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Quantum cosmology is a branch of theoretical physics that attempts to understand the universe on a quantum, rather than classical, scale. Though it may seem initially absurd to describe something as fundamentally large as the universe through a branch of physics that typically focuses on the world of the microscopic, quantum cosmology may actually help explain the major questions that lie at the heart of understanding the universe. One of the primary aims of quantum cosmology is to explain the state of the universe at the time of the Big Bang, since many properties of the universe may be explained if the origins of the system are understood.
To understand quantum cosmology, it is first crucial to have a basic grasp of quantum physics. Whereas classical physics considers the realm of larger objects, such as planets, solid objects, and anything that can be seen with the naked eye, quantum mechanics deals with the realm of atomic and subatomic particles and waves. In many cases, objects on a quantum scale behave according to rules that seem wholly different those for than macroscopic objects. Nevertheless, some physicists believe that the behavior of larger objects corresponds to the rules of quantum mechanics; thus large bodies, such as the universe, may be better understood if they can be described at a quantum level.
The key area of investigation in quantum cosmology is the behavior and state of the universe just following the Big Bang. Since origin-related questions cannot be answered through observation, the general means of developing theories is by looking at the current state of the universe, then extrapolating backward to the Big Bang to discover how the process started. Ideally, knowledge of the origins of the universe garnered through quantum cosmology will eventually allow scientists to predict, with a high degree of probability, the future of the universe.
Some physicists have embraced quantum cosmology because it allows a path around the enormous problem created by examining the origins of the universe with general physics. According to Stephen Hawking, among others, the universe likely began as a singularity, around which the laws of general physics are known to break down. To have a hope of accurately understanding the conditions following the Big Bang, quantum physics may be preferable because it is not known to be subject to a similar breakdown near a singularity.
Quantum cosmology is a relatively new branch of theoretical physics, dating only to the mid 20th century. As such a new field, it naturally includes far more questions than answers about the origins and behavior of the universe. Nevertheless, this fascinating field has attracted some of the brightest minds in physics, and seems poised to allow significant discoveries in the coming centuries.