'Ingenious' Experiment Closes Loopholes In Quantum Theory

Annanag writes: A Bell experiment in the Netherlands has plugged loopholes in the theory of quantum mechanics using a technique called entanglement swapping to combine the benefits of using both light and matter. It's Nobel-Prize winning stuff. Quoting: "Experiments that use entangled photons are prone to the ‘detection loophole’: not all photons produced in the experiment are detected, and sometimes as many as 80% are lost. Experimenters therefore have to assume that the properties of the photons they capture are representative of the entire set. ...

[In the new work], researchers started with two unentangled electrons sitting in diamond crystals held in different labs on the Delft campus, 1.3 kilometers apart. Each electron was individually entangled with a photon, and both of those photons were then zipped to a third location. There, the two photons were entangled with each other — and this caused both their partner electrons to become entangled, too.

This did not work every time. In total, the team managed to generate 245 entangled pairs of electrons over the course of nine days. The team's measurements exceeded Bell’s bound, once again supporting the standard quantum view. Moreover, the experiment closed both loopholes at once: because the electrons were easy to monitor, the detection loophole was not an issue, and they were separated far enough apart to close the communication loophole, too."

Comments

Wait, physics doesn't work either?

[damn_registrars]

This did not work every time.

I thought we were just picking on psychology today. Now we have a physics study that doesn't always work on the front page as well. Why is the physics study so awesome when it doesn't work all the time but psychology is evil if it doesn't?

Re:Wait, physics doesn't work either?

[Anonymous Coward]

You're trolling, right? There's a big difference between the two things...

Even if the entanglement experiment didn't work every time, it did enough to demonstrate that it's extremely unlikely that the results can be explained through chance. There's nothing wrong with this.

Hopefully if someone else repeated the entanglement experiment, they'd obtain similar results. The criticism of psychology study was the inability to reproduce the study and obtain similar results.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

The real reason for this barrage of science failures is how Slashdot responded to the proposition to teach people about the limits of understanding in each field of study.

A lot of people were posting and modding that Science should still be described as a collection of infallible knowledge for various reasons. So now we see the articles and studies pointing out how shit the processes and papers of all fields of science really are.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

The difference is, that we are speaking here about a failure rate of singular events, which is a technical problem, and requires a larger population of events for sufficient confidence.

That is contrary to the results the previous article, that regardless of the population size, we cannot reproduce the result, which is a systemic problem.

Re:Wait, physics doesn't work either?

[damn_registrars]

That is contrary to the results the previous article, that regardless of the population size, we cannot reproduce the result, which is a systemic problem.

No. That is not how psychology works. It is not ethical to conduct psychology experiments on arbitrarily large groups of people. You cannot say that the experiment was expanded to a point where you can make a statement about it "regardless of the population size".

It is shameful that you were modded up for that comment, it shows how little people on slashdot understand about psychology.

Re:Wait, physics doesn't work either?

[MyAlternateID]

The real reason for this barrage of science failures is how Slashdot responded to the proposition to teach people about the limits of understanding in each field of study.

A lot of people were posting and modding that Science should still be described as a collection of infallible knowledge for various reasons. So now we see the articles and studies pointing out how shit the processes and papers of all fields of science really are.

Large organized projects involving multiple people and intricate data tend to be shit, news at 11. Governments are the best examples of this but you also see it in corporations and not surprisingly science isn't magically exempt from the problems that occur whenever groups of people try to work together.

The real question is - exactly wtf is entanglement anyway? I can find lots to read about what it looks like and how it behaves... but what's the underlying mechanism? Is there even the most speculative explanation of it?

Re:Wait, physics doesn't work either?

[MyAlternateID]

No. That is not how psychology works. It is not ethical to conduct psychology experiments on arbitrarily large groups of people. You cannot say that the experiment was expanded to a point where you can make a statement about it "regardless of the population size".

Wouldn't that then make it even harder still to reproduce experimental results, which only further erodes the status of psychology as a science? You only seem to be confirming his point. That ethical concerns are part of the cause is irrelevant. He was discussing effect.

It is shameful that you were modded up for that comment, it shows how little people on slashdot understand about psychology.

The more they understand about it, the worse it looks. It's too bad for you if you don't like that. If you have some interest in the outcome, for example if you yourself are a psychologist, it would be considered a minimal level of integrity to disclose that ... since we're speaking of ethics now. Oh further along those lines, I wonder just how much the field is influenced by the incredible profitability of prescription drugs? I bet that would be a fascinating research topic.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

Well to be fair, little people on Slashdot don't understand much of anything, but that's to be expected, right?

Re:Wait, physics doesn't work either?

[Paradise Pete]

... but what's the underlying mechanism?

Nobody knows. It just "has" to be that way.

Re:Wait, physics doesn't work either?

[oh_my_080980980]

Actually it's the same thing, the ability to reproduce results. So it's a far comment. The author is jumping to conclusions. One experiment proves little. When others replicate, if any do, they you have something.

Re:Wait, physics doesn't work either?

[oh_my_080980980]

Look up the definition of science some time then post a comment. Hint, science isn't determined by the subject one studies but by the methods one uses.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

obviously you don't understand statistics, or scientific method...

Re:Wait, physics doesn't work either?

[nintendoeats]

I have a BA in philosophy and I took as many courses as I could on science and epistemology. The general concensus in these fields (of course with some disenters) is that you will always be able to ask this question about anything once you reach the scale boundries of our knowledge. When we say "gravity", what we really mean is a collection of rules which we are able to consistently produce accurate predictions from when applied to our observations. We can describe how a waterfall works in terms of gravity, but then when we ask how gravity works we must defer to some other system which then itself we will need to explain in terms of something else etcetera. I once grilled a chemist friend on what he meant when he said "electrons will always try to such and such" and he was stumped. It wasn't fair, because really the questions I was asking were based on a false appreciation of what the human study of natural law is able to be. Entanglement is a set of circumstances which we observe under certain conditions and believe are related to the point that we can give them a name. So are an apple, rugby, paint thinner and pornography. It is our own need for certainty that makes it difficult for us to accept this limitation of language and meaning.

Re:Wait, physics doesn't work either?

[suutar]

yep, and they replicated their result 245 times. The typical psych experiment doesn't have that luxury; it takes too long and too much effort.

Re:Wait, physics doesn't work either?

[suutar]

indeed, hypothesis tested by experiment. But lack of reproducibility calls into question the effectiveness of the testing.

Re:Wait, physics doesn't work either?

[MyAlternateID]

Look up the definition of science some time then post a comment. Hint, science isn't determined by the subject one studies but by the methods one uses.

Rather than making childish snide remarks (welcome to the net, eh?) try to understand what I am actually saying.

Reproducing the results of a scientific experiment using sound methodology is the only way to confirm that those results are valid. If those results cannot be reliably reproduced, then what you have is an idea or a philosophy, not a science.

It's the same reason phrenology was abandoned after being recognized for the pseudoscience it really was. There was no ability to reliably and repeatedly demonstrate its alleged findings. That's exactly what distinguishes science from pseudoscience. The "subject one studies" is immaterial, and I question your honesty for pretending like anyone was claiming otherwise.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

Yes, Oh My, what a retard...

Re:Wait, physics doesn't work either?

[MyAlternateID]

I have a BA in philosophy and I took as many courses as I could on science and epistemology. The general concensus in these fields (of course with some disenters) is that you will always be able to ask this question about anything once you reach the scale boundries of our knowledge. When we say "gravity", what we really mean is a collection of rules which we are able to consistently produce accurate predictions from when applied to our observations. We can describe how a waterfall works in terms of gravity, but then when we ask how gravity works we must defer to some other system which then itself we will need to explain in terms of something else etcetera. I once grilled a chemist friend on what he meant when he said "electrons will always try to such and such" and he was stumped. It wasn't fair, because really the questions I was asking were based on a false appreciation of what the human study of natural law is able to be. Entanglement is a set of circumstances which we observe under certain conditions and believe are related to the point that we can give them a name. So are an apple, rugby, paint thinner and pornography. It is our own need for certainty that makes it difficult for us to accept this limitation of language and meaning.

I appreciate your explanation. On the one hand, it almost sounds hopeless because the rabbit hole is bottomless, but at least we can enjoy increasingly more effective technology along the way. On the other, I can now rephrase my question thusly: "in terms of what other system could we try to explain the observed phenomena that we call entanglement?" Specifically (while I realize it cannot be used to transmit information), how is it faster than light? Is the concept of locality a defensible one?

Re:Wait, physics doesn't work either?

[nintendoeats]

Unfortunately I'm not at all equipped to answer those questions, and I hope that somebody here is. The one thing I can contribute is that it is theoretically possible for us to develop an internally consistent system of natural laws which both fit and predict all observable phenomena. If that were to happen then the question of what explains (or "causes", a term fraught with complication) that system would be purely academic and almost certainly unprovable, since we would already have developed the ability to predict and explain anything which we might use as a subject for experiment. Quantum physics may be on the edge of such system. It would be cooler if it wasn't though :p

Re:Wait, physics doesn't work either?

[Will.Woodhull]

To borrow, and mangle, a quote from B.W.:

"Psychology is not rocket science. Hell, it isn't even sociology."

Re:Wait, physics doesn't work either?

[Anonymous Coward]

Thank you, now let's see them do this at three or more different labs on different continents and post the results.

Re:Wait, physics doesn't work either?

[slew]

"in terms of what other system could we try to explain the observed phenomena that we call entanglement?" Specifically (while I realize it cannot be used to transmit information), how is it faster than light? Is the concept of locality a defensible one?

Interestingly enough like most effects of quantum mechanics, entanglement does not have an easy macroscopic analog to compare. One way to think about it is that it is a type of emergent behavior because of the rules that QM appear to follow.

More specifically, entanglement is kind of emergent behavior that is a logical consequence of conservation rules and quantum superposition states. If you believe in the QM rules regarding conservation (e.g, conservation of say spin), and QM rules involved with superposition wave function collapse (e.g., so called "observation"), the emergent consequence of these rules is a behavior we call entanglement.

The macroscopic analog is sort of as follows. Suppose you have 1 balls and 2 boxes. By some method hidden from you, the ball into one of the two boxes and it is sealed. If you believe in conservation of balls, The two boxes are now entangled. You can move them arbitrarily far apart and then open one box, if it has a ball, you instantly know the other doesn't have a ball.

Where this breaks down is how you put the ball in the box. In the QM version of this, the method of which you put the ball into the box doesn't really put the ball into the box, it simply puts a type of probability of a ball into a box. Interestingly enough, the box can act sort of like a 1/2 ball in the box until you open it and then it "collapses" and is either a ball or not ball. The strange part is how can it act as if there is a 1/2 ball in the box before you open it? If you think of the decision being made when you seal the box, there is some sort of locality, but if you think of the decision being made when you open the 1/2 filled box, there is non-locality and you need to use a concept like entanglement as an emergent behavior.

That is 1/2 ball in the box (part particle, part wave) is QM and nobody really understands that part, so there's really not an analogous macroscopic system on which to understand it, because the systems we are familiar with don't follow those rules.

On the concept of locality, it's really unknown. We generally think of distance and time (warped by general relativity) as the way we measure locality (e.g., light cones, etc), but there isn't a clear idea if there isn't a macro-dimension or holographic way that alters our understanding what is local or non-local. Using current theories, we already speculate that there are singular violations of locality (e..g, EPR's or worm-holes, etc), and we don't understand the fabric of space-time (e.g quantum gravity) well enough to say if our current theories about this are descriptive enough to yield our current intuitions about space-time locality or if it will be as weird as QM.

Re:Wait, physics doesn't work either?

[Gestahl]

On the other, I can now rephrase my question thusly: "in terms of what other system could we try to explain the observed phenomena that we call entanglement?"

Math. Specifically, complex linear algebra.

Re:Wait, physics doesn't work either?

[iris-n]

obvious troll is obvious.

Re:Wait, physics doesn't work either?

[rgbatduke]

"Entanglement" is a philosophically difficult arena. According to quantum theory, there is just one wavefunction for the entire Universe. However, we as observers are part of that wavefunction observing another part of that wavefunction with a really, really, big chunk of the whole wavefunction effectively unobservable but still coupled to the observer (part of the wavefunction), the measuring apparatus (part of the wavefunction), and the "experiment" (yep, part of the wavefunction. Everything is "entangled", but quantum mechanics also predicts that large systems approximated with a random phase condition will behave like a classical system, and the usual rule is that we treat a measurement apparatus as a classical system that breaks the entanglement of a measured systems and forces it "unpredictably" into a separable state. But even this is words, not equations although random phase approximations are indeed equations and are used frequently in field theory.

The only coherent explanation of this that I am aware of is the process of:

a) Starting with a density matrix (or other representation) for "the Universe".

b) Use the Nakajima-Zwanzig approach of splitting the (fully entangled) density matrix up into two parts -- a "system" that you will continue to treat as a quantum system, and a "bath" -- everything else -- which would also include the measuring apparatus if you were trying to describe an experiment. One then accepts the fact that one cannot know or prepare the state of the bath (which is really, really big being the rest of the Universe and everything) and so one makes a statistical approximation of the bath (taking the trace) which essentially eliminates the pesky entanglement but also breaks useful things like unitarity and in a sense, conservation laws. One them creates projection-valued operators and transforms the equations for the system into stochastic or semiclassical equations of motion.

c) IIRC your final result is quantum mechanics for the system expressed as a non-Markovian integrodifferential equation that is almost impossible to solve. However, if one makes a Markov approximation (forces it to be time-local, delta-correlates time) you end up with a decent explanation for things like spontaneous decay as an "exponential" process rather than a punctuated unitary process. You go one way, you can make it into a Langevin equation, go another you can make it more like Fokker-Planck.

