Beta

Slashdot: News for Nerds

×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

European Researchers Propose Quantum Network Between Earth and ISS

Unknown Lamer posted about a year ago | from the accidentally-unleashes-cthulhu dept.

Communications 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).

cancel ×

209 comments

Entangled Photons? (0, Offtopic)

Anonymous Coward | about a year ago | (#43412241)

Sounds like some real Gordon Freeman shit to me.

Re:Entangled Photons? (5, Funny)

SJHillman (1966756) | about a year ago | (#43412485)

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.

Re:Entangled Photons? (0)

Anonymous Coward | about a year ago | (#43412581)

I nostalgia'd.
Thanks, Sir.

"Quantum Entanglements in Spaaaaaaaace" (0)

Anonymous Coward | about a year ago | (#43412245)

Coming soon with Mike Nelson and Kevin Murphy

Re:"Quantum Entanglements in Spaaaaaaaace" (2)

CodeHxr (2471822) | about a year ago | (#43412273)

And Miss Piggy?

Ansible (-1)

Anonymous Coward | about a year ago | (#43412267)

Sounds like the beginnings of the ansible from Childhoods End

Re:Ansible (2, Informative)

bsane (148894) | about a year ago | (#43412513)

Enders Game

Re:Ansible (3, Informative)

SteveFoerster (136027) | about a year ago | (#43412643)

Re:Ansible (1)

bsane (148894) | about a year ago | (#43413447)

Oh- right... I remember now that in the book its named after some other SciFi, but I never knew the source.

Re:Ansible (2)

SteveFoerster (136027) | about a year ago | (#43413585)

I am nerd. Hear me roar.

Re:Ansible (-1)

Anonymous Coward | about a year ago | (#43412775)

Knew I got that wrong, but work got in the way of my correction.

Re:Ansible (1)

wonkey_monkey (2592601) | about a year ago | (#43413083)

Sounds like, but wouldn't be anything like.

Will they also (0)

blackholepcs (773728) | about a year ago | (#43412279)

Will they also build a Battle School? If so, I wanna go.

Re:Will they also (0)

cfulton (543949) | about a year ago | (#43412897)

I'd mod you up for you sig alone if I had mod points.

10,000 times faster than the speed of light? (4, Interesting)

schneidafunk (795759) | about a year ago | (#43412289)

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.

Re:10,000 times faster than the speed of light? (5, Insightful)

UnHolier than ever (803328) | about a year ago | (#43412351)

It is instantaneous, but you can't measure zero - all you can measure is "it took less than x picoseconds" where x depends on your timer's precision, and from this infer "it went at least this fast".

Re:10,000 times faster than the speed of light? (2)

MouseTheLuckyDog (2752443) | about a year ago | (#43413093)

Given that according to SR there is no such thing as simultaneity at two different locations in space, how can you tell it was instantaneous?

Re:10,000 times faster than the speed of light? (0)

Anonymous Coward | about a year ago | (#43413733)

You take into account the time the signal from a sensor takes to get to you and then there is simultanity. Easiest if you sit in the middle with two sensors on a (helper) line at the same distance from you in opposite directions. Let the sensor send a light beam to the middle once something is at that location.

Re:10,000 times faster than the speed of light? (3, Informative)

Immerman (2627577) | about a year ago | (#43413131)

>It is instantaneous
Correction: current theory postulates that it is instantaneous, but theory can only be known to be accurate to within the limit of our measuring devices, so "at least 10,000 times faster than light" is the more accurate statement. The whole point of the ISS experiment will be to see if the addition of more potentially confounding factors causes the measured reality to depart from the predicted behavior.

Re:10,000 times faster than the speed of light? (1)

TheDarkMaster (1292526) | about a year ago | (#43413453)

Exactly.

No (2)

iris-n (1276146) | about a year ago | (#43413185)

This is bullshit. The scientific content behind this claim is that "nonlocal realistic models that reproduce the results of quantum mechanics must have speed of communication at least 10,000 faster than the speed of light in some arbitrary ference frame that we've chosen".

