Quantum Trickery - Einstein's Strangest Theory

breckinshire writes "The New York Times is running an interesting story on Einstein's strangest theory. The theory was brought to light this past fall when 'scientists announced that they had put a half dozen beryllium atoms into a "cat state." [...] These atoms were each spinning clockwise and counterclockwise at the same time.' It is an interesting writeup for even the uninitiated and also concentrates on Einsteins role as a 'founder and critic of quantum theory.'"

Support one of the non-registration required sites

[Saven Marek]

Support one of the sites giving this story for free. Google news link [google.com.au]

Re:Founder?

[Anonymous Coward]

Einstein was a founder of quantum theory, along with Planck, Heisenberg, Pauli, Dirac, Schrodinger and many many more. There was no single founder.

Don't forget Schrödinger, Heisenberg, and Dir

[Anonymous Coward]

They had something to do with it.

Re:Founder?

[krazikamikaze]

Sure, it's called Plank's constant because Plank was the first to assume energy was quantized, but it was just seen as a mathematical trick (to make the correct prediction for black body radiation) until Einstein used it to explain the photoelectric effect.

Non-registration article text

[User 956]

Einstein said there would be days like this.

This fall scientists announced that they had put a half-dozen beryllium atoms into a "cat state."

No, they were not sprawled along a sunny windowsill. To a physicist, a "cat state" is the condition of being in two diametrically opposed conditions at once, such as black and white, up and down, or dead and alive.

These atoms were each spinning clockwise and counterclockwise at the same time. Moreover, like miniature Rockettes, they were all doing whatever it was they were doing together, in perfect synchrony. Should one of them realize, like the cartoon character who runs off a cliff and doesn't fall until he looks down, that it is in a metaphysically untenable situation and decide to spin only one way, the rest would instantly fall in line, whether they were across a test tube or across the galaxy.

The idea that measuring the properties of one particle could instantaneously change the properties of another one (or a whole bunch) far away is strange to say the least -- almost as strange as the notion of particles spinning in two directions at once. The team that pulled off the beryllium feat, led by Dietrich Leibfried at the National Institute of Standards and Technology, in Boulder, Colo., hailed it as another step toward computers that would use quan- tum magic to perform calculations.

But it also served as another demonstration of how weird the world really is according to the rules known as quantum mechanics.

The joke is on Albert Einstein, who, back in 1935, dreamed up this trick of synchronized atoms -- "spooky action at a distance," as he called it -- as an example of the absurdity of quantum mechanics.

"No reasonable definition of reality could be expected to permit this," he, Boris Podolsky and Nathan Rosen wrote in a paper in 1935.

Today, that paper, written when Einstein was a relatively ancient 56 years old, is the most cited of Einstein's papers. But far from demolishing quantum theory, that paper wound up as the cornerstone for the new field of quantum information.

Nary a week goes by that does not bring news of another feat of quantum trickery once only dreamed of in thought experiments: particles (or at least all their properties) being teleported across the room in a microscopic version of "Star Trek" beaming; electrical "cat" currents that circle a loop in opposite directions at the same time; more and more particles farther and farther apart bound together in Einstein's spooky embrace now known as "entanglement." At the University of California, Santa Barbara, researchers are planning an experiment in which a small mirror will be in two places at once.

Niels Bohr, the Danish philosopher king of quantum theory, dismissed any attempts to lift the quantum veil as meaningless, saying that science is about the results of experiments, not ultimate reality.

But now that quantum weirdness is not confined to thought experiments, physicists have begun arguing again about what this weirdness means, whether the theory needs changing, and whether in fact there is any problem.

This fall, two Nobel laureates, Anthony Leggett of the University of Illinois and Norman Ramsay of Harvard University, argued in front of several hundred scientists at a conference in Berkeley about whether, in effect, physicists are justified trying to change quantum theory, the most successful theory in the history of science. Leggett said yes; Ramsay said no.

It has been, as Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, noted, "a 75-year war." It is typical in reporting on this subject to bounce from one expert to another, each one shaking his or her head about how the other one just doesn't get it.

"It's a kind of funny situation," N. David Mermin of Cornell University, who has called Einstein's spooky action "the closest thing we have to magic," said, referring to the recent results. "These are extremely difficult experiments that

Re:Founder?

[Beolach]

It says "a founder", not "the founder". Einstein and Planck can both be considered joint founders of quantum theory, along with Bohr, Heisenberg, Schrödinger, and others.

Re:Entangled atoms for FTL comm? - No

[RedLaggedTeut]

Strange that you bring up that entangled atoms allow faster than light communication.

