Realism in QM: Existing Before Measurement?

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Discussion Overview

The discussion revolves around the concept of realism in quantum mechanics (QM), particularly whether entities like electrons exist with definite properties, such as location, prior to measurement. It explores various interpretations of QM, including realist and anti-realist perspectives, and delves into the implications of these interpretations on the nature of reality as understood in physics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that realism implies the existence of entities before measurement, questioning how one can know of their existence without observation.
  • Others clarify that "realism" has multiple definitions depending on context, such as the measurement problem or Bell inequality violations.
  • There is a discussion about the Copenhagen interpretation, which posits that an electron has no definite location until measured, representing an anti-realist view.
  • Some participants argue that realist interpretations suggest electrons do have a location prior to measurement, while others challenge this by stating that such claims are assumptions rather than established facts.
  • Several participants emphasize the importance of defining terms clearly when discussing realism in QM, referencing the EPR paper and concepts like "counterfactual definiteness."

Areas of Agreement / Disagreement

Participants express differing views on the nature of realism in QM, with no consensus reached on whether electrons have a location before measurement. The discussion remains unresolved, with competing interpretations being presented.

Contextual Notes

Participants note that the definitions of realism can vary significantly, and the implications of these definitions depend on the specific interpretation of quantum mechanics being discussed. There are also references to the necessity of prior investigation into the topic to engage meaningfully in the discussion.

Nick V
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I think it's the idea that things exist even before we measure them, correct?
 
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There are many different definitions, depending on who is using the word and in what context.

In the context of the measurement problem, "realism" usually means that a universe obeying physical laws continues to exist even after all observers have died.

In the context of Bell inequality violations,"realism" may mean "have a deterministic explanation", eg. http://arxiv.org/abs/0909.0015.
 
Nick V said:
I think it's the idea that things exist even before we measure them, correct?

There are several related concepts floating around under the general name "realism", and if you search this forum for previous threads you'll find several of them. It's generally a bad idea to use the word without also stating exactly what you mean by it - and if you search this forum for previous threads you'll also find plenty of examples of this :)

The starting point has to be the discussion of "elements of reality" in the EPR paper, which we've already pointed you at several times. You should also find a precise definition of "counterfactual definiteness" (google and searches here will be helpful).

This thread will be summarily closed if your next post in it does not show some evidence that you have done this investigation and that you have also read any responses posted to the thread by the science advisors.
 
atyy said:
There are many different definitions, depending on who is using the word and in what context.

In the context of the measurement problem, "realism" usually means that a universe obeying physical laws continues to exist even after all observers have died.

In the context of Bell inequality violations,"realism" may mean "have a deterministic explanation", eg. http://arxiv.org/abs/0909.0015.
Does it contribute to the idea that electrons have a location, even before we measure/observe them?
 
Nick V said:
I think it's the idea that things exist even before we measure them, correct?
And how would you know "that things exist" if you don't observe them? I will be very disappointed with PF if this thread drags on.
 
samalkhaiat said:
And how would you know "that things exist" if you don't observe them? I will be very disappointed with PF if this thread drags on.
In copenhagen interpretation, the electron literally has no location prior to measurement. This is an example of an anti realist interpretation.
 
Nugatory said:
There are several related concepts floating around under the general name "realism", and if you search this forum for previous threads you'll find several of them. It's generally a bad idea to use the word without also stating exactly what you mean by it - and if you search this forum for previous threads you'll also find plenty of examples of this :)

The starting point has to be the discussion of "elements of reality" in the EPR paper, which we've already pointed you at several times. You should also find a precise definition of "counterfactual definiteness" (google and searches here will be helpful).

This thread will be summarily closed if your next post in it does not show some evidence that you have done this investigation and that you have also read any responses posted to the thread by the science advisors.
Ok,what I mean is, in realist interpretations of QM, does an electron have a location before it is measured? In copenhagen interpretation (anti realist) it doesn't have location until it is measured. But what about realist interpretations?
 
Nick V said:
In copenhagen interpretation, the electron literally has no location prior to measurement. This is an example of an anti realist interpretation.
You asked about REAL THINGS, did you not? The coordinates of the electron (i.e. its location) IS NOT a real thing. Apples and chairs are real things.
 
samalkhaiat said:
You asked about REAL THINGS, did you not? The coordinates of the electron (i.e. its location) IS NOT a real thing. Apples and chairs are real things.
Isn't that only according to the copenhagen interpretation?
 
  • #10
Nick V said:
Isn't that only according to the copenhagen interpretation?
That is according to PHYSICS. I don't talk "interpretation".
 
  • #11
samalkhaiat said:
And how would you know "that things exist" if you don't observe them?
You don't. Instead, the claim appears an assumption and the interpretations which make that assumption are classified as "realist". Of course this assumption has consequences that must be accepted along with the assumption. (This remark is for the OP - Samalkhaiat already understands this).

I will be very disappointed with PF if this thread drags on.

When it's dragged along enough to bother you... report it! We mentors are extraordinarily powerful, but our clairvoyance is still a bit weak compared with some of our other superpowers - If no one reports it, we may assume that no one is bothered by it yet.
 
  • #12
Nugatory said:
You don't. Instead, the claim appears an assumption and the interpretations which make that assumption are classified as "realist". Of course this assumption has consequences that must be accepted along with the assumption. (This remark is for the OP - Samalkhaiat already understands this).

But isn't that what realist interpretations of QM are? That electrons have a location before it is measured?
 
  • #13
Nick V said:
But isn't that what realist interpretations of QM are? That electrons have a location before it is measured?

I said "This thread will be summarily closed if your next post in it does not show some evidence that you have done this investigation".

We're there.
 

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