In the past days, the launch of a Chinese "Quantum Satellite" was widely reported in world news. Most articles seem to agree that the satellite is part of an experiment to demonstrate Quantum Key Distribution; however, China's state-owned news service CRI goes further than this by claiming:

The satellite's two year mission will be to develop "hack-proof" quantum communications allowing users to send messages securely and at speeds faster than light.

Does the QUESS satellite really have that capability?

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    unless there's recent discoveries I've not heard about, I would hazard a guess that the answer is that the media have misunderstood how quantum entanglement actually works. Aug 18, 2016 at 13:56
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    I think this would be a better fit on Physics. The answer there (as here) would be "No", but there you might get a better explanation of what that satellite does do. Aug 18, 2016 at 13:56
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    There already exist several question about the satellite on Physics and rather more on the question of superluminal communication using entanglement on, so don't post there with doing a careful search and some reading first. Aug 18, 2016 at 14:01
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    @BorderlineBaguette Yeah, pretty sure. Quantum entanglement is non-local, but not in a useful way that allows to break causality/communicate faster than light.
    – Bakuriu
    Aug 18, 2016 at 16:32
  • In other words - the observation says if you perform the same measurement on an entangled pair of particles, you always get the opposite results. One interpretation says there is some sort of quantum information that travels infinitely fast that ensures that, but the fact is, one side cannot determine anything about what the other side did, and the results are the same no matter in which order each side makes their observations - because general relativity says the order isn't even defined. Yes, getting a theory that includes both quantum mechanics and relativity as predictions will be tricky. Aug 19, 2016 at 19:10

1 Answer 1


It is considered impossible to transmit information faster than light. It has been never achieved in an experiment and the scientific consensus it is that it's impossible.

A good breakdown of the arguments is here.

In short, faster-than-light travel of information is equivalent to time travel, which is ripe with paradoxes.

More information on wikipedia

The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.

Superluminal communication is believed to be impossible because, in a Lorentz-invariant theory, it could be used to transmit information into the past. This contradicts causality and leads to logical paradoxes.

Wikipedia also mentions the no communication theorem which specifically applies to quantum information theory.

In physics, the no-communication theorem is a no-go theorem from quantum information theory which states that, during measurement of an entangled quantum state, it is not possible for one observer, by making a measurement of a subsystem of the total state, to communicate information to another observer. The theorem is important because, in quantum mechanics, quantum entanglement is an effect by which certain widely separated events can be correlated in ways that suggest the possibility of instantaneous communication.

In fact, this directly disproves the CRI article, which claims

The tiny particles act as if it's in two places at the same time - a phenomenon known as "superposition."


in practice it means that calculations can be carried out faster than light. [sic]

In other words, the article is confusing quantum entanglement ("spooky action at a distance", without communication of information), with quantum computing, which would allow us to calculate stuff really fast, but... not faster than light, which is meaningless.

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    caveat: light might be slowed down in other mediums, such as fiber. Thus communicating via air would be faster... but still at the speed of light.
    – Sklivvz
    Aug 18, 2016 at 17:37
  • Let us continue this discussion in chat.
    – Sklivvz
    Aug 19, 2016 at 15:44

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