If you could only listen to someone talk about one topic for the rest of your life, what would it be, and why?

I'm going to metagame this one and say "current events".

Trains.

My kid is a train kid, I'm already listening to it non-stop, I won't make things worse for me or him.

Hello fellow parent. I feel your anguish. I have star wars and dinosaurs. Tbh I'm not even mad, most of the times... I'd just need some more time in the morning before the uninterrupted stream of words!
- Exactly. He's turning into a Lego kid, but uh, did you know that Lego has trains? (They recently put out a gorgeous Oriental Express train that even I want now.). My biggest gripe about trains is they take up so so so much space.
  
  I am excited for his teenage years for when he wants to sleep in and I get to wake him up.
  
  But today is Christmas, and if you celebrate, Merry Christmas. (Mine is waking now, and it's 430 am, time to stall him for 2 hours, as my daily gift to momma)

Carl Sagan or Richard Feynman talking about physics or astronomy.

Feynman. No question.

The universe.

Everything that has ever happened has occurred in the universe as far as anyone knows. Including all fiction.

My husband talking about something he's passionate about and makes him happy. It doesn't matter what, I love how excited he gets when he's explaining something that matters to him.

Honestly, nothing. No matter how strong my interest is in something, it will eventually shift dramatically and I'll have trouble listening to any other thing.

I had to listen to a guy talk about the fanfic he was writing for 4 hours. So anything but that I suppose.

Music

Story telling I'd ask them to improvise or use known stories to give me examples, I now have stories for a lifetime

Astrophysics/cosmology. I'm more artsy geek than STEM geek, but there is a tremendous amount of beauty found in what we know and don't know about the universe.

Food. I love cooking and baking and recipe planning and eating and thinking about food and talking about food

I'd pick J.R.R. Tolkien and Middle-earth, no hesitation

The science of how color is reproduced via display technology, including colorimetry, photometry, and signal processing

"When we reached SuperTwist monochrome passive matrix LCD's we thought we'd reached the peak for universal display technology; great contrast, cheap to manufacture, and low power."
- Peak universal display tech and monochrome?? Who said this?

Animal behavior. I never get bored learning about biology and specifically, all the interesting behaviors that animals have learned to reach their goals. Like elaborate mating dances, or long distance communication of whales.

Don't you put that evil on me. That sounds like a decent approximation of hell.

Yeah, I'd rather be deaf.

One subject I could manage (psychology/AI if it has to be nonfiction or mysteries if fiction counts), but not one voice.

Warhammer. There is so much lore and battle reports out there you could fill your life.

Also I am being cheeky by not specifying Fantasy or 40K so I get both.

Philosophy.

Privacy

richard stallman

Do we get to pick the person? I'd say Nigella Lawson talking about cooking.

Food

They didn't say you could eat it. You just have to listen to endless speeches about it. Is "food" your final answer?
- I love talking about food, so yes. Listening to it would be pleasant.

Sam Harris about moral philosophy.

I find his reasoning to be incredibly logical and easy to follow. On top of that he has a really pleasant voice.

Touhou lore I think.

Link for people who don't know what it is?

I’d listen to the Verizon commercial guy explain how if he can hear me now, that it’s good. A simple subject, a search for truth. Is it good to always be able to hear someone? I don’t know, yet. This is the kind of Hell I can get behind, just me and that sorry son of a bitch. Decades, millennia—CAn yOu HeaR Me nOW?

…

Good

Ethics. It touches on every other subject.