Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is retrocausality?

  1. Sep 18, 2008 #1
    i looked it up on the wiki page and was a little hard for me to understand.
  2. jcsd
  3. Sep 19, 2008 #2
    It pretty much means exactly what wiki says – You have a Timelike separated events A happening before B with some effect happen at A depending on what independent is done at B where the choice of what happens at B in not affected at all by what had already happened at B, rather that some aspect of what happens at A is caused by the result at B.

    Why would we even consider retrocausality? Because of apparent QM non-local behaviors between Spacelike separated events. (Timelike & Spacelike both on Wiki under Spacetime)

    Retrocausality, that almost no one believes is true or can be proved, is one of many unrealistic ways that might demonstrate the existence of “Non-Local” reality. But applied inside certain very limited microscopic limits the idea can work out mathematically rather nicely to describe and predict some results. Feynman diagrams are probably the most famous of those limited examples.
  4. Sep 20, 2008 #3
    wouldn't this in a way defy Qm as they theorize probablitly of all events which are relatively independent. however if A is casued by B, then it sounds very very fate like. I believe in FAte (no imnot religious im atheist) but in the scientific way. i nelieve that everythin is meant to happen due to sapce-time. space time isa llways reversing in imaginary relative perspectaves
  5. Sep 20, 2008 #4
    Well sure, so would any experimentally proven correct re-interpretation of oQM like MWI etc. If for no other reason; QM claims that no other description can be more complete that what Copenhagen QM already allows. Hence the claim to being as complete as it can get.

    The only place retrocausality has been useful is in limited unrealistic analogies (Feynman diagrams) that do not challenge the completeness of QM.

    None of the alternative interpretations of QM have come close to describing a more correct or complete view of behaviors and IMO retrocausality is far short of matching what QM can discribe.
  6. Sep 20, 2008 #5
    Starting with Newtonian mechanics. The laws of physics are time symmetrical at the level of interacting particles. The distinction between 'cause' and 'effect' is only temporal order. Cause proceeds effect. Applying retrocausality assummes a reversal in order; an absurdity.

    On top of Newtonian mechanics add thermodynamics, viscosity and friction; addition of processes that are not symmetrical on replacement of t with -t. In the case of thermodymanics the conditions that lead to 4 fast particles in one side of a box and 4 slow particles in the other side on might call trivial thermodynamic retrocausality; the entropy at a later time is only trivially decreased.

    I don't see how you apply notions of cause and effect to spacelike separated events.
  7. Sep 20, 2008 #6
    I don't - Only a Non-Local discription such as QM can.
    If you want to know how take the time to learn about "Feynman diagrams"; wiki, google, or theard scheach here all all OK IMO.
  8. Sep 20, 2008 #7
    I misspoke, then.

    I'm curious as to where causality or retrocauality has any applicability in nonlocal interpretrations of quantum mechanics. If there's really anything to say about it, as the Wikipedia article asserts without substance, I'd be interested.
  9. Sep 20, 2008 #8
    If you want to know how take the time to learn about "Feynman diagrams"; wiki, google, or theard scheach here all all OK IMO.
  10. Sep 20, 2008 #9
    You got the hiccups Randall?

    Retrocausality really has no applcability in any interpretation of QM except Cramer's "transactional" interpretation, which he speculates would allow you to send a message back in time. No other mainstram interpretation has retrocausality as a relevant or even existant feature.
  11. Sep 20, 2008 #10
    Thanks peter. I guess it's about time I looked into what Cramer's talking about.
  12. Sep 21, 2008 #11
    "You got the hiccups" I have no idea what that slang might mean - care to explain.

    Are you saying Feynman is not mainstream - Do you know what "Feynman diagrams" are?
    Care to explain to Phrak what an arrow pointing at a downward angle in a Feynman diagram means to mainstream scientist. Mainstream scientific analysis of quantum microscopic behaviors of virtual and force particles has been in use for years.

    Remember: Mainstream scientists are allowed to use Non-Local, (That includes Unrealistic) descriptions at the microscopic level as they limit themselves from extending Unrealistic assumptions to anything macroscopic..

    Did you just have a hiccup?
  13. Sep 21, 2008 #12
    It's cool, Randall, and thanks for responding. Pete was just making a small joke, not intended to offend, I'm sure.

    The problem is over interpretation of the languge. Whenever one heards talk about interpretations of quantum mechanics it's about how to interpret the meaning of fundemental quatum mechanics, rather than --I don't know--, an 'instantiation' like a quantum field theory.

    So that actually brings up a very good question: "Why leave quantum field theory out, in considering interpretations of quantum mechanics?"
  14. Sep 22, 2008 #13
    I still don’t see the joke or point in minimizing Feynman contributions to mainstream science.

    "Why leave quantum field theory out” What makes you think that is happening, there are plenty of books on QFT.
  15. Sep 22, 2008 #14
    The joke was that you repeated yourself verbatim rather than answer the man's question directly. A little passive-aggressive IMO.
  16. Sep 22, 2008 #15
    But that question could not have been asked if the repeated reply had not been already ignored and Feynman Diagrams had actually been looked up.
    So I’d see it as a pat on the back to help interrupt a series of question “hiccups” as you’d call it.

    Have you formed Your Opinion on if Feynman application of backwards time is mainstream or not yet?
  17. Sep 22, 2008 #16
    1) I do not take Feynman's application of backwards time arrows in his diagrams to be physical retrocausality so much as a hueristic. Those are two different things and Phrak was obviously talking about the former.

    2) Please see my post in forum feedback. This little exchange is what prompted it. I have nothing else to add.
  18. Sep 22, 2008 #17
    Sorry you for some reason took offense - but to be honest I could easily see my making the same PF forum complaint about your behaving sarcastically in a passive aggressive manner and bring up unrelated issues in a thread.
    But when I think I see people behave that way I assume they completely understand whatever the issue may be or my position on it – hence I have no complaint nor lose any sleep over it.
    Don’t know what to tell you other that then to adopt the same attitude.

    IMO Sudhirking and Phrak are both doing just fine, and have what they need here.
    That they see some folks have different opinions I sure comes as no surprise.

    So I'm out of this one as well, with nothing more to add.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook