Probability quantum world obeys local realism is less than one in a billion

https://phys.org/news/2017-07-probability-quantum-world-local-realism.html

by jonbaer • 9 years ago

70 45 9 years ago

enkid• 9 years ago

Could someone explain the implications of this? If locality is broken, would that mean that sending a message faster than light would be possible (theoretically)?

krastanov2• 9 years ago

The result from the experiment is not surprising and it has been done in less stringent fashion many times before. It is just a real-world realization of the though experiment behind Einstein's spooky action at a distance (look up Bell measurements / Bell experiment / EPR "paradox").

This gives you way more obfuscated information than you probably want: https://en.wikipedia.org/wiki/Bell_test_experiments

Basically, if you set up an experiment where two entangled particles are send far apart and you are not very careful with the derivations, it would look like you can communicate faster than light between the two entities holding the two particles. Turns out that it does not work, and while it does give fascinating insights about the weirdness of quantum mechanics it is not useful for FTL communication.

However, it is definitely useful for encrypting messages that can not be decrypted no matter how much computational power you have (even if you have fancy computational oracles).

jrue• 9 years ago

Faster than light communication would violate causation, meaning you could send a message that would arrive before it was sent. What happens if you instruct yourself to not send it in the first place? This is the paradox. So, how to get around that? Perhaps parallel universes? Other dimensions? Or maybe just that the quantum world is designed to violate locality in very precise ways that don't affect the macroscopic world, or break any causation rules. I always find it fascinating how a concept like entanglement — two particles that are connected by some faster-than-light phenomenon — can coexist with the macroscopic world, yet perfectly prevent messages from being sent between two points. Same with quantum teleportation. The science says that it can happen, but the no-cloning theorem prevents duplicates from being made through teleportation. As strange as the quantum world is, it somehow doesn't seem to ever break causation rules (yet).

oldandtired3• 9 years ago

The problem is that (as far as we know) we cannot determine when two (remote from each other) events take place relative to each other when we are constrained by the speed of light.

We cannot determine which occurred first. This is a limitation due to the information communication limit. So the theoretical basis (for consistency purposes) is that faster than light motion would violate causality.

If on the other hand, there is an absolute frame of reference, then all events can be related (in time) to this absolute frame of reference. In this case, no matter how much faster we can move above the speed of light, no violation of causality would be possible, we could always determine the relative positions in time of any and every event, no matter how remote from each other.

Since we do not know (as in, we cannot determine if such a frame of reference actually exists) of any such absolute reference frame, we are unable to determine in reality what would happen in the event of faster than light motion. The mathematical basis of the prevalent theories give causality violations in such events.

The universe is much stranger and more unknown than what is purported to be understood. Always keep in mind that no matter what theories are currently in vogue, they are a very pale and simplistic understanding of the reality that we live in. Every theory we currently use is flawed and fails in some way. That is not to say that they don't have utility. They do, but they are also limited in that utility.

The problem that is faced today is that people (quite intelligent people for that matter) forget that the mathematical descriptions they use in formulating theories and models of the universe around are always simplified models. There are always simplifying assumptions made. Too often, these assumptions are so hidden that those promulgating the theories get so caught up in their theories success that they forget that it is a limited and faulty description of reality. This then leads to some of the fantastical beliefs that they will then propagate.

This effects things all areas of science and the upshot is that when problems are highlighted with specific parts of the theories in question, there is a great amount of effort undertaken to defend the theory instead of applying critical thinking to the problem and looking for better alternative descriptions.

An example is the Standard Model of Subatomic Particles. One of the basic assumptions is that the Big Bang occurred. This underpins the entire model. Yet how often does this particular assumption actually get stated as being a fundamental assumption for the theory/model.

In conflict with this is the Theory of General Relativity. One of the "results" of the GR Theory is these strange entities called "black holes". Singularities that are quite problematic in any finite universe. Simply put, a universe in which "black holes" exist cannot be started by a "big bang". The singularity that is the "big bang" won't go bang since the gravity is way above anything escaping.

So we have impasse and hence, we have illogical assumptions underpinning some of our quite workable theories/models at the macro and micro levels. We must always remember that, though our theories are useful, they are a very flawed and incomplete model of reality.

The other thing to remember is that it should be fun to try and discover more about our reality. Too often, many who support one view or another (in terms of what theory or theories are applicable - witness the conflict between string theory and non-string theory defenders), come across as being afraid of their opponents.

