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IS the Moon There If No One Looks? Or Is There No “There” There?

Elementary particles do not need to be in a particular place until they are observed and then that's where they are

In last week’s podcast,,” our guest host, neurosurgeon Michael Egnor, interviewed idealist philosopher of science and physicist Bruce Gordon on how the quantum physics that underlies our universe makes much more sense if we have a non-materialist view of reality. Even then, it challenges our conventional view of how nature “must” work: We were introduced to the quantum eraser experiment, which showed that what happens at the level of individual particles depends on whether you choose to measure or not. This segment looks at non-locality, the science of being in no one particular place. Elementary particles can do that too:

This portion begins at 12:36 min. A partial transcript, Show Notes, and Additional Resources follow.

Bruce Gordon: So another phenomenon that’s really quite fascinating is a phenomenon of non-localizability of individual particles. The individual particle can’t be two places at once. Furthermore, it can’t serve as an infinite source of energy. So you can’t run the power needs of New York City on a single electron from here to eternity, right? If you make those two physically very reasonable assumptions, then in the quantum mechanical formulism, you can demonstrate that the particle in question has zero probability of existing in any bounded region of space, no matter how large. You can close various loopholes to make it kind of a rock solid result.

So what does that mean? It means that unobserved quanta don’t exist anywhere in space, and thus have no existence apart from being observed. Interestingly enough, there have been experiments conducted that would support quantum formalism. What does that mean then? It means that as far as microscopic material individuals are concerned, while particles may have pragmatic utility with respect to the measurement results that we observe, and with respect to say macroscopic appearances, it has no basis in unobserved mind independent reality. So that’s just another example that would lead in the same direction as the quantum eraser experiment that I talked about.

Note: In April 1985, David Mermin, director of the Laboratory of Atomic and Solid State Physics at Cornell University, asked in Physics Today,“Is the moon there when nobody looks?” “Einstein maintained that quantum metaphysics entails spooky actions at a distance; experiments have now shown that what bothered Einstein is not a debatable point but the observed behaviour of the real world.”

The idea did not apparently originate with Mermin: From the Philosophy Forum: “Albert Einstein is reported to have asked his fellow physicist and friend Niels Bohr, one of the founding fathers of quantum mechanics, whether he realistically believed that ‘the moon does not exist if nobody is looking at it.’ To this Bohr replied that however hard he (Einstein) may try, he would not be able to prove that it does, thus giving the entire riddle the status of a kind of an infallible conjecture—one that cannot be either proved or disproved.”

We can reasonably assume it does but we can never prove it.

Bruce Gordon: Here’s another one that’s absolutely fascinating. It’s been dubbed the quantum Cheshire cat phenomenon. You may recall from the story of Alice in Wonderland that Alice observes this grinning Cheshire cat (pictured, 1865 edition) that then disappears, leaving only its grin. Alice remarks that she’s “Often seen a cat without a grin, but never a grin without a cat.”

In essence, that’s what’s going on here because certain experiments — in particular, one using a neutron interferometer — have separated the properties of neutrons from any sort of substrate. So micro physical properties don’t necessarily require a substrate. What did the experiment do? Well, it sent the position of neutrons along one path and their spins along a separate path.

So that’d be kind of like sending a top along one path, and the fact that it was spinning along a separate path. Or the redness of an object along one path and the location of that object along another path. Micro physical properties then can be separated from any idea of a substrate. They can be abstract properties moving through space.

So what do you get then? It would seem that under appropriate experimental conditions, quantum systems are decomposable into disembodied properties. A collection of Cheshire cat grins, if you will. So how is it that an abstract property could exist without any sort of substrate? Well, it can’t. Of course being a good kind of neo-Aristotelian yourself, you would see properties as kind of mental abstractions from particulars… Not existing in and of themselves, but only in the objects.

Michael Egnor: But the property could exist in a mind.

Bruce Gordon: Yes, that’s exactly where I’m headed.

There is no physical substrate, but the property has to inhere in something, so it’s inhering in the mind that perceives it. So in a way you could look at the properties, the quantum mechanical properties as kind of abstract particular properties, tropes even. But the tropes have to inhere in something. What they inhere in is a mental substance, not a physical one.

Michael Egnor: What’s particularly fascinating as you point out, is how a deep look at the peculiarities, at the counterintuitive aspects of the quantum world, suggests that only an an idealist metaphysics could make sense of all this. That materialist, or perhaps even dualist metaphysical perspectives fail at the quantum level. But the idealist perspective doesn’t.

What I’m fascinated with, particularly in neuroscience, is the fact that there are aspects of the hylemorphic perspective of Aristotle and St. Thomas that really do seem to make sense of empirical scientific results in very nice ways. I would love to see some kind of consilience between idealism and Aristotelian metaphysics. But idealism, as a theory of physics, is the only one that seems to me to be viable.

Bruce Gordon: One of the things that we didn’t talk about is the possibility of macroscopic superpositions as well…

Next: Could the world above the level of the particle be superposed in this way?

Here’s the first part of this podcast: In quantum physics, “reality” really is what we choose to observe Physicist Bruce Gordon argues that idealist philosophy is the best way to make sense of the puzzling world of quantum physics. The quantum eraser experiment shows that there is no reality independent of measurement at the microphysical level. It is created by the measurement itself.

Here are stories from Bruce Gordon’s previous podcast with host Michael Egnor, where he defends idealism as a way of making sense of nature:

Why idealism is actually a practical philosophy. Not what you heard? Philosopher of science — and pianist — Bruce Gordon says, think again. Is reality fundamentally more like a mind than a physical object? Many are sure of the answer without understanding the question.


A physicist and philosopher examines panpsychism. Idealism says everything is an idea in the mind of God. Panpsychism says everything participates in consciousness (thus is not just an idea). Bruce Gordon thinks that, for a thing to be conscious, there must be something that it “is like” to be that thing. Can panpsychism demonstrate that?

Show Notes

  • 00:23 | Introducing Dr. Bruce Gordon
  • 03:03 | The mind-dependent character of reality
  • 06:50 | What counts as a measurement?
  • 12:36 | The phenomenon of non-localizability of individual particles
  • 14:34 | The quantum Cheshire Cat phenomenon
  • 17:18 | The idealist perspective
  • 18:37 | Wrapping in Aristotelian and Thomistic thought

Additional Resources

Podcast Transcript Download

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IS the Moon There If No One Looks? Or Is There No “There” There?