Quantum Superposition & Philosophy

[Elvin12]

According to Quantum Physics (or at least my understanding of it), when a particle is not observed it doesn't exist in the way one imagines is to be. Instead, it is a wave function with infinite possibilities (sum-over histories by Feynman), and only when observed it takes on a definite state. This what I got from books that I've read, but its still quite hard to understand as how a particle interferes with itself while traveling through a double-slit and why exactly is it the observer that chooses the fate of Scholidinger's cat in the box?
One other thing I'm wondering has more to do with philosophy but can be tied in here also. Geroge Berkeley said that if no one looks at a tree, it doesn't exist, in other words "esse est percipi" or "to be is to be perceived". Scientists have found that even particles large enough to be observed by microscopes (bucky-balls) also interfere. So I'm wondering whether George Berkley is right, and a tree doesn't exist if not perceived, but rather a wave function with infinite different possibilities?
If what I said makes no sense, I apologize, but please correct me so I have a better understanding.

 

[Fredrik]

These are a few of my earlier posts that you might find useful:

https://www.physicsforums.com/showthread.php?p=2983773
https://www.physicsforums.com/showthread.php?p=2925950

This one contains a comment about the question "is the moon there when nobody looks?":

https://www.physicsforums.com/showthread.php?p=2796814

 

[yoda jedi]

According to Quantum Physics (or at least my understanding of it), when a particle is not observed it doesn't exist in the way one imagines is to be. Instead, it is a wave function with infinite possibilities (sum-over histories by Feynman), and only when observed it takes on a definite state. This what I got from books that I've read, but its still quite hard to understand as how a particle interferes with itself while traveling through a double-slit and why exactly is it the observer that chooses the fate of Scholidinger's cat in the box?
One other thing I'm wondering has more to do with philosophy but can be tied in here also. Geroge Berkeley said that if no one looks at a tree, it doesn't exist, in other words "esse est percipi" or "to be is to be perceived". Scientists have found that even particles large enough to be observed by microscopes (bucky-balls) also interfere. So I'm wondering whether George Berkley is right, and a tree doesn't exist if not perceived, but rather a wave function with infinite different possibilities?
If what I said makes no sense, I apologize, but please correct me so I have a better understanding.

not on nonlinear quantum mechanics (unlike standard quantum mechanics).

 

[StevieTNZ]

There was an interesting article published by Nature earlier this year entitled 'No Moon There'. You can read it here: http://www.engr.ucr.edu/~korotkov/news/2010-NatPhys.pdf

 

[yoda jedi]

There was an interesting article published by Nature earlier this year entitled 'No Moon There'. You can read it here: http://www.engr.ucr.edu/~korotkov/news/2010-NatPhys.pdf

i read it time ago.
i waiting the result on more big object like:

http://www.fqxi.org/community/articles/display/103

Tejinder Singh
http://arxiv.org/abs/0711.3773

argues that quantum theory is intrinsically nonlinear, and goes to the standard linear limit for microscopic objects. THe nonlinear theory goes to the classical limit for large objects, but departs from linear quantum mechanics for mesoscopic objects.

Because of the nonlinearity, the lifetime of two superposed states is no longer infinite. It decreases as the number of atoms in the object under study increases, going from an astronomically large value for microsystems, to extremely small values for macrosystems. Thus somewhere in between, the superposition lifetime ought to be measureable in the laboratory.


----------------------
in any case the final theory have to be nonlinear.
read:
https://www.physicsforums.com/showthread.php?t=374854

-----------------
http://arstechnica.com/science/news/2009/10/quantum-gravity-theories-meet-a-gamma-ray-burst.ars

...A value this close to the Planck length means that quantum gravity models in which there's a linear relationship between photon energy and speed are "highly implausible" That leaves other quantum gravity options open, including those in which the the relationship is non-linear. Hopefully, theoreticians will be able to devise real-world tests for some of these...

