Einstein and Quantum Theory
Albert Einstein famously rejected parts of the theory of quantum mechanics. His skepticism is understandable. The theory, after all, said that a single subatomic particle could occupy multiple places at the same time. A particle could move from one location to another without traversing the space between. And multiple particles that had previously interacted and then separated by vast distances, could somehow “know” what each other was up to. It didn’t seem to align with what scientists thought they knew.
.. Even though Einstein was never fully satisfied by it, quantum mechanics is now generally accepted as the fundamental way of the world.
.. One of the hard-to-get-your-head-around concepts at the heart of quantum mechanics is called superposition. Simplistically, superposition is the idea that something can be in multiple states at the same time. A single electron can have both up and down spin, a single photon can travel both this path and that one, and, conceptually, a luckless cat in a box can be both dead and alive. Until you check, that is. Once the electron’s spin is measured, or the photon is tracked, or the box lid is lifted, the system goes classical and assumes either one state or the other.
The lifting of the lid causes decoherence—another oddity of the quantum world. For a system to exist in a state of superposition it must not interact with its environment at all, including observers or scientific instruments. The loss of any information from the system to the environment—the lid being lifted and the condition of the cat becoming known—causes the system to decohere.
.. Particles that interact with one another enter into a strange relationship with one another. This relationship, known as entanglement, is preserved as long as the two particles remain sheltered from the rest of the environment, lest their entanglement decohere.