Physicists found a new quantum paradox that casts doubt on a pillar of reality

https://www.sciencealert.com/a-new-quantum-paradox-throws-the-foundations-of-observed-reality-into-question

by walterbell • 6 years ago

186 152 6 years ago

sciencealert.com

4ad• 6 years ago

Actual paper: https://arxiv.org/abs/1907.05607

mellosouls• 6 years ago

Rendered for web:

https://www.arxiv-vanity.com/papers/1907.05607/

jonahbenton4• 6 years ago

I don't know to what degree the metaphor is accurate but as a non-physicist I find thinking about quantum mechanical experiments easier if I think of them as running code on a vast decentralized computing infrastructure.

The concept of "measurement" is just executing code on one node that populates local registers- "creating" not "measuring". Yes- by running code you are pulling on a reality fabric that we still know almost nothing about. But I find it easier to visualize than relying on my colloquial/non-QM intuition in words like "measuring"- which implies something like a single centralized reality database, not a creative decentralized infrastructure. QM experiments seem to create things, not measure them.

Would love to learn metaphors of folks in the space.

thechao• 6 years ago

I’m just now teaching myself QM (20 years after school). I can tell you that in QM, seemingly innocuous phrases like “locality” have highly unintuitive, nonstandard meanings. I’m just now getting a glimpse at how amazingly fucking awful pop-sci QM articles are.

If you’re interested in QM, read “The Theoretical Minimum”; the second book gets into QM. There are video lectures of the same material that complement the series, we’ll.

jonahbenton4• 6 years ago

Appreciate the reference, cheers.

ssivark• 6 years ago

This perspective is interesting and potentially valuable, but it must be emphasized that quantum mechanics has linear evolution and hence “no cloning”. That means, when the registers are quantum objects, there is no such thing as copying a value into a register — there is only one version of each object, and you’re always manipulating it directly. That’s one aspect which leads to very difficult questions when thinking of “creating” at local nodes — because it’s the same object/copy that’s accessed at different nodes by various observers — so how can we ensure consistency of observations?

jonahbenton4• 6 years ago

Thanks, understood- the metaphor wasn't intended to imply the registers themselves were quantum objects, more that the process of observation / measurement of some quantum phenomenon- metaphorically- could be a creative/derivative process. That metaphor/mental model would conflict, to some degree, with the centralized/cache coherency metaphor you cite, that aligns more with colloquial understanding of "measure."

Whether one is more appropriate than another I don't know. But I find the decentralized model produces more interesting naive questions for me to puzzle over. Of course those questions likely lead in a completely wrong direction. Cheers, thanks for engagement.

ahelwer3• 6 years ago

An alternative way to view measurement is that you're just entangling yourself with the quantum system, and are as much in superposition as the system itself.

jonahbenton4• 6 years ago

Thanks, yeah. With this view I run into trouble understanding what constitutes "entry into" and "exit from" superposition.

menzoic• 6 years ago

Veritasium has a great video that explains the concept of parallel worlds vs wave collapse in a single world https://youtu.be/kTXTPe3wahc

amelius2• 6 years ago

Nice video. Now I wonder if God uses structurally shared data structures in his implementation of the world. I also wonder if there can be a kind of continuous description of branching that is more amenable to calculus than the discrete tree-like branching.

c1ccccc14• 6 years ago

I think MWI actually predicts continuous branching. The prescription for MWI is just to run the Schrodinger equation forwards in time. So the branching would look like one blob of probability gradually becoming bimodal, and then splitting into two components with less and less overlap. (There might also be 3-or-more-way branches, not just binary splits.)

sidcool• 6 years ago

Great video. I have a question though. Is there a non zero probability that any two versions of the same person in many worlds could interact with each other?

bondarchuk2• 6 years ago

The original Wigner's friend paradox: https://en.wikipedia.org/wiki/Wigner%27s_friend

The paradox seems to rest on magical thinking about consciousness, and if one simply accepts that a conscious observer can be in a superposition like any other piece of matter, the paradox is resolved.

And, from the article:

For Wigner, this was an absurd conclusion. Instead, he believed that once the consciousness of an observer becomes involved, the entanglement would “collapse” to make the friend’s observation definite.

But what if Wigner was wrong?

Well, obviously Wigner is wrong, sorry for being flippant.

In this paper (preprint here: https://arxiv.org/pdf/1907.05607.pdf), the magical thinking about consciousness seems to be transmuted into "“Absoluteness of Observed Events” (i.e. that every observed event exists absolutely, not relatively)". The authors (it appears to me) mean by this that if an observer performs an experiment, while this observer is himself in a superposition, we have to regard the outcome of the experiment as absolute (i.e. not in a superposition) because it was made by a (conscious) observer.

In my opinion, both "Absoluteness of Observed Events", and the equivalent from the layman's article, "When someone observes an event happening, it really happened", is a disingenuous and confusing way of talking about observers who are in a superposition. We have crossed over from "quantum mechanics is weird" to "these superficially intuitive but clearly false assumptions about quantum mechanics are weird".

(by the way, I read the article here: https://theconversation.com/a-new-quantum-paradox-throws-the... because that site doesn't think I'm a robot and then redirects me to the homepage after filling out the captcha)

TheOtherHobbes• 6 years ago

You might consider reading the original paper. Because the experiment doesn't rely on conscious observers at all. (Unless you think photons are conscious, which I'm assuming you don't.)

bondarchuk2• 6 years ago

Well, that's the point. The experiment shows that one of three assumptions has to be false. But one of these (AOE) being false is not surprising or concerning at all, when dealing with non-conscious observers (such as photons, indeed). With conscious observers it would be concerning to some (not to me, but to Wigner and presumably the authors), because of the supposition that there's something special about conscious observers (i.e., magical thinking, IMHO). So what has this paper really shown? Absoluteness of Observed Events is false when the observers are photons, which (my layman's assumption) should surprise exactly nobody. And then they propose to repeat the experiment with an AI in a quantum computer as the observer. Lol.

scythmic_waves• 6 years ago

(Unless you think photons are conscious, which I'm assuming you don't.)

Well, panpsychism is a thing and is actually having a bit of a renaissance.

devit• 6 years ago

It indeed seems so, i.e. that there is no paradox in the many-worlds and possibly other interpretations (as a non-expert in quantum physics).

How did they manage to get the paper accepted in the (supposedly selective) Nature Physics journal though? Is there something we are missing?

MrPatan• 6 years ago

You're not missing anything. Maybe just the last step of lowering your opinion of the journal.

GoblinSlayer5• 6 years ago

Such experiments criticize copenhagen interpretation, so as long as CI is moving, criticism is solid.

squibbles• 6 years ago

Translating the thought experiment to an actual physical experiment is something worth appreciating.

A possible lack of absoluteness of observed events has implications for what observations may or may not be reconcilable using existing scientific methods.

canjobear3• 6 years ago

if one simply accepts that a conscious observer can be in a superposition like any other piece of matter, the paradox is resolved.

It’s not so simple. Suppose you’re in a box and observe a quantum experiment, and then I open the box and observe you. Then before I open the box you’re in a superposed state |x> + |y>, corresponding to the two possible outcomes x and y. Fine, no problem so far. But what is your own subjective experience? You, subjectively, inside the box, will only ever observe yourself to be in |x> or |y>, never |x> + |y>. Even if from the outside your brain can be said to be in a superposed state, your experience of the world is not superposed.

oopsiforgot7• 6 years ago

If you embrace many worlds all these issues go away.

ahelwer3• 6 years ago

Many-worlds interpretation takes care of this. Anyway, how do you know your experience of the world cannot be superposed? Have you ever been in superposition? We make up stories to maintain consistent histories all the time.

Tuna-Fish2• 6 years ago

Either you believe in collapse, so there are two of you, who each observed different things, and one of those will at some point cease to exist, or you embrace the Everett interpretation, and so there are two of you who each observe different things and go on to live their separate lives.

phkahler2• 6 years ago

I always thought Schoedingers cat should have been a person instead, just to point out this very problem.

Ericson2314• 6 years ago

Multiple words <----> modal logic; possibility mode <----> monad.

Your friend is in the monad, now you are too. No big deal.

tbabb• 6 years ago

The |y> superposition of you has one experience, and the |x> superposition of you has a different experience. The |y> version has no information about the |x> experience, and vice versa, because those two states are orthogonal in Hilbert space. This is essentially the prediction that results in the Everett many worlds interpretation.

If you somehow had an experience of "both outcomes simultaneously", that would violate the quantum mechanical prediction that there is no mutual information between the two superpositions. There are two brain states, an x state and a y state, and they know nothing about each other.

To each brain state (with the limited information available to it) it would appear that something "definite" had happened, even though in the global picture, a superposition still exists.

brundolf• 6 years ago

It's interesting the way some scientists have been biased into this kind of magical thinking, probably because the integrity of conscious observation is so central to their practice/worldview. Nobody is free from the pressure of cognitive dissonance.

kmm2• 6 years ago

We're veering away from physics here, but isn't consciousness actually quite "magical". It's beyond remarkable to me that stimulating nervous tissue, composed of quite mundane things like protons and electrons, yields a subjective experience. I know many people reject the hard problem of consciousness, but to those who don't, the implications of thought experiments like Wigner's friend, like superpositions or entanglement of subjective experiences, are truly paradoxical. You are calling certain viewpoints obviously wrong or false because you adhere to certain philosophical viewpoints. There's nothing wrong with that, and they're all justifiable, but none of them are complete consensus among philosophers.