 

[StevieTNZ]

What is the difference between linear and nonlinear quantum mechanics (perferably without all the mathematics).

 

[yoda jedi]

What is the difference between linear and nonlinear quantum mechanics (perferably without all the mathematics).

the linearity refers to the fact that there is no change (superposition stay forever, there is no collapse) is "LINEAR" (linear schrodinger equation).
in nonlinear model things change, there is breakdown of superposition, there is a collapse (nonlinear schrodinger equation).


...suppose you make a quantum measurement of an observable of a quantum system which is in a superposition of two states. The way nonlinearity destroys superposition is as follows : when a measurement begins, one of the two states starts to grow exponentially, while the other starts to decay exponentially......

 

[Fredrik]

...suppose you make a quantum measurement of an observable of a quantum system which is in a superposition of two states. The way nonlinearity destroys superposition is as follows : when a measurement begins, one of the two states starts to grow exponentially, while the other starts to decay exponentially......

I wouldn't call that "destroying" the superposition. What you're describing is just a superposition that leads to predictions that are practically indistinguishable from the predictions derived from an eigenstate. This wouldn't get rid of the philosophical problems associated with the (IMO misguided) assumption that the wavefunction describes a single reality.

 

[yoda jedi]

I wouldn't call that "destroying" the superposition. What you're describing is just a superposition that leads to predictions that are practically indistinguishable from the predictions derived from an eigenstate. This wouldn't get rid of the philosophical problems associated with the (IMO misguided) assumption that the wavefunction describes a single reality.

collapse=no superposition

 

[Fredrik]

collapse=no superposition

Yes, but "exponentially decaying magnitude of the coefficients of all but one term in a superposition" ≠ collapse.

 

[yoda jedi]

Yes, but "exponentially decaying magnitude of the coefficients of all but one term in a superposition" ≠ collapse.

and

to predictions that are practically indistinguishable from the predictions derived

double answer:

...The growth/decay process can be said to be `complete' over some calculable time scale tau. Now suppose we were to suddenly take away the measuring apparatus `during' the measurement, [i.e. after a time less than tau since the start of measurement] the state we will be left with is a certain superposition of the two states of the kind that is not seen in ordinary quantum mechanics. It is a sum of an exponentially grown state and an exponentially decayed state - this prediction is different from quantum mechanics. If we feed such a state into a second measuring apparatus, `quickly' after the first partial measurement, the outcome will be different from that predicted by quantum mechanics......

 

[Zarqon]

In answer to the OP:

There is a large difference between a Tree and the bucky-balls of that experiment, and that is that the tree is interacting with it's environment. It may not have any human observing it, but there are still many other things that "observe" it, in the form of being in contact with it, such as the air, and the ground it stands on etc. The significance of these things is that information about the trees existence constantly leaks into the rest of the world, making it impossible to remain in a superposition state.

You will find that for all the experiments that are being done with large quantum objects, the single most difficult things to accomplish experimentally, is to be able to create enough isolation of the object from the rest of the world, and even "from itself" because even the objects own different internal degrees of freedom can destroy superposition states. The latter usually means that you have to cool the object down to it's motional ground state, which rapidly becomes harder and harder to do with increasing object size.

 

[SprocketPower]

So what you're saying, Zargon, is that the object perceives itself or is perceived by its environment, so that there is no real superposition or it's only momentary which would collapse the MWI.

 

[yoda jedi]

So what you're saying, Zargon, is that the object perceives itself or is perceived by its environment, so that there is no real superposition or it's only momentary which would collapse the MWI.

there are no collapses on MWI.
the objectification is due to a process called "Environment Induced Superselection"
and the other branches (superpositions) goes according the MWI.

 

[SprocketPower]

By "would collapse the MWI" I meant that the theory would not hold. I take it from your answer it still would.

