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Quantum Experiment Shows Effect Before Cause

Soulskill posted more than 2 years ago | from the enjoy-the-headache dept.

Science 465

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.'

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465 comments

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First before I even posted! (0)

Anonymous Coward | more than 2 years ago | (#39787259)

Ain't that a geographical oddity?

Re:First before I even posted! (0)

Anonymous Coward | more than 2 years ago | (#39787301)

"Effect And Cause"

I guess you have to have a problem
If you want to invent a contraption
first you cause a train wreck
And then you put me in traction
well first came an action
And then a reaction
But you can't switch around
For your own satisfaction
Well you burnt my house down
Then got mad at my reaction

Well in every complicated situation
There's a human relation
Making sense of it all
Take a whole lot of concentration
Well you can blame the baby
For her pregnant ma
And if there's one of these unavoidable laws

It's just that you can't just take the effect and make it the cause

Well you can't take the effect
And make it the cause
I didn't rob a bank
because you made up the law
Blame me for robbing peter
Don't you blame Paul
Can't take the effect
And make it the cause

I ain't the reason that you gave me
No reason to return your call
You built a house of cards
And got shocked when you saw them fall
Well I ain't saying I'm innocent
In fact the reverse
But if your heading to the grave
you Don't blame the hearse
You're like a little girl yelling at her brother
Cause you lost his ball

You keep blaming me for what you did
And that ain't all
The way you clean up the wreck
Is enough to give one pause
You seem to forget just how this song started
I'm reacting to you
because you left me broken hearted

See you just can't just take the effect and make it the cause

Re:First before I even posted! (-1, Offtopic)

Progman3K (515744) | more than 2 years ago | (#39787871)

Liked it, would read again

Re:First before I even posted! (0)

Anonymous Coward | more than 2 years ago | (#39787327)

That's because I just decided so.

Premature ejaculation (-1)

Anonymous Coward | more than 2 years ago | (#39787265)

So I can jizz in your dad's ass before insertion? So now we have to worry about quantum premature ejaculation events?

Re:Premature ejaculation (-1)

Anonymous Coward | more than 2 years ago | (#39787947)

So I can jizz in your dad's ass before insertion? So now we have to worry about quantum premature ejaculation events?

No. Since it's all you've ever had you can just carry on as usual.

WILDCAT IS ON TEH SPOKE (-1)

Anonymous Coward | more than 2 years ago | (#39787271)


In other quantum news . . . (5, Funny)

Tanman (90298) | more than 2 years ago | (#39787321)

Nevermind -- why bother telling you if you already know :-(

I for one welcome... (-1)

Anonymous Coward | more than 2 years ago | (#39787323)

our self-determining photon overlords!

Time delay - info from the future? (1)

noh8rz3 (2593935) | more than 2 years ago | (#39787337)

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!

Re:Time delay - info from the future? (5, Informative)

Anonymous Coward | more than 2 years ago | (#39787405)

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

Re:Time delay - info from the future? (2)

hvm2hvm (1208954) | more than 2 years ago | (#39787557)

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...

Re:Time delay - info from the future? (-1)

Anonymous Coward | more than 2 years ago | (#39787603)

Yep, I am also a huge fan of crashing stock markets. They are very cool indeed.

Re:Time delay - info from the future? (4, Funny)

Anonymous Coward | more than 2 years ago | (#39787741)

They want sub-millisecond latency on high-frequency transactions? We'll give them negative latency! Let's see what they do then!

Re:Time delay - info from the future? (2)

Binestar (28861) | more than 2 years ago | (#39787579)

Article says! It's on the order of 14billionths of a second.

Re:Time delay - info from the future? (4, Informative)

slew (2918) | more than 2 years ago | (#39787943)

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.

Cabling? (4, Funny)

number6x (626555) | more than 2 years ago | (#39787653)

FTFA:

That little bit of cabling was enough to ensure that anything that happened at Victor occurred after Alice and Bob had done their measurements.

They probably hired the cable guy that got fired from CERN [wikipedia.org] a few months ago.

Re:Cabling? (5, Funny)

uigrad_2000 (398500) | more than 2 years ago | (#39787809)

They actually decided to one-up the CERN-OPERA people.

They fired the cable guy before they even hired him!

