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Question about Quantum mechanics

mike3

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Hi.

I saw this:

http://physicsworld.com/cws/article/news/27640

Some physicists are uncomfortable with the idea that all individual quantum events are innately random. This is why many have proposed more complete theories, which suggest that events are at least partially governed by extra "hidden variables". Now physicists from Austria claim to have performed an experiment that rules out a broad class of hidden-variables theories that focus on realism -- giving the uneasy consequence that reality does not exist when we are not observing it
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They found that, just as in the realizations of Bell's thought experiment, Leggett's inequality is violated – thus stressing the quantum-mechanical assertion that reality does not exist when we're not observing it.
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Is this right -- or is this sloppily reported? As if it's true, I'd wonder about some things. Namely, the fact that we did not always exist, and that "living organisms" are so damned fragile -- how could the universe be dependent on something so fragile to exist? And how did that fragile thing arise, if no universe could have existed "before" we did, since it depends on us to exist? That would create a seemingly very strange idea: that the universe is not 13.7 billion years old (at least), but is only a few tens or hundreds of thousands of years old (so in a sense, the "young world" Creationists would be right -- kind of, though their preferred Bible-creation date of 6,000 years would not be), and only appears to be 13.7 Gyr old. This would seem to lend credence to a sort of variation on the "omphalos" theory:

http://en.wikipedia.org/wiki/Omphalos_hypothesis

and it would also make one wonder what caused its bringing into existence at the young age. Did God really miraculously create it and then fabricate it so as to look old? It really starts to sound too YECy for comfort.

To me it makes much more sense the universe can go back 13.7 billion years, so I must either be missing something here, this is reported badly, or both... So what is it?

Does anyone have access to the paper, and is expert enough to figure out just what was determined by this experiment?

(EDIT: But maybe the Biblical date could be right -- we could have "observed" into existence all the fake evidence that humans existed earlier... :) Lol.)
 
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Disclaimer: I am not a physicist.

mike3 said:
http://physicsworld.com/cws/article/news/27640

Some physicists are uncomfortable with the idea that all individual quantum events are innately random. This is why many have proposed more complete theories, which suggest that events are at least partially governed by extra "hidden variables". Now physicists from Austria claim to have performed an experiment that rules out a broad class of hidden-variables theories that focus on realism -- giving the uneasy consequence that reality does not exist when we are not observing it
Click to expand...

They found that, just as in the realizations of Bell's thought experiment, Leggett's inequality is violated – thus stressing the quantum-mechanical assertion that reality does not exist when we're not observing it.
Click to expand...

Is this right -- or is this sloppily reported?
Click to expand...
Sloppily (or sensationally) reported. There are at least two obvious problems with the underlined sentences:
  1. The word "reality" doesn't mean what you think it means.
  2. The word "we" doesn't mean what you think it means.
In this context, the word "reality" refers to its usage in the famous paper by Einstein, Podolsky, and Rosen: "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?" The abstract of that paper begins by saying
Einstein/Podolsky/Rosen said:
In a complete theory there is an element corresponding to each element of reality. A sufficient condition for the reality of a physical quantity is the possibility of predicting it with certainty, without disturbing the system.
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Using an argument that comes perilously close to using the second sentence above as a necessary and sufficient definition of reality, EPR conclude that quantum mechanics is incomplete. That led to the search for so-called hidden variable theories.

Bell's inequalities ("On the Einstein Podolsky Rosen Paradox") (and the experimental results that violate those inequalities) showed that hidden variable theories cannot simultaneously be all of the following:
  • complete
  • realistic (in the sense of EPR)
  • compatible with local causality
For more on this, see Arthur Fine's article in the Stanford Encyclopedia of Philosophy.

As for the reporter's use of the word "we", it would appear to include elementary particles and other non-living things. Using the word "we" to mean everything is one of the usual first steps in the familiar arguments for quantum consciousness, which is woo.

Anton Zeilinger has a new book out: Dance of the Photons: From Einstein to Quantum Teleportation. That book is aimed at a popular audience, and I suspect that this news release had something to do with the book's PR campaign.

I'll quit there, and let actual physicists explain what's really at issue with Zeilinger's experiments.
 
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Dancing David said:
Here is one counter:
http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.4000v1.pdf
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I don't agree with much of anything in that article. For example, it asserts "Therefore, violation of Bell’s inequality implies that locality has to be abandoned." That's flat-out false, as there is a counter example (the "many worlds" interpretation, which violates Bell's inequality but is perfectly local).

Regarding the OP, let me re-emphasize a couple of points that W.D.Clinger made.