Coming back to physics, there's an assumption you and other commenters are silently making, which is that quantum mechanics is even applicable to macroscopic objects like humans. The largest objects which have been shown to act wave-like are a few thousand atoms large. While it's indisputable that at the lowest level the universe is fundamentally quantum mechanical, it's a little brazen to extrapolate that over more than 20 orders of magnitude. As a physicist myself, I'll believe it when I see it, and I'm looking forward to getting results from proposed experiments like FELIX and its successors.

https://en.wikipedia.org/wiki/Free-orbit_experiment_with_las...

keymone7• 6 years ago

Pretty sure I’m dunnig-krugering this, but is consciousness really that magical?

Nervous system evolved from ability to respond to external stimuli to centralized control of various processes to evaluation of risks/benefits of actions and finally to predictive modeling of external processes. Rudimentary concept of “self” and understanding of surrounding environment exists in various animals, so why is it strange that an animal with most complex brain has the most sophisticated concept of “self” and it’s placement in the ultimate surrounding environment - the universe?

GoblinSlayer5• 6 years ago

Coming back to physics, there's an assumption you and other commenters are silently making, which is that quantum mechanics is even applicable to macroscopic objects like humans.

It follows from schrodinger equation, it provides no exception for macroscopic objects. You can say quantum effects indeed happen at the lowest level, and macroscopic behavior follows what happens at the lowest level. It's a question of reducibility.

The largest objects which have been shown to act wave-like are a few thousand atoms large.

Large objects have wave-like behavior, e.g. you can't determine their size with femtometer resolution, they don't suffer from ultraviolet catastrophe and have macroscopic quantum effects like superconductivity.

freeexpression• 6 years ago

Article is hard to read since someone butchered it for ideological reasons:

https://en.wikipedia.org/w/index.php?title=Wigner%27s_friend...

francasso• 6 years ago

Sorry but there is nothing obvious about any of it. It all boils down to the measurement problem and entanglement. While I don't like psi-epistemic interpretations either, it's not like there is anything clearly inconsistent with them, or like psi-ontic and psi-complete interpretations make more sense or are devoid of issues. They all have problems and make assumptions that are hard to swallow, and if you believe any of them and start ridiculing others you are pretty much picking sides with no good evidence. So while you might have already pledged your faith, other people with probably as much understanding of the issues or more haven't.

Thorentis2• 6 years ago

From the Wikipedia:

"From the point of view of the friend, the measurement result was determined long before Wigner had asked about it, and the state of the physical system has already collapsed. When now exactly did the collapse occur? Was it when the friend had finished their measurement, or when the information of its result entered Wigner's consciousness?"

This to me, shows just how hand-wavy the whole superposition/quantum collapse stuff really is. I have to say I side with Einstein with his view that everything is already in one state or the other. We don't cause the system to choose a state when we measure it. We simply discover the state it was already in. It is one thing to assign a probability to which state we will find it in. It is quite another to create an entire theory around quantum measurement.

There is nothing mysterious about this paradox. The friend performs the measurement ans discovers the state of the particle/system. Wiger doesn't know about it, but that doesn't mean it's not in that state, he just isn't aware of it yet. The fact this is a paradox just seems like silly mind games.

incognition• 6 years ago

QM is not hand wavy and gives precise results for many practical problems. Your theory is wrong as per one of the simplest quantum experiment - the single electron double slit problem.

jlokier5• 6 years ago

how hand-wavy the whole superposition/quantum collapse stuff really is

Superposition isn't particularly hand-wavy. It's the basis of various technologies, and of precise numerical models we use to build technologies.

Quantum collapse is hand-wavy, and that's because it is not well understood. It might not exist (in which case superposition of mind-states is a thing), or it might exist (in which case mind-states may be definite). Quantum mechanics that we can calculate doesn't give an answer either way, even though it gives lots of other answers very precisely and correctly.

Wiger doesn't know about it, [...] just seems like silly mind games.

When only applied to a single measurement it does seem like silly mind games, you're not wrong.

The motivation for those thought experiments was to try to reason back from the consequences found from more complex behaviour observed with multiple measurements, back to a simple system with only one measurement.

