Term Paper on Quantum Entanglements | Quantum Theories | Physics

Here is a term paper on quantum entanglements.

Quantum entanglement means multiple particles are linked together in a way that means the measurement of one particle’s quantum state controls the possible quantum states of the other particles within the linked group. As such, these particles act on one another, much as the friends of our younger selves did. Let’s look at this principle a little closer to understand what science has observed.

The Classic Quantum Entanglement Example:

The classic example of quantum entanglement is called the EPR Paradox. The EPR Paradox (or the Einstein-Podolsky-Rosen Paradox) is a thought experiment intended to exhibit the inherent paradox in the early formulations of quantum theory.

This thought experiment is among the best-known examples of Quantum entanglement. The paradox involves two particles that are entangled with each other according to quantum mechanics. Under the Copenhagen interpretation of quantum mechanics, each particle is independently in an uncertain state until it is measured, at which point the particle’s state becomes certain.

At that exact same moment, the other particle’s state also becomes certain. The reason that this is classified as a paradox is based on the fact that it appears the two particles must have communicated at speeds greater than the speed of light, a conflict with Einstein’s theory of relativity. This paradox was at the heart of a debate between Albert Einstein and Niels Bohr.

In the more popular Bohr formulation of the EPR Paradox, an unstable spin o particle decays into two different particles, Particle A and Particle B, both heading in opposite directions. Because the initial particle had spin o, the sum of the two new particle spins must equal zero.

If Particle A has spin +1/2, then Particle B must have spin -1/2 and vice versa in order to equal zero. According to the Copenhagen interpretation of quantum mechanics, until a measurement is made, neither particle would have a definite state. Both particles are in a superposition of possible states, with an equal probability of having positive or negative spin.

There are two key points within this paradox that make it troubling to scientists:

1. Quantum physics explanations state that until the moment of the measurement, the particles do not have a definite quantum spin, but instead are in a superposition of possible states.

2. Upon measuring the spin of Particle A, we know for sure the value we’ll get from measuring the spin of Particle B.

Another words, whatever Particle A’s quantum spin is set by a measurement, then Particle B must somehow instantly know what the spin is that it is supposed to take on. As Einstein pointed out, this is a clear violation of his theory of relativity.

Niels Bohr and others defended the standard Copenhagen interpretation of quantum mechanics, as supported by experimental evidence. The explanation is that the wave function which describes the superposition of possible quantum states exists at all points simultaneously.

The spin of Particle A and the spin of Particle B are not independent quantities, but are represented by the same term within the equations. The instant the measurement on Particle A is made, the entire wave function collapses into a single state. Therefore, no communication is occurring at the speed of light.

This relationship means that the two particles are entangled. When you measure the spin of Particle A, that measurement has an impact on the possible results you could get when measuring the spin of Particle B. This has been verified by Bell’s Theorem.

A fundamental property of quantum theory is that prior to the act of measurement, the particle does not have a definite state, but is in a superposition of all possible states. Imagine for a moment a cat in box with limited oxygen. Because the cat is unobserved, the cat is both dead and alive, since there is no way to definitively say what the cat’s state is. Yet, upon opening the box, the cat’s state is immediately defined, just as when a particle is measured and its position is clearly defined.

Though this interpretation does mean that the quantum state of every particle in the universe affects the wave function of every other particle, it does so in only mathematically. There is really no sort of experiment which could ever truly discover the effect in one place showing up in another.