The known problem with this is that no information actually is transferred as far as we know; it is is only acquired at both ends at the same time (that is, you can't decide what you read).

Entangled atoms allow safe FTL cryptography though, because uncovering and reading the state of the atom creates a bit of a key that is shared at both ends.

The Copenhagen Interpretation

[broothal]

Bohr and Heisenberg made a popular interpretation of the duality paradox called The Copenhagen Interpretation [wikipedia.org]. Needless to say, Einstein disagreed with this interpretation.

Re:Don't expect to understand.

[kestasjk]

More anthropologists these days are leaning towards the idea that humans evolved next to riversides and on beaches. (Bipedalism came about because of wading, it explains the lack of hair, webbed fingers, ability to hold our breath, the direction of the hairs on our body, the shape of our noses, etc, etc.) The same point you made still applies, but I just thought I'd point out that the savannah theory of human evolution is going the way of the theory of Newtonian mechanics at a subatomic level.

Re:Clockwise=Counter-Clockwise

[kirinyaga]

In fact, the spin stay the same from any perspective. I.e. the particle is "spinning" exactly the same way whatever the angle you look at it : you watch it from the top, from the left, from behind, you always see it spinning clockwise, a bit like if it turns to face you. It's call the "spin" because its property _looks_ like it was spinning, but the particle doesn't really move or turn. Actually, a particle doesn't have a form, it isn't a sphere. Form is like temperature : temperature being the average speed of individual atoms inside a set of atoms, temperature only exist at a macro level, that is for a large set of atom. For a single atom, temperature doesn't exist. It's the same for form, thus for "spinning". Those are called _emergent_ properties (i.e. properties of a whole that cannot be predicted from properties of the parts), and they are meaningless for particles. In the case of this weird instant remote "action", the two linked particles are in fact a _single_ entity. There is no sending of information since the two are only one "thing" : the two don't have the same property, the particle pair have a property. Indeed, for the same reason particles doesn't have a form, their _identity_ is not what you may think. If two particles have exactly the same property, they, err, _it_, is the same particle. And, since it is a property of the pair, you cannot choose it, thus sending information, the particle pair just has it. Of course you can select particle pairs with the property you want before sending them apart, but then they have to travel at the speed of light, no instant communication is possible. And whatever you do by acting on one won't do anything to the other, they just share the same property. Thus, what is troubling is not this but the fact that before you "look" at a particle property, the particle has all the values this property can take at once (e.g. clockwise AND counterclockwise). When you "look" at it, when you try to measure the property, one of this value is then selected. The paradox is while the previous experiment seems to tell us this value is chosen from the beginning (particles seems to share an initial property, revealed once you look at them), the quantum mechanics proves the actual value you observe is randomly selected at the time you observe it and not before. What is tranported by the particles from the time they are emitted is not the value of the property but the very property itself. Another reason why a particle properties define this particle identity : particles doesn't have a "soul", an inner hidden self thing, they only are what they appear to be.

Re:Entangled atoms for FTL comm?

[judmarc]

If I remember some of the stuff I've read correctly, it's a bit more complicated than the article's summary made it seem, and no, it doesn't make FTL communication possible.

What the experiments have shown is that if A and B are "entangled," then whatever state A is observed to be in, B will be in that state also, regardless of whether A and B are too far apart at the time the observation is made to have any communication with each other. This can be thought of as Einstein characterized it, as "spooky action at a distance," i.e., the observation of A somehow affects B (which is what makes the action spooky, since there is no known way for any information to be communicated between the two). However, it can also be thought of in other ways - for instance, that A and B were in the same state when they were entangled (though there's no way to determine that for sure, since the states aren't observed at that time), and the observations of A and B are just showing the states they've "always" been in. In the latter way of thinking, the spooky part is that these randomly selected particles always turn out to have the same state when observed. It's like sticking your hand into your sock drawer 100 times at random and always coming up with matched pairs.

Re:Founder?

[Edward Kmett]

The EPR (Einstein, Podolsky and Rosen) states WERE originally proposed as an attack on quantum mechanics, but the argument swung the other way.

Strangely enough, almost all of the power of quantum computing derives from the strange consequences of this would-be counter-example.

Quantum teleportation and basically all of other quantum computation tricks use qubits in EPR states, but even 'teleportation' doesn't really allow sending information faster than light, since you have to send conventional bits of information about the observations in order to reconstruct the quantum state on the other end.