But when you have many measurements with entanglement, of which there are numerous physical experiements and confirmations by now, the idea that there are just multiple, correlated probabilistic states ready to be observed that we're not yet aware of is not consistent with physically measured behaviours. Those measurements aren't hand-waving, they are hard data, even though my explanation here is hand-waving and doesn't go into it.

I side with Einstein with his view that everything is already in one state or the other

Numerous experimental results now contradict this view, or require other strange things to be true about the world (for example superdeterminism was mentioned in the article).

xdarnold• 6 years ago

Your position is more or less defensible, but you will have to accept some compromises to your description of the universe that most physicists find untenable.

Actually, it is Bell's Theorem / Inequality and related experiments that are relevant here. https://en.wikipedia.org/wiki/Bell%27s_theorem

These experiments were really the nail in the coffin for Einstein's position for most physicists. Having to admit non-local hidden variables is a pretty distasteful result.

lisper7• 6 years ago

if the "friend" is a human-level artificial intelligence running in a massive quantum computer.

Well, there's your problem right there. No AI can run on a quantum computer. Intelligence is inherently a classical phenomenon because it requires copying information, and quantum states cannot be copied, only classical states can be copied.

The classical world "emerges" from the quantum world when you take a quantum system and choose to consider only a subset of its degrees of freedom. When you do that, what results is a "mixed state" which behaves classically. This is not a reflection of any (meta)physical reality, it's just a consequence of your point of view. But here's the thing: you yourself are a subset of a quantum system, and so you yourself have no choice but to take this point of view. You cannot ever take the "god's-eye view" and "see" the whole system. That is fundamentally impossible because "seeing" requires copying information, quantum states can't be copied yada yada yada. Even God cannot "see" the god's eye view!

Zenst• 6 years ago

quantum states cannot be copied

Wouldn't quantum entanglement enable a comparable ability?

boomboomsubban• 6 years ago

I may be wrong, but I'm fairly sure you need to entangle the particles before they become a quantum state.

gjhan• 6 years ago

Entanglement means that there are systems with highly (more-than-classically) correlated state - that the combined state is something that can’t be represented by considering the systems independently - not that the states are the same. The no-cloning theorem prohibits a process that takes the state of a system and replicates it on another system. It’s certainly possible to have or to generate entangled sets of systems that have identical separable state, but not to copy an arbitrary state.

amelius2• 6 years ago

Intelligence is inherently a classical phenomenon because it requires copying information, and quantum states cannot be copied, only classical states can be copied.

Ok, so make classical pointers to quantum states and copy the pointers instead of the quantum states :)

adrianN• 6 years ago

I'm not convinced that intelligence requires copying information in the way that the no-cloning theorem forbids. Approximate cloning is not forbidden for example.

lisper7• 6 years ago

The problem is not copying internal states, the problem is I/O. A given instance of a quantum computation can only be queried once before it decoheres and goes "poof" because the querying process itself decoheres the system. So a quantum computer can never pass the Turing test because it cannot even participate in the Turing test without destroying itself.

c1ccccc14• 6 years ago

A good point, but quantum computation can do anything that reversible classical computation can. If you do your entire computation while keeping all the qubits in the {|0>, |1>} basis, then performing a CNOT onto a qubit initialized to |0> will work as a classical copy. (It will fail to truly copy the quantum state, but that's fine.) You just need a large enough supply of qubits initialized to |0> for all the copies you plan to do.

lisper7• 6 years ago

quantum computation can do anything that reversible classical computation can

Well, yeah, but that "reversible" hedge is quite significant. Reversible means you have to retain all of your intermediate states, and it is far from clear that you could build a reversible AI that would run for more than a few milliseconds before consuming all of the available resources in its light cone.

You just need a large enough supply of qubits initialized to |0> for all the copies you plan to do.

Yes, and that produces exactly the same problem: it is far from clear that there are enough qbits in the universe to build a quantum AI this way.

You also have a more fundamental problem, which is that neither quantum computers nor reversible classical computers can do I/O, so how are you going to demonstrate that this thing is in fact an AI? It can't even participate in a Turing test, let alone pass one.

nicoffeine• 6 years ago

Intelligence is inherently a classical phenomenon because it requires copying information, and quantum states cannot be copied, only classical states can be copied

I don't agree with this. The recent research in quantum biology[1] suggests that biology at least can read from quantum states -- birds may use it to navigate, our sense of smell may be a quantum interaction, and plants appear to use quantum properties to achieve almost perfect efficiency for photosynthesis. The human eye may be able to detect a single photon.[2] General quantum activity also seems possible, since lithium-6 and lithium-7 appear to produce different pharmacological results despite being only one neutron apart[3].

