Quantum Experiment Confirms Causality Is Fuzzy (physicsworld.com) 163
"An experiment has confirmed that quantum mechanics allows events to occur with no definite causal order," reports an article shared by long-time Slashdot readers UpnAtom and jd. Researchers at the University of Queensland in Australia believe this could link Einstein's general theory of relativity to quantum mechanics, according to Physics World:
In classical physics -- and everyday life -- there is a strict causal relationship between consecutive events. If a second event (B) happens after a first event (A), for example, then B cannot affect the outcome of A. This relationship, however, breaks down in quantum mechanics because the temporal spread of a particles's wave function can be greater than the separation in time between A and B. This means that the causal order of A and B cannot be always be distinguished by a quantum particle such as a photon.
In their experiment, Romero, Costa and colleagues created a "quantum switch", in which photons can take two paths. One path involves being subjected to operation A before operation B, while in the other path B occurs before A. The order in which the operations are performed is determined by the initial polarization of the photon as it enters the switch.... The team did the experiment using several different types of operation for A and B and in all cases they found that the measured polarization of the output photons was consistent with their being no definite causal order between when A and B was applied. Indeed, the measurements backed indefinite causal order to a whopping statistical significance of 18 -- well beyond the 5 threshold that is considered a discovery in physics.
Science Magazine applauds the experiments for "obliterating our common sense notion of before and after and, potentially, muddying the concept of causality.
In their experiment, Romero, Costa and colleagues created a "quantum switch", in which photons can take two paths. One path involves being subjected to operation A before operation B, while in the other path B occurs before A. The order in which the operations are performed is determined by the initial polarization of the photon as it enters the switch.... The team did the experiment using several different types of operation for A and B and in all cases they found that the measured polarization of the output photons was consistent with their being no definite causal order between when A and B was applied. Indeed, the measurements backed indefinite causal order to a whopping statistical significance of 18 -- well beyond the 5 threshold that is considered a discovery in physics.
Science Magazine applauds the experiments for "obliterating our common sense notion of before and after and, potentially, muddying the concept of causality.
Really? (Score:2)
Science Magazine applauds the experiments for "obliterating our common sense notion of before and after and, potentially, muddying the concept of causality.
If anything I'd say a big "Duck you" was in order for guaranteeing that no non-physicist will ever understand quantum physics ever again. ... But on the other hand, it might get me out of the dog house for getting drunk and breaking the living room table...
Re:Really? (Score:5, Funny)
You got drunk because you were going to break the table.
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That third person was only doing that because she knew her husband was going to leave her because of that. And he was going to leave her because he was the barman who served the first guy a drink in order to break the table he should have won at the auction.
Re:Really? (Score:4, Interesting)
I'm terrible at even classical physics so please be gentle. But does this experiment show anything other than that if two events are sufficiently close to each other in time, an observer can't determine the order in which the events took place? From the experiment description, it sounds like A didn't actually cause B and B didn't cause A in their experiment. What they showed was that if A had caused B or B had caused A, we wouldn't be able to prove it without designing an experiment with greater time separation.
In classical terms. You got drunk. You broke the table. The two events were simultaneous. We can't know if the events were related or how. Maybe you're always stinking drunk by noon and the table got broken when you tried t swat a fly with your wine bottle.
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> when you measure the polarization state of one of the photons it appears to instantly effect the polarization state of the other photon (no matter the distance). It does not matter what photon you measure first, the state seems to instantly impact the state of the other photon
Feynman's explanation was that it was the SAME photon. i.e. There was no "spooky action at a distance."
The funny thing is that the EPR paradox is much older [technologyreview.com] then previously thought.
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Feynman's explanation was that it was the SAME photon. i.e. There was no "spooky action at a distance."
Can you provide a reference to this Feynman explanation? This does not seem like an accurate characterization of him. Generally he avoided interpretation explanations and just stated what actually happens. Feynman was very aware of the "spooky action at a distance" and would not have explained entanglement as the same photon. He was instrumental in the path integral approach which treats the photon as taking all paths, but he is very clear that this is a mathematical construct for calculating the probab
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No, they absolutely know the order of events. And the order of events dictates a certain outcome.
But if they place the events close enough together, suddenly the outcome is no longer tied to the correct order of events. In other words, sometimes it looks like they happened in the opposite order, even though that is temporally impossible.
