Quantum physics mimics spooky action into the past

Apr 23, 2012
This abstract illustration shows four particles of light can be produced and manipulated in such a way that one can later decide in which quantum state two of the particles have been. Credit: Jon Heras, Equinox Graphics Ltd.

Physicists of the group of Prof. Anton Zeilinger at the Institute for Quantum Optics and Quantum Information (IQOQI), the University of Vienna, and the Vienna Center for Quantum Science and Technology (VCQ) have, for the first time, demonstrated in an experiment that the decision whether two particles were in an entangled or in a separable quantum state can be made even after these particles have been measured and may no longer exist. Their results will be published this week in the journal Nature Physics.

According to the Austrian physicist Erwin Schrödinger, entanglement is the characteristic trait of quantum mechanics. In addition to its crucial role for the foundations of physics, entanglement is also a key resource for upcoming technologies such as quantum cryptography and quantum computation. Entangled particles exhibit correlations which are stronger and more intricate than those allowed by the laws of classical physics. If two particles are in an entangled , they have perfectly defined joint properties at the expense of losing their individual properties. This is like having two dice which have no orientation until they are subject to measurement, upon which they certainly show the same (random) side up. In contrast, so-called separable quantum states allow for a classical description, because every particle has well-defined properties on its own. Two dice, each one of them with its own well-defined orientation, are in a separable state. Now, one would think that at least the nature of the quantum state must be an objective fact of reality. Either the dice are entangled or not. Zeilinger's team has now demonstrated in an experiment that this is not always the case.

The authors experimentally realized a "Gedankenexperiment" called "delayed-choice entanglement swapping", formulated by Asher Peres in the year 2000. Two pairs of entangled photons are produced, and one photon from each pair is sent to a party called Victor. Of the two remaining photons, one photon is sent to the party Alice and one is sent to the party Bob. Victor can now choose between two kinds of measurements. If he decides to measure his two photons in a way such that they are forced to be in an entangled state, then also Alice's and Bob's photon pair becomes entangled. If Victor chooses to measure his individually, Alice's and Bob's photon pair ends up in a separable state. Modern technology allowed the team to delay Victor's choice and measurement with respect to the measurements which Alice and Bob perform on their photons. "We found that whether Alice's and Bob's photons are entangled and show quantum correlations or are separable and show classical correlations can be decided after they have been measured", explains Xiao-song Ma, lead author of the study.

According to the famous words of Albert Einstein, the effects of quantum entanglement appear as "spooky action at a distance". The recent experiment has gone one remarkable step further. "Within a naïve classical word view, quantum mechanics can even mimic an influence of future actions on past events", says Anton Zeilinger.

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More information: Experimental delayed-choice entanglement swapping: Xiao-song Ma, Stefan Zotter, Johannes Kofler, Rupert Ursin, Thomas Jennewein, Časlav Brukner, and Anton Zeilinger. Nature Physics (2012) DOI: 10.1038/NPHYS2294

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kochevnik
1.8 / 5 (10) Apr 23, 2012
Torsion scalar waves cause quantum entanglement and allow consciousness to sculpt emergent material "reality"
jamesrm
1 / 5 (2) Apr 23, 2012
"Him card read good"
Cynical1
1 / 5 (2) Apr 23, 2012
So you are saying this team used scalar torsion waves to "sculpt" the desired entanglement? Or just to measure them?
antialias_physorg
4.4 / 5 (7) Apr 23, 2012
Within a naïve classical word view, quantum mechanics can even mimic an influence of future actions on past events

Woha. That is neat.

Now the weird thing would be if Alice and Bob entangled their photons but Victor decided to mesaure it so that they cannot be in an entangled state.
brt
4.5 / 5 (8) Apr 23, 2012
"Within a naïve classical word view, quantum mechanics can even mimic an influence of future actions on past events", says Anton Zeilinger.

Yes, that would be how a naive person would view it, which is why Zeilinger shouldn't confuse people by saying things like that.
jack_sarfatti
1 / 5 (2) Apr 23, 2012
Why "mimic"? Why is this not a real retro-causal effect?
antialias_physorg
4.6 / 5 (9) Apr 23, 2012
Why "mimic"? Why is this not a real retro-causal effect?

Because - as with all entanglement effects - there is no information transmission taking place. Causality demands a priori knowledge (if THIS then THAT). But in this case youz just know THAT and can then backwards say something about THIS without being able to force either of the two to be in a particular state.
kevinrtrs
1.5 / 5 (15) Apr 23, 2012
"Let there be light." Who said that? What a profound statement, too.
This might just shed light on how plants are able to transfer energy using quantum entanglement. Or not.
Cynical1
1 / 5 (2) Apr 23, 2012
"Let there be light." Who said that? What a profound statement, too.
This might just shed light on how plants are able to transfer energy using quantum entanglement. Or not.


That was a statement by the man who wrote the book of Genesis. Not that he was present at the actual event, mind you.

And yes, it has the potential to shed new light on photosynthesis.

