Slashdot Mirror
Quantum Experiment Shows Effect Before Cause
steveb3210 writes "Physicists have demonstrated that making a decision about whether or not to entangle two photons can be made after you've already measured the states of the photons."
Here's the article's description of the experiment: 'Two independent sources (labeled I and II) produce pairs of photons such that their polarization states are entangled. One photon from I goes to Alice, while one photon from II is sent to Bob. The second photon from each source goes to Victor. Alice and Bob independently perform polarization measurements; no communication passes between them during the experiment—they set the orientation of their polarization filters without knowing what the other is doing. At some time after Alice and Bob perform their measurements, Victor makes a choice (the "delayed choice" in the name). He either allows his two photons from I and II to travel on without doing anything, or he combines them so that their polarization states are entangled. A final measurement determines the polarization state of those two photons. ... Ma et al. found to a high degree of confidence that when Victor selected entanglement, Alice and Bob found correlated photon polarizations. This didn't happen when Victor left the photons alone.'
Ain't that a geographical oddity?
Nevermind -- why bother telling you if you already know :-(
The summary doesn't say what the time delay is between when Alice and bob measure their polarization and when victor makes his choice. Presumably it's on the order of femtoseconds or something. But imagine if the delay was longer, say microseconds - you could build transistors with this kind of feedback loop. Or imagine if you chained a million of them together in series, like on a cvd wafer or something. Then you start to seriously have a reverse-time information loop going!
http://en.wikipedia.org/wiki/Thiotimoline
"To those who are overly cautious, everything is impossible. "
These damn physicists have proven that God does not exist. Any proof with the PSR as the hypothesis is now moot.
*Looks at physics degree.*
*Tosses it in the trash.*
Victor should decide not to entangle the photons whenever Alice and Bob's polarizations are correlated. That'll rip physics a new one...
Stop. The. Presses.
Did they account for loose wires?
It would be a shame if they end up with egg on their faces like the nice folks at OPERA.
The picture certainly looks like future events influence the past,
At that level it's irrelevant as there isn't anything practical we can do with it, at least at this time, or perhaps the way we measure time doesn't work well at that level of granularity, in any event the most likely explanation is the one no one has come up with yet.
"If any question why we died, Tell them because our fathers lied."
AIUI, the notion that information can't be transferred faster than the speed of light is based on the fact that it would violate causality. I have wondered whether causality is an assumption rather than an actual property of the universe.
If it is (I'm not qualified to interpret this experiment), we'll have a lot of new physics coming down the pike over the next few decades.
Sheesh, evil *and* a jerk. -- Jade
I don't even know where to begin with this one.
Better re-check that cable, first.
one month until a New-age quack publishes a book on how to harness this phenomenon for better health, improved intimacy, and financial success!
Victor is Bipolarized making him erratic and unpredictable. Might want to try adding lithium atoms into the mix and see if the results stabilize.
The effect happened before the cause.
I was already confused before reading the article, that proves effect before cause.
More studies have to be done to see how the correlation relates to the time interval between observation and choice, the current setup was just a few nanoseconds' delay.
Corruption is convincing someone that the selfless ideal is the same as their selfish ideal.
1. PROFIT!!!
2. ???
3. Collide some photons!
Now they've found a way to prove that video games cause violence!
"I like to lick butts!" by MobileTatsu-NJG (#32700246) (Score:5, Informative)
I already heard about the neutrinos going FTL, which turned to be a measurement glitch.
Now these guys say "causality isn't really a thing"? I'm not even going to hold my breath.
P = NP
forgive the flamebait AC...
It appears a causality disturbance allowed slashdot to post this after ars technica did yesterday.
This...doesn't sound like effect before cause. I am not a scientist.
Alice and Bob's photon polarizations should exist in a superposition of all possible states (let's say correlated and uncorrelated). Victor's choice, before he makes the choice, is a superposition of all possible states (entanglement and not entanglement).
Is it Alice and Bob's pressing the 'measure now' button (but not themselves looking at the result), or is it Alice and Bob's actually looking at the result that's happening before Victor makes his choice?
If: 1) Alice and Bob press the 'measure now' button, 2) Victor makes his choice, then 3) Alice and Bob look at their results
Then: I don't think it's effect before cause because Alice and Bob's observation (not their equipments' observation) happens after Victor makes his choice.
