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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.'
Nevermind -- why bother telling you if you already know :-(
http://en.wikipedia.org/wiki/Thiotimoline
"To those who are overly cautious, everything is impossible. "
*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...
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
The summary doesn't say what the time delay is between when Alice and bob measure their polarization and when victor makes his choice.
FTFA:
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
I don't even know where to begin with this one.
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.
I was already confused before reading the article, that proves effect before cause.
1. PROFIT!!!
2. ???
3. Collide some photons!
The argument goes like this:
`I refuse to prove that I exist,' says God, `for proof denies faith, and without faith I am nothing.'
`But,' says Man, `The Babel fish is a dead giveaway, isn't it? It could not have evolved by chance. It proves you exist, and so therefore, by your own arguments, you don't. QED.'
`Oh dear,' says God, `I hadn't thought of that,' and promptly disappears in a puff of logic.
`Oh, that was easy,' says Man, and for an encore goes on to prove that black is white and gets himself killed on the next zebra crossing.
So, are they working on something that makes light travel a long distance and/or go slower before making that "decision", thus achieving a substantial delay that could actually be used for "time travelling information"? That would probably crash the stock market over night because of sensationalist media combined with ignorance but it would still be very cool...
ics
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.
Article says! It's on the order of 14billionths of a second.
Do you Gentoo!?
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
10:1 says that once the (alice->victor | bob->victor) delay is longer than the speed of light delay from alice->bob the effect vanishes. The result seems consistent with causation being an effect at slower scales than the speed of light, which comes back to the basics of modern physics: Everything is goofy when you get near C.
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)
First of all, quantum effects like this don't allow the passage of information (no quantum entanglement effect does, it would violate relativity). Alice and Bob don't know if their photons are entangled simply by examining them. As a rule, quantum effects are worthless for transmitting information of any kind: both parties know what the other's state is if they know the photon's were entangled, but that is insufficient to transmit any kind of information (it is very useful for encrypting information, but not transmitting it), so you cannot build a useful transistor system using this.
Secondly, the Ars article rightly points out that concluding that effect proceeded cause should be rejected without much much better evidence. I can't explain the results, but throwing out causality so rapidly would be foolish.
One thought I had was that the detectors might actually be in a quantum state (basically, entangled with the photon they observe) after making their observation, which isn't collapsed into an entangled (or not) state with the other photon until Victor makes his decision. In other words, these results might not show up if you increase the timescale, because the quantum state of the detectors after they sense the photons (which, if it lasts long enough, can be affected by Victor after they detect the photon polarization without violating causality) might collapse before he decides to entangle the photons or not. I am, of course, not a quantum physicist, so that might not be possible.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
They want sub-millisecond latency on high-frequency transactions? We'll give them negative latency! Let's see what they do then!
... what happened to the cat?
Article says! It's on the order of 14billionths of a second.
When you say it like that, it sounds small, but if I did my math right, 14billionths of a second is the same amount of time as 28 clock cycles on a 2GHz processor.
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, precluding the idea that the setting of the BiSA caused the polarization results to change. While comparatively few photons made it all the way through every step of the experiment, this is due to the difficulty of measurements with so few photons, rather than a problem with the results.
I think your hypothesis has merit. There is nothing in quantum mechanics that tells us the state of Alice's and Bob's detector cannot be linked to the state of the BiSA.
The speed of light is known with a precision that goes quite beyond that. After that, the timing is a simple question of arithmetic.
Those who can, do. Those who can't, sue.
I have a pretty bad grasp/understanding of this stuff, but if two atoms are entangled, changing the state in one affects the other, right?
No. All that happens is that when the particles are entangled they will have a correlated state when measured. e.g. if one has positive spin the other will have negative. Measuring -- or changing -- the state breaks the entanglement, so you can't simply use it like an FTL telegraph.
Besides, they are working on this now, so it hardly seems futile?
They are not working on FTL communication. The "quantum communication" they are talking about is like the GP said, in a sense a new form of encryption. You can't use entanglement to communicate FTL. However you can use it to determine if your communications have been intercepted -- due to the property that measuring the entangled particles breaks the entanglement. This is awesome because it means you could transmit a shared encryption key, and detect if anyone snooped it, and either send a new one if it was, or use the shared key if it wasn't.
