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In physics, there are two main ways to model the universe. The first is the classical way. Classical models such as Newton’s laws of motion and Einstein’s theory of relativity assume that the properties of an object such as its position and motion are absolute. There are practical limits to how accurately we can measure an object’s path through space and time, but that’s on us. Nature knows their motion with infinite precision. Quantum models such as atomic physics assume that objects are governed by interactions. These interactions are probabilistic and indefinite. Even if we constrain an interaction to limited outcomes, we can never know the motion of an object with infinite precision, because nature doesn’t allow it.

These two theoretical worlds, the definite classical and indefinite quantum, each work extremely well. The classical for large, massive objects such as baseballs and planets, and the quantum for small, light objects such as atoms and molecules. But both of these approaches break down when we try to study massive but small things such as the interiors of black holes, or the observable universe in the earliest moments of the big bang. For that has all the properties of general relativity with all the properties of quantum theory. This theory is sometimes referred to as quantum gravity, but right now we don’t know it would work.

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