The lovely thing about this approach is that it renders moot all sorts of nonsense, such as EPR paradoxes and "wavefunction collapse". It is perfectly clear that in the Universal wavefunction no such paradox or collapse can occur. They are simply expressions of our ignorance of phase and state whenever we try to isolate some part of the whole and pretend that it is a standalone "system" that can ever be decoupled from everything else. Schrodinger's cat paradoxes disappear as there is no paradox in the Universal wavefunction, only when we try to project the state of the cat against our ignorance of phase and interaction with the outside Universe. The cat, if you like, cannot be entangled separately from its preexisting entanglement with the rest of the Universe, and we only get into trouble when we have to force it by partitioning the system in order to get a chunk small enough to work with.

Hope this helps. I doubt it will. Very few people seem to be in touch with Nakajima-Zwanzig and the Generalized Master Equation these days, and don't treat problems like this as OPEN quantum systems as opposed to closed systems with a classical measurement apparatus, which is a place you only get to on the far side of the N-Z GME ritual.

rgb

Re:Wait, physics doesn't work either?

[lgw]

The real question is - exactly wtf is entanglement anyway? I can find lots to read about what it looks like and how it behaves... but what's the underlying mechanism? Is there even the most speculative explanation of it?

Here's the best answer I can give you - I think it's true, and not so over-simplified as to be wrong.

The universe has some underlying state. We don't have direct access to that state - not only is it not directly observable, it's not directly related in any intuitive way to the state we can observe. There's this arbirtary-seeming transform between underlying state and what we observe (it only seems odd or arbitrary because all our intuitions are based on human-scale observables, and are not at all directly informed by this underlying state). This underlying state seems to be well-defined and deterministic, forwards and backwards in time. The observable universe is not.

Entanglement is a feature of how observations relate to underlying state - a feature of the transform. In very simple experiments we can measure specific properties of, say, an electron. We can't measure all of them, for a given electron, because the transform just doesn't work that way, but we can measure some. However, that's deceptive, because you can't really track that property of that electron over time, in non-trivial cases. If e.g. two electrons interact, become entangled, your observations are now a function of both electrons' underlying state, and that's a different transform from 2 non-entangled electrons.

There are two key concepts here. The first is that the whole notion of "particle" is a handy but false oversimplification. It can lead you to all sorts of false intuitions about how particles behave. Fundamentally, individual e.g. electrons don't have unique identities. The underlying state is a single electron field, which other fields can interact with, in a way that can sometimes be simplified as "particle interactions", for a simpler mental model, but you can't go too deep with that model. An example: "two electrons collide in an accelerator, and two electrons leave, which is which?" That question is "not even wrong", it's just nonsense. Thinking of electrons as billiard balls colliding is simply not a helpful model, as it just misses the point of the interaction.

"Entanglement" happens just when the "particle" mental model fails: you can no longer pick two disjoint areas in the electron field and consider them as independent "electrons", but instead you have to reason about two areas which may be quite disconnected in space and time. E.g., you might know for sure that one electron is spin-up, and one spin-down, but have 0 information about which is which. None of that matters to the underlying state: there's just one electron field, and the only truly correct way to reason about it it to reason about the whole field all the time, and so this is only half of "WTF is entanglement".

The second concept gets too much into the math to explain well, but in a hand-wavy way it's this: "what is measurement?". There are older interpretations about measurement causing wavestate collapse and so on, but they're wrong because of that word "cause". Measurement is simply the observer becoming entangled with the observed. Measuring one entangled electron doesn't "cause" the other electron to do or become anything. The underlying state is unchanged, which is why there's no faster-than-light effect. In some cases, this is an overly pedantic distinction, but it matters when the difference between QM and intuition matters. In a two-slit experiment where you see an interference pattern at your detector, if you add a measuring device to one slit suddenly you don't see that interference pattern. Informally we might say the second observer "caused" this change, but formally that's wrong, it's just that a system with 2 slits and 2 detectors behaves differently from a system with 2 slits and one detector, and it doesn't matter which detector the electron passes first, because (see above) an "electron" as a discrete particle is fiction anyway, and both detectors are entangled with the electron field already, or they couldn't measure an electron anyhow.

Re:Wait, physics doesn't work either?

[HiThere]

I'm not sure I consider those replications, as they are all using the same equipment, and if there were a systematic problem, then there might well be a systematic effect.

OTOH, this is, essentially, a replication of experiments done previously, with a couple of added features, and it's results are consistent with those prior experiments. *THAT* I do consider a replication.

Given the nature of publishing, the study that confirms this one will also need to have some changes. It shouldn't be that way, but journals won't print *mere* replications, you've got to have some extension.

Re:Wait, physics doesn't work either?

[ceoyoyo]

I think the answer is "we don't really know." One of the criticisms of the standard model is that, although it has fantastic predictive ability, it doesn't have much explanatory ability. It can't even tell you something as seemingly simple as why an electron has the rest mass that it does.

However, you might find the phase/state/configuration space formulation of quantum mechanics more intuitively satisfying. You can imagine a quantum system as being a particular state space with rules restricting how you can move.

Maybe some new developments, such as the holographic hypothesis, will provide more explanatory power.

Re:Wait, physics doesn't work either?

[nintendoeats]

I'm intrigued by the elimination of the word cause to which you allude. I like this very much because it fits in very well with the philosophy. If you ask somebody what the word cause means they will only be able to give you similies of the word cause, but nothing else that stands up to scrutiny. They might say "well, it's a factor without which the event would not have taken place", but then it is clearly in defiance of what we want to say for me to claim "I drove to Ottawa yesterday because there are roads. I couldn't have driven to Ottawa without roads, but neither did I drive there because there were roads. A set of circumstances existed under which me driving to Ottawa was an event that was going to happen. From your description, entaglement appears to be a way of replacing cause with sets of circumstances that only care about the entire state of the system. Cool!

Re:Wait, physics doesn't work either?

[ceoyoyo]

Your "underlying state" seems equivalent to a "hidden variables" theory. Note that the Bell inequality says that if the universe is local (no action at a distance, special relativity, etc.) then hidden variable theories cannot reproduce the observations of quantum mechanics.

It's possible the universe really does have a deterministic nature that is hidden from us, but if that's true then the laws of physics are not local. We tend to shy away from that option because of the success of special relativity, and prefer the other: that the universe really doesn't have a deterministic underlying reality.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

Infinite regress can be invoked to discourage asking ANY questions.

You were asking fair questions - your chemist friend just didn't know the answers. That's not a bad thing.

It's the need for certainty that prevents us from embracing the infinite, not the other way around. (Said with a sense of humour.)

Re:Wait, physics doesn't work either?

[Godwin O'Hitler]

Wow. +1 "Enlightening".

Re: Wait, physics doesn't work either?

[Anonymous Coward]

Just another way of defining irrelevance.

Photons dont perceive time. They travel at 'c'. The closer u get to c the slower time gets from our point of view until it stops. C is speed / 0 seconds. it doesnt matter how slow u go if its in 0 seconds. Its still.infinite speed relatively. There are almost an infinite number of vacuum points between the bonds of any material even diamond so if it can get to a speed of c in just one of those then bam its not a particle any more and its entire lifetime is destined in that instant. Its influences are everywhere
whether its a few kms in the netherlands or across the stars. ..even if it was sdpc'd at that instant in a vacuum free material which it undoubtedly wasn't

Re:Wait, physics doesn't work either?

[ceoyoyo]

You're mixing up generally irreproducible results and a situation where a proportion of reported results are not replicated.

Modern psychology is very much a science, using the scientific method. However, due to the difficulty of studying it, the requirements for publishing a result are low enough that many of them turn out to be incorrect (not reproducible). That these results are eventually found to be incorrect is a validation of the scientific nature of psychology.

ANY subject involving a complex, difficult-to-study subject is going to have the same problem. Most fields like that, psychology, medical science, ecology, systems biology, etc., prefer allowing reasonable sized studies (usually less than a few million dollars) to be published, knowing that they may be incorrect, then replicating the interesting ones. Particle physics has tended to go the opposite way, where high profile results are not published until the confidence is very high, but those results also cost billions to achieve. Lots of less high profile results are, of course, held to lower standards.

The real lesson to take from the problem of replicability is not snide "psychology isn't a science" but rather that being published in a journal (hopefully) means that the study was done in a scientific way, but is no guarantee that it's true.

Re:Wait, physics doesn't work either?

[david_thornley]

Locality doesn't work. These experiments can be done with electrons, and we can measure the spin. If one electron has spin up, the other will have spin down if measured along the same axis. If the measurement axes are different, you can calculate how likely one electron is to have spin down if the other measures as spin up based on assumptions. It turns out that the observed probabilities don't match the ones you'd get if they had what you'd expect if the relation was based on locality. Look up Bell's theorem.

Re:Wait, physics doesn't work either?

[MetricT]

Entanglement may actually have a macroscopic analog, just not one we have experienced yet. Spend some time Googling the "ER=EPR Conjecture".

The TL;DR is "entanglement and wormholes are different manifestations of the same underlying thing"

Re:Wait, physics doesn't work either?

[david_thornley]

You can get a very limited idea of entanglement by thinking of two envelopes, one red card, and one black card. If you put one card in each envelope, you've got envelopes entangled in the sense that if you open one you know the color of the card in the other, wherever it may be.

Now, we figure that we can open the envelopes in different ways with different but related results (if we open them at the bottom, the cards change color, and if we open right along a side it's random which card is which color, and it gets more complicated), that we can open the envelopes differently (one at the top and one at the side, for example), and that we can influence the probabilities by opening the envelopes in certain ways that aren't explained by the original state of one black and one red. This is where it gets complicated.

Re:Wait, physics doesn't work either?

[david_thornley]

There are sciences where we can't conduct experiments, astronomy being the obvious one. Hypothesis tested by observation includes these.

Re:Wait, physics doesn't work either?

[lgw]

our "underlying state" seems equivalent to a "hidden variables" theory.

No, it's just the sloppiness of English trying to represent math, or perhaps my lack of facility with one of those in trying to craft a metaphor.

To extend my above metaphor: there's no hidden "observable" state. The underlying state is not "this one spin-up, that one spin-down" (which is forbidden), because there are not electron identities anyhow, but instead "exactly one of them is spin-up". As you measure one of them, there are now three entangled things: the two electrons and your detector, and there's a set of allowed observables given all that, when you add the second detector, now there are 4 entangled items. It's not non-local, it's just a constraining of the set of allowed states for the complete system.

Re:Wait, physics doesn't work either?

[suutar]

That's probably a better phrase, I agree. While the definition of "experiment", as I understand it, does include "set up a telescope and see what's there" (being "an act for the purpose of discovering") the common perception includes setting up equipment to ensure that what you're watching turns out to be interesting :)

Re:Wait, physics doesn't work either?

[nintendoeats]

It can be invoked to discourage any question, and I don't believe that it should stop us for looking for answers. However, there is no point in denying a logically true fact. In my view the only way to be both intellectually honest AND productive is to say "I will never be able to fully explain anything, but the more I can the better".

Re:Wait, physics doesn't work either?

[lgw]

Everything in physics works in both time directions (you have to swap some signs +/- when you reverse time, but it all works). Causality as "a chain of related events over time" is a real thing, even if what you place in the chain may be somewhat arbitrary, but the direction, which is cause and which is effect, isn't so well defined. At the QM scale it's arbitrary. In human experience, a film played in one direction looks different than in the other because, ultimately, of the energy input from the Sun breaking the symmetry.

Re:Wait, physics doesn't work either?

[Apolloe]

Bell's inequality shows that both local hidden variable AND stochastic theories cannot reproduce the observations of quantum mechanics. Bell's theorem showed that the universe is non-local, regardless of your preferred interpretation. Bell himself promoted a pilot wave interpretation.

Many people have misunderstood Bell's result to be saying something against hidden variable theories. It isn't. It is saying something against locality.

Re:Wait, physics doesn't work either?

[damn_registrars]

It is shameful that you were modded up for that comment, it shows how little people on slashdot understand about psychology.

The more they understand about it, the worse it looks.

Quite the opposite most of the time. A big problem here is that a lot of people (particularly people on slashdot, though this happens in many other circles as well) think they know a lot about psychology because they have read a lot of angry rants against it, even though they have never had formal exposure to the fundamentals or history of psychology.

If you have some interest in the outcome, for example if you yourself are a psychologist, it would be considered a minimal level of integrity to disclose that ... since we're speaking of ethics now.

I am not a psychologist. I have friends and colleagues who are, and I took psychology as an undergrad. My work is in a more contemporary hard science.

It is noteworthy that you call up ethics here, when earlier in the same comment you said

That ethical concerns are part of the cause is irrelevant.

Nice of you to so consistently show concern for ethics.

Oh further along those lines, I wonder just how much the field is influenced by the incredible profitability of prescription drugs?

Last time I checked, few states allow psychologists to write drug prescriptions, that job is usually left to (medical school trained) psychiatrists (wikipedia shows only three states grant that ability to psychologists in the US). Psychologists have little to gain financially by encouraging pharmacological treatments for their patients.

I bet that would be a fascinating research topic.