This means that this number is completely irrelevant, i.e., does not measure anyhting related to the real world.

What can be said, scientifically, about the speed of this channel is that it is the speed of light, because we can only actually measure the presence of the information on the other side after a light signal is sent from one party to the other.

The fact that it looks instantaneous is more of an artifact of our mathematical formalism, and a common philosophical misunderstanding about the nature of the quantum state (i.e., people regard it as objective rather than subjective).

Re:No (2)

lgw (121541) | about a year ago | (#43413569)

What can be said, scientifically, about the speed of this channel is that it is the speed of light, because we can only actually measure the presence of the information on the other side after a light signal is sent from one party to the other.

The fact that it looks instantaneous is more of an artifact of our mathematical formalism, and a common philosophical misunderstanding about the nature of the quantum state (i.e., people regard it as objective rather than subjective).

That doesn't follow. You can only confirm the measurements agree after a speed of light delay, but you can perform the measurements at very close to the same time (the 10000x speed of light number is just the resolution of the clocks that confirm when the measurements were taken).

And WTF is "subjective vs objective" about the spin of a particle? Sure, the word "spin" is arbitrary (likely nothing is actually spinning), but it's an objectively measurable property just like charge or mass.

Re:10,000 times faster than the speed of light? (1)

slashmydots (2189826) | about a year ago | (#43413443)

While that statement does sound comically stupid and would basically be a "divide by zero" problem, I think they're talking about time to transmit including translation and error correction + processing time inside the NIC divided by just processing time inside the NIC. Honestly, I would think that's closer to 3x faster over that short of a distance but whatever, lol.

Re:10,000 times faster than the speed of light? (1)

Anonymous Coward | about a year ago | (#43413785)

Exactly what does instantaneously mean? We don't line in a Newtonian universe!

Only 250 miles to the ISS (2)

pellik (193063) | about a year ago | (#43412329)

While the ISS may be only 250 miles above the ground, I can't imagine they only intend to do tests when the ISS is directly above the transmitter. I suspect the journalist completely failed at understanding the spatial relationship between a space station and a spot on the ground.

Re:Only 250 miles to the ISS (5, Interesting)

jabuzz (182671) | about a year ago | (#43412479)

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:Only 250 miles to the ISS (1)

buchner.johannes (1139593) | about a year ago | (#43412547)

Also, different curvature.

Re:Only 250 miles to the ISS (1)

camperdave (969942) | about a year ago | (#43412645)

I suspect that if you want to see if something is affected by gravity, it's helpful to make observations at different points in the gravity well.

Oooh gravity experiment (4, Interesting)

sandytaru (1158959) | about a year ago | (#43412357)

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!"

Re:Oooh gravity experiment (3, Insightful)

iggymanz (596061) | about a year ago | (#43412405)

wrong, it is actual science and the way things behave, and the equations are complete (outside of realm of heavy space-time curvature such as near black hole). It is just different from the mental model most humans have. Nothing stopping anyone from taking prerequisite basic calculus and then basic quantum mechanics course.

Re:Oooh gravity experiment (2)

khallow (566160) | about a year ago | (#43412469)

It took more than a basic QM course before I had a real inkling of what was or might be going on. Even now, I have to handle this stuff gingerly with some rather complicated math tools, my intuition sucks.

Re:Oooh gravity experiment (2)

jabuzz (182671) | about a year ago | (#43412649)

Well saying they are complete is wrong. Both General Relativity and the Standard Model are correct within experimental error within the tested limits, which does leave very little wiggle room. However they are not complete and very unlikely to be complete even in regions of normal space-time curvature.

It would be like saying Newtonian Mechanics was complete at the beginning of the 20th Century. Sure within experimental error at the time it appeared complete. However we now know that it was not. A combination of experiments with smaller uncertainties and moving to a faster speeds showed that for certain.

The problem is getting to regions of high space-time curvature or reducing the uncertainties in our experiments is very hard and very expensive and nobody has managed to do it yet. When they do it will hopefully provide the insight necessary to come up with a way of unifying gravity and quantum. mechanics.

