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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

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:

A partial transcript, Show Notes, and Additional Resources follow.

Michael Egnor: When I was in college, I was a biochemistry major and I took some courses in quantum mechanics. It was noted in the course that when you look at the most fundamental properties of subatomic particles, matter seems to disappear. That the reality of the subatomic particles is that they’re mathematical concepts. It utterly fascinated me that, at its basic structure, reality is an idea which fits very nicely with idealism. Dr. Gordon is an expert on idealism and on the philosophy of science. What do you think about all this?

Bruce Gordon (pictured): Well, certainly my own path to idealism was paved by my reflections on the metaphysics of quantum physics. So I’m deeply sympathetic to the questions that you’re raising.

Quantum physics is a highly mathematical theory that describes the nature of reality at the atomic and subatomic level. The mathematical descriptions of quantum physics have a variety of experimentally confirmed consequences that — I would say — preclude the possibility of a world of mind-independent material substances governed by material causation.

We live in a reality that seems very much to be described by classical Newtonian kinds of mathematical descriptions. However, at the most fundamental level that’s not the case.

Note: Newton’s Laws of Motion, formulated by Isaac Newton, describe — in simple terms that can be rendered in mathematics — the way objects and force behave in the visible world around us. For example, Newton’s First Law can be phrased: “objects tend to ‘keep on doing what they’re doing’ (unless acted upon by an unbalanced force).” – “Newton’s First Law,” (Physics Classroom).

No “law of nature” makes moving objects stop. They stop because forces act on them. Otherwise, they would just keep moving. Similarly, no “law of nature” makes still objects stay put. They stay put because no force is acting on them, causing them to move.

The world we can see around us works on these kinds of principles. But down at the level of, say, electrons, the types of rules followed — while strict — are quite different.

Bruce Gordon: Let’s take a look at some interesting quantum experiments that point toward the mind-dependent character of reality… Fundamentally, we’ve got a situation in which reality at the quantum level does not exist until it is observed. I think one of the most fascinating ones is the quantum eraser experiment.

When you’re not observing reality, it seems to behave in accordance with the Schrödinger wave equation, and various relativistic expressions of that. But when you are observing it…

Note: The Schrödinger wave equation “is a partial differential equation that describes the dynamics of quantum mechanical systems via the wave function.“ – Electrical4u.com The equation describes, using mathematics, what quantum systems do when no one is trying to measure them.

Bruce Gordon: So what does the “delayed choice“ quantum eraser experiment do? Well, it tries to measure which path a particle would have taken after interference in the wave function has been created that is inconsistent with that particle’s behavior. So you’ve got a splitter of some sort. It’s going to divide the quantum wave function and send it along two different paths. Then you’re going to make a measurement along one of the paths to see what’s happening.

That interference can be turned off or on by choosing whether or not to look at which path the particle has taken after the interference already exists.

Now if you don’t look, you get an interference phenomenon at the end. If you do look, the wave function instantaneously collapses and you detect the particle along that pathway. So choosing to look erases the wave function and gives the system a particle history.

Bruce Gordon: This experiment has been performed under what would be called Einstein Locality Conditions. In other words, no signal could have passed — subject to the limiting velocity of the speed of light — between the components of the system to cause the effect that you’re observing.

The very fact that we can make a causally disconnected choice of whether wave or particle phenomena are manifested in a quantum system essentially shows that there is no measurement-independent and causally connected, substantial material reality at the micro physical level. It is created by the measurement itself.

Michael Egnor: What counts as a measurement?

Bruce Gordon: What can count as a measurement is any sort of interaction that would localize the wave function and yield a determinant local result. That could involve a conscious observer, or it might not involve a conscious observer.

Michael Egnor (pictured): What sort of measurement wouldn’t involve a conscious observer? Does it matter how much you pay attention? If I’m a little preoccupied, do I not get much interference, but maybe a little? Because it really implies that there is an actual something that is observation and it’s an on or off thing, it’s yes or no. There’s no in between…

Say, for example, that I’m a physicist who is looking at a quantum system, and I’m actually looking at the oscilloscope, or whatever our modern instrument is, when it’s happening. Everybody would say, “Well, that’s an observation for sure.”

But let’s say that I’m not in the room and I’m just taping it but I plan to look at it later. Is that an observation? If I change my mind and decide not to look at it, does that change the system?

I’m fascinated by what we mean by an observation because in reality, an observation is a continuum. I mean, I could be watching something, then my mind wanders. I’m thinking about lunch. Does that make the system go back into indeterminacy? Then it becomes determined again when I focus on it?

Bruce Gordon: Not necessarily, if you’ve got decoherence happening in the quantum metaphysics of the world around you. So how do we bring this into relationship with idealism…?

In fact, I was going to talk about some other experiments to kind of further massage people’s intuitions with respect to the nature of the reality that undergirds these sorts of phenomena. Let me talk about at least a couple more. Then we’ll come back to the question of, “What’s going on when we’re not looking?”

Michael Egnor: Right. Is the moon there if no one’s looking at it?

Next: So is the moon there if no one is looking at it? Or is there no “there” there?

Here are stories from Bruce Gordon’s previous podcast with host Michael Egnor, where he defends idealism as a reasonable 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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In Quantum Physics, “Reality” Really Is What We Choose To Observe