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Physical Review A

Comment on “Nonlocality, counterfactuals, and quantum mechanics”

Henry Pierce Stapp

Published Sep 1, 1999• 11 citations

Abstract

A recent proof [H. P. Stapp, Am. J. Phys. 65, 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters' choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell's theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A 59, 126 (1999)] argues that some such reality assumption has been ``smuggled'' in. That argument is examined here and shown, I believe, to be defective.

DOI: 10.1103/physreva.60.2595

Related papers

Nonlocality, counterfactuals, and quantum mechanics

William George Unruh

Stapp [Am. J. Phys. 65, 300 (1997)] has recently argued from a version of the Hardy-type experiments that quantum mechanics must be nonlocal, independent of any additional assumptions such as realism or hidden variables. I argue either that his conclusions do not follow from his assumptions or that his assumptions are not true of quantum mechanics and can be interpreted as assigning an unwarranted level of reality to the value of certain quantum attributes.

Physical Review A•Jan 1, 1999•36 citations

Reply to “Comment on ‘Nonlocality counterfactuals, and quantum mechanics’ ”

William George Unruh

Stapp [preceding Comment, Phys. Rev. A 60, 2595 (1999)] has argued that my criticism of his nonlocality proof is wrong. I point out that counterfactual arguments are fraught with dangers, and that any such claim should use them in a conservative manner. A reanalysis of his claims continues to lead me to the conclusion that the nonlocality of quantum mechanics remains unproven.

Physical Review A•Sep 1, 1999•2 citations

Reply to ‘‘Stapp’s algebraic argument for nonlocality’’

Henry Pierce Stapp

The logical structure of my recently proved nonlocality theorem [Phys. Rev. A 46, 6860 (1992)] is examined from the perspective of the theory counterfactual conditionals. It is shown in detail why the argument of Dickson and Clifton [preceding Comment, Phys. Rev. A 49, 4259 (1994)] does not substantiate their claim.

Physical Review A•May 1, 1994•10 citations

Comment on ``Possibility of quantum mechanics being nonlocal''

Henry Pierce Stapp

A recent proof, formulated in the symbolic language of modal logic, shows that a well-defined formulation of the possibility mentioned in the title is answered affirmatively. In the paper being commented upon several proposals were made about how to translate this symbolic proof into prose, and it was concluded, on the basis of those proposed translations, that either the proof was invalid or that an unwarranted reality assumption was made. However, those interpretations deviate in small but important ways from the precise logical path followed in the proof. It is explained here how by staying on this path one avoids the difficulties that those deviations engendered.

arXiv:quant-ph/9806070•Jun 21, 1998•0 citations

Comment on “Nonlocal character of quantum theory,” by Henry P. Stapp [Am. J. Phys. 65 (4), 300–304 (1997)]

Abner Shimony, Howard Stein

A 1997 paper by Henry Stapp attempts to achieve a definitive argument for his long-sustained thesis that quantum mechanics implies a nonlocality inconsistent with the locality of relativity theory. His argument assumes both the validity of counterfactual reasoning under certain circumstances and the free choice of performance of experiments, and it specifically refrains from any assumptions about “elements of physical reality” as understood by Einstein, Podolsky, and Rosen. In Sec. I we drastically condense his argument but retain his central principle of inference, called “LOC2,” which he claims is a consequence of relativistic locality. By careful attention to counterfactual reasoning we then throw doubt upon this claim and hence upon his argument as a whole. In Sec. II we answer Stapp’s reply to our critique of the 1997 paper. Section III is a postscript, commenting briefly on Stapp’s answer to Sec. II.

American Journal of Physics•Aug 1, 2001•18 citations

Comments on Unruh's Paper

Henry Pierce Stapp

Unruh has commented upon my recent proof that certain predictions of quantum theory are incompatible with the assertion that no influence of any kind acts backward in time in any Lorentz frame. Unruh fails to make a necessary distinction between statements that assert the existence of values, and statements that assert the existence merely of correlations between possible values. Consequently his argument fails to show that my proof involves a tacit or hidden reality assumption that is alien to quantum theory.

arXiv:quant-ph/9801056•Jan 23, 1998•0 citations

A recent proof [H. P. Stapp, Am. J. Phys. 65, 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters' choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell's theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A 59, 126 (1999)] argues that some such reality assumption has been ``smuggled'' in. That argument is examined here and shown, I believe, to be defective.

A recent proof, formulated in the symbolic language of modal logic, shows that a well-defined formulation of the possibility mentioned in the title is answered affirmatively. In the paper being commented upon several proposals were made about how to translate this symbolic proof into prose, and it was concluded, on the basis of those proposed translations, that either the proof was invalid or that an unwarranted reality assumption was made. However, those interpretations deviate in small but important ways from the precise logical path followed in the proof. It is explained here how by staying on this path one avoids the difficulties that those deviations engendered.

A 1997 paper by Henry Stapp attempts to achieve a definitive argument for his long-sustained thesis that quantum mechanics implies a nonlocality inconsistent with the locality of relativity theory. His argument assumes both the validity of counterfactual reasoning under certain circumstances and the free choice of performance of experiments, and it specifically refrains from any assumptions about “elements of physical reality” as understood by Einstein, Podolsky, and Rosen. In Sec. I we drastically condense his argument but retain his central principle of inference, called “LOC2,” which he claims is a consequence of relativistic locality. By careful attention to counterfactual reasoning we then throw doubt upon this claim and hence upon his argument as a whole. In Sec. II we answer Stapp’s reply to our critique of the 1997 paper. Section III is a postscript, commenting briefly on Stapp’s answer to Sec. II.

Unruh has commented upon my recent proof that certain predictions of quantum theory are incompatible with the assertion that no influence of any kind acts backward in time in any Lorentz frame. Unruh fails to make a necessary distinction between statements that assert the existence of values, and statements that assert the existence merely of correlations between possible values. Consequently his argument fails to show that my proof involves a tacit or hidden reality assumption that is alien to quantum theory.