Not a surprising result (Score:2)
You got drunk because you were going to break the table.
This and the summary fails to understand QM properly. In QM the time of an event is not well determined. The smaller the energy change associated with an event the less well determined the time of the event.
To think of a classically equivalent question it would be like asking exactly when does a wave hit a beach? The wave has a finite size and hits the beach over a range of time as it comes in at a slight angle to the shore so it is impossible to pick on exact instant and say that is exactly when the wa
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I think the point is if you imagine a photon to travel from A to B and then to C, and thing P happens at A and Q at B, and detection of state at C, then you expect the events to happen PQ.
You only expect this if you don't have a rudimentary understanding of QM. Wave-particle duality means that a photon can be at both A and B at the same time just like a wave can hit the beach of a range of times and places. Given that which event happens first is no longer clear at all.
Really it means that the concept of motion is different at the quantum level.
Not at all. The photon is not behaving as a point-like particle here where it passes through A and then B. Think of it as a wave which can be at both A and B at the same time because of its finite size.
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Really it means that the concept of motion is different at the quantum level.
Not at all. The photon is not behaving as a point-like particle here where it passes through A and then B. Think of it as a wave which can be at both A and B at the same time because of its finite size.
Er... that was my point. At the quantum level the behaviour is different to classical, and this causes people not familar with QM issues with interpreting things. Obviously I failed to explain what I meant... In both parts of your reply I think you are acually trying to agree with me but didn't realise we are in agreement.
Re:Really? (Score:5, Insightful)
Science Magazine applauds the experiments for "obliterating our common sense notion of before and after and, potentially, muddying the concept of causality.
If anything I'd say a big "Duck you" was in order for guaranteeing that no non-physicist will ever understand quantum physics ever again. ... But on the other hand, it might get me out of the dog house for getting drunk and breaking the living room table...
Non-physicists may not understand quantum mechanics, but they're in good company.
I think I can safely say that nobody understands quantum mechanics. -- Richard Feynman
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Then how the hell are people going to get their Quantum cars repaired?
Re:Really? (Score:4, Funny)
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"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint... it's more like a big ball of wibbly wobbly... time-y wimey... stuff." - The Doctor
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I think I can safely say that nobody understands quantum mechanics. -- Richard Feynman
Somebody needs to apply machine learning to quantum mechanics. I'm pretty sure an AI can be taught to understand it, without the baggage of normal physics.
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Tell me about it. Anyone getting in a relationship in 2018 has to be mental.
Just tried it. Proof! (Score:2)
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If you glance at what this boring Trumptard writes, you can know how stupid the bitch is before you read it. Trump level stupid.
It's really no weight on me personally, but you seem really troubled by your homosexual fantasies about me. Maybe if you posted using an actual account name instead of your cowardly little anonymous rants, you'd feel more confident about getting in touch with your sexual desires. It'll make you feel better, truly. All of this toxic vitriol can't be good for you, since you're the only person drinking it up. Pretty sad, really. Poor thing.
Unpaywalled version (Score:5, Informative)
https://arxiv.org/abs/1803.043... [arxiv.org]
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Instructions unclear, text read before clicking the link.
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As I understand it
Found the problem.
If you want to dispute the results, you need to either find a flaw in their experiment or analysis, or perform your own experiment that reaffirms causality. Just saying Nuh-uh doesn't do it.
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So why do you have the idea that a particle's position in time is any better defined?
Important hint, further experimentation has shown that not only can you not KNOW the exact position and velocity of a particle, it doesn't HAVE an exact position and velocity. That's how quantum tunneling works.
Re: seems specious (Score:2)
Particles are uncertain in time. You cannot distinguish space and time, so uncertainty in one applies to the other.
Can we be sure? Yes. Time diffraction is well known. You can have a spacial or a temporal diffraction grating, they work identically.
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As well as the more familiar position / momentum uncertainty principle, there is a similar and related energy / time uncertainty that follows the same logic.
delta E multiplied by delta t must be greater than or equal to hbar.
Th greater the precision with which you define the energy of a system you are observing the less precisely you can define the time of the event being measured.
http://galileo.phys.virginia.e... [virginia.edu]
Why do we always assume that time moves forward? (Score:5, Insightful)
I've been thinking about time lately. Why do we assume we only move forward in time? We move forward and backward in all the other dimensions, why assume we aren't oscillating back and forth in time? What difference would that make if we were? How would we know?