Re:Time delay - info from the future? (5, Informative)

Baloroth (2370816) | more than 2 years ago | (#39787723)

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.

Now they've done it (0)

Anonymous Coward | more than 2 years ago | (#39787345)

These damn physicists have proven that God does not exist. Any proof with the PSR as the hypothesis is now moot.

Re:Now they've done it (5, Funny)

Yvan256 (722131) | more than 2 years ago | (#39787535)

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.

Re:Now they've done it (0)

Anonymous Coward | more than 2 years ago | (#39787807)

How do you arrive at that conclusion, exactly?

Sigh... (5, Funny)

InvisibleClergy (1430277) | more than 2 years ago | (#39787373)

*Looks at physics degree.*

*Tosses it in the trash.*

Re:Sigh... (5, Funny)

cdrudge (68377) | more than 2 years ago | (#39787561)

Shouldn't that be updated to be:

*Tosses it in the trash*

*Looks at physics degree*

Re:Sigh... (1, Funny)

Yetihehe (971185) | more than 2 years ago | (#39787751)

Top-posting

No, what?

Do you know what is the worst practice on usenet?

Paradoxical (5, Funny)

myrdos2 (989497) | more than 2 years ago | (#39787375)

Victor should decide not to entangle the photons whenever Alice and Bob's polarizations are correlated. That'll rip physics a new one...

Re:Paradoxical (1)

bill_mcgonigle (4333) | more than 2 years ago | (#39787527)

shhh! That's the halt instruction for our universe.

Re:Paradoxical (1)

myrdos2 (989497) | more than 2 years ago | (#39787611)

Hmmm... if we were to keep Alice and Bob one light-millisecond from Victor, could we send messages back in time? Imagine we're continually repeating the process of emitting photons as in the summary.

1) An earthquake happens. Victor entangles the photons.
2) Alice and Bob detect correlated polarizations, and instruct Victor to entangle his photons.
3) This process continues, bringing us one millisecond backwards in time at each step. (Minus the time to perform the measurements and inform Victor)
4) Lab staff notice that Alice and Bob have spontaneously correlated polarizations, and deduce that a disaster will shortly occur.

Re:Paradoxical (1)

hvm2hvm (1208954) | more than 2 years ago | (#39787727)

Yeah, I really like that. Kind of like the signals sent in medieval times (and in LOTR for example) by lighting up torches(towers) at predefined locations in a domino effect.

Still, creating a paradox would be cooler - i.e. telling victor to entangle the photons when they get different results or vice versa. Maybe that makes time go backwards or something like that just to avoid the paradox

Re:Paradoxical (1)

dward90 (1813520) | more than 2 years ago | (#39787747)

I'm not sure how serious you are, but I'll point out the problem at the risk of killing the joke. The issue is in step 2. Photons travel at the speed of light (by definition). Because we cannot send information faster than the speed of light, the photons arrive at Victor strictly before any message from Alice and Bob.

Re:Paradoxical (1)

myrdos2 (989497) | more than 2 years ago | (#39787819)

I suppose using any of these techniques to slow light would destroy the entanglement? http://en.wikipedia.org/wiki/Slow_light [wikipedia.org]

Re:Paradoxical (1)

skids (119237) | more than 2 years ago | (#39787823)

Photons can also bend their paths, so just because they travel from Alice/Bob to Victor doesn't mean Victor is that many light-meters away. The photon could be traveling in a circle. But then, I don't know what that does to polarization :-)

Re:Paradoxical (2)

Baloroth (2370816) | more than 2 years ago | (#39787829)

Not true: we can make photons travel much much slower than c (the speed of light in a vacuum), while transmitting the information up to c, which means we could certainly communicate information faster than the photons travel to Victor. In fact, most fiber optic cables IIRC transmit light at ~3/4 the speed of light in a vacuum.

Of course, it still almost certainly wouldn't work. I actually wouldn't be surprised if anyone setting up such a system noticed that Victor entangling the photons didn't correlate Alice/Bob's photons once Alice/Bob started communicating with him before he decided to entangle them. Quantum mechanics tends to work like that: you can't really use the effect to transmit information.