Also, Anti Alias - I'm not sure I get the lack of information transfer in entanglement. Isn't that what an entangled state would imply? I was under the impression that one entangled entity exhibited a like reaction to a stimulus of the other. Maybe my understanding of the current definition is wrong...
hemitite
5 / 5 (5) Apr 23, 2012
What if Bob & Alice's findings are actually controlling Victor's choice?
Terriva
1 / 5 (7) Apr 23, 2012
Torsion scalar waves cause quantum entanglement and allow consciousness to sculpt emergent material "reality"
Emergent reality is the aether reality, because emergence can be modeled only with particle gas in physically relevant way (without underlying physical model the "emergence" is just postmodern abstract term without actual content, geometry the less). This delayed choice experiment is therefore imaginable with dense aether model of 4D space-time with common water surface in 3D. You can make the the water surface more dense with interference of underwater waves - these underwater waves are scalar and they're spreading much faster, than the surface ripples. Therefore you can influence the outcome of experiment at distance with speed, which is higher, than the speed of light.
Terriva
3 / 5 (6) Apr 23, 2012
BTW "scalar torsion waves" are oxymoron, or not? "Scalar" means just the absence of higher-rank tensor field, including vector and torsion fields.
Turritopsis
1 / 5 (2) Apr 23, 2012
Imagine a 2 metre rope tied to an anchor, begin vibrating it. Now tune the frequency of the rope to create a single oscillating wave (so a sort of 3 anchor points exist). One zero point at your hand, one at the 1 metre point (centre wave), and 1 at the anchor.

I'm not sure I get the lack of information transfer in entanglement


When the length of rope from 0-1m is in peak phase, the 1-2m portion is in a trough. When the 0-1 is troughed the 1-2 is peaked.

The 2 wave halves are interdependent, change in state of 1 constitutes a change of state in the other, there is no information exchange involved between the 2 wave halves. The only information input is your hand causing the wave oscillation.
Skultch
1 / 5 (1) Apr 23, 2012
Maybe I'm just now beginning to understand entanglement as 'particles are in every possible state until measured' but this experiment seems to provide more evidence for that. No?
Oysteroid
1 / 5 (2) Apr 23, 2012
Why "mimic"? Why is this not a real retro-causal effect?

Because - as with all entanglement effects - there is no information transmission taking place. Causality demands a priori knowledge (if THIS then THAT). But in this case youz just know THAT and can then backwards say something about THIS without being able to force either of the two to be in a particular state.

But hold on a sec. The article appears to claim exactly that:

"If he decides to measure his two photons in a way such that they are forced to be in an entangled state, THEN also Alice's and Bob's photon pair becomes entangled" (CAPS mine).

Isn't it the causality?

Also, the article briefly mentions that the particles may even no longer exist but their state was decided by something that hasn't yet happened.

I'm not really trying to argue with you, I just don't see how you can get away from retroactive causality in this setup.
Oysteroid
3.4 / 5 (5) Apr 23, 2012
Or look at it this way: they say the modetn quantum optics allows them to delay the time Victor makes his choice. By how much? As I understand it, pretty much indefinitely, correct?

If so, what's to prevent Alice and Bob from writing down their observations and hence prediction of Victor's choice on a bit of paper and tell him: hey, we KNOW what your choice will be a second (or a minute or a year...) from now.

Does it mean that the poor Victor now has no choice but to do exactly what they've written on that bit if paper? What happened to the free will?

I'm not too sure which of the two explanations is more mind-boggling :-)
Turritopsis
3.3 / 5 (6) Apr 23, 2012
@Oysteroid,

When evaluating the nature of light the experimental apparatus can be set up in 2 ways:

1. To test for the wave like nature of light. The results show true, light is a wave.

2. To test for the particle like nature of light. These results also come back as true, light is a particle.

Now it seems that entanglement is also subject dependent. When you check to see if the particles are entangled, you see they are. When checking to see if the particles aren't entangled, they aren't.

Strange is the reality at the quantum level. To me this shows a lack of understanding of the most basic principles.

For eg, maybe light is neither a particle or a wave, maybe it is something completely unrelated presenting itself in the form of both when inspected. Maybe quanta has nothing to do with waves or particles. Quanta could be something even more fundamental in nature.
Oysteroid
2.3 / 5 (3) Apr 23, 2012
Sorry, but that has nothing to do with causality.
(btw, I did study quantum physics so you don't have to explain the basics to me:-)

To follow up on your own example, you would have something akin to a person in another room to deduce based on HIS choice what YOUR choice of the experiment will be. That's if we reason in forward direction.

Conversly, you could claim, that YOUR action affected what HE did in the past.

Either way doesn't look good.
eloheim
3 / 5 (2) Apr 24, 2012
The reason there is so faster-than-light transfer of information is because each individual is just looking at a string of random values, which only become extraordinary when their PATTERN is compared to the pattern of the other participants. And whether the data is correlated or not, it still, in isolation, appears random; the trick is that when COMPARED with the other strings of values, you will see that different patterns emerge depending upon whether or not Viktor correlated the particles.

