Re: Question regarding observer's role in QM

From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 08/31/04 

Date: Tue, 31 Aug 2004 10:23:55 +0200

aryalok wrote:
> Quantum theory states that observation crates a reality. i.e. Quantum
> object is represented by its wave function until some one looks at
> it.At that time, wave function representing an object collapses and
> quantum object [i.e. photon,electron etc) takes definite state.

First, not quantum theory itself says that, but only a particular (still
popular) interpretation of it, namely the Copenhagen interpretation.

Second, even after the collapse, the object is still described by a
wavefunction - one which corresponds to the particular observation taken.

> Hence here is the question. What does observation means? Is it human
> observation or observation by any creature?

"Observation" is an unfortunate choice of word. "Measurement" would be
better; and in modern times, "interaction with the environment" fits
even better. Try reading up on "decoherence".

http://en.wikipedia.org/wiki/Copenhagen_interpretation
http://en.wikipedia.org/wiki/Interpretation_of_quantum_mechanics
http://en.wikipedia.org/wiki/Decoherence

> If cat or a dog looks at a photon passing through a Young's double
> slit setup what will be the pattern on the screen? Will there be an
> interference pattern or a particle pattern?

Particle pattern.

Bye,
Bjoern