How does physics allow for the existence of observers?

  • #26
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Loren Booda said:
Taking into account the past several posts, is an observer describable in classical or quantum mechanical terms?
Words only have demonstrable meaning according to their function in a given context. In a quantum mechanical sense, an observer can be both the observer and not at the same time. In other words, something entirely incomprehensible without a specific context. This is why I assert that the only way modern physics can actually describe an observer is relativistically.
 
  • #27
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balkan said:
no it's not... you just want to read it that way in order to preserve the philosophical argument...
it's mega-highly different from classical physics... the position is incalculable and impossible to predict, that's miles away from classical physics... and that has got nothing to do with our measuring equipment... you were the one bringing the measuring equipment up, and i tried to explain what is meant by "collapsing" of the wave... probably not well enough though... note how your quote says "is said"...
My quote says "is said"? What are you referring to?

the notion of having the electron being in an area of probabilty, but "collapsing" when being observed, is made in order to make the point clear, that it cannot be predicted in any way... i.e. to avoid confusion and make a clear difference from classical physics...
at least that's what our teachers say when we ask them...
But you are making a distinction between classical and quantum physics from an epistemic view only. I'm claiming, as the article will suggest, that there is indeed an ontological difference. It has to do with alot more than just "we say it isn't anywhere because we cannot know or predict where it is." That is just a statement of epistomology. There is an actual difference between where a subatomic particle actually IS as opposed to a ball on a pool table. It's not just a statement of what we can know about that particle.


and there's always something to discuss... people still discuss whether or not evolution exists...
I am talking about among scientists themselves. I'm not talking about Joe Sixpack. I'm sure scientists don't question evolution. There has been much confusion and disagreement among scientists about the interpretation of Qm results. This would not be the case if it were only a theory of epistomology.
 
  • #28
selfAdjoint
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Whatever your intepretation of QM, the particle is definitely not a classical object like a billiard ball. The math you have to use, however you interpret it, guarantees that. Even Bohm's version is not classical, since it has instantaneous changes over distances. Quantum mechanics, with its non-classicality, has passed a huge number od tests and is now the standard way to handle small energy things in the lab. Philosophers who persist in using classical conceptions are just painting themselves into a corner.
 
  • #29
The big dillema for many is the nature of QM and what it says about our universe. This is what Einstein had a problem with and this is what led to the debates between him and Neils Bohr. We know that these things exist as a wave of probabilities until observed. This begs the question, why is there symmetry between conscious beings? In other words why does the universe appear to us in this particular state instead of another state? What caused the universe to choose this state out of all probable states?

Take John Wheeler's thought experiment and the delayed choice experiment. In short, an observer determines the state of the photon after it has already passed through the slits. This is mind-boggling, it's like we caused something to happen "after" it has already occured. It's like time is frozen until observation occurs. If anyone needs me to go into the double-slit experiment or the delayed choice experiment I will.

So the question is what or WHO caused the probability wave of the universe to collapse and appear to us in this fashion. I know some try to eliminate the role of the observer through no collapse theories like many worlds but Copenhagen, Bell's Theorum and delayed choice shows the observer affects which measurement occurs. I think this among other things points to a metaphysical origin.

THANK YOU, LORD JESUS!
 
  • #30
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selfAdjoint said:
Whatever your intepretation of QM, the particle is definitely not a classical object like a billiard ball. The math you have to use, however you interpret it, guarantees that. Even Bohm's version is not classical, since it has instantaneous changes over distances. Quantum mechanics, with its non-classicality, has passed a huge number od tests and is now the standard way to handle small energy things in the lab. Philosophers who persist in using classical conceptions are just painting themselves into a corner.
The sad part about this is that it is the less philosophical and more scientific types that tend to make this mistake(in this forum). This is just what I've observed. I think they hesitate to accept the strangeness because of all the wild interpretations that people will naturally think up as a result. I can provide links to these threads if you'd like.
 
  • #31
vanesch
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haroldjrbw said:
So the question is what or WHO caused the probability wave of the universe to collapse and appear to us in this fashion. I know some try to eliminate the role of the observer through no collapse theories like many worlds but Copenhagen, Bell's Theorum and delayed choice shows the observer affects which measurement occurs. I think this among other things points to a metaphysical origin.
Let us try to put things in order.

Quantum theory describes the state of a system as something that is evolving unitarily and reversibly as a function of time. But that state is experimentally inaccessible. When we "decide to make a measurement" we have to stop that time evolution, and from the state at hand (as a mathematically calculated entity) we can calculate probabilities of what's going to be the result of the measurement. According to the observed outcome, the state now jumps into an eigenstate corresponding to that result, and then evolves from there on unitarily.
For all practical purposes, this algorithm of calculating probabilities of measurements WORKS. It is von Neuman who formalized it.

And now comes the crux of the Measurement Problem:
how come that the evolution of a state, "unobserved" is radically different from an "observation". Both are mathematically incompatible, because the "observation" operation is a probabilistically chosen projector, and the "evolution" operation is a unitary operator.
If we think of "observation" as a physical phenomenon as any other, we have a problem. This problem still stands out. Modern theories such as string theory or quantum gravity do not add much to it, because they fundamentally still work within that framework.

You could think that the question is open to scientific inquiry, because you could ask the question as "what is performing the measurement ?", in that it must somehow make a difference if I consider the apparatus that performs the measurement to be part of the system (and _I_ am the observer), or not, and the apparatus is performing the measurement. However, decoherence theory (an application of QM) indicates that from the moment that we need a macroscopic system (many degrees of freedom, coupled to a thermal bath) as a measurement apparatus, it will not make a difference in the outcome if we include it in the system or not!
So on one hand decoherence is a blessing, because it tells you that the theory of QM is self-consistent: you can choose at what point you decide that the measurement is made without changing the predictions ; on the other hand it makes experimental inquiry into the measurement problem very hard.

There are ways to tackle the problem, but all of them are vey strange. One is that, in the end, consciousness is what performs the measurement. Another is that nothing performs the measurement (many worlds); but in that case, our subjective experience *chooses* a worldline.
Finally, a more down-to-earth approach is to try to slightly modify quantum theory, such that state evolution is not quite unitary, and can give rise to collapse (by introducing nonlinearities). But this approach has the difficulty that whatever you twiddle in QM, you seem to change the very accurate predictions which have been verified up to now.

cheers,
Patrick.
 
  • #32
selfAdjoint
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Copenhagen View

Good post, Patrick!

I have been reading on the home page of http://www.mth.kcl.ac.uk/~streater/ [Broken] - he of Streater and Wightman. He seems to adopt what I would call a modern Copenhagen view. He refuses to quantize the measuring apparatus and treats it as a classical system subject to classical probability. Then he can develop rigorous ways to combine that probability with the probability of the quantum system being measured. And this gives him a consistent picture. I suppose he could justify that based on the fast diagonalization of decoherence, spilitting the problem into a fullly decohered part of the environment, the apparatus, and a coherent part, the quantum system.
 
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