I also fall into the camp of supporting the Orch-OR theory of consciousness[4], which claims that our interpretation of a classical system for brains is incorrect, and that neurons have internal structures called microtubules which can maintain quantum states. Microtubules have been known to exist for decades, but it was thought that their purpose was purely structural. Anirban Bandyopadhyay demonstrated[5] that these structures appear capable of storing information at the quantum level.

Orch-OR would explain how anesthesia works, and how biology with classically simple brains are capable of extremely complex lifecycles and self-organization. I don't know enough about neuroscience to have any real insight on its validity, but there seems to be a huge disconnect between where we think we are with AI and the results so far. I have watched a butterfly navigate through a chain link fence on a windy day, and that kind of computation doesn't seem possible in a classical model, from a space or an energy perspective.

Even God cannot "see" the god's eye view!

The strongest argument I see for a concept of God is the fact that the universe doesn't break. Quantum brains provide some interesting possibilities for the privacy of thought co-existing with some sort of perfect originator. In any case, given the amount of computation it would take just to model the biology of one person and the underlying quantum states, I am almost positive that we are not in a simulation.

[1] https://royalsocietypublishing.org/doi/10.1098/rspa.2018.067...

[2] https://www.nature.com/news/people-can-sense-single-photons-...

[3] https://www.quantamagazine.org/a-new-spin-on-the-quantum-bra...

[4] https://en.wikipedia.org/wiki/Orchestrated_objective_reducti...

[5] https://aip.scitation.org/doi/abs/10.1063/1.4793995

robocat• 6 years ago

No AI can run on a quantum computer

Each quantum calculation can be collapsed to a state, and that state could then be fed to the next quantum calculation etc. etc.

Would you call a series of such quantum calculations a quantum computer, or not?

lisper7• 6 years ago

For the purposes of being a stand-in for Wigner's friend, no, obviously not. The whole point of the thought experiment is that the "friend" observer exists in a superposition.

narag2• 6 years ago

So in your opinion, does this thought experiment can be translated to a "real" experiment now or in a not-so-distant future, like in our lifetimes?

lisper7• 6 years ago

That depends on what you mean. If you mean using a simple system (like a single photon) as a stand-in for Wigner's friend, that has already been done. That's what the OP was about. If you mean using a complex entity like an actual human or an AI that can pass a Turing test, I'll give long odds against.

henearkr2• 6 years ago

The part that seems the most dubious to me is the "choice":

2. It is possible to make free choices, or at least, statistically random choices.

I don't see what would be really compelling in that.

If it's false it would just mean that our actions are all kind of mechanistically decided by other events, and that does not shock me.

Other point:

1. When someone observes an event happening, it really happened.

What if it really happened in the reality of the observer (and maybe not in other realities)? What is meant by "reality"? Some insight is to be gained by precising what we call the reality, in relation to the corpus of all the observations in what we believe is our universe.

coliveira• 6 years ago

The main problem of quantum interpretation is the supposed, artificial, distinction between observer and observed system. In a quantum world this distinction is not possible, every event capable of "observing" a system is itself part of the system, modifying it. That's why such interpretations (postulating this separation) give all kinds of strange paradoxes that are impossible to solve. In the quantum world, there is no such thing as an observer, it is just all part of the system.

Consider for example the system composed of a pool table. In classical physics we can assume we can always measure the position and momentum of all balls in the table. But what would happen if measurement was not possible without big changes in position and velocity? Suddenly the whole notion of "observation" would lose its meaning, and the only way to describe the pool table is as a probabilistic mesh of balls moving around in uncertain directions.

henearkr2• 6 years ago

Yes, I think you put your finger on it. As the observer is part of the system, his "reality" is as much superposed, entangled, etc., as the quantum events that compose it (himself and his observation too).

That would give credit to the multiverse interpretation of quantum mechanics then.

Maybe the observation process of a quantum phenomenon by a human observer is akin to the orthogonalization of a matrix:

as the observer becomes entangled with the observed particle, each possible observer-eigenstate (i.e. any observer in "his reality") ends up observing an eigenstate of the observed quantum phenomenon, instead of a dirty superposition.

To call it "orthogonalization of the observer-observed system" would be more descriptive than "wave-collapse", but the main difference is that the orthogonalization treats in parallel all possible outcomes, each linked to a different state (outcome) of the observer too, whereas the "collapse" view insists on the fact that the observed eigenstate is unique. And moreover, at least in mathematics, there are conditions for the orthogonalization to be possible at all, so that should be interesting.

cmehdy• 6 years ago

Even in the classical world we measure that pool table by interacting with it. If I stand next to the table and see it, it's because light hit it and then hit my eyes - but I've absorbed whatever light might have gone on its course through me as an observer and maybe hit the table again eventually (attenuated), and I also happen to emit some light myself. My body being present and warm, my breathing of air in the room, etc.. creates convection currents of air, which affect the fluid mechanics of the same volume of air that the balls are in.

