Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Purpose and Plan

A. Pais

Published Aug 25, 2005• 0 citations
Publisher

Abstract

Abstract It must have been around 1950. I was accompanying Einstein on a walk from The Institute for Advanced Study to his home, when he suddenly stopped, turned to me, and asked me if I really believed that the moon exists only if I look at it. The nature of our conversation was not particularly metaphysical. Rather, we were discussing the quantum theory, in particular what is doable and knowable in the sense of physical observation. The twentieth century physicist does not, of course, claim to have the definitive answer to this question. He does know, however, that the answer given by his nineteenth century ancestors will no longer do. They were almost exactly right, to be sure, as far as conditions of everyday life are concerned, but their answer cannot be extrapolated to things moving nearly as fast as light, or to things that are as small as atoms, or—in some respects—to things that are as heavy as stars.

DOI
10.1093/oso/9780192806727.003.0001

Related papers

Should we believe the physicists?

J. B. Kennedy

It must have been around 1950. I was accompanying Einstein on a walk from The Institute for Advanced Study in Princeton to his home, when he suddenly stopped, turned to me, and asked me if I really believed that the moon exists only if I look at it. The nature of our discussion was not particularly metaphysical. Rather, we were discussing the quantum theory … (Abraham Pais, 1982) There is an old debate in philosophy about whether the world outside our minds exists at all. In the early-seventeenth century, Descartes pioneered the new mechanical and geometrical view of material reality in which every event was determined. But he also believed that we each had a soul and that our will was free. Thus he had to insist that matter and the soul were entirely different: the mind-body split was born. Descartes's critics soon pointed out that a soul confined within the “veil of perception” had no direct evidence that its perceptions were true. Perhaps they were mere illusions or some sort of cinematic film projected by God? Bishop Berkeley went so far as to suggest that there are no bodies outside the mind, and that perceptions were the only reality: “to be is to be perceived”. Samuel Johnson thought this was all twaddle. He famously rebutted Berkeley by kicking a stone, as if to say that its reality was painfully obvious. During the past 30 years, there has been a resurgence of these sorts of questions.

•Jul 30, 2002•0 citations

Einstein's Moon

Daegene Song

An account of the subjective elements of quantum mechanics or of whether, as Einstein famously asked, the Moon exists when nobody is looking at it.

Physics-Uspekhi•Sep 30, 2012•1 citation

Einstein's Moon

Danhua Song

An account of the subjective elements of quantum mechanics or of whether, as Einstein famously asked, the Moon exists when nobody is looking at it.

•Aug 15, 2010•0 citations

Quantum mysteries for anyone

N. David Mermin

We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it. A. Pais As O. Stern said recently, one should no more rack one's brain about the problem of whether something one cannot know anything about exists all the same, than about the ancient question of how many angels are able to sit on the point of a needle. But it seems to be that Einstein's questions are ultimately always of this kind. W. Pauli Pauli and Einstein were both wrong. The questions with which Einstein attacked the quantum theory do have answers; but they are not the answers Einstein expected them to have. We now know that the moon is demonstrably not there when nobody looks. The impact of this discovery on philosophy may have been blunted by the way in which it is conventionally stated, which leaves it fully accessible only to those with a working knowledge of quantum mechanics. I hope to remove that barrier by describing this remarkable aspect of nature in a way that presupposes no background whatever in the quantum theory or, for that matter, in classical physics either. I shall describe a piece of machinery that presents without any distortion one of the most strikingly peculiar features of the atomic world. No formal training in physics or mathematics is needed to grasp and ponder the extraordinary behavior of the device; it is only necessary to follow a simple counting argument on the level of a newspaper braintwister.

Cambridge University Press eBooks•Mar 15, 1990•0 citations

Letters to Jeff Nicholson

Christopher A. Fuchs

June 1996, “Cyclic Never-Endings” Yes, yes, I like Montréal! Does that finally answer your question? The only thing I really miss about the states is having a swarm of good physicists around me. El Jeffy 1: You know, I really miss listen to you babble about quantum mechanics. Nobody around any more to tell me that the moon isn't there when I'm not looking; you even had me believing for a while . Damn, if I had only stayed there a bit longer…perhaps you would have remained a true believer! August 1996, “Laws of Thought” [Referring to the phrase “Quantum Mechanics is a Law of Thought.”:] El Jeffy 2: I was just reading about the mathematician George Boole, the guy who invented Boolean Algebra. In 1854 he published a book called An Investigation of the Laws of Thought, on which are founded the mathematical theories of logic and probabilities. Is that where your lovely little phrase comes from? Yes indeedy, that's exactly where it comes from. Quantum Mechanics is a Law of Thought. God I like the ring of that. August 1996, “Plagiarists” El Jeffy 3: I am disappointed in you. I never realized that you plagiarized that from poor ol' Boole. Can't think up your own catch phrase, eh? I think the phrase bothers me far less when applied to something like Boolean algebra. It still gives me the heebies when you refer to real live physical systems with such terminology .

