Quantum mechanics, which recently turned 100 years old, ranks as the most successful theory in the history of physics. Yet on a fundamental level, we still don’t understand what quantum mechanics is saying about how the world works.
Any standard textbook will tell you that the dynamics of quantum mechanics are based on two axioms—mathematical rules that allow us to theoretically compute the outcome of an experiment. Surprisingly, these two axioms are self-contradictory. They present one of nature’s deepest mysteries: the quantum measurement problem—the fact that the quantum rules describing an object to be measured don’t seem to apply to the object doing the measuring. This disturbing contradiction suggests that different physical laws apply to the observer and the observed.
One proposal to resolve the paradox is the Many Worlds interpretation of quantum mechanics. Many Worlds demands that our universe actually be a multiverse. The idea is often considered fringe, even silly. Lately, however, experimental progress has been changing the situation. Scientists have been able to measure quantum effects in larger and more complex systems and over great distances, blurring the line once thought to separate the scale of observer and observed. These signs that quantum rules might cross over into the macroscopic realm are making many physicists reconsider Many Worlds. But what does this notion really mean for the universe we call home?
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