The most commonly prescribed (in terms of patients who have had it prescribed to them) drug for mental health use is Prozac, which has been available generic for some time. Once a drug has become available generic, the profit is nearly gone. If you want to look in to the prescribing rates of new drugs for mental health versus other health conditions, and compare which are prescribed more quickly, that may indeed be an interesting topic. Your bias is so evident here though that I would be shocked if you were to ever attempt to undertake such a study.

Re:Wait, physics doesn't work either?

[fyngyrz]

See, what you're missing is simply that it's turtles all the way down.

Re:Wait, physics doesn't work either?

[fyngyrz]

No. That is not how psychology works.

Certainly not. Since psychology doesn't work. Period.

Re: Wait, physics doesn't work either?

[Demena]

Name a non theoretical place where a photon achieves c. C is the unobtainable velocity - even by a photon as there is no true vacuum. Division of anything by zero in the way you are using it results in infinity, notc.

You are coming upon an old conundrum. Does every particle "know" about every other particle or not? How does a rotating reference frame know it is rotating? The side that you are taking will be disproven if gravity waves are found. That is a vast oversimplification but I think the question is still open. I am willing to be corrected.

Re: Wait, physics doesn't work either?

[master_p]

The Bell's theorem is based on the assumption that if there are local variables that are hidden, the result measured spins of the particles would be linearly correlated to the angles these particles are created from.

I do not see how this assumption is valid though. Particles are not billiard balls. Particles may have properties that force their spin into specific correlations. It is stupid to accept that local variables would mean linear correlation.

Re: Wait, physics doesn't work either?

[Anonymous Coward]

C is the unobtainable velocity - even by a photon as there is no true vacuum

One of the important results of QFT is that the properties we measure of particles we measure already takes into account the false vacuum.

Not the same AC, as the GP seems to make the same mistake as a lot of people when taking into account time dilation, but not length contraction, and also additional nonsense.

Re: Wait, physics doesn't work either?

[Anonymous Coward]

Bell's inequality just applies to the probabilities of systems based on the probabilities of how things act when not entangled. It isn't specific to polarization or spin behavior, although the systems easiest to measure usually use on of those. And when it comes to projecting spin onto a specific axis, there is a nice, heavily verified, relationship that just amounts to being vector projection.

Re:Wait, physics doesn't work either?

[damn_registrars]

No. That is not how psychology works.

Certainly not. Since psychology doesn't work. Period.

It is a safe bet that if you are willing to make such a sweeping and silly generalization that you haven't studied psychology yourself much - if at all. You encounter successful applications of psychology in your daily life regularly without realizing it, and the influence of psychology on other sciences is also significant.

Re:Wait, physics doesn't work either?

[Anonymous Coward]

I tend to agree. I'm an instrumentalist / pragmatist.

Re: Wait, physics doesn't work either?

[therealkevinkretz]

Systemic

Re:Wait, physics doesn't work either?

[cwsumner]

See, what you're missing is simply that it's turtles all the way down.

No it isn't! Didn't you see "The Color of Magic" ? 8-)

Re: Wait, physics doesn't work either?

[Anonymous Coward]

In Special Relativity the constant c is simply the (theoretical) velocity of a massless particle. "c" is the sole parameter of the Poincare group, which is the symmetry group of Special Relativity. It is *defined*, rather than measured. However, for various reasons outside of Special Relativity photons are expected to be massless. Experiment bounds the upper limit of the photon mass as _very very very_ close to c.

Free space takes its definition from a particular choice of "c" as the parameter of its symmetry group. Experiment may someday reveal that our choice of "c" needs a slight adjustment, or alternatively (and more shockingly) that photons and other gauge bosons are not massless and therefore should not move at "c" in free space.

However, there is a LOT of evidence (from all sorts of experiments in vastly unrelated fields) that the speed of light is c to within present-day measurability. A substantial amount of that evidence also involves non-vacuum conditions, where e.g. diffraction or birefringence is calculable in a background independent way (i.e., making no assumptions about free space), which in turn suggests that the particular choice of "c" in defining free space is almost certainly correct.

Is quantum mechanics a theory?

[Viol8]

A theory is supposed to explain something. Quantum mechanics doesn't explain anything, its more a mathematical description of *what* happens, not *why* it happens. As far as I'm aware the "why" still eludes us as much as it did 100 years ago when Einstein and Bohr were arguing it out.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Science doesn't explain why at all. How could it?

No number of cannonballs dropped off of towers will tell you why they fall.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

A theory is a piece of supposition about the universe (normally dressed in mathematical formalism), backed up by observation. It helps us predict future events.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

A mathematical description of what happens is exactly what one wants. If you cannot show anything, what happens and is not covered by the mathematical description, and you can deduct things what will happen, that wasn't known before, then you have a theory.

If you want an answer to the question why, you are not looking for science.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

A theory is supposed to explain something. Quantum mechanics doesn't explain anything, its more a mathematical description of *what* happens, not *why* it happens. As far as I'm aware the "why" still eludes us as much as it did 100 years ago when Einstein and Bohr were arguing it out.

No, if you want "why" or "truth" look into the philosophy department.
Quantum mechanics describes a fucking ton of things, from the cohesion of atoms and molecules, to the workings of conductors, semiconductors en passant light and light/matter interactions. And much much more.

Re:Is quantum mechanics a theory?

[N7DR]

Even most physicists don't understand Feynman's point that QM is called "mechanics" for a reason: it's a set of mechanical rules for getting the right answer. It tells you nothing about how the universe operates behind the scenes so as to produce the same answer as QM. Feynman's little easy-to-understand book on QED should be read by everyone who thinks that QM is more than a tool for performing calculations. (And read Tegmark's book for an example of what happens when an intelligent person reads meaning into QM.)

Regarding the actual article: at first sight, this looks like a great experimental verification of something that no one (as far as I know) doubted; but it's always good to confirm another prediction of QM that appears bizarre to us.

Re:Is quantum mechanics a theory?

[Viol8]

"No number of cannonballs dropped off of towers will tell you why they fall."

Umm, gravity.

Re:Is quantum mechanics a theory?

[blazer1024]

Why does gravity exist?

Re: Is quantum mechanics a theory?

[Anonymous Coward]

And nobody understands how gravity works (we only understand the side effects of gravity).

Re:Is quantum mechanics a theory?

[Viol8]

"No, if you want "why" or "truth" look into the philosophy department."

Thats a bit defeatist. Science has always been about explaining the "why". Why is the sky blue, why do the planets going around the sun etc.

"Quantum mechanics describes a fucking ton of things"

It doesn't really explain anything. Its a convenient probabilistic bucket to put stuff in that we don't really understand but like to give it a name anyway.

"What" is for engineers. Physicists should always be aiming to answer the "why". Anyone can use equations, explaining why they work and where they come from is should be theoretical physics main goal, even if ultimately there's a level of reality we can't understand or progress beyond. No hand waving philosphers should be required.

Re:Is quantum mechanics a theory?

[GuB-42]

What eludes us is the interpretation. Or in other words, we didn't find a way to fit this theory in our limited human minds. But the theory works, and it explains things, with maths.
The interpretation is important, but only because it makes working with the theory more intuitive and therefore allow us to progress faster. However, the true essence of any theory in modern physics lie in its mathematical description and how well it matches reality.

Re:Is quantum mechanics a theory?

[Tablizer]

It's true that a model is not necessarily an explanation. Epicycles had predictive value (if tuned well), but almost all agree it's not how planetary motion "works". Newton gravity is considered a better explanation because it's the simplest working model: Occum's Razor.

If a better model comes along, we may make that the top model, ie, the "best explanation so far". Maybe there is no gravity, only something that happens to fit our gravity model. We do more experiments to find that out by testing the model more and testing alternative models.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

entropy dictates energy prefers averaging out to stasis by going in every conceivable direction...throw a big mass in the mix that absorbs said energy into the form of vibrating electrons; whatever is adjacent to said matter will be acted on by energy from every other vector sans the aforementioned one..thereby being pushed towards matter rather than attracted? that or i have nofingclue

Re:Is quantum mechanics a theory?

[Viol8]

Things fall because of gravity. Thats an explanation. Why does gravity exist is another question entirely. There's probably endless levels of reality to go down through.

Re:Is quantum mechanics a theory?

[Rob Riggs]

"No number of cannonballs dropped off of towers will tell you why they fall."

Umm, gravity.

Why does gravity exist?

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Gravity is just a label we put on the phenomenon that causes the cannonballs to fall. We don't know why this phenomenon emerges, thus we don't know why cannonballs fall.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Measurements on two particles are dependent because the particles are entangled. That's an explanation. Why does entanglement exist is another question entirely.

There is no necessity that reality consists of endless levels. There can be a "rock bottom" of existence that just "is", and cannot be explained.

Re:Is quantum mechanics a theory?

[MyAlternateID]

Fuckin' magnets, how do they work?!

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Quantum mechanics explains chemistry, how atoms bind together to form molecules. You call that nothing?
The fact that you can predict from first QM principles that CH4 is a stable molecule, and OH4 is not (but H2O is) is well beyond a "probabilistic bucket" I would say.

Re:Is quantum mechanics a theory?

[suutar]

It's been about explaining the "why" questions that really translate to "what's happening that results in this phenomena".

Re:Is quantum mechanics a theory?

[TooManyNames]

Gravity exists because spacetime, curved by massive bodies, effectively changes what it means to have inertial reference frames from the more intuitive Newtonian notion. Take away the massive bodies and spacetime flattens, straight lines are Euclidean, and gravitational attraction goes away. Gravity, then, exists due to the interaction between mass and spacetime.

Of course, you could ask why that interaction exists, and keep asking the question as more explanations are found. I don't know that that'd ever end, but I guess you could eventually hit some inherent axiom or self-referential property of nature. If you're asking for some ultimate underlying conscious intention, though, you may find yourself disappointed, or at least you should accept the possibility that such a question may simply not apply.

Re:Is quantum mechanics a theory?

[MyAlternateID]

There is no necessity that reality consists of endless levels. There can be a "rock bottom" of existence that just "is", and cannot be explained.

If it cannot _ever_ be explained, not by any level of understanding and technology, then you're really just using a non-traditional description of theology.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Why does gravity exist?

No such thing, it's just curved spacetime...

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Science has never tried to explain the WHY. Science is about the HOW. That's a fundamental staple of the scientific method. Once we understand HOW science is basically done. This isn't to say science won't find some answers as to "WHY" but that's not the goal.

The mathematical theory we call quantum mechanics does an incredible job of describing the HOW. And lets not pretend this is just some idea someone dreamed up one night, this is a mathematical theory that was put forth decades before we had the ability to test any of it.

We now have the ability to test it, and the theory is passing each and every test, the results we see in labs are the exact results predicted by the theory.

Gravity is a theory. The theory doesn't ask WHY and doesn't attempt to answer it, what it does do however, is explain HOW gravity affects us and provides repeatable, and falsifiable tests we can run against it. We've proven gravity exists, it's a basic fact and life on this planet requires it, because we were evolved within the system that has gravity.

WHY does gravity work as it does, and what is the underlying mechanism? We don't know, but if we have any hope of knowing, it will be quantum physics that explains it.

The Higgs for example, yes I know that's still arguable, but the THEORY makes sense and if we have indeed found evidence of the Higgs, the theory was right. Mass doesn't actually exist, mass is the resistance offered by the "ether" as objects move through it. This changes everything, if we can prove we've found the Higgs.

The problem with WHY is that the goal posts are static, we can never get a definitive answer because science doesn't really do "absolutes", science does 99% sure. Why did the planets form as they did? We answered that by discovering the HOW. But then, the why becomes why is the universe built in such a way to have these natural laws? We can't answer that because we live in this universe and simply can't fathom one with different laws of nature.

The WHY is left to philosophy until we can uncover enough of the HOW to explain away any silly WHY questions.

Quantum entanglement is real, testable, repeatable, and falsifiable. Just because we're not at a stage that we can explain the underlying mechanisms, doesn't mean the theory is wrong.

Beyond that, just because you can't find this information doesn't mean it's not out there, google is NOT the be all end all source of information, and in relation to quantum mechanics and more to the point, entanglement, this is still a fresh field. I suspect that if you ACTUALLY wanted to understand it, you'd buy some of the same books I did and actually read them.

In short (haha I know) Quantum mechanics explains fucking reality, I'm not sure how much more "explaining" you need.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

or you have at least a cursory understanding of basic mathematics.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Gravity is just a word to label the force that causes things to accelerate in a downward direction. It doesn't explain anything. You could as easily say things fall because of gremlins.

Re:Is quantum mechanics a theory?

[gtall]

"Newton gravity is considered a better explanation because it's the simplest working model"

Yes, and no. The simplest has a certain charm to it, but that doesn't make it more correct. What makes a theory more correct, aside from predictive value, is how well the elements and relationships of the theory correspond to elements and relationships of the physical system.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

It doesn't really explain anything.

It was created in the first place to explain things, and deal with stuff like atomic structure and the ultraviolet catastrophe where previous theories failed. It goes on to address a large number of experiments now, including many done by undergrad students in a routine lab course. Just about anything involving atomic or small scale electron behavior end up involving quantum mechanics. There are plenty of electrical and semiconductor devices, especially like a tunneling diode, that are explained by quantum mechanics. You can develop phenomenological explanations for how some of them work, but quantum mechanics gives a more fundamental approach that allows better design and optimization beyond just extrapolation of device behavior.