QM is complete? Really? (2)

Immerman (2627577) | about a year ago | (#43413289)

Not quite true. The equations appear to be complete - i.e. they appear accurate to within the limits of current experimental error; however, assuming we're not living in The Matrix, the equations are only a mathematical model of a physical reality that we still have very little understanding of, hence the various superstring, etc. theories that seek to explain the equations. Prediction is only half of what science strives for, and the understanding still eludes us.

Moreover, there are theoretical inconsistencies between QM and Relativity, which implies that one or both mathematical models are still incomplete. Glossing over that fact is likely to prove quite similar to the preeminent experts in the late 1800's who stated that everything in science was known except for a few minor unexplained phenomena such as black-body radiation, etc. Investigating those inconsistencies eventually exposed almost every established theory in physics as fundamentally incomplete, and in the absence of evidence to the contrary that seems to be the safe bet for the current situation as well. After all, rigorous science is only a few centuries old, and every major advance to date has revealed far more questions than answers.

Re:Oooh gravity experiment (0)

Anonymous Coward | about a year ago | (#43412801)

If you study quantum mechanics instead of just reading the pop culture, you'll get answers besides "You wouldn't understand." Seriously; the whole "it is but it isn't" crap that keeps getting repeated is like 1% of the issue. If you want to understand, start by learning a LOT of linear algebra. Once you are very strong in that, the rest is actually pretty easy.

Re:Oooh gravity experiment (0)

Anonymous Coward | about a year ago | (#43413277)

"If you think you understand quantum mechanics, you don't understand quantum mechanics."
Richard Feynman

Re:Oooh gravity experiment (1)

Anonymous Coward | about a year ago | (#43413271)

Quantum entanglement ("spooky action at a distance") is only a real thing if you accept the idea that observing something really does cause it to change state, and that a whole swathe of reality suddenly and magically disappears. In any other part of physics, the idea of throwing away half your (energy/momentum/whatever) would be anathema; here, it's canon. I can't help feeling that nothing, other than our perception, is actually changing, and that the established view is simply wrong - in actuality, we make two measurements, we find they're correlated (fine), then we infer spurious cause and effect based on a faulty interpretation and make a fallacious deduction (not fine). I predict that, in this and all such experiments, no limits will be found on the distances, speeds, time-ordering, immunity to environment or indeed anything else of the "effect" being observed - because there's nothing actually happening. Sadly, "you won't find anything, ever" is only capable of disproving that assertion - and it's hard to think of anything capable of supporting it.

60's TV Sci Fi plot outline - just to show that other things are, at least in principle, worth thinking about:

Planet Halcyon 5 is critically short of the energy it needs to prevent its core imploding. To resolve the crisis, Spock proposes the use of "entangled" Sigmatau particles, Alpha and Beta, each of which is in a superposition of state X and state Y. He creates the pair, and beams particle Alpha to the surface of Halcyon 5, where Kirk is waiting. Particle Beta he beams to a space beacon in orbit around the Halcyon star. Using his tricorder, Kirk examines particle Alpha to trigger the state collapse. Instead, what happens is that Kirk himself becomes entangled - there's a Kirk X who sees particle Alpha in state X (call that Alpha X), and a Kirk Y who sees it in state Y (call that Alpha Y). Independently, back on the Enterprise, Spock examines particle B - and becomes similarly entangled, as Spock X and Spock Y. But now Kirk X is entangled, via Alpha X and Beta X, with Spock X - so when they compare results, bingo, they match. Kirk X flips a switch down on the planet, and limitless power flows from the star to the planet for no readily-identifiable reason other than plot necessity (a security officer in a red uniform is too slow in avoiding the incoming energy surge and dies as a brief, glowing outline, but otherwise everything goes smoothly). Meanwhile, Kirk Y is similarly entangled with Spock Y, with the same result; Spock Y draws a similar conclusion, the same energy flows, but when he flips the switch things go horribly wrong, and the Enterprise, planet and whole solar system are destroyed in an explosion of enormous proportions. But that's OK, because Kirk Y and Spock Y both had pointed beards. Cut to Spock X speculating about what *might* have happened; roll credits.

