Entanglement is the strange and beautiful property of certain quantum particles to become so deeply linked that they share the same existence. According to quantum theory, that link should be maintained whatever the distance between the particles, whether the width of an atom or the diameter of the universe.

This led Einstein to claim that the instantaneous effects of entanglement would lead to “spooky action-at-a-distance” in violation of special relativity which prevents faster-than-light signals.

Nobody knows how the different predictions of relativity and quantum mechanics can be resolved. However, entanglement has been measured in numerous experiments over relatively short distances on Earth. The tests involve two entangled particles, photons say, being sent to distant experimenters who then perform measurements on them.

In every one of these tests, the results agree entirely with the predictions of quantum mechanics. And yet naysayers continue to unearth loopholes that allow them to claim that there is a way in which the results are fixed, perhaps because quantum mechanics works only only over the short distances that can be exploited on Earth or by the existence some kind of hidden variable that determines in advance how the particles will behave when they are separated.

There is one way to settle the matter for sure: send entangled photons to two orbiting astronauts on board different spacecraft with large relative velocities. That leaves no room for hidden variable theories or any other fix because the peculiarities of special relativity allow both astronauts to claim the measurement on their photon was performed before the other.

Today Anton Zeilinger from the University of Vienna in Austria, says he wants to try just such an experiment and has put together an impressive international team to design and promote idea. The team has submitted its proposal, called Space-QUEST, to the European Space Agency in the hope that one end of the experiment could hosted on the Columbus module, Europe’s orbiting laboratory attached to the International Space Station.

The other observer need only be on the ground since Zeilinger has already proven that single photons can be bounced off orbiting satellites and detected on the ground.

That should please mission planners for the International Space Station which has yet to host a single significant experiment in space. Zeilinger’s Space-QUEST experiment looks like a genuine attempt to push the envelope of physics. The quicker they get it into orbit, the better.

Ref: arxiv.org/abs/0806.0945: Space-QUEST: Experiments with Quantum Entanglement in Space