Re:Is quantum mechanics a theory?

[alteran]

Gravity is not just an explanation-- it's the LAW.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

No, the key point is your description needs to match observations, and have predictive power. If it continues to do so after many tests, and you can't come up with a fundamental explanation, "why," at worst you have is phenomenology, which is still a large part of science.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

I'm pretty sure it's not the Mogwai that's making things fall.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Things fall because of gravity. Thats an explanation.

No, that's wordplay. That's assigning a temporary variable.

What is x?

y=x.

Okay, dumbass, what is y?

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Why do people think that naming something is the same as explaining it?

Re:Is quantum mechanics a theory?

[Anonymous Coward]

You seriously invoke infinite regress?!

You're not the only one doing that on this thread, but seriously, what a bunch of stuffy, staid minds. You mights as well say "We don't like such impertinent questions!"

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Why does mass appear to curve space-time? (Same question really, just phrased differently.)

Re:Is quantum mechanics a theory?

[Anonymous Coward]

IQ test
The comment by Vio18 is worth discussing = you fail
The comment is obviously silly, and should be ignored = you pass

Re:Is quantum mechanics a theory?

[HiThere]

There *are* interpretations of quantum mechanics which *do* explain the "meaning" of the equations. (I'm guessing that's what you mean by "why".) Unfortunately there are several different interpretations that are consistent with the math. My favorite is the Everett-Graham-Wheeler multiworld model, but it's not the only alternative, and so far there seems to be no way to choose between them. But there are only a few interpretations, so most possible ideas of how things could work, and what it all means, are incorrect.

E.g., if you hypothesize that some god is running things, you need to presume that he's systematically interfering with the experiments (or that he just created the universe 3 seconds ago complete with all internal evidence of consistency). If you do, that is consistent with quantum theory. But it's not a very useful interpretation, as it doesn't allow you to make any predictions. Another useless theory is "When the universe happened to come into being, it was set with a series of values that specify everything that is ever going to happen down the the sub-atomic level from the first instant of existence until the final end. That can be made consistent. (Actually, that one is useful if you combine it with a theory that the simplest possible set of constraints was used.)

The multiworld hypothesis basically says that the universe splits with every quantum interaction, and you move forwards into all of the results with a probability density that reflects the probability of the quantum events involved. At the high level that we interact with things that translates into "an honest die has a 1/6 chance of coming up with a 6". So it's one of the useful interpretations. And the Copenhagen interpretation basically says "Shut up and calculate. No explanation is possible.". Most working physicists prefer the Copenhagen interpretation, because it makes things simpler (without changing the math). There are others. Look up "implicate order" for example.

Re: Is quantum mechanics a theory?

[HiThere]

Sorry, that's Newtonian. Einstein's gravity exists because mass warps space-time. Now as to why it does that.....

Re:Is quantum mechanics a theory?

[Anonymous Coward]

A lot of people were laughing at these clowns because of this lyric. That's right. They were laughing at clowns. Literal clowns. With no sense of irony.

Second, when a layperson starts to openly wonder about the mysteries of electro-magnetism, do they deserve ridicule and scorn?

Re:Is quantum mechanics a theory?

[HiThere]

Actually I worked for awhile on a variation of that, but it depends on the presence of mass slowing time, so that particles experience a slight preference to end up in slower time than in faster time. You've got to rewrite the equations to describe space as flat, and all the bending to be handled by variations in the speed of time (WHAT???, but yes). I was assured that this was a reasonable and valid thing to do. I never did learn enough quantum theory to try to convert this into a general theory of gravity, but I think it would work.

But that's just mechanism. Mechanism can't answer "why?". Why demands an agent with a purpose. So the real answer is that English doesn't properly describe the universe, and implicitly attributes to various things characteristics that they don't have. (It may not just be English, perhaps it's a part of the essential human thought process. That kind of assumption could be an asset in detecting a lurking predator.)

Re:Is quantum mechanics a theory?

[Tablizer]

I need clarification of that. There are no "elements" in Newtonian gravity. Epicycles can be quite accurate if enough "layers" are used. Think of it as "circular regression".

Re:Is quantum mechanics a theory?

[david_thornley]

Gravity is inertia through curved spacetime. It happens that mass has a local effect on spacetime that distorts geodesics.

And now, all together...

What's inertia, and why does it happen like that? What's spacetime? What does it really mean for spacetime to be curved? Why does mass curve spacetime? What is mass?

You can get at least partial answers to some of these if you ask somebody who knows more than I do, of course.

Re:Is quantum mechanics a theory?

[david_thornley]

Theology isn't an experimental science. Physics is. We can be sure that something works in physics even if we don't understand it. How are we supposed to be sure that anything in theology works in the real world?

Re:Is quantum mechanics a theory?

[david_thornley]

The difference between quantum mechanics and just any convenient probabilistic bucket is that it has excellent predictive value. Using the known principles of quantum mechanics, we can calculate what we'll observe in all sorts of experiments, and the experimental agreement is extremely good.

As it happens, there's a lot of numbers that are vital in making these predictions, and there's a lot of them with no obvious relation to each other, which look completely arbitrary. In science, when we learn something, it usually leaves more questions. That's what makes it fun.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

The problem I have (as a layperson admittedly) with the shut-up-and-calculate notion is how will that lead to a new theory? I think that people trying to make sense of QM by interpreting what is happening is more likely to lead to new predictions or a more complete theory. For example the pilot wave interpretations lead to DeBroglie-Bohm where it includes an additional governing equation not present in other interpretations. Though according to this professor it lags behind regular QM in the prediction area thus far.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

The problem I have (as a layperson admittedly) with the shut-up-and-calculate notion is how will that lead to a new theory?

The same way you've always made new theories: question assumptions, try new ideas... shut-up-and-calculate with the new ideas. Mathematicians come up with new ideas and theories for things often completely disjoint from physical concepts. And usually new ideas are a dime a dozen, but ideas that can be put down in a formal sense and used to make quantitative predictions are in much shorter supply.

Re:Is quantum mechanics a theory?

[Anonymous Coward]

Gravity exists because spacetime, curved by massive bodies, effectively changes what it means to have inertial reference frames from the more intuitive Newtonian notion. Take away the massive bodies and spacetime flattens, straight lines are Euclidean, and gravitational attraction goes away. Gravity, then, exists due to the interaction between mass and spacetime.

I thought gravity was mediated by an, as yet unobserved, particle called the graviton though? How can effects of the curvature of something fundamental like space-time be mediated by a particle?

Re:Is quantum mechanics a theory?

[CmdrTamale]

particles experience a slight preference to end up in slower time than in faster time

That's what refraction does for rays and waves, always turning toward the slowest direction. Is that any help? Can you give any references? Your work sounds interesting.

And to respond to the initial question - gravity exists because we agree on the narrative.
--
Your ideas are intriguing and I wish to subscribe to your newsletter.

Re:Is quantum mechanics a theory?

[HiThere]

Sorry, I never worked out the math. I did talk to a physics grad student about the concept (of refactoring the equations to put all of the distortion into time) and he said it was valid. I was never an advanced math student, and tensors baffle me, so I'm not the person to work out the math. I just throw out the idea from time to time to see if someone else will develop it.

But I do think it would work.

Loopholes in the experiments not the theory

[Barbecue911]

I'm not an quantum physicist, but the loopholes appear to be in the experiments intended to demonstrate the "spookiness" of quantum theory, not the theory itself:

The first Bell test was carried out in 1981, by Alain Aspect’s team at the Institute of Optics in Palaiseau, France. Many more have been performed since, always coming down on the side of spookiness — but each of those experiments has had loopholes that meant that physicists have never been able to fully close the door on Einstein’s view.

Re:Loopholes in the experiments not the theory

[multimediavt]

I'm not an quantum physicist, but the loopholes appear to be in the experiments intended to demonstrate the "spookiness" of quantum theory, not the theory itself:

The first Bell test was carried out in 1981, by Alain Aspect’s team at the Institute of Optics in Palaiseau, France. Many more have been performed since, always coming down on the side of spookiness — but each of those experiments has had loopholes that meant that physicists have never been able to fully close the door on Einstein’s view.

I'm gonna argue with you on this new info not closing loopholes in the theory. Until there is proof (demonstrable and repeatable) to back a theory there are loopholes or gaps in the theory. Once the gaps and loopholes have been closed through experimentation the theory comes closer to being fact and not theory. The loopholes existed in the quantum entanglement experiments because of less than ideal methodology, testing conditions, apparatus, etc. in trying to apply the theory to reality.

Re:Loopholes in the experiments not the theory

[elfprince13]

Proof is a word for mathematicians, not for statisticians.

Re:Loopholes in the experiments not the theory

[Anonymous Coward]

Proof certainly is a word for statisticians, as statistics is a branch of mathematics, and everything should be backed up by mathematical proofs. Intro stats courses don't show this, but anything beyond the basic cookbook stat test course should be like any other abstract math course: full of proofs. Now inductive logic on the other hand...

Re:Loopholes in the experiments not the theory

[Anonymous Coward]

So the mathematical proof of how propensity score analysis, the statistical approach to estimating causality in observational studies is for...?

Re:Loopholes in the experiments not the theory

[Barbecue911]

I won't argue that there are still holes in the theory. But those are holes similar to the gaps in the theory of evolution. The theories are sound as a whole but there are still mysteries to be solved.

spirit of creation keeps blips in sequence

[Anonymous Coward]

almost in a tailspin now over our selfish neglect of each other...... catch our breath... in the moms we trust

Obvious flaw

[Anonymous Coward]

I take a photon, I split it into two identical photons. I filter Photon 1 for a property X, Photon 2 goes into an experiment. I only consider results from the experiment when Photon 1 had property X (and thus so did Photon 2 and thus the experiment shows results only for photons carrying property X).

This is the issue here, the proof of entanglement is false, it is simply a filtering effect, you are not setting the photon to have X, you are detecting WHICH photons have X, and choosing the corresponding result, which... bingo.... is a result for X!

This experiment does not fix that, because they do the exact same filtering to determine the photons are 'entangled'. In other words its 245 entangled pairs out of N set where N is very large. The only time they would fail is if two photons were emitted so close together that there was not enough time between the two photons being emitted for the electronic circuit (usually called a coincidence circuit) to separate them. Bells hypothesis (a statistical claim that there is no hidden variable shared by both photons) is moot because the *TIME* they were emitted is the variable they are both tagged with. They do not carry a property, the experiment is designed to SLOWLY pump in photons so they can be split based on time. The property is time.

--------

But there is a second issue here, Protons (the +ve particle) are in the QM model, you can predict the behavior of the proton, and QM believers claim that detecting it position SETS it position, and before it was detected its position was undefined, fuzzy.

However protons are not fundamental particles anymore, deep inelastic scattering showed they are made of smaller particles. So you never detected the proton AT ALL, you simply detected the net result of the effects of these sub-proton particles. That net result jumped around, not the proton. Likewise you could not have 'set' the position of the proton, because it does not exist! It was just an effect of multiple smaller particles on the detection mechanism.

I usually describe this as the "flock of starlings" effect. If all you can see is a flock and not the individual bird, the flock appears to jump and leap and disappear and reappear. But it is simply the effect of a detector that can only see flocks and not birds.

Electrons are also considered to be fundamental in physics *currently*, yet we have a dipole experiment that shows they are not fundamental particles.

You can induce a dipole in an electron (a +ve -ve axis), showing electrons are made of both +ve and -ve stuff. In other words they're not fundamental either.

So QM model is broken here too, the electrons position appears to jump around, but its the net effect of these +ve and -ve things its made of.

Re:Obvious flaw

[Anonymous Coward]

Electrons are also considered to be fundamental in physics *currently*, yet we have a dipole experiment that shows they are not fundamental particles.

You can induce a dipole in an electron (a +ve -ve axis), showing electrons are made of both +ve and -ve stuff. In other words they're not fundamental either.

Citation please? A quick look at Wikipedia shows "Experimentally, the electric dipole moment is too small to measure in all experiments to date"...

Re:Obvious flaw

[Anonymous Coward]

I usually describe this as the "flock of starlings" effect. ...

And usually there are plenty of posts explaining why this is wrong... you only ever reply to the ones that lack content though, claiming they don't give examples. Yet there are plenty of comments that give examples of experiments and situations that conflict with your posts that say nearly the same thing every time. As soon as someone actually takes the time to look things up or write things out, you ignore them

Electrons are also considered to be fundamental in physics *currently*, yet we have a dipole experiment that shows they are not fundamental particles.

Funny how your claims contradict physicists that don't see them as nonfundamental despite the same tests and include predictions of dipole moments...

Re:Obvious flaw

[wonkey_monkey]

I take a photon, I split it into two identical photons

Do you? That's very clever of you. People have won Nobel prizes for less.

I usually describe this as the "flock of starlings" effect. If all you can see is a flock and not the individual bird, the flock appears to jump and leap and disappear and reappear. But it is simply the effect of a detector that can only see flocks and not birds.

Yes, you do keep describing it that way. And you've been told several times why you're wrong, but you just won't listen.

However protons are not fundamental particles anymore, deep inelastic scattering showed they are made of smaller particles. So you never detected the proton AT ALL, you simply detected the net result of the effects of these sub-proton particles. That net result jumped around, not the proton. Likewise you could not have 'set' the position of the proton, because it does not exist! It was just an effect of multiple smaller particles on the detection mechanism.

