Technically, I am a strong atheist, which means I hold "the philosophical position that God or gods do not exist. It is contrasted with weak atheism, which is the lack or absence of belief in God or gods, without the claim that God or gods do not exist." Make no mistake: I do not claim that I can prove that there is no God; it is simply my belief. However, please don't write and tell me that I have "faith" that there is no God, since "faith" has implications which don't make sense for atheists. One can't have "faith" in nothingness.
So if I can't prove it, why do I believe it, especially since I was raised an Orthodox Jew? Well, I can describe how I arrived at atheism and perhaps that will do. As early as I can remember, I believed in God, since that's what I was taught by my parents. I was a curious child, though, and I always had questions. I was also cocky and didn't believe anything just because somebody said it. My first doubts probably started when some of my early rebbeim said things which I knew to be untrue or believed to be immoral. Being curious, if a Rabbi contradicted a science book, I did more research. In the end, I found the science books to be more credible than my Rabbis, who, while intelligent and learned in one particular field, were demonstrably ignorant in other matters. Once I realized that it was possible for Rabbis (and secular teachers, too, of course) to be incorrect, I became a skeptic. If I was taught something which seemed wrong and was testable, I would test it. If it weren't testable, I would do research and find the most credible sources I could come up with.
Eventually, I realized that if Rabbis could be wrong, perhaps the Torah could be wrong. After all, what made me believe it was the word of God other than the claims of Rabbis I knew to be fallible? I started thinking about Breishit (Genesis) since it makes many claims which are relatively testable as compared to stories about people who supposedly lived 3000 years ago. The six days' account of creation seemed to contradict Evolution, which I had come to believe in through my readings, but I could reconcile the two if I sort of squinted and told myself, "Well at least the Genesis story is presented in mostly the right order."
The first thing that really tripped me up was the idea of the firmament:
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. (Genesis 1:6-7.)
What was this? First of all, this seems to imply that the Earth is the center of the Universe. But more imporantly, it clearly states that some firmament actually exists and there's water on top of it. To my understanding, no such thing exists. I was troubled. I went to one of the smartest Rabbis I knew and I asked him what the firmament was. He said, "I always thought of it as the stratosphere." Huh?? That didn't make any sense at all. Combined with the other curious parts of the Genesis story like the fact that it took place in 6 days, that there was no mention of dinosaurs or of mass extinctions (pre-Flood), that it doesn't appear to agree with evolution, that it doesn't seem to realize that the Moon is a satellite nor that the Earth is a planet, I decided it must not be literally true.
Well, so, maybe it was metaphorical. Maybe it was just a pretty story. But then what about the rest of the Torah? Was the Flood just a story? How about Abraham? I was a big reader of fiction as well as science books and the stories in the Torah certainly read like fiction. Don't Adam and Eve, Cain and Able, Isaac and Ishmael, Isaac and Esau sound like fiction? Aren't they a little too pat to be historical record? Joseph and the multicolored coat? Come on, now. What about Egypt? How do I know that even happened?
I read about other religions, past and present. I wondered, did the Greeks and Romans literally believe in their mythologies? How were my Rabbis so sure that the Torah is true but the New Testament is false? Why were the Muslims as confident that they're right as we were that we were? Wasn't it unlikely that I was just born into the right denomination of the one true religion? Didn't Muslims and Baptists and Catholics all think the same thing? Why hadn't all the smartest, best, and most learned people in the world converted to Orthodox Judaism if it's so obvious that we were right?
I was going to have to look at it objectively. I couldn't directly test whether a given religion was correct, since religions are so slippery. You disprove one thing, and the apologists say, "Oh no, that doesn't mean what you think it means. It means [this entirely different thing.]" I started to think about that phenomenon a little bit more. It was interesting that as scientific knowledge grew, religious claims seemed to get milder and milder. Long ago before videorecorders and Richter scales, Moses supposedly split a sea. Before we knew that the Earth rotates, the Greeks believed a god pulled the sun around the earth each day. The Egyptians thought the sun was God. Jesus supposedly walked on water. But it was fascinating that whenever we figured out how something works, religion simply accepted our explanations and shifted their claims to less impressive events. We started understanding weather better, and religions stopped claiming that the gods made it thunder and rain, at least directly. God Himself (or Herself or Theirselves) became less specific. God became abstract.
Okay, so maybe God was this abstract Thing which didn't directly cause thunder or give people leprosy for lying anymore. Maybe the Torah stories were just for the people who lived back then, so that they would understand. But if God wrote the Torah, or if God even talked to Moses, or talked to anyone, why didn't He take some easy steps to alleviate suffering? Couldn't he have just explained about tiny, invisible bugs that cause illness? If God exists at all, why does He allow such misery in the world? Why the earthquakes and the holocaust and child slavery? Why does the Torah hate gay people so much? Why does it allow slavery and condone genocide (e.g. of the Midionites and Amalek?) Even if it's not literal, even if the Torah is just allegory, and even if God inspired it rather than dictated it, shouldn't it be a better book? Shouldn't it be more moral?
I stopped believing the Torah wasn't written by people living thousands of years ago. I mean, what would it look like if it had been written by people who lived in Israel thousands of years ago? Wouldn't it reflect their ignorance and their knowledge and their hangups and prejudices? Doesn't it?
I started thinking about whether the Universe could exist in the absence of God. I read Stephen Hawking's book A Brief History of Time. I noticed that although he went out of his way to deny being an atheist, his book presents a good case for a Universe that runs by itself according to a bunch of math and physics and randomness. Hawking didn't know what caused the Big Bang, but it sure looked like the Universe has been taking care of itself since then. I read Carl Sagan. I realized how incomprehensibly huge the Universe is. I decided there's no reason for such an enormous Universe if the whole point of creation was humanity. I read Dawkins. Obviously, he was a fanatic atheist with a chip on his shoulder. But he made a lot more sense than most of the religious apologists I'd read.
Then I started reading philosophy. I read Bertrand Russell's Why I am Not a Christian and a whole bunch of stuff online. I found that Russell's and others' arguments made a lot of sense to me.
Eventually, I came to the conclusion that I no longer believed in God. I can't prove that God doesn't exist, but as John McCarthy wrote, "An atheist doesn't have to be someone who thinks he has a proof that there can't be a god. He only has to be someone who believes that the evidence on the God question is at a similar level to the evidence on the werewolf question."