My brain can't really perceive much of any of that and does a lot of filtering of information, and we've designed the pool table to be something we grasp and play with easily so the relative inertia of the balls will mostly overcome all the more minor terms to take into account wrt fluid mechanics, but all of that is classical physics already. "Closed systems" might only exist conceptually.

tsimionescu8• 6 years ago

Well, the problem is that the reality we observe daily is not at all like quantum reality. We know exactly where our instruments are, even though we know that they are completely stationary. There is no particle/wave duality to tennis balls.

This is the origin of the problem of observation - the predictions of quantum mechanics break down at some point, and we have no idea why. In particular, this happens very clearly when our measurement instruments directly interact with a quantum system, so we call this 'the measurement problem'.

Of course, we can postulate that in fact, despite all of our observations, both subjective and objective, the classical world also behaves quantically but we just can't notice it happening (e.g. the Many Worlds interpretation does this).

We can also say that the quantum world does NOT in fact behave that way, but that the universe is perfectly deterministic and just set up in such a way that we can never observe events that contradict this vision of the universe (superdeterminism claims this - that for example you will always happen to choose the right dial on a measurement apparatus to observe entanglement, but that there is no fundamental reason why that should happen - it could theoretically happen otherwise, but in this universe, ever since the big bang, it has been decided that at some point you will set that dial in the particular way that will make you observe the entanglement result).

There are other theories that postulate that quantum mechanics is in fact deterministic, but very hard to predict, but there are non-local effects (deBroglie-Bohm pilot wave theory is such an example).

We can also ignore the whole hope of trying to understand all this, and simply use the math if and when we need it to predict particle phenomena.

tsimionescu8• 6 years ago

You may say that it's not surprising, but in fact all statistical-style reasoning relies on it. If the universe is superdeterministic, than no kind of statistical reasoning makes any sense, since everything is already set in stone, there is no probability to any event, it has either happened already or will never happen. Since there is no freedom or even randomness, there are no statistically independent events or measurements.

elwell6• 6 years ago

no kind of statistical reasoning makes any sense

Probabilities are useful when you don't have perfect knowledge. But yes, they are an illusion. In truth, every event has a 100% chance of happening. And things that didn't happen aren't real events, they just seemed to be possible, but we were wrong.

08-152• 6 years ago

Take a look at these three statements [...] they cannot all be true

Okay, so we have to kill one. The easiest one to kill is

It is possible to make free choices.

In other words, quantum mechanics is incompatible with free will. This is clearly shocking to any physicist who believes in Free Will (as defined by philosophers thousands of years ago). But hasn't Free Will been recognized as nonsense for at least two centuries by now?

katmannthree• 6 years ago

But hasn't Free Will been recognized as nonsense for at least two centuries by now?

Among some, sure and it's not just physicists [1].

Acknowledging that the concept we've called free will is not likely to be real has some troubling implications regarding how we've structured our society which is likely one of the reasons it's not talked about very often.

[1] https://www.youtube.com/watch?v=ihhVe8dKNSA

elwell6• 6 years ago

The members of a system can 'experience' free will from their perspective, but it's a still a deterministic line of causation; their free will is part of the determinism.

mensetmanusman2• 6 years ago

We, the figures of your imaginative simulation, have free will, but have decided that you do not.

tsimionescu8• 6 years ago

In fact, all statistical experiments, from clinical trials to observations of Bell's Inequality depend on the idea that there exists either free will or true randomness (and that we can base our decisions on that source of randomness). If neither exist, then there is no such thing as statistically independent events, and no way to make statistical observations (since that would imply that your choice of what to measure would always be correlated with the result of your measurement).

08-152• 6 years ago

either free will or true randomness

Isn't unpredictability enough?

thayne• 6 years ago

How is this a new paradox? Isn't this paradox the whole reason for different interpretations of Quantum Mechanics?

gliese1337• 6 years ago

I'm pretty sure "many-worlds is false" is not, in fact, a "pillar of reality".

Zenbit_UX3• 6 years ago

Whenever I hear about weird shit from the realm of quantum physics (this theory, double-slit, etc..) I can't help but think:

Why would I hardcode values for imperceptible objects, that would take an enormous about of ram and cpu time to constantly update values in the off chance it's needed.

Much more efficient to optimize for what the _player_ can see at their perspective. Oh and I should probably code in some error handling in the fluke event one of these particles is detected, I'll just calculate their position retroactively, the user will never be able to tell and we can host way more players due to the reduced memory.