 

[Zarqon]

No, I did not mix MWI or any other interpretation into my statement. What I said is true regardless of beliefs, beucase all interpretations agree (as far as we know today) on measurement outcomes, and in this case the probability amplitude for the tree being there is always 1. I was just saying that the reason that such a large object as a tree won't be in a superposition state is because of all it's near-infinite number of degrees of freedom (for example vibrational and rotational modes between the molecules), and because all of the connections that it has to other objects. The wavefunction will never be isolated enough that you could get to a point where no information leaks out, destroying the superposition.


Also, the tree being there or not suffers from additional problems, such as violating energy conservation. If you look at the quantum experiments that deals with superpositions, you will see that they conserve all properties. An typical example is a single ion being in a superposition of either "being excited" or "being in ground state + there being an extra photon equal to the energy difference between the states". In the tree case you would first have to define a state that has the matching energy/momentum etc. as the tree without there actually being a tree, before one could even begin to talk about superpositions of the states.

 

[Elvin12]

"Any modification of the apparatus that can determine which slit a photon passes through destroys the interference pattern,[5] illustrating the complementarity principle: that light (and electrons, etc.) can behave as either particles or waves, but not both at the same time.[8][9][10] However, an experiment performed in 1987[11] produced results that demonstrated 'which-path' information could be obtained without destroying the possibility of interference. This showed the effect of measurements that disturbed the particles in transit to a lesser degree and thereby influenced the interference pattern only to a comparable extent"
This is from wikipedia page:
http://en.wikipedia.org/wiki/Double-slit_experiment

So what does this mean, that the particle can in fact be observed, but there is a certain limit on how much? wouldn't that prove Objective collapse theory true?

 

[SprocketPower]

Elvin12,

Objective collapse is indetermistic, but what about SD? How would that explain superposition?

 

[GodPlaysDice]

an answer to the OP:

I think it depends on the interpretation of quantum physics you prefer. If you would agree with the Copenhagen interpretation you would say it doesn't matter because you could never know anyway. I, with my limited knowledge of the subject, think that the tree is in a constant superposition throughout space, and that we just perceive it to be at a particular place at a certain point in time for whatever reason.

PS. could anyone recommend a book on quantum physics without all the math, something more suitable for someone in high school or pregrad college? i'd appreciate it.

 

[SprocketPower]

GodPlaysDice,

I can recommend Quantum World by Ken Ford and Introducing Quantum Theory by McEvoy and Zarate, which I have, but also Understanding Quantum Mechanics by Roland Omnès, Quantum World and Quantum Theory by J.C. Polkinghorne, and Quantum: a Guide for the Perplexed by Jim Al-Khalili, which look to be very good, too, and which I'll probably get also (I have already ordered Quantum Theory by J.C. Polkinghorne).

These are not mathematical and are fairly short but very substantial so are not heavy going. You can get them through Bookfinder.

 

[GodPlaysDice]

SprocketPower,

Thank you, I am looking forward to reading them. I recently read Quantum: A Guide for the Perplexed. I suggest you get it; it explains alternate interpretations of QP well, and also has a great chapter on the history of QP. It is a good book to read if you are a visual learner (it has lots of pictures).

 

[Silentshado]

What you guys fail to include in your theories is the mind and consciousness. You have a broad knowledge of quantum physics yet you don't see the truth held within the facts. You say that the tree isn't in superposition because its information leaks etc. What you fail to recognise is that the tree doesn't even exist. There isn't a single pre-existing feature of reality that is independent of our minds. Our minds are all powerful tools of creation. Therefore instead of discovering the universe we are actually creating the universe around us.

 

[Silentshado]

Another excellent book and movie is 'what the bleep do we know?' . Really life changing. The movie is excellent but the book goes much deeper into QP.

 

[Fredrik]

What you guys fail to include in your theories is the mind and consciousness. You have a broad knowledge of quantum physics yet you don't see the truth held within the facts.

And I suppose the fact that you don't understand quantum physics is what helps you see the truth?

What you fail to recognise is that the tree doesn't even exist. There isn't a single pre-existing feature of reality that is independent of our minds. Our minds are all powerful tools of creation. Therefore instead of discovering the universe we are actually creating the universe around us.

