Quantum entanglement is often described as faster than light because it allows for an instantaneous correlation between two or more particles, regardless of the distance separating them. This apparent "faster-than-light" behavior arises from the way entangled particles are connected on a quantum level.
When two particles become entangled, their quantum states become linked in such a way that the state of one particle cannot be described independently of the other. This means that measuring one particle's properties instantly provides information about the corresponding properties of the other particle, regardless of the spatial separation between them.
This seemingly instantaneous connection between entangled particles goes against our classical intuition and the limitations imposed by the theory of relativity, which states that no information or influence can travel faster than the speed of light. This is why Albert Einstein referred to quantum entanglement as "spooky action at a distance."
Einstein was troubled by the idea of non-locality in quantum mechanics, where a measurement on one particle could instantly affect another particle, regardless of the distance between them. He found it philosophically unsatisfying because it appeared to violate the principle of locality, which suggests that events should only be influenced by their immediate surroundings.
Einstein, along with Boris Podolsky and Nathan Rosen, proposed a thought experiment known as the Einstein-Podolsky-Rosen (EPR) paradox in 1935. The EPR paradox aimed to show the apparent incompleteness of quantum mechanics by highlighting what they considered to be its non-local nature. They argued that the theory must be missing some "hidden variables" that could explain the correlation between entangled particles without requiring instantaneous action at a distance.
However, subsequent experiments, particularly those conducted by physicist John Bell in the 1960s and 1970s, showed that the predictions of quantum mechanics were in conflict with any theory based on local hidden variables. Bell's inequalities and subsequent violations of these inequalities in experiments provided strong evidence in favor of the non-local nature of entanglement.
While quantum entanglement allows for seemingly faster-than-light correlations, it is important to note that it cannot be used to transmit information faster than the speed of light. The correlation between entangled particles cannot be exploited for faster-than-light communication, as it is not possible to control the outcome of the measurement on one particle to transmit meaningful information to the other.
So, while quantum entanglement may exhibit non-local correlations, it does not enable practical faster-than-light communication and remains a fascinating aspect of quantum physics that continues to be studied and explored.