It would seem to me that god is a junior dev and no one reviewed his pull requests.

rantwasp3• 6 years ago

disagree on the junior dev part and on the god part.

what you’re describing is called “simulation theory” and it has been proposed and discussed at length

i think lazy evaluation makes sense in that context. i also think that having a few basic rules and after that applying them consistently across your simulation space make sense. if your basic space unit of reality is way smaller than the sims in it can perceive and measure they’re gonna start making stuff up

Zenbit_UX3• 6 years ago

disagree on the junior dev part and on the god part.

Good lord, some people here are definitely on the spectrum. FYI that was an attempt at humor. In case you want to mimic human social behavior in the future: you don't _disagree_ with a joke, you either find it funny or you don't.

what you’re describing is called “simulation theory” and it has been proposed and discussed at length

I'm aware of the theory, just like everyone else whose seen the matrix or read Elon's Twitter feed. For the record, I was merely illustrating a point; both our universe and the code we write share certain optimizations that would seem to be too coincidental to be random.

sgillen• 6 years ago

One problem with this view is that “unobserved” particles still take up a large (possibly larger?) amount of computation. Rather than being in one position, it acts like a wave, being a little bit in every possible allowable position. These probability waves also interact with each other (which is what the double slit experiment demonstrates).

That being said if it was demonstrated that un collapsed wave functions are somehow more efficient to calculate that would definitely give credence to the simulation hypothesis.

Zenbit_UX3• 6 years ago

That being said if it was demonstrated that un collapsed wave functions are somehow more efficient to calculate that would definitely give credence to the simulation hypothesis.

Well said. I can certainly imagine a few functions that may prove to be more efficient at generating waves than fixed known positions + velocity for every subatomic particle in the universe.

Here's the part that really takes us off the rails, if we assume for a minute that we are in a simulation and that the parent world has godlike resources compared to our own and they likely have similar hardware concepts (ram, cpu, gpus, maybe even ASICS) then what functions are more efficient would depend on which hardware they have less of.

If ram is plentiful why not have fixed known values for every particle? Store it in memory and let the gpu detect collisions.

If gpus are plentiful (my guess) and we're bound by ram limitations, best to only store positions of things that are visible and clear the rest out of ram for more important calculations.

Imagine how inefficient it would be to render and simulate black holes colliding on the other side of the universe if the players will never even notice. Just queue up the function and run it on off-peak hours. Save the extra server resources for other simulations running in parallel.

If I'm right - a big if - we're likely an anomaly or early prototype among the simulations, one in which the dev team never imagined a race would evolve and progress enough to measure the bounds of their container. If I'm right again on this last point, we're likely being monitored closely to decide if subsequent patches require more resources to simulate completely and avoid player's realizing they're in a simulation or accept it as a remote possibility and move on.

booleandilemma2• 6 years ago

He did it all in 6 days though. That's less than a full sprint.

tourist2d• 6 years ago

It could also be that our universe takes up so little resources on "gods" computer ;)

seventhtiger• 6 years ago

I always wondered about the "computability of the universe" and its compressibility.

If the universe is actually compressible, then object permanence may actually be a trick, like it is in video games. Objects are generated on demand and deleted to save space and processing.

If it's not compressible, which is where I lean, then the full universe must be fully computed every time. No savings can be made, and any delay in computing an object might propagate and cause recalculation cascades for other objects. I lean this way because from my layman's understanding, quantum mechanics act similarly to random seeds, which increases entropy by a lot.

If it's not compressible, then the smallest computer able to simulated the universe is at least as big as the universe itself.

Ataraxy• 6 years ago

If you had infinite memory and energy such optimizations wouldn't be needed to begin with.

jlokier5• 6 years ago

That model of efficiency (RAM and CPU time) is based on classical computation.

When your underlying model of computation is full quantum computation, it's simpler to just run everything at once. It takes no energy if you run everything without picking out a scenario (but in a kind of "tree falling in a forest" way), and more energy if you select out specific scenarios to look what happened (I/O is expensive). Counter-intuitively, the computation part of quantum systems is free in ways that we consider classical computers expensive to run. It's reversible and doesn't consume any energy.

That may seem like it's avoiding the point, after all what does it take to run the "underlying model of computation".

But what I'm trying to say is that "quantum all the way down" (see also turtles) is as much a valid model as "mechanical computation all the way down", which your picture relies on. Neither of them is more fundamental.

It may seem like quantum-all-the-way-down is a bit artificial, because we can in principle run quantum simulations on classical computers, which seem simpler. But it turns out we can't. There is a fundamental intractability barrier for simulations above an arbitrary tiny size, which means we can only simulate interesting quantum systems using other quantum systems. It really is quantum-all-the-way-down.

