Céline Boisserie-Lacroix: To put it simply, part of our knowledge of the world is very basic, acquired directly through experience. We see the world, and then we gain knowledge from it. Then, there’s another way of acquiring knowledge, a more rational one: through reasoning, reflection, etc. Are the knowledge we gain in quantum physics different from the knowledge we gain in classical physics, where these two ways of acquiring knowledge line up?

Aurore Young: Yes, from a broader perspective, because we can observe phenom-ena that don’t appear in the macroscopic world (the classical world). From knowl-edge standpoint, we know we are expanding our view because we observe more phenomena. We can reconstruct a mathematical object that has no relevance for classical physics, but that does for quantum physics. But to me, it’s still reality.

Caroline Delétoille: But, for instance, I discussed with an emeritus physicist, and he was explaining to me a quantum phenomenon he’s been working on. I said to him: “Well, it looks like magic, because it really seems like something I would never have imagined in my head.” And he said: “No, it’s quantum physics. You just need to admit that it’s like this, and not think it’s magic. It’s real life. Once you stop trying to explain it rationally, just follow the equation, take the measurement, and you’ll move forward”.

Aurore Young: Something feels like magic until we understand it. Maybe there are things we’ll never be able to understand because we’re made in a way that doesn’t allow us to access this kind of knowledge. So maybe something will always remain magical. But when he said we need to abandon a certain rationality, maybe he meant we need to abandon the hope of understanding why it’s like that. The “why” is a very broad question. And maybe that’s philosophy.

Maybe, as physicists, we try more to answer the question of how. If I have this initial condition, what will happen? And how? But the why, we don’t deal with. That’s philosophy, or even metaphysics, not really physics. I would say, when this emeritus professor says we should just follow the equation and rationally try to understand why it’s like this, yes, I can agree with that. Because there are so many “why” questions we can’t answer. So let’s just focus on what will happen if we con-duct this experiment and try to predict what will happen. That’s what interests us, and that’s enough. There are already plenty of things we don’t understand yet, but might hope to understand. The “why” part, we leave it to others.

Caroline Delétoille: To philosophers and artists, right?

Aurore Young: A lot of physicists become philosophers after their careers, like Niels Bohr. He started as a physicist, then developed a philosophical point of view. But those are precisely philosophical viewpoints. From the physicist’s perspec-tive, these aren’t things that are proved or tested. Maybe we just need to make a distinction between the two.

Céline Boisserie-Lacroix: There are different orders of truth, right?

Aurore Young: I’m not sure what you mean by “truth”.

Céline Boisserie-Lacroix: A scientific truth, for example. Or a theory, whether it’s scientific or philosophical, we try to prove that it’s true.

Aurore Young: When you talk about scientific truth, you’re talking about some-thing that can be observed in our reality. But when you talk about truth, like the truth, I don’t know what that is.

When I observe quantum phenomena at the microscopic scale, I think I’ve devel-oped a sort of intuition about this specific scientific truth. But I will always have this sense of strangeness when I think about the why, when I ask myself why it’s