Cambridge University Press eBooks•Jan 6, 2011•0 citations

Einstein's Moon

Danhua Song

An account of the subjective elements of quantum mechanics or of whether, as Einstein famously asked, the Moon exists when nobody is looking at it.

arXiv:1008.2892•Aug 15, 2010•0 citations
Abstract It must have been around 1950. I was accompanying Einstein on a walk from The Institute for Advanced Study to his home, when he suddenly stopped, turned to me, and asked me if I really believed that the moon exists only if I look at it. The nature of our conversation was not particularly metaphysical. Rather, we were discussing the quantum theory, in particular what is doable and knowable in the sense of physical observation. The twentieth century physicist does not, of course, claim to have the definitive answer to this question. He does know, however, that the answer given by his nineteenth century ancestors will no longer do. They were almost exactly right, to be sure, as far as conditions of everyday life are concerned, but their answer cannot be extrapolated to things moving nearly as fast as light, or to things that are as small as atoms, or—in some respects—to things that are as heavy as stars.
It must have been around 1950. I was accompanying Einstein on a walk from The Institute for Advanced Study in Princeton to his home, when he suddenly stopped, turned to me, and asked me if I really believed that the moon exists only if I look at it. The nature of our discussion was not particularly metaphysical. Rather, we were discussing the quantum theory … (Abraham Pais, 1982) There is an old debate in philosophy about whether the world outside our minds exists at all. In the early-seventeenth century, Descartes pioneered the new mechanical and geometrical view of material reality in which every event was determined. But he also believed that we each had a soul and that our will was free. Thus he had to insist that matter and the soul were entirely different: the mind-body split was born. Descartes's critics soon pointed out that a soul confined within the “veil of perception” had no direct evidence that its perceptions were true. Perhaps they were mere illusions or some sort of cinematic film projected by God? Bishop Berkeley went so far as to suggest that there are no bodies outside the mind, and that perceptions were the only reality: “to be is to be perceived”. Samuel Johnson thought this was all twaddle. He famously rebutted Berkeley by kicking a stone, as if to say that its reality was painfully obvious. During the past 30 years, there has been a resurgence of these sorts of questions.
We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it. A. Pais As O. Stern said recently, one should no more rack one's brain about the problem of whether something one cannot know anything about exists all the same, than about the ancient question of how many angels are able to sit on the point of a needle. But it seems to be that Einstein's questions are ultimately always of this kind. W. Pauli Pauli and Einstein were both wrong. The questions with which Einstein attacked the quantum theory do have answers; but they are not the answers Einstein expected them to have. We now know that the moon is demonstrably not there when nobody looks. The impact of this discovery on philosophy may have been blunted by the way in which it is conventionally stated, which leaves it fully accessible only to those with a working knowledge of quantum mechanics. I hope to remove that barrier by describing this remarkable aspect of nature in a way that presupposes no background whatever in the quantum theory or, for that matter, in classical physics either. I shall describe a piece of machinery that presents without any distortion one of the most strikingly peculiar features of the atomic world. No formal training in physics or mathematics is needed to grasp and ponder the extraordinary behavior of the device; it is only necessary to follow a simple counting argument on the level of a newspaper braintwister.
June 1996, “Cyclic Never-Endings” Yes, yes, I like Montréal! Does that finally answer your question? The only thing I really miss about the states is having a swarm of good physicists around me. El Jeffy 1: You know, I really miss listen to you babble about quantum mechanics. Nobody around any more to tell me that the moon isn't there when I'm not looking; you even had me believing for a while . Damn, if I had only stayed there a bit longer…perhaps you would have remained a true believer! August 1996, “Laws of Thought” [Referring to the phrase “Quantum Mechanics is a Law of Thought.”:] El Jeffy 2: I was just reading about the mathematician George Boole, the guy who invented Boolean Algebra. In 1854 he published a book called An Investigation of the Laws of Thought, on which are founded the mathematical theories of logic and probabilities. Is that where your lovely little phrase comes from? Yes indeedy, that's exactly where it comes from. Quantum Mechanics is a Law of Thought. God I like the ring of that. August 1996, “Plagiarists” El Jeffy 3: I am disappointed in you. I never realized that you plagiarized that from poor ol' Boole. Can't think up your own catch phrase, eh? I think the phrase bothers me far less when applied to something like Boolean algebra. It still gives me the heebies when you refer to real live physical systems with such terminology .