If god came up with the quantum-all-the-way-down version, I'd say that's pretty clever, because it's way more efficient than anything you would implement, with your old-school classical RAM and classical CPU.

rantwasp3• 6 years ago

this is not convincing at all. we pretend that we can have perfectly isolated quantum systems (a particle, a few particles) and we can reason about and extrapolate the findings. we cannot have isolated particles - they can be regarded as isolated for experimental purposes but the reality is that probably the whole universe is a massive wave function that encompasses everything and we can approximate in some really special cases (ie system above).

we also pretend that consciousness is something special and altering the state a somewhat complicated wetware had consequences on “reality”. it doesn’t.

the measurement problem is an extremely good example of how we think. a measurement does not make sense to a cow. it’s abstract. we made it up. we have conventions that help make it useful, but those conventions break down when our senses (or things we use to amplify out senses) cannot measure what we want to measure.

colordrops• 6 years ago

Based on my very limited understanding it seems that anything that interacts with a system can be treated as an "observer", and thus a chain of observations can occur as one particle interacts with the next, enlarging the system that is in superposition for the next observer.

Do physicists axiomatically treat a "conscious observer" as an atomic unit? It seems the case based on neurological and psychological research that the mind is actually not a single unit but many units working together, and the sense of a singular self is an illusion, which would correlate with the fact that we are made up of a conglomeration of atoms and systems made of these atoms.

When we say that a person is observing a quantum system, could this actually be a cascade of observations of various parts of the mind rather than a singular event, since the mind is not monolithic?

On a side note (and perhaps unrelated), if different parts of the brain/mind could be in different quantum states, could this be a factor in how the mind operates?

stared• 6 years ago

Have it ever happened o you that you read "a pillar of reality" and it turned out to be more than a clickbait?

Me neither.

(To make it clear: the content is interesting, even if clearly for popular science audience (some statements about physics are false, e.g. "These are all intuitive ideas, and widely believed even by physicists." The title is worth a tabloid.)

booleandilemma2• 6 years ago

I'm still trying to figure out what exactly the discovery is, if there's any.

mensetmanusman2• 6 years ago

Maybe our dream state is how we resolve and wipe quantum paradoxes from our days experience.

hggfkkbcfd• 6 years ago

One this I always notice to be missing from discussions of quantum physics is the effect of scale. Does differences scale have relativistic effects, in a similar manner to differences in internal frames, and if at what do events in one scale frame of reference become simultaneous of an observer in another?

Note: IANAP

Strilanc3• 6 years ago

The article lists three assumptions that one might intuitively think hold. The problematic assumption is this one:

When someone observes an event happening, it really happened.

Given the experiment from the paper, I would rephrase this assumption as "it's not possible to rewind things". But obviously inside a computer simulation made up of operations that are all individually reversible, it's trivial to rewind things.

The experiment sets up a situation where certain information is reversibly recorded, and then the records are unmade by temporarily rewinding. The rewinding is obfuscated by hiding it inside of a measurement that is incompatible with the presence or absence of the record. I guess the authors might disagree about the measurement implying rewinding, but as a bit of evidence I'll note that Scott Aaronson and Yosi Atia have shown that performing the measurement in question over a simulated agent is at least as expensive as rewinding the simulated agent [1]. Whatever is being done, it is doing some seriously expensive screwing around with the agent's state. It's like the experiment has a step where you feed the human through a giant meat processing plant, and for some reason everyone is pretending that's not somehow important.

Basically, the authors are appealing to the intuition that humans are big complicated in-practice-irreversible things, so clearly a record is permanent if it has affected the state of a human. But then they imagine instantiating the human's state inside a ridiculously powerful computer capable of reversibly simulating time advancing and of performing operations that have been engineered specifically to mess with the presence or absence of the record's effects on the human's state. Surprise surprise, the record gets messed with. Then for the actual experiment the big complicated ball of dependent spaghetti that is a human is replaced by a nice simple photon going along one path or another path.

1: https://www.scottaaronson.com/blog/?p=4786

zxcvbn4038• 6 years ago

So, Schrödinger's cat has been alive the whole time and it’s rest of us in a state of superposition because the cat is conscious but can’t observe anything outside the box? Or because we are conscious and the cat conscious, we all retain our states regardless if we are in or out of the box?

BTCOG• 6 years ago

Think of it as LOD generation in a game. As something observes or is near enough to observe, atomic matter is generated on demand. The Matrix; our simulation.

Physicists found a new quantum paradox that casts doubt on a pillar of reality

Related Stories