So in one sense, the original Einstein concern about information traveling faster than the speed of light is valid. It just takes a different form to fit into quantum mechanics.

Re:Founder?

[Beolach]

Yes and no. There were several aspects of the some of the emerging quantum theories that Einstein argued against, but that's actually a significant part of how he contributed to the development of quantum mechanics; and really all of the founders of quantum mechanics did the same thing: when Bohr, Heisenberg and Pauli first proposed the Copenhagen interpretation (as of 1997 the most widely-accepted interpretation of quantum mechanics), Einstein didn't approve of it - but neither did Planck or Schrödinger. And there were several theories that form the basis of quantum mechanics that Einstein developed. So just because he argued against aspects of quantum theory that are now generally accepted, does not mean that he wasn't a significant contributor to its development.

Re:Entangled atoms for FTL comm? - No

[Kjella]

The known problem with this is that no information actually is transferred as far as we know; it is is only acquired at both ends at the same time (that is, you can't decide what you read).

Entangled atoms allow safe FTL cryptography though, because uncovering and reading the state of the atom creates a bit of a key that is shared at both ends.

Not really FTL, it's more like a read-once OTP. You entangle two atoms, which is like creating two identical OTPs (even though you do not know the values). You then split the atoms (OTPs) at sub-light speed. You can then read out the same OTP at both ends. You still need to encrypt/send at sub-light speed/decrypt. The big point is that the OTP is verifiably *one time*, it can not be read twice. I suppose you can call it "security by quantum obscurity", since the entire point is that the key is kept behind a veil of quantum mechanics.

Re:wouldn't that be...

[pnewhook]

Moreover, I thought Einstein was referring to the uncertainties of the quantum theory (i.e. Schrödinger's cat) when he said, "God does not play dice", meaning that he didn't accept it. Anyone care to enlighten me?

To severely paraphrase, Einstein believed the unverse has a fundamental, simple order to it. To have random unknown chance (for example the probability waves) be part of the equation severely bothered him and was the fundamental part of quantum physics that he could not accept. That was also why he believed there was some model underneath quantum physics that would predict and bring determinism to the randomness.

Re:Question about Q-phys

[paologat]

I've been curious what is the justification for support of:

• particles are in multiple simultaneous states until measured causing the distributed probabilities to collapse into a definite known state

over the seemingly more 'classical':

• the particle has a definite position and momentum, but our measuring devices are too clumsy / interactive to measure one without affecting the other before another measurement can be made. For example if we measure something by zinging it with a photon and remeasuring the (same?) photon after it interacts with it, then it causes it to do something else before we can zing it again.

What you are suggesting is a hidden variables theory. Basically, each quantum particle should "know" the results of all possible measurements that someone might perform upon it, and act accordingly.

The problem is that experimental results rule out any "reasonable" hidden variables theory! For more information, check out the EPR Paradox [wikipedia.org] and Bell's Inequality.

Re:Non-registration article text

[Anonymous Coward]

These atoms were each spinning clockwise and counterclockwise at the same time.

While you can say the atoms have spin, saying they are spinning is taking the abstraction too far. QM spin does not mean that a particular particle is spinning around. If it did, several particles would spin *faster* than the speed of light. It just means that the idea of spin to explain certain processes in a macroscopic system are being explained in the microscopic quantum states, but with a process that is more fundamental than a charge distribution spinning around, for example.

Now that that's settled, the paradox doesn't sound so scary. Though it is certainly not pretty.

Re:Non-registration article text

[pyite]

My guess is that Feynman would have been more apprehensive than most to say that he understood quantum mechanics.

Re:Bullshit - bad reporting, not bad science

[Sique]

As Mr Zeilinger's Office is just some floors below mine, I can tell you: The experiments are real, and the results are in a way that the interpretation is valid. Sorry for your intuition. But reality sometimes bites.

One point of clarification

[missing000]

EPR does not allow communication because the states of the entangled matter in question cannot be known prior to measurement at the end points and is completely random.

EPR does suggest (and this has been proven in tests) that states measured at one side of the entangled matter are exactly opposite of those on the other side thus enabling a method of distribution of random sets without comprimise (as measuring in transit violates the sets).

So, if you want to call it teleportation, go ahead, just understand that you are just "teleporting" randomness.

Re:Einstein was right, these guys are still on cra

[lawpoop]

"Bohr and his followers want to transfer a property of the mind (knowledge) to a property of nature (reality)."

Hey, mind and reality are not diametrically opposed opposites, as 3000+ years of western philosophy would have you believe.