Consider the double slit experiment. Everyone reading this by now knows that if you send a single photon through a double slit it refracts as a wave until it hits the screen, then the "waveform" collapses and becomes a single point of light. Now imagine that quantum particle moving forward a ways, then moving backward a ways, vibrating back-and-forth in time. Each time it vibrates backward it interacts with itself as it's waveform briefly overlap it past self at the edges. This would cause it to refract against itself through the double slit. Then, once it's finally made it to the screen it appears to the observer as a single photon.
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I'm not high! I swear! I've been sober since.... shit.
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It's a fun thought experiment, but how could you make an experiment to test that?
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Have the [elec|posi]tron move through Los Angles. It will get tagged up, and we could observe the tag (or reverse tag) on the next pass.
I wish that I were joking. SpaceX's crew access arm got tagged in LA on the way to Cape Canaveral, you can clearly see where it was cleaned off in this photo of the arm installed at LC-39A:
http://www.spaceflightinsider.... [spaceflightinsider.com]
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Graduate assistant: "Sir, but if we do this, wouldn't it end the universe as we know it?"
Professor: "That's called science, girl. Now, do you want me to sign off on your thesis defense or not. Throw the switch!"
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"No, because in a universe this big it's a stone-cold certainty that (a) intelligent life has already evolved a huge number of times, and (b) someone, somewhere has already done it. And we're still here. Throw the switch, if you would be so good."
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Your post reminds me of this Youtube video I came across recently: https://www.youtube.com/watch?... [youtube.com]
Re:Why do we always assume that time moves forward (Score:5, Interesting)
Look up time reversibility [wikipedia.org] and you'll see that it's not that this hasn't been considered (because math would tend to presume you can negative change in time). It notes that at the quantum level "the weak nuclear force is not invariant under T-symmetry alone; if weak interactions are present reversible dynamics are still possible, but only if the operator also reverses the signs of all the charges and the parity of the spatial co-ordinates (C-symmetry and P-symmetry)."
It's one reason some physicists have argued that perhaps anti-particles are merely their like particles going backwards through time and hence exhibiting reverse charge/spacial parity. Waves though are inherently time reversible. But particle-wave duality has everything as a wave, so that's something of an incongruence. There's also the small wiggle that a photon is its own anti-particle, so it if were to simple reverse in time randomly it'd self-annihilate.
My limited understanding of physics is that things like photons don't do that because anything travelling at the speed of light doesn't experience time/change, so the only way it could change directions is if the path it traveled on changed. Everything else that has mass is constantly changing and its those changes that derive its mass (warpage of space) and whatever charge it has. If it were to repeatedly move back/forward through time, then it would repeatedly engage in this conversions and we'd see gravity/charge ripples a lot more frequently than we do or there'd be more to it--the force of each ripple would be smaller (so the total observed would add up to the same) and movement speed would have an inverse effect on the charge (presuming that faster particles don't move more back/forward in time their charge smaller charge would be spread out over a wider area). That's not what observation/math currently shows.
Basically, any idea you come up with has to line up with the math/observations we already have while you introduce new math and/or observations with either the former leading to the latter or the latter requiring the former because the current math doesn't work. As much as we don't comprehend quantum mechanics, we do have math and observation that match and we're not seeing observations that inherently fail the math. This experiment, AFAIK, is really separate because causality is much more a presumption based on the math we have (ie, it's a convenient axiom to describe things). Now, if you could use this experiment to disprove the current math, that'd be interesting/useful (show that if you throw away the axiom and use some new axioms that match this experiment, the math fails).
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starts running backwards from our perspective.
would manifest strictly locally
Aren't those mutually exclusive? Assuming you meant our perspective as being from outside the black hole.
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Mathematically I would fully agree.
However try and get your head around our control. We would like to think we are masters of our own universe but if we're oscillating backwards and forwards through time and setup in a way that we can only remember the past but not the future wouldn't it stand to reason that there is no such thing as free will?
Am I untyping this right now and just can't remember it? Were you destined to get this reply from me but you didn't know because you can't remember the future?