Okay, let's ignore the fact that you're just plain wrong. Why do electrons, which are fundamental particles, behave the same way?

Re:Obvious flaw

[Anonymous Coward]

Same thing on every quantum mechanics story, and the only reason it doesn't get torn apart every time is because people get tired of making the same debunking replies. After making detailed counterpoints and seeing no response or change, there isn't much motivation to waste more time. But keep on posting, because on Slashdot if you say it enough times it becomes true and upmodded if you can outlast opposition.

Re:Obvious flaw

[Anonymous Coward]

How much does a flock of starlings poop in a day? About as much as you vomit forth your half-baked nonsense?

Re:Obvious flaw

[fyngyrz]

European starlings, or African starlings?

Loopholes

[Anonymous Coward]

What loopholes?

Re:Loopholes

[Anonymous Coward]

The Sanity Clause, for one.

Re:Loopholes

[Anonymous Coward]

You still believe in Sanity Clause?

Does flipping one electron now flip the other?

[Anonymous Coward]

Does the fact that the two separated electrons are now entangled mean that flipping one of the electrons will now flip the other? Supposedly, quantum entanglement can't be used for communications but I've never understood why. Even if flipping one electron *might* flip the other, it means you could communicate because error-correcting protocols work pretty well over noisy communications channels.

Re:Does flipping one electron now flip the other?

[qbast]

Because you don't get to 'flip' anything without breaking entanglement. You can just measure one electron and be sure that the same measurement will give you the same result in entangled one. It is like having two random number generators with the same seed - they always give the same (random) answer, but it does not allow you to transmit anything.

Re:Does flipping one electron now flip the other?

[sexconker]

Supposedly, quantum entanglement can't be used for communications but I've never understood why.

Because when you separate entangled particles you can't add information to them later.

You have a coin that has a heads side and a tails side.
You flip it in location A.
Without looking, you cover the top of the coin.
While it lies flat on the table, you cut it in half, separating the two faces.
You leave the top half in location A, never looking at it.
You carry the bottom half to location B 1 light year away.
You flip the bottom half over to look at it.
You learn that heads was on the bottom.
You immediately learn that tails was on the top.
But that information didn't travel faster than the speed of light. You carried it with you at subluminal speed. No one at location A can change the outcome of the coin flip after you reach location B.

Re:Does flipping one electron now flip the other?

[gstoddart]

Alright, smartass ... I'm going to make up a thought experiment, because I really have no idea how this shit works either.

Say I have locations A and B, each with the end point of two pairs of entangled particles. Say they're 1 light year apart.

At site A, the first particle of the first pair is in a state, but you can't see it. At site B, the second particle of the first pair can be read. Site B knows the state of the first pair, site A doesn't.

If site B flipped their part of the second pair into a known state which told you the state of the first pair, hasn't that information traveled faster than light.

Because surely I can come up with some number of entangled pairs which allows me to send Morse code from site B to site A, no? Eight pairs lets me send a byte?

You may not be able to add information later, but can't you use other ones to relay information.

I never really understand this, but it seems like you can combine more than one entangled pair to construct a scenario in which you can send data faster than the speed of light.

Site B instantly knows the state of your particles in site A, and can then force other particles into states which relay that information back ... if this takes less than two years, isn't it, by definition, faster than light?

(I don't claim this is valid, and I'm not sure it is, I'm just trying to wrap my head around this)

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

See https://en.wikipedia.org/wiki/EPR_paradox -- in the first paragraph it says:
"...the usual modern resolution is to say that measuring one particle does instantaneously affect the other, but that this does not involve transmission of information."
If measuring one particle does instantaneously affect the other, how is this like your coin example, where the coins are separated and don't affect each other?

Re:Does flipping one electron now flip the other?

[swillden]

As I understand it, when you flip the state of one of an entangled pair, you break the entanglement. So site B can do what they like with the second pair, but site A won't know what they did. But IANAP and it's been over two decades since I took physics. Oh, and although my old textbook is on the shelf behind me, I'm too lazy to turn around and look at it :)

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

You can just measure one electron and be sure that the same measurement will give you the same result in entangled one"
"IN ENTANGLED ONES" being the key point. Only for photons that are entangled, which they determine by filtering based on time.

i.e. Is the photon from Electron X entangled with the photon from Electron Y? (Measure it, if it is entangled then you can look at the electron results, otherwise discard the result as 'unentangled'). Of *those* *entangled* result, 245, worked. But actually over 9 days they ran a shit load of photons and discarded most of the results.

Wet paint 1 is red or blue, I'm not sure
Wet paint 2 is red or blue, I'm not sure
I shoot a ball through Wet paint 1
I shoot a ball through Wet paint 2
I *entangle* ball 1 and ball 2 (i.e. detect if they have the same color paint on them and discard the result if not).
Then I measure the color of Wet Paint 1.

Wet paint 1 was determined to be blue, and thus wet paint 2 was also blue by spooky distance effect.... well most of the time, sometimes the paint didn't stick to the ball.

That is what these experiments dissolve down to. The test for 'entanglement' is the link between the two photons, and adding the electrons into the mix, and then ONLY considering the electron part of the experiment for Bells ignores the bigger picture.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

Think of it as if the particles are in lock-step with one another, and make movements that follow one another. Let's then say that you disturb one. After you disturb one, then they're no longer in lock-step, and you have no idea what state the undisturbed one resides in after you've disturbed your local one.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

Only if the communications channel isn't pure noise...

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

If site B flipped their part of the second pair into a known state which told you the state of the first pair, hasn't that information traveled faster than light.

They can "flip" (this is normally called a measurement or operation) their pair into one of many states. But which one is purely random.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

Only for photons that are entangled, which they determine by filtering based on time.

There are other experiments that work with entangled electrons, and yet others that work with entangled psuedo-particles.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

If site B flipped their part of the second pair into a known state which told you the state of the first pair, hasn't that information traveled faster than light.

You can't force the particle into a particular state, as the entanglement is a particular state of its own, and forcing a particular state overwrites that. The other site would end up with an un-entangled photon in a random state as if you just measured your end. There are operations you can perform that change things, but they always produce the same distribution of observations at one end. I.e. if one end expects a 50-50 split in two possible outcomes, no changes at the other end will change that, so you will never know if your outcome was random or correlated, etc., until you compare measurements from both sites.

Re:Does flipping one electron now flip the other?

[wonkey_monkey]

There's no control over which way the electron flips, so no way to send a message that way. And there's no way to measure whether or not an electron has or has not flipped, so no way to send a message that way, either.

Re:Does flipping one electron now flip the other?

[wonkey_monkey]

If site B flipped their part of the second pair into a known state...

You can't flip it into a state of your own choosing without first breaking the entanglement. I think.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

That's not how it works. Here's how it works.

1. You entangle 2 quarters together.

2. You fly one quarter to Alpha Centauri. You can look at it all you want, you just can't measure it. (aka flip it).

3. After it reaches Alpha Centauri, the astronaut who brought it flips it and gets heads.

4. Back on earth, the quarter is sitting on a shelf, crickets chirp.

5. Eventually someone on earth picks up the quarter and flips it. It comes up heads. Spooky.

6. The person at Alpha Centauri knew the quarter on earth would flip to heads, but it's not like he could use that for communication.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

The EPR experiment detected the electron flipping (probably through a magnetic pulse). You don't have to know which way the electron flipped because you can use the time between electron flips to send the information. And the electrons don't even have to reliably flip (just some of the time) because error-correcting codes can detect and correct data transmission problems.

Re:Does flipping one electron now flip the other?

[Anonymous Coward]

The only way to see change in the state is to measure it before and after, and the first measurement will destroy entanglement. There is no way to measure when an entangled state changes into an unentangled state because the other end was measured. Measuring one half of an entangled pair doesn't cause the other end to "flip" but to just select one of two (or more) states it was in superposition of.

Re:Does flipping one electron now flip the other?

[Kjella]

Because you don't get to 'flip' anything without breaking entanglement. You can just measure one electron and be sure that the same measurement will give you the same result in entangled one. It is like having two random number generators with the same seed - they always give the same (random) answer, but it does not allow you to transmit anything.

That's the "local hidden variables" theory, in which both particles are set with some quantum state at entanglement and don't interact later but which we know is false. If we angle the detectors, collapsing the quantum state at one end will cause correlation at the other end that can't be explained by hidden variables. The funny thing is though is that in order to measure the correlation you need both sets of measurements, which you have to transfer from one to the other at classical speeds so you don't get FTL communication. But the change happens FTL, even though you can't determine it until later. Every time you think you understand QM, it just gets weirder.

Why is nobody talking about the potential

[Anonymous Coward]

The potential "for implementing device-independent quantum-secure communication and randomness certification."

What's difficult to infer is, did they essentially communicate at a distance faster then C? Are they getting better (more reliability and predictability) at creating a device that can communication at long distances 'instantly'?

Re:Why is nobody talking about the potential

[Anonymous Coward]

Because this has already been proven impossible. Can't cite, because I don't understand this stuff.. But the wikipedia page says so... https://en.wikipedia.org/wiki/Superluminal_communication

Re:Why is nobody talking about the potential

[Anonymous Coward]

Yes and no, it depends on if you want actual facts or just random nonsense from slashdot.

Two entangled particles share the same properties, the spooky action at a distance (Einstein) states that if you affect one, you affect both, instantly, there's no gap, as if that information is travelling faster than light.

Or, one could postulate, that those particles are in fact 1 string in a 4 or 5 dimensional universe and we can only interpret that from a 3 dimensional point of view, that string becomes a single point, or particle, for us.

In any event, if you entangle particle A with particle B and then nudge A to give it a clockwise spin, the theory states that particle B will reactive with a counterclockwise spin. Instantly, you touch one, and the other reacts, thousands or more miles away, instantly.

As we refine the tests we'll get closer to finding out if this works as theorized, and most importantly, if we can use it for instant communication. Particles have many states, mostly based on the rotation. Morse code requires 2 states. Binary requires 2 states. See where this could be leading to?

What really blows my mind is the double slit experiment. Some poster about went on about particles and wakes and yadda yadda.

There are no particles, that's the only truth in that post. What we have are waves, probability waves from the math, but in reality we have witnessed electrons, photons, and buckyballs, all act as both a particle AND a wave, depending on how the test was being measured. This test leads to this nonense of "observing the test changes the outcome" It's not about you watching with your eyeballs. It's about the fact that you can NOT measure something without affecting it. You can either know exactly where this "particle" was at a point in time, or it's velocity. You can not accurately get both.

In the case of the double slit experiment, without detectors in place to basically track the photon, the things acted as waves, travelling through both slits at the same time and creating an interference pattern, just like light. But.. once some detectors are placed in there to actually measure which slit the photon went through, the things did NOT go through both slits and did not create an interference pattern.

As far as I'm concerned this was one of the most important tests in scientific history, but people rarely actually LEARN about it, they read a summary, gain a half assed understanding of about 3% of it, then post about how it's hogwash.

Re:Why is nobody talking about the potential

[Anonymous Coward]

In any event, if you entangle particle A with particle B and then nudge A to give it a clockwise spin, the theory states that particle B will reactive with a counterclockwise spin.

No, you can't nudge particle A into a particular state, as that overwrites the original state: the entanglement.

Instantly, you touch one, and the other reacts, thousands or more miles away, instantly.

Only for a very specific and narrow categories of "touch."

If you are going to complain about people not learning about the subject first, maybe you should follow your own advice.

Re:Why is nobody talking about the potential

[iris-n]

No. And no. This is just plain impossible.

What they did was to violate a Bell inequality, without cutting any corners (is this corner-cutting that is named as "loopholes" in the experiment). This proves that the world is not deterministic (if you believe in relativity).

Re:Why is nobody talking about the potential

[david_thornley]

There's no way to communicate FTL this way, as you can only observe. For quantum secure communication, take one each of lots of entangled particles, and measure them in order as you need randomness to encrypt your message. Send it. Only the person with the entangled particles can determine what the randomness was. It's something like a high-tech one-time pad, except that it can't be copied without knowing how you're measuring the particles, and if it's copied it's destroyed. A message can be intercepted, but it can't be intercepted without the recipient's knowledge.

Re:Why is nobody talking about the potential

[Apolloe]

Violations of Bell's inequality do not show that the universe is not deterministic. They show that it is non-local. Even stochastic theories violate Bell's inequality when they insist on maintaining locality. This is a common misunderstanding of Bell's inequality. Bell himself was a determinist about these matters, and promoted a pilot wave interpretation of Quantum Mechanics.

Entanglement

[Anonymous Coward]

A lot of quantum confusion can be dispelled by realizing that particles don't really exist. There are a bunch of phenomenae that look like particles, but also look like wavelike perturbations of a field. Since we don't really have any good mental analogies of what's "really" happenening, we have to fall back on mathematical descriptions. So the general concept is that you can glom two waves/particles together so that you cannot describe them individually any more. From my limited understanding, I don't think there's a mechamism so much as it's inherent to quantum mechanics to be able to construct systems like this.

Re:Entanglement

[Anonymous Coward]

There are a bunch of phenomenae that look like particles, but also look like wavelike perturbations of a field.

If we could just settle on calling them wavicles, people would be less likely to get hung up because of their preconceived notions of waves and particles. They're both and neither.

Re:Entanglement

[OakDragon]

There are a bunch of phenomenae that look like particles, but also look like wavelike perturbations of a field.

