http://arstechnica.com/science/news/2010/0...=1#comments-bar

Quantum decking anyone?

Um...not really. The whole idea with quantum entanglement is that you end up with two identical photons (for example), and if you make a change to photon A (which, for the purpose of this example, is in Europe) the same change will be made to photon B (which, for this example, is in America).

So it would only work if you had data transferred in a medium that COULD be entangled, and then you would have to have an identical medium for every single node you wanted to work on. This would also raise some really awkward questions when a corp starts asking why you've got an exact match for a quantum entangled storage device they happen to own.

What that technology WOULD be useful for, however, is instantaneous communication between two disparate points. But it'd be prohibitively expensive at the same time, not to mention extremely limited.

And you can still only send quantum information, you can't send normal information (e.g. internet data, strings, 1s and 0s, voice, picture...) at least, not yet.

So, what's this quantum entanglement entail? It's not 1's and 0's that spell out "cat", it's actual live and dead cats? Why can't this "quantum information" be used to send real information?

Converting usable data in quantum is just the next step.

I read yesterday about a chip that stores data on a quantum level. Tiny dot speeds hi-tech future.

You entangle* two particles such that they both have the same quantum state. That is, their spin.

Then as you change one, the other changes in the same manner.

It's really hard to explain, even by physicists. Mainly because what causes it can't be observed (attempting to do so causes the experiment to fail).

Good movie to watch, "What the Bleep Do We Know!?: Down the Rabbit Hole"

*The way this is done is by creating a projection of particles (protons -> light) and separating out each particle based on its spin. The "Clockwise" particles are attracted in one direction, the "Counterclockwise" in another. Each of the two fields will have a the same spin as every other particle in that field and the opposite spin from the particles in the other field. By clever manipulation of where these fields overlap, you can create areas where any given particle has a spin different from every other particle.

Its one of those weird "measure it and it changes" things.

Very good explanation, Draco18s.

I'd be a bit wary of What the Bleep Do We Know, though. While a very entertaining and eye-opening movie, it contains many factual errors and misinterpretations that might be a bit difficult to spot, especially if you're not all that much into physics.

My favorite QM quote ever came from I believe an MIT professor:

"If Quantum Mechanics makes sense to you, you obviously haven't studied it enough yet."

The biggest thing I could see with entanglement would be instantaneous, 100% secure communication channels. It would be literally hack-proof, since the act of hacking would destroy the entanglement or contaminate the connection enough to betray tampering.

True, but it at least attempts to explain quantum mechanics to the layman. It might not be factually perfect, but it isn't boring to watch.

As a grad' student in particle physics, I tend to avoid these movies as much as I can. They tend to make me cry.

I have yet to see any documentary film about quantum mechanics that doesn't end up saying a pile of crap at some point. Quantum Cafe, one of the parts of the "Elegant Universe", has been praised as an "excellent introduction to QM", is full of major errors (that bias for the manyworld interpretation of QM is just wrong and talking about it as if it was scientific fact is totally misguiding) and inaccuracies.

As for the so-called quantum teleportation, it is an interesting phenomenon but a misnamed one; nothing is teleported, and as opposed to what lots of pseudo-scientific works of fiction (or even worse: popularization mags) often say -I'm looking at you, Eclipse Phase-, it doesn't allow to cheat special relativity. No FTL comms through this stuff. Of course, that makes the truth far less sexy than the fiction or mags.

Agree with all points.
(I should point out that I'm a digital arts major, but I really enjoyed reading about theoretical physics.
Had to watch What the Bleep Do we Know!? in a Metaphysics course and I pointed out the flaws in some of the stuff that was said.)

I still do not understand why information is not able to be transmitted through this medium. Instead of 0 and 1 you have a spin direction. But is that not the same net effect as on and off just with more possibilities? And why would those other possible spin directions stop you from translating one spin direction to 0 and another to 1 to transmit your data? I am quite confused by the people saying this.

Honestly I haven't figured out why not either.

It has something to do with the very act of reading the particle's state, alters the particle's state.

I dunno. QM gives me a headache.



-karma

Practical Shadowrunning implications:

1) The information has to be transferred between particles conventionally.

Generally, the entanglement information is sent by fiber optic cables. In this case, it was sent by (if I'm reading this link correctly) light (laser?) transmission between two telescopes. ("The research team designed two types of telescopes to serve as optical transmitting and receiving antennas.")
http://www.physorg.com/news193551675.html

The reason I bring this is that a lot of science fiction stories are all too happy to suggest that "quantum entangled particles" can be "entangled" without any tangible connection, even allowing communications to exceed the speed of light. This isn't correct - conventional, speed of light limits apply, and you need some sort of mundane transmitter and receiver (radio, fiber optic, etc.)

2) It's also important to note that the entangled particles stay separate. Star Trekkian teleportation ain't happening because matter isn't moving. You're exchanging information, not mass.

I think I need to go have a talk with the Illusive Man.

an article on the subject......I'm a bit vague on it

http://en.wikipedia.org/wiki/Quantum_entanglement

aye. gets tiring after a dozen times hearing someone has a new way to do something faster than the speed of light.

Im more confused now!

So youre saying that it cant be observed and its no faster than any other form of communication. So um what good is it?

I thought the whole point of entanglement was the effect when observed anyway. That normally when you observe the state it has a random chance of being any spin, but if they are entangled then when you observe them they have the same spin direction. Is this not accurate? And if it is why is it useless for transmitting information? And if its useless for transmitting information what in blue blazes is the point of it and how is anyone able to tell that they are in fact entangled at all?

The answers in this thread make very little sense to me!

I believe they actually have the opposite spin.

And its not so much that it's useless to transmit information, its that it doesn't transmit it any faster.

Case and point, you can make light itself travel faster than light. But as I understand it, in so doing, you lose any information encoded into the beam.

It is sci-fi so it works. Seriously no one knows what the future holds. All too many times in history we have found out new ways to abuse physics so things we thought we knew we no longer know the same way. Why is there this weird assumption that this time we got it right? So maybe some time in the future they can find a way to make quantum entanglement break the FTL barrier and be a form of instantaneous communications. As sci-fi goes mass effect was nice in that is maintained a pretty nice balance between soft and hard sci-fi.

I have to find the article again, but it discussed the "real science" behind many video games.

When they asked a physicist about the Mass Effect quantum-entangled comms, it basic response it that the comms are bullshit. Wouldn't work.




-karma

In fact as an information transfer system it is useless! why? because you have to know when to observe the particle. look too soon and you will change its state by looking at it. Also once the entangled particles have been observed and have their own spins they are not going to be entangled anymore so their spins are not coupled.

because information is bound by the speed limit of light. One might as well consider sending string theory to send photons faster than the speed of light. breaking the FTL barrier is not like breaking the sound barrier, but harder. being able to send a photon into a vacuum and then catch up with it in an Einstein gedanken experiment manner is theoretically impossible. The theory that says so is a modification on Newtons Laws and has been proven many times.

hi hi

I found This Review to be informative about the veracity of the aforementioned quantum physics movie.

Sure for as we understand physics now. This idea that we got it figured out this time baffles me. Yes its proven as we understand it, that does not mean someone can't figure out something we never even conceived of that violates/circumvents the laws as we currently know them. It has been done many times in the past before, why do we assume we are so smart that we got it down pat this time.

Nah. Everyone knows we know everything we'll ever know now. Just like we knew no one would ever break the sound barrier. Just like we knew phlogiston was what made fire. Just like we knew the universe revolved around the earth. Just like we knew the world was flat. Oh wait, do those things sound silly to us today? Guess what. Once upon a time they sounded as accurate and unquestionable as our current understanding of science today. Breakthroughs and discoveries are called breakthroughs and discoveries for a reason.

Its fiction. Its supposed to be speculative.

hi hi

I think some people are confusing superstition with science. The concept that the universe rotated around the Earth was not a scientific theory, and was certainly never proven by experiment. The sound barrier was never a scientific theory that was thought to be unbreakable. Bullets were breaking the sound barrier since gunpowder was invented (part of the reason those early test planes were shaped like bullets) I mean whips have been doing it since the invention of whips.