Re:Oooh gravity experiment (1)

slashmydots (2189826) | about a year ago | (#43413483)

Everything was sci fi before it was science. But before sci fi, it's theory. So, it is a valid theory. It makes perfect sense too. 1 particle, 2 locations in space. You affect one, the other reacts without a particle or wave traveling between them. It just "happens" because it "is." And causality violations are just made-up logical bullshit with no basis in physics. Black holes violate physics logic too and yet, there they are. Reading the data off just one without affecting it is the hard part but they already solved that over a year ago....and it was on Slashdot *facepalm*

Not Much Advantage Gained (1)

biohazardpb4 (2893251) | about a year ago | (#43412377)

With the ISS being in LEO, not much distance is truly gained from a far simpler terrestrial experiment at opposite equatorial points, it would seem.

Re:Not Much Advantage Gained (3, Insightful)

femtobyte (710429) | about a year ago | (#43412461)

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.

Re:Not Much Advantage Gained (1)

camperdave (969942) | about a year ago | (#43412823)

The far simpler explanation is that if you are testing the effect of gravity, it's essential to have two different points in the gravity well.

Re:Not Much Advantage Gained (1)

lgw (121541) | about a year ago | (#43413123)

Perhaps, but the ISS is only ~5% farther from the center of the Earth than sea level, so that's only a ~10% difference. Seems like gravity would have to have a huge effect on quantum entanglement for that to matter.

Re:Not Much Advantage Gained (3, Interesting)

femtobyte (710429) | about a year ago | (#43413305)

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.

Always a letdown. (2)

mikeulus (1307315) | about a year ago | (#43412445)

Can someone please explain to me why this can't be used for instantaneous communication purposes? From everything I've understood so far, the answer is still no, it can't be used to transmit information, just measure state of the particle at a particular point in time.

Re:Always a letdown. (5, Funny)

Shimbo (100005) | about a year ago | (#43412545)

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.

Re:Always a letdown. (1)

mikeulus (1307315) | about a year ago | (#43412573)

I like you.

Re:Always a letdown. (1)

Anonymous Coward | about a year ago | (#43413751)

No you don't.

Re:Always a letdown. (5, Informative)

jabuzz (182671) | about a year ago | (#43412557)

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.

Re:Always a letdown. (1)

mikeulus (1307315) | about a year ago | (#43412659)

This is the first explanation that has actually clicked with me.

Re:Always a letdown. (1)

deadweight (681827) | about a year ago | (#43413549)

+1 Every other explanation I have read was lame - this is such a simple answer too.

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43412689)

Not yet. anyway. Someone will borrow another sci fi concept and magically make it work.

Re:Always a letdown. (5, Informative)

MyLongNickName (822545) | about a year ago | (#43412739)

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.

Re:Always a letdown. (1)

iggymanz (596061) | about a year ago | (#43412743)

you can transmit your finding to the other person, at equal or less than lightspeed, so they don't have to measure theirs. BUT they won't get that information instantly, so the whole thing is useless for FTL comm. What is can be useful for is secure communications as "reading" one of two or more entangled particles affects the state of them all.

Re:Always a letdown. (2, Interesting)

Anonymous Coward | about a year ago | (#43412833)

So, you can't control the spin on either particle?

Re:Always a letdown. (1)

jellomizer (103300) | about a year ago | (#43412841)

So they are two particles that are are in sync with each other. So the information doesn't travel faster then light, it is just implied.

So if we try to change the spin in a meaningful way we would break the sync thus they will no longer be entangled?

Re:Always a letdown. (2)

lgw (121541) | about a year ago | (#43413333)

So they are two particles that are are in sync with each other. So the information doesn't travel faster then light, it is just implied.

Not quite, but the reasoning is subtle. Say you have 2 spin-entangled particles, such that the spins must be opposites. You have to pick an angle to measure spin (up or down). If the same angle is used for measuring both particles, the results will always be 100% correlated (one up, one down).

