Don't have all the information? In the quantum world, that doesn't matter

Jul 26, 2011 by Miranda Marquit feature

(PhysOrg.com) -- When it comes to the rules of the quantum world, it seems that almost everything goes against intuition. In the case of the way ignorance of the whole implies ignorance of at least one of its parts, the situation seems to be counterintuitive. "When viewed in a classical sense, you would be inclined to think that a strong ignorance of the whole has to be accompanied by significant ignorance of at least one of its parts," Stephanie Wehner tells PhysOrg.com. "However, this conjecture turns out to be false in quantum theory."

Wehner is a scientist at the National University of Singapore. She worked with Thomas Vidick at the University of California at Berkeley to examine the role of ignorance in quantum theory. Their work can be read in : “Does Ignorance of the Whole Imply Ignorance of the Parts? Large Violations of Noncontextuality in .”

“Originally, we were motivated to study this problem from a cryptographic perspective,” Wehner explains. “However, we soon found that our exploration had implications for understanding the fundamentals of how quantum states work.”

Wehner and Vidick set out to see about exposing ignorance in cases of quantum communication. “Our problem can most easily be described by an example.” Wehner says. “Let’s say that you study a book that has two pages: one and two. You are going to sit an exam in this class, and you only had a small amount of time to study. You don’t know everything that is on page one and page two. Can I point to a page that you don’t know, thereby exposing your ignorance? Classically, this is indeed true: For example, if you only know the information on page one, I can point to page two and expose your ignorance. I can catch you.”

Classically, this scenario makes sense. Ignorance of the whole does imply ignorance about at least one of the parts. However, in the , it doesn’t work this way. “Quantumly, there is no way for me to expose your ignorance in this way. If I challenge you, you can guess the information – even if you don’t know it all – almost perfectly. It’s very counterintuitive.”

Wehner points out that the result has some strong implications for our understanding of the quantum world. “We haven’t really fully explored this effect yet. There are many weird quantum effects we still know little about, but this one is particularly intriguing as it deals with the basic question of how knowledge itself behaves in a quantum world.”

She goes on to point out that this research says something about fundamental differences in classical versus quantum knowledge. “It really makes a difference if the memory you have is classical or quantum. We are merely at the beginning of understanding these differences.”

Wehner says that she is planning to look more closely at the structure of quantum states. “Our example demonstrates that this effect can be rather dramatic. But does it always have to be this way? And, how do we tell?”

Additionally, Wehner would like to be able to design an experiment that would show this effect, since she and Vidick approached it theoretically. “In the end,” she admits, “our paper probably raises more questions than it answers. But it offers a good place to start, and a good beginning towards a deeper understanding of what distinguishes quantum from classical knowledge.”

Explore further: Quantum physics just got less complicated

More information: Thomas Vidick and Stephanie Wehner, “Does Ignorance of the Whole Imply Ignorance of the Parts? Large Violations of Noncontextuality in Quantum Theory,” Physical Review Letters (2011). Available online: link.aps.org/doi/10.1103/PhysRevLett.107.030402

4.4 /5 (14 votes)

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User comments : 17

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TheWalrus
5 / 5 (12) Jul 26, 2011
Does my confusion about this article mean that I understand it?
jamesrm
5 / 5 (8) Jul 26, 2011
Ah, the sound of one hand clapping in 11 dimensions
rawa1
2.4 / 5 (5) Jul 26, 2011
IMO it's just reversed version of the well known holographic principle, in which information about each part of the quantum system brings an information about the rest of this system. At the water surface model it corresponds the ancient Huygens-Fresnel principle, in which every point becomes a source of a spherical wave, and the sum of these secondary waves determines the form of the resulting wave at any subsequent time.
jscroft
3.4 / 5 (5) Jul 26, 2011
Yah you're right. That's MUCH clearer.
Code_Warrior
not rated yet Jul 26, 2011
Nobody could have ever guessed at what might be on page 2 during classical times. Apparently, the concept of guessing did not exist until quantum mechanics came along. Boy, do those old classical physicists have egg on their faces.
Raygunner
5 / 5 (1) Jul 26, 2011
So if I understand this right (and I seriously doubt ANY understanding on my part), it seems that even if you ask for an answer on a small piece of information, this small piece - even if it is disassociated completely from the information at hand - that small piece of information really has ALL of the information. Yes, that sounds holographic to me and very fractal sounding too. Could we be tapping into a quantum database embedded in the fabric of the universe? Or maybe we are just starting to ask the right questions in the right way that unveils this database? Here it is folks - the quantum universal internet!
Y8Q412VBZP21010
not rated yet Jul 26, 2011
Ah, the sound of one hand clapping in 11 dimensions


