The Observer Effect

Does the observer effect only work with humans? How about babies and young children? Or chimpanzees? Does there have to be a certain level of consciousness for it to work?
- Charmian Parkin (age 61)
Pembrokeshire, Wales

I guess you're asking about the "observer effect" in quantum mechanics. To the best of our knowledge, it has no particular connection with consciousness of any sort. When a small, simple quantum system interacts with the big outside world, the two usually become "entangled". That means that the quantum system has no well-defined quantum state, but rather a collection of different states, each paired with a different state of the big outsides. We say that the different quantum possibilities of the little system have "decohered". (For more info, "decoherence" is a good search term.) At any rate, the quantum interference between the decoherent possibilities is lost. 

So far as we know, observers are just among the many big things that can interact with little quantum systems.

Mike W.

(published on 12/29/2013)

Mike W. kindly answered my question, but I'm still confused. I just read a long passage about the observer effect, including eg. a quote from Prof Jeffrey Schwartz 'The role of observation in quantum physics cannot be emphasized too strongly. .....only through an act of observation does a physical quantity have an actual value'. Is this view now out of date. or is it a matter of contention?
- charmian parkin (age 61)
Pembrokeshire, Wales

I think it's fair to say it's still "in contention". Some interpretations hold that the quantum state is purely a form of information  and that the laws of quantum mechanics represent the development only of that information. The underlying physical reality is then held to be so remote as to have no known representation, if it exists at all. In some sense, this is a return to the solipsistic views of Bishop Berkeley.  It is hard to refute this position, but many of us find it unsatisfying.

In trying to sort through the various interpretations, it may help to try to isolate any ways in which they would have different implications. Other aspects, no matter how different they may sound, may be good subjects for agnosticism.

What seems almost beyond question, however, is that any physical reality would be ay least as remote from our intuition as the quantum state is.

Mike W.

(published on 12/29/2013)