Lemmings, please read the post don't blindly downvote because you don't like the title - this is a debate forum so if you don't want to debate, unsubscribe or just ignore, thank you!
final edit: I guess I overlooked the sentence in the sidebar that says, “A place for theists to come and debate atheists”. I am myself atheist (using the definition in that same sidebar) so please forgive me and treat this as a debate between atheists. Thanks everyone for the great responses so far. The original post follows:
As the title says - if you believe that our scientific worldview is accurate and mostly complete, and that consciousness is entirely explained by the interaction of atoms in our bodies, then you must believe in reincarnation.
Here's the reasoning. If you believe your consciousness now is the same consciousness that existed in your head when you woke up this morning, despite the fact that the atoms that cause your consciousness are now arranged slightly differently and interacting differently, then there's not just one single arrangement of atoms that will cause the experience of "you" - there are many.
If you believe, as I do, that the consciousness that exists in your head now is the same consciousness that existed in your head as a child many years ago, and is the same consciousness as the one that will exist in your body when it is decades older, then there must be a whole set of different atomic arrangements which all generate the same unique conscious mind.
The universe today is actually fairly young. It's expected that it will continue for hundreds of trillions of years. It is a huge amount of time, and if atoms have come together in the right way to produce my consciousness now, after only 13 billion years, then it's reasonable to suppose that over the next many trillion years, the right arrangement of atoms will occur again at some future time long after this body is gone. And in fact, it's reasonable to suppose that this very same consciousness will be produced many many times over.
I do see one other option: consciousness is recreated anew every single moment, and we only have the impression of being a single continuous consciousness thanks to memory telling us what the previous consciousnesses that lived in our bodies experienced.
So which do you believe? You will live for ever, or you actually only live for a split second?
I'm not any kind of Buddhist or anything. In fact I'm vehemently opposed to religions of all kinds. I do believe science offers the best way to look at the world. Unlike religion, science starts from the reality that we do not know anything for sure.
Science questions everything and, from a starting point of pure ignorance, has gradually, cautiously and carefully, built up a coherent worldview that delivers real results - which is so much more than any religion can say.
However there are still very big and very important questions that have not been answered, and which we do not seem any closer to answering - to name but two, why am I me and not someone else, and what will happen to me when I die.
These are extremely important questions, and the honest approach right now is to say, "I don't know" and continue to live in ignorance.
By posing the question of this debate post, I'd like to challenge the seemingly widespread belief amongst atheists that once we die, we disappear as if we never existed. That might be a possibility, but it is far from the certainty that many atheists believe it to be.
I guess I overlooked the sentence in the sidebar that says, “A place for theists to come and debate atheists”. So please forgive me and treat this as a debate between atheists.