If we could just settle on calling them wavicles, people would be less likely to get hung up because of their preconceived notions of waves and particles. They're both and neither.

These things are subjected to so many tests, maybe we should call them "testicles."

Re:Entanglement

[david_thornley]

Yes, but the preconceived notions of waves and particles are useful in understanding these things. You just have to keep in mind that everything that small is both, but not at the same time.

Re:Entanglement

[Zeroko]

You can have it be both at the same time, at least hypothetically. E.g. (almost surely completely impractical) if you send an operating double-slit apparatus through a larger double-slit apparatus & vary independently whether the small & large ones are configured to show particle-like or wave-like behavior.

Or maybe just send something mundane (photons or electrons or whatnot) but measure one attribute looking for wave behavior & another looking for particle behavior (& obviously choose attributes that can be simultaneously measured).

Re: Entanglement

[Anonymous Coward]

Slithy toves.

Re:Entanglement

[david_thornley]

If you're measuring one attribute of wave behavior, you've got waves. If you're measuring one attribute of particle behavior, you've got particles. If you try to measure one of each, you'll get waves or particles, depending on what actually winds up being measured.

And being a Dutch experiment...

[johannesg]

...the electrons were moved between labs on a bicycle.

Ah, the Dutch! Whether it is a dike or a quantum theory, they can plug the holes ;-)

Re:And being a Dutch experiment...

[Tablizer]

Spooky bicycles at a distance

Loopholes closed in Quantum mechanics?

[140Mandak262Jamuna]

I don't get it. I thought the loopholes in classical mechanics is the quantum mechanics. If you close the loopholes and make it deterministic, then you are back to Newton, baby! Its all canon firing balls horizontally but what would happen if due to curvature the earth surface falls more rapidly than the canonball.

Re:Loopholes closed in Quantum mechanics?

[Anonymous Coward]

In general, there is no the loophole, and this is talking about a specific kind of loophole in a category of experiments. The conclusions of previous experiments that found violation of Bell's inequality say either it is because there are no local variables, there is super-determinism, or because of XYZ. The XYZ is a loophole, that there is a possible third option beyond the original two allowed for by Bell's prediction. It is a reference to weakness specific to a particular experimental setup. Depending which setup you are dealing with, the particular loophole is different. This has nothing to do with making quantum mechanics deterministic or regressing back to classical physics.

This is huge

[iris-n]

Guys, this is huge. People have been doing versions of this experiment for decades, every time making it more refined, in order to be able to reach the striking conclusion with the fewest possible assumptions: that the world is not deterministic. The quantum randomness is not our ignorance, is a fundamental property of nature.

What they did was to violate a Bell inequality, without using the most questionable extra assumptions (called loopholes) people normally use to extract a conclusion from this experiment: that the separated laboratories are not somehow communicating to conspire to produce the desired outcome, or that the photons they detect are indeed a good representative of all the photons that were emitted in the experiment (normally people can detect only a small fraction of the photons).

I am a quantum physicist, and I know the science behind this experiment very well. If anybody wants to ask me anything, I'd be glad to oblige.

Re: This is huge

[RossMartin2552]

In a separate post I described a means by which this would give FTL communication. Sorry to ask you to go find it, but I'm curious what's wrong with it. I believe it gets around the traditional issue with detecting bits from one side of an entangled pair by putting both of the pair right next to each other, and detecting whether they're entangled or not to get a '1' or '0' communicated. It requires that you can entangle the pair (or not) at a third location, which apparently is done in this experiment.

Re: This is huge

[iris-n]

Your scheme would work, if one could deterministically entangle the electrons at a distance, but one can not.

The issue is that this technique (called entanglement swapping, look it up), gets the photons, and tries to entangle them; sometimes you succeed, sometimes you fail. For them, this is not a problem, because they can just discard the cases where they failed and do the experiment with the other electrons, but for you it is, as you need to be able to entangle them or not at will.

In general, it is a simple theorem to prove that you cannot send information by doing measurements on a part of an entangled quantum system, so any similar scheme is doomed to fail.

Re: This is huge

[RossMartin2552]

It's not a problem that you sometimes succeed and sometimes fail to entangle the electrons. You just do it enough times that you can distinguish between "sometimes they become entangled" and "they never become entangled", and the ability to distinguish between these two allows you to communicate a bit.

Re:This is huge

[Anonymous Coward]

Does the experiment still assume counterfactual definiteness?

Re: This is huge

[RossMartin2552]

The simple theorem that one can't communicate information based on partial state of a quantum-mechanical system: in this case, don't we have the entire state of the system, not a partial state? After the electrons are caused to be entangled (or not) by some action at a remote location (by entanglement swapping), the entire quantum mechanical state is now held locally in the two electrons. (Correct?). We can therefore measure it to obtain information, and the theorem doesn't apply or limit this.

Re: This is huge

[Anonymous Coward]

The problem is you can't distinguish between when the electrons are entangled or not in this setup, and if you just look the electrons you get something that actually satisfies Bell's inequality and doesn't look like entanglement. It is only when you add information from the measurement of the photons that tell you when they were entangled that you can see correlation. There is no measurement that the locations with the electrons can make to tell what the location with the photons has done, it is only when you combine measurements from all locations that you see a correlation.

Re:This is huge

[Anonymous Coward]

Are there predictions made by any QM interpretation that differ from the standard QM? If so how far away technologically are we from being able to test those predictions? For example would the LHC (or it's successor), Event Horizon Telescope, LISA, or some next gen CMBR telescope, etc. have any chance of testing those predictions.

Re: This is huge

[iris-n]

How do you communicate a bit using this distinction? Let's say I want to send '0', how do I do it?

It is a problem. Let's say the probability of getting them entangled is 0.5 (I'm too lazy to look it up now). Then you do the thing one time, you don't entangled the electrons, awesome, and they read '0'. Then you want to send them another '0', you do the thing, now they do get entangled, and they read '1'. Shit, now what? You cannot control what they are going to read! They do know the results of your measurements (first not entangled, then entangled), but this is just classical correlation, not communication.

Re: This is huge

[iris-n]

No, the state that describes the system is the electrons together with the photons, you are doing a measurement on the photons, you are doing a measurement in a part of the state.

Look, this is a very fundamental property of quantum mechanics, it just doesn't make any sense for it to fail. The whole thing would go down in flames.

Re:This is huge

[iris-n]

What do you mean by the experiment?

One needs counterfactual definiteness to derive the Bell inequalities, so yes, one needs to assume that (among other things) to conclude the world is not deterministic. But the experiment itself is just collecting measurement statistics, so it does not need to assume anything like that.

Re:This is huge

[iris-n]

Yes. The outcome of the Wigner's friend experiment (Described in more detail by David Deutsch in section 8 of this paper). In that case, the Copenhagen interpretation predicts that we would see no interference, whereas the Many-Worlds interpretation would say that we would see interference.

These experiments you mention have no chance of testing that, because they are looking for completely different stuff. What the interpretations of quantum mechanics differ on is how very large and complex quantum systems behave. I think it will remain impossible in the foreseeable future to do the experiment as described. But in my opinion, a good enough simplification can be done if we have a universal fault-tolerant quantum computer. That, is not that far. I would guess 20 years, if funding keeps constant at the current level.

Re:This is huge

[Apolloe]

Violations of Bell's inequality do not show that the universe is not deterministic. They show that it is non-local. Even stochastic theories violate Bell's inequality when they insist on maintaining locality. Bell promoted a deterministic interpretation of Quantum Mechanics -- pilot waves -- that have all the same experimental predictions as the typical indeterministic interpretation.

Whether you think the world is deterministic or stochastic at heart, you have to give up on locality. The book 'Quantum non-locality and relativity' by Tim Maudlin shows how even non-deterministic local theories violate the inequality.

Re:This is huge

[Anonymous Coward]

That is amazing! Thank you.

So if we give up locality we can keep determinism, right? So what if we assume for a second that the holographic principle is true and somehow the information that makes us up is on the 3 dimensional (2+1) boundary of our lightcone rather than us really being particles at the center of the cone. Would that information being so far away on the boundary like that fulfill the non-locality requirement somehow?

One more if you would, does ER=EPR satisfy non-locality and allow determinism?

Re:This is huge

[iris-n]

Yes, one can have determinism without locality. This is done, for example, in Bohmian mechanics. But I would warn you against giving up locality in this way. What we need is an extremely conspiratorial kind of action-at-a-distance to be able to predict (actually postdict) the observed results. The choice of measurement they are going to make in one of the diamonds must determine, faster than light, the result of the measurement being done on the other diamond. Needless to say, very few people (mostly philosophers) take this idea seriously.

As for you other questions, I do not know enough about them to dare giving you an answer, but from what I know, they seem hardly relevant to the matter at hand.

Re:This is huge

[iris-n]

Technically speaking, Bell's theorem needs determinism and locality to apply, so to conclude that the world is not deterministic, one does need to assume that the world is local. Since I know of no serious scientist that wouldn't assume the world is local*, I can safely say the conclusion of the experiment is that the world is deterministic.

When you write

Even stochastic theories violate Bell's inequality when they insist on maintaining locality.

I think you meant that they respect Bell's inequality no? Otherwise your argument wouldn't make sense. I think what you're talking about is a class of theories known as factorizable; they respect Bell's inequality, even though they allow the outcomes to the random. But it is easy to show (shown by Fine in 1982) that these theories are mathematically equivalent to local deterministic theories, so they are simply not relevant. Since you haven't given me any details, I can only speculate (and no, I'm not going to read a book to understand what you're talking about).

But this point is moot, since I know of a local non-deterministic theory that can violate Bell inequalities: quantum mechanics.

* I know personally one crazy bastard that thinks the world is nonlocal, and I have heard rumours about a couple of others. And I know personally almost every scientist working in this field.

Re: This is huge

[RossMartin2552]

Ah, that explains it. Apparently entanglement isn't being swapped in "entanglement swapping". Instead, it just entangles more things together.

Re:This is huge

[daaxix]

I am an expert in polarization, since they are using polarization optics, how is the experiment valid when polarization through a fiber optic is maintained via birefringence? Doesn't this interaction affect the entanglement? (Polarization maintaining fibers work by interacting with the coherence properties of a classical light wave, so a single polarized photon would be interacting with its environment, thus invalidating the experiment).

Re:This is huge

[Apolloe]

Assuming I have the phrases around the right way, I meant that local stochastic theories violate Bell's inequality, just like deterministic local theories do. It is a common misunderstanding, even among physicists, that experiments like these have shown trouble only for local hidden variable theories. The fact is that Bell's inequality is violated by any account you like -- stochastic or deterministic -- so long as you insist on locality.

Locality is the problem, not hidden variables. I completely understand that you're not going to read a book to see my point defended. People are busy, and I only posted it in case you wanted to see. You could also check out a paper by the same author which I think will discuss the matter, but I haven't read this paper myself.

One final note. Suppose that in fact we had to choose between indeterminism and non-locality. I think that indeterminism is the crazier of the two options by a long shot. Non-locality can be understood, while indeterminism is, by its very nature, incomplete. If it came down to a choice between the two, non-locality should win hands down. At any rate, it doesn't matter. The universe is shown to be non-local by these experiments anyway, regardless of your views on determinism.

Re:This is huge

[Anonymous Coward]

Photons in such experiments interact with their environments all of the time, via things like mirrors and prisms. How they are affected really depends on the nature of the environmental interaction, if that interaction should affect the state under study. Even if it is not perfect, then it would be analogous to weak measurements and not affect it all (or even most) of the time.

Re:This is huge

[Anonymous Coward]

Ah, but that's the beauty of ER=EPR, which says that the math of Einstein-Rosen Bridges and of the EPR Paradox are the same. From the link in the post above:

Like initials carved in a tree, ER = EPR, as the new idea is known, is a shorthand that joins two ideas proposed by Einstein in 1935. One involved the paradox implied by what he called “spooky action at a distance” between quantum particles (the EPR paradox, named for its authors, Einstein, Boris Podolsky and Nathan Rosen). The other showed how two black holes could be connected through far reaches of space through “wormholes” (ER, for Einstein-Rosen bridges). At the time that Einstein put forth these ideas — and for most of the eight decades since — they were thought to be entirely unrelated.

But if ER = EPR is correct, the ideas aren’t disconnected — they’re two manifestations of the same thing. And this underlying connectedness would form the foundation of all space-time. Quantum entanglement — the action at a distance that so troubled Einstein — could be creating the “spatial connectivity” that “sews space together,” according to Leonard Susskind, a physicist at Stanford University and one of the idea’s main architects. Without these connections, all of space would “atomize,” according to Juan Maldacena, a physicist at the Institute for Advanced Study in Princeton, N.J., who developed the idea together with Susskind. “In other words, the solid and reliable structure of space-time is due to the ghostly features of entanglement,” he said. What’s more, ER = EPR has the potential to address how gravity fits together with quantum mechanics.

Re: This is huge

[iris-n]

Actually, it is being swapped; the initial state is (left electron entangled with left photon) and (right electron entangled with right photon), and the final state is (left electron entangled with right electron), with the photons destroyed. So the entangled was swapped from electron-photon to electron-electron.

Re:This is huge

[iris-n]

Hmm, polarisation-preserving fibers are commonplace in quantum optics experiments, never heard of any problem with them. One thing you should keep in mind is that there are no "classical light waves", only photons, so one would need a very strange kind of interaction to be able to preserve the polarization of "macroscopic states" while fucking up the polarisation of individual photons.