Oh. You have to get points for that.
Code_Warrior
3.5 / 5 (4) Jul 26, 2011
***Click of lighter, sound of bong hit, hold it, exhale*** Soooo....... if I understand what you're saying RG...... like, this article has like, all the answers to all the questions........ Damn....... That's some heavy shit RG..... Fire up that bong dude.....
Raygunner
not rated yet Jul 26, 2011
Got a name now - Universal Quantinet!

I dunno, sounds like a hair product or something.
hush1
5 / 5 (1) Jul 27, 2011
Don't be silly. You were only asked to accept the Krein-Milman theorem. And the "see other" theorems too.

http://en.wikiped..._theorem

It's not your fault. If you practice hard enough, you too, will be able to fill in what led the authors to this work(?) and what they read beforehand.

You decide. Between entertainment or boredom. After the first page you will know.
Raygunner
not rated yet Jul 27, 2011
Hush1, are you saying that quantum effects are "filling in the blanks", so to speak, as the theorem reads?

What I'm taking away from this is that the information is a subset - with the extra, missing, or not revealed info possibly being holographically stored as a whole or connected (entangled to where it needs to be to reveal the additional information not classically linked?) somehow around or through the quantum state being manipulated for the information. I did not read anything about the test setup so I'm not sure how they arrived at this conclusion.

I do believe we are just barely tapping the surface on this. "They" are waiting for us to finally figure it out! If it goes dark you know the government has it under lock and key.
eachus
not rated yet Jul 27, 2011
I think hush1 missed the point. If he wants to look at the Krein-Milman theorem, the quantum equivalent not only covers non-convex shapes, but shapes in higher dimensions and even disjoint sets.

Of course the next question is about causality. If I know part of the state of your mind, and vice-versa can we build a quantum telephone that allows instant communication from Earth to Mars, or from past to the future?
Husky
not rated yet Jul 27, 2011
..or it could be that all the quantuminformation isn't worth jack, and frankly anybodies guess..
hush1
1 / 5 (1) Jul 27, 2011
I conjectured about the authors and their work. I submit we are causal beings and are comfortable with causal existence. Presently.

I submit further we are capable of much more than this. In the future we will experience 'discomfort' with theories (of science) which tell us we are as simple as our abilities of abstraction and prediction allow. This 'premonition' already permeates our way of thinking. We are more becoming more and more predictable and sure of who and what we are and how we work. We anticipate this. We are finite. We are fascinated with the infinite (states, if you will). Something beyond predictability and simplicity. Our ability to reduce our existence and ourselves to predictability and simplicity creates dichotomy - comfort and discomfort.
Also susceptible - to eventual control and understanding - our emotions and feelings.

In the QM world, being incomplete, simple and predictable means nothing. We are all what QM needs:
Insufficient and necessary.
Kafpauzo
3 / 5 (2) Jul 27, 2011
From the article:

"When viewed in a classical sense, you would be inclined to think that a strong ignorance of the whole has to be accompanied by significant ignorance of at least one of its parts," Stephanie Wehner tells PhysOrg.com. "However, this conjecture turns out to be false in quantum theory."


This is nothing new. Amazingly strong ignorance of the whole is quite possible even when all the parts are known. Just look at Fox news, the Tea party movement etc.
jscroft
1 / 5 (1) Jul 28, 2011
Amazingly strong ignorance of the whole is quite possible even when all the parts are known. Just look at Fox news, the Tea party movement etc.


Haha whatever, troll.
Pete1983
not rated yet Jul 28, 2011
@iscroft - How was that trolling? I found it quite amusing.

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