Revisiting the Completeness of Quantum Theory: A Scientist's Perspective

[apeiron]

Sorry for being so stubborn, but I don't see any logical contradiction between the complementarity of reality (your point) and the lack of predictive completeness of QM (my point). Both can be true at the same time. Where is the error?

Put this way, I am more in agreement. QM does predict probabilities and in this sense is not complete. The question then was who to blame? Is reality actually only ever in some definite state and so a better theory could be complete? Or is reality never fully definite, and so always inherently a little spontaneous even in the most constrained circumstances we can imagine?

I agree with the former (QM is incomplete) but disagree with the latter (QM is in-completable).

And I prefer to think QM reveals something deep about the mistaken assumptions we might be making about reality. So instead of trying to get rid of the uncertainty/nonlocality/indeterminancy, I see it as a description of the initial conditions.

 

[computerphys]

Put this way, I am more in agreement. QM does predict probabilities and in this sense is not complete. The question then was who to blame?

Heisenberg uncertainty principle, I'm afraid. It seems to be a fundamental feature of nature. We are dealing with non-deterministic processes and QM can only address some general patterns of behavior that become deterministic, but never their non-deterministic root. This limitation is due to the very concept of science, unable to deal with things not based on rules:

Morpheus: I've seen an agent punch through a concrete wall. Men have emptied entire clips at them and hit nothing but air. Yet their strength and their speed are still based in a world that is built on rules. Because of that, they will never be as strong or as fast as you can be.

Sorry for the apparently out of context citation, but think twice about it ...

The world that is built on rules is QM. But nature is superior.

Now, next question should be: why is everybody so sure that QM is complete, when, in fact it is not?

 

[GeorgCantor]

Now, next question should be: why is everybody so sure that QM is complete, when, in fact it is not?

Well Einstein might have been right after all that there is an underlying reality(and so qm is incomplete), but after Bell, if realism is to hold, that underlying reality has to involve ftl influences(non-local pilot waves, angels, gods, or some other godly influence; I reject the infinite number of universes on occam's razor grounds). Or perhaps realism is at fault, or both realism and locality altogether. It's really a personal issue and how you want to spend your life thereon. The old mechanistic, clockwork Newtonian universe is dead, so my personal feeling is that both realism and locality will go down the rabbit hole, but take your pick, if so you wish(while the option of choosing is still there).

 

[SW VandeCarr]

Heisenberg uncertainty principle, I'm afraid. It seems to be a fundamental feature of nature. We are dealing with non-deterministic processes and QM can only address some general patterns of behavior that become deterministic, but never their non-deterministic root.

The HUP is a different issue. It involves the measurement of two complementary variables, one of which can in principle be exact. If you know the exact position of a particle, you cannot know it's exact momentum and vise-verse. In fact if you think about it, you can apply the HUP to a bowling ball as well as to any moving particle wrt some reference system. To obtain the momentum, an object must move, making its position uncertain for any measure of momentum at the same time.

 

[computerphys]

The HUP is a different issue. It involves the measurement of two complementary variables, one of which can in principle be exact. If you know the exact position of a particle, you cannot know it's exact momentum and vise-verse. In fact if you think about it, you can apply the HUP to a bowling ball as well as to any moving particle wrt some reference system. To obtain the momentum, an object must move, making its position uncertain for any measure of momentum at the same time.

Your explanation of HUP is perfectly compatible with a fundamental non-deterministic behavior of the system. When you get a certain eigenvalue at a measurement outcome, QM cannot predict it because this process is non-deterministic. So, HUP is not a different issue, unless you find a logical contradiction somewhere between your point and mine.

 

[GeorgCantor]

The HUP is a different issue. It involves the measurement of two complementary variables, one of which can in principle be exact. If you know the exact position of a particle, you cannot know it's exact momentum and vise-verse. In fact if you think about it, you can apply the HUP to a bowling ball as well as to any moving particle wrt some reference system. To obtain the momentum, an object must move, making its position uncertain for any measure of momentum at the same time.

This classical description is invalid. Think about the relationship between the HUP and an electron in a box.

