The concept of entanglement in quantum mechanics is indeed fascinating and can seem counterintuitive. However, it's important to clarify a few key points.
When two particles become entangled, their quantum states become correlated in such a way that the state of one particle cannot be described independently of the state of the other particle. This correlation persists even when the particles are physically separated, which is why entanglement is often referred to as exhibiting "spooky action at a distance."
One of the fundamental aspects of entanglement is that the exact state of each entangled particle is not determined until it is measured. Before measurement, the particles exist in a superposition of multiple states, and it is only through measurement that a specific outcome is obtained. This property is known as quantum indeterminacy.
The interesting aspect of entanglement is that the measurement of one particle instantaneously affects the state of the other particle, regardless of the physical distance between them. This phenomenon has been experimentally verified in numerous studies and is considered a fundamental feature of quantum mechanics.
The "spooky action at a distance" phrase, coined by Albert Einstein, Boris Podolsky, and Nathan Rosen in their 1935 paper, refers to this non-local influence. It implies that the outcome of a measurement on one particle is dependent on the measurement of the other particle, even if they are separated by large distances. This behavior is not explainable by classical physics, which is why it was initially viewed as paradoxical.
To date, no theory or experiment has shown that the entangled particles' outcomes were predetermined at the time of their entanglement. In fact, extensive experimental evidence supports the view that the outcomes are probabilistic and not determined until measured. Various experiments, including Bell tests, have demonstrated violations of Bell's inequalities, which indicate the presence of non-local correlations beyond what can be explained by classical physics.
While entanglement can be challenging to comprehend intuitively, it is an extensively studied and verified phenomenon within the framework of quantum mechanics. It remains an active area of research with practical applications in fields such as quantum computing and quantum communication.