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European Researchers Propose Quantum Network Between Earth and ISS
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).
From the article: "As we recently reported, another research group recently showed this quantum channel to be at least 10,000 times faster than the speed of light."
I don't get it. I thought it was instantaneous and that number is just a crap number based on distance.
Some people die at 25 and aren't buried until 75. -Benjamin Franklin
Quantum entanglement is one of those more sci-fi than actual science, and yet it's a real thing we can't quite explain yet. Testing whether it's affected by gravity is a very cool method of poking the phenomenon a bit more. Maybe one day we'll get an answer besides "It's a quantum thing! You wouldn't understand!"
Occasionally living proof of the Ballmer peak.
Presumably, the ability to shoot a beam of light >250 miles, without needing to build a 250-mile-long evacuated beamline, is a major advantage gained. The Earth is surrounded by this annoying thing called "the atmosphere," which wreaks havoc with light traveling only a few miles; the faster you can get out of the atmosphere (by, e.g., shooting straight up), the easier it'll be to get any useful amount of light to the other end.
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.
Very few scientific advances have been made without a few Unforeseen Consequences, but that's no reason for Apprehension or Questionable Ethics so we may just need to Forget About Freeman.
Can someone please explain to me why this can't be used for instantaneous communication purposes?
QE is rather like being married. You know that whatever you decide, your partner will want to do the opposite. However, no actual communication is involved.
Basic explanation. So I have two entangled particles, and we move them apart so you have one and I have one. At this point we have no idea what the spin on either of them is, in fact it is not determined till we try and measure it, but they must be different. I now measure the spin on mine and find it is +1, meaning yours is -1 "instantly". You can now measure the spin on yours to confirm that.
The problem is because the spin of the particle is undetermined until I read it and when I do read it the result will be random, there is no way to transmit any useful information.
Can someone please explain to me why this can't be used for instantaneous communication purposes?
Because that would require FTL transfer of energy/information.
It's like if three people were in a room and #3 put a nickle in #1's pocket and a dime in #2's pocket completely randomly. They all know there is only the possibility of a nickle or a dime but 1&2 won't know what coin until they actually look in the pocket.
#1 flies to Mars on a rocket.
#2 stays on earth and looks in his pocket. He now knows instantaneously the value of the coin in #1's pocket on Mars.
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Space game using normal deck of cards: http://BattleCards.org
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.
Not yet. anyway. Someone will borrow another sci fi concept and magically make it work.
No they won't. There is a certain cult that treats science as a religion and refuses to understand that there are basic laws of physics that constrain us. FTL communication causes a litany of paradoxes and trying to turn quantum entanglement into a FTL communication device shows a fundamental lack of understanding of what is going on.
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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.
What the article fails to point out is that actually nothing is travelling faster than light. This is the fancy equivalent of shining a bright laser on the moon and moving it around so that it appears that the bright spot on the surface moves at a velocity in excess of c. There is no problem with this because no information is transmitted from one point on the moon to another point on the moon faster than c - the only information which is transmitted is from the person pointing the laser to the moon. In the same way no data is transmitted between the two people making the measurements because neither has any control over the outcome of their measurement.
1. Put a really long stick so that the ends reach the two points you want to communicate.
2. Push the stick from one end and it moves at the same time on the other end for instantaneous FTL communication.
3. Sell sticks to day traders.
4. Profit.
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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 due to relativistic effects.