However, if the measurements are taken at different angles, the results will be somewhat random. If the measurements are at 90 degrees to one another, the results will be 0% correlated. If the measurements are at some angle not a multiple of 90 degrees, something surprising happens. If the information were in a "hidden variable", predetermined, then the correlation would be linear with the angle between the detectors. It's not. It varies with cosine^2 (IIRC - Wikipedia says cosine).

Re:Always a letdown. (1)

DahGhostfacedFiddlah (470393) | about a year ago | (#43412881)

This still bothers me. Just because a spin is unobserved doesn't mean it's not there.

I still don't understand how this is different from sending a red card and a blue card to two friends. When one opens theirs, they "instantaneously" know the contents of the other. But that doesn't mean the contents weren't predetermined the moment I sent the cards.

Re:Always a letdown. (1)

iris-n (1276146) | about a year ago | (#43413121)

Jackpot! This is the whole issue. Just observing these correlations means nothing, as you said, the same data comes out of our friends with the cards.

But the reason we are fascinated by entanglement is that there is more to it. We can actually prove that no theory in which the contents of the letters were predetermined (and FTL communication does not exist) can reproduce the correlations that can be produced via entangled states. This is the famous Bell's theorem [wikipedia.org] .

Re:Always a letdown. (1)

femtobyte (710429) | about a year ago | (#43413139)

Up to the point you describe, the classical (a pair of cards with different colors) and quantum (a pair of photons with different polarizations) systems behave the same. However, there are some nifty features of the quantum system that can't happen classically. For example, you can rotate the polarization of one entangled photon (without knowing what it is) --- then, measure both photons, and they'll still be in opposite polarizations, even if you carried out the polarization rotation and measurement so far apart that no "signal" had time to travel, even at the speed of light, from one to the other (what Einstein would call "spooky action at a distance").

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43413439)

For example, you can rotate the polarization of one entangled photon (without knowing what it is) --- then, measure both photons, and they'll still be in opposite polarizations, even if you carried out the polarization rotation and measurement so far apart that no "signal" had time to travel, even at the speed of light, from one to the other (what Einstein would call "spooky action at a distance").

If that is the case, couldn't you use something like morse to send an FTL message?
I mean, if you can modify the polarity within a certain timebase, changing or not changing
the polarity can be messages and if the distance is large enough, even if it takes a certain
amount of time to create the message, it will still be faster than light.

Re:Always a letdown. (1)

femtobyte (710429) | about a year ago | (#43413615)

Nope. You can't tell on the receiving end whether or not the bit you're measuring was or was not rotated. A measured '1' could be a 'rotated 0' or an 'unrotated 1', so you know absolutely nothing about what the message sender is doing (only that, if she measured her bits right after you measured yours, she'd see the opposite values).

Re:Always a letdown. (1)

Lemmeoutada Collecti (588075) | about a year ago | (#43413461)

If we can influence them to rotate, can we influence them to not rotate as well? Because if that were the case, we would have the basic for a 2 bit communication system.

For example: measure the receiving end at 1 second intervals. Three rotations = start of message. From there, rotate = 1 and no rotate = 0. Rinse, repeat.

I would imagine that the reason we don't have this is because we can't influence them not to rotate.

Re:Always a letdown. (1)

femtobyte (710429) | about a year ago | (#43413579)

Doesn't work --- on the receiving end, you have no way to tell whether or not the bit was rotated on the opposite side. You see a random bit; suppose it's a 1. There's no way to tell whether this was a 0 "to start with" then rotated, or a 1 "unrotated." The original states of the bits are random: you can't produce entangled bits knowing that one side starts with all 1's, and the other starts with all 0's.

Re:Always a letdown. (1)

nsaspook (20301) | about a year ago | (#43413703)

Even in the classic universe groups of 'things' can have properties that can change at FTL speeds but they like "spooky action at a distance" effects with entangled photons can't transmit information FTL.

