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    More: Interesting, quantum, Nature Physics, quantum entanglements, polarizations, winners, measurements, photons, similarities  
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5109 clicks; posted to Geek » on 25 Apr 2012 at 12:36 PM (2 years ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2012-04-25 09:33:00 AM  
[whoa.jpg}
 
2012-04-25 09:47:33 AM  
It's too early for me to read this shiat...
 
2012-04-25 10:28:35 AM  
i635.photobucket.com
Seriously, that's some trippy stuff.
 
2012-04-25 10:45:33 AM  
So basically if the present is dictated by future events, the present can change the past. I have some serious quantum linking to start doing.
 
2012-04-25 10:50:02 AM  

Tell Me How My Blog Tastes: So basically if the present is dictated by future events, the present can change the past. I have some serious quantum linking to start doing.


I'm soooo gonna remember getting a blow job while posting this.
 
2012-04-25 12:39:57 PM  
I submitted this with a better headline tommorow.
 
2012-04-25 12:40:36 PM  
Not surprised.

i.imgur.com
 
2012-04-25 12:49:23 PM  
Thiotimoline Lives.
 
2012-04-25 12:51:51 PM  
Old news is so entangling.
 
2012-04-25 12:53:33 PM  
So basically if the present is dictated by future events, the present can change the past. I have some serious quantum linking to start doing.

FTFA: "Nevertheless, this experiment provides a realization of one of the fundamental paradoxes of quantum mechanics: that measurements taken at different points in space and time appear to affect each other, even though there is no mechanism that allows information to travel between them. "


Here's what I read: Alice and Bob don't really talk to each other, but when Victor goes away on a business trip, he gets all suspicious and shiat, and when he comes back, he's all "YOU SLUT ALICE!" and that pisses off Alice, so she farks Bob because, why not? She was always curious what Bob would be like. She always loved Victor, though. But Victor is a bit jealous, and now he's gone off the deep end, so Alice thinks, fark it, he already thinks I'm farking Bob, I might as well do it. Now they're entangled.
 
2012-04-25 01:18:36 PM  
nothing more than a neat bar trick, i'll say.
 
2012-04-25 01:36:12 PM  
i239.photobucket.com

My brain is full
 
2012-04-25 01:46:16 PM  
I'm still not convinced that this doesn't all come down to physicists not really understanding what the hell is going on and not having the tools to actually be able to tell.

This back-and-forth maybe it's A or maybe it's B but it's only B if you look at C first crap seems like the exact kind of results you get when you're only seeing a part of a more complicated system that is not magic time-travel but something you just don't understand.
 
2012-04-25 02:09:43 PM  

Nicholas D. Wolfwood: Thiotimoline Lives.


+1, Asimov.
 
2012-04-25 02:13:29 PM  
What if Victor only entangles his two photons if the photons received by Alice and Bob are uncorrelated with each other?
 
2012-04-25 02:24:52 PM  
As I recall, quantum entanglement is the bases of FTL communications in the Mass Effect universe... cool stuff.
 
2012-04-25 02:31:20 PM  
The future starts tomorrow!
 
2012-04-25 02:38:37 PM  

dready zim: What if Victor only entangles his two photons if the photons received by Alice and Bob are uncorrelated with each other?


Then you defeat the entire experiment.

In a very dumbed down nutshell here's what I took away from it - they've seemed to measure that after bob and alice get 1 photon each from 2 seperate photon pairs, these photons are seperable at this point (not entangled) and measure them. Victor then gets a photon from both sets of pairs. He gets 2 photons. They are at this point seperable and not entangled. He than, unaware of what alice or bob's photon measurements were, randomly will decided to entangle or not entangle those photons. Apparently it was fairly consistent that if he entangled them bob and alices photons would show entanglement. If he didn't entangle them then bob and alice's measurements would show that their photons were seperable (not entangled).

I'm sure I've probably missed the mark, but like I said - that's what I took away from it.

Here's the actual paper - bLink
 
Skr
2012-04-25 02:43:54 PM  
In Mass Effect, I remember that the subspace communications was handled with Quantum entanglement. Pretty cool concept, basically you could flip your side off and the entangled would change state as well no matter the distance. Doing that, it could basically simulate binary 0's 1's or I suppose primitive Morse code. It was video game science, but it would be cool if it worked.
 