Having a robust defence of your view is fine, but when it descends to ad hominem attacks, then all I see is fearful little people and not intelligent critical thinkers.

deepnotderp2• 9 years ago

Locality != causality

Sending a message faster than light violates causality (sidenote, it would mean the end of free will). Fortunately , information cannot be sent faster than light via quantum entangled particles, the formal theorem is called the "no communication theorem".

oldandtired3• 9 years ago

Free will is not determined by a limitation on the speed of light. The problem is that we cannot determine via an absolute frame of reference when two events have occurred in time. The assumption is that causality will be violated if we are able to send a message faster than the speed of light, this is a mathematical solution only in the event that there is no absolute frame of reference.

Since we do not know if there is one or not, we make the simplifying assumption that there is none. Whether or not this assumption is correct is not determinable at this time.

If we are able to send messages at some speed faster than the speed of light (by any factor you wish), we will still be in the same situation as we are now, not being able to determine when two events have occurred relative to one another.

If we find that we are able to send instantaneous message between any two points, we will then have found the absolute frame of reference to measure when two events have take place. Causality will not be violated in either scenario.

n4r92• 9 years ago

The No Communication Theorem only guarantees against instantaneous communication. Quantum theory on its own says nothing about the speed of light.

lisper• 9 years ago

No. See this video for an explanation:

https://www.youtube.com/watch?v=dEaecUuEqfc

Or this paper:

http://www.flownet.com/ron/QM.pdf

k4002• 9 years ago

No. Correlation is nonlocal, causality is not.

krastanov2• 9 years ago

This is just a fancy way to say that there is yet another Bell test experiment that confirms the Bell inequality[1]. The technology behind that is amazing, both in terms of practical immediately useful engineering and in terms of fundamental physics, but the title is just a pretentious obfuscated way to phrase it.

[1]: To be precise, it says that the chance that the Bell inequality is violated is very small.

eternauta3k• 9 years ago

It's worth reading the article for the details on loopholes.

n4r92• 9 years ago

I believe you've got it the wrong way round. The point of Bell tests is to confirm that Bell inequalities are violated. If anything I think the title is underselling it. I would replace "quantum world" with "nature".

deepnotderp2• 9 years ago

I'm curious what hacker news readers think about Andrew Friedman's work on closing the "free will loophole" in bell's theorem.

winter_blue• 9 years ago

If there is anything such as free will, then it has to arise out of indeterminacy in the particles that constitute the human form.

If every particle in the human body could be acocunted for, and its next state predicted deterministically based on a fixed set of laws, that means no living organisms have free will, and are merely executing a program whose behavior and outcome is determined solely by its initial state. There is no "ongoing input" in the form of free will decisions/choices.

And you need to take the realistic philosophical consequences of that very seriously ... if there is no free will ... I simply cannot imagine how someone can live with that. You might as well kill yourself now, since you are nothing but a robot.

I really do despise (and am horrified) by a worldview that says we're all robots, and have no free will. Learning about indeterminacy at the quantum level was a huge relief. It's a logical deduction/conclusion that this low-level indeterminism is likely amplified into "choice" in human beings.

themgt2• 9 years ago

It's a logical deduction/conclusion that this low-level indeterminism is likely amplified into "choice" in human beings.

I would agree, and it's a concise way of putting it. It's easy to criticize the idea of quantum consciousness since no one yet can understand or explain how it would be physically possible, but in a deep way the idea of brains "capturing" / amplifying indeterminacy is extremely attractive.

jjaredsimpson• 9 years ago

Randomness doesn't give you free will.

If you substitute direct choice of a particular next state and instead are only allowed to sample a state space, you still aren't free to choose.

Said another way: flipping a coin cant't make Harvey Dent free.

dwaltrip2• 9 years ago

If you can't tell that you are a "robot", does it really matter?

Does that steak taste any worse? Does the sunset seem less beautiful? Do your decisions feel less real?

Enjoy the ride! You only have 1 ticket =)

thwarted• 9 years ago

And you need to take the realistic philosophical consequences of that very seriously ... if there is no free will ... I simply cannot imagine how someone can live with that.

