Measurements on the reality of the wavefunction
nature.com
nature.com
The mainstream view in modern physics (for the past 30 or so years, I believe) is rather that the wavefunction is the fundamental description of reality, at least in the sense that classical effective knowledge theories are not plausible models.
My interpretation of this paper on quick glance is that it is an attempt to experimentally demonstrate that only effective knowledge theories with very strange properties would suffice to explain observations, thus strengthening the "wave-function is fundamental" viewpoint.
I ask from the perspective of a B.S. Physics cum computer software person... which, I think, might not be too far removed from the perspectives of most HN peeps...
Getting a solid understanding of the fundamentals of the various fields is more of a coursework sort of thing. There's a bunch of quantum lectures on MIT's open courseware - anything Allen Adams will be great. If you're a book kind of person I believe I enjoyed Shankar but it's been a while.
Have you seen the experiments of Yves Couder?
Hypothetically, if a model like that produced an exact mathematical equivalent of quantum theory wouldn't that be more satisfying? It would also destroy some of the notions that have been mathematically proven - like EPR and Bells' inequality. A lot of people are unsatisfied with QM and looking for something more tangible - including physicists.
Apparently pilot wave theory was never soundly rejected, the crowd just went in a different direction.
While I would also prefer that quantum mechanics turns out to be quite classical at its heart - with objective reality, locality and all that - it seems a pretty bad idea to expect or even assume that nature works the way we prefer it to and that it will be easily understandable for human brains. Actually, the longer we struggle to make sense of all of that, the more likely it seems to me that everything is actually radically different from the way we have looked at it for the past century.
destroying Bell's inequality would be the key. It would be very satisfying. I'd say Nobel prize and forever in history books satisfying. Unfortunately (as i myself is on the ERP side and came to a something like pivot wave on my own while trying to explain the double-slit) there is no reasonable explanation for observed Bell's violations except for the explanation by QM (which for a "realist" like me sounds just like "will of God spreading FTL" :)
Note: actually i haven't been able to find good (for my criteria) Malus law verification for single photons - the law is the basis of Bell's violation claims in photon polarization experiments. Slight modification of the law on top of Einstein's proposed modification - with resulting law being pretty reasonable for single photon situation while still preserving classic law in the case of classic light ray - actually produces the Bell violation in the classic "local realism" explanation. So i still hope a bit :)
Pilot wave theory produces the same predictions (as do all interpretations of QM), so in some sense it's valid, but it's an ugly attempt to brush the fundamentals under the carpet; it makes some simple cases simpler, but it makes the really interesting QM harder. It's not wrong, in the same way that constructing Newton's laws in a rotating frame of reference is not wrong - but it's less pleasant to work with for most interesting problems, and obfuscates the physical reality.
We might separate interpretations according to their ontology:
1. de-Broglie Bohm: The particle has a real (though hidden) configuration.
2. Many Worlds: The wavefunction is real and fundamental.
3. Ensemble/Consistent histories/Copenhagen/"Shut up and calculate": Nature is fundamentally probabilistic. Measurements have ontological status, and talking about what happens between measurements is suspect (in various ways, depending on the theory).
From what I can tell most physicists fall into category #3.
I'm unclear on which point you disagree.
For example, Griffiths (who introduced consistent histories) describes the wave function as "a mere mathematical tool or pre-probability for calculating probabilities which can, if one wants, be obtained using different solutions to Schrödinger’s equation." He goes on to contrast this to MWI and Bohmian mechanics, which treat the wave function as fundamental, are both deterministic, and are minority viewpoints. [1]
In much the same way, I don't think that particle physicists really think that matter is made of tiny strings.
I might actually buy a copy of this paper, I'd be curious to see what new experiments they have done to more closely demonstrate the physicality of the wavefunction.
Most 'media physicists' fall into category #3. It is from my understanding that most 'practicing physicists', by association, fall into category #1 (QFT).
I mean... this is fundamental human knowledge we are talking about... isn't there some better way of doing this than $32-a-pop?
>All research papers from Nature will be made free to read in a proprietary screen-view format that can be annotated but not copied, printed or downloaded...
>Annette Thomas, chief executive of Macmillan Science and Education, says that under the policy, subscribers can share any paper they have access to through a link to a read-only version of the paper’s PDF that can be viewed through a web browser.
The person who linked the original article didn't use the special link to the "free, but proprietary" format.
Nature put a paywall on top of the article and then someone published the paywalled link on HN.
But yes, my understanding is that anybody with institution access to Nature can now share a link to the Nature publication.
I suppose it is possible that Nature's version is substantially different, but if that were the case it would cast a huge shadow of doubt over Nature's editorial process, as well as the claims made in the paper itself.
Half correct. The authors retain copyright for changes due to feedback (peer review), as the authors themselves would have modified the paper to address any feedback. You are correct that the actual paper in the Nature formatting (and possibly associated copy-editing) are under Nature's copyright.
The whole argument seems to me silly, because the epistemic view requires that indistinguishable particles in fact are merely undistinguished particles. That is, the epistemic view requires that reality behaves quantum mechanically when no one is looking at it, whereas what we observe is that reality behaves quantum mechanically when no one can look at it.
These are completely different situations. In one case it is what we do know that matters--which is an epistemic state--in the other it is what we can know that matters, which is an ontic state. And it turns out that reality does limit what we can know, and this has dramatic consequences.
The clearest example of this is the heat capacity of solids. Heat capacity is a measure of how the temperature increases as you add heat energy to an object. The temperature is just the average energy per state in the material, so the heat capacity is a very direct measure of the number of states the collection of particles constituting a material can be in.
It is very simple to show that particles that cannot be distinguished have a different number of states from particles that can be distinguished even if they don't happen to be at the moment. For example, consider two coins: if they can be distinguished they have four possible states, HH, HT, TH and TT. If they can't be distinguished then HT and TH are the same state (because there is no way, even in principle, even if you're god) to distinguish the left coin from the right coin. So there are only three states.
You can do something similar with particles in a crystal lattice and show that they are indistinguishable. So it isn't a question of what we do know, but what we can know, and that is determined by ontology, not epistemology.
The problem is that the ontology of the wavefunction is non-classical in the extreme. Because it is nonlocal it violates the law of non-contradiction from the perspective of locally causal beings (us). That makes it hard to understand, but it doesn't make it any less real. It just means reality is weird, which at this point in history shouldn't come as a huge surprise to anyone.