The enemies of Democracy are
Not exactly. Let me explain: when you observe a property of one of an entangled pair of objects, you automatically know the state of the other. This isn't exactly a problem, until you add Heisenbergs uncertainty principle, which states that the more you know about one property of an object, the less you can know about another (position and velocity of an electron being the classic example, but for entangled objects a better example is spin and velocity).
If observing the spin of one entangled electron lets you know the spin of both (but changes the speed only of the first, since you only observed that electron), then you logically should be able to observe the speed of the other entangled electron (which would alter it's spin... but you already know that) and know both spin and speed of both electrons precisely. This violates the uncertainty principle, so instead what happens is observing the spin of the first electron causes both electrons to change in speed, but they do so randomly: in other words, you can change one of an entangled pair by observing the other, but you cannot do so in a controlled fashion. Again, to do otherwise would be to allow one to know both spin and speed of the electron, which is impossible.
Similar logic holds true for entangled photons: observing one changes the other, but not in a controlled fashion. However, both parties can know the polarity of the other's photon (if they are entangled) just fine, which allows them to share certain secret information, which is why quantum networks are theoretically 100% secure. Anyone trying to eavesdrop will actually change the state of the photons by doing so, which can be detected. The details are, obviously, somewhat complex.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
That reminds me of the old joke.
One day, the teacher asked Johnny, "What's the difference between 14 billionths and 15 billionths?
Johnny answered, "That's what I say, What's the fuckin' difference?!"
You are welcome on my lawn.
cf. Asimov, I "The Endochronic Properties of Resublimated Thiotimoline" Astounding Science Fiction, March 1948
Summary Article: https://en.wikipedia.org/wiki/Thiotimoline
You'll end up with two subprime mortgage contracts before you even have a house to lose.
They're wise to that now. The foreclosure notices go out before your approved. These guys are crooked, not stupid!
The speed of light was not the problem. The problem was the timing of the detection of the neutrino. Slight - but significant - difference.
Those who can, do. Those who can't, sue.
Assuming you know enough information to determine that a particle has been disentangled (and I think that this is the case), then you have faster-than-light transmission of information.
Nope. The only way you'd know that the particles had been disentangled is when the person on Mars sent you, via normal communication channels, the information they had measured and you saw that it was not correlated with what you had measured.
That's what was going on in this experiment -- Alice and Bob could not tell just by looking at their individual particles whether or not they were entangled. Even comparing their measurements doesn't tell them, since they could have gotten the same results as they would have in the case of entanglement through chance alone. Only when Victor told them which particles were entangled could they sort their data sets into entangled and non- and see that in fact the entangled set showed the expected correlation.
BTW, this is at a high level how Quantum Encryption works -- along with regular data, you send information about your entangled particle. If the information was snooped, then the entanglement is broken, and what you measure will have no correlation with the measurements you were sent. That's the only way to tell. You can't just look at the particle and say "yep, it's entangled".
The enemies of Democracy are
Ok, let's rephrase the experiment. You have four photons - A, B, C, D. A starts off entangled with B, C starts off entangled with D.
What the experiment appears to show is that if B is then entangled with C, then A is effectively entangled with D. In other words, entanglement is transitive. What it does NOT show is a violation of causality, unless I'm seriously misunderstanding the results.
(There may be other alternative explanations, but I'm satisfied that the results can be explained without resorting to violations of causation.)
However, I am going to throw in another thought -- IF it is established that causation is indeed violated, the Many Worlds theory of quantum mechanics must be false. (The Many Worlds theory says that the universe splits at the event, and that the measurement simply tells you which universe you're in - until then, there's a given probability you're in any of the possible universes. However, the event hasn't taken place at the time of the measurement here, so all probability waves must coexist, so you should observe every possible state. This isn't what's observed. Ergo, one or both of Many Worlds and Violation of Causality must be wrong.)
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Results like this really shouldn't surprise anyone. We have strong reasons, both theoretical and experimental, to believe that CPT invariance is an exact symmetry of the universe. To put it more simply, the laws of physics work identically forward and backward. There is no "preferred direction" of time. The fact that one direction seems to us to be "forward" reflects our local environment (we live on an entropy gradient), not any fundamental property of time. Boltzmann understood this back in the 19th century. So retrocausality shouldn't surprising.
