European Researchers Propose Quantum Network Between Earth and ISS 209
New kalalau_kane writes with this tidbit from Extreme Tech: "A group of European researchers has proposed the largest quantum network yet: Between Earth and the International Space Station. Such a network would see entangled photons transmitted over a distance of 250 miles — two or three times greater than previous quantum communication experiments. Not only will this be the first quantum experiment in space, but it will allow the scientists to see if entanglement really is instantaneous over long distances, and whether it's affected by gravity."
The proposal (licensed CC BY).
10,000 times faster than the speed of light? (Score:5, Interesting)
I don't get it. I thought it was instantaneous and that number is just a crap number based on distance.
Oooh gravity experiment (Score:5, Interesting)
Re:Only 250 miles to the ISS (Score:5, Interesting)
I doubt the extra 400km you get from doing it on the ISS is the point, because picking two points on the earth's surface that are opposite each other would be 12740km apart so the extra 3% is hardly significant.
Probably of more interest is that the ISS is doing an average speed of around 27,800 km/h which is sufficient for relativistic effects to noticeably come into play. In addition the ISS is in a different frame of reference to anything on the ground. These factors are much more interesting than the extra distance.
Re:Always a letdown. (Score:5, Interesting)
Because the universe doesn't seem to like causation violation, so all its operating principles preclude faster-than-light (which, in Einsteinian relativity, is equivalent to "faster-than-causality") information transmission.
A rough "classical" analogy for quantum entanglement is: seal two cards, one white and one black, in a pair of envelopes. Shuffle the envelopes, and give one to a person who travels to the Moon. Whenever they open their envelope, they'll instantaneously know what the other envelope contains. However, this doesn't instantaneously "transmit" any information: all the information was "transmitted" when the person carried their envelope to the moon, at under the speed of light.
The "quantum" part of Quantum Entanglement adds some fun not-in-classical-physics features to this analogy. For example, you can make a machine that will flip a black card to white and white to black (without telling you which); when the person on the moon puts their envelope through such a device, it can still stay "in sync" with the other envelope (when they are both opened afterwards, they'll still have opposite-colored cards). However, no information is transmitted: the Earth person has no way of knowing (unless you tell them through speed-of-light-or-slower channels) whether or not the Moon person has used the card-flipping machine; once they've checked their own envelope, the entanglement is broken and changing the Moon envelope's contents no longer changes the one on Earth.
Re:Always a letdown. (Score:2, Interesting)
So, you can't control the spin on either particle?
Re:Not Much Advantage Gained (Score:4, Interesting)
Depending on the experiment, 10% differences can be pretty obvious to measure. With the best atomic clocks, we can now see relativistic effects due to gravitational potential differences corresponding to 1m height change in the lab. Without understanding the experiment, you have no way to judge whether 10% differences are negligible or whoppingly huge compared to experimental sensitivity.
Re:Only 250 miles to the ISS (Score:4, Interesting)
it is fast enough that they can notice the difference in very accurate clocks...thus it is relativistic
for example GPS Satellites loses about 7 microseconds a day [ohio-state.edu] due to relativistic effects.