If: 1) Alice and Bob press the 'measure now' button, 2) Alice and Bob look at their results, then 3) Victor makes his choice
Then: It might be effect before cause because Alice and Bob's observation (not that of their equipment) happens before Victors' choice.
Or... Let's say it's the second if/then. From Alice and Bob's point of view, until they make their observations, Victor exists in a superposition of selecting and not selecting entanglement. When Alice and Bob make their observations, the Victor possibilities just collapse to the one that fits with their observations.
My head hurts. Everything I've read about quantum mechanics (a bit, not much) tells me this is supposed to happen when people think about it.
I really which quantum people would stop acting like they know what they are talking about.
This is just a really shitty description/way of looking at a series of events and is more or less wrong in the same way that saying your traveling back in time by looking at old stars in the sky from far off distances.
The only thing out of order here is the observers note taking and logic. Due various other quantum flux it may appear to happen in a certain order even though it didn't and its just a matter of appearance due to propagation effects.
Its a bad observation and bad description of that observation, not a causality violation.
I'm going to go hide in a closet for the next few days, hugging my knees and rocking gently back and forth.
Just a glitch in the matrix....
...richie - It is a good day to code.
Or at least try...
So a key part of the experiment was that the pair of photons sent to "Victor" went through a 104 meter cable to ensure that whatever Victor did, Alice and Bob measured their polarizations first.
Presumably, one could extend this cable to increase the amount of time between Alice and Bob's measurement and Victor's decision to entangle or not.
Presumably long enough for Alice and Bob to send the result of their measurement to Victor.
And then instead of an RNG, Victor chooses to entangle based on whatever would contradict Alice and Bob's measurement.
Come on, we have to try...
P.S. the paper says they aren't violating causality, and it only looks like they are if you're looking at it wrong.
The enemies of Democracy are
The experiment in the article is ... awesome. Though if history is any indication, hoards of raving Slashdoters will try their damnedest to force this into a classical mechanistic world-view.
So here's a fun experiment you can do at home! (Craftsmanship is important for good results.)
1) Start by setting up up a classic double-slit experiment. A laser pointer and some household junk is all you need.
* Observe the interference pattern.
2) Stop denying that you went to see "Avatar" 36 times and grab a couple pairs of 3D movie glasses.
2a) Alternately, you can just buy a polarizing filter sheet. (this is the better way)
3) Being careful to note orientation of the filter, place the filters in front of the slits with one oriented 90 degree to the other. (This is only tricky because the distance between the two slits is so small.)
* What happened to the interference pattern? You "tagged" the individual photons so that you could, in principle, know which slit they passed through, so instead of going through both, they went through just one.
4) Place a third sheet of polaroid between the slits and the detector screen, oriented half-way between the two other filters (if one sheet is vertically oriented and the other horizontally, this sheet will be oriented at 45 degrees)
* The interference pattern is back? WTF? You took the tag away, so that you couldn't know which slit a photon passed through. You "erased" the which-path information so each photon went through both slits, instead of just one of them.
Do the experiment. Accept that the physical world is weird as shit. Shut-up and calculate.
Required reading for internet skeptics
FTFA:
They probably hired the cable guy that got fired from CERN a few months ago.
What this article is saying, is that victor's decision to entangle his photons has a direct effect on the results that alice and bob get from their double blind measurements.
So, either there is retrograde communication on time's axis, or....
The decision that victor makes is predetermined, by the act of measurement undergone by alice and bob. (Meaning victor doesn't really have as much free will as he thinks he does.)
Proposed followup experiment:
Alice and bob examine their photons, tell each other, but not victor. Victor decides to entangle or not entangle. Examine new correlation.
This will test "does a correlation between alice and bob indicate that victor will entangle?".
If it does, you have a reasonably strong test case for many worlds.
Subatomic laws
Scientific pause
Synchronicity
With one of these you get this effect all the time, they go haywire *before* you do anything wrong...
http://arxiv.org/pdf/1203.4834v1
One explanation of the results, should they hold up is that Alice, Bob, and Victor's actions were predetermined before the photons were generated and thus had to correlate.
You could say that the actors then had no free will, or you could imagine a scenario where somehow the actions of all three were entangled via an earlier free will choice.
