Back to the serious business at hand: Copenhagen is really about mankind's constant, hopeless quest for understanding, of the universe and of each other. Another person's motivations and feelings can't ever be nailed down.
"The fundamental bass note of it is human puzzlement at the world," Beale agrees. "The blackness of not knowing. Inside the human brain, inside the human soul, is the dark."
Cumberbatch takes up the theme. "The way atomic physics works is a metaphor for these three people trying to understand their motivations looking through the mists of time," he says. "That's what Michael's done so beautifully, because it's not a patronising way to represent the arguments: it is what science is. Science has come from the human, not the other way round. Our idea and understanding of it is through our sensory filter. Whether that be a process of mental theory or observable, experimental, tenable science, it's a beautiful metaphor for these three people trying to understand each other - and then you've got war splitting everything apart."
Perhaps it's not too much of a stretch to suggest that, for someone at the level of fame Cumberbatch enjoys/suffers, there's special resonance in the idea of piecing together an image of a person that can never be correct. Cumberbatch's every move is now monitored, but do any of his fans really know him?
"They know you from the trail you leave with your work," he replies, the slightest edge of frustration in his voice. "They assume things about you because of who you play and how you play them, and the other scraps floating around in the ether. People try to sew together a narrative out of scant fact."
Says Beale: "Some of it's harmless. There are funny things. I recently broke my finger on stage, and apparently I struggled on through great pain. I know that's going to reappear: my bravery. Actually I wasn't in any pain at all because that's not what you do when you break your finger: some adrenaline kicks in and it just feels odd. But I love the idea that I struggled on. That's fine."
Not that Cumberbatch would, in any case, ever be so blithe or inelegant as to carp about the attention he gets. "I have been around for ten years. I don't want to complain or explain. It's a thing that will pass. It's part of a predictable pattern."
Does he worry about portraying real people and events? "Not when you're in Michael Frayn's hands, no. Yes, you have a responsibility. It's an examination of various interpretations of what happened and why, rather than definite statements or a political axe to grind. He takes care of that."
A radio studio is sanctuary from the crazy world outside, but what makes Cumberbatch a particularly good fit for the medium is his deep, commanding voice, which incidentally has given him a busy sideline in narrating adverts. Listen the next time you have to sit through a commercial break. Insurance, dog food, digital cameras: Cumberbatch's brushed-suede vowels will be there somewhere.
Radio's focus on the pure power of the human voice is something that genuinely excites him. "I love Radio 3. I'm Radio 3 in the car as well. And Radio 4: I change between the two, I'm not religious about it. Radio's something I go back to if I've been out of the country for any length of time. I still find the magical art [when acting on radio] of what effect you are having, how the space is constructed, what the mic's doing, is a mystery. It's nice to really intensely concentrate on and listen to the word and the sense of the word. Radio's a joy. It's just a joy."
Copenhagen is available on iPlayer until 20 January