What predictions does this "theory" make that are different from the predictions made by other theories? What experiments have confirmed that your "theory" makes better predictions than other theories?

The fact that a brain is creating a model of (some aspects of) the world around it, using information about the actual world obtained through the sensory organs, doesn't mean that there isn't an actual world out there.

Another excellent book and movie is 'what the bleep do we know?' . Really life changing. The movie is excellent but the book goes much deeper into QP.

I'm sorry, but that movie is complete crackpot nonsense. The people who made it know almost nothing about physics, and they don't understand what science is.

 

[Fredrik]

PS. could anyone recommend a book on quantum physics without all the math, something more suitable for someone in high school or pregrad college? i'd appreciate it.

"QED: The strange theory of light and matter", by Richard Feynman.

 

[Borek]

Another excellent book and movie is 'what the bleep do we know?' . Really life changing. The movie is excellent but the book goes much deeper into QP.

This is a banned topic, see forum rules.

 

[GodPlaysDice]

What you guys fail to include in your theories is the mind and consciousness. You have a broad knowledge of quantum physics yet you don't see the truth held within the facts. You say that the tree isn't in superposition because its information leaks etc. What you fail to recognise is that the tree doesn't even exist. There isn't a single pre-existing feature of reality that is independent of our minds. Our minds are all powerful tools of creation. Therefore instead of discovering the universe we are actually creating the universe around us.

If everything in the universe is created by our minds, where did our minds come from? How could something that is (supposedly) not real (our minds) create something else, may it be real or not?

 

[SprocketPower]

GodPlaysDice,

Great, I'll certainly buy the Al-Khalili book.

 

[Maui]

If everything in the universe is created by our minds, where did our minds come from?

Does the opposite approach answer in any way the deep questions? If everything in the universe is not created by our minds, where did the universe come from?

How could something that is (supposedly) not real (our minds) create something else, may it be real or not?

I wonder that too. But how can something supposedly non-existent(universe) create itself, may it be real or not?

How far can we really go by staying totally rational and reasonable, i.e. dismissing anything that doesn't fit our worldview? I am willing to argue that the biggest hinderance towards future progress in science is its past success in building models based on classical-like approximations.

 

[wuliheron]

How far can we really go by staying totally rational and reasonable, i.e. dismissing anything that doesn't fit our worldview? I am willing to argue that the biggest hinderance towards future progress in science is its past success in building models based on classical-like approximations.

I'd go a bit further than merely the success of past approximations in physics and say the problem is as much cultural and innate:

Ritual
Well established hierarchies are not easily uprooted;
Closely held beliefs are not easily released;
So ritual enthralls generation after generation.
Harmony does not care for harmony, and so is naturally attained;
But ritual is intent upon harmony, and so can not attain it.
Harmony neither acts nor reasons;
Love acts, but without reason;
Justice acts to serve reason;
But ritual acts to enforce reason.
When the Way is lost, there remains harmony;
When harmony is lost, there remains love;
When love is lost, there remains justice;
But when justice is lost, there remains ritual.
Ritual is the end of compassion and honesty,
The beginning of confusion;
Belief is a colourful hope or fear,
The beginning of folly.
The sage goes by harmony, not by hope;
He dwells in the fruit, not the flower;
He accepts substance, and ignores abstraction.

 

[ZapperZ]

How far can we really go by staying totally rational and reasonable, i.e. dismissing anything that doesn't fit our worldview? I am willing to argue that the biggest hinderance towards future progress in science is its past success in building models based on classical-like approximations.

Show an alternative that works.

Zz.

 

[wuliheron]

Show an alternative that works.

Zz.

Some of the greatest scientific discoveries were the results of dreams and accidents.

 

[ferenan]

It's a great question OP. A great mystery and perhaps the only mystery. Feynman said if you can answer this question you can answer everything about quantum mechanics.

