Quantum Entanglement defines the relation between two particles separated by a distance. This distance could be as small as one centimeter or thousands of light years. The relation is defined by the interaction between these two particles. For example, when two particles are entangled, one particle will be observed spinning upward, and the other particle will be spinning downward. This means that they possess properties correlating each other.
When the particles are not entangled, they possess individual identities. When they become entangled, they lose their individual identities. Now, they have a single identity that defines both of them. The interesting phenomenon is that any change in one particle reflects the effect in the other particle irrespective of the distance between them. Moreover, once the entanglement has been established, it will stay there irrespective of the distance. The particle seems to know about the other particle, even if they are separated by a large distance.
“Spooky Action At A Distance”
Regarding quantum entanglement, Albert Einstein called it “Spooky Action At A Distance”. One of the hypothesis could be that if the entangled particles experience changes instantly, even when they are separated by light years, there’s must be some unknown force traveling faster than light that instigates the changes in properties. Einstein rejected this explanation, as according to him, nothing could travel faster than light. There must be some unknown “local forces” that affects the entangled properties of these particles. According to him, particles possess “real” properties that are visible when we observe them.
Bell’s Inequalities
If Einstein’s theory is to be believed, what behavior explains this phenomenon? Bell’s Inequality tries to answer this question. These are the equations that try to justify whether the quantum entanglement is associated with quantum theory or classical physics.
When you do the calculations assuming the Einstein’s theory of realism and local forces, Bell’s Inequality equations are satisfied. You have to assume that particles possess real properties and nothing can travel faster than light.
After doing the calculations, if you get a value lower than a certain number, Bell’s Inequalities are proved, and Einstein’s theory is also validated. But, most of the conducted experiments arrived at a value that was larger than that certain number. This states that either of the two assumptions is false.
Applications We See Today
Quantum Entanglement finds applications in various devices and services. It can be used in Quantum Clocks for ultimate precise values, encryption of data in the form of Quantum Key Distribution (QKD), super-powerful computers, modern microscopes, and navigational compasses. However, the technology is still to be developed in full before we could see such devices created. If all goes well, one day we could even see quantum teleportation becoming a reality. Some researchers also believe that understanding quantum entanglement will also help us know more about developing quantum computing.
Scientists are still understanding the quantum world more, and it’s something really exciting. While we cannot see such instances in the macro world, it’s one of the things that works out all the time in the atom and particle world.
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