Quantum entanglement: faster-than-light communication? ⚡

Quantum entanglement remains one of the most mysterious phenomena in modern physics. It seems to allow particles to communicate instantaneously, thus defying the speed of light.


In quantum mechanics, a particle is not a precise point but rather described by a wave function, a cloud of probabilities indicating where we might find the particle upon measurement. When two particles share the same quantum state, they are said to be entangled.

Entanglement means that measuring a property of one particle immediately informs us about the property of the other. For example, if two electrons are entangled and one is observed with a 'spin up' relative to a given axis (which can be likened to a binary '1'), the other will necessarily be observed with a 'spin down' (a binary '0'), regardless of the distance separating them. This correlation has no notion of temporality.

Can we then conclude that we have successfully transmitted a binary '0' to the distant particle, instantaneously?

This apparent "instantaneous communication" is not actual communication and does not violate the theory of relativity. Indeed, although the states of the particles are linked, a local measurement on one of the particles is necessary to reveal the state of each particle. It is thus not possible to determine whether a '0' or a '1' is present on one or the other of the particles before observing one of them.

Moreover, the value '0' or '1' is not predetermined before the measurement; it is the measurement itself that determines the state of the particle. This phenomenon was confirmed by Alain Aspect's experiments in the 1980s, showing that the information was not already present before the measurement (absence of "hidden variables"). Quantum entanglement therefore does not allow for the transmission of information faster than light. It rather shows a non-local connection between particles, which remains a subject of intense research in quantum physics.

The implications of quantum entanglement are vast, ranging from quantum cryptography to quantum computing. Understanding this phenomenon could open new technological and scientific pathways.

Despite the advances, quantum entanglement continues to raise fundamental questions about the nature of reality and the limits of our understanding of the Universe.