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T violation and Zitterbewegung (Score:4, Informative)
Why do we assume we only move forward in time? We move forward and backward in all the other dimensions, why assume we aren't oscillating back and forth in time? What difference would that make if we were? How would we know?
Physics is not invariant under time reversal and we can unambiguously determine if time were suddenly reversed. Note that this is not related to entropy e.g. a shattered plate would not leap off the floor and reassemble itself if time were reversed this is far more fundamental than that.
Oscillations of kaon and B mesons have been shown to violate time-reversal symmetry so, if the "direction" of time were suddenly reversed we would know this because these oscillations would have the opposite bias.
There is a relativistic quantum behaviour similar to what you describe - called zitterbewegung - but only in space. Essentially electrons can be shown to hypothetically be travelling back and forth at the speed of light but direction biased so that the net movement is in the classical electron's direction at the classical speed.
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Why do we assume we only move forward in time?
I would hazard that, despite all the quantum mechanical masturbation, no one has ever done it, or even been able to point to anyone or anything as having actually done it, ever, as being the primary reason.
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I have read that the concept of time as unidirectional is a "construction adopted by physicists and others for its unraveling properties." In other words time going forward is a useful way of observing a system whereas in some less scientific cultures time is seen as cyclical in nature. But even in physics the unidirectional time can be traded for the frequency domain where all phenomena are a composition of cycles, and one can be trained in thinking very skillfully in that domain.
Makes perfect sense to me... (Score:4, Funny)
I was confused with the description of the results of this experiment before they even did it.
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I know what will follow next... (Score:2)
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They already have justification, and it's called "being successful". CEOs are the very few people who have had a substantial majority of their random decisions lead to success.
Or at least their decisions might as well be random as at all but the lowest levels of management there are far two many variables for anyone to have any meaningful control.
This just in.... (Score:1)
The universe simulator is a mess of spaghetti code and ugly hacks.
Marvel at the complexity of the macro-scale physics available in this application, but do not look behind the curtain. Be aware that certain boundary conditions - for example, extremely large point-size masses, recursive division of the basic set of subatomic particles, or investigating causality conditions on said particles - can cause unpredictable effects in your universe simulation that may require a restart and loss of existing saved sta
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Determinism & Transistors (Score:3)
The implications to Determinism should be interesting; it could either put a huge hole in the concept, OR provide an explanation for the 'uncaused causer' aside from the traditional solution of 'God did it'.
Moreover, I'm REALLY wondering why this effect was never previously noticed in transistor logic; it should apply to electron signals, not just photon polarity. I wonder if it could be utilized for some kind of quantum-scale out-of-order execution.
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wtf is "uncaused cancer"?
No determinism in QM (Score:2)
The implications to Determinism should be interesting
Not really because there is no determinism in quantum mechanics, only probabilities of outcomes.
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The point is though that, at a fundamental level (as we understand it currently) the universe is non-deterministic. Which is a very good thing if you believe i
Thiotimoline (Score:3)
So maybe we really can have thiotimoline [gizmodo.com] after all?
We know about time diffraction (Score:2)
That's been around for some time.
We know that there is no discrete space and time, only spacetime, which means uncertainty applies to spacetime.
So we've known things get interesting.
We know there are limits to just how interesting because information is conserved and time travel allows infinite information.
What we don't know is where between those limits things get. This will help.
Timey-Wimey (Score:2)
Do not blink. By the way, just because time is NOT a linear progression from cause to effect, do not try to kill statues by staring at them. On the other hand, I could be wrong. In which case, blink and you're dead.
Quantum Fuzziness is required for continuity (Score:3)
As far as I can tell: the apparent continuity of Space & Time requires Quantum Fuzziness, otherwise there would be no continuity -- as there would be no connection between Past & Future, nor between anything separated in Space.
Without this fuzziness, even elementary particles like quarks could not hold themselves together, how else could one part of a quark stay in connection with the other parts?
Remember that Einstein taught us that Space & Time are commingled -- events that appear simultaneous will not be so to an second observer that is moving wrt to the first.
Space & Time Fuzziness allows us to control our feet, as our heads are experiencing time at a faster rate than our feet (General Relativity shows that things deeper in a gravitational field will experience time running slower). Note that if you live to be a hundred, the cumulative difference will be less than one microsecond!