I think in order to move forward, we are going to have to have a better idea about the relationship between mind and reality.

Note: I am not saying that people create reality with their minds or anything like that. All I am saying is that mind and reality are not opposites. They have some other kind of relationship, and we should more clearly define it.

Re:The other explanation

[couch_warrior]

Sorry - Multiple parallel universe, but expressed in lay terms, however clumsily ( granted it may require more than 5 dimensions). Hidden variable is intruiging, but not as comforting.

Re:Founder?

[kisak]

I guess you wanted to be funny, but the joke is on you. The Planck constant was named the Planck constant by Einstein himself, who was the first to understand that the constant Planck introduced in his equations to derive the black body radition law actually was a fundamental physical constant. (Planck himself just thought it was a clever mathematical trick). Einstein assumed that light comes in quanta (the so-called photon) to explain the photo-electric effect, and Einstein understood that the Planck constant gives the size of the quanta (together with the frequency of the light). In 1905 Einstein created the fundament of quantum mechanics and relativity with two ground breaking articles, while a third paper on Brownian motion gave the first direct evidence for the existence of atoms. Not bad for a Swiss patent clerk.

As a side note, the history is a bit similar to the Boltzmann constant which was named by Planck after he understood that the constant Boltzmann had introduced in his equation (giving a microscopic theory of entropy) was one of the fundamental physical constants.

Transactional Theory of QM

[robert.elliott.smith]

Some people commenting on this thread will find the transactional theory of quantum mechanics [washington.edu] (powerpoint) of interest. (Less clear cut paper in HTML here [washington.edu]).

In my opinion, this is the most reasonable, extant interpretation. From my perspective, it says that the paradoxes of QM are perceptual, arising from our perception of time as entirely forward moving. If waves move backwards in time (as in the transactional theory), everything makes sense, though it won't appear to make sense to us.

Re:Founder?

[einhverfr]

Schroedinger's cat is a poor thought experiment because it is inconsistant with the observational concept of the Copenhagen Interpretation. If the cat is capable of observing its own state, then doesn't that cause the wave-form to collapse?

If not, then you have a problem I call the "Schroedinger's Lab Assistant" problem where if you have two individuals measuring spins of entangle electrons independantly, the measurements should indicate that each one is spinning both directions *until* one attempts to communicate the findings with the other. And then, when this communication is attempted, the findings will change themselves back in time to make themselves internally consistant. Again, I am not sure that this ever happens in the real world. Anyway, it is not a very parsimonious explenation and seems to me to be confusing the map with the territory.

I would *highly* suggest reading "Physics and Philosophy" by Werner Heisenberg. He explains the apparent randomness and uncertainty as quantum interferance and suggests that the Copenhagen Interpretation works not because the observation creates the propreties but rather because those properties are dependent on factors outside our observation ("the exact position and velocity of all other [particles] in the universe"). In this regard, they are not really any more random than any other physical system (say, for example, dice), but appear so due to our non-omnicience.

Re:The other explanation

[jc42]

The formula for a circle is x^2 + y^2 = r^2; for the sphere it is x^2 + y^2 + z^2 = r^2. What happens with the sum of x[n]^2 + x[n-1]^2 + x[n-2]^2... = r^2 as n approaches infinity?

Google for Hilbert Space. Or ask wikipedia, where there's a simple definition and lots of links to further reading.

A Hilbert Space has countably-infinite dimension, but only points whose sums-of-squares value is finite; i.e., only points a finite distance from the origin are in the space. This doesn't mean that the origin is special, of course; one can easily prove that all points are a finite distance from each other, so choosing another point in the space as origin won't change the set of points.

There has been a lot of theoretical work on Hilbert Spaces. They are important to Quantum Mechanics.

Re:One point of clarification

[einhverfr]

When we refer to the speed of light as the cosmic speed limit, we refer to the speed of light in a vacuum. Not in, say, a diamond with a refractive index of 2.7....

Now, as long as we are in this area, I would suggest that you look into birefringence. In birefringence, the right-angle polarities are refracted differently because they travel through the crystal at different speeds.

Personally I suspect that it will eventually be possible to have spooky communication at a distance. The reason why we can't do it yet is because you have no way of knowing the state prior to re-entangling the particle. With electrons it will probably never be possible, but with photons, it might specifically because it may be possible to split entangled pairs along known property lines (birefringence being especially useful here). Note that this would be limited to wired environments though and would require currently unforeseen technological breakthoughs I believe, though I don't know enough about polarizations of laser beams to say whether it might be possible with current technology and advanced manufacturing.