For example in Maxwell equations
Induced polarization current P has no constraints about speed.

http://arxiv.org/pdf/physics/0405062v1.pdf [arxiv.org]
http://www.iasf-roma.inaf.it/congress/public_html/Congress/Ardavan%20Rome.pdf [iasf-roma.inaf.it]

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43413149)

Practically, it's not all that different, since it's tough to use this for any purpose, but technically, it's different because the "cards" are both red and blue. So it's more like sending a card to each person which is red on one side and a blue on the other, and after the first person throws card 1 in the air and sees it land red side up, card 2 is guaranteed to fall blue side up.

Re:Always a letdown. (1)

wonkey_monkey (2592601) | about a year ago | (#43413337)

Try Bell's theorem [wikipedia.org] . I once read a very good explanation involving boxes with three hidden lights, but I can't for the life of me remember which book it was in. Sorry!

Re:Always a letdown. (2)

lgw (121541) | about a year ago | (#43413345)

See here [slashdot.org] for amore detailed answer. The difference is subtle.

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43413401)

If you buy into the "many worlds" interpretation of QED, the unobserved spin is both up and down until you measure it, and then you land in either the up/down world or the down/up world, but there's no possible way to know beforehand which way it'll go (which might be the case if the spin was "already there" but unobserved).

Re:Always a letdown. (1)

MouseTheLuckyDog (2752443) | about a year ago | (#43413169)

Hmm. Take ten entangled pairs. Sequence them 1-10. ( It doesn't have to be ten. )
Split the pairs up.
Use an encoding invariant under bitwise not set one set of pairs to some value.
Read the other set of pairs value.
Seems to me information was transmitted.

Of course QE is something that most people didn't talk about till after I finished grad school.

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43413361)

Read the other set of pairs value.

The values you read will always appear random. They don't seem interesting until you get the values read from the other pair. Then it becomes obvious they aren't really random.

Re:Always a letdown. (1)

femtobyte (710429) | about a year ago | (#43413445)

The problem in your scheme is "set one set of pairs to some value": you can't do that. Quantum mechanics forbids you from setting one side of the pair to values you want (without first breaking the entanglement, so the other side won't see the results).

Re:Always a letdown. (0)

Anonymous Coward | about a year ago | (#43413495)

Is it possible to adjust the spin and create a communication method along the lines of morse code?

Basically what the spin is itself wouldn't matter, but the fact that it changed is what provides the communication.

Re:Always a letdown. (1)

spyke252 (2679761) | about a year ago | (#43412569)

Generally, a communicant needs to borrow a classical communications channel to express which state the pair collapsed into- Wikipedia has a good article on this. http://en.wikipedia.org/wiki/Quantum_teleportation#Protocol [wikipedia.org]

Re:Always a letdown. (3, Insightful)

nsaspook (20301) | about a year ago | (#43412607)

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.

Re:Always a letdown. (4, Interesting)

femtobyte (710429) | about a year ago | (#43412657)

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. (1)

lgw (121541) | about a year ago | (#43413499)

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.

I take issue with that somewhat: as I understand it, FTL communication will only interfere with causality in highly contrived circumstances, where the endpoints of the communication are moving at relativistic speed relative to one another. An ansible that would break if the distance between the endpoints changed rapidly would protect causality.

Re:Always a letdown. (1)

femtobyte (710429) | about a year ago | (#43413757)

FTL communication interferes with causality (within Einsteinian relativity, which so far seems to be a pretty solid theory) because if you have something that looks like FTL communication in one reference frame (a signal is sent from spacetime point A which arrives 1 year later at spacetime point B, which is 2 light years away from A), then there exists some other frame in which causality is violated: B receives the signal *before* A sends it (in this case, there's another frame where A and B are at the *same location,* except B is the time *a year before* A sends the signal; this would allow all sorts of causality-violating paradoxes, like B leaving a message for A saying "don't send the message we just received from you!"). You may consider the circumstances "contrived" in the sense that you need huge velocity differences between the frame in which A precedes B, and that in which B precedes A --- however, "contrived" or not, the theory breaks down. A theory describing how the universe works shouldn't depend on how good your ansible structural engineers are; and, we actually can create particles traveling much faster than the required frame boost for this example, and observe that they behave according to relativistic theory.