I'll consider the realistic philosophical consequences of that seriously once they are presented. Your inability to imagine how someone can live with that doesn't provide any support for, and isn't an example of, what those realistic philosophical consequences are.

if there is no free will ... You might as well kill yourself now

So if one doesn't have choice, one should choose to kill oneself? This makes no sense.

anst• 9 years ago

Free will arising from quantum indeterminacy, well, that's a thought of Robert Penrose. The bad news is that even he didn't manage to convince others and the theory didn't really took off. In other words, we are not yet ready to understand such a link.

However, there is the Strong Free Will Theorem of Conway and Kochen. Essentially, they prove that "if humans have free will, then elementary particles already have their own small share of this valuable commodity", see http://www.ams.org/notices/200902/rtx090200226p.pdf

xaa• 9 years ago

I was really into this question a few years ago. I had quite a bit of existential angst about it as well.

I read Penrose, etc, but at the end of it could not find any plausible mechanism for humans having free will in the sense of uncaused causation. But I use a modified version of Daniel Dennett's take on it: we CAN choose, we just can't choose what we choose.

Another way of looking at it is to have two different "modes" for thinking of free will: in everyone's daily lives, they use the "traditional" view (how else could we have such things as moral praise or blame?), but when you look at the human brain as a physical system, you use the deterministic/pseudodeterministic view.

ThrustVectoring• 9 years ago

Free will has more to do with tort law than quantum physics. Any attempt to get at "free will" through something other than legal analysis, game theory, and psychology is fundamentally misguided and is making type errors about what laypeople are talking about when they say "free will".

simonh• 9 years ago

A thousand time yes.

Free will only makes sense in the context of an individual Actor. So we can talk about my free will for example. But for that free will and the choices I make to be mine, they must logically be dependent on my state at that time. If they are not determined by my state, then those choices are in no way mine. Furthermore in order to be free choices, they must not be primarily determined by external influences such as threats or misinformation.

This is not a tautology. It's a necessary requirement if any choices are to be ascribed to an agent that the state of the agent must determine the choice. Why this is in any way controversial really eludes me. So are our choices pre-determined? In the sense we are talking about, yes. Is that a problem philosophically? Sure, but philosophy and the real world have no obligation to be convenient to our expectations or desires.

k4002• 9 years ago

'free will' is unfortunate name. If randomness causes something instead of deterministic prosess, how is that free will? 'random choise loophole' does not sound so grand.

shellbackground• 9 years ago

I've been thinking on that topic for about a year now to justify my own behavior and actions.

Free will implies, that there should be genuine "actor", that's behind all one's choices and actions. If you will try to dig down and find your own actor, you soon will discover, that all choices produced by that actor are actually based on your previous experience, so all actions are actually predefined by your own experience.

The presence of genuine actor essentially leads to question "who is behind actor's actions?", which inevitably leads to infinite regress that can't be resolved.

I like to see how modern science there comes close to various teachings like Buddhism, moving from external world (non-self) to internal (self).

eternalban2• 9 years ago

[A]ll actions are actually predefined by your own experience.

Your past actions and deterministic plumbings of material body constrain the future possibilities but they do not remove the possibility of further choice, in the general case.

Rumi's father -- both father and son were Muslim mystics -- tells an amusing tale of how the question of predeterminism and free-will was settled in their day in his spiritual diary:

   In Khwarazm the great majority [are] Mu'tazilis. No one there ever
   claims to have had a 'vision of God'. The people think of themselves
   as freely acting makers of their own lives. If they meet up with
   Jabriya, one who believes everything is predestined, they cuff him
   about the head and say "It's God's plan that I do this."

   Khwarazm is tough on the predestined people. Their houses are plundered
   and as they walk about in poverty they are clubbed and beaten. Mu'tazilis,
   on the other hand, enjoy the wealth they seize from the Jabriyas, these
   lazy ones who never initiate anything. "That is God's business" they say.

   Theirs, evidently, is to suffer in both worlds.

As for the faculty of 'Choice' in the Human being, he wrote:

   "By the One who sets the Earth with rivers pouring through in mist
    below mountains, and two oceans with a strip of land in between" (27.61),
    we move the elements into various shapes without their consent, but
    Human beings, unlike water and trees, have a choice. They are given dignity,
    discernment, and the evolutionary wisdom that can move from death to new
    life, again to die and be restored on another level of Existence.

    You have many choices about the ways you live and work and change and survive.
    Say you fall into an ocean. You may give up and sink, or you may try to
    swim to the shore.

