Science › Quantum world
No faster-than-light messages
1980· Idea
ProvenTested many times; part of working physics.
Despite entanglement's instant correlations, it cannot be used to send any message or information faster than light.
See it on the Science map →How it works
Each side of an entangled pair sees purely random results. The correlation only shows up when both sides compare notes, and comparing needs an ordinary signal limited by light speed. Nothing done to one particle changes the odds seen at the other. So relativity's speed limit survives, and cause still comes before effect. This was proven formally in 1978–1980.
Why it matters
It is how quantum theory and relativity coexist. It rules out sci-fi 'quantum radios' and means quantum teleportation still needs a normal message.
Think of it like
Like two sealed envelopes with matching random numbers: opening one reveals the other, but nobody chooses what it says, so no news travels.
How we know
Proven mathematically from quantum theory (Eberhard 1978; Ghirardi, Rimini and Weber 1980). No experiment has ever produced a faster-than-light signal using entanglement.
Still a mystery
Why nature allows instant correlations yet forbids using them is not fully understood; some researchers try to derive quantum theory from this principle.
Connections (2)
▸Quantum entanglement is still bound by No faster-than-light messagesProven
The relationship
Measuring one entangled particle reveals the correlation, but each side's results look completely random on their own. Only by comparing results through an ordinary channel does the pattern appear. Since no choice on one side changes the odds seen on the other, entanglement carries no usable information faster than light.
How the link was found
Philippe Eberhard (1978) and Ghirardi, Rimini and Weber (1980) proved this 'no-communication theorem' from quantum theory.
Why it's proven
It is a mathematical theorem within quantum mechanics, and every experiment agrees, including teleportation demonstrations, which always require a normal signal.
Open questions and mysteries
Why nature permits correlations stronger than classical but not strong enough to signal is a puzzle; Popescu and Rohrlich showed in 1994 that stronger ones would not break relativity.
▸No faster-than-light messages protects Causality and light conesProven
The relationship
Entangled particles show linked results however far apart they are, which looks like instant influence. But each side's individual results are random and cannot be chosen, so no one can use entanglement to send a message. Because no information travels faster than light, cause still comes before effect for every observer, and relativity and quantum physics coexist.
How the link was found
Proven as the no-communication theorem by Philippe Eberhard (1978) and Ghirardi, Rimini and Weber (1980).
Why it's proven
It is a mathematical result within quantum theory, and every entanglement experiment, including the 2015 loophole-free Bell tests, shows correlations but no usable faster-than-light signal.
Open questions and mysteries
Why nature allows instant correlations but forbids instant messages is a deep puzzle, and interpretations of quantum physics disagree on what is really going on.