Delayed Choice Quantum Eraser get rich quick scheme

[Crow T. Robot]

I have just finished reading the wikipedia article "Delayed Choice Quantum Eraser." It contains the following paragraph:

The results from Kim, et al. have shown that, in fact, observing the second photon's path will determine the particle or wavelike behavior of the first photon at the detector, even if the second photon is not observed until after the first photon arrives at the detector. In other words, the delayed choice to observe or not observe the second photon will change the outcome of an event in the past.

So... let's assume I have the means to do such an experiment. Today (day 0) I put multiple photon pairs through the experiment, keeping all the "second" photons unobserved (in a cyclotron, maybe?). I establish an encoding method, assigning certain photon pairs to certain numbers. Using my encoding method, I deduce today's (day zero's) winning lottery number, and bet it heavily. Tomorrow (day 1), I read the paper, see the winning lottery number, and, using the encoding scheme I established on day zero, selectively observe or don't observe the proper photons, effectively sending the winning lottery number back through time to my (day zero) self.

What is wrong with this scheme? If NOTHING is wrong with this scheme, I GOT DIBS ON IT FIRST <g>!!!!!!!!

 

[Cyphermage]

I have just finished reading the wikipedia article "Delayed Choice Quantum Eraser." It contains the following paragraph:

The results from Kim, et al. have shown that, in fact, observing the second photon's path will determine the particle or wavelike behavior of the first photon at the detector, even if the second photon is not observed until after the first photon arrives at the detector. In other words, the delayed choice to observe or not observe the second photon will change the outcome of an event in the past.

So... let's assume I have the means to do such an experiment. Today (day 0) I put multiple photon pairs through the experiment, keeping all the "second" photons unobserved (in a cyclotron, maybe?). I establish an encoding method, assigning certain photon pairs to certain numbers. Using my encoding method, I deduce today's (day zero's) winning lottery number, and bet it heavily. Tomorrow (day 1), I read the paper, see the winning lottery number, and, using the encoding scheme I established on day zero, selectively observe or don't observe the proper photons, effectively sending the winning lottery number back through time to my (day zero) self.

What is wrong with this scheme? If NOTHING is wrong with this scheme, I GOT DIBS ON IT FIRST <g>!!!!!!!!

Quantum mechanical non-locality cannot be used to violate causality. This is a well-established principle. You might think you could generate entangled pairs of photons, and then tell from one of a pair what observation was made on the other one some time in the future. In reality, you must have information transmitted through a conventional channel about the other observation in order to "see" the non-local collapse.

So information can never be transmitted faster than the speed of light in a vacuum, no matter what types of things are going on involving the non-local reduction of entangled quantum states now separated by macroscopic distances or times.

Back before this aspect of non-local collapse was completely understood, there was a lot of crank science based on the notion of communication from the future to the past. Gary Zukov wrote a book called "The Dancing Wu-Li Masters," which contained some now-disproven things about non-locality and Bell's Paradox.

 

[Crow T. Robot]

Quantum mechanical non-locality cannot be used to violate causality. This is a well-established principle. You might think you could generate entangled pairs of photons, and then tell from one of a pair what observation was made on the other one some time in the future. In reality, you must have information transmitted through a conventional channel about the other observation in order to "see" the non-local collapse.

So information can never be transmitted faster than the speed of light in a vacuum, no matter what types of things are going on involving the non-local reduction of entangled quantum states now separated by macroscopic distances or times.

Back before this aspect of non-local collapse was completely understood, there was a lot of crank science based on the notion of communication from the future to the past. Gary Zukov wrote a book called "The Dancing Wu-Li Masters," which contained some now-disproven things about non-locality and Bell's Paradox.

So is the wikipedia article "wrong" in some sense? You state that "This is a well-established principle." The information in the article seems to disagree. Don't get me wrong, I don't want to argue with someone who understands this far better than I do, I just want to learn by asking the more knowledgable, via my little thought experiment.

 

[Cyphermage]

So is the wikipedia article "wrong" in some sense? You state that "This is a well-established principle." The information in the article seems to disagree. Don't get me wrong, I don't want to argue with someone who understands this far better than I do, I just want to learn by asking the more knowledgable, via my little thought experiment.

There is nothing wrong with the article. The article, in fact, specifically states...

It should be noted that causality or relativity are not actually violated by this phenomenon as no usable information actually travels faster than the speed of light, or back in time. One can only verify the results of such an experiment using normal speed of light communications.

This is consistant with what I said in my prior post, that you can only see the non-local effect if you have information transmitted via a conventional channel.

 

[Crow T. Robot]

But what mechanism prevents my scheme from working? That's what I fail to grasp from the article. It seems to say I can effect the state of a photon -in the past- but then says no meaningful information can be passed back in time. If the 'back in time" me is aware of what a state "means," via a predefined code, and the back in time me observes the photon, haven't I been sent information from my future self? If I actually tried this, would the message I received be cosmically translated to "read the last paragraph of the article?" I guess a more logical way to ask would be, "if I actually tried the experiment I proposed, it would fail. Why?"

 

[Cyphermage]

But what mechanism prevents my scheme from working? That's what I fail to grasp from the article. It seems to say I can effect the state of a photon -in the past- but then says no meaningful information can be passed back in time. If the 'back in time" me is aware of what a state "means," via a predefined code, and the back in time me observes the photon, haven't I been sent information from my future self? If I actually tried this, would the message I received be cosmically translated to "read the last paragraph of the article?" I guess a more logical way to ask would be, "if I actually tried the experiment I proposed, it would fail. Why?"

Because you need to know the result of the observation of the particle in the future in order to tell whether the particle in the past is exhibiting wavelike or particle-like properties. Although this is a tiny amount of information compared to the particle wavefunction, it is needed to correctly interpret the other measurement in a way which demonstrates non-local communication.

In other words, No Free Lunch, No Backwards in Time Communication You can Use for Anything, and No Winning the Lottery.

 

[Crow T. Robot]

HEY! I think I got it! Darn shame about the lottery, though... <g>

 

[Ziggurat]

So... let's assume I have the means to do such an experiment. Today (day 0) I put multiple photon pairs through the experiment, keeping all the "second" photons unobserved (in a cyclotron, maybe?). I establish an encoding method, assigning certain photon pairs to certain numbers.

But you can't do that. When you measure two entangled photons, you know that their polarization will be perfectly correlated. But you do not know what that polarization will be. So the future you can measure the polarization, and then know that the past you will measure the same polarization, but that polarization is still random. You can't make the photon be polarized in any particular direction prior to the measurement, which means you can't encode any information. The only acts that can force the polarization into a particular direction will also destroy the entanglement, so you won't have any correlation. The past you still only sees a randomly polarized photon, the fact that he knows it's perfectly correlated with some photon to be measured in the future still tells him no information.