We also have known since the 1960s that if you accept time reversibility and retrocausality, most of the "strange" features of quantum mechanics disappear: the collapse of the wave function, the uncertainty principle, entanglement, etc. All of these are just illusions created by ignoring the fact that the future is influencing the present. Time symmetric versions of quantum mechanics really should be much more widely known than they are.
"I'm too busy to research this and form an educated opinion, but I do have time to tell everyone my uninformed opinion."
No problem, I had to have it explained to me once too. They say newborns have an intuitive understanding of some basic physics, but nobody is born understanding quantum mechanics.
Frankly I don't think anyone dies understanding quantum mechanics. :)
The enemies of Democracy are
Apparently you missed a chapter in the Interpretation of QM - one interpretation is that it requires observation by a conscious mind to cause decoherence, meaning that the measuring equipment is itself in a state of superposition up until the moment that Alice and Bob check the readouts. This interpretation has been largely relegated to cocktail conversations by scientists because it appears impossible to test, but has a certain appeal to philosophers, mystics, and New Age types.
One side effect of the interpretation - it makes conscious life inevitable in any universe theoretically capable of supporting it: the entire universe will be in a state of near-infinite superposition, with all possible "timelines" coexisting until one of them gives rise to a conscious mind, at which point the entire system collapses to only those states consistent with that mind's existence.
An interesting theory I heard recently: If you postulate that the fundamental constants of the universe are themselves prone to fluctuation (something we have no data about), especially in the first few moments of the universe, then you have an explanation for why they seem to be fine-tuned to allow the existence of life - all other values belonged to possible states that were lost in the collapse, leaving only the state most conductive to the rapid evolution of consciousness.
Since the meter is defined as the distance light travels in 1/299792458 second
You forgot "in a vacuum."
Thanks
Fredrick Brown via Gutenberg: The first time machine, gentlemen," Professor Johnson proudly informed his two colleagues. "True, it is a small-scale experimental model. It will operate only on objects weighing less than three pounds, five ounces and for distances into the past and future of twelve minutes or less. But it works."
The small-scale model looked like a small scale—a postage scale—except for two dials in the part under the platform.
Professor Johnson held up a small metal cube. "Our experimental object," he said, "is a brass cube weighing one pound, two point three ounces. First, I shall send it five minutes into the future."
He leaned forward and set one of the dials on the time machine. "Look at your watches," he said.
They looked at their watches. Professor Johnson placed the cube gently on the machine's platform. It vanished.
Five minutes later, to the second, it reappeared.
Professor Johnson picked it up. "Now five minutes into the past." He set the other dial. Holding the cube in his hand he looked at his watch. "It is six minutes before three o'clock. I shall now activate the mechanism—by placing the cube on the platform—at exactly three o'clock. Therefore, the cube should, at five minutes before three, vanish from my hand and appear on the platform, five minutes before I place it there."
"How can you place it there, then?" asked one of his colleagues.
"It will, as my hand approaches, vanish from the platform and appear in my hand to be placed there. Three o'clock. Notice, please."
The cube vanished from his hand.
It appeared on the platform of the time machine.
"See? Five minutes before I shall place it there, it is there!"
His other colleague frowned at the cube. "But," he said, "what if, now that it has already appeared five minutes before you place it there, you should change your mind about doing so and not place it there at three o'clock? Wouldn't there be a paradox of some sort involved?"
"An interesting idea," Professor Johnson said. "I had not thought of it, and it will be interesting to try. Very well, I shall not ..."
There was no paradox at all. The cube remained.
But the entire rest of the Universe, professors and all, vanished.
14 billion divided by 2 billion would be 7.
Right?
28cycles = (14/1Billion) sec * 2BillionCycles/sec (the paper says 14ns-313ns which is my interpretation)
0.142858rep cycles = (1/14Billion) sec * 2BillionCycles/sec (a possible misinterpretation)
7sec^2/cycles = 14Billion sec * 1sec/2BillionCycles (a very strange interpretation given unit analysis)
So although your statement appears to be mathematically correct, I fail to see how it is applicable to my statement...
