Quantum myth 4: The only reality is the measured reality

pellman

We are discussing the Demystifier's paper "Quantum mechanics: myths and facts". http://xxx.lanl.gov/abs/quant-ph/0609163

Previously:
Myth 1 http://www.physicsforums.com/showthread.php?t=229497
Myth 2 http://www.physicsforums.com/showthread.php?t=230693
Myth 3 http://www.physicsforums.com/showthread.php?t=232102

QM implies that there is no reality besides the measured reality

The topic here is that the claim "QM implies that there is no reality besides the
measured reality" is itself a myth. By myths we mean widely repeated statements which, true or false, are not something we can validly assert given our current understanding.

My first reaction to the topic statement is that it would be exceedingly difficult to define. However, I think what is meant here is that the results of QM imply there are no hidden variables: quantifiable aspects of physical reality which (within the formulation of QM) are unobservable but whose values influence observable quantities.

My first question has to do with the transition from section 5.2 to 5.3 & 5.4. In 5.2 we are definitely talking about a classical quantity s. All along 5.3 it seems we continue to talk about the same classical system but in a quantum-like formulation. Then in section 5.4 right after eq 40 we find the sentence,

"The fact is that if this were the case, then it would contradict the predictions of QM!"

Did we pass from classical to quantum somewhere along the way?

comote

I think this "myth" is a "myth" itself. I interpret QM not as "a-realist" as far as reality is concerned but rather agnostic. To claim anything about reality beyond the results of experiment would be outside the scope of QM(and science).

QM does not say whether or not there is a more fundamental reality beyond observation. QM simply does not concern itself with such things.

Discussing a reality beyond observation in QM, or science in general, is like trying to use science to discuss God, it's just not created to handle such questions.

dx

If they can influence observable quantities, isn't that the same as being measurable?

Demystifier

As the titles of subsections indicate, the transition from classical to quantum occurs in Sec. 5.3. Mathematics of this section is classical, but the interpretation in terms of NEW VARIABLES sigma_1 and sigma_2 is quantum. Classically, such an interpretation would be meaningless. This is all explained there, you only need to read it more carefully.

Demystifier

For an intuitive explanation of EPR, Bell, hidden variables, and all that, by an analogy from everyday life, see also
http://www.physicsforums.com/blogs/d...ariables-1477/

Aeroflech

Hmm...that doesn't look right to me. With people being used as an example, the (unspoken) assumption that there is something 'beyond' their responses that can be seen. However, in QM, you can't, even in principle, look 'behind' what quantum systems 'say'. This would not be a problem if, say, postulating a 'theory' with a 'something behind' in it implied something in the 'stories' we find that could not be predicted by 'theories' that didn't postulate as such could not accommodate without complications, then a belief in the something 'behind' the stories is justified(as much as the scientific method allows). From what I've seen, though, this is not the case with QM.

peter0302

So is the point of the "sexual" interpretation of quantum mechanics (can we call it that officially? :)) that particles lie?

pellman

I'm just too busy to post lately and will be traveling for the next month. I had hoped to get through all the myths by now. Thanks to Demystifier and everyone else. I plan to take this up again in late June.

Todd

Demystifier

It IS possible that there is something behind QM, but of course not without complications. For example, it must violate some "common-sense" properties such as locality.

Demystifier

In a sense, yes. More precisely, this property of quantum mechanics is called - contextuality. In different contexts (different measurement setups) particles behave differently.

Phrak

"I would like to think the Moon is there, even when I am not looking at it." -AE

Aeroflech

But isn't 'realism', in the end, another 'common sense' notion?

Demystifier

Of course!
Moreover, in my opinion the realism is more "common sense" than locality, which is why I find the Bohmian interpretation the most convincing interpretation of QM. (See also my blog.)

Hans de Vries

I would say say that..


Realism stands in the way of dreams like:

- mind over matter
- psychic powers
- the solipsist controlling the world by brainpower
- eternal live
- or just making the slot machine go jackpot by mental concentration.

Locality stands in the way of dreams like.

- Beam me up Scotty teleportation.
- Extragalactic space travel.
- Interactive communication with remote civilizations.


I guess only dull and boring people like me would like to see both of
them uphold, spoiling all those dreams. I would do a pretty bad job
as a pop-sci magazine editor. But hey, Realism and Locality also have
their positive sides...


Realism stands in the way of nightmares like:

- The solipsist erasing the world population when he is bored
- with his live and downloads a new game from the matrix.
- Your bank account is still there if you don't look.
- and you bank account is save from the guy who empties
- slot machines with his mental powers.

Locality stands in the way of nightmares like:

- Ultra energetic extragalactic events destroying the world
- instantaneously instead of taking billions of years to reach us.
- Remote civilizations whipping us out after they concluded that
- earth is suitable for colonization.


Additionally, Realism and Locality are very desirable for people
who have the more modest dream of understanding and figuring
out how nature works...


Regards, Hans.

Fra

I want to make a small comment in defense of observer relative views or "solipsism" :)

My view of the solipsist (the observer) information view is not that each observer is free to reason arbitrarily about what he sees and thus come up with arbitrarily twisted ideas of his environment.

IMO, what prevents such absurd things is that due to the feedback between environment and observer. The fact that the "solipsists" are communicating with each other should impose a dynamical selection. I would expect statistically there to be an emergent concensus even among solipsists so that deviations are less like to be stable enough to frequently populate the world. So while no reasoning is banned, the collective pressure from feedback from the environment will make sure there emerges a local consensus.

So even though one might think that the reasoning of a solipsist is totally arbitrary, the dynamical effect in a network of interacting solipsists would be that after all, the reasoning is not arbitrary because structures that selfcontradict also selfdestruct in a given environment. But there is still a difference as I see it between picturing a fundamental deterministic concensus or a emergent concensus by evolution and selection.

This is not unlike biology. One might say thay a yeast cell can not live in very hot water.
But noone can stop us from putting a live culture of yeast into hot water. It will probably live for some seconds and have some inital stress responses powered by internal energy pools in vain as some final struggles. So although yeast cells are not a priori banned for appearing in very hot water, they are simply unlikely to be observed there. So in the emergent sense one can say that there is not living yeast in very hot water. But that doesn't precent that this is transiently so.

So in the emergent sense, to predict a living yeast cell is very hot water is "wrong". But that doesn't mean they need to be banned from there. They are unlikely to be observerd, that's all. Similarly I imagine that certain type of solipsist reasoning is less likely, and thus wont frequently populate a given enviroment.

So in summary, a solipsist interpretation of QM doesn't imply that anything goes or that an observer can warp the galaxy by brainpower. Sure an observer can think the galaxy is warping, but unless that is supported by the feedback ina consistent way, such reasoning is not stable and won't persist.

/Fredrik

Phrak

Just so that words have meaning...

Einstein Realism- “If, without in any way disturbing a system, we can predict with certainty the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.” (from the EPR paper)

Einstein Locality- “The following idea characterizes the relative independence of objects far apart in space (A and B): external influence on A has no direct influence on B; this is known as the Principle of Local Action, which is used consistently only in field theory. If this axiom were to be completely abolished, the idea of the existence of quasi-enclosed systems, and thereby the postulation of laws which can be checked empirically in the accepted sense, would become impossible.” (via Wikipedia)

I freely admit that at times, when attempting to understand quantum mechanics, my intent was to establish realism of some sort. Not for any intellectually sound reason, but because without it, it's a problem left unresolved.

Phrak

I hope I haven't been a thread-killer, here.

These principle of locality and realism are, after all, opinion, even if they can be considered to carry substancial weight due to the source. And the last word on quantum mechanics hasn't been written just yet.