Céline Boisserie-Lacroix: That’s why we are not on the same level in this dis-cussion. Because when I said there are all these approaches, it’s important to understand that what we mean by “system” is the whole observation system. This includes the particle being observed, the experimental setup that lets us observe it—in your case, a microscope, the different optics, the visualization system, etc.—and, of course, you. So, what we’re trying to figure out in this philosophical theory is whether the properties of a particle could exist or be known independently of the observation system.

Aurore Young: Yes, it’s just a bit weird because I get what you mean about prop-erties, but for the object itself, we know that if we repeat an experiment, we’ll observe something. It won’t just come out of nowhere. But yes, as long as I haven’t observed it, I cannot exactly predict its property.

Céline Boisserie-Lacroix: Yes, absolutely.

Aurore Young: But once I’ve observed it, I know where it will be, to some extent. And I know I’ll measure something.

Céline Boisserie-Lacroix: Basically, whether you want to know the spin or another property, you can’t know it in advance. It only becomes clear once you observe it. This is what the famous Schrödinger’s cat experiment explains: you can’t know whether the cat is alive or dead until you open the box—that’s what we mean by property here.

Aurore Young: I mean, we know the cat is here. It’s in the box, but what we don’t know is which of its properties is there.

Céline Boisserie-Lacroix: Yes, if its property is being alive or being dead. If we can’t know this property independently of any act of observation or any obser-vation system, then it raises the question of whether this property can be known in the absolute, or even if it has any reality outside of the observation.

We often distinguish between properties independent of the observer, like dan-gerous, and those that depend on the observer, like scary or funny. For example, I might say this joke is funny, maybe only if I laugh at it. If we go back to this distinction, we can then ask: since we have these two distinct types of properties, what can we say about the properties of quantum objects?

Aurore Young: But how does this challenge the notion of reality? Because we’re talking about some properties of objects, and these are objects at the microscopic level. In our world, which we call “classical”, science can predict exactly what’s going to happen. So, why are we even discussing reality? Because we know these objects exist, we just don’t know the reality of some of their properties.

Céline Boisserie-Lacroix: It’s about the question of properties of things that make up our world.

Aurore Young: Yes, okay.

Caroline Delétoille: We were actually talking with a researcher in Paris, and he was saying that there are about fifty articles a day on the questions raised by quan-tum physics and physicists. And it sparked a little animated discussion within the research community, just like this one.

Aurore Young: Yeah, there are many interpretations about what exactly lies behind the reality of certain properties of certain objects. So yes, this raises a lot of debates, but I think it’s mostly a question of interpretation. But maybe that’s exactly what philosophy is about, and quantum philosophy in particular.