Quantum-entanglement deniers? (2)

DavidHumus (725117) | about a year ago | (#43412455)

Wow - a dozen or so messages and not yet one from quantum-entanglement (QE) deniers.

Re:Quantum-entanglement deniers? (1)

i kan reed (749298) | about a year ago | (#43412489)

What is quantum entanglement denial? I mean, I understand people will believe lots science to be false for a ton of stupid reasons, but I haven't heard of this one. Could you explain their position?

Re:Quantum-entanglement deniers? (2)

femtobyte (710429) | about a year ago | (#43412553)

I don't know what particular form of QE denial DavidHumus has run across, but what I've seen usually (like most denialisms) starts with some critical misunderstanding of QE: e.g "QE lets you transmit information faster than the speed of light"; then concludes "you can't transmit information faster than c, thus QE is bunk!".

Re:Quantum-entanglement deniers? (0)

Anonymous Coward | about a year ago | (#43412655)

>What is quantum entanglement denial?

This: http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments

After decades of trying, no experiment to-date has verified Bell's "theorem" or the existence of spooky, instantaneous, non-local action-at-a-distance.

Experimental data is perfectly compatible with Einstein's non-local realism.

Re:Quantum-entanglement deniers? (0)

Anonymous Coward | about a year ago | (#43412665)

Oops I meant Einstein's local realism haha

Re:Quantum-entanglement deniers? (2)

ArcadeMan (2766669) | about a year ago | (#43412953)

Talk about a quantum mistake.

Re:Quantum-entanglement deniers? (1)

lgw (121541) | about a year ago | (#43413419)

Well, QE deniers still have a leg to stand on. The experiments so far aren't quite conclusive yet. But since all the evidence thus far points to QE and not intuition, it's likely only a matter of time and experiments like this one until that door is shut.

Entanglement enshmanglement (0)

Anonymous Coward | about a year ago | (#43412693)

"Jan. 16, 2012 — Researchers have devised a proposal for the first conclusive experimental test of a phenomenon known as 'Bell's nonlocality"

http://www.sciencedaily.com/releases/2012/01/120116112608.htm

There is still not a shred of evidence for Bell's theorem or that Einstein's local realism is wrong and yet they talk about "entanglement"!

See here: http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments

Why has something QM predicted not been demonstrated after decades of trying? It's a worrying sign that something is wrong in QM.

The best experiment to my knowledge, Ansman, is quite accurate and actually seems to suggest that Einstein was right and spooky action at a distance is WRONG.

Quantum Entanglement Does Not Transmit Info (2)

MyLongNickName (822545) | about a year ago | (#43412705)

No, the article isn't suggesting this, but every time quantum entanglement gets brought up on Slashdot, someone suggests how we can use it to communicate FTL. Quantum entanglement is the equivalent of instantaneously sending a random message (more complicate than that, really). No information is actually transmitted. The first time I tried to wrap my head around Quantum Entanglement, I thought it could be used to communicate to far-away places (even other planets) with no latency, but as I understood more, my hopes were dashed.

Re:Quantum Entanglement Does Not Transmit Info (0)

Anonymous Coward | about a year ago | (#43412767)

>Quantum entanglement is the equivalent of instantaneously sending

There's no evidence for "spooky action at a distance". See http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments

I wonder if that is the reason you can't send information faster than light. Because the influences effecting the "entanglement" are themselves restricted to light speed?

Re:Quantum Entanglement Does Not Transmit Info (1)

slashmydots (2189826) | about a year ago | (#43413367)

Actually, you were wrong before and you're wrong now. Get over it. NASA knows what they're talking about. You still do not. There was a slashdot article years ago about a method discovered to transmit data between entangled particles.

Re:Quantum Entanglement Does Not Transmit Info (1)

MyLongNickName (822545) | about a year ago | (#43413465)

Care to post a link?

Re:Quantum Entanglement Does Not Transmit Info (1)

femtobyte (710429) | about a year ago | (#43413497)

Perhaps there was a Slashdot article with a lousy summary (shocking!) that mislead uninformed people into thinking NASA had a method for transmitting data between entangled particles, but NASA does not have a method for transmitting data between entangled particles.