These days people do not like the Copenhagen Interpretation. They prefer dechoherence or MWI. Dechoerence (simply) states that at some point when objects are large enough their wave function collapses. A flimsy answer imho especially as we are now observing macroscopic objects (although in very specific states) in a superposition. It is based on peoples reluctance to think that our reality may be much stranger than we imagine. MWI is a whole other concept which also imho adds way to much philosophical baggage, but is still fascinating in itself and profound. It is worth noting that MWI was laughed at for decades as being ridiculous. It is only now as we struggle to come up with any other explanation that it is being taken seriously, not because there has been a breakthrough in the concept (I am sure that is a controversial statement, but true). In effect it allows mathematicians and physicists to be exactly that, and not philosophers. It allows room foward in our thinking without getting stuck in a seeming dead end. That does not make it true though.

But what does the Copenhagen Interpretation really have to say on the matter. Of course not much. But we can rule out what it does not say and where confusion arises. It is often thought that only a conscious observer can collapse a wave function. I think even the founders of the theory often went down this route (even if only to mock it as Schroedinger did). They certainly placed a heavy emphasis on consciousness. But really all it says is that we as conscious observers can know for sure that the superposition has collapsed as we do not experience one, not that we have caused it as such. At what stage or at what time it collapsed is an unknown. Add it temporal and spatial superposition and it all comes very confusing. An observation now could in theory have an effect 10 billion years ago! Further more, even if we know we are observing something not in a superposition, to an outside observer separate from us ,they can consider us as being in a superposition of states. So us being conscious alone is not enough to definitively collapse a wave function as we can be considered to be in a superposition with our environment by someone else who has yet to observe us. So a wave function collapse is not either a true or false thing. It is MUCH more subtle than that, and it is this point that causes the most confusion as we like to make things fit our everyday understanding. Just as a object can be in superposition of two or more states at once, the superposition can be both existing and non existing! Agghh, my heard is starting to spin. This ridiculous level of uncomprehensabilty has certainly put many people off as explained before, it seems impenetrable by science. But the evidence seems to very strongly lead us down this path. The only way around it is by proposing MWI. So which is it. DO we give up realism (that objects have any definitive properties or existence) along with locality (EPR), or do we just give up locality and (simply! or NOT) propose an effective infinite amount of parallel realities!

Where does all this get us? I have no idea! The problem is every idea seems untestable. We would need to separate ourselves from reality to stand a chance. Or hopefully some massive steps forward in our understanding of physics will get us there. The answer will be profound though. We will not be able to look at reality the same again.

 

[wuliheron]

For me the assumption that we must find a definitive answer or that one even exists is flawed.

That was the same mistake made with Newtonian Mechanics; the assumption that we had a definitive explanation. To paraphrase Einstein, creating a new theory is not like tearing down a barn and erecting a skyscraper. It is more like climbing a mountain, gaining new and more expansive vistas on our adventurous way up. The place from which we started can still be seen, but our view has simply become broader.

Perhaps there is no top of the mountain or, at least, none accessible to mere mortals. Like so many other things in life we can choose to bang our heads against the wall in frustration or simply accept the situation and move on. After all, what is life without at least a little mystery?

 

[ferenan]

For me the assumption that we must find a definitive answer or that one even exists is flawed.

I quite understand. But it is hopeless for us all to take this attitude too seriously. We need those who strive to forward our understand in science as it will lead to breakthroughs in understanding and at the very least lead to new technologies which we all enjoy. Their entire premise may be wrong that the universe and for that matter fundamental reality can be so easily pigeon holed into understandable logic concepts. I certainly feel a huge resistance from scientists to accept the possibility that realism is not as fundamental as we think. The whole searching for smaller and smaller building blocks of matter seems flawed given their ethereal nature. How does string theory really gel with non locality? We just cannot seem to give up the concept that matter is a physical thing with a definitive place and structure. Still I for one would be devastated if people stopped trying!