 

[imiyakawa]

why is everybody so sure that QM is complete, when, in fact it is not?

Everyone, you must remember computerphys's pointed definition of a complete theory (which you may disagree with, but he's just outlining a semantic category).

One that predicts experiments of results - probability distributions aren't even good enough for this theory to be complete! So, he's saying QM is in-completable if collapse to discrete state is random (and even acausal) because it doesn't fit this definition.

Based on the category he has assigned to a complete theory, he is correct if there is an acausal random element to nature. Based on other categories that you may prefer, the assertion of in-completeness in principle is incorrect.

No point debating language any more.

 

[computerphys]

No point debating language any more.

Yes, I think all this thread is related to the meaning of the word "complete". Nevertheless I find a problem accepting the mainstream concept the word "complete" has in science. Would you agree with the following case?

A.- Science has a complete explanation of the Jedi's force at Star Wars Universe.
B.- No way! Tell me, what explanation is that?
A.- None.
B.- But you told me that science had a complete explanation ...
A.- That's right. What I have just told you is all that science can say about the Jedi's force. And according to definition #1 this is a "complete theory".
B.- Oh, man, I hate scientists!

Well, it seems B is a bit disappointed about the concept of "complete theory".

In my opinion, definition #1 for a "complete theory" should be seriously considered and reviewed because it may lead to important misunderstandings. I never would say a pool is full(complete) just because I ran out of water to fill it anymore. And you?

 

[imiyakawa]

I don't think we need to discuss language categories any more. "In my opinion, definition #1 for a "complete theory" should be seriously considered and reviewed because it may lead to important misunderstandings." I'm sure physicists aren't lazying about :D There are people chasing determined interpretations and random interpretations. Where else should they be searching?

"it seems B is a bit disappointed"

It's because A. is incorrect. If acausal randomness, in the third line A. should have said "acausality". "None" is a bit misleading.

"B.- Oh, man, I hate scientists!"

B.'s annoyance is well understood, but if reality is acausally random then it's acausally random.

 

[Pythagorean]

Just to interject with some actual QM, HUP isn't the only UP. Google general uncertainty principle and read about when operators commute and eigenvector redundancies. There's no reason to focus on HUP in particular. It might even be more apropriate to review the math involved. The first google result has a discussion on it, with math.

(which in QM, the observables like position and speed are operators, not variables. The wave function is the variable)

 

[computerphys]

B.'s annoyance is well understood, but if reality is acausally random then it's acausally random.

Probably, if A hadn't told B that science had a "complete theory" for Jedi's force, B would feel much better.

The problem is not that QM is unable to explain certain experience. The problem is science claiming it to be complete, letting people misunderstand the current fundamental limitations science has found and cannot avoid.

That "acausally random" behavior of nature, should we call it "magic"? Being random, its explanation becomes unreachable by science, isn't it? What about telling people that the noise they can observe in a digital picture is "magic"?

Are all these questions irrelevant and just about "language categories"?

do you feel honest when saying QM is complete?

 

[robheus]

No scientific theory is ever complete.

 

[computerphys]

No scientific theory is ever complete.

If that is so obvious, what is the point of discussing the completeness of Quantum Theory? Why did Einstein insist at this point? Why did Bohr utter much the contrary? How many physicists do you think are there that accept the incompleteness of Quantum Theory? Very few, I'm afraid.

 

[Fuzzystuff]

If that is so obvious, what is the point of discussing the completeness of Quantum Theory? Why did Einstein insist at this point? Why did Bohr utter much the contrary? How many physicists do you think are there that accept the incompleteness of Quantum Theory? Very few, I'm afraid.

I accept that it is incomplete. I don't think science could provide a complete theory. That is my personal belief.

 

[harroxelas]

I think of it tis way:

If we think it's complete and it's in fact complete, no harm done.

If we think it's complete and it's in fact incomplete, we loose!

If we think it's incomplete and it's in fact complete, we'll just look for something that isn't there. No harm done, except that people could be working on some other field.

If we think it's incomplete and it's in fact incomplete, let the joy of discovery continue!

So I think it's best to think it's incomplete!