-Ryan
AUWYHSTOT (Acronyms are Useless When You Have to Spell Them Out Too)
when Victor selected entanglement, Alice and Bob found correlated photon polarizations
thereby giving the best possible proof that correlation does not imply causality.
... what happened to the cat?
Nice to see Alice and Bob finally making friends with Victor.
Alice get Ia and Bob gets IIa and Victor get Ib and IIb. Alice and Bob do their measurements. Alice and Bob then can compare their measurements and find that Victor was fiddling with the equipment on his end or not. What constitutions "no communication passes between them during the experiment"? Does Victor have to do his measurements to determine that the experiment is over, or Can I shoot Victor as the only one who knows whether he diddled the equipment or not and his message would still exist in the hands of Alice and Bob?
Gods must be crazy ...
Why are we using SLASH and SLASH SLASH for designations when 1 and 2 are clear and effective? Or A,B Z,X I,II etc....
are college students not getting smacked in the head for making up unclear designations anymore? My profs would fail you for using silly things like the summary uses.
WE have two photons, let's call them % and @ would equal a paradox of failure in the colleges I attended.
http://arxiv.org/pdf/1203.4834.pdf
So effects effect causes?
FTFY
So, assuming entanglement across time, what's the limit. In this case, we're talking billionths of seconds.
Could it be done in seconds? Hours? Years?
If you observe the expected result with enough time before the action, can you alter the action?
Give a few seconds (or less) of lead-time and a reliable source and either you're going to have some *very* rich scientists or the high-frequency-trade based stock market will be gone rather quickly.
So effects cause causes?
http://abstrusegoose.com/455
"This study is invalid, Causation does not imply Correlation" posts.
"First of all, quantum effects like this don't allow the passage of information..."
Okay, we all know that is the accepted dogma that everyone states.
However, isn't it also usually said that cause must precede effect? Which this experiment plainly (well... kind of plainly) shows, that law being violated.
This shit is so weird, I think we can expect to see SOME of our previously held beliefs challenged, right? Otherwise why bother experimenting at all.
The very fact that causality is being violated maybe could be used in some obscure way to create a morse-code entangled optical network of zero latency, if we can figure out a way.. Maybe... If we have a law that says it's impossible, maybe that law has some limitation that we didn't realize before, or didn't understand the full implications of. They come up with some insane, nifty stuff.
Spooky action at a distance indeed. Cool shit!
We're just living in a simulated universe that employs lazy evaluation.
Make no mistake, the arrow of causation is still there, it just has no requirement that it follow our linear perception of time. Simulation of a past event can and will be delayed until information about that event is required, which means it's perfectly normal for the universe to resolve future events before past events.
Quantum entanglement is very cool, but it's not relevant to photons. Photon travel at the speed of light, and experience infinite length contraction and infinite time dilation. "Before" and "after" simply to not exist in the photon's inertial frame.
All they've done is demonstrate special relativity, not quantum entanglement.
A series of quantum experiments shows that measurements performed in the future can influence the present. Does that mean the universe has a destiny—and the laws of physics pull us inexorably toward our prewritten fate?
http://discovermagazine.com/2010/apr/01-back-from-the-future
Is this related to Arizona's new anti-abortion / anti-contraception law that declares that women are legally pregnant two weeks before conception?
(Yeah, I know it's not that simple, but it is still an astonishingly dishonest act to push an agenda.)
I believe I already commented on this last week.
Try to keep up.!
I posted before I RTFA
The Official Site of 1337 Pwnage
There does not appear to be an effect of any kind on the difficulty of the material in an article, i.e. how much of the Slashdot audience is likely to understand it, versus the rate and amount of comments.
I draw the conclusion that the bullshit level must rise, given everything else remains constant.
mov ah, 4ch
int 21h
As with all delayed choice experiments, the past is not being changed by the future. The article would have you believe that Alice and Bob, without any information from the future Victor, can determine if their measurements are correlated or not. This is not true. If it were, then the future can affect the past. For these experiments, photons from the various detectors are checked for time correlation, to identify that the measurements occur for the same pair of entangled photons. Only measurements by all three participants, with the appropriate time delay, are declared to be "a measurement".
Lots of photons are measured by Alice and Bob, that are not measured by Victor. Why? It is Victor's "delayed choice" of whether or not to entangle the photon that determines which events Victor measures. He will not measure anything that could give him more information about the entangled system than is allowed by the Heisenberg Uncertainty Principle.
So, Victor's choice changes which photons, as measured by Alice and Bob, are going to be included in the test.
The future does not change the past. But, information from the future can change what information we can extract from the past.
I have been working on the development of a computer which can calculate a chain of reasoning that is needed to justify any arbitrary conclusion given any starting data set. I think it will sell to governments, economists and political parties like hotcakes.
It is now quite evident that the solution is going to lie in the realm of quantum computing.
cf. Asimov, I "The Endochronic Properties of Resublimated Thiotimoline" Astounding Science Fiction, March 1948
Summary Article: https://en.wikipedia.org/wiki/Thiotimoline
How is Victors delay decision in this experiment only 14 billionths of a second?
Light travels about 1ft/ns in a vacuum. Given the index of refraction of a typical optical delay line your looking at about 2/3's vaccume speed for the same trip thru a fiber cable.
341 feet thru vacuum requires ~341 billionths of a second (~341 ns)
Add in the fiber delay and your at roughly 500 billionths of a second.
Just how long are alice and bobs polarization detectors? What gives?
No, it is just proof that:
1) we still have no clue what Quantum Entanglement is
2) Quantum Mechanics is still very weird.
"Causal events" may very well break down horribly in either of them pretty damn easily.
No usable information is sent over, as far as we know.
So it doesn't really break that "law" of "no information faster than the speed of light".
Not everyone believes in the no-communication theorem, however.
Even Special Relativity never outlawed it. It just prevents sub-luminals from hitting C, it doesn't prevent things from existing at speeds naturally higher than C.
This stuff is literally at the fringes of known science.
You should expect quite a few things to be invalidated in the next few decades.
Almost certainly going to happen, especially related to quantum mechanics and the standard model, and likely the very fundamental concept of information itself.
Science is at a very exciting point in time right now and I can't wait to see more from this experiment.
Just a shame that some scientists are terrible people.
We just heard of a very big example when the leader behind the FTL neutrino paper was forced to leave because everyone WHO SIGNED THE PAPER complained. Hypocrites. Anything and everything to crush others to save their own asses...
People assume that time is a strict progression from cause to effect, but actually, from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbley, timey-wimey... stuff.
I am the Eschaton. I am not your God. I am descended from you, and exist in your future. Thou shalt not violate causality within my historic light cone. Or else.
I can't remember any details at the moment, but I'm fairly certain that several experiments have been done to test for the existence of "hidden mechanisms" governing the apparent QM weirdness, especially in the early days, and all came back negative.
I think I found a loop hole. They have to discard all the failed attempts of the entanglement swapping (75% of the time). Not to mention a 4.4% efficiency of even getting photons through the long fiber to Victor. I don't have Nature Physics, but from the preprint on arxiv.org:
"The probabilistic nature of the Bell-state projection with linear optics decreases the success probability to 1/4." page 15
Though a more honest way to say this might be, that only when Alice and Bob have correlated photons, would it be possible to get the entanglement swapping to work. If we tried to swap the entanglement based when Alice and Bob did not get correlations its clear it would never happen. Their interpretation relies on a strange post selection of the data. If their experiment checked to see if Alice and Bob first got a correlation, and only then tried to do entanglement swapping, I think the experiment would not appear to violate any sense of causality. Its only because they throw away 75% of the data (the failed attempts at entanglement swapping) that the experiment appears magic. I think those 75% contain most of the uncorrelated results from Alice and Bob as there is a reason those attempts failed. Ie. its not chance if Alice and Bob have already performed the measurement. Its only "chance" if we pretend that we don't know.
In order to even detect this effect you need at least two things:
Suggesting that Victor do something different depending on whether Alice and Bob detect correlated photons is nonsense because you can only detect the correlation in the statistics of many trials. It makes no sense to say a single event was correlated or uncorrelated. If you could that this would be a form FTL communication which it's not.
Like it or not, our intuition is based on classical mechanics. Human brains are very good at sticking new information into existing pigeon holes. Almost always, when someone is talking about "understanding" entanglement experiments such as this they mean creating a microscopic classic model in their heads that would explain these results. It's been proven mathematical that these classic models don't work.
One recurring problem is that many people (often, but not always people have not learned quantum mechanics) intuitively believe that there must be a classical model behind the results somehow. This is similar to the belief that there is always a logical explanation for a magician's trick. For the trick this intuition is great but for quantum mechanics it is lousy. You have to leave your classical intuition at the door when you enter the world of quantum mechanics. Unfortunately some people start with their erroneous classical intuition and then extrapolate to all sorts of nonsense. Since they are starting from a totally incorrect assumption, they are able to prove just about anything but it is all nonsense.
It's just a correlation. There is no FLT anything here. It is only FTL when you insist on the existence of an underlying classical model and we know that all such classical models are wrong.
We don't see the world as it is, we see it as we are.
-- Anais Nin
In other quantum-related experiments (slit observations, as we like to call them, e.g.) one finds seemingly deterministic results, no?
When Victor selects entanglement he sends an effect backwards in time to the original photons.
AccountKiller
This must be the research that will lead to the creation of the wires that transmit information faster than light we had a few months ago.
A couple years ago there was an item about predicting mistakes before they happened.
Maybe, just maybe time doesn't flow the way we think it does if the effect can happen before the cause.
"Our fiber-optic cables are so good, they deliver the signal nanoseconds before it's transmitted!"
Wow! I got a -1 mod before I even wrote this post. Quantum, dude.
Table-ized A.I.
First post!
If the result back-propagates through time, then how could you ever have seen any different result?
Depending on what Victor chooses to do, he's going to open the folder detailing Alice and Bob's findings and those findings are always going to describe Victor's decision. Otherwise there's no linearity to time. You can't possibly have some effect that is working to cause this to happen while Alice and Bob still somehow did something different. Doesn't that make sense?
So either those times when Victor's decision did not affect A and B were after some error had occurred in the experiment, or, the effect or force isn't really happening at a quantum level but is happening due to insufficient control on the experiment.
"Stratigraphically the origin of agriculture and thermonuclear destruction will appear essentially simultaneous" -- Lee
This is even better than the news item about how the Psychic Network went out of business due to unforeseen financial difficulties.
Sorry, but gray text on gray background is making my eyes bleed.
No?
"Motivated by the question, which kind of physical interactions and processes are needed for the production of quantum entanglement, Peres has put forward the radical idea of delayed-choice entanglement swapping. There, entanglement can be "produced a posteriori, after the entangled particles have been measured and may no longer exist". In this work we report the first realization of Peres' gedanken experiment. Using four photons, we can actively delay the choice of measurement-implemented via a high-speed tunable bipartite state analyzer and a quantum random number generator-on two of the photons into the time-like future of the registration of the other two photons. This effectively projects the two already registered photons onto one definite of two mutually exclusive quantum states in which either the photons are entangled (quantum correlations) or separable (classical correlations). This can also be viewed as "quantum steering into the past"."
The researchers are assuming the actions of Victor to select a specific polarization and entanglement are somehow independent of the entire quantum configuration space. In other words, they're assuming free will, and the existence of external magical souls that are somehow independent of reality.
If you assume determinism, Victor's actions should be consistent with the configuration space, and so when measurements are made by Bob and Alice that are correlated, it increases the probability that Victor will choose to entangle.
First Post !!!
Remarkably similar to the stories I've heard from people who OD'd on LSD.
If Alice and Bob are the same person looking at the rate of correlation between the 2 streams of photons, Victor will be able to transmit a message *backwards in time* to them by deciding to entangle or not. If this is not the point, then there isn't a point to the experiment at all.
Oh my god. The Spoke is back? I've been wondering what it actually was since it came around the first time. Is it like "streets ahead"? Or like "miles ahead"? On the ball? On the spot? In the house? Off the rails? At some point I got the impression that Nickelodeon had some sort of News or "Cool New Stuff" segment called The Spoke, but I don't know where I got that impression. Is it a pure troll invention, or an ancient Internet custom I just never became aware of. Any information you can give me would be appreciated. I would like wry much to be "on the spoke" as far as this idiom is concerned.
The paternity suits would be a bitch... but I haven't had an orgasm yet!!! Where's my Minority Report!!!
Get on da spoak
Due to the 104-meter fiber-optic cable, Victor's measurements occurred at least 14 billionths of a second after those of Alice and Bob
Should have used Monster cables...