On cannot pre-determine what Viktor will do, because the other half of the revelatory pattern does not exist until he makes his measurement.
CardacianNeverid
5 / 5 (4) Apr 24, 2012
I'm not sure I get the lack of information transfer in entanglement. Isn't that what an entangled state would imply? -PseudoCynical

Not at all, as that would violate SR. You may be confused because you've heard entanglement used in the context of quantum communications protocols, but it cannot be used as an actual communication channel (information transfer), just for correlations between entangled states.
bluehigh
1 / 5 (2) Apr 24, 2012
As Carl says .. Extraordinary claims require extraordinary evidence. Perhaps these people have a faulty connector or a screw loose. When you reach the conclusions in this article then common sense dictates that a mistake or misunderstanding has occurred. I like pineapples.

vacuum-mechanics
1 / 5 (2) Apr 24, 2012
By the way, according to conventional quantum mechanics, it is interesting to note that nowadays physicists still do not know why and how (particle such as) electron can act both wave and particle property! May be understood wave-particle duality (in paper below) could guide to solve the quantum entanglement problem we are facing.

http://www.vacuum...id=17=en
antialias_physorg
5 / 5 (3) Apr 24, 2012
Isn't that what an entangled state would imply? I was under the impression that one entangled entity exhibited a like reaction to a stimulus of the other.

It's a subtle point on how information is defined.
For more info look into Shannon information theorem:
http://en.wikiped...n_theory

But basically entanglement says that the entangled entities will be in the same state, but that you cannot determine which state that will be until you look (and that you cannot 'set' or 'force' this state after entanglement has taken place). So there is no actual information *encoded* in the entangled pair because information transmission requires a priori knowledge of the information you want to transmit. (And hence measuring entanglement does not transmit any infomation at FTL speeds)
twasnow
1 / 5 (1) Apr 24, 2012
what about the information which is weather or not they are entangled, never mind the "state", to make this simpler lets say their are just 2 states heads and tails, this means their are 4 possibilities for the outcome of measurement at Alice and Bob, narrow that down to the info that matters; either Alice and Bob are the same or different. There is a 1 in 2 chance that when separate, they will be measured as separate, so 20 measurements will provide 1 in 1000000 conclusiveness of the entanglement or not.

The computer choosing whether or not to entangle at victor is just needs to be fed information of say a "coin flip", for which victor will choose entangled if heads, separate if tails, so long as Alice and Bob are pre-conditioned to know the encoding, then they will know the results of the coin flip before it happens. Currently all this would have to happen within a few billionths of a second but what if we can delay victors measurement longer..
Tachyon8491
1.4 / 5 (5) Apr 25, 2012
Einstein hiself disagreed with predictive causality but insisted on determinative causality - the one is ontological and the other epistemological. If a "this" does not cause a "that" then we have indeterministic a-causality, effects without cause. IMO the fact that the change of state of one of an entangled pair causes superluminal, non-local effect in the other implies the essential element of information transfer, even if that can only be monitored in restrospect.
Cave_Man
1.7 / 5 (3) Apr 28, 2012
I dont see the confusion over these types of effects, or the dble slt experiment

I will explain my take on the subject. The 'energy' associated with subatomic particles is moving through space-time dimensions in a way that contradicts causality if you take an approach which defines the words certainty or whole in terms of the "particle/wave" paradigm as being finite, discrete, set-value constructs consisting of either smaller set-value components or a self referential basis of quantity.

If subatomic particles are a form of energy which is related to the energy inherent in or facilitated by space-time dimensions then quanta becomes an arbitrary point based only on initial observation.

I call it the difference between being something and knowing something.

You are here now, where will you be when you are dead? Once you are dead you wont experience time, right? Then how will you tell the difference between right now, the past relative to now or the future in which you live and die..
Skultch
1 / 5 (1) Apr 28, 2012
If subatomic particles are a form of energy which is **related to the energy inherent in or facilitated by space-time dimensions** then quanta becomes an arbitrary point based only on **initial** observation.


I'm not following the parts in between **. Are you saying observations cause matter to emerge from energy; that all matter is like entangled particles, in that they are making all other matter "turn into" mass. If so, why? If not....wut?
originalentropy
3 / 5 (2) May 15, 2012
There is no such thing as 'simultaniousness'. The (inter-)action that actually takes place is determined in a timeless state: The observation, the 'always now'. Until that moment anything not observed can be in any legitimate state, for instance entangled.
originalentropy
1 / 5 (1) May 15, 2012
And I'd like to add that de observations of Bob, Alice and Victor are most likely to be dependend in an entangled way, until all three observations are made, independent of who outruns the other in temporal sense. This might mean that the observation may come before the event took place, dependent on how the temporal relations are defined.
Mike_Massen
2.3 / 5 (3) Jun 11, 2012
"Let there be light." Who said that? What a profound statement, too.
This might just shed light on how plants are able to transfer energy using quantum entanglement. Or not.
FFS kevinrtrs please extricate yourself from attachment to a book from "Voices in the head" it does you no credit and makes you out to be a cult follower - a mere sheep that cannot think independently...

Humans have come up with all sorts of profound statements before and after any bibles from *any* culture, wakey wakey, bye bye !

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