# Relationship between cause and effect in quantum physics **URL:** \ **Category:** Factual Questions\ **Created:** [November 22, 2017, 5:06pm UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418 "2017-11-22T17:06:51Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [November 22, 2017, 5:06pm UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/1 "2017-11-22T17:06:51Z")
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](http://boards.straightdope.com/sdmb/showthread.php?t=659950) old [threads](http://boards.straightdope.com/sdmb/showthread.php?t=809327). (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](https://en.wikipedia.org/wiki/Grover%27s_algorithm#Quantum_partial_search). With n qubits, we start with a superposition of 2[sup]n[/sup] 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? ---
**Author:** ![Bone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bone/32/407_2.png) [@Bone](https://boards.straightdope.com/u/Bone)\ **Post date:** [November 23, 2017, 12:28am UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/2 "2017-11-23T00:28:51Z")
Moved from Great Debates to General Questions at OP request. [/moderating] ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [November 23, 2017, 12:29am UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/3 "2017-11-23T00:29:38Z")
Is this, like, Schroedinger’s Thread? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 23, 2017, 12:32am UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/4 "2017-11-23T00:32:22Z")
What button _did_ you push, **Bone**? ---
**Author:** ![Bone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bone/32/407_2.png) [@Bone](https://boards.straightdope.com/u/Bone)\ **Post date:** [November 23, 2017, 12:33am UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/5 "2017-11-23T00:33:35Z")
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: > [@septimus](#): > > 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](http://boards.straightdope.com/sdmb/showthread.php?t=659950) old [threads](http://boards.straightdope.com/sdmb/showthread.php?t=809327). (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](https://en.wikipedia.org/wiki/Grover%27s_algorithm#Quantum_partial_search). With n qubits, we start with a superposition of 2[sup]n[/sup] 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. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [November 23, 2017, 6:08am UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/6 "2017-11-23T06:08:54Z")
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. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [November 23, 2017, 4:05pm UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/7 "2017-11-23T16:05:56Z")
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. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [November 23, 2017, 6:27pm UTC](https://boards.straightdope.com/t/relationship-between-cause-and-effect-in-quantum-physics/802418/8 "2017-11-23T18:27:55Z")
> [@septimus](#): > > 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.