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Old 11-22-2017, 12:06 PM
septimus septimus is online now
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Relationship between cause and effect in quantum physics

We've had a number of questions recently about modern physics; let me ask my own. (Perhaps this belongs in GQ, though I'm not sure there is any simple answer.)

In a very recent thread, some of our physicists suggested that the temporal relationship between cause and effect is not clear-cut. I Googled to try to find that thread, but came up only with two old threads. (I obviously missed the first thread since I was intrigued by Huw Price's ideas long before 2012.)

So ... consider Grover's algorithm for quantum computing. With n qubits, we start with a superposition of 2n states; do some calculations on these qubits; let "the wave function collapse"; and ... Presto! a solution is found faster than possible with classical computing. It seems magic, almost as though a future event (an oracle's recognition of search success) reaches backwards in time and causes the qubits to assume that desirable pattern.

My eyes glaze over long before I can properly grasp Grover's algorithm (and a simple intuitive explanation would be appreciated) but I don't think full understanding is needed for my question. I just want to ask: Is this algorithm a good example of what physicists mean when they speak of cause-effect relationship being unclear? Is it possible to speak of the future oracle "causing" the qubit behavior?

A follow-up question relates to the alleged quantum tunneling associated with the high efficiency of chlorophyll's energy conversion. Isn't this due to an algorithm like Grover's?
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Old 11-22-2017, 07:28 PM
Bone Bone is offline
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Moved from Great Debates to General Questions at OP request.

[/moderating]
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Old 11-22-2017, 07:29 PM
Ethilrist Ethilrist is offline
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Is this, like, Schroedinger's Thread?
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Old 11-22-2017, 07:32 PM
Chronos Chronos is offline
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What button did you push, Bone?
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Old 11-22-2017, 07:33 PM
Bone Bone is offline
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Ok, that was very strange. The OP was from septimus, but it was started in GD so I moved it. Now, it shows me as the thread starter. Sorry about that, septimus - I'm not sure what happened there. Here was the OP:
Quote:
Originally Posted by septimus View Post
We've had a number of questions recently about modern physics; let me ask my own. (Perhaps this belongs in GQ, though I'm not sure there is any simple answer.)

In a very recent thread, some of our physicists suggested that the temporal relationship between cause and effect is not clear-cut. I Googled to try to find that thread, but came up only with two old threads. (I obviously missed the first thread since I was intrigued by Huw Price's ideas long before 2012.)

So ... consider Grover's algorithm for quantum computing. With n qubits, we start with a superposition of 2n states; do some calculations on these qubits; let "the wave function collapse"; and ... Presto! — a solution is found faster than possible with classical computing. It seems magic, almost as though a future event (an oracle's recognition of search success) reaches backwards in time and causes the qubits to assume that desirable pattern.

My eyes glaze over long before I can properly grasp Grover's algorithm (and a simple intuitive explanation would be appreciated) but I don't think full understanding is needed for my question. I just want to ask: Is this algorithm a good example of what physicists mean when they speak of cause-effect relationship being unclear? Is it possible to speak of the future oracle "causing" the qubit behavior?

A follow-up question relates to the alleged quantum tunneling associated with the high efficiency of chlorophyll's energy conversion. Isn't this due to an algorithm like Grover's?

***
ETA: ok, not sure what happened, but the original thread was moved, and my reply got disconnected from the thread. I've merged them so now all should be right with the universe.

Last edited by Bone; 11-22-2017 at 07:35 PM.
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Old 11-23-2017, 01:08 AM
Senegoid Senegoid is offline
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It seems like septimus may not have posted his OP until after you moved it to GQ. Clearly, moving the as-yet-unposted post to GQ in turn caused him to then post it in GD so Bone could move it to GQ.
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  #7  
Old 11-23-2017, 11:05 AM
septimus septimus is online now
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This thread seems to have turned into a discussion of a thread transfer anomaly, with OP question ignored. Perhaps it would be best to close this thread. I'll start a new thread that, hopefully, will get off to a better start.
  #8  
Old 11-23-2017, 01:27 PM
samclem samclem is online now
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Quote:
Originally Posted by septimus View Post
This thread seems to have turned into a discussion of a thread transfer anomaly, with OP question ignored. Perhaps it would be best to close this thread. I'll start a new thread that, hopefully, will get off to a better start.
You got it. Closed.

samclem, moderator.
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