Q1: Two independent? sources produce photons whose states are entangled? How does that make sense?
Q 2: How do you establish that Bob and Alice's selection of correlated filters did not cause Victor to choose entanglement? Isn't that a valid interpretation of the results?
Q 3: What does "combines them so that their states are entangled" mean? How is this done? How does it differ from an experiment to determine if the polarizations agree?
ah quantum computers...
Imagine playing a first person shooter on a quantum computer, using a quantum entanglement network and you actually have negative ping times.
So you are fragging people before you shoot the weapon :P
The wave-function is nothing but a correlation machinery that organized nature's limited resources to properly fall into place (without upsetting causality as the correlations can only be sorted in hindsight).
This demystified view of QM is still very much overshadowed by the Quantum Hippie version that makes for better headlines. I.e. non of the pop science sites clearly report this tidbit of the authors wisdom. Causality violation draws more web traffic.
Sounds very similar to the delayed choice quantum eraser experiments performed by Wheeler et al. The main difference sounds like the use of polarized filters instead of the double slit diffraction.
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
This will open new revenue paths to quantum healers, now they can heal you before you even have symptoms
Can someone explain this using a car analogy?
Neutrinos, anyone?
Great Intellect...
One photon always lies, and one always tells the truth. What one question can you ask to find out how to get back to your village?
Extra credit: should you switch paths if there's a goat on the other one?
Ain't that a geographical oddity?
Look carefully, this post has actually affected the whole thread before I posted this post.
They are essentially relying on "post hoc ergo propter hoc" (after this, therefore because of this) which is a logical fallacy.
They are saying "Look! We can actually show 'pre hoc et propter hoc!' " (before this and because of this). Well, sorry, even if Victor acted beforehand, thinking this implies causation of what happens next would still be a logical fallacy. The idea that it does even when he acts after his "effect" is either perpetuating the same fallacy, or (as I suspect) just downright silly.
The key part is that Victor is entangling *already existing* photons.
In a classical world, Victor would look at both photons and if their spin are opposites, he would say that they are entangled, if not he'd say that the entanglement has failed: no causality issue here but when Victor has successfully "entangled" photons, Alice and Bob's photons are "entangled"..
Presumably, one could extend this cable to increase the amount of time between Alice and Bob's measurement and Victor's decision to entangle or not.
Presumably long enough for Alice and Bob to send the result of their measurement to Victor.
And then instead of an RNG, Victor chooses to entangle based on whatever would contradict Alice and Bob's measurement.
Come on, we have to try...
Unfortunatley, unless you know of a way to remove yourself from the causality timestream, you'll never see a contradictory result. Even if you tell Victor, and he does the opposite, history will simply rewrite itself to align the results, and you'll just end up with an argument with Alice and Bob lambasting Victor for not sticking to plan, and doing the opposite.
t0 Alice+Bob=Non-entangled ...
t1 Alice+Bob tell Victor
t2 Victor "does the opposite" and doens't entangle
--change propogates backward to t0
t0' Alice+Bob=Non-entangled
t1' Alice+Bob tell Victor
either you're stuck in an infinite loop, or more likely, t1' is muddled such that the communication to Victor remains the same (or doesn't happen) and Alice and Bob are pissed as hell at Victor for "spoiling" the experiment by not doing what was "agreed."
I'm more interested in the trading applications of this, particularly if you can put together a 24 light-hour loop of cable and respond to "go/no-go" trading decisions. :-)
The Future of Human Evolution: Autonomy
Well *I* know with 100% certainty that if I entangle my girlfriend's long hair that she will get mad at me! I know she's going to get mad even BEFORE I entangle her beautiful strands. I already know the effect! How cool!!!
If you've propery defined cause/effect, etc. all this "paradox" talk seems to me to be saying "we found a contradiction, we proved that contradictions exist!" Right, and Socrates is both mortal and immortal. He has died, but he is immortal. Proof that one can be immortal and still die! Ok, the point is, times were, when contradictions arose, the foundations of the theory had to be revised or the reasoning process in the experiment was found to be incorrect. THey're tallying up contradictions, and merrily plodding along as tho these things can be real in nature ...
This may be hint that the backward only, readonly time machine is possible :D.
