hankaaron said:The key point that I am trying to make is that you must not think of the two entangled particles and wholly separate enties. They are, in essence, one particle. For each photon split through the crystal, try to think of the split particles as one. Then apply MWI of QM.
But it depends on the interpretation, no? In the Bohmian interpretion, the particles are discrete separate entities but they are both steered by a "pilot wave" which in some sense allows things that happen to one particle to influence the other particle FTL. And what about an advocate of the MWI who is also committed to the idea that the MWI should be understood in a way that preserves locality? Here it seems like it'd be more complicated to say to what extent the detection of the two particles should be viewed as causally "separate" if the detection-events have a spacelike separation...DrChinese said:Welcome to PhysicsForums, hankaaron!
I think you make a great point. Entangled particles, as well as unobserved "split" probability waves: these do not take on a classical form and do not follow classical rules. Often, when people get confused with things like DCQE or similar experiments, the issue is they are applying a classical view. Entangled photons are not really separate. And photons going through a double slit (if which path not known) do not really go through a single slit.
It's random in the sense that the experimenter can't control it, but it's not random in the sense that the probability a given idler goes to D1 or D2 must always be 50/50, even if you already know where the corresponding signal photon was detected.YLW said:Thanks JesseM but isn't the choice of whether to go to D1 or D2 made randomly by a beam splitter?
I don't think there's any real need to suppose such a thing, but it really depends on what interpretation of QM you prefer, the transactional interpretation does feature some form of backward causality while the others do not.YLW said:Thanks once again JesseM, I really have little or no physics understanding so in your view it is less likely that there is any backward causality or information traveling backwards in this case?
The problem is that all of the different "interpretations" of quantum mechanics are identical in terms of their experimental predictions, so they can't be treated as distinct scientific theories that we can test to see which is right...which one you prefer depends more on philosophical preferences than anything else. Personally I think the many-worlds interpretation is actually the simplest conceptually and so I would favor it based on [PLAIN , but that's a philosophical argument rather than a scientific one.YLW said:Sorry, one more question. So what do the majority of accepted theories advocate? And what's your view?
YLW said:Sorry, one more question. So what do the majority of accepted theories advocate? And what's your view?
From what I've gathered the MWI is more popular among physicists than the Bohm interpretation, perhaps because of its bare-bones quality of just taking the equations for wavefunction evolution between measurements in the Copenhagen interpretation, and saying those equations prevail at all times, with nothing special happening during measurements (I think some physicists who advocate the MWI as a way of thinking about QM don't actually care about whether the other branches of the universal wavefunction are 'real' in an ontological sense, though...look at Stephen Hawking's first comment here for example). Look at the poll mentioned here for example, or at Steven Weinberg's first comment in this exchange, where he follows the suggestion of a Bohm advocate to poll his colleagues on their opinions of the Bohm interpretation:Frame Dragger said:For better or worse, SQM formalism dominates, with The Copenhagen Interpretation as the backdrop. I'm not advocating that, but it's certainly the most popular.
I'd say the most popular non-standard Interpretation is The de Broglie-Bohm Pilot Wave theory, which is the only commonly accepted Hidden Variable theory to survive non-locality.
I have carried out the experiment you requested. At the regular weekly luncheon meeting today of our Theory Group, I asked my colleagues what they think of Bohm's version of quantum mechanics. The answers were pretty uniform, and much what I would have said myself.
First, as we understand it, Bohm's quantum mechanics uses the same formalism as ordinary quantum mechanics, including a wave function that satisfies the Schrodinger equation, but adds an extra element, the particle trajectory. The predictions of the theory are the same as for ordinary quantum mechanics, so there seems little point in the extra complication, except to satisfy some a priori ideas about what a physical theory should be like.
There is also the point that it does not seem possible to extend Bohm's version of quantum mechanics to theories in which particles can be created and destroyed, which includes all known relativistic quantum theories.
It is not true that the only alternative to Bohm's version of quantum mechanics is the Copenhagen interpretation, for which I share your reservations. These days most physicists who think about it at all understand quantum mechanics in terms of the Everett many-histories approach. In any case, the basic reason for not paying attention to the Bohm approach is not some sort of ideological rigidity, but much simpler --- it is just that we are all too busy with our own work to spend time on something that doesn't seem likely to help us make progress with our real problems.
JesseM said:From what I've gathered the MWI is more popular among physicists than the Bohm interpretation, perhaps because of its bare-bones quality of just taking the equations for wavefunction evolution between measurements in the Copenhagen interpretation, and saying those equations prevail at all times, with nothing special happening during measurements (I think some physicists who advocate the MWI as a way of thinking about QM don't actually care about whether the other branches of the universal wavefunction are 'real' in an ontological sense, though...look at Stephen Hawking's first comment here for example). Look at the poll mentioned here for example, or at Steven Weinberg's first comment in this exchange, where he follows the suggestion of a Bohm advocate to poll his colleagues on their opinions of the Bohm interpretation: