Starting around 2:16 in this excerpt from The Atheism Tapes, Jonathan Miller and Daniel Dennett are talking about people who profess to believe in an “immaterial soul” that goes on after the death of the “physical body”.

Jonathan Miller says:

I find it very hard to see how they can actually formulate or conceive the notion of an immaterial continuity of an unembodied self – of how it would know that it was in fact the thing that had once been the embodied person, with a particular name, with particular projects. It’s always seemed to me that the notion of projects, and trajectories, and hopes and plans and so forth, are all tied up with being embodied.

Daniel Dennett says:

Yes, and I think that everybody cheats when they think about this. I mean in the way that scientists cheat too, when they imagine hard-to-imagine things. So people, when they imagine an immaterial soul – they don’t! They imagine a sort of ghosty sort of semi-transparent material object that’s got arms and legs and a particular physical location, but just isn’t quite physical. It’s sort of like a hologram. And they know that that’s not right. They know that a soul isn’t really like that. And they know they can’t really imagine an immaterial, disembodied soul. But that’s all right, these things are hard to imagine! “Physicists can’t imagine quantum mechanics, and we can’t imagine an immaterial soul. But, you know, we can try, and it doesn’t hurt to think about, you know, people playing harps sitting on clouds.”

I often ask my students, when they were children and reading comic books or watching on television, did it ever bother them that Casper, the friendly ghost, could both fly through a wall, and catch a ball? I mean, why doesn’t the ball just go right through his hand? And almost all of them say, Oh yes, they had noticed this mildly discomfiting inconsistency, but everybody goes along with the gag. But everybody notices that this is not really consistent.

There’s a big difference between a scientist trying to visualize quantum mechanics and a person trying to imagine an immaterial soul, which is really an immaterial person, which is a contradiction in terms. Dennett reminds us that a truly immaterial thing would not even have “a particular physical location,” to say nothing of arms and legs.

Physicists try to visualize the inner workings of atoms because atoms almost certainly exist. Quantum effects are hard to visualize because they seem to require contradictory predicates: very small entities are, famously, sort of “like waves,” and also sort of “like particles.” But this is an apparent contradiction, caused by limited understanding and limited vocabulary. One can imagine a future in which we can speak with perfect clarity about the inner workings of atoms. But in the idea of an unphysical person there is an inherent, a priori contradiction.