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- Thread starter DrZoidberg
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Vanadium 50

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you ask, when loses the linearity ? macroscopic object superposition, where is the limit ?

maybe at 10

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actual limit, 430 atom molecule interference.

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As others said, QM applies at all scales; however, as objects become larger, heavier and

more complex, they tend to interact more intensely with their environment, in a way that

tends to destroy many of the typical quantum mechanical effects, like interference.

Look up 'environmentally induced decoherence' for a more in-depth explanation for this

phenomenon.

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The reason there is still disagreement as to what constitutes measurement is that it makes no experimental difference according to quantum mechanics. The way QM works under the Copenhagen interpretation is that you have to split the world into two parts, the “observer” or measurement device, and the “observed” or the particles you’re measuring.

The measurement device is assumed to behave classically. The particles in the observed system are in a superposition of states described by the wave function which keeps evolving until it interacts with the classical measurement device. The question is where to draw the line. You could consider a photon to be the observed system and an atom to be the measuring device, but you can also consider the photon-and-atom system as in a superposition of states, and take a Geiger counter to be the measurement device. So there is this von-Neumann chain, going from elementary particles to Geiger counters to human beings, and we have to decide where to cut it off.

Von Neumann proved in his famous "Bible" of QM that regardless of where you cut the chain, you would get the same experimental results. But he argued that wherever you cut the chain you have things made out of particles on each side of the cut, so there’s no principled way to place the cut in the middle. So he decided that you should place the cut between the human mind and the human body, because he believed that the mind is non-physical. Hence "consciousness causes collapse" was born. Nowadays, the most popular view is decoherence, where there is no real collapse, it's just that when you have a large number of particles in the environment interacting with the system, the wave function becomes smeared out and looks like it has collapsed. So decoherence gives us a reasonable place to cut the chain, when the number of particles involved reaches a critical number so that interference effect become negligible.

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i say actual experimental limit.

there are planned experiments on bigger objects, that way they test quantum mechanics versus macro-realistic theories (if macroscopic objects obey macrorealism, or whether QM prevails).

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not proved yet.As others said, QM applies at all scales

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Vanadium 50

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but the maths doesnt exclude it.not proved yet.

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You're right about the correspondence theorems, but those don't really describe the emergence of classicality from quantum theory. In fact, that emergence is still considered a mostly unsolved problem (despite all the advances in decoherence theory and related subjects).

Ehrenfest's theorem and other correspondence theorems only show that it is sensible to assume that classical behavior can be generated by quantum systems, in one way or another. That mostly refers to classical trajectories of certain quantities. But for explaining real classical behavior you have to explain the lack of interference (decoherence, in the 70s and 80s mostly) and the the uniqueness of classical properties (i.e. the measurement problem)

While the lack of interference is understood quite well, the measurement problem is still not understood fundamentally.

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mfb

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It is just an experimental limit, and the limit becomes bigger and bigger.

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Right stevie

this one with a kg mirror.

The LIGO Science Collaboration Experiment, New J. Phys. 11 073032 2009.

-----

**Large Quantum Superpositions and Interference of Massive Nanometer-Sized Objects**

O. Romero-Isart, A. C. Pflanzer, F. Blaser, R. Kaltenbaek, N. Kiesel, M. Aspelmeyer, J. I. Cirac

6 Jun 2011.

...this includes experiments in a hitherto unachieved parameter regime where collapse theories predict quantum mechanics to fail, or even more general tests of quantum theory against full classes of macrorealistic theories...

...we shall discuss the application of using this experiment to test theories beyond quantum mechanics that provide an objective collapse of the wavefunction for suﬃciently large objects.....

------

http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.1236v1.pdf [Broken]

...Another motivation to consider the possibility that quantum physics is only an approximation to a deeper underlying theory...

.

this one with a kg mirror.

The LIGO Science Collaboration Experiment, New J. Phys. 11 073032 2009.

-----

O. Romero-Isart, A. C. Pflanzer, F. Blaser, R. Kaltenbaek, N. Kiesel, M. Aspelmeyer, J. I. Cirac

6 Jun 2011.

...this includes experiments in a hitherto unachieved parameter regime where collapse theories predict quantum mechanics to fail, or even more general tests of quantum theory against full classes of macrorealistic theories...

...we shall discuss the application of using this experiment to test theories beyond quantum mechanics that provide an objective collapse of the wavefunction for suﬃciently large objects.....

------

http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.1236v1.pdf [Broken]

...Another motivation to consider the possibility that quantum physics is only an approximation to a deeper underlying theory...

.

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If you're curious, here's an experiment from 2002 which does just that: Matter-wave interferometer for large molecules.Buckyballs have been used and they produced a very tiny but distinguishable interferencepatterneffect (or so they tell me).

And here's one from 2011 using molecules made up of 430 atoms: Quantum interference of large organic molecules.

I think that's what yoda jedi was talking about.

It looks like experimentalists are in a long-term race to see who can send the biggest object through a beamsplitter and still show de Broglie interference.

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If you're curious, here's an experiment from 2002 which does just that: Matter-wave interferometer for large molecules.

And here's one from 2011 using molecules made up of 430 atoms: Quantum interference of large organic molecules.

I think that's what yoda jedi was talking about.

right, another

http://www.nature.com/nphys/journal/v8/n5/full/nphys2262.html

http://arxiv.org/pdf/1111.1979v2.pdf

and resulting in a modification of the Heisenberg uncertainty relation.

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

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Macroscopic quantum phenomena

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

superposition/interference on 10

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