But this point is moot anyway, because the rules of the game allow the experimenters to do anything before the choice of setting in each individual diamond is decided. So what they do is sent a lot of photons, trying to get the diamonds entangled, failing most of the time, and then when they succeed, they generate the measurement settings and do the measurement.

Re:This is huge

[iris-n]

What I can say for sure is that at this point ER=EPR is pure speculation, so I wouldn't be so eager to draw conclusions for it. If you want to know more about its implications, you should ask some quantum gravity guy (i.e., not me).

Re:This is huge

[iris-n]

Thanks for sending me the paper, now I know what you're talking about.

First of all, let us clear up something: what Bell showed is that any deterministic and local theory (you can call it local hidden variable theory if you want, it's just a name) will respect Bell inequalities (in the experiment in question, they will achieve a value of the correlation S that will respect the Bell inequality S <= 2). Since we can violate the inequality in Nature (they achieve S = 2.42), the assumptions must be wrong.

So, in principle, you can deny either determinism or locality to allow the correlations to violate Bell inequalities. What most physicists do is to deny determinism, and keep locality. Maudlin's preference is to deny locality, and to go with Bohmian mechanics, which is explicitly deterministic and nonlocal. But Maudlin makes a false claim, that Bell proved that no "local" theory can violate Bell inequalities, independent of determinism. This is simply false, as any simple study of Bell's theorem will show you. This is just Maudlin's "theorem". So, in the end, his claim is that there is no theory that is non-deterministic, local, and can violate Bell inequalities.

To support his claim, he says that quantum mechanics itself is nonlocal, denying the standard way out of Bell's theorem.

The reason he claims quantum mechanics is nonlocal is because of the "nonlocal collapse of the wave function", which is indeed a problem in some stupid interpretations of quantum mechanics, as the Copenhagen interpretation, that make the wavefunction collapse. The standard way out for Copenhagens is to claim that the collapse of the wave function is not a physical process, just a calculating device. This is just a lame excuse that explains nothing (but I mention because is extremely common).

What one does need is an interpretation of quantum mechanics that does not collapse the wavefunction, like Many-Worlds. About this, Maudlin just babbles incoherently:

That does not prove that Many Worlds is local: it just shows that Bell’s result does not
prove that it isn’t local. In order to even address the question of the locality of Many Worlds a
tremendous amount of interpretive work has to be done. This is not the place to attempt such
a task.

Re: This is huge

[Anonymous Coward]

Could entanglement be used to securely generate the exact se one-time pad keys on two secure sites, both of which are connected over insecure optical (or radio) links?

This would be huge for cryptography: the exact same guaranteed random stream of keys in two locations. It's tamper proof: any eavesdropping on the key-stream would destroy the synchronization of the keys.

Re: This is huge

[Anonymous Coward]

But even this result does not rule out one of Bell's theories: that our universe is "super deterministic" (for example a computer simulation), correct?

Re:This is huge

[Apolloe]

Maudlin shows in the book I referenced how local indeterministic theories also violate Bell's inequality. But it's not just Maudlin: Bell himself proved what Maudlin claims. Howard Wiseman thinks that the confusion comes about for the reason that Bell had two papers. The first paper in 1964 argued from the twin premises of locality and determinism, leaving the impression that one could give up just one of these. In his 1976 paper, Bell made it clear that the problem derives from locality alone. Wiseman writes:

In 1976, Bell proved that his new concept of local causality (based implicitly on the principle of common cause), was ruled out by Bell correlations. In this 1976 theorem there was no second option, as there had been in the 1964 theorem, of giving up hidden variables. Nature violates local causality.

Maudlin is not mistaken, and is not alone. A more detailed paper by Wiseman: http://arxiv.org/pdf/1402.0351v2.pdf.

Re:This is huge

[iris-n]

What? No, come on, this doesn't make any sense! The theorems of 1964 and 1976 are the same! In 1976 Bell chose to conflate both assumptions into one that he calls "local causality", but local causality is exactly the same as the conjunction of determinism and locality. Wiseman does not agree with Maudlin at all, he is just charitably explaining where Maudlin made a trivial mistake.

Come on, In my previous reply I thought you had an interesting point about the locality of quantum mechanics, but now this is just an uninteresting wordplay.

Maudlin is wrong, and trivially so. Moreover, he is alone. To see how fringe are his views, please read this paper of Werner, which is a comment on the paper "What Bell did".

Re: This is huge

[iris-n]

This isn't "one of Bell's theories". But you are correct, this is not ruled out. But please keep in my that superdeterminism cannot be ruled out in principle, so I don't think it is an interesting assumption.

Re: This is huge

[iris-n]

Yes, this is exactly the point of quantum key distribution, using Ekert's protocol.

Re:This is huge

[Apolloe]

None of this is just 'wordplay'. What's at stake is precisely what one has to commit themselves to in order to reconcile their view of the world with what experiments have shown.

Showing that the world is random/indeterministic at heart is not enough of a sacrifice. If you look at what Werner says carefully, you will see precisely what it is one is required to accept to keep locality:

The state change only becomes effective when the results from the two labs are brought together and are jointly analyzed, which can happen centuries later. Bohmians like Maudlin tend to confuse such changes in distributions with a change in the world, because the notions of states and wave functions are reified, and considered as some real thing out there

Note here that locality is maintained by not having any appropriate change in the world until the two labs bring their results together! This is what I take Wiseman to be referring to when he talks about giving up on correlation. In the Nature article I linked earlier:

But one can go further, by recalling that local causality rests on two principles: Einstein’s principle of relativistic causality, and the principle of common cause. Thus Bell’s 1976 theorem can be restated as: either causal influences are not limited to the speed of light, or events can be correlated for no reason.

...

Those who hold Einstein’s principle to be inviolable (the localists) must conclude that some events are correlated for no reason. A challenge for them is: if correlations do not necessarily imply a cause, when should scientists look for causes, and why?

and from the arxiv.org paper,

In conclusion, for a proper appreciation of the foundational importance of Bell’s theorem to physics, information science, and the philosophy of causation, one should be familiar with both the 1964 Bell’s theorem and the 1976 Bell’s theorem, even though they are logically equivalent. The former proves that quantum phenomena are either nonlocal (in a “causation by agents” sense) or undetermined, while the latter proves that quantum phenomena violate local causality (in a “common cause for correlations” sense).

While Wiseman, Werner, and Maudlin may be all saying subtly different things, their understanding seems to me largely the same. Maudlin shows (as Bell did), that embracing indeterminism isn't enough. What Wiseman points out is that the choice isn't between locality and indeterminism, but between locality and correlation. What Werner says is that the correlation comes from entirely local events, presumably late occuring: when the labs bringing their results together. You have given up on indeterminism, but that isn't one of the options on the table.

As I said before, if indeterminism is the price to pay for keeping lcality, then we're much better off ditching locality. The same goes if one is referring to giving up on correlation of events. But keep in mind the kind of correlation here one needs to give up: it's the correlation we find in the kind of experiment given in this slashdot article. These are very *strong* correlations. How crazy does a view have to be before we give up locality?

Re:This is huge

[iris-n]

The state change only becomes effective when the results from the two
labs are brought together and are jointly analyzed, which can happen
centuries later. Bohmians like Maudlin tend to confuse such changes in
distributions with a change in the world, because the notions of states
and wave functions are reified, and considered as some real thing out
there

Note here that locality is maintained by not having any appropriate change in the world until the two labs bring their results together! This is what I take Wiseman to be referring to when he talks about giving up on correlation. In the Nature article I linked earlier:

No, it's not. Werner is talking about the nonlocality of the wavefunction collapse, whereas Wiseman is talking about abandoning Reichenbach's common cause principle.

But one can go further, by recalling that local causality rests on two principles: Einstein’s principle of relativistic causality, and the principle of common cause. Thus Bell’s 1976 theorem can be restated as: either causal influences are not limited to the speed of light, or events can be correlated for no reason.

...

Those who hold Einstein’s principle to be inviolable (the localists) must conclude that some events are correlated for no reason. A challenge for them is: if correlations do not necessarily imply a cause, when should scientists look for causes, and why?

and from the arxiv.org paper,

In conclusion, for a proper appreciation of the foundational importance of Bell’s
theorem to physics, information science, and the philosophy of causation, one should be
familiar with both the 1964 Bell’s theorem and the 1976 Bell’s theorem, even though
they are logically equivalent. The former proves that quantum phenomena are either
nonlocal (in a “causation by agents” sense) or undetermined, while the latter proves
that quantum phenomena violate local causality (in a “common cause for correlations”
sense).

Let me clarify what they are talking about: Bell's theorem follows from local causality. Local causality itself can be derived either from the conjunction of determinism and locality, or from the conjunction of Reichenbach's common cause principle and locality. So, if you want to keep locality, you have to give up determinism (as shown by Bell's first theorem) and Reichenbach's common cause principle (as shown by Bell's second theorem, in a more modern reading). Maybe reading this paper of Wiseman will make things clearer.

While Wiseman, Werner, and Maudlin may be all saying subtly different things, their understanding seems to me largely the same. Maudlin shows (as Bell did), that embracing indeterminism isn't enough. What Wiseman points out is that the choice isn't between locality and indeterminism, but between locality and correlation. What Werner says is that the correlation comes from entirely local events, presumably late occuring: when the labs bringing their results together. You have given up on indeterminism, but that isn't one of the options on the table.

As I said before, if indeterminism is the price to pay for keeping lcality, then we're much better off ditching locality. The same goes if one is referring to giving up on correlation of events. But keep in mind the kind of correlation here one needs to give up: it's the correlation we find in the kind of experiment given in this slashdot article. These are very *strong* correlations. How crazy does a view have to be before we give up locality?

Come on, Werner and Wiseman largely agree, but they are talking about different things. Maudlin is in violent disagreement with everybody else. But I'm repeating myself here. What I'd like to point out is what exactly is meant by "giving up on correlation of events". What one needs to give

Re:This is huge

[Apolloe]

I'm not seeing much of a disagreement with me in your latest reply. For the most part, you appear to be restating in your own words things I've also said. I think we now agree on what the choice is: locality, or common cause. If you want to maintain locality then you have to deny a common cause in these entanglement experiments. That is, even though the 'entangled' particles demonstrate properties that are highly correlated, the correlation nevertheless lacks a common cause. Or, has a common cause that occurs AFTER the experiment is performed (or thereabouts). Do you agree with this characterisation?

And to conclude, I'd like to bet that you are not a physicist (probably a philosopher?), if you think it is in any way tenable to abandon locality.

I'm in favour of letting people see the results of their bets. I have a background in physics, but my main area is indeed philosophy, so well done :)

I would be interested to hear why you think abandoning locality would be a big problem.

Re:This is huge

[iris-n]

I'm not seeing much of a disagreement with me in your latest reply. For the most part, you appear to be restating in your own words things I've also said. I think we now agree on what the choice is: locality, or common cause. If you want to maintain locality then you have to deny a common cause in these entanglement experiments. That is, even though the 'entangled' particles demonstrate properties that are highly correlated, the correlation nevertheless lacks a common cause. Or, has a common cause that occurs AFTER the experiment is performed (or thereabouts). Do you agree with this characterisation?

Good that we have cleared things up. I can agree with your characterisation if you are more specific about "common cause": what we have to give up is Reichenbach's common cause principle, which is not the only sort of common cause imaginable. In fact, we know the correlations exist because of the entangled state, so the state is some kind of common cause, just not Reichenbach's.

And to conclude, I'd like to bet that you are not a physicist (probably a philosopher?), if you think it is in any way tenable to abandon locality.

I'm in favour of letting people see the results of their bets. I have a background in physics, but my main area is indeed philosophy, so well done :)

I would be interested to hear why you think abandoning locality would be a big problem.

Ahá! For once the stereotypes worked =)

Well, for starters, it is hard to reconcile nonlocality and relativity; it requires the nonlocal influences to be some conspiratorial sort that do not actually lead to any superluminal signalling, and I find this conspiracy distasteful. Furthermore, it makes the scientific endeavour very suspect, if not actually impossible. A key hability in science is to isolate some system, control its variables, and see how changing them affect the system. In a nonlocal world, the first step of isolating the system is already impossible, so you're not going to be able to have much control over your system, and this reduces what you can learn about it.

Re:This is huge

[Anonymous Coward]

Well, for starters, it is hard to reconcile nonlocality and relativity

It conflicts violently with the mathematical structure of modern SR by forcing an extension of the degrees of freedom available in flat spacetime (i.e., you can't just use the Poincaré group as the symmetry group; "c" is just that group's single free parameter, corresponding to the speed of a massless particle).

If you extend Poincare you wind up with a system of differential equations that is symmetric hyperbolic. At that point you are probably better off investigating a full non-metric TOE, since you will probably fail PPN analysis.

"Conspiracy" along the lines of superdeterminism is one way out of that, but not the only way.

Re:This is huge

[hr raattgift]

ER=EPR is designed to avoid superluminal representations of the Poincare group (which is the symmetry group of Special Relativity, and which has "c" as its sole free parameter, corresponding to that of a massless particle; photons are expected to be massless).

Avoidance of non-locality even gets a explicit mention in section 3.1 of the Malcadena & Susskind paper http://arxiv.org/abs/1306.0533

So, no, ER=EPR does not satisfy non-locality.

