I work at a gas station. This home schooled kid is a flat earther and talks non stop. He's generally a nice person, but his views are awful and polar to mine.
I try not talking, but he continues to talk to me.
No one is going to read your mind, unless you speak about it.
Express your opinion about it, mention that you are not interested in either talking or listening about it. Be polite, but be straightforward. Mention that whatever be the case and irrespective of their opinion, you are not interested in a conversation about it. Also mention that you both are at work, and it will be for best interest for both of you if you can concentrate on work related matters.
Next time they approach you for a dialogue or monologue, mention the same and also the time after. Simply don't encourage them by listening to what they have to say, if possible engage in other activities and say, "as I mentioned earlier, can we not talk about this please?". Repeat couple of times and they should get the point.
To supplement the already good top answer: some general actionable advice for this and any other topic that comes up at work that you don't want to discuss.
When they start on the topic, cut in and stop it, but don't go all-guns-blazing straight away. Ramp up slowly. I suggest the following levels, with roughy 1-2 times per level before moving to the next.
Could we not discuss this? Would you mind if we don't discuss this?
I'd (rather not / prefer not to) discuss this
Let's not discuss this
Do not discuss this
Just to deal with the unlikely case that it continues beyond this, the next step is to escalate to management as harassment. There is zero chance that anyone reasonable would continue beyond this point, and if they choose to do that, they choose to face the consequences.
I feel you are a nice guy, and I respect you having your opinions.
But in this matter, I disagree so strongly that I doubt if I'll be able to rely on you acting sensible and to-scientifically-proven views. And we are handling shit that explodes here!
I appreciate your company, but talk to me about anything else, no more flat-earth thing, please.
Just a few ideas:
1) Maybe just humour him. I talked in detail to a flat earther once and his general point was that while there's supposedly scientific evidence for a round earth, none of this is things you can directly verify. For example, the blue marble photo could be faked. Even Eratosthenes' experiment can't be reproduced by an individual; it depends on knowledge of the distance and direction between Alexandria and Syene.
2) Fight fire with fire. I heard of an anti-vaxer who was won over by being persuaded that anti-vax was actually a Russian conspiracy. Potentially you could do something similar, I don't know, maybe flat earth is a rumour created by NASA because they found platinum reserves on the South pole.
3) Use body language. If you don't want to talk, avoid pointing your body towards him, tut and look distracted while he's talking, walk off without explanation, etc.
I don't think any of these are brilliant, but I hope they give you some ideas.
A polar view is not bad, what is bad is dismissing ideas without proper Socratic argument. Since he is a nice person that means he would be open to open discussion, do NOT question him but do question the base of his and your own views.
This might be an opportunity for both of you to grow. Give him a good question to think about, and ask him to do the same. That would make him think before talking.
Somebody who was home schooled did not have anyone to talk to, he is a victim of his parents views, he did not chose to become what he is.
Regarding the flat earth or round earth, what difference makes to either of you? If earth was a rhombus balanced on a peanut would not help with either of you saving a dime.
I have worked with people who spend their time making fun of flat earthers, I couldn't care less about the shape of the earth but I was annoyed with them not having a clue about celestial mechanics and size of milky way and not having anything new to teach me.
The real question you needs to ask yourself is would you would have been any different if you had to live his life? and how the hell you can work together to be more than what you are individually?
Flat earth or spherical earth does not make an iota of difference in either of your lives, but being able to work cooperatively with those who you don't agree with will give you a real skill anywhere you work.
Tell him to present you a actually working model of a flat earth (all-in-one, like a globe does...) that can represent day/night cycle simultaniously with seasons and moon/sun eclipses with tides across the opposing sides on that same model without the sun jumping and beeng a spotlight! then you will listen to him and be sure to record it for the "Revolution"-History-Classes surely to be teached in the new world order! (I'm serious, still searching youtube for the evidence, because: where else??!!!)