Superposition is a pathetically weak and improvable condition that is based solely on uncertainty. I don’t know what the photon's polarization is; therefore it is polarized in all possible states? NO NO NO It has the POTENTIAL to be in any polarized state until it is measured. As soon as we measure it, our measurement "collapses the wave function" into whatever state we observe; that does NOT prove that it was in all states before we measured it ... wave function collapse (used to "prove" superposition) is a sick sick joke. It is perfectly good science in other regards though...
Schrodinger's cat is another great misrepresentation of this concept. It is NOT the person who opens the box (and collapses the waveform) that killed or didn’t kill the cat. If the cat is dead it was directly caused by the radioactive decay event that triggered the release of the poison that killed the cat and more importantly the felinicide was caused by the asshole scientist that put the cat in the box in the first place. At no point in time was the cat dead and alive simultaneously simply because we didn’t observe the decay event doesn’t mean it did not happen at some specific point in time. If you follow the many worlds interpretation the cat can be dead and alive at the same time but only in different worlds. In any one world the cat will only be one or the other NEVER BOTH. /rant off...
Cause comes before Effect?
A time loop on the quantum level would explain it, perhaps the fabric of time isn't moving straight line if you look close enough (or fast enough rather).
Tell me when they figure out how to use this on the dating scene... "Can I end up entangled if I move in for the kiss"
Personally, I would want to know more about the "random" number generator they used at 'Victor'. A little signal contamination could go a long way to screw up an experiment like this.
This sounds weird, but it really is much less weird once you understand it. This has nothing to do with causality, it is just random correlation. In quantum mechanics statistics of measurement is independent of who performs the measurement first (provided the measurements are something that is called commutative, as is the case here). This is the crucial piece of information. The author of this report (about the original paper) is confusing correlation with causation (the original paper does not do this). Importantly, no information can be sent using this technique at a speed faster than the speed of light - this is a prerequisite for causality problems.
Does this result contradicts QM? The answer (I think) is NOT... and If it does not contradict QM then there is no causality violation.
I think there are two interpretations of the results one of which is effect-after-cause and the other cause-after-effect. If we project the state vector after measurement of particles 1 and 4 (as we should) and then we calculate the amplitude of obtaining + and - for the Victor's "entanglement swapping" measurement, then we should get the same results. So the entanglement swapping protocol is not really swapping anything. It is just the same protocol but it does nothing on particles 1 and 4 because their states are fully determined by the initial measurements.
Then there is another way to see this (cause-after-effect). The authors say "[Victor's measurement] effectively projects the two already registered photons onto one definite of two mutually exclusive quantum states in which either the photons are entangled (quantum correlations) or separable (classical correlations). This can also be viewed as quantum steering into the past". The word **projects** is key. We could choose to apply the projector after Victor's measurement instead of after Bob and Alice measurements and the maths still work fine. It is a kind of time symmetry.
Note that if we look at Bob and Alice's measurements when Victor chooses to "swapp" we should find no correlation. We have to take into account what result Victor gets on his swapping measurement. If we discriminate for each of the two possible outcomes then and only then we get the (apparent) correlations.
Fernando Martin-Maroto
Does this result contradicts QM? The answer (I think) is NOT... and If it does not contradict QM then there is no causality violation.
I think there are two interpretations of the results one of which is effect-after-cause and the other cause-after-effect. If we project the state vector after measurement of particles 1 and 4 (as we should) and then we calculate the amplitude of obtaining + and - for the Victor's "entanglement swapping" measurement, then we should get the same results. So the entanglement swapping protocol is not really swapping anything. It is just the same protocol but it does nothing on particles 1 and 4 because their states are fully determined by the initial measurements.
Then there is another way to see this (cause-after-effect). The authors say "[Victor's measurement] effectively projects the two already registered photons onto one definite of two mutually exclusive quantum states in which either the photons are entangled (quantum correlations) or separable (classical correlations). This can also be viewed as quantum steering into the past". The word **projects** is key. We could choose to apply the projector after Victor's measurement instead of after Bob and Alice measurements and the maths still work fine. It is a kind of time symmetry.
Note that if we look at Bob and Alice's measurements when Victor chooses to "swapp" we should find no correlation. We have to take into account what result Victor gets on his swapping measurement. If we discriminate for each of the two possible outcomes then and only then we get the (apparent) correlations.
Fernando Martin-Maroto