So, are they working on something that makes light travel a long distance and/or go slower before making that "decision", thus achieving a substantial delay that could actually be used for "time travelling information"?
Under the simple interpretation, nothing "goes back in time." It's essentially two Schrodinger's cats (A & B) being in a superimposed state for several nano-seconds. Then V adds a constraint, and eventually the A, B, and V information bubbles interact and collapse into an observed state that the scientists record.
The meta-computer that runs our universe probably printed a log message like 'ATOMIC MERGE-OP unexpected long delay on eval: d=7m, t=23ns.' If scientists persist in this sort of research, the person running this universe will probably just ^C the app.
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.
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.
That's the key point. As soon as Alice or Bob lose isolation (e.g. by deciding on a stock trade,) the state collapses and there is no information from the future.
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.
They say newborns have an intuitive understanding of some basic physics, but nobody is born understanding quantum mechanics.
Well, in all honesty, how do you know - I mean, it not like we can ask. Maybe newborn babies do have an innate understanding of quantum mechanics, and we spend the first few years of their life to make them unlearn it? ~
Segmentation Fault, Core Dump:
14 billionths of a second != 14 billion per second
Damn.
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...
Partly correct. It's been years since I've had a QM class, so I'd have to dig through the wiki page for details, but Bell's Theorem states that no *local* hidden variable theory offers as complete a description of reality as traditional QM. Apparently, testable predictions can be drawn from the theorem, and so far none of the experiments done have contradicted it (although it may be rather early to call it confirmed, based on a quick look at the wiki page). In any case, none of this says anything about the possible existence of *non-local* hidden variable theories. A local hidden variable theory (IIRC) could render QM non-weird from a classical standpoint, but part of the usual QM weirdness is non-locality, so it currently appears we will be stuck with some sort of strangeness even if we find a more complete version of QM.
This is part of the problem with the math we try to use to describe the universe. We don't handle zeroes and infinities very well.
For example, something goes all batshit at the speed of light. If you try to apply the math of Relativity to something traveling at c, then you get a meaningless answer that there is no time. When you try to figure out what's beyond the event horizon of a black hole (where gravity's acceleration is greater than the speed of light), the answer comes up that there is no space, that the entire mass of thousands of stars would be contained in a single point that is infinitely smaller than the Planck length: a singularity. When you try to figure out the transition across the event horizon of a black hole, it seems that something falling into one will take forever to get there, while on the inside of the black hole everything that's in it was always in it.
Is anybody working on some math that take the weird out of it all?
Fun with Anagarams! LADS HOST, SHALT DOS. HAS DOLTS. AD SLOTHS, HATS SOLD. ASS HO, LTD.
I RTFA, and I didn't like the (lack of) explanation.
As usual, QM's explanation is saying "uncertainty" very slowly and profoundly. (Slowly for the dim-witted among us, profoundly for the benefit of the Nobel selection committee).
Seriously. TFA states that the measurements are not literal, and correlation between measurements happens after the fact.
So: quantum entanglement gives you a way to defeat uncertainty, by letting you measure the mutually exclusive information from a set of correlated particles... Except no it doesn't, because you can't be certain of your measurements.
And: clever experiments like this let you send information back in time.... Except that no it doesn't, because the universe still has plausible deniability (i.e. you only thought you sent information back in time, but it turns out, the universe was going to do what it did anyway and/or your measurements of what happened are uncertain).
Congratulations, QM fags. You've found another brilliant way to show how fucking retarded you are.
"Prediction: within 10 years, Windows will be a Linux distribution." Me, 7-6-2016
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.
This is awesome because it means you could transmit a shared encryption key, and detect if anyone snooped it, and either send a new one if it was, or use the shared key if it wasn't.
Please pardon my ignorance, but this is my train of thought:
So you send me an encryption key. I put it in my quantum container for safekeeping, board a giant rocket-ship and fly to Omicron Persei 8. 2000 years after launch I am supposed to report if there is sentient life on Omicron Persei 8. So If I meet Omicronians, I will "snoop" on your encryption key, and if not then I will not. Can you instantly "detect" it? How is this not an FTL communication?
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
Noone said the detection would be instantaneous
In order for the two parties to detect their communication was snooped at, they have to 'talk' to each other to compare measurments outcomes. that doesn not happen FTL