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Q & A: observers in relativity and quantum mechanics

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Most recent answer: 07/07/2017
Q:
Relativity and Quantum Mechanics both have an observer effect. Do you think they are related? Both the constancy of the speed of light and the observer effect in the double slit experiment seem to need a conscious observer.
- Jonathan Milks (age 47)
Sandy Hook, Ct. U.S.A.
A:

At the level of your description, they aren't really related except by the use of the word "observer".

There isn't really an observer "effect" in relativity. There are just different descriptions of the same events from different viewpoints. Various time and distance numbers come out different in the different frames. That's just like looking at something from different angles, except a little more general since time gets involved too.

The effect in quantum mechanics doesn't  involve viewpoints in the same way. When small things obeying nice clean quantum equations start to lead to states with a mixture of different large-scale outcomes (e.g. a live cat or a dead cat), the world seems to turn into just one of those outcomes, following a probability rule. Now there may be versions of the world with all of the outcomes, with versions of you in each, in which case I guess you could say that the outcome depends on viewpoint: which you? But then the outcome would really depend on viewpoint: the cat living or dying are really different outcomes, not just two descriptions of the same outcome. 

So conscious observers really have nothing to do with relativity. Since all conscious observers are large-scale objects (by quantum standards) we may have nothing special to do with that either. It may be that some deeper understanding will lead to a picture in which the very fact of consciousness limits the perceived descriptions of the quantum world to that tiny fraction of descriptions in which the state is expressed as a sum of parts in which large-scale things have rather definite values in each part. So maybe someday the limitations of our consciousness will be seen as a key to the current form of our description of quantum mechanics.

Mike W.


(published on 07/07/2017)

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