Because belief in a deity is rather nonsensical when a God isn't really necessary for the creation of the universe or any of the subsequent events and occurrences.
I'll give you a simple history of the Universe - this includes the scientific theories of the Big Bang and Evolution, don't confuse or mix the two up:
The universe seems to have formed approximately 13.7 billion years ago in a rapid and massive expansion of space-time called the big bang. After the initial inflation, the energetic particles cooled, and nuclear reactions created what was to become matter, which eventually clumped together to form galaxies and stars. Over the course of stellar evolution heavier elements were produced, leading to later generation stellar systems having planets sometimes largely made of those heavy elements - rocky planets.
Our solar system is roughly 4.5 billion years old, and features a handful of such rocky planets and smaller debris, along with four gas giants, which are largely composed of lighter elements and compounds. After a long period of cooling, our planet became hospitable to the evolution of the very complex organic compounds which are now known to be abundant in the universe. One collection of said compounds typed this not long ago, while another collection is now reading it.
yes. it is thought that the big bang was the "creation" (expansion) of the universe. and more specificly that the earth started when two big asteroids colloided. i like to think that God started the big bang.
ok if you think that the big bang theory started the world then, how did Heaven and Hell start?
Most Atheists AND scientists you find out there aren't going to believe in something as unprovable as heaven or hell - you might get some 'Christian scientists' (a contradiction in terms) give you some vague handwave about metaphysical planes of existence but that's about it.
If one embraces religion as being true, following their holy book correctly, then there is always going to be a bias in the way that they conduct research or experiments and how they interpret findings. I'm not saying that the casual observer has to decide between being religious and following scientific theories as being correct but the researcher bias you get with strongly religious people tends to make their findings skewed and untrustworthy.
If you don't believe in heaven and hell then where you going when you die, cause to me i can't think of anywhere else.
If it helps you to get a better understanding then think of it as being like the time before you were born - you, as a thinking and feeling entity, don't exist any longer. Brain functioning ceases and all those little electric signals stop too, you're dead and gone but you won't feel a thing or even notice it because you won't exist.
