I don't know, and I don't think anyone does.
I think there are some things which as humans we don't have the capacity to understand, and I think death is one of them. I would like to think there is an afterlife, and part of me refuses to believe there isn't, but perhaps that is just human instinct.
All I know is that we have this wonderful life now and we must make the most of it.
What I will say, though, is that I think it is arrogant and narrow-minded to say 'there is definitely no afterlife'. Think about it, we are all living on some random rock in the middle of a huge dark space we know nothing about. We don't know
anything as humans, and we create all these rules, beliefs and conventions to make up for that. I wouldn't be surprised if everything we know about science is wrong too - it is simply beyond our understanding.