When getting into psudo-science magic relating to quantum mechanics, it is important to remember the Correspondence Principle. Which, in a nutshell states that: "Any new theory must give the same answers as the old theory where the old theory has been confirmed by experiment."

When Einstein came up with relativity, objects didn't start falling up. Relativity gave the same answers that Newton did except in extreme situations like near the speed of light or calculating Mercury's orbit.

Just because this is highly appropriate for this thread:

http://www.365tomorrows.com/03/05/hold-on-to-something/

But I thought that was the problem Einstein had with entanglement, in the EPR thought experiments, action at a distance, and FTL information exchange.

Then again, I'm definitely in the "knows enough to know that he doesn't know enough category" so please enlighten me.

the nice thing about quantum data transfer is that its complicated enough that you wont bump into it at everyday systems, but you can still throw it in as a curve-ball if some uppity hacker thinks he can crack a major bank and wire some millions to his offshore account.

Honestly, physicists would get a wider (not better) audience if the just took half of the unobservable quantum baloney and explained it the way they should.

I'm starting to see the wisdom in just saying a wizard did it or god said you can't go that fast...

As far as the references to alchemy and the shape of earth... those were never theories, but hypothesis. When a hypothesis is tested and it is shown over many experiments that a mathematical model really is a mathematical model of the world and not just sillyness it gets to be a theory (or law after people get tired of trying to disprove it and it has good physics politics). If a mathematical model will predict what happens it can't be dis proven only shown to not be the whole story.

Are you suggesting the speed of light might be increased one day?

hi hi

In the strictest sense, physics does not tell us that going faster than light is impossible. (although it is impossible to achieve via reaction acceleration) What it does say is that going faster than light will necessarily involve time travel into the past. This is all well and dandy for quantum mechanics, but once you start transmitting data faster than light, you break causality.

Tachyons. That is all.

I wonder if you could use this as a fool proof alarm, as in if there is an observer it changes the quantum state and sounds an alarm? The problem is figuring out how to observe a change without observing the current state.

Eggy

Unless causality runs in reverse. (It could)

hi hi


- emphasis mine

- that is all.

They do, however, fit into the current mathematical models of The Universe As We Know It. Meaning that a particle that cannot travel slower than the speed of light doesn't violate causality.

hi hi

Exactly, we wouldn't be able to interact with them in an information transferring manner, whether or not we could even perceive their existence. As they say, if your theory cannot predict future events, it isn't a very good theory.

Correct, but it doesn't mean they can't exist.

hi hi

Neither does it mean that a magic invisible teapot that lies between the Earth and Mars cannot exist either, but the burden of proof lies with the hypothesis, not the skeptic. Until someone can find an situation where a phenomenon makes a detectable difference, it might as well make no difference.

I <3 Bertrand Russel.

And as a physicist, I could say we couldn't care less. We build models to describe observations and make predictions; we don't deal with metaphysics and what "really exists or not". Fundamental interactions could in fact be due to gnomes, for all we know; yet, what we care about is how to describe them in a way that allows for accurate predictions via Quantum Field Theory. And the model doesn't have room for tachyons.

As for the analogy between the speed of sound and the speed of light, there has never been a physical argument that the sound barrier couldn't be broken. Alas, special relativity is a very tough little theory. I'm not going to predict that FTL travel/data transfer will never exist, but I am not betting on it as it looks quite unlikely.

As much as it hurts me to say this I must... then why are there so many theoretical physicists involved with string theory and areas of string theory that they admit will never be able to be tested?

Um no that will stay relatively consistent I think. I am saying that some one may bypass or circumvent a way to exceed the speed of light or travel distances that would make it seem like you were going faster than light, or learn something more about the speed of light that allows data or other objects to travel faster than it. Sort of like newtons laws they still exist and work, but we learned more and now they still are solid except under situations where we use relativity. So who is to say in the future we don't have something where we say relativity is still solid except under situations where we use the cupcake theory or whatever.

My sad guess based on human nature is that is where the grants are.

that would be really sad. I think physics has been badly infiltrated by Set theorists, theoretical topologists and philosophy majors.