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How many people are atheists? 
It's hard to know how many atheists there are. For one thing, not everyone means the same thing by "atheist". Also, some religions are consistent with atheism of some kind, so that a person can follow that religion and be an atheist at the same time. Jainism is like this, to some extent Hinduism, and some forms of Buddhism. Those people may describe themselves as members of the religion rather than as atheists. Another problem is that atheists are persecuted in some places, so people in those places may not be willing to admit to atheism.
It's been estimated that about twelve percent of everyone in the world describe themselves as "nonreligious", which is one definition of atheist. But only about two and a half percent describe themselves as "atheist".
Where is atheism practiced? 
What are the main beliefs of atheism? 
Atheists believe lots of different things. Some are deeply spiritual people. Just as there are lots of different kinds of theists —people who believe in gods (perhaps one, perhaps many)— there are just as many different kinds of atheists — people who, whatever else they believe, don't believe in gods.
Many atheists believe in the value of skepticism, and of science. These two are very closely related. Skepticism is questioning beliefs and asking for evidence to support them. The basic premise of science is that we should choose our theories about the physical world based on experimental evidence.
Nonreligious atheists are often secular humanists. Secular humanism emphasizes morality, rationality, and social justice. It says that the world is governed by natural laws, rather than supernatural beings; and that the difference between right and wrong comes from the nature of humans, and of the world, and of the way humans live together, rather than from supernatural beings.
Many atheists, especially nonreligious ones, place a lot of importance on tolerating other people's beliefs. That doesn't mean not criticizing others' beliefs; skepticism requires us to question beliefs, whether our own beliefs or other people's. But it does mean not persecuting others for their beliefs.
Some secular humanists promote spoof religions. This can promote tolerance for others' beliefs while at the same time pointing out the dangers of not being skeptical enough. A spoof religion that has gained some attention in recent years is the Church of the Flying Spaghetti Monster, also called Pastafarianism. In 2005, the Kansas school board voted to allow Intelligent Design —the idea that the complexity of the world can only be explained by its being created by God— to be taught in biology classes, alongside evolution. A physics graduate, Bobby Henderson, sent the board a letter saying that since he believed the world was created by a flying sphaghetti monster, they should teach that alongside the other theories. Two years later, the board reversed its decision. If you see someone on the Internet say "Thank FSM" instead of "Thank God", the "FSM" stands for "Flying Spaghetti Monster".
Different kinds of unbelief 
The word atheism is used in at least two different ways. Technically, the word means "without gods"; that is, atheism is not believing in any god(s). But —careful!— not believing in gods is different from believing there are no gods. Not believing in gods names something you don't believe in: gods. Believing there are no gods names something you do believe in: you believe that there are no gods. The word "atheism" is sometimes used for one of these things, sometimes for the other. So to keep them straight, we call the not-believing-in-them weak atheism, and the believing-there-aren't-any strong atheism. All strong atheists are weak atheists (because you can't believe they do and at the same time believe they don't exist). But many weak atheists are not strong atheists (because they neither actively believe gods exist, nor actively believe gods don't exist).
Some people also distinguish between weak atheists who have never thought about whether gods exist, and weak atheists who have thought about it. Weak atheists who haven't thought about it are called implicit atheists. Baron d'Holbach, a French philosopher in the 1700s, wrote "All children are born Atheists; they have no idea of God." When children have no notion of gods, they can't have thought about whether gods exist. Weak atheists who have thought about it are called explicit atheists.
There's another word you may have heard: agnostic. People sometimes use that word to mean someone who doesn't have an opinion on whether gods exist — a weak atheist. But the word agnostic was actually coined (that is, invented as a word) specially to mean something different from that. It was coined in 1869 by an English Biologist named Thomas Henry Huxley, who promoted Charles Darwin's theory of evolution. He defined the word to mean someone who believes that it's impossible to know whether or not gods exist. Yes, that's naming something that agnostics do believe in: they do believe that there's no knowing whether or not gods exist.
What texts does atheism hold sacred? 
Something is sacred if it is treated with deep respect and reverence. You don't have to believe in any supernatural being to hold something sacred. However, so far there are no texts that are widely viewed with that level of reverence by secular humanists.
There are some books that are widely respected by secular humanists. Richard Dawkins, an outspoken modern critic of theism, has written a number of books exploring the implications of the theory of evolution — which is of much interest to secular humanists, as evolutionary theory explains how simple laws of physics can give rise to the vast complexity of the world without any need for supernatural beings to make the complexity happen. His most famous book on this subject is The Selfish Gene, which is about the theory of evolution itself; another is The Blind Watchmaker, which explores in detail one example of evolution producing something so complex that, once produced, it looks as if someone had designed it. He has also written a book specifically about religion, called The God Delusion.
A work associated with both skepticism and spoof religion is The Illuminatus! Trilogy, a science fiction/fantasy work that carries conspiracy theories to absurd extremes, and so teaches readers to be skeptical about conspiracy theories (and skeptical about most everything else, too).
The spoof religion Pastafarianism has a book setting forth its core beliefs, The Gospel of the Flying Spaghetti Monster, published in 2006 by Bobby Henderson who "founded" the Church with his letter to the Kansas school board.
What are some main holidays and practices of atheism? 
Since the 1990s, there has been increasing observation of Darwin Day on February 12, a commemoration of Charles Darwin, the discoverer of evolution, on the anniversary of his birth. You don't have to be a secular humanist to want to commemorate Charles Darwin, but it does enjoy some popularity among secular humanists.
The spoof religion Pastafarianism has several holidays. One Pastafarian holiday, called simply Holiday, occurs around the same time of year as Christmas, Kwanzaa, and Hanukkah and does not have a fixed precise date. So, any use of the phrase "Happy Holidays" or "Holiday greetings" is claimed to be evidence of support for Pastafarianism.
What is the history of atheism? 
Who are some famous people who have practiced atheism? 
- Douglas Adams
- Richard Dawkins
- Sigmund Freud
- John Lennon
- Susan B. Anthony
- Brad Pitt
- Thomas Edison
- Helen Keller
- Mark Zuckerberg
- Bertrand Russell
What is a story from atheism? 
There is a popular story about French astronomer and mathematician Pierre-Simon LaPlace and French Emperor Napoleon I. Like many such stories, it apparently didn't happen quite the way it is told, but the truth isn't too far from the story.
The story, as usually told, says that in the early 1800s, LaPlace presented Napoleon with a copy of his Mécanique Céleste (Celestial Mechanics), a set of books about how the solar system works. Napoleon asked him why he had written all these books about the workings of the solar system without mentioning God, to which LaPlace replied (so the story goes) "Je n'avais pas besoin de cette hypothèse-là" — "I had no need of that hypothesis".
The story is often taken to mean that LaPlace had not needed to suppose the existence of God. Actually, the issue with the Mécanique Céleste seems to have been whether God has to intervene to make the solar system work. More than a century earlier, English physicist Isaac Newton had claimed that if the solar system were left to work on its own for long enough, eventually the planets would wobble out of their orbits, unless God intervened to keep the solar system stable. LaPlace disagreed with this; he believed that no divine intervention was needed to keep the solar system stable.
It's also not clear whether LaPlace actually said the exact words "Je n'avais pas besoin de cette hypothèse-là" to Napoleon. However, this saying ("I had no need of that hypothesis") is often quoted as a model of skepticism.