(It's mostly designed to try to preserve AdS/CFT in the face of the AMPS paradox, which strongly suggests that not all of AdS/CFT gauge/gravity, semiclassical gravity as an EFT outside the horizon, unitarity, or the "no drama" conjecture (and thus the strong Einstein Equivalence Principle) can be simultaneously valid. However, the introduction of a truly huge number of wormholes to a model of the universe is not calculationally attractive, and does not really help with intuiting the internal state of physical black holes any more than AdS/CFT has done so far. Additionally, it requires a modification of QFTs such as the Standard Model for at least some infallers (cf. p 36 at Polchinski's http://www.slideshare.net/joep... .))

Re:This is huge

[Apolloe]

Just some quick comments (that is, in terms of how much time I spent thinking about the reply).

Good that we have cleared things up. I can agree with your characterisation if you are more specific about "common cause": what we have to give up is Reichenbach's common cause principle, which is not the only sort of common cause imaginable. In fact, we know the correlations exist because of the entangled state, so the state is some kind of common cause, just not Reichenbach's.

I think that the seriousness of what is given up here has not been fully appreciated. Yes, the results are correlated, but to maintain locality you need to give up the idea that the cause of that correlation is to be found inside the light cone in the past/present. Note again Werner, in the paper you provided, talking about labs bringing their results together, perhaps centuries later. If you stick to locality, then the common cause must be in the future! That is to say, the correlation occurs when the labs bring their results together. It's not just a matter of giving up on some particular notion of common cause. The reason why you need to give up on common cause is because no local, existing in the past cause can explain the correlation. If you think there is an explanation for the correlation, and you think the world is local, then you need to look in the future. That's how I understand the matter anyway, and it fits with what I've read on the topic and why Werner talks at all about labs bringing results together centuries later.

To put this another way: When you look at Wiseman's paper I linked, and reject Principle 25, you give up on the claim that there is a cause of the correlation for entangled particles. If you want to then claim that there is a reason or cause for the correlation, you need to replace Principle 25 with something else. What will you replace it with? If I understand correctly, you will have to replace it with an in-the-future common cause. E.g., when the labs bring their results together. Anything that lies in the past/present light cone will violate Bell's inequality.

Well, for starters, it is hard to reconcile nonlocality and relativity; it requires the nonlocal influences to be some conspiratorial sort that do not actually lead to any superluminal signalling, and I find this conspiracy distasteful.

The reasons why you cannot communicate using these superluminal signals has to do with epistemic limitations. The reasons are not conspirational, and entirely explicable. Perhaps we will one day discover other superluminal phenomena that won't have the same epistemic limits.

Furthermore, it makes the scientific endeavour very suspect, if not actually impossible. A key hability in science is to isolate some system, control its variables, and see how changing them affect the system. In a nonlocal world, the first step of isolating the system is already impossible, so you're not going to be able to have much control over your system, and this reduces what you can learn about it.

This is not a new problem, but something scientists have been grappling with for centuries. (Almost) every system we experiment on now is not fully isolated from the external world. Suppose you're doing research in thermodynamics -- how easy s it to completely isolate your system from the external world? We might be getting better at it, but the fact that we have not been able to do this perfectly in the past hasn't stopped us from exploring our universe. I don't see how a nonlocal world is going to tip us over the edge from making science "very difficult" to "impossible". So far as I am aware, the only non-local event we have discovered so far is with entangled particles. It doesn't seem particularly common, and hasn't stopped us doing experiments like that which this Slashdot post is about.

Overall, compared to the alternative, accepting that the world is non-local still seems like a no-brainer to me :)

Experimental issues

[daaxix]

This experiment has a big problem, as an applied optics (polarization specific) expert, they use polarization entanglement, but then run the light through fiber optics.

The problem is that fiber optics (even polarization preserving designs) have a terrible issue with preservation of polarization states.

I haven't read the paper in detail yet, but I don't know how they can mitigate this issue...

Empiricism is doomed -- and that's a good thing

[Anonymous Coward]

I think we're being too fuzzy on terms here. Science is about providing empirical explanations of observed phenomenae, hopefully sufficient to predict future observations. "Why" is a question that can be answered, but it's mostly about describing phenomenae; often the fuller explanations elude us. I would even say that's true as a rule, since empiricism can only explain things to the limit of observational error.

Whether you like it or not, quantum mechanics is an accurate description of how the universe works on the subatomic level. It is, in point of fact, an extremely accurate description. To say that we (collectively) do not understand it is foolish: your everyday life is filled with devices that rely on quantum mechanics. Your problem is that you have no conceptual tools to be able to intuitively understand it. This is normal. We do not normally observe reality at that level. It is a foreign country, where even our concept of what observation is breaks down.

Ultimately, empirical science will never be able to explain all phenomenae. To do so would require godlike omniscience:

Who sees with equal eye, as God of all,
A hero perish or a sparrow fall,
Atoms or systems into ruin hurled,
And now a bubble burst, and now a world.

The borders of our knowledge will forever be filled with increasingly hard to observe objects and events. To the optimist, it represents new worlds to be discovered. To the pessimist, it represents the futility of truth-seeking. Philosophy is the search for truth, and empiricism (i.e. science) is one way to pursue truth. It is far from perfect, and there are questions that it cannot answer, truths that are not subject to observation or measurement. Some truths, like 1 + 1 = 2, are true by principles of logic. Some truths transcend logic and observation -- at this point we call in more general philosophers. To acquire a proper mental framework for scientific understanding, I recommend reading the wikipedia articles on 'Philosophy of Science' and 'Empiricism'.

What are the odds?

[Anonymous Coward]

Einstein said none of the wierd stuff, there is just some hidden state we can't see.

If this is true then some for the particles should have the correct values of the hidden state to make the entanglement experiment work.
If this is true, then some of the particles should have the wrong state and not work in the experiment.

They got it to work with 245 particle pairs.
They said this passed some statistical significance test. (Bell's test)

How come they did not mention how many tests failed to get to 245?
Are the odds of working versus non-working particles not part of the test?

This seems to give FTL communication

[RossMartin2552]

If we modify this situation just slightly, it seems to give FTL communication. Here's how we modify it. Instead of electrons 1 and 2 being 1.3 kilometers apart, we put them in the same room, "room X". And we don't have just one electron, but instead very many. We put the "third location" very far away. Perhaps light-years away. At the third location, we decide whether we want to send a '1' or a '0'. If we decide to send a '1', we entangle many of the photons, which entangles the electrons in room X. If we decide to send a '0', we don't entangle anything. At room X many light-years away, we detect whether the electrons are entangled or not. This is detectable, correct? Doesn't this allow us to receive a '1' or a '0'? Don't we now have FTL communication? What am I missing?

Re:This seems to give FTL communication

[Anonymous Coward]

This is detectable, correct?

No. The only way to tell if something was entangled or not is to classically communicate the results of measurements at both end, and see if they correlated or not. By yourself, there is no way to tell if you are holding half of an entangled pair or just an un-entangled particle.

Re: This seems to give FTL communication

[RossMartin2552]

You didn't read what I wrote. In this setup, both halves of the entangled pair are in the same room. So the problem you mention doesn't exist.

Re: This seems to give FTL communication

[Anonymous Coward]

If both halves of the the entangled pair are in the same room, then there is no mechanism allowing for any communication at all between distant locations.

Re: This seems to give FTL communication

[Anonymous Coward]

If you aren't talking about splitting up the entangled pair, then there is no connection between your distant locations, short of old-fashioned classical communication anyway. Entangling a pair of photons in a far away lab doesn't magically entangle electrons in room X. The only way to have photons cause electrons to become entangled is through an electromagnetic interaction, as in the photons need to scatter off or be absorbed by the electrons.

Re: This seems to give FTL communication

[RossMartin2552]

This experiment apparently allows one to entangle electrons sitting in the same room based on actions in a far removed location. If you can do that, then you can choose to entangle them or not at the far removed location and test whether they're entangled or not locally, thus achieving FTL communication. Entanglement based on actions at a far removed location is the mechanism for FTL communication. It is apparently real. (?)

Re: This seems to give FTL communication

[Anonymous Coward]

They previously entangled the electrons with the photons, and the same long distance communications principles apply. You still have to entangle the photons with electrons before separating them, and you have to then send the photons to a distant locations waiting for speed of light for them to get there. There is no measurement of the electron pair that tells they are in this relationship until you measure the results of the photons at the distant location.

The simplest examples of entanglements talk of things where you can measure both halves of a pair and get either the same or opposite measurements depending on the setup. This is a much larger system, and it involves more than just the electrons.

Re: This seems to give FTL communication

[Anonymous Coward]

Entanglement is just a state that involves multiple particles, and it is not limited to two particles. They entangle each of two electrons with each of two photons, then have those two photons interact. This creates a four particle entanglement. Measuring just a portion of the system does not show its entanglements with other parts of the system, and the entanglement can't change the distribution of local measurements for one part of the system. No matter what is done with the photons, the electrons with have the same distribution of measurements as far as one can tell, unless one looked at measurements of all parts of the system.

Re:This seems to give FTL communication

[HiThere]

No, you can't detect whether an electron is entangled or not. More correctly, you can't detect what it is entangled with since, IIUC it's always entangled with SOMETHING. This is actually one of the things that makes it difficult to do the experiment, as keeping the electron from shifting what its entangled with is difficult. (Actually, different characteristics of the electron can be entangled with different targets.)

Every interaction between particles yields an entanglement, you just can't usually figure out what is entangled with what along what characteristic. So we treat known entanglement as something special. What's special is not the entanglement, it's that we know.

OTOH, I am not a physicist. If I have this wrong, perhaps someone more knowledgeable will correct me.

The entanglement works with the right electrons

[Agent0013]

If they could only get some of the photons to entangle, then how do we know that the ones that would not entangle were not due to the state of the original electrons. If the electrons are in opposing states, then when you entangle a photon with it and try to entangle it with another photon that has been entangled with the other electron, it will refuse to entangle unless the two electrons are in a compatible state. I don't think you can leave out the failed to entangle photons like that. It seems that they tell you something important about the system.

CS guy question:

[snadrus]

Does this open the door up to FTL communication?

Re:CS guy question:

[Anonymous Coward]

No, and there are already a bunch of comments and threads above explaining why not, as there are in nearly every story on such topics.

Re:CS guy question:

[iris-n]

It is easy to prove that it is not possible to send information by doing measurements on a part of an entangled state, so no, I'm afraid this is completely useless for FTL communication.

Re:This is huge, how about superdeterminism?

[shoor]

I am a quantum physicist...If anybody wants to ask me anything, I'd be glad to oblige.

OK, I'll bite. You said in your post that the world is not deterministic. Does the new experiment disprove superdetermism?

Just to show where I'm getting this from I did glance just now at the wikipedia article on Bell's theorem and, I quote:

There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the 'decision' by the experimenter to carry out one set of measurements rather than another, the difficulty disappears.

Even though I don't get a lot of this stuff, I do sort of think I get the idea that if things were superdeterministic, like we're all somewhere in a pattern created by a rule 110 machine or something, that there would be no need for either instantaneous communication or a hidden variable in order to have 'entanglement'.

Re:This is huge, how about superdeterminism?

[iris-n]

This is true, superdeterminism is a way out of the conclusion of the experiment.

That is why I said they only did the experiment without using "the most questionable extra assumptions". The assumption that the world is not superdeterministic is very reasonable, IMHO. Without it, one cannot even do science. For example, in a superdeterministic world, the wavefunction of a photon will depend on which measurements you are making on it, so there isn't such a thing as "the" wavefunction of the photon, and it is not possible to learn anything about it. It is this kind of conspiratorial correlation that superdeterminism uses to produce the violation of a Bell inequality. For me, it's insanity on the level of Last Thursdayism: logically consistent, unfalsifiable, and nobody will ever take seriously.

But I'm troubled by your last sentence:

that there would be no need for either instantaneous communication or a hidden variable in order to have 'entanglement'.

We don't need this stuff to have entanglement. Entanglement is just a property of Nature, it's there whether you want it or not. What we need instantaneous communication for is to create the appearance of entanglement in a hypothetical world that would be classical (or, technically speaking, has hidden variables). Since our world is quantum, this is of no concern.

Re:This is huge, how about superdeterminism?

[shoor]

Entanglement is just a property of Nature, it's there whether you want it or not.

Hmm, now that's a comment that troubles me a bit. Somewhere in this discussion somebody said that Richard Feynman (Ironically, I'm reading Surely You're Joking Mr Feyman right now.) said it's called Quantum Mechanics because we don't really understand it, it's just some mechanical rules. Your description of entanglement seems to be the same thing. I think scientists are like kids who always ask 'why'. Everytime their parents give them an answer, they ask 'why'. They're still asking 'why' about entanglement. If it turned out that everything was superdetermined, then they'd be asking 'why' to that as well.

What follows is a train of thought I've had when reading philosophical stuff and watching things like "Closer to the Truth". It isn't my personal 'belief', I'm way too agnostic to have such a complicated 'belief', but I think it might be appropriate to throw it out here:

This superdeterminism smacks of predestinationism, which is a religious notion that troubles people over the 'free will' question. To my mind, if it turned out the universe was a giant computer running a deterministic program, it wouldn't make us 'predictable', because the only way to get ahead of the Universe's own CPU clock would be to have an even bigger, faster computer than the whole universe. The future is set the same way the past is set, it just hasn't become the past yet for us. Phyiscist types are always talking about space-time, and how one observer can 'see' the future of another. Maybe it is all one big lump, Past, Future, Present, but living through it is still life, isn't it?