A few questions

[Doubting Thomas]

1. Do you think it is possible to know why the universe exists?

If you mean how the universe came to be, then possibly yes. This is what the Big Bang theory hopes to prove. If you mean "why" as in a cosmic reason for our existence, there's nothing that says there has to be a reason like that. I personally don't need any cosmic or supernatural reason for my existence, I'm just happy to be here on the planet for the short time I get.

2. How do you think morality can exist without objective authority or verification?

People know they would like to be treated decently, and most people reciprocate. That's how the idea of "treat others as you want to be treated" came about. But in general, the laws of the society are usually needed to keep order.

3. If there is no afterlife, what motivation would/should anyone have for living any particular way, such as trying to live ethically, civilly, healthily, or any specific way?

Again, it goes back to the "treat others as you'd want to be treated" idea. Societies throughout history have known that allowing people to murder, cheat, or steal isn't good for society. And frankly, the idea of eternal punishment has not had much of a deterrent on Christians committing crimes, since the majority of people in prison in the U.S. are Christians.

4. If there is no afterlife and no essential or ultimate meaning to existence, why should an atheist care if someone believes in a religion and, indeed, if believing in a religion would make their life easier, would that bother you as an atheist?

I don't care what religion someone wants to believe in until they try to force it upon me or into the public or government. When we have religious people who try to hinder scientific advancement because of ancient superstitious religious beliefs, then I have a problem. We rational, thinking people know that religion tends to hamper a society. Furthermore, spreading the idea that I am not as good a person as they are because they believe in a religion or believing that I'm an evil, immoral person because I don't follow a religion harms my quality of life.

5. Can you be absolutely certain, without a doubt, that God or something supernatural does not exist?

Not totally 100% certain, but the burden of proof is upon those making the religious or supernatural claims. So far it's fairly obvious to me that all beliefs in gods or the supernatural appear to be made up by superstitious humans who couldn't understand the world & universe they live in. As science progresses, we find fewer and fewer reasons to keep believing in the superstitions, especially when they don't stand up to scientific discovery.