Also Relativity shows why things moving art different speeds experience Time at different rates.
So even parts of the same quark will experience Time differently. Again this fuzziness is required to hold it together - albeit, fuzzily!
This Quantum Fuzziness is consistent with Heisenberg's Uncertainty Principle.
"Nothing" exists at a point in Space & Time. A bullet does not exist at a single point in Space. If you fire a rifle and the bullet hits armour, the front of the bullet stops while the back of it keeps moving for a while -- partly because a bullet is not perfectly rigid (this the most noticeable effect), and partly because it takes time for the back of the bullet to notice the front part has stopped (Relativity again). Without Space & Time Fuzziness, how would the back of the bullet 'find out' that the the front part has stopped?
Blamenomics (Score:1)
Politicians will use this to blame recessions on their successors instead of predecessors.
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Is this really new? (Score:2)
quote: "If a second event (B) happens after a first event (A), for example, then B cannot affect the outcome of A."
But is that really what classical physics says? Does the chain of cause-and-effect not work when you trace the timeline in reverse? Then B can be interpreted as the cause of A. I think I can remember something about physicists struggling to explain why there is an arrow of time: why there is even a distinction between past and future.
Consider the decay of an unstable isotope. What "causes"
What does it say about Many Worlds Interpretation? (Score:2)
As someone who barely has a clue about QM, I loved your reply.
Another question for you:
The experiment seems to prove the photon definitely goes through both paths. Doesn't that prove Copenhagen decoherence?
And if so, does it not turn multiverse theory from Occam's favourite to Occam-says-no?
SchrÃdinger (Score:2)
So in other words the damned cat is a zombie.
Old news, future news (Score:2)
--Thomas
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Alright, a new feature for your camera (Score:1)
This means that the causal order of A and B cannot be always be distinguished by a quantum particle such as a photon.
Great, soon we can take spooky pictures [dailymail.co.uk] from the past (or the future).
What? (Score:2)
In classical physics (beams of light), some of the light follows one path while the rest follows the other. In quantum physics (single photons) you have superpositions so that a single photon follows both paths - so in either theory the two events happen in both orders.
RIP Journalism (Score:2)
... the measured polarization of the output photons was consistent with their being no definite causal order between when A and B was applied.
Their what? Their being? Strangely, the sentence would, sort of, make sense if there was a full stop after the word being, but otherwise I think the word you were looking for was 'there'.
Next time a journalist asks why it's so hard to write error-free code feel free to point this gem out.
(Excuse rant, cuppa required!)
Quantum Mechanics at the Slashdot Level (Score:2)
I'm pretty sure everyone reads the article and then comments. Thank goodness quantum mechanics doesn't happen on the macro scale. Imagine how crazy this board would be.
Memes (Score:1)
Slashdot does science speech like no other (Score:2)
This is some grade A science speech mumbo jumbo. Get this guy to write some Star Trek dialog!
Well, that explains our release schedule. (Score:2)
Fuzzy and with uncertain causality.
Bring on the FTL drives! (Score:2)
The rule of thumb was that that you could have any two of FTL, Relativity, and strict causality. Relativity's been increasingly well-tested, and everybody has just assumed strict causality existed despite a lack of rigorous evidence, and so FTL had to go.
But now that we've torpedoed strict causality, that should make FTL genuinely plausible, should it not?
Re: Protect yourself with APK Hosts File Engine... (Score:1, Insightful)
Your hosts file shit doesn't protect against speculative execution vulnerabilities no matter how much you lie and claim it does. Shut the fuck up and stop spamming.
Re:Immortal. (Score:4, Funny)
"But do not forget this one thing, dear friends: With Time Lords a day is like a thousand years, and a thousand years are like a day." - BBC
Temporal Yoda (Score:2)
horse, the cart before, you put
Grow old, you do.
haiku (Score:5, Funny)
Quantum mechanics
The order does not matter
until classical
Copenhagen, anybody? was Re:haiku (Score:2)
Quantum mechanics
The order does not matter
until classical
hmmm. Niels, is that you? Let's call this the Copenhagen Haiku -- clever, but not quite right. :)
How about...
Quantum mechanics
The order does not matter
nor does classical
One universe, one set of rules, eh?
You're putting the Bohr before the Newton. (Score:2)
Newton shot first.