Re:Paradoxical (1)

myrdos2 (989497) | more than 2 years ago | (#39787941)

Sigh. You're probably right. Still, I've been fascinated by the tantalizing possibility of using quantum effects for communication since reading this: http://www.sciencemag.org/content/321/5897/1812.short [sciencemag.org]

Re:Paradoxical (4, Interesting)

Ruie (30480) | more than 2 years ago | (#39787917)

I'm not sure how serious you are, but I'll point out the problem at the risk of killing the joke. The issue is in step 2. Photons travel at the speed of light (by definition). Because we cannot send information faster than the speed of light, the photons arrive at Victor strictly before any message from Alice and Bob.

Just use a fiber optic cable to make them wait longer. Or bounce between mirrors in a zigzag - this way light trajectory can be long, but the spatial distance can be short.

Re:Paradoxical (2)

TexVex (669445) | more than 2 years ago | (#39787637)

Entanglement implies correlation, but correlation does not imply entanglement.

Re:Paradoxical (1)

hvm2hvm (1208954) | more than 2 years ago | (#39787771)

Same thing... Entanglement implies correlation -> if victor decides not to entangle the photons (for whatever reasons) and alice and bob get uncorrelated measurements it's still a paradox, isn't it?

Re:Paradoxical (1)

John Bayko (632961) | more than 2 years ago | (#39787651)

Victor should decide not to entangle the photons whenever Alice and Bob's polarizations are correlated. That'll rip physics a new one...

That would require observing the Alice / Bob results first, thus "changing" the Victor photons before he can do anything.

Re:Paradoxical (1)

hvm2hvm (1208954) | more than 2 years ago | (#39787787)

So once victor knows from alice and bob whether the measurements are correlated, the photons are already entangled/not entangled? That seems like a method for passing information into the future...

Re:Paradoxical (1)

hvm2hvm (1208954) | more than 2 years ago | (#39787795)

We now have a bidirectional time machine.

Re:Paradoxical (1)

wonkey_monkey (2592601) | more than 2 years ago | (#39787705)

Wouldn't it be more interesting for Victor to entangle when Alice and Bob's polarizations aren't correlated? What would that mean?

Re:Paradoxical (0)

Anonymous Coward | more than 2 years ago | (#39787821)

Thanks to Bob, Victor and Alice dumb people can enjoy this story too!

Re:Paradoxical (1)

CanHasDIY (1672858) | more than 2 years ago | (#39787945)

Victor should decide not to entangle the photons whenever Alice and Bob's polarizations are correlated. That'll rip physics a new one...

Sounds like the most boring ménage à trois in human history...

Past, present, and future :D

Loose wire? (1)

Anonymous Coward | more than 2 years ago | (#39787377)

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.

Re:Loose wire? (1)

pushing-robot (1037830) | more than 2 years ago | (#39787831)

I wouldn't worry. After seeing the results, the researchers said they'll be extremely careful when they actually perform the experiment.

So what (1)

koan (80826) | more than 2 years ago | (#39787381)

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.

Re:So what (1)

Anonymous Coward | more than 2 years ago | (#39787451)

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.

>Time's arrow shown to point both ways. Slashdotter unimpressed.

Reads like an Onion article.

Re:So what (1)

NatasRevol (731260) | more than 2 years ago | (#39787681)

Onion comment?

Re:So what (0)

Anonymous Coward | more than 2 years ago | (#39787549)

So what if passing air over a certain shape causes a slight vacuum above it and more pressure below it. It's irrelevant as there isn't anything practical we can do with... oops, gotta catch my flight!

I'm hoping you're not employed in any field which requires an inquiring mind.

causality (4, Interesting)

Black Parrot (19622) | more than 2 years ago | (#39787385)

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.

Re:causality (0)

Anonymous Coward | more than 2 years ago | (#39787423)

Remember, if researchers have free will, then so do elementary particles. [wikipedia.org]

Re:causality (3, Funny)

RyuuzakiTetsuya (195424) | more than 2 years ago | (#39787461)

Given that now cause/effect are now uncertain...

are you sure about that? :)

Re:causality (0)

Anonymous Coward | more than 2 years ago | (#39787521)

Riiiiiiiiight... and neutrinos are now superluminal.