    Salvation is your decision.

OscarCunningham• 9 years ago

The title is a typical example of "transposing the conditional". What they mean is P(observations|local realism) < 10^-9, but what they wrote is P(local realism|observations) < 10^-9.

Science publications should know better!

atemerev5• 9 years ago

Interestingly enough, if you are to design a really big and scalable MMO game (with topological metrics, as opposed to a location graph), you will probably introduce similar hacks to overcome limitations. There will be "speed of light" and "time dilation" analogues as the result of limited computing power. You'll get rid of "realism" early enough, as the result of limited memory — why keep the word stored, when you can procedurally generate it on demand? And it is natural to think in interaction probabilities — implementing a random number source and using it consistently is much cheaper than tracking all collisions on micro scale.

These results look somewhat different in modern MMO games (e.g. EVE Online), as computing nodes are arranged within a network (a large graph). But imagine a "computational fabric", with atom-scale nodes arranged topologically (a space made of computronium). What kind of effects would be natural to implement there, and what are the hacks to use?

My hypothesis is that what you'll get in such arrangement, if you are to design your simulation efficiently, is quantum mechanics, more or less.

mikhailfranco• 9 years ago

Is there any published work along these lines?

atemerev5• 9 years ago

There are some papers on relativistic effects appearing naturally in connected lattices with interacting nodes, but the rest are my speculations (or I wasn't looking hard enough). I am currently looking for a PhD position in physics and/or network science to explore this line of thought.

lou1306• 9 years ago

But these "hacks" are provably needed only in the reality we live in. Let's say we are in a simulation and the finite speed of light is just a hack... Then you are implying that, outside of the simulation, speed of light is not finite: otherwise limiting it would not be a hack, but a realistic simulation. Now, all our knowledge in physics and information theory are based on the finite speed of light.

Therefore we should prove that computing power is limited even in a world where light has infinite speed (and I'm not sure it is), before deciding what a "simulation hack" is. Right now I only see a lot of "We are in a simulation, and the outside world is just like this one, but different"

atemerev5• 9 years ago

Perhaps (and why not?) — I am not trying to answer big cosmological questions here, or even to put any evidence for or against the simulation hypothesis. I only want to figure out whether it is possible to obtain quantum mechanics (or something similar) as a limit of some computational constraints in some hypothetical environment.

BoiledCabbage• 9 years ago

Let's say we are in a simulation and the finite speed of light is just a hack... Then you are implying that, outside of the simulation, speed of light is not finite: otherwise limiting it would not be a hack, but a realistic simulation

Not necessarily. I don't think op is necessarily arguing we're in a simulation. It might simply be that we're looking at things wrong.

We fundamentally believe that computation rests upon physics. What if that's backwards, what if physics rests upon computation - and computation is the most fundamental element of the universe. While it may sound absurd at first, it's no more or less absurd than "natural laws make everything go". Somewhere we have to assert there is a bottom and it is allowed to exist - and it's rules just work. We currently just set that to physics.

But if it were computation instead there could be a law of computation that you can't compute and an "infinite" universe and infinite instant communication due to the multiplicative factor of communicating. And this results in a "speed of information"/light.

Who knows, maybe Brooks Law about software really is a fundamental law of the universe. ;)

gus_massa• 9 years ago

The problem with your hypothesis is that quantum mechanics make the calculation more difficult/costly, not more efficient.

The easiest way to show this property are quantum computers. If you have a quantum computer with n qbits, you have 2^n combinations, so to simulate a quantum computer in a classical computer you need O(2^n) time. So it's very inefficient.

[On the other hand, for a small set of lucky problems, if you construct a quantum computer you can solve in polynomial time some problems that require exponential time in classical computers. (But remember that not every problem get this speedup, and it's very difficult to construct a general quantum computer with more than a few qbits.)]

pizza• 9 years ago

Is there anything related to the idea that even though physics limits information to at most the speed of light, you can still guarantee that "two events c*t distance apart both follow the laws of physics" in less than t time (0, really), so "the laws of physics affects things everywhere" is in some sense superliminal?

Even if the inputs really only rely upon states which are together unknowable before t (which includes the knowledge that two events occur in the first place..) - in this sense, no information is transferred, I suppose.

Probability quantum world obeys local realism is less than one in a billion

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