Re:Quantum Entanglement Does Not Transmit Info (1)

Immerman (2627577) | about a year ago | (#43413545)

Heh, many years ago I actually designed the theory for a FTL communication channel - all I needed was a way to use N remotely entangled particles to generate N+1 of them (or a serious boatload of particles to start with). The essential element being that, while random, the probability distribution can in fact be manipulated. It makes for a very "noisy" transmission medium, but with enough redundant bandwidth it should be possible to get a message through.

But then despite multiple attempts I've yet to understand how FTL communications, even instantaneous, would in any way break causailty. So maybe there's something in QM I've overlooked as well. If anyone can explain that one I'd love to hear it - I can see several ways in which it would result in *apparent* causality violations to a 3rd observer unaware of the FTL channel, but no way in which a signal could possibly be looped back to be received before it was sent, so no *actual* causality disruption could occur.

Re:Quantum Entanglement Does Not Transmit Info (0)

Anonymous Coward | about a year ago | (#43413719)

I don't know where this example come from, but it enlightened me. Imagine that you have a pair of gloves and that you give each one to a different friend (it's our entangled particles going their way). When you ask one of your friend if he has the left-hand glove (that's the measure), you immediately know that the other has the right-hand one (that's a really less spooky and dramatic effect).

Largest quantum? (1)

Chas (5144) | about a year ago | (#43412949)

Cognitive dissonance at its finest!

entanglement != faster-than-light transfer (-1)

Anonymous Coward | about a year ago | (#43413053)

Guys, for the love of ... Read god damn manual (even wiki will suffice) -- quantum entanglement does not allow you to transfer information at faster-than-light speed. Ignorant morons

at least the 5th story in a row (1)

slashmydots (2189826) | about a year ago | (#43413349)

This has got to be the 5th story in a row where I will attempt to convince incredibly stupid people that quantum entangled particles have a practical use EXACTLY LIKE THIS. I believe we last left off at people screaming that entangled photons can't transmit data between "them" (it's really sort of not 2 particles). Also that data can't travel faster than the speed of light, which is doesn't and yet does. You're all 1.5 years worth of wrong so far.
Let's see, how many times do you think I have to copy and paste "entanglement really is instantaneous over long distances" because some slashdotters believe that professional physicists believe it's true. This is a real thing! You're stuck in the 1980's with your high school physics degree, modding me down because I'm saying it's possible. Well, here it fucking is, right in your damn face.

Re:at least the 5th story in a row (1)

MyLongNickName (822545) | about a year ago | (#43413507)

You still think you can transmit data faster than light. How cute.

Re:at least the 5th story in a row (1)

femtobyte (710429) | about a year ago | (#43413543)

I am a professional physicist. Entanglement does indeed appear to be "instantaneous over long distances". However, no data is transmitted through this process. You're half-right, half-wrong: right on the part most people don't argue against, and entirely wrong on the important question of data transmission. And you're all wrong on thinking you're in any way qualified to comment on this question, because you're obviously not.

Simulation (1)

RoccamOccam (953524) | about a year ago | (#43413633)

Hasn't entanglement and "spooky action at a distance" been proposed as evidence of the universe as simulation? In other words, the simulation doesn't resolve an observation until it is needed?

can't change spin? (1)

Pro923 (1447307) | about a year ago | (#43413765)

But I thought that the magic was that you could change the spin on one and the other would be affected. If that's true then why couldn't you use it for zero latency communications? (minus the initial speed of light 'connection'). If it's false, well then I understand why everyone says that it's useless.

This is great (1)

TheSkepticalOptimist (898384) | about a year ago | (#43413779)

But really, we can't find some better form of energy? We can soon instantly transmit data faster than light across hundreds of miles yet still need to explode dinosaur juice to make our mechanical wagons move?

Load More Comments
Slashdot Account

Need an Account?

Forgot your password?

Don't worry, we never post anything without your permission.

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>
Create a Slashdot Account

Loading...