In quantum physics the "collapse of the wave function" is an important concept.

My question is basically: What causes the collapse of the wave function?

Maybe the answer is not known at this time.
But I'm interested in one specific answer, that the collapse is caused
by a consciousness (whatever that is) being made aware of the result
of the experiment.

Have there been any experiments that shows this to be true?

Have there been any experiments that point in another direction?

Additionally of cource I'm interested in any answer to the first
question: What causes the collapse of the wave function?

What is the most popular view on this in the year 2006?
Is there a general agreement (among physicists) on the answer?

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Request for Question Clarification by hedgie-ga on 27 Oct 2006 10:53 PDT

Hi

1)
Is there a general agreement (among physicists) on the answer?

No. Most physicists consider the question (too) philosophical - and do not
discuss it. I do not think there was any poll.

2)
Have there been any experiments?

No. No one so far brought it from philosphy to a specific prediction.

3) There is a historical element to it. When Bohr formulated Copenhagen 
 interpretation, he defined experiment and observer in macroscopic terms,
 Much later people considered 'quantum state of the universe'
(observer included) and the meaning of the collapse changed.

3) Some physicists believe brain has unique function (not really consciousness
 but some structure (Tubulae, retina,  ..) in the eye or body, or absorbtion,
 or any amplification to macroscopic scale.

There is a lot (of clever arguments and nonsense) written about it. 
Some references are collected here:
  
http://dmoz.org/Society/Philosophy/Philosophy_of_Science/Physics/Mind-Body,_Consciousness,_Quantum_Computing/


If you want to know more, please clarify your answer in view of this info 
and comments.

I can provide more detailed summary.
You can also expire the question.

Hedgie

You might find this of interest.

"The argument for an objective wave function collapse: Why spontaneous
localization collapse or no-collapse decoherence cannot solve the
measurement problem in a subjective fashion" by Fred H. Thaheld.
http://arxiv.org/ftp/quant-ph/papers/0604/0604181.pdf

First of all the collapse of the wavefunction is not certain to be a 
fundamental aspect of reality. There are interpretations of quantum 
mechanics where it is an artifact of other root causes.

For instance in the many worlds interpretation observing a particle would
split *you* in many versions, each one observing the particle in each 
different location, each wondering what caused this collapse.

In the Bohm pilot wave interpretation each particle is guided by its pilot 
wave. The wave causes wave-like phenomena, the particle particle-like 
phenomena (I am simplifying here, but that is the relevant feature of the 
interpretation for your question). There is no wave collapse. There is 
also only one universe.

Now assuming there is a collapse of the wavefunction, even then it can be 
dissasociated from consciousness. The Winger friend thought experiment shows 
this (essentially Winger's friend observes Schrodinger's cat, Winger 
observes it and his friend later). Did the friend collapse the state of the 
cat, or did he enter a superposition of states, to be collapsed by Winger 
later? There is no reason to prefer one to the other.

Nevertheless, the connection of consciousness to the wavefunction collapse 
appears appealing to many scientists. And if there is no physical reason to 
conclude it, there is no reason to exclude it either. It just makes a bad 
argument in physics since it brings in an extra factor (and a big one too!) 
that is not needed to explain observed behavior. It may be a compellling 
philosophical argument (depending on your approach), but Occam's razor seems 
to preclude it as a required explanation in physical theories because it 
is not necessary, and the effect may even be an artifact of other features.

Two quick wikipedia links:

http://en.wikipedia.org/wiki/Consciousness_causes_collapse
for a short discusion of your question, and

http://en.wikipedia.org/wiki/Wigner%27s_friend
for the Winger's friend thought experiment.