systems are highly susceptible to environmental interactions and decoherence. Interactions with the surrounding environment cause the delicate quantum states of particles to rapidly "collapse" into definite states. This process, known as decoherence, effectively prevents macroscopic objects from maintaining superposition or existing in multiple places simultaneously.
In summary, while quantum theory allows for the existence of superposition at the microscopic level, the principles of classical physics govern the behavior of macroscopic objects, including humans, and prevent them from being in two places at the same time.