Entanglement is a concept in quantum mechanics where two or more particles become correlated in such a way that the state of one particle is immediately related to the state of the other particle, regardless of the distance between them. This correlation is often referred to as "spooky action at a distance."
It is important to note that entanglement does not allow for faster-than-light communication. While the correlation between entangled particles is instantaneous, it cannot be exploited to transmit information faster than the speed of light.
When two particles are entangled, their properties become linked, and any changes made to one particle will affect the other, no matter the separation between them. However, the actual information transfer or communication happens when the entangled particles are brought together and measured. This measurement process requires classical communication, which is subject to the speed of light limitation.
For example, let's say we have two entangled particles, one on Earth and another on a distant star. If we want to use them as a communication channel, we would need to separate them, send one to Earth and keep the other on the star. Any change made to the particle on Earth would instantaneously affect the one on the star. However, to transmit information, we would need to measure the state of the particle on Earth and then send that measurement result to the star using conventional methods, which are limited by the speed of light.
Therefore, entanglement cannot be used for faster-than-light communication or to create an interstellar telephone. It is a fascinating phenomenon with numerous applications in quantum information processing and quantum computing, but it does not violate the fundamental speed limit of the universe, which is the speed of light.