Re:causality (1)

skids (119237) | more than 2 years ago | (#39787589)

the notion that information can't be transferred faster than the speed of light is based on the fact that it would violate causality

Well, it would pose problems to the way modern physics interprets the concept of spacetime (and not without ample experimental evidence.). If you asked someone with a more newtonian view of the universe, something traveling over the speed of light isn't going back in time, and so there's no causality violation.

Anyway this experiment would seem to leave open the question as to whether the Victor measurement could be performed in time to inform Alice and Bob, unless that can be ruled out by other factors.

Re:causality (1)

Tempest451 (791438) | more than 2 years ago | (#39787607)

Personally, I think causality is an abstract like infinite mass. The mathematics make the claim in infinite mass at light speed, without factoring in the effects to space-time itself.

Re:causality (1)

Tempest451 (791438) | more than 2 years ago | (#39787627)

If you accept that matter can never occupy the exact same space at the exact same time, you become assured that you can never move fast enough to catch yourself before you start.

Re:causality (-1)

Anonymous Coward | more than 2 years ago | (#39787689)

Stop assuming nothing can travel faster than the speed of light.

We have 'proof' that the speed of light is not constant over time, the universe would not exist in its current configuration if the speed of light was the absolutely limit of speed.

In this particular case, all information was coordinated in the past, so events lead up to the observations in the experiment.

Its like calling in for a pizza tomorrow at 6pm, then tomorrow at 5:55pm telling your wife that you were going to go back in time and order a pizza so it would arrive in 5 minutes, the only difference is in this experiment, the scientists haven't figured out that they made that phone call a day a head of time.

If this was truly effect before cause, then you could trigger effect without cause by observing the effect and then never performing the cause because you could observe the effect and then decide not to do the cause.

Re:causality (2)

Chris Burke (6130) | more than 2 years ago | (#39787805)

I have wondered whether causality is an assumption rather than an actual property of the universe.

Causality is absolutely an assumption, one that physicists have understood that they are making -- among others -- for a long time. It might be an invalid assumption that only appears to be correct most of the time.

And what a fucking weird world would that be? Could we even reason about such a universe? It might be impossible.

I know I'm not going to let go of this assumption until there is some very, very convincing evidence.

OK... (2)

dc5464 (869897) | more than 2 years ago | (#39787431)

I don't even know where to begin with this one.

Re:OK... (2, Funny)

Anonymous Coward | more than 2 years ago | (#39787531)

don't worry, you've already decided......

Conclusions posted before Experiment (0)

Anonymous Coward | more than 2 years ago | (#39787439)

Better re-check that cable, first.

T-minus... (2)

dmitrybrant (1219820) | more than 2 years ago | (#39787453)

one month until a New-age quack publishes a book on how to harness this phenomenon for better health, improved intimacy, and financial success!

There's a simplier solution (5, Funny)

Grayhand (2610049) | more than 2 years ago | (#39787459)

Victor is Bipolarized making him erratic and unpredictable. Might want to try adding lithium atoms into the mix and see if the results stabilize.

Re:There's a simplier solution (4, Funny)

Victor_0x53h (1164907) | more than 2 years ago | (#39787721)

<sigh>

This is really first post (0)

Anonymous Coward | more than 2 years ago | (#39787471)

The effect happened before the cause.

Great Deal... (2)

M0j0_j0j0 (1250800) | more than 2 years ago | (#39787483)

I was already confused before reading the article, that proves effect before cause.

Maybe I'm Understanding This Wrong (1)

mentil (1748130) | more than 2 years ago | (#39787507)

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.

Re:Maybe I'm Understanding This Wrong (2)

plalonde2 (527372) | more than 2 years ago | (#39787693)

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.

The new get rich scheme! (4, Funny)

agent_vee (1801664) | more than 2 years ago | (#39787509)

1. PROFIT!!!
2. ???
3. Collide some photons!

Re:The new get rich scheme! (4, Funny)

DeadDecoy (877617) | more than 2 years ago | (#39787709)

That sounds like how most grant-funded research occurs.

Finally! (0)

MobileTatsu-NJG (946591) | more than 2 years ago | (#39787517)

Now they've found a way to prove that video games cause violence!

Extraordinary Claims Require Extraordinary Proofs (0)

Anonymous Coward | more than 2 years ago | (#39787525)

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.

Thus (0)

Anonymous Coward | more than 2 years ago | (#39787529)

P = NP

time delay from ars technica (0)

Anonymous Coward | more than 2 years ago | (#39787539)

forgive the flamebait AC...
It appears a causality disturbance allowed slashdot to post this after ars technica did yesterday.

Is It Effect Before Cause? (0)

Anonymous Coward | more than 2 years ago | (#39787571)

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.

Re:Is It Effect Before Cause? (1)

mcavic (2007672) | more than 2 years ago | (#39787815)

That's kind of what I was thinking. I don't know much about quantum mechanics, but I believe one of the premises is that the act of making an observation can affect the outcome of that observation. When we think that Alice is predicting Victor's choice, how do we know that Alice isn't actually determining Victor's choice?

Re:Is It Effect Before Cause? (1)

hvm2hvm (1208954) | more than 2 years ago | (#39787881)

If I RTFA correctly it's the second case but with another measurement at the end for good measure (hehe)... But you are right, if it's the first case, this is basically just quantum physics being wacky.

Re:Is It Effect Before Cause? (1)

ciggieposeur (715798) | more than 2 years ago | (#39787897)

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.

Their "equipments' observation" is their observation. There's nothing special about sentience.

Reality versus Obeservation (5, Interesting)

Anonymous Coward | more than 2 years ago | (#39787573)

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.

That is fucking terrifying (0)

Anonymous Coward | more than 2 years ago | (#39787581)

I'm going to go hide in a closet for the next few days, hugging my knees and rocking gently back and forth.

Glitch.... (1)

richieb (3277) | more than 2 years ago | (#39787631)

Just a glitch in the matrix....

Let's violate causality! (4, Informative)

Chris Burke (6130) | more than 2 years ago | (#39787643)

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.

Re:Let's violate causality! (2)

mark-t (151149) | more than 2 years ago | (#39787869)

I might suggest that although their measurements are made before Victor's decision, I expect that the results of their measurements could not reliably be communicated to Victor prior to his decision.

Quantum Physics @ Home (4, Interesting)

narcc (412956) | more than 2 years ago | (#39787647)

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.

result of "many worlds" being true? (5, Interesting)

wierd_w (1375923) | more than 2 years ago | (#39787661)

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.

Re:result of "many worlds" being true? (1)

Anonymous Coward | more than 2 years ago | (#39787843)

Proposed Experiment.

Alice and Bob trade stocks by decisions to polarize or not to polarize a light beam. Polarize= Buy. Not Polarize= Sell.

Victor sets up his stock trading robot to entangle or not entangle and buy and sell accordingly.

Profit!

Effect without a cause (2)

Spy Handler (822350) | more than 2 years ago | (#39787665)

Subatomic laws
Scientific pause
Synchronicity

You guys *really* need to get a girlfriend. (1)

Anonymous Coward | more than 2 years ago | (#39787677)

With one of these you get this effect all the time, they go haywire *before* you do anything wrong...

the full paper (1)

Anonymous Coward | more than 2 years ago | (#39787697)

or there is no free will (2)

rritterson (588983) | more than 2 years ago | (#39787715)

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.

correlation v.s causality (0)

Anonymous Coward | more than 2 years ago | (#39787737)

when Victor selected entanglement, Alice and Bob found correlated photon polarizations

thereby giving the best possible proof that correlation does not imply causality.

ok, but... (2)

mridoni (228377) | more than 2 years ago | (#39787757)

... what happened to the cat?

Growing network of friends (1)

imbusy (1002705) | more than 2 years ago | (#39787779)

Nice to see Alice and Bob finally making friends with Victor.

So lets see if I get this (1)

medv4380 (1604309) | more than 2 years ago | (#39787785)

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?

Just one note: (0)

Anonymous Coward | more than 2 years ago | (#39787811)

Gods must be crazy ...

Why Slash and slash,slash? (0)

Anonymous Coward | more than 2 years ago | (#39787853)

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.

arXiv link to the article PDF (0)

Anonymous Coward | more than 2 years ago | (#39787859)

http://arxiv.org/pdf/1203.4834.pdf

Re: Let me get this straight... (0)

Anonymous Coward | more than 2 years ago | (#39787955)

So effects effect causes?

FTFY

Spread (1)

phorm (591458) | more than 2 years ago | (#39787957)

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.

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