2012-04-25 03:04:23 PM  
Mass Effect wasn't the first to use the concept, and I'm sure it won't be the last.

Ansible
 
2012-04-25 03:14:30 PM  

AsprinBurn: Mass Effect wasn't the first to use the concept, and I'm sure it won't be the last.

Ansible


I -knew- I had seen it elsewhere as well. My first encounter with it was in Scott Cards work.

Thanks for the link. :-)
 
2012-04-25 03:30:40 PM  

CrazedHatter: As I recall, quantum entanglement is the bases of FTL communications in the Mass Effect universe... cool stuff.


The down side in this experiment was that no matter what Victor did on his end, Alice's photon was only turned green or red. Most of the other scientist felt like this was a big let down after the build up Victor had done.
 
2012-04-25 04:12:21 PM  
FTFA: "delayed-choice entanglement swapping"

Ah, my new "go-to" phrase to explain why my first marriage failed!

//see, today was not a total waste.
 
2012-04-25 05:22:12 PM  

cefm: I'm still not convinced that this doesn't all come down to physicists not really understanding what the hell is going on


To some extent, yes, that's true. The challenge is (partly) this:

The world of everyday experience takes place in 3 space dimensions and one of time. We describe systems by where each piece is and when it is there. Four coordinates.

But quantum systems aren't like that at all. The "space" they take place in is a configuration space. The whole system is at one point in the configuration space, even though the pieces are at different places in regular spacetime.

Here's an analogy that might help: imagine you have a sealed black box. You can only measure its volume, temperature and pressure; and you can draw a three-dimensional graph with axes of volume, temperature and pressure, showing the "position" of the box in the V/T/P "configuration space". You could even plot its path through that space over time as it cools and the pressure drops, say. The important thing though is that although the box is filled with billions of atoms all zipping around in regular space, the entire box is only at one point in V/T/P configuration space at any instant. Make sense?

And quantum systems are essentially like that (only their configuration space has many more dimensions). When two photons are entangled, as in this and other "spooky action at a distance" experiments, they become a system that is at one point in configuration space, even though they might be widely separated in regular time and space; so as far as QM is concerned its not a problem for measurements of them to be instantly correlated. As far as the math of QM is concerned, this experiment does exactly what you would predict.

Back to your original comment: Although physicists know how to work the math, nobody really knows whether conventional spacetime is more fundamental or configuration space is more fundamental. If spacetime is more fundamental and configuration space is no more than a tool for calculating outcomes, we need a deeper understanding of QM in order to explain what the hell is going on in entanglement experiments. If configuration space is more fundamental, we need to figure out how spacetime emerges, and this is intimately connected with all the other questions of how quantum uncertainty washes out in the macroscopic world.

/The above explanation is technically completely wrong in every important way, but it may help you to visualize what is going on
 
2012-04-25 05:35:31 PM  

monkybunney: dready zim: What if Victor only entangles his two photons if the photons received by Alice and Bob are uncorrelated with each other?

Then you defeat the entire experiment.

In a very dumbed down nutshell here's what I took away from it - they've seemed to measure that after bob and alice get 1 photon each from 2 seperate photon pairs, these photons are seperable at this point (not entangled) and measure them. Victor then gets a photon from both sets of pairs. He gets 2 photons. They are at this point seperable and not entangled. He than, unaware of what alice or bob's photon measurements were, randomly will decided to entangle or not entangle those photons. Apparently it was fairly consistent that if he entangled them bob and alices photons would show entanglement. If he didn't entangle them then bob and alice's measurements would show that their photons were seperable (not entangled).

I'm sure I've probably missed the mark, but like I said - that's what I took away from it.



No, that's a pretty good explanation. Alice and Bob each create a pair of entangled photons; if Victor takes the two spare photons from Alice and Bob and entangles them in turn, all four photons are now entangled with each other.

BUT the reason you can't use this for communication (scifi games, books and movies aside) is this: The only way you can tell if anything strange happened is to bring all the measurements made by Alice, Bob and Victor together. If Alice looks at her own results, it looks like a random series of outcomes, up or down (say). It's only when she brings her results to Bob that they go "woah! everytime I measured Up, you measured Down!" (this is what the "correlated" part means in the description) -- and of course the business of bringing the results together for comparison can't be done faster than the speed of light, thus preserving causality. Neat, no?
 
2012-04-25 05:47:50 PM  

czetie: BUT the reason you can't use this for communication (scifi games, books and movies aside) is this: The only way you can tell if anything strange happened is to bring all the measurements made by Alice, Bob and Victor together. If Alice looks at her own results, it looks like a random series of outcomes, up or down (say). It's only when she brings her results to Bob that they go "woah! everytime I measured Up, you measured Down!" (this is what the "correlated" part means in the description) -- and of course the business of bringing the results together for comparison can't be done faster than the speed of light, thus preserving causality. Neat, no?


Are you sure? Isn't the point less about comparing the two to say "woah" and more of just using it to see positive vs. negative spin and that acting like a computer bit? Not to really call Mass Effect 'correct on the physics' but my non-PHD brain seems to think that would make sense. You quantum entangle two particles. Take one with you and leave the other at home base and watch it. If it suddenly shifts it spin, that means something. You don't need to go back and compare it to the home-base particle, you'd just know that it shifted because someone told the home-base particle to shift.

Or am I thinking about this wrong? can you not just sit there and watch for the particle to start spinning in a different way?
 
2012-04-25 07:10:23 PM  

OceanVortex: czetie: BUT the reason you can't use this for communication (scifi games, books and movies aside) is this: The only way you can tell if anything strange happened is to bring all the measurements made by Alice, Bob and Victor together. If Alice looks at her own results, it looks like a random series of outcomes, up or down (say). It's only when she brings her results to Bob that they go "woah! everytime I measured Up, you measured Down!" (this is what the "correlated" part means in the description) -- and of course the business of bringing the results together for comparison can't be done faster than the speed of light, thus preserving causality. Neat, no?

Are you sure? Isn't the point less about comparing the two to say "woah" and more of just using it to see positive vs. negative spin and that acting like a computer bit? Not to really call Mass Effect 'correct on the physics' but my non-PHD brain seems to think that would make sense. You quantum entangle two particles. Take one with you and leave the other at home base and watch it. If it suddenly shifts it spin, that means something. You don't need to go back and compare it to the home-base particle, you'd just know that it shifted because someone told the home-base particle to shift.

Or am I thinking about this wrong? can you not just sit there and watch for the particle to start spinning in a different way?


OK, that's an extremely common misconception (and one that's perpetuated by sloppy journalism). Let's say Alice stays at home with particle A and Bob goes off to Betelgeuse with particle B and he wants to use entanglement to let Alice know the moment he arrives.

The simple version is this: When Bob measures the spin of his particle, he gets a particular result -- let's say Up. He immediately knows that Alice will measure Down when she measures her particle. BUT Alice doesn't notice anything happen to her particle unless she measures it -- by definition, to "notice" something you have to measure something -- and when she does, she will find it is spin Down, and she knows Bob measured Up. The result each one gets is completely random... apart from the fact that they are guaranteed to be opposite each other.

The tricky part about entanglement (and the part that journos often make confusing) is that only the acts of measurement are connected: Bob can't force his particle into the Up orientation and have that cause Alice's particle to go spin Down. Changes made to one particle aren't communicated to the other. As soon as Bob does something to change the spin of particle B, it is no longer entangled with particle A, so Alice detects no change. The only thing either Bob or Alice can do is to measure their own particle's spin, and thereby know what the other will measure.

Now, this leads to a more sophisticated argument (which is actually what I think you're suggesting). Before either Alice or Bob measures their particle, both A and B are in a quantum superposition -- either one could turn out to be Up or Down, as long as the results correlate. So you might ask "Aha! If Bob's measurement causes the quantum superposition to collapse, can Alice use the fact of the superposition collapsing to receive the "I'm here" message from Bob?" Or even better, if they have several pairs, Bob can send a binary message by choosing to measure and thus collapse some of his particles, using "collapsed" to mean 1 and "superposed" to mean 0. Unfortunately, that doesn't work either. The argument is a bit more subtle than I can get into here, but basically the only way for Alice to know whether the state of particle A is collapsed or not is to measure it in a way that causes it to collapse or to break it's entanglement. All she gets out of the measurement is an Up or Down -- and there's no way for her to know whether she measured first, causing her particle to collapse to Up or Down, or whether Bob measured first and A's state was already collapsed. This is the point where people usually go "No, but, what about..." and unfortunately we're into a chapter or two of a really good popular physics text to understand why there really are no loopholes.

But the key thing in all of this is that entanglement is a read-only state: changing B doesn't change A, but reading B determines what will be read from A.

Entanglement is really hard to explain because nothing in the macroscopic world behaves remotely like it. It's so counterintuitive in fact that some physicists argue that entanglement is the defining characteristic of quantum behavior, and that it would make more sense to start with entanglement as a given and derive all the other unexpected behaviors of quantum systems from there than the other way around.
 
2012-04-25 07:51:13 PM  

czetie: OceanVortex: czetie: BUT the reason you can't use this for communication (scifi games, books and movies aside) is this: The only way you can tell if anything strange happened is to bring all the measurements made by Alice, Bob and Victor together. If Alice looks at her own results, it looks like a random series of outcomes, up or down (say). It's only when she brings her results to Bob that they go "woah! everytime I measured Up, you measured Down!" (this is what the "correlated" part means in the description) -- and of course the business of bringing the results together for comparison can't be done faster than the speed of light, thus preserving causality. Neat, no?

Are you sure? Isn't the point less about comparing the two to say "woah" and more of just using it to see positive vs. negative spin and that acting like a computer bit? Not to really call Mass Effect 'correct on the physics' but my non-PHD brain seems to think that would make sense. You quantum entangle two particles. Take one with you and leave the other at home base and watch it. If it suddenly shifts it spin, that means something. You don't need to go back and compare it to the home-base particle, you'd just know that it shifted because someone told the home-base particle to shift.

Or am I thinking about this wrong? can you not just sit there and watch for the particle to start spinning in a different way?

OK, that's an extremely common misconception (and one that's perpetuated by sloppy journalism). Let's say Alice stays at home with particle A and Bob goes off to Betelgeuse with particle B and he wants to use entanglement to let Alice know the moment he arrives.

The simple version is this: When Bob measures the spin of his particle, he gets a particular result -- let's say Up. He immediately knows that Alice will measure Down when she measures her particle. BUT Alice doesn't notice anything happen to her particle unless she measures it -- by definition, to "notice" something you have to measure something -- and when she does, she will find it is spin Down, and she knows Bob measured Up. The result each one gets is completely random... apart from the fact that they are guaranteed to be opposite each other.

The tricky part about entanglement (and the part that journos often make confusing) is that only the acts of measurement are connected: Bob can't force his particle into the Up orientation and have that cause Alice's particle to go spin Down. Changes made to one particle aren't communicated to the other. As soon as Bob does something to change the spin of particle B, it is no longer entangled with particle A, so Alice detects no change. The only thing either Bob or Alice can do is to measure their own particle's spin, and thereby know what the other will measure.

Now, this leads to a more sophisticated argument (which is actually what I think you're suggesting). Before either Alice or Bob measures their particle, both A and B are in a quantum superposition -- either one could turn out to be Up or Down, as long as the results correlate. So you might ask "Aha! If Bob's measurement causes the quantum superposition to collapse, can Alice use the fact of the superposition collapsing to receive the "I'm here" message from Bob?" Or even better, if they have several pairs, Bob can send a binary message by choosing to measure and thus collapse some of his particles, using "collapsed" to mean 1 and "superposed" to mean 0. Unfortunately, that doesn't work either. The argument is a bit more subtle than I can get into here, but basically the only way for Alice to know whether the state of particle A is collapsed or not is to measure it in a way that causes it to collapse or to break it's entanglement. All she gets out of the measurement is an Up or Down -- and there's no way for her to know whether she measured first, causing her particle to collapse to Up or Down, or whether Bob measured first and A's state was already collapsed. This is the point where people usually go "No, but, what about..." and unfortunately we're into a chapter or two of a really good popular physics text to understand why there really are no loopholes.

But the key thing in all of this is that entanglement is a read-only state: changing B doesn't change A, but reading B determines what will be read from A.

Entanglement is really hard to explain because nothing in the macroscopic world behaves remotely like it. It's so counterintuitive in fact that some physicists argue that entanglement is the defining characteristic of quantum behavior, and that it would make more sense to start with entanglement as a given and derive all the other unexpected behaviors of quantum systems from there than the other way around.


That is incredibly interesting and helpful, thanks! That makes much more sense. You were right, I was confusing the concept of "adding spin" with simply observing the spin. So there isn't a way for Alice to "know" whether what she was observing was random (because Bob wasn't there yet) or directly related to what Bob was doing (his signal).

Just as one more round of "what if"... If they had a pre-determined time of observation ("at Noon tomorrow, Bob should observe the particle, then Alice knows to look at it at 12:01") would that help? So Alice knows her observation is directly related to the fact that Bob already observed it? Or do we face the same problem that Bob can't control what happens to the particle, so all Alice will see is that the spin is "up", she'll know that means that Bob's spin is "down"... but so what?

I suppose Alice can sleep better at night feeling a small connection to her secret lover Bob, somewhere out there in the universe, knowing at least something about him... that his pet proton's spin is "down".
 
2012-04-25 07:56:10 PM  

OceanVortex: czetie: OceanVortex: czetie: BUT the reason you can't use this for communication (scifi games, books and movies aside) is this: The only way you can tell if anything strange happened is to bring all the measurements made by Alice, Bob and Victor together. If Alice looks at her own results, it looks like a random series of outcomes, up or down (say). It's only when she brings her results to Bob that they go "woah! everytime I measured Up, you measured Down!" (this is what the "correlated" part means in the description) -- and of course the business of bringing the results together for comparison can't be done faster than the speed of light, thus preserving causality. Neat, no?

Are you sure? Isn't the point less about comparing the two to say "woah" and more of just using it to see positive vs. negative spin and that acting like a computer bit? Not to really call Mass Effect 'correct on the physics' but my non-PHD brain seems to think that would make sense. You quantum entangle two particles. Take one with you and leave the other at home base and watch it. If it suddenly shifts it spin, that means something. You don't need to go back and compare it to the home-base particle, you'd just know that it shifted because someone told the home-base particle to shift.

Or am I thinking about this wrong? can you not just sit there and watch for the particle to start spinning in a different way?

OK, that's an extremely common misconception (and one that's perpetuated by sloppy journalism). Let's say Alice stays at home with particle A and Bob goes off to Betelgeuse with particle B and he wants to use entanglement to let Alice know the moment he arrives.

The simple version is this: When Bob measures the spin of his particle, he gets a particular result -- let's say Up. He immediately knows that Alice will measure Down when she measures her particle. BUT Alice doesn't notice anything happen to her particle unless she measures it -- by definition, to "notice" some ...


Hey, *she* came on to *me*...what was I supposed to do about it? Victor wasn't around.

Besides, it was just the one time...we're over it.
 
2012-04-25 08:11:11 PM  

OceanVortex: If they had a pre-determined time of observation ("at Noon tomorrow, Bob should observe the particle, then Alice knows to look at it at 12:01") would that help?


Not terribly. First off, "noon tomorrow" varies based on where you are. I'm not just talking about timezones, but the actual passage of time- Relativity is a biatch, that way. It's impossible to make things simultaneous. But even if you worked through the math and got people to observe the particle at the same time, all you've done is flipped a coin onto a glass table. The person standing over the table sees heads, the person lying under it sees tails. The coin doesn't let them communicate anything.

czetie: But quantum systems aren't like that at all. The "space" they take place in is a configuration space. The whole system is at one point in the configuration space, even though the pieces are at different places in regular spacetime.


And that's why I'm having a problem understanding where the causality violations come into play. The system isn't closed until Victor does something with his particles. So the actual state of Alice and Bob's measurements remains undefined. It's just another case of the quantum eraser, although in this case we're controlling the "erasure" by choosing which particles actually end up entangled.
 