First, "observation" is relevant only insofar as it indicates that a large object consisting of many particles must have interacted with the system in question. Any such interaction has the same sort of effect.

Second, "reality" doesn't exist any more solidly during such an interaction than it does before or after. (If anything it's the opposite.)

What's really going on is that QM tells us that reality is truly very different from what we think it is. We don't notice the effects of QM because we ourselves are macroscopic objects, constantly "measuring" our environment as we interact with it. It's only when we do careful experiments on isolated single particles or very small collections of them that we notice that our intuitions for how things should behave - at a very, very basic level - are quite wrong.

For example, quantum mechanics tells us it's possible to have something in a state where it simultaneously has both one characteristic and its opposite (for example, it can both be spinning in one direction and the opposite direction), or two seemingly mutually exclusive properties (for example, being both in one location and another, or even under some circumstances existing and not existing). Being both large and naive, we find that strange - but that is reality.
 
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What if I only exist because some beetle looked at me? What if I only exist because some bacteria is aware of a patch of my innards?
 
Many-worlds is a fantastic concept without much to support it, though it could be true. Where does the energy come from, for example, for a new universe to continually pop up with each collapse of a particle? Does that not trouble some who hold to it as a viable scientific concept?

On the subject of locality, it would take a lot to show all the papers involved and discuss each one, but the research does indicate locality is violated even if you conceive of a many-worlds explanation of new universes by the zillions being produced instantly all the time (and then some must be erased as the collapse is reversed, which some used to think couldn't happen but has been shown to be the case).

Locality is violated clearly through entanglement. It is here to stay as a scientific theory, I believe. The simplest explanation seems to elude many in science, and that is that particles are connected via entanglement outside space-time. What Einstein called spooky action at a distance is no longer spooky once one drops outdated materialist presumptions. The physical form, the discrete form of particles is a derived or secondary function. It's root state is immaterial and so outside space-time, entangled particles are connected. They exist as one information system and are non-local. This has been repeatedly demonstrated and was predicted by quantum mechanics. The discrete form, what people think of as physical, is a product of it's existence outside space-time as an information system connected regardless of time and space. That's what QM demonstrates.

In my opinion, it's clear evidence that the universe is fundamentally immaterial.
 
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sol invictus said:
What's really going on is that QM tells us that reality is truly very different from what we think it is. We don't notice the effects of QM because we ourselves are macroscopic objects, constantly "measuring" our environment as we interact with it. It's only when we do careful experiments on isolated single particles or very small collections of them that we notice that our intuitions for how things should behave - at a very, very basic level - are quite wrong.

For example, quantum mechanics tells us it's possible to have something in a state where it simultaneously has both one characteristic and its opposite (for example, it can both be spinning in one direction and the opposite direction), or two seemingly mutually exclusive properties (for example, being both in one location and another, or even under some circumstances existing and not existing). Being both large and naive, we find that strange - but that is reality.
Click to expand...

Isn't it more that particles don't exist in any state at all as far as discrete forms but as potentials for discrete form until "observation" occurs where a form must be taken?
 
randman said:
Isn't it more that particles don't exist in any state at all as far as discrete forms but as potentials for discrete form until "observation" occurs where a form must be taken?
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I think that's one way of viewing it, but it's not the only consistent viewpoint.

(not an expert)
 
You can google Anton Zeilinger and read some of his papers and interviews. The idea of local realism is that reality exists independent of the observer. In other words, it's in a definite state regardless of us. This has been shown not to be valid for a long time in QM. Just the 2-slit experiment alone shows us that. What we think of as reality is just what genuine reality shows us. Reality itself is perhaps not so measurable.
 
As far as the hypothesis that God created the world already seemingly old like someone would a replication of an antique, there are other ways to look at the issue.

Personally, I think science will discover and is beginning to, that the past is not static. The universe is space AND time, as one system. The past may well be still being formed in part by the present and future.
 
sol invictus said:
I don't agree with much of anything in that article. For example, it asserts "Therefore, violation of Bell’s inequality implies that locality has to be abandoned." That's flat-out false, as there is a counter example (the "many worlds" interpretation, which violates Bell's inequality but is perfectly local).
Click to expand...

It was a paste and run, so sloppy on my part. I doubt I would have caught it.
 
randman said:
The idea of local realism is that reality exists independent of the observer. In other words, it's in a definite state regardless of us.
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Although standard, that way of putting it is easily misinterpreted as in the OP. In my opinion, it would be better to say local realism is a doctrinal position that insists quantum observables are always in a determinate eigenstate determined by the wave function plus other local variables whose nature is not yet known to science.

That definition of local realism wouldn't sell many books, but would be less prone to misinterpretation.

