Researchers have uncovered a fundamental link between the two defining properties of quantum physics. Stephanie Wehner of Singapore's Centre for Quantum Technologies and the National University of Singapore and Jonathan Oppenheim of the United Kingdom's University of Cambridge published their work today in the latest edition of the journal Science.
The result is being heralded as a dramatic breakthrough in our basic understanding of quantum mechanics and provides new clues to researchers seeking to understand the foundations of quantum theory. The result addresses the question of why quantum behaviour is as weird as it isbut no weirder.
The strange behaviour of quantum particles, such as atoms, electrons and the photons that make up light, has perplexed scientists for nearly a century. Albert Einstein was among those who thought the quantum world was so strange that quantum theory must be wrong, but experiments have borne out the theory's predictions.
One of the weird aspects of quantum theory is that it is impossible to know certain things, such as a particle's momentum and position, simultaneously. Knowledge of one of these properties affects the accuracy with which you can learn the other. This is known as the "Heisenberg Uncertainty Principle".
Another weird aspect is the quantum phenomenon of non-locality, which arises from the better-known phenomenon of entanglement. When two quantum particles are entangled, they can perform actions that look as if they are coordinated with each other in ways that defy classical intuition about physically separated particles.
Previously, researchers have treated non-locality and uncertainty as two separate phenomena. Now Wehner and Oppenheim have shown that they are intricately linked. What's more, they show that this link is quantitative and have found an equation which shows that the "amount" of non-locality is determined by the uncertainty principle.
"It's a surprising and perhaps ironic twist," said Oppenheim, a Royal Society University Research Fellow from the Department of Applied Mathematics & Theoretical Physics at the University of Cambridge. Einstein and his co-workers discovered non-locality while searching for a way to undermine the uncertainty principle. "Now the uncertainty principle appears to be biting back."
Non-locality determines how well two distant parties can coordinate their actions without sending each other information. Physicists believe that even in quantum mechanics, information cannot travel faster than light. Nevertheless, it turns out that quantum mechanics allows two parties to coordinate much better than would be possible under the laws of classical physics. In fact, their actions can be coordinated in a way that almost seems as if they had been able to talk. Einstein famously referred to this phenomenon as "spooky action at a distance".
However, quantum non-locality could be even spookier than it actually is. It's possible to have theories which allow distant parties to coordinate their actions much better than nature allows, while still not allowing information to travel faster than light. Nature could be weirder, and yet it isn't quantum theory appears to impose an additional limit on the weirdness.
"Quantum theory is pretty weird, but it isn't as weird as it could be. We really have to ask ourselves, why is quantum mechanics this limited? Why doesn't nature allow even stronger non-locality?" Oppenheim says.
The surprising result by Wehner and Oppenheim is that the uncertainty principle provides an answer. Two parties can only coordinate their actions better if they break the uncertainty principle, which imposes a strict bound on how strong non-locality can be.
"It would be great if we could better coordinate our actions over long distances, as it would enable us to solve many information processing tasks very efficiently," Wehner says. "However, physics would be fundamentally different. If we break the uncertainty principle, there is really no telling what our world would look like."
How did the researchers discover a connection that had gone unnoticed so long? Before entering academia, Wehner worked as a 'computer hacker for hire', and now works in quantum information theory, while Oppenheim is a physicist. Wehner thinks that applying techniques from computer science to the laws of theoretical physics was key to spotting the connection. "I think one of the crucial ideas is to link the question to a coding problem," Wehner says. "Traditional ways of viewing non-locality and uncertainty obscured the close connection between the two concepts."
Wehner and Oppenheim recast the phenomena of quantum physics in terms that would be familiar to a computer hacker. They treat non-locality as the result of one party, Alice, creating and encoding information and a second party, Bob, retrieving information from the encoding. How well Alice and Bob can encode and retrieve information is determined by uncertainty relations. In some situations, they found that and a third property known as "steering" enters the picture.
Wehner and Oppenheim compare their discovery to uncovering what determines how easily two players can win a quantum board game: the board has only two squares, on which Alice, can place a counter of two possible colours: green or pink. She is told to place the same colour on both squares, or to place a different colour on each. Bob has to guess the colour that Alice put on square one or two. If his guess is correct, Alice and Bob win the game. Clearly, Alice and Bob could win the game if they could talk to each other: Alice would simply tell Bob what colours are on squares one and two. But Bob and Alice are situated so far apart from each other that light and thus an information-carrying signal does not have time to pass between them during the game.