2012-04-25 08:22:37 PM  
So...future events determine past decisions?

If I'm understanding this correctly, it means that if I make chocolate milk tomorrow, it would influence/cause my girlfriend to pick up milk and my boss to pick up chocolate syrup for me today...?

Add me to the "mind full of f*ck" camp...

/Off to take my meds and lie down.
 
2012-04-25 09:29:03 PM  

t3knomanser: And that's why I'm having a problem understanding where the causality violations come into play. The system isn't closed until Victor does something with his particles. So the actual state of Alice and Bob's measurements remains undefined. It's just another case of the quantum eraser, although in this case we're controlling the "erasure" by choosing which particles actually end up entangled.


Yes, I think that's just more sloppy journalism. There's no causality violation. What makes this interesting is that it introduces a third participant, Victor, who can decide whether or not to entangle Alice's and Bob's photons after they have measured them... so how do those photons "know" whether or not to be entangled when they are measured? This is, it has to be conceded, profoundly counterintuitive in the everyday macro world, just like other "quantum eraser" and "delayed choice" experiments that you mention; yet precisely in accordance with what the equations of QM predict. If we knew how to make sense of this (other than mathematically), we would probably understand QM much better than we do.

What is probably more impressive about this experiment is not the conceptual ground it breaks (it doesn't) but that they were able to do it all. Entanglement experiments are freakishly difficult to conduct.
 
2012-04-25 09:49:45 PM  

lowbrowdotorg: So...future events determine past decisions?

If I'm understanding this correctly, it means that if I make chocolate milk tomorrow, it would influence/cause my girlfriend to pick up milk and my boss to pick up chocolate syrup for me today...?

Add me to the "mind full of f*ck" camp...

/Off to take my meds and lie down.


No, other way around. Future decisions determine past measurements, but only sort of, and definitely not causality running backwards. Very loosely it's as if your girlfriend can buy chocolate milk and regular milk today, put one in your fridge and one in hers without looking at which is which... and which one you find in your fridge is somehow determined by something your boss does tomorrow. But not really, because macroscopic objects don't behave like that, and they don't because entanglement is a very special and very fragile state.

One way to think about entanglement is in terms of information: if you think of the up/down state of a particle as one bit, normally you'd expect two particles to have one bit each. Even when they are in a quantum state where the value of the bit isn't fixed until it's measured, there's still one bit. But when two particles are entangled, their spin states are sharing just one bit. Instead of the four possible states of two independent particles (U/U, U/D, D/U, D/D), there are only two states ((U/D, D/U). There is less information in the system than we would naively expect. And what makes this weird to us is that the two particles that share that one bit can be widely separated in space. Incidentally, this has led some physicists to suggest an approach to QM in which the amount of information is the most fundamental thing, and all this nonsense about spin states and entanglement is just us clumsily trying to impose our classical interpretation on top.
 
2012-04-25 10:18:28 PM  

czetie: lowbrowdotorg: So...future events determine past decisions?...


Czetie, you are now officially favorited as "Quantum Physics Genius" on my Fark.
Thank you very much for all the insight!
 
2012-04-26 05:40:46 AM  
All of this time-travel entanglement talk reminds me of one of the best MST3K host segments ever:

Hey, anybody seen my chicken puppet?

/Prince of Space may not be the best episode of MST3K, but it certainly ranks in the top three.
 
2012-04-26 07:22:49 AM  

OceanVortex: "Quantum Physics Genius"


If only... "simplifier/communicator of actual quantum physics genii" would be closer, but either way I'll take it :)
 
2012-04-28 12:41:47 AM  
I didn't like TFA. I'm not going to read it.
 
2012-04-28 12:57:41 AM  

cefm: I'm still not convinced that this doesn't all come down to physicists not really understanding what the hell is going on and not having the tools to actually be able to tell.

This back-and-forth maybe it's A or maybe it's B but it's only B if you look at C first crap seems like the exact kind of results you get when you're only seeing a part of a more complicated system that is not magic time-travel but something you just don't understand.


I don't suppose it might occur to that you're actually just restating the gist of TFA, though you apparently don't realise it.
 
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