Here's a nice introduction to quantum reality, written at a level appropriate for high school or freshman students:

N D Mermin. Is the moon there when nobody looks? Reality and quantum theory. Physics today, April 1985, pages 38-47.

randman said:
This has been shown not to be valid for a long time in QM. Just the 2-slit experiment alone shows us that. What we think of as reality is just what genuine reality shows us. Reality itself is perhaps not so measurable.
Click to expand...
Quantum mechanics reminds me of an "Ask Ayn Rand" column in the student newspaper at MIT, circa 1976, quoted from memory:
Dear Ayn:

I agree with Objectionable Philosophy that reality must be as we perceive it, since otherwise it would be confusing. My friend says that doesn't follow, and whenever I press the point he turns inside out and vanishes. What can I say to convince him?

Confused

Dear Confused:

Your friend is obviously a solipsist. My advice is to buy yourself a new friend.

Ayn
​
 
randman said:
Many-worlds is a fantastic concept without much to support it, though it could be true. Where does the energy come from, for example, for a new universe to continually pop up with each collapse of a particle? Does that not trouble some who hold to it as a viable scientific concept?
Click to expand...

No, because no energy is required. It's not really that new universes "pop up" - it's better to think of there having been an ensemble of identical universes prior to the measurement, after which one half (or other fraction) of the ensemble diverged from the other.

On the subject of locality, it would take a lot to show all the papers involved and discuss each one, but the research does indicate locality is violated even if you conceive of a many-worlds explanation of new universes by the zillions being produced instantly all the time (and then some must be erased as the collapse is reversed, which some used to think couldn't happen but has been shown to be the case).
Click to expand...

No, it doesn't. We've discussed that at some length here before. In a nutshell, many worlds is nothing more or less than unitary evolution of the wavefunction according to the Schrodinger equation, and therefore if the interactions in the Hamitonian are local, so is the evolution.

Locality is violated clearly through entanglement.
Click to expand...

Nope. Not at all - not in many worlds, at least.

randman said:
Isn't it more that particles don't exist in any state at all as far as discrete forms but as potentials for discrete form until "observation" occurs where a form must be taken?
Click to expand...

Words are imprecise. Mathematically, the particles are in a definite state before the measurement - it just happens to be a superposition of the two states that correspond to definite values for the measured variables.
 
Bohmian mechanics does away with much of the seemingly irrational aspects of quantum theory. As a layman, I find it more intuitive than the mainstream approach.

LINK
 
sol invictus said:
What's really going on is that QM tells us that reality is truly very different from what we think it is. We don't notice the effects of QM because we ourselves are macroscopic objects, constantly "measuring" our environment as we interact with it. It's only when we do careful experiments on isolated single particles or very small collections of them that we notice that our intuitions for how things should behave - at a very, very basic level - are quite wrong.

For example, quantum mechanics tells us it's possible to have something in a state where it simultaneously has both one characteristic and its opposite (for example, it can both be spinning in one direction and the opposite direction), or two seemingly mutually exclusive properties (for example, being both in one location and another, or even under some circumstances existing and not existing). Being both large and naive, we find that strange - but that is reality.
Click to expand...

This ^^^

In other words, people often put the cart before the horse with QM (or pretty much any kind of non-"common sense" physics). They make the mistake of thinking that the universe should behave in a "sensible" manner which caters to their preconceptions. QM flies in direct contradiction to this anthropomorphic bias.
 
randman said:
As far as the hypothesis that God created the world already seemingly old like someone would a replication of an antique, there are other ways to look at the issue.

Personally, I think science will discover and is beginning to, that the past is not static. The universe is space AND time, as one system. The past may well be still being formed in part by the present and future.
Click to expand...

So what kind of "super time" measures the "non-static" changing of the past? This seems almost like the universe would have another time coordinate in addition to the one it already has...
 
Hartle and Hawking had a scheme in which the history of the universe is the sum (Feynman path-integral style) of all compact geometries in the past that match the current geometry of the universe in the present. In some sense, the past is "formed by" the present (if they're right, anyway), though I don't think it makes sense to say that is "changed".
 
But W.D., local realism is not just applicable to quantum physics. I thought my definition (standard one) would help clear up the misunderstanding. It's not that the world isn't there when you don't look at it. It's there.

The question is whether what is there in terms of physical, discrete form is independent of us, or partly determined by us or responsive to us.

Argghh...but you get the point. On a macro-level, this idea is more of a religious and spiritual one, that your state of consciousness, or faith in your heart, etc,....causes reality to respond in some way.

What if that concept is actually borne out to be true in science?

That'd be something.
 
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