If they can't talk, they won't always win, but by measuring on quantum particles, they can win the game more often than any strategy which doesn't rely on quantum theory. However, the uncertainty principle prevents them from doing any better, and even determines how often they lose the game.
The finding bears on the deep question of what principles underlie quantum physics. Many attempts to understand the underpinnings of quantum mechanics have focused on non-locality. Wehner thinks there may be more to gain from examining the details of the uncertainty principle. "However, we have barely scratched the surface of understanding uncertainty relations," she says.
The breakthrough is future-proof, the researchers say. Scientists are still searching for a quantum theory of gravity and Wehner and Oppenheim's result concerning non-locality, uncertainty and steering applies to all possible theories including any future replacement for quantum mechanics.
Explore further:
Quantum cryptography: No Signaling and quantum key distribution
More information:
Journal paper: sciencemag.org/content/330/6007/1072.abstract
Additional info: www.damtp.cam.ac.uk/user/jono/ … nty-nonlocality.html
Jarek
It's like when we know that there is blue and red ball, when we get known one color, we immediately (faster than light) get information about the second color...
The color distribution could be chosen in some deterministic, but not known to us way - there is nothing strange in that model representing our knowledge on local, deterministic system becomes nonlocal and nondeterministic (another example - maximal entropy random walk).
What is strange is that many people try to see such model representing our knowledge - which can only return probability distribution of scenarios - not as effective, thermodynamic-like, but as fundamental ...
KwasniczJ
Yevgen
This sounds like a different way to derive Bells inequality (which of cause would be just a repeating
a work for 70ties):
http://en.wikiped..._theorem
KwasniczJ
MaeWest
KwasniczJ
The article disputed was published quite recently. Such "WHY" questions aren't actually very important in mainstream physics, which asks "HOW" first, just after then it asks for causality. Both noncausality, both uncertainty principle are theorems - not axioms of quantum mechanics and they could be derived anytime from first principles.
I'm not judging such approach by now - I'm just describing, how science is working.
Objectivist
Wait--what?
Kedas
Nature act always the same so sometimes you don't need to measure it to know what is happening.
NeuroPulse
What is that supposed to say???
Going
genastropsychicallst
Javinator
I've always found this concept interesting as I don't believe that we or any computer we make can process information faster than the speed of light (ie. computers are based on components which transfer information within the computer slower than lightspeed. Similar with our brains.)
KwasniczJ
stereolove
Foolish1
Is the paper saying "steering" allows a shared game to be won more often using quantum effects than would otherwise be possible with just fake random chance using the above simple PRNG setup?
(This is just an example so I can understand information..not a hidden variable subscriber:)
From what I can make out from the paper they say you can set dependant variables in a coherent system subject to the constraint no information can be conveyed across all possible states but I'm not sure how or if this can translate into anything real such as better chance of winning their shared game.
Are there new previously unknown properties of "spooky" being offered with this work?
gwrede
Of course, then I need Hidden State. But I've read explanations, books, and listened to Wise Men trying to explain that Hidden State is impossible. (As if we could prove that we DO KNOW EVERYTHING about the two particles.) IMNHO, either they merely cite what they've learned by heart, they pretend they understand any of it, or much worse, their explanation is intractable. Which it is either because the person doesn't understand after all, or he merely can't communicate clearly.
Now, please, someone, anybody, point me to a text that convinces me there can be no hidden state. From then on, I promise to not ever try to understand physics. I'll just Believe whatever they say.
stereolove
I think you are still entangled. Eentangled in the similiar moment because of getting the new responsability for your new role (in this case as uncle) as part of this common one big event which was established once when you have been together/ or informed that you both exist together. No matter if I have the information about that new existing fact/factor! or not. My role is existing and so my responsibility for this role doesn't starts not only when i'm informed about this fact. So Non information is no excuse for a you as persuasive factor. So „Magic of you're presence“ in this bigevent means your function as sign is existing, doesn't matter you or someone else is aware about this or is informed or not. Thats for me what makes the hidden factor. Because sometimes i have no chance to be welltimed informed in my position.
GuruShabu
If you read Julian Barbour (http://platonia.com/).
What IF SPACE is something different?
Have you spend a minute on that before engaging in a fierce discussion based on two very incompatible assumptions (GR and QM) about space?
One has to understand that space in General Relativity and Quantum Mechanics is NOT the same!
While in QM space is STILL Newtonian, GR treats it in a very different way.
I have not enough time or energy to write about this very important difference but if one does not understand this the discussion above is irrelevant.
stereolove
Of course you are right, it's the most important thing i believe to start all this with a concrete, probably radical new understanding of that you call space.
I'm not familiar with the ideas and theories of your Julian Barbour but indeed the personal understanding of all the still „mystical“ aspects depends on from
the question which concept of space and time is yours.
It could be an interesting and knowledge accellerating way to focus on the task finding a simple idea of time and space (IOE) observing the entire subject than to concentating mainly on determimd aspects. This IOE than perhaps could be the platform for developing step by step a theory of everything (TOE) via worldwide internetworking and bundeling all new findings under a commen new angle of view.
Skeptic_Heretic
Many in the physics community are starting to reinvestigate hypotheses that call for instant information transfer or definitive non-locality. After all, everything can be broken down into wave forms and what we perceive very well could be an illusion created by our interactions with reality.
For example, describe typing using only the fundamental forces and not aspects of language seen outside of fundamental forces. The reality you would draw is wholly different from what your eyes would see.
stereolove
1) as Present Perfect/Timepoint (life/nature,wave, impulse/subawarness, roles, Beeing/Reality. Sign/In form-ation ... QM?!) and
2) as Present Tense/Timespace (life/existence, matter, particle, selfawareness,acting, will, Doing/Possibility, Dialog/Communication ... GR?!)
This idea + the intuition that c (constant) is more a distance than a speed makes QRGR easier understandable also as nonphysicist ... at least for me!
dtxx
MorituriMax
As the universe expanded and the four forces emerged from the expanding big bang and all points moved away from each other, wouldn't there need to be something going on that kept the four forces tuned right? I mean, we already know (theoretically) that space itself doesn't violate the FTL limit as it expands, just the objects in that space.
dtxx
Besides, the Copernican principle is far from absolute or proven. All of our knowledge of extrasolar space is informed by the copernican principle and depends completely on it.
MorituriMax
Skeptic_Heretic
It would have to otherwise the doppler effect wouldn't be seen in light traversing the void, at least according to current models.
Skultch
Why?
Also, I'm sorry, I know you and others have answered this before, but I have to ask again. What is space(time)? Is it material, or just a description of position (x,y,z,t) relationships between particles? IOW, is spacetime a noun or an adjective? How certain are we about the answer?
Skeptic_Heretic
If spacetime wasn't a medium with impact upon material, and by extension energy, dynamics then light wouldn't stretch, it would simply appear to have a lesser speed.
Think of driving a highway at 60 miles an hour, that never gets longer, but extends at a speed greater than 60 mph and you still get to your destination on time.
Two of those aspects must be false unless your car is growing in size in relation ot the road traveled thus far.
Auxon
Skeptic_Heretic
Yes, well just because it's called the void, doesn't mean it's empty. Modern definition would be interstellar space decoupled from the interstellar medium.
MaxwellsDemon
The answers to questions like these will most likely be the basis of the next revolution in theoretical physics.
Because the two seemingly irreconcilable models of physics that we apply every day, GR and QM, answer these questions completely differently…and yet both yield correct answers.
GR defines spacetime as a geometrical construct. Matter/stress/energy influence this geometry, and vice versa, but in GR spacetime is a purely dimensional phenomenon. However, and crucially, GR does not explain the [i]mechanism[/i] of this interaction, it simply predicts the magnitude of it.
QM on the other hand throws the idea of “empty spacetime” right out the window – there is no “void” in QM, there’s only a seething background of virtual particles, and the closer you look the more chaotic it is.
So briefly: there isn’t an explicit definition of spacetime that satisfies both theories, and theorists are currently working on resolving the question.
Skeptic_Heretic
KwasniczJ
http://en.wikiped...astrophe
If you consider vacuum as a particle environment, then the space-time is a density gradient of it, comparable to water surface. After then the time dimension is the direction parallel with gradient and the space dimension(s) are the direction(s) perpendicular to this gradient, i.e. parallel with water surface. This simple model for example explains, why time direction has an arrow, wheres the spatial dimension(s) hasn't.
KwasniczJ
At the close distances all objects will appear deformed, blurred and fuzzy due the dispersion of surface waves with density fluctuations of underwater, resulting from Brownian motion of water molecules. This perspective models the quantum mechanics phenomena.
At the larger distances the surface waves are spreading like so-called capillary waves, which are driven with surface tension of water nearly exclusively. Such waves aren't affected with motion of underwater very much, because the water surface is behaving like thin elastic membrane for these waves. These waves are mediating perspective of general relativity at large distances, which is background invariant.
Skeptic_Heretic
Secondly, the VC comes from the Voyager predictions, not the predictions of GR. This also provides a potential alternate explanation for the voyager anomaly. You wouldn't experince virtual particle pressure differentiated from gravitation until you left the presence of large bodies, ie: the sun.
KwasniczJ
KwasniczJ
It has no meaning to speculate about it: with general relativity all objects should collapse into pin-point singularity - soon or later. Whereas in quantum mechanics all objects should expand into infinity instead. So whenever you're observing some stable object, you can be sure, it violates both theories at the same moment. These theories aren't compatible mutually at all.
Skeptic_Heretic
Ethelred
Stupefying. However did you come up with that?
GR predicts that the UNIVERSE, not every object, must be EITHER expanding or collapsing.
Ethelred
KwasniczJ
http://arxiv.org/.../9512025
That's incredibly vague countergument.
Ethelred
You do know that gravity is ATTRACTIVE don't you? That GR has BEEN tested and it worked. If it had no way to deal with attraction then it wouldn't work?
I thought not. Nothing but that level of ignorance could explain that preposterous statement. Nothing in that link that shows an equal level of ignorance either.]
Do you strap yourself down or something. What is that keep you on the Earth? I use gravity myself.
Stupefying is too mild a word.
Troll is more likely considering you ARE a troll in the first place.
Ethelred
MaxwellsDemon
Kwasniscwszerpski:
Skeptic_Heretic is right. Legitimate scientists know that the gravitational field is a negative energy field. Note the minus sign in the equation for gravitational potential energy:
U = -Gmm/R
Source: http://en.wikiped...l_energy
In fact all binding energy fields possess negative energy, which is why bound systems have less mass than their unbound constituents.
KwasniczJ
You just didn't understand my objection. Quantum mechanics predicts energy density of vacuum 10E+121 GeV/m3 (roughly the inverse value of third power of Planck constant). Whereas from general relativity follows, energy density of vacuum is lower then 10E+14 GeV/m3.
Do you really believe, you could correct such disagreement of 107 orders of magnitude by consideration of gravitational field as a negative energy field? Does the -10E+14 GeV/m3 sound really better in comparison to 10E+121 GeV/m3, then the 10E+14 GeV/m3 value?
http://en.wikiped...astrophe
S_H is just an OT troll - you can ignore him safely.
Skeptic_Heretic
You're on the internet, read something, anything, and lose that Oliver Lodge 1810 mentality. I'm sorry, I have 3 research papers published and peer reviewed, pre-doctorate. I've worked on 2 lineac systems and I did two tours at RHIC. What do you have to support your stance, sophist?
KwasniczJ
Skeptic_Heretic
I don't have 42 screen names on Physorg, if that's what you measure as "credit within the field".
People like you put a bad taste in my mouth. You're nbasically the Ray Comfort of Physics, disgustingly ignorant of reality, but ready to act as an authority on everything.
Why don't you crawl back into that Kosovo basement you lurched out of before I start digging onto your internet life as I have Marjon's.
KwasniczJ
MaxwellsDemon
Source: http://en.wikiped...um_state
This 'intrinsic ground-state energy of free space' has since been at least theoretically unified with the cosmological constant to explain 'dark energy,' the highly uniform cosmic energy that's accelerating galaxy clusters apart